This lesson covers the various duties, techniques, and skills a chaining crew member must learn to perform chaining operations safely, efficiently, and effectively. It also covers some of the devices used in chaining itself. Because methods of measuring horizontal differences with a tape, chain, and/or electronic measuring instruments are critical to successful chain crew procedures, this lesson will also discuss direct linear measurements. As a crew member, you should be concerned not only about the task at hand but also about potential hazards to which you may be exposed in the field. Always recognize precautions and safety measures applicable to the survey field crew. This lesson covers precautions, safety measures, and additional duties the crew normally performs.
When you have completed this lesson, you will be prepared to:
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1.0.0 Duties of a Chaining Crew Member
2.0.0 Methods of Direct Linear Measurements 3.0.0 Field Party Safety 4.0.0 Additional Duties of a Survey Crew |
Chaining operations include more than the specific task of chaining. Several other tasks are undertaken as part of the process. In some cases, these duties can be modified or tailored contingent upon the job, terrain features, and other conditions that may affect the speed and accuracy of the operation.
During fieldwork, communication is essential. Sometimes you may be close enough to use voice communication; but more often, hand signals will be necessary. Use standard voice signals instead of shouting to avoid misunderstanding. Use hand signals when circumstances require. There are standard hand signals (Figure 13-1), but any set of signals mutually agreed upon and understood by all members of the party can be used.
Figure 13-1 – A surveyor’s hand signals.
Always face the person you are signalling. If it is difficult to see the other person, hold white flagging when giving signals. When signals are given over snow-covered areas, red or orange flagging is more appropriate.
Standard hand signals include:
Figure 13-2 – Hand signals for numerals.
o One- Right arm extended diagonally down to the right from the body
o Two- Right arm extended straight out from the body
o Three- Right arm extended diagonally up and out from the right shoulder
o Four- Left arm extended diagonally up and out from the left shoulder
o Five- Left arm extended straight out from the body
o Six- Left arm extended diagonally down to the left from the body
o Seven- Both arms extended diagonally down and out from the body
o Eight- both arms extended strait out from the body
o Nine- Both arms extended diagonally up and out from the body
o Zero- Hitting the top of the head with an up and down motion of the palm
Indicate a decimal point using a signal that is easily distinguishable from the other signals. Ensure that you can see both the left and right side of your signalman for numeral signals one through six. Use numeral signals only when it is absolutely necessary. Numeral signals are often misinterpreted, which results in mistakes. Always use hand signals consistently, and ensure that all survey team members are completely familiar with them.
A crew must clear a line ahead when chaining (or taping) across brush-covered country. Before you start to swing, make sure that no one is within range. You may cut ordinary scrub growth in unsettled areas more or less as needed. If, however, you encounter large trees or shrubs that may be of value, consult your party chief for advice. Even though a tree or shrub lies directly on the chaining line, it is never absolutely necessary to cut it down. If preserving the tree or shrub is desirable, you can always triangulate around it or bypass it by some other method, as described later in this lesson. The principle technical problem in clearing the line is keeping on the line. When possible, this is accomplished with natural foresights, that is, bearings taken on natural or artificial objects lying ahead. If there is no distinctive object lying on the line of bearing ahead, keep the line by blazing ahead. Set up the compass and sight ahead on a tree lying as far ahead as possible. Blaze that tree (using red or white flagging as a marker is also an acceptable method for marking), then clear a line toward the tree. If growth is too high and thick for a sight to be made, work ahead by looking back and aligning on a couple of markers on the line already covered.
To run a line by instrument from a point of known location to point B, for example, and given a distance and direction ahead, the instrumentman usually proceeds with the following:
If the chainmen are using a 100-foot tape, and have trained the instrument along the line of direction, the head chainman walks away with the zero-foot end of the tape, while the rear chainman holds the 100-foot end on the point plumbed by the instrument. After the head chaiman has walked out the whole 100 feet, a plumb bob is dropped on a cord from the zero-foot mark to the ground. The instrumentman sights along the line and thus determines the direction in which the head chainman must move to bring the plumb bomb onto the line. The “move right” or “move left” signal is given if needed. When the head chainman has been brought by signal to the vicinity of the line, the instrumentman signals for the final placement of the plumb bob by calling out, “To you!” (Meaning “Move the plumb bob toward yourself!”) or “Away!” (Meaning, “Move the plumb bob away from yourself!”). When the plumb bob is exactly on the line, the instrument man calls out, “Good!” or “All right!” The head chainman then marks the point indicated by the plumb bob in the correct manner. The first 100 feet is then considered measured on the given line of direction. 13-9 If the distance to be measured is long, the chainmen will eventually proceed beyond the scope of the instrument as it is then set up. The instrumentman must shift the instrument ahead to the last point marked by the head chainman. When the instrument has been set up over this point, the instrumentman must reorient the telescope to the line of direction. To do this, he or she usually plunges the telescope (rotates it vertically) and backlights on a point on the line already laid off. In taking backlights, the instrumentman is guided by the rear chainman who holds on, or plumbs over, the point. When the telescope has been trained on the backsight point, it is again plunged. The telescope is trained in the desired direction.
If the chainman can site the point on the ground through the telescope, he or she may simply hold on the point; that is, hold a pencil point, chaining pin point, plumb bob point, or some other appropriate indicator on the point (Figure 13-3).
Figure 13-3 – Short sight indicators.
Whatever the indicator may be, it is essential to hold it in an exactly vertical position. For short sights, it is also essential that the shaft of the indicator be relatively slender so that the vertical cross hair can be aligned with sufficient exactness.
If intervening low growth or some other circumstance makes sighting the point on the ground impossible for the instrumentman, the chainman must plumb over the point, using the plumb bob and cord. If the distance is too far for observation of the plumb bob cord, the cord should be equipped with a plumb bob target, or you may use a range pole. In the absence of a target when using the plumb bob, you may tie a piece of colored flagging to the cord or use a handkerchief (Figure 13-4).
Figure 13-4 – Target substitution.
Some chainmen prefer to hold the plumb bob and cord with the cord running over the forefinger. Others prefer to run the cord over their thumb. If you are plumbing high (that is, required to hold the cord at chest level or above), learn to brace your holding arm with your other arm, and against your body or head or both, to avoid unsteadiness and fatigue. When there is wind, you may find it difficult to hold the plumb bob suspended over a point. It will tend to swing back and forth. You can overcome this problem by bouncing the point of the plumb bob slightly up and down on the point. For a long sight, it is much better to plumb over a point with a range pole. For a short sight, however, the shaft of a range pole is too thick to permit exact alignment of the vertical cross hair. For long sights, or for sights on a point that is to be sighted repeatedly, constructing a semi-permanent target is often desirable. There are no definite rules for constructing targets because they are typically built from materials at hand. Use your ingenuity to ensure that the target is high enough to be seen, strong enough to withstand prevailing winds, and is plumbed over a point (Figure 13-5).
Figure 13-5 – Semi-permanent targets.
In general, control surveys deal with established points. To define these points, surveyors have to mark them. Certain points are made permanent, and others are temporary. A long term line, for example, may be marked at each end with a bronze disk set in concrete, or with a center-punched metal rod driven flush with the ground. For less permanent control points, wooden stakes or hubs with nails, shiners, and floggings are typically used.
Always set a driven marker exactly vertically on the point it is supposed to mark. If you drive it on a slant, the top of the marker will not define the correct location of the point. To drive the marker vertically, first align it vertically; then, using a sledgehammer or other type of driving implement, strike each blow squarely on the flat end of the hub or stake. You will normally drive a wooden hub to mark the exact horizontal location of a point, usually for the purpose of plumbing an instrument over the point. Consequently, the top of a hub (or other markers used for the same purpose) will not normally need to extend much above the ground line. Mark the precise location of the point is marked by a hub tack, punch mark, or other precise marker driven or set in the top of the hub. For work on asphalt roads or runways, you’ll find it easier to use flagging or a soda pop top and a nail as a marker; in concrete and other hard surfaces, you can use orange paint or a star-drilled hole plugged with lead. The choice of markers depends on the surveyor’s judgment as well as the purpose of the survey. In frozen or otherwise extra hard ground, use a bull-point to start a hole for a stake or hub. Remember that the stake or hub will 13-11 follow the line of the opening made by the bull-point. Therefore, if the bull-point is not driven vertically, the stake or hub will not be vertical either.
In surveying, a monument is a permanent object or structure used where a point or station must be retained indefinitely for future reference. It may simply consist of a conspicuous point carved on an outcrop of a ledge rock or it may be constructed in concrete (Figure 13-6).
Figure 13-6 – Common types of survey monuments.
The top of the monument should have an area large enough to include the required point and any necessary reference data. The depth of the monument should be sufficient to extend below the frost line. If the depth of the frost line is unknown, a minimum depth of three feet is generally accepted. Other factors, such as soil condition and stability of foundation, may also affect the depth of the monuments. Check the area for soil stability to provide an adequate foundation. A monument settles in the same manner as any other structure if it does not have an adequate foundation. Mark the exact location of the point on a monument by chiseling an “X” on the surface or by drilling a hole with a star drill and hammering in a lead filler or grouting in a length of brass stock (often called a copper). When grouting a copper, use neat cement grout because a fluid grout would flow into and fill the small space around the copper. If the point can be placed at the same time as the casting of the monument, the copper can be pushed down into the surface of the monument before the concrete begins to harden. If you are near an armory, you may be able to obtain large, expended brass shell casings. The primer end of a shell casing makes an excellent survey point marker when it is embedded in a concrete monument. With a little imagination and ingenuity, you can easily design and construct adequate survey monuments.
Mark a point with identification information and any additional relevant data. You can make temporary identification marks with keel and more permanent ones with paint. An even more permanent mark consists of a metal plate set in concrete. Mark a point that indicates a traverse station with the symbol or number of the station, such as “STA. B” or “STA. 21”. Mark a point on a stationed traverse with the particular station, such as 2 + 13-12 87.08. Frequently, a point will serve as a traverse station and a bench mark. A bench mark is marked with an identifying symbol and usually the elevation. In marking such an elevation, do not use a decimal point, as in 317.22 feet. Instead, raise the figures that indicate the fractional part and underline them.
Tie in or reference all control points. Record the ties or reference points in the field book as you establish them in the field. The record may be made by sketch, work description, or the combination of the sketch and notes. You must reference the control point to some permanent type of object in its vicinity; if no such objects exist, drive reference hubs at points where they are unlikely to be disturbed. These ties are important in recovering control points that have been covered or otherwise hidden or in reestablishing them accurately if they have been removed. Record the reference location of a particular point on the remarks page of the field book (Figure 13-7 and 13-8).
Figure 13-7 – Natural and manmade reference points.
Figure 13-8 – Accurate methods for tying points.
For a permanent control point, such as a triangulation point, monument, or bench mark, prepare a complete station description individually for each station. The field offices of the National Oceanic and Atmospheric Administration or the National Geological Survey have these station descriptions on separate cards. They do this so they can easily run a copy for anyone requesting a description of a particular station. They also maintain a vicinity map on which these points are plotted, and these station descriptions are used in conjunction with this map. The Navy’s public works offices also maintain descriptions of stations within their naval reservation and its vicinity for immediate reference. Referencing points are ideal for recovering points that have been covered or otherwise hidden and reestablishing points accurately. As you gain more experience, you may be assigned the task of writing a station description. When writing a station description, be sure to describe the location in detail, and make a sketch showing the location, ties, as well as magnetic or true meridian. Make your description concise and clear, and be sure to test its effectiveness by letting another engineering tech (preferably not a member of the survey party that established the point) interpret your description. From the feedback of the interpretation, you can determine the accuracy of your written description. Your description, for example, should be written as follows (Figure 13-8): “Point A—plugged G.I. pipe 65.21 ft SE of NE corner of PWC Admin. Bldg. (Bldg. 208) and 81.42 ft from the SE corner of same building. It is 18.18 ft W of the center of a circular manhole cover located in Saratoga Street.”
1.4.5 Protecting Markers
Protect markers from physical disturbance by erecting a temporary fence (or barricade) around them. Sometimes guard stakes embellished with colored flaggings are simply driven near the hub or similar marker to serve as deterrence against machinery or heavy equipment traffic. Protect permanent markers with fixed barricades, such as steel or concrete casing.
| Test Your Knowledge 1. What actions should the rodman take in response to a boost-the-rod signal?
2. What term is used to describe consecutive sights taken through a telescope for the purpose of keeping chainmen on line?
3. When an important station is marked with a hub, measurements are made to one or more other points and recorded in a field notebook to assure what information?
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One of the most fundamental surveying operations is the measurement of horizontal distance between two points on the surface of the earth. Generally, there are two basic methods used: direct and indirect. Direct linear measurements, as explained earlier in this lesson, are methods used for determining horizontal distances with a tape (or chain) and/or with an electronic distance-measuring instrument. Indirect methods to take measurements use the transit and stadia or the theodolite and stadia. This section will discuss the common methods of direct linear measurements.
The most common method used in determining or laying off linear measurements for construction surveys, triangulation base lines, and traverse distances is called chaining. The name is carried over from the early days when surveyors used the Gunter’s chain and the engineer’s chain. Today, it is more appropriate to call this operation taping because the steel tape has replaced the chain as the surveyor’s measuring device. This manual, however, will use chaining and taping interchangeably.
The smallest chaining party could consist of only two people—one at each end of the tape. To lay off a line to a desired distance, one person holds the zero end of the tape and advances in the direction of the distant point, while the other holds a whole number of the tape at the starting point. The person ahead, holding the zero end, is the head chainman; the other person is the rear chainman. In ordinary chaining operations, if the distance being measured is greater than a tape length, it is necessary to mark the terminal point with a range pole. In this way, the rear chainman can keep the head chainman aligned at all times whenever a full tape length or a portion of it is transferred to the ground. The head chainman also acts as the recorder, and the rear chainman is responsible for keeping the tape in alignment. If more speed or precision in taping is required, additional personnel are assigned to the party. This relieves the chainmen of some of their duties and permits them to concentrate primarily on the measurement. For more precise chaining, a three-man party is essential. In addition to the head and rear chainmen, a stretcherman is part of a three-man party. The duties of the stretcherman are to apply and maintain the correct tension on the tape while the chainmen do the measuring. The head chainman still acts as the recorder and reads and records the temperature of the tape. Either of the two chaining parties described may have additional personnel assigned as follows:
Tapes generally come equipped with a reel; however, it is not always necessary to replace a steel tape on the reel at the end of each work period. A tape can be easily coiled and thrown into a circular roll. Grasp the 100 foot graduation on the tape face with your left hand. Using your right hand, take in five feet of tape at a time. Place the 95 foot mark over the 100 foot mark, next the 90 foot mark over the 95 foot mark—holding these five-foot marks firmly with the left hand so that the tape will not turn over. Continue this operation for the entire length of the tape, placing each five-foot division over the preceding one until reaching the zero graduation (Actually, you can start at either end of the tape, whichever is convenient.) As you are taking in the tape, you will notice that the coils fall into a figure eight shape. When coiling is complete, square up the tape ribbons. The leather thong at the 100 foot end should be on the underside of the coil next to your hand. Wrap the thong around the complete coil. Continue wrapping until there is just enough of the thong left to insert it through the coil at about the 50 foot graduation. Draw the thong firmly back against the completed windings of the thong. You can throw the tape into a more compact circular roll by giving the figure eight a twist, (Figure 13-9).
Figure 13-9 – Throwing the tape into a circular roll.
Now, tie the tape with the remaining thong. To use the tape again, reverse the process. Be sure to let the tape out from the zero end in the same way that it was wound. Walk away from the end of the tape as you unwind it to prevent kinks.
When taping distances on a relatively level surface and of the third or lower order accuracy, laying the tape on smooth ground or paved road or supporting its ends by taping stools/stakes is appropriate. In horizontal chaining, hold the tape horizontally, and project the positions of the pertinent graduations to the ground by a plumb bob and cord. For ordinary chaining on level ground, you will generally use the following procedures:
1. Set a range pole on line slightly behind the point toward which the taping will proceed. The rear chainman, with one chaining pin, is stationed at the starting point of the line to be measured.
2. The head chainman, holding the zero end of the tape and with 10 pins in hand, then moves forward, toward the distant point while using the range pole as a guide. Assuming that the tape was already off the reel when they started, the rear chainman watches the tail end (the 100-foot mark) of the tape as the head chainman moves forward.
3. When the rear chainman sees that the tail end is about to reach position, he or she uses the verbal cue, “Chain!” to solicit the head chainman to stop and look back. The rear chainman holds the 100 foot mark at the starting point and checks the alignment; then signals the way the head chainman should move to bring the chaining pin in line. While doing this, they are both in a kneeling position, the rear chainman facing the distant point, and the head chainman to one side facing the line so that the rear chainman has a clear view of the range pole. The head chainman, while stretching the tape with one hand, sets the pin vertically on line a short distance past the zero mark with the other hand. Then by pulling the tape taut and making sure that the tape is straight, the head chainman brings it in contact with the pin, while the rear chainman, watching carefully for the 100 foot mark to be exactly on the point calls, “All right‘’. At this point, the head chainman relocates the pin to exactly the zero mark of the tape and places it sloping away from the line. The head chainman pulls on the tape again to make sure that the zero mark really matches the point where the pin is stuck in the ground and calls “All right” or “Stuck”. This is a signal to the rear chainman to release the tape so he can continue forward for the next measurement. The chainmen repeat this process until the entire distance is measured. 4. As the rear chainman moves forward, the pin is pulled from the point. Thus, there is always one pin stuck in the ground, and the number of pins in possession indicates the number of 100 foot (stations) tape lengths they have measured from the starting point to the pin in the ground. Every time the head chainman runs out of pins, the rear chainman comes forward, and both of them count the pins in the rear chainman’s possession. There should be 10 pins.
When a full tape length is measured, two chainmen support the ends. The tape may be laid on a level ground surface, such as a paved road or railroad rail, or suspended between stools or bucks set under the ends of the tape. For precise measurement, such as a base line measurement, the tape is supported at midpoint or even at quarter points by bucks or stakes. In horizontal taping over sloping or irregular terrain, one end of the tape is held on the point at ground level, while the other end is supported high enough to make the tape horizontal. The rear chainman holds a full graduation of the tape at the point near the ground, and the head chainman, holding the zero end, projects the desired distance to the point on the ground by using the plumb bob (Figure 13-10).
Figure 13-10 – Horizontal taping on a slope.
Any misalignment of the tape, either horizontally or vertically, will result in an error in the measurement. Misalignment always results in a recorded distance that is too long, or a laid offline that is too short. This is obvious, since the shortest distance between two points is a straight line. Keep the tape straight and level at all times.
A tape supported or held only at the ends will hang in the shape of a curve, called a catenary. Depending on the tension or pull applied at the ends, this catenary will become shallower or deeper, and the distance between the supported ends will vary considerably. To standardize this distance, apply a recommended “standard” tension when you are measuring. Attach a spring balance or tension handle to one end of the tape and measure the correct standard tension. The amount of standard tension is discussed later under “Making Tape Corrections”. Maintaining a constant tension for any length of time by a hand pull is uncomfortable and can be erratic. For easier chaining, each chainman uses a pole or rod from one half inch to two inches in diameter, and about six feet long. The leather thong attached to the tension handle is wrapped around the pole at the proper height. The chainman braces the bottom end of the pole against the outside of his or her foot and applies tension by bracing his or her shoulder against the pole and shifting his or her body weight until the correct tension reads on the scale. This position can be held steadily and comfortably for a comparatively long time. Measuring distances less than a full tape length requires the clamp handle (or “scissors clamp”), which is attached to the tape at some convenient point along its length. The handle permits a firm hold on the tape and furnishes a convenient attachment for a spring balance. When properly used, the handle will prevent the tape from kinking.
A chain tape may be either a plus (or add) tape, or a minus (or subtract) tape. On a plus tape, the end foot, graduated in subdivisions, is an extra foot, lying outside the zero foot mark on the tape and graduated away from the zero foot mark. On a minus tape, the end foot, graduated in subdivisions, is the foot lying between the zero foot mark and one foot mark and graduated away from the zero foot mark and toward the one foot mark. This difference is significant for measuring a distance of less than a full tape length. Suppose that you are measuring the distance between point A and point B with a 100 foot tape, and the distance is less than 100 feet. Suppose that you are the head chainman. To start, you and the rear chainman are both at point A. You walk away from point A with the zero-foot end of the tape. Because this is a plus tape, the tape has an extra foot beyond the zero-foot end, and this foot is subdivided into hundredths of a foot, reading from the zero. You set the zero on point B, or plumb it over point B then call out, “Take a foot”. The rear chainman then pulls back the first even foot graduation between A and B to point A, or plumbs it over point A. As an example, if this is a 34 foot graduation, the rear chainman will call out “thirty-four”. Now read the subdivided end foot graduation that is on or over point B. Let’s say it is the 0.82 foot graduation. You call out, “Point eight two‘’. The rear chainman rechecks the even-foot graduation on point A and calls out, “Thirtyfour point eight two”. As you can see, your subdivided foot reading is added to his even foot reading; hence, the expression “plus” tape. Suppose now that you are measuring the same distance between the same points, but using a “minus” tape, that is, a tape on which the subdivided end foot lies between the zero-foot and one foot graduations. This time when you walk away with the zero-foot end, you set the one foot graduation on point B and call out, “take a foot”. The rear chainman then hauls back the first even-foot graduation between A and B to point A but this time on the 35 foot graduation so the rear chainman calls out, “thirty-five”, which is your cue to read the subdivided foot graduation on point B. This time it is the 0.18 foot graduation, so you call out, “Minus point one eight”. The rear chainman mentally subtracts the 0.18 foot from 35.00 feet and calls out, “Thirty-four point eight two”. When you are also acting as the recorder, be sure to recheck the subtraction before you record the distance in the field notebook.
The range pole is set on line slightly behind the point toward which the taping will proceed. Line may be given (that is, the person with the range pole may be guided or signaled onto the line) by “eyeball” (that is, by eye-observation alignment by the rear chainman or someone else at the point from which chaining is proceeding) or by instrument.
The methods used in slope chaining are similar to those used in chaining on level ground, though there are some minor differences. In slope chaining, the tape is held along the slope of the ground, the slope distance is measured, and the slope distance is converted, by computation, to horizontal distance. The slope angle is usually measured with an Abney hand level and clinometer; however, for precise measurement, it is measured with a transit. In using the clinometer, take the slope angle along a line parallel to the slope of the ground or along the tape that is held taut and parallel to the slope of the ground. To use the clinometer, sight on an object that is usually a point on a pole approximately equal to your Height of Instrument (HI); that is, the vertical distance from the ground to the center (horizontal axis) of the sight tube. While sighting the object, rotate the level tube about the axis of vertical arc until the cross hairs bisect the bubble as you look through the eyepiece. Then, read either the slope angle or percentage on the vertical arc and record it along with the slope distance measurement. Compute the horizontal distance, or in other words, apply the tape correction. If you are marking the station points, apply the corrections to the slope distances as the chaining progresses. Compute these corrections mentally, by calculator, or by using a table. If the ground slope is fairly uniform, and if the tape corrections do not exceed one foot, a plus 100 foot tape is very useful to establish these station points. The head chainman determines the slope correction first, and then lays off the true slope distance that gives a horizontal distance of 100 feet. If the slope is less than two percent, no slope correction is required. Slope corrections are discussed later in this lesson.
2.1.5 Horizontal Chaining
In horizontal chaining, the tape is supported only at its ends and held in a horizontal position. Plumb bobs are used to project the end graduations of the tape (or, for a less-than-tape length measurement, an end and an intermediate graduation) to the ground. Be very careful when you use the plumb bob both in exerting a steady pull on the tape and in determining when the tape is horizontal. 3lumbing Plumbing is complete when the tape is in horizontal alignment and under the proper tension. The rear chainman holds a plumb bob cord at the proper graduation of the tape, and the point of the plumb bob about one-eighth of an inch above the marker from which the measurement is being made. When the plumb bob is directly over the marker, the rear chainman calls, “mark”. The head chainman holds a plumb bob cord at the correct graduation of the tape with the point of the plumb bob about one inch above the ground. He or she allows the plumb bob to come to rest; sees that the tape is horizontal; checks its alignment and tension; and when the rear chainman calls, allows the plumb bob to fall and stick in the ground. This spot is then marked with a chaining pin. At times, in rough country, a small area around the point may require clearing for dropping the plumb bob. Because the clearing is usually done by kicking away small growth, this type of clearing is commonly called a kickout. To determine the approximate location of the kickout, the head chainman may call, “line for kickout” and then “distance for kickout”. At “Line for kickout”, the rear chainman or instrumentman gives the approximate line by eyeball. At “distance for kickout”, the rear chainman holds approximately over the starting point without being too particular about plumbing.
2.1.5.2 Leveling the Tape To make the tape level when two chainmen are making a horizontal measurement on a slope, the person at the lower level is holding the end at chest level while the person at the higher level is holding it at knee level (Figure 13-11). To maintain the tape in a horizontal position, the chainman at the lower level holds the hand level. By studying the position of the other chainman, he or she decides that it would be possible to hold the tape at chest level. The chainman at the lower level then holds the hand level at about the height of his or her own chest level and trains it on the other chainman. It indicates that a level line from his or her own chest level intersects the person of the other chainman at that person’s knee level, and so calls out, “at your knee” thus informing the other chainman where to hold the end of the tape. 13-20 Figure 13-11 – Horizontal chaining using plumb bobs.
2.1.5.3 Breaking Tape The term breaking tape is used to describe the procedure for directly measuring horizontal distance on sloping ground, or through obstacles that do not permit the use of a full tape length. The procedure used in breaking tape is the same as ordinary chaining on level ground, except that the distances are measured by using portions of a tape (Figure 13-12). Figure 13-12 – Measuring horizontal distances by the “breaking tape” method. Generally, you will start breaking tape when the slope of the existing ground exceeds five percent (this depends also on the height of the chainmen). The reason for breaking tape is that the chainman on the lower ground will have difficulty holding the tape steady and horizontal when that chainman’s point of support exceeds his or her height. You also break tape to avoid hazardous measurements, such as crossing power lines and making measurements across a heavily traveled highway. To measure the horizontal distance by the “breaking tape” method, the chainmen may proceed as follows: 1. The rear chainman stations at point A. 2. The head chainman pulls the tape forward a full tape length uphill toward point B and drops it approximately on line with the two range poles. 13-21 3. He or she then comes back along the tape until reaching a point at which a partial tape length, held level, is below the armpits of the rear chainman at point A. 4. At this point, the head chainman selects a convenient whole-foot graduation, and the chainmen measure off the partial tape length (distance Aa) from starting point. 5. Then, the head chainman calls out, “holding sixty”, so that the rear chainman knows what graduation is held when the measurement is made. As in other chaining methods, the rear chainman always checks the alignment. After the pin is placed, the rear chainman (leaving the tape lying in position) moves forward to point “a” and gives a pin to the head chainman who, in turn, moves to point b. To make sure that the rear chainman takes the right graduation, the head chainman calls out, “hold sixty”. This procedure is repeated until a full station is measured or until a full-tape length measurement is possible. To measure distance “bc”, both chainmen will probably use plumb bobs to transfer the distance to the ground. Remember that the rear chainman gives the head chainman a pin only at each intermediate point of a tape length. He keeps the pin at full tape lengths to keep track of the number of stations laid out as in ordinary horizontal chaining.
2.1.5.4 Laying Off a Given Distance Frequently, a chaining party is required to lay off a given distance and establish a new point on the ground. This is measuring by using a known distance on the tape and transferring it to the ground. If the distance is greater than a tape length, then the procedure described for measuring a full tape length is followed for the required number of full tape lengths. The remaining partial tape length is then laid off by setting the rear chainman’s plumb bob at the appropriate tape graduation.
A 100 foot tape should, in theory, indicate exactly 100.00 feet when it is in fact measuring 100.00 feet. However, a tape supported only at the ends has a sag in it, so when it indicates 100.00 feet, the actual distance measured is less. Even a tape supported throughout on a flat surface can be slightly longer under tension than it is without tension. Also, a tape will be longer when it is warm than when it is cold.
All tapes are graduated under controlled conditions of temperature and tension. When the tapes are taken to the field, these conditions change. The tape, regardless of the material used to make it, will be either too short or too long. For low accuracy surveys, the amount of error is too small to be considered. As accuracy requirements increase, however, variations caused by the temperature and sag must be computed and used to correct the measured distance. In the higher orders of accuracy, the original graduation is checked for accuracy or calibrated at intervals against a standard distance. This standard is usually two points, a tape length apart, that have been set and marked using a more precise tape or a tape already checked. The standard may be just the precise or checked tape (known as the king or master tape). This tape is kept in a safe location and is not used for making field measurements, but only to check the accuracy of the field tapes. For the highest orders of accuracy, the tapes are sent to the National Bureau of Standards, U.S. Department of Commerce, Washington, DC, 20234, for standardization under exact conditions of tension, temperature, and points of support. A tape standardization certificate is issued for each tape, showing the amount of error under the different support conditions and the coefficient of expansion. The certificate (or a copy) is kept with each tape. For field operations, the tapes are combined in sets; one is selected as the king tape, while the others are used as field tapes. The standard tension for a tape supported throughout is 10 pounds, and the standard temperature is 68 degrees Fahrenheit. Standard length is, simply, the nominal length of the tape. A 100 foot tape, for example, at a temperature of 68°F, supported throughout, and subject to a tension of 10 pounds, should indicate 100 feet when it is measuring exactly 100 feet. To calibrate a 100 foot tape means to determine the exact distance it is actually measuring when it indicates 100 feet, while being supported throughout, at a temperature of 68°F and under a tension of 10 pounds. In addition to the National Bureau of Standards, many state and municipal authorities provide standardizing service.
Suppose now that you send a 100 foot tape to the Bureau of Standards to be calibrated; the bureau will return a certificate with the tape. Assume that the certificate states that when the tape, supported throughout at a temperature of 68°F, and under a tension of 10 pounds, indicates 100 feet, it actually measures 100.003 feet on the standard tape. The tape, then, has a standard error (also called tape error) of 0.003 feet for every 100 feet it measures. This tape “reads short.” Depending on the order of precision of the survey, you may have to apply this as a correction to measurements made with this particular tape.
Whether you add or subtract, the standard error depends upon the direction of the error. The tape in the previous example indicates a distance that is shorter than it actually measures; in other words, when you use this tape to lay off a distance of 100 feet, the line is actually 100.003 feet. The decision to add or subtract the error depends upon whether you are measuring to determine the distance between two points or to set a point at a given distance from another. Assume first that you’re measuring the distance between two given points, and the distance as indicated by the tape is 362.73 feet. The total tape error is 0.003 times the number of tape lengths. In this case, it is 0.003 x 3.6273 = 0.0108819 feet, which rounds off to 0.01 foot. Then add the tape error. The correct distance between the two points, then, is 362.74 feet. Suppose now that with the same tape, you are to set a point 362.73 feet away from another point. Your correction here will be applied in the opposite direction. Since the tape reads short, the laid tape distance of 362.73 feet is longer than 362.73 feet by the amount of the total correction for standard error (0.01 foot). Therefore, you must subtract the total tape error. To lay off a distance of 362.73 feet with this tape, measure off a distance of 362.72 feet. Suppose now that the Bureau of Standards calibration certificate states that when a tape indicates 100.00 feet under standard conditions, it is actually measuring only 99.997 feet. Again, the standard error is 0.003 feet per 100 feet, but this tape “reads long”; that is, the interval it indicates is longer than the interval it is actually measuring. Suppose you measure the distance between two given points with the tape and find that the tape indicates 362.73 feet. The total standard error is still 0.01 feet. Because the tape reads long, however, the distance it indicates is longer than the distance it actually 13-23 measures. Therefore subtract the total standard error and record the distance between the given points at 362.72 feet. Suppose you are using this same tape to set a point 362.73 feet away from another point. Again, the total standard error is 0.01 feet. Because the tape reads long, however, a measurement of 362.73 feet by the tape will actually be less than 362.73 feet. Therefore, add the total correction for standard error, and measure off 362.74 feet by the tape. 2.1.6.4 Correcting for Temperature Variation Take a 100 foot steel tape that has been calibrated at a standard temperature of 68°F. The coefficient of thermal expansion of steel is about 0.0000065 units per 1°F. The steel tape becomes longer when its temperature is higher than the standard and shortens the same amount when it is colder. The general formula for variation in temperature correction is as follows: Ct = 0.0000065(T- To) Where Ct = Correction for expansion or contraction caused by variation in temperature. L =Tape calibrated length To = Standard temperature (usually 68°F) T = Temperature during measurement From the above formula, you can deduce that the correction for a 100 foot tape is about 0.00065 feet per 1°F, which is about 0.01 feet for every 15°F change in temperature above or below the standard temperature of 68°F. The temperature correction applies in the same manner and direction as the standard tape error. If the tape measurement is taken at a higher temperature than standard, the tape will expand and read short; naturally the correction should be added. The error caused by variation in temperature is greatly reduced when an Invar tape is used.
2.1.6.5 Correcting for Sag Even under standard tension, a tape supported or held only at the ends will sag in the center, based on its weight per unit length. This sag will cause the recorded distance to be greater than the length being measured. When the tape is supported at its midpoint, the effect of sag in the two sections is considerably less than when the tape is supported only at its ends. As the number of equally spaced intermediate supports increases, the distance between the end graduations will approach the length of the tape when supported throughout its length. The correction for the error caused by the sag between the two supports for any section can be determined by the following equation: Cs = w 2 l 3 24t 2 Where Cs = Correction for sag (in feet) w =Weight per unit length of tape (in pounds per foot) l = The length of the suspended section of tape (in feet) t = Tension applied to the tape (in pounds) 13-24 For full tape-length measurements, the correction for sag is usually taken care of by calibrating the tape. The tape must be calibrated regardless of how it is supported and under standard temperatures and tension. To reduce the value of the horizontal correction for sag, the Bureau of Standards suggests standard tensions for tapes supported at only the ends as follows:
Generally, for a heavy 100 foot tape weighing about three pounds that was standardized, whether supported throughout or at the ends only, the systematic error per tape length caused by sag is as follows:
For the engineering technician’s survey work, measurements are normally in the lower order of precision. The correction for sag varies with the cube of the unsupported length; for short spans, it is often negligible.
2.1.6.6 Correcting for Slope
When you take a measurement with a tape along an inclined plane (along the natural slope of the ground), the taped distance is greater than the horizontal distance. The difference between the slope distance and the horizontal distance (s – d) is called the slope correction. Always subtract this correction from the slope distance. To compute for the slope correction, you should know either the vertical angle, A, or the difference in elevation, h, between the taped stations. When you use the vertical angle, the formula for slope correction is as follows: Ch = s Vers A Since Vers A = (1 – cosA) then Ch = s(1 – cosA) where Ch = The slope distance correction s = The tape slope distance (usually a tape length) A = The vertical angle When you use the difference in elevation, the approximate formula derived by the Pythagorean Theorem of a right triangle for the slope correction (Figure 13-13), for the slope correction is as follows: h2 = s2 – d2 Figure 13-13 – Correction for slope distance. 13-25 h2 = (s + d)(s – d) s – d = h2 s + d But for a small slope, d is approximately equal to s; therefore, s + d = 2d and since Ch = s – d Ch = h2 2s For slopes greater than five percent, a closer approximation of can be determined by expanding the formula to: 3 42 2 8s h s h Ch ==
2.1.7 Preparing Chaining Notes
There are several general, yet important principles applicable to all types of field notes. Recording of accurate measurements and other data is essential, as is inclusion of any additional information required to identify and clarify the data. Field notes must be legible and accurate. Record all notes in pencil; a 3H or 4H pencil is best for the job. A pencil that is too soft blunts too quickly; one that is too hard makes a faint mark and scores the paper. In the field, carry a pocketknife or pocket pencil sharpener to keep your pencil sharpened. Erasures are not permitted in field notes. Suppose that in the course of chaining several intervals you make a 10 foot “bust” in one of the intervals by misreading 10 feet as 20 feet. After you total up the distance, some circumstance leads you to suspect that the total is off. You recheck the work and discover where you made the bust. The notebook record for that interval must be changed. Make the change by crossing out the wrong entries and entering the correct ones above them—not by erasing the wrong entries.
2.1.7.1 Recording Notes for Horizontal Chaining There are typical examples of a horizontal chaining conducted for a closed traverse (Figure 13-14). The chaining party started at station A and chained around by way of B, C, and so on. Arriving back at A, the party reversed its direction and chained back around by way of E, D, C, and so on, as a check. The distance recorded for each traverse line was the mean (average) between the forward measurement and the backward measurement. 13-26 Figure 13-14 – Notes for horizontal chaining. Note on the bottom left-hand side of the data page that the tape had a standard error of 0.013 feet per 100 feet of tape. The error is marked “ + ”, meaning that the amount of error should be added to the measurement as indicated by the tape since the tape was reading short. The corrections in the “Correction” column indicate that only correction for standard error was made. If corrections for temperature and sag had been made, the algebraic sum of all three would have been entered in the correction column, or additional columns for temperature and sag correction would appear. The symbol for each station is listed in the first column on the data page. Opposite, on the remarks page, a description of the station is recorded. In the second and third columns on the data page, the measured forward and backward distances between adjacent stations are recorded. The average distance is recorded in the fourth column. In the fifth column, the standard error of 0.013 feet per 100 feet of tape is computed for each mean measurement. In the sixth column, the result of this error, added to the mean measurement, appears as the “Corrected Length”. The sum of the corrected lengths appears below as “Total Length Perimeter.”
2.1.7.2 Recording Notes for Slope Chaining
There are many good examples of slope chaining notes (Figure 13-15). Notice that on the data page, extra columns have been assigned for the temperature of the tape at each interval, the difference in elevation between supports, and the slope distance. Under “Tape Corr.” in the fifth column, enter the standard error for each interval. The tape had a standard error of 0.013 feet per 100 feet; therefore, the standard error for each interval except the last is 0.013 feet. For the last interval of 73.18 feet, the error works out as 0.009 feet. The “Temp. Corr.” column is located to the right of the “Tape Corr.” column. For the first two intervals measured, the temperature of the tape was 78°F, or 10°F above standard. The correction amounts to 0.01 foot for each 15°F above standard; therefore, the total temperature correction for each of these intervals equals the value of x in the equation: 13-27 10 x 15 0.01 = The total temperature correction is 0.007 feet. Because the temperature was above standard, the tape lengthened and was reading short. So add the corrections as indicated by the plus signs. To the right of the “Temp. Corr” column is the “Slope Corr” column. Subtract its entries as indicated. Use the equation to compute the slope correction: 2s h C 2 h = For the first taped interval, h is 6.0 feet and s is 100 feet. Therefore: h2 = 6.02 = 36.0 feet 2s = 2 x 100 = 200 feet Compute the slope correction as follows: 0.180 feet 200.00 36.00 = The “Total Corr” column is next to the column for slope correction, and contains the algebraic sum of the three corrections for each taped interval. In the “Horiz. Dist” column, determine each value by subtracting the total correction for each interval from the measured slope distance for that interval. At the bottom of this column, the sum of the horizontal distances appears. This is the horizontal distance from station K to station L. Figure 13-15 – Notes for horizontal chaining. 13-28
2.1.8 Solving Surveying Problems by Tape
Before modern instruments for measuring angles directly in the field were devised, the tape (or rather, its equivalent, the Gunter’s chain) was often used. This tape was used not only for measuring linear distances but also for measuring angles more accurately than was possible with a compass.
2.1.8.1 Laying Out a Right Angle In laying out a right angle (or erecting a perpendicular) by tape, apply the basic trigonometric theory that a triangle with sides in the ratio of 3:4:5 is always a right triangle. Assume that on the line AB (Figure 13-16); using a 100 foot tape to run a line from C perpendicular to AB is most appropriate. If a triangle with sides in the ratio of 3:4:5 is a right triangle, then one with sides in the ratio of 30:40:50 is also a right triangle. From C, measure off DC, 30 feet long. Set the zero-foot end of the tape on D and the 100 foot end on C. Have someone hold the 50 foot and 60 foot marks on the tape together and run out the bight. When the tape becomes taut, the 40 foot length from C will be perpendicular to AB.
2.1.8.2 Measuring an Angle by Tape There are two methods commonly used to determine the size of an angle by tape: the chord method and the tangent method. Apply the chord method, using the example in (Figure 13-17). Suppose you want to determine the size of angle A. Measure off equal distances from A (80.0 feet), and establish points B and C. Measure BC; assume that it measures 39.5 feet. Now determine the size of angle A by applying the following equation: bc c)b)(s2(s cosA1 −− =− in which c)b(a feet99.7 2 1 s =++= First, solving for: 1 - cosA Figure 13-16 – Laying out a right angle using a 100 foot tape. 13-29 we have 0.12128 6400 776.2 6400 2(19.7)(19.7) cosA1 =− == Since 1 – cosA = 0.12128 cosA = 1.00000 – 0.12128 = 0.87872 Reference to a table of natural functions shows that the angle with cos equal to 0.87872 measures, to the nearest one minute, 28°29’. The intervals measured off from A are equal in this example for mere convenience. The solution will work just as well for unequal intervals. In determining the size of an angle by the tangent method, simply lay off a right triangle and solve for angle A by the common tangent solution. Suppose you want to determine the size of angle A (Figure 13-18). Measure off AC a convenient length (for the sake of example, 80.0 feet). Lay off CB perpendicular to AC and measure it; for the sake of example, it measures 54.5 feet. Compute the angle using the following formula: 0.68125 80.0 54.5 tanA == The angle with tangent 0.68125 measures 34°18´.
2.1.8.3 Laying Off an Angle of a Given Size
Assess an angle of a given size by applying the tangent right triangle solution (Figure 13-19). To lay off a line AC from A, 25° from line AB, measure off a hypothetical 80.0 feet from A to establish point B. Erect a perpendicular from B (the dotted line in Figure 13-18). Measure off along the perpendicular side (opposite side), the distance that, Figure 13-17 – The chord method. Figure 13-18 – The tangent method. 13-30 when divided by the adjacent side, will give the value of the natural tangent of 25°. Use the following formula: 80.0 a tan25 =° a = tan2580.0 ° The tangent of 25°is 0.46631, so a = 80.0 x 0.46631 = 37.3 feet Measure off 37.3 feet from B to establish point C. A line from A through C will form an angle of 25° from AB.
2.1.9 Identifying Chaining Mistakes and Errors In surveying, there is a significant distinction between errors and mistakes. Errors result from factors such as the effects of nature, the physical condition of the personnel performing the survey, and the condition of instruments. Mistakes, however, are simply human blunders. While errors may be compensated for, mistakes can be detected, corrected, and better yet, prevented only by the exercise of care.
2.1.9.1 Common Mistakes Mistakes may result from poor work habits, lack of judgment, or confusion. They are often costly, time consuming, and difficult to detect. The easiest way to avoid them is to establish a finite procedure and follow it, being constantly alert during the operations in which mistakes are possible. Some of the more common mistakes are as follows:
2.1.9.2 Recognizing Common Errors
There are two types of errors: accidental and systematic. An accidental error is, generally speaking, one that may have a varying value. Examples include:
Figure 13-19 – Laying off an angle of a given size.
You can minimize accidental errors simply by being careful, but they cannot be entirely eliminated. A systematic error has a constant value. The standard error in a tape, for example, is a systematic error. Temperature and sag corrections are applied to correct that particular systematic error. Systematic errors in general can be compensated for or otherwise eliminated by the application of corrections.
2.1.10 Caring for and Maintaining a Survey Tape If a steel or metallic tape gets a kink in it, it is consequently subjected to strain. The tape, in the best case scenario, will be distorted at the point where the kink lies. At worst, if the strain is strong enough, the tape will break at the point where the kink lies. Kinks, therefore, are to be avoided at all costs; it is especially important to avoid putting a strain on a tape that has a kink. Under favorable circumstances, when a tape is shifted ahead, the head chainman may simply drag it over the ground. The rear chainman should not assist by dragging that end because this develops a curve in the tape. This curve may snag on an obstruction or cause a kink. When a tape is being dragged, the rear chainman should simply allow the end to trail along. The cardinal rule is “keep the tape straight.” When taping in traffic, plan your moves in advance and make the measurement as quickly as you can. If possible, do not let vehicles run over the tape; however, if this is absolutely unavoidable, be sure the tape is laid flat and taut on the road. Never let a vehicle run over a tape laid on a soft or rugged ground surface. Tapes are made as corrosion-resistant as possible, but no steel tape is entirely immune to corrosion, especially when used around salty water. Always wipe the tape dry before putting it away, and oil it periodically with light, rust-resistant oil. If a tape does rust, rubbing it with light steel wool dipped in a rust-removing compound is the best and safest way to remove the rust. Tapes, especially those in reels, should be removed from the reel and inspected each week for signs of corrosion. A damp climate in your area of operations could easily start corrosion of tapes.
2.1.11 Splicing a Tape In spite of being carefully handled, tapes sometimes break. Rejoin a broken tape by splicing. Repair a relatively light tape with a punch-and-rivet tape splicer and repair stock (Figure 13-20). A repair stock consists of a length of tape of the same thickness and width as that of the broken tape. When reparining a tape, use a good section of the tape for calibration (matching a whole-foot mark). Place the section used for calibrating beside the broken section to maintain the original length of the tape after rejoining it. 13-32 Figure 13-20 – A punch-and-rivet tape splicer with repair stock. In splicing a broken tape, first align and rivet the repair stock at one end of the break. Next, place the repair stock on the face of the other section of the tape by using the calibrating section as a measure for the break splice. Insert one rivet at a time and arrange rivets in a triangular pattern. Do not place rivets closer together that one-fourth inch from center to center. Using a three-edge file, file partially through the surplus stock diagonally across the tape. The segment of the surplus will readily break off, leaving a clean splice. Repair heavy steel tapes in a similar manner, using a tape repair kit.
The electronic distance-measuring system is incorporated in various present-day surveying practices, including traverse and triangulation network. In traverse measurements, accurate distances are directly measured in a straight line and with minimum instrument setups. In triangulation, the system is used to conduct base line measurements precise enough to maintain survey accuracy. In the electronic distance-measuring system, the length of a linear interval is determined by using equipment that sends out an electronic impulse of some sort, such as a radar microwave or a modulated light wave, and measures the time required for the impulse to travel the length of the interval. The velocity or rate of travel of the impulse is known. Therefore, once the time is also known, the length of the linear interval can be determined by applying the well-known equation “distance = rate x time.” Two types of Electronic Distance-Measuring devices (also called EDMs) commonly used today are microwave devices and light wave devices.
2.2.1 Measuring by Microwave Devices The microwave distance-measuring device is an electronic instrument that transmits precisely controlled radio waves between two units. The waves are compared and electronically changed into a visually readable form from which the distance between the units can be computed. 13-33 The unit that originates and transmits the modulated radio waves is called the master (Figure 13-21). The unit at the opposite end of the line from the master is known as the remote. The two are identical instruments, each being adaptable to use as either master or remote. The remote unit receives the original transmission, interprets it, and puts it on a new carrier. It then amplifies this new modulation and retransmits it to the master. The master analyzes the new transmission and translates it into a trace on a cathode ray tube that can be read visually. The trace information is converted into a distance based on the velocity of the radio waves. Because atmospheric conditions affect this velocity, apply corrections for temperature and barometric pressure according to instructions. Each instrument is equipped with a shortwave telephone set. By this means, the person at each instrument can maintain communication with the other. Further details of the system operating methods are available through the manufacturer’s instructions.
2.2.2 Measuring by Light Wave Devices The light wave measuring device uses electro-optical instruments to measure distances accurately. The device consists basically of two units: the measuring unit (transmitter/ receiver) and the reflector unit. The distance is measured by precise electronic timing of a modulated light wave after it travels to, and when it returns from, a reflector at the other end of a course (Figure 13-22). When the instrument receives the reflected light flash, it registers readings that can be converted into the linear distance between the instrument and the reflector (with corrections made for atmospheric conditions). Like their microwave counterparts, the light wave distance-measuring devices are capable of first order base lines in triangulation and all orders of traverse distance measurements. Most of these instruments have a rated range of 200 to 50,000 meters. Figure 13-22 – Typical configuration of a light wave distance-measuring device. Figure 13-21 – Setting a microwave distance-measuring unit. 13-34 Treat these instruments, like all delicate scientific equipment, with proper care and operator maintenance so that they may continue to be available for use. Refer to the instrument manufacturer’s manual for instructions on basic operation, care, adjustments, calibrations, and other details of the system.
| Test Your Knowledge 4. In a three-person chaining party operation, who keeps a complete record of all measurements made by the party?
5. In beginning a horizontal chaining operation, the rear chainman, with one chaining pin, stations him or herself at the starting point. The head chainman then moves towards the distant point to be measured holding what part of the tape and a total of how many chaining pins, respectively?
6. In measuring the exact length of a building using the minus tape, what is the length of the building if the 65 foot mark is held at the outer face of the end wall when the head chainman calls out “Minus point three six”?
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A surveying field party is frequently working its way through rugged terrain a long distance away from any professional medical assistance. Working through brush, felling trees, scaling bluffs, and crossing streams are all hazardous activities. The use of sharp-edged tools, such as machetes, brush hooks, axes, and hatchets is equally hazardous. Besides those dangers inherent in the work itself, a party may be exposed to a variety of natural dangers, such as those created by weather conditions, reptiles, insects, and poisonous plants. In some areas, there may be dangerous wild animals or even dangerous domestic animals, such as vicious dogs or angry bulls. When a party is working along a thoroughfare with vehicular traffic, the danger of being hit by a vehicle is ever-present. In the midst of such a variety of constant dangers, the only way to prevent injury is through the exercise of constant care and vigilance. Every person in a party must be aware of all existing hazards, be able to recognize a hazardous situation, and be trained to take the correct preventive measures. Indeed, it is common practice for surveying field crews to prepare a checklist of essential items, personal protective equipment, communication gear, and other miscellaneous items relative to the line of work.
If personal injuries do occur, they must be taken care of to the extent possible by the application of first aid. First aid is the emergency care given sick or injured persons until regular medical or surgical aid can be obtained. Every person in a field party, however junior in rate and experience, must be able to administer first aid. A chaining party may consist of only two persons, one of whom may be very junior in rate and time in service. If the party chief is the one injured, the junior member will be responsible for administering first aid. As a rule, field crew members should be familiar with the telephone number and location of the hospital or dispensary nearest to where their party will be operating, have a transport vehicle available and ready, and have valid government vehicle operator’s licenses. In addition, they should keep a first-aid kit handy at all times.
For all weather hazards, the best preventive measure is adequate protective clothing. When frostbite is a possibility, wear a hat that covers your ears, gloves/mittens for your hands, and cold weather footgear for your feet. These are the primary areas most subject to frostbite. Wear a hat when there is danger of heatstroke. Unless or until you are immune to sunburn (by tanning), keep your skin concealed from the sun. Fair haired or sandy-haired individuals, even when they tan, may be susceptible to a form of skin cancer caused by exposure to sunlight. If you are in this category, keep the skin covered whether you “tan” or not. In general, when you set forth with a field party, wear or carry with you clothing that will provide adequate protection against the weather— not just the weather conditions at the time you set forth, but as they may develop before you get back.
The safest assumption regarding snakes or insects you do not recognize is that they are poisonous. The poisonous snakes of North America belong to the viper family. The distinguishing characteristics of a viper are a flat head and a thick body. The most common North American viper is the rattlesnake, distinguishable by a row of hard rings, called rattles, on the tail. The snake makes a rattling sound with them when it is angry or alarmed. The banded, or timber, rattler of the northeastern United States is smooth and silver-gray in color. The diamondback rattler of the United States deep south is silver-gray with a diamond-shaped pattern on the skin. The western diamondback rattler has the same diamond pattern, but is a copper color. The red rattler of southern California is a deeper copper color. Besides the rattlesnake, the most common North American poisonous snake is the water moccasin, sometimes called the cottonmouth because of a white mouth lining that the snake exposes when preparing to strike. The skin of the water moccasin is dark brown with black bars on the upper side and black blotched with yellowish white on the under side. The reddish brown copperhead has no rattles. This viper is found especially in uplands of the eastern Unites States. The most common poisonous insects encountered in North America are the black widow spider, the tarantula, and the scorpion. The black widow (which may be encountered anywhere in the United States) is recognizable by its small, shiny black body. The tarantula is a long-legged, hairy member of the spider family, found chiefly in and close to Texas. The scorpion, found mainly in the semi-tropical parts of the United States, resembles a lobster or crawfish in shape.
The Standard First Aid Training Course contains an extensive section on poisons. However, it does not mention a type of poisoning to which survey parties are particularly exposed— poisoning from contact with poisonous plants. Exposure to poisonous plants is not likely to be fatal (although it can be, under certain circumstances), but it can cause a lot of misery and considerable reduction in on-the-job efficiency. The most common poisonous plants in the United States are poison ivy, (including a variety called poison oak) and poison sumac, both of which occur everywhere in North America. These plants contain and exude a resinous juice that produces a severe reaction when it comes into contact with the skin of the average person. The first symptom of itching or a burning sensation may develop in a few hours or even after five days or more. The delay in the development of symptoms is often confusing when an attempt is made to determine the time or location where contact with the plant occurred. The itching sensation and subsequent inflammation, which usually develops into watery blisters under the skin, may continue for several days from a single contamination. Persistence of symptoms over a long period is most likely caused by new contacts with the plants or by contact with previously contaminated clothing or animals. Severe infection may produce more serious and painful symptoms such as abscesses, enlarged glands, fever, or other complications. Secondary infections are always possible in any break in the skin that occurs when the watery blisters break. With poison ivy, the next development is usually the appearance of a scabrous, deep red rash over large skin areas. With poison sumac, large blisters filled with a thick yellowish white liquid strongly resembling pus usually occur. When the blisters break, this liquid runs over adjacent skin areas, enlarging the area of infection. The resinous juice exuded by these poisonous plants is almost entirely non-volatile; that is, non-evaporating or will not dry up. Consequently, the juice may be carried on clothing, shoes, tools, or soil for long periods. In this way, it may infect persons who have not come into contact with the plants themselves. Individuals have, in fact, been severely infected by spores carried through air by smoke from burning plants. Infection by resinous juice carried on the fur of animals is another possible mode for exposure. To avoid contact with the plants themselves, know what they look like. Poison ivy has a trefoil (three leaflets) leaf (Figure 13-23). The upper surface of the leaflet has a shiny, varnished appearance. The variety called poison oak has a serrated leaflet, or lobed, edges like that of an oak leaf (Figure 13-24). Ordinary poison ivy is usually a vine; and poison oak is usually a bush. In the flowering season, both types produce clusters of small white berries. 13-37 Figure 13-23 – Different varieties of poison ivy leaves. Some sumacs are poisonous, but others are harmless. It is difficult to distinguish the leaf of a poisonous sumac from the leaf of a nonpoisonous sumac. The only way to tell the poisonous plant from the harmless one is by the fruit. Both plants produce a drooping fruit cluster. The difference lies in the color of their fruits—that of the harmless sumac is red; that of the poison sumac is white. Outside of the fruit season, avoid contact with all sumacs. There are no “do-it-yourself” remedies for plant poisoning. Treatment for poisonous plant exposure must be administered or at least supervised by professional medical personnel. While treatment must be administered professionally, if you have reason to believe that you have been infected, wash thoroughly with water and an alkaline laundry soap. Do not use an oily soap (most facial soaps are oily) because they tend to spread the poison. Lather profusely, and do not rinse the lather off, but allow it to dry on the skin. Repeat this procedure every three to four hours, allowing the lather to dry each time. If job conditions make contact with plants unavoidable, wear gloves and long sleeve shirts and keep all other skin areas covered. When you remove your clothing, take care not to allow any skin area to come into contact with exposed clothing, and launder all clothing at once.
The standard source of information on the safe use of dangerous field equipment and other safety precautions is Safety Precautions for Shore Activities, NAVMAT P-5100. A copy of this publication should be available in your technical library. Since tools are a Figure 13-2 – 3RisonRDN 13-38 potential source of danger in all occupations, inspect them periodically to assess whether they need any repairs and/or replacements. Only use tools that are in good condition. There should be no loose heads on any hand tools. Keep sharp-edged tools sharp. Store all tools safely when they are not in use. If you temporarily lay down tools with sharp blades or points, place them in such a way that no injury can result to anyone. Use sheaths or guards to carry sharp-edged or pointed tools from one place to another. If no sheath is available, carry a sharp-edged or pointed tool with the edge or point away from your body and take care not to injure others with it. When working near other people, carry your range poles or level rods vertically against your body so that you will not injure another person’s head or eyes if you turn suddenly. Do not hold a stake or bull-point with your hand around the shank while another person is driving it with a sledgehammer. Do not let a tape or plumb bob cord slide fast through your hands. Always use tools correctly and for the task for which they are intended. For example, when cutting brush near the ground with a machete, swing away from your legs and feet. Never cut at short range from your body. Be sure that the radius of your swing is clear of obstructions, such as vines or twigs that might deflect the intended direction of the swing. Use your full arm’s length to get a safe-swing radius. Always work at least 10 feet away from the nearest person. If it is necessary to use an ax to clear an area, prevent painful blisters by wearing a pair of thin gloves. Above all, use common sense and consider the possible results of your actions. To climb poles and trees safely, use authorized climbing equipment. A lineman’s pole climbers are made of steel and have a strap loop and short spur. Tree climbers have straps, pads for protection against friction, and a longer spur for penetrating bark. To avoid falling, use both the belt and the straps. Except in an emergency, never work in or on trees during a high wind. Watch out for power lines that may be in contact with the tree you are climbing. Always conduct burning operations in the clear, where the fire will not ignite tree leaves or limbs, dry wooded areas, or nearby buildings. Remember that it is imperative to extinguish all burning or smoldering material completely before leaving it unattended. When practicable, use only nonflammable solvents for cleaning instruments. Do not leave the caps off or the stoppers out of flammable liquid containers. Use solvents only in well ventilated locations.
A party working on a busy roadway is in constant danger of being struck. Every motion made by a member of such a party must be made with constant and complete awareness that vehicular traffic is proceeding as usual. Taking the following precautions, however, can minimize that danger:
| Test Your Knowledge 7. Which of the following descriptions is characteristic of poisonous snakes found on the North American continent?
8. What North American poisonous snake shows the white lining inside its mouth just before striking?
9. A poisonous plant has a juice that is nonvolatile. This means that the juice of this plant will:
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A survey crew member may perform other tasks, including:
Generally, the maintenance of surveying equipment and accessories involves proper cleaning and stowage. For example, steel tapes, brush hooks, axes, chain saws, and so forth, must be cleaned and dried and, if necessary, a thin coat of oil applied after each day’s work before equipment is stored for the night. Never stow any surveying gear (especially if made of ferrous material) without checking it thoroughly to ensure it is clean and dry— this is particularly important for steel tapes. 13-40 Sengineering techBEEs have a multitude of jobs done under variable conditions, sometimes using the same equipment, sometimes using different equipment. Because of this, neglecting the proper care of equipment for even one day can result in rusty, inoperable equipment, and financial responsibility for government property loss or damage due to negligence falls on you. Regularly sharpen surveying clearing tools, and replace any broken handles (especially those on sledgehammers). For delicate equipment, consult the manufacturer’s handbook or other applicable publications before attempting any servicing or cleaning. When necessary, ask your senior engineering tech to explain the correct procedure.
Party chiefs prepare lists of equipment and supplies needed for each day, and it is the responsibility of everyone in the survey party to review the list and ensure that everything needed is in fact present on the list. When reviewing the field party’s essential needs list, remember to consider your personal needs in addition to the equipment necessary for the job, especially if the job is a significant distance from base camp. In a triangulation survey, for example, your stations are generally situated in remote places. You may be ferried to your station point by helicopter or by some other means, depending on the location and the mode of transportation available. Be sure to take extra drinking water to jobs like this, and do not discard your excess water until you are safely back to base camp.
In the field, devices necessary for maintaining personal hygiene and field sanitation are improvised. If you are surveying at a remote location, you are unlikely to find a waterborne sewage system available for your use. The typical alternative is digging a “cat hole” about one foot deep and burying all waste completely. Always dispose of garbage properly during field surveys. Whenever possible, avoid burning dry garbage on site. Disposal bags offer a good means of preventing litter; use them whenever available. In extremely hot climates, your supply of potable water will run low at a faster rate. To avoid dehydration, you must treat your own water or face infections or diseases such as dysentery, cholera, diarrhea, and typhoid fever. It is imperative that water taken from any source (such as lakes, rivers, streams, and ponds) be properly treated before being used, as all these sources are presumed to be contaminated. To treat water for drinking, use either a plastic or aluminum canteen with the water purification compounds available in tablet form (iodine) or in ampule form (calcium hypochlorite). When disinfecting compounds are not available, boiling the water is another method for killing disease-producing organisms.
The field survey crew is likely to be assigned a vehicle to transport people and equipment to and from the jobsite. Before operating the vehicle, the operator will give it a prestart check to make sure that it is ready to run. When a vehicle is assigned to you, an operator’s daily pre-service maintenance report is issued at the dispatch office. Use this form to record or log items in the vehicle that require attention as observed during the prestart check and during the working day. Other information, such as mileage readings, operating hours, and fuel consumption may also be required.
| Test Your Knowledge 10. In addition to surveying duties, a survey crew member may be responsible for picking up trash.
11. All lake, river, stream, and pond water is presumed what?
12. Boiling is a sufficient method for killing disease-producing organisms in water.
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In this lesson, you were presented with information relating to direct linear measurements and field survey safety. You were introduced to the specific duties of a chaining crew member including marking control reference and monument points, making direct linear measurements, correcting measurements and preparing chain notes. This topic addressed solving surveying problems with the tape, identifying chaining mistakes and errors, caring for and maintaining survey tape, and splicing tape. You also learned about measuring with the Electronic Distance-Measuring System, with both a microwave device and a light wave device. You were presented with information relating to field party safety, which emphasized first aid administration, protection from weather, avoidance and treatment of poisons in nature, safe use of equipment, and caution in high traffic situations. The end of this lesson was devoted to the additional duties of the survey crew in which you learned about survey equipment maintenance, preparation for essential needs, field sanitation maintenance, and prestart vehicle checks.
1. The instrumentman is moving his right arm, which is extended upward, and to the right. What message is he signaling to the rodman? A. The rodman must move the rod to the right. B. The rodman must move the top of the rod to the right until it is vertical. C. The rodman must move the rod to the left. D. The rodman must move the top of the rod to the left until it is vertical. 2. An instrumentman extends both arms upward. What does this indicate to the rodman? A. Move forward. B. Reverse the rod. C. Pick up the instrument. D. Face the rod. 3. The instrumentman extends both arms out horizontally from his shoulders and waves them up and down. What message is he giving to the rodman? A. Come in B. Pick up the instrument C. All right D. Move forward 4. In clearing the chaining line, what should you do when a valuable tree lies directly in your path? A. Triangulate around it B. Request that the owner cut down the tree, or that he allow you to cut down the tree C. Cut it down D. Choose a different chaining line 5. For what reason should a chainman use an indicator that is narrower than a range pole when holding on or plumbing over a point for short sights? A. To enable the instrumentman to align the indicator exactly with the vertical cross hair of the instrument B. To enable the instrument to sight beyond the point C. To enable the chainman to carry out duties without becoming fatigued D. To enable the chain man to hold the indicator steady 13-43 6. When running a line from point A to point B, what action does the instrumentman take when he or she “plunges” the telescope? A. Turns the telescope 180 degrees to the right from a sight on point A to a sight on point B B. Rotates the telescope vertically from a sight on point A to a sight on point B C. Turns the telescope 180 degrees to the left from a sight on point A to a sight on point B D. Moves the telescope from point A to point B 7. When plumbing over a point, which of the following actions should you take to overcome the problem of wind blowing the plumb bob back and forth? A. Rest the point of the plumb bob on the point being plumbed. B. Bounce the point of the plumb bob slightly up and down on the point being plumbed. C. Shorted the plumb bob cord. D. Have a second person hold the point of the plumb bob steady on the point being plumbed. 8. You should mark the horizontal location of a point over which to plumb a transit by which of the following means? A. A flag or chaining pin B. A leveling rod or range pole C. A precise marker driven or set in the top of the hub D. A bull-point or spad 9. Survey control points are marked in the field by which of the following means? A. Bronze disks set in concrete B. Center-punched metal rods driven flush with the ground C. Wooden stakes or soda pop tops and nails driven flush with the ground D. Each of the above 10. In addition to an identifying symbol, what marking is usually placed on a bench mark constructed by surveyors to identify a point for a construction project? A. The abbreviation for bench mark, BM B. The elevation of the bench mark C. A number showing the order in which the bench mark is to be considered D. A number denoting the distance of the bench mark from the point of beginning 13-44 11. As survey control points are established in the field, in what manner are they recorded in the field notebook? A. By sketch B. By word description C. By either A or B, or a combination of both D. By detailed drawing 12. What tool is used to mark a terminal point in a chaining operation when the distance being measured is greater than the tape length? A. Surveyor’s arrow B. Chaining pin C. Philadelphia rod D. Range pole 13. When the head chainman runs out of chaining pins, what total number of pins should the rear chainman have? A. 0 B. 1 C. 9 D. 10 14. Which of the following devices helps apply the correct tension to a tap that is supported at its ends only? A. Taping stool B. Spring balance C. Scissors clamp D. Chaining buck 15. Including the 0 foot mark, a total of how many whole foot marks are indicated on a 100 foot plus tape? A. 99 B. 100 C. 101 D. 102 16. When slope chaining, which of the following can you obtain by direct reading? A. Slope angle only B. Slope angle and slope distance C. Horizontal distance only D. Slope angle and horizontal distance 13-45 17. In horizontal chaining operations, a call of a “mark” from the rear chainman signals the head chainman to take which of the following actions? A. Pull the end of the tape B. Stick a chaining pin into the ground C. Measure the tension on the tape D. Release the plumb bob 18. When team members are making a horizontal measurement on a slope, the chainman on the lower level determines at what height the chainman on the higher level will hold the tape by using what instrument? A. A transit B. A theodolite C. A hand level D. A plumb bob 19. In which of the following situations should the breaking tape method of measuring be used? A. Determining the horizontal distance between points on terrain having a six to one slope ratio B. Measuring the width of major access roads C. Measuring horizontal distances in heavily wooded and obstructed areas D. All of the above 20. A two-person party is using the breaking chain procedure and a 100 foot tape to chain a line on a steep slope. When, if ever, does the rear chainman give the front chainman a chaining pin? A. Each time only a 25 foot distance is measured B. Each time only a 50 foot distance is measured C. Each time an even foot distance of less than 100 feet is measured D. Never 21. The standard error of a 100 foot tape can be determined in which of the following ways? A. By calibration by the Bureau of Standards B. By comparison with a length of a calibrated 100 foot tape C. By comparison with a known 100 foot distance D. By each of the above means 22. When calibrating a tape, remember that the standard tension and corresponding temperature for a 100 foot tape supported throughout is what? A. 5 pounds at 65 degrees B. 10 pounds at 68 degrees C. 15 pounds at 68 degrees D. 20 pounds at 65 degrees 13-46 23. A 100 foot tape has a standard error of 0.003 feet. What is the total error for a taped distance of 471.56 feet (rounding off to the nearest 0.01 foot)? A. 0.00 B. 0.01 C. 0.02 D. 0.05 24. Under standard conditions, a tape indicates 100.00 feet when it should actually measure 99.996 feet. Using this tape, how far should you measure to see a point 450 feet away from another point? A. 449.96 B. 449.98 C. 450.02 D. 450.04 25. A tape has a standard error which causes it to indicate 99.996 feet when it actually measures 100.00 feet. What is the actual distance between two points if the taped distance is 259.05 feet? A. 259.04 B. 259.05 C. 259.06 D. 260.00 26. A steel tape is used to lay out the distance from point A to point B. If the thermometer attached to the tape reads 79 degrees, what is the actual distance laid to offset the effect of change in temperature? A. 168.09 B. 168.99 C. 169.01 D. 169.07 27. A steel tape is used to lay out the distance from point A to point B. If the thermometer attached to the tape reads 35 degrees, how much should be added or subtracted to the measurement in order to compensate for the change in temperature? A. Add 0.02 feet B. Subtract 0.02 feet C. Add 0.04 feet D. Subtract 0.04 feet 28. A three pound, 100 foot tape is used to measure 60 feet. If the chainman maintained a pull of 20 pounds what is the correction of sag? A. 0.02 feet B. 0.03 feet C. 0.04 feet D. 0.05 feet 13-47 29. When is the slope correction subtracted from the taped slope distance? A. When taping uphill only B. When taping downhill only C. When applying the slope correction formula for 10 percent slopes only D. Always 30. When determining accurate slope correction, what is the maximum slope for which you should use the following formula? s h Ch 2 2 = A. 5% B. 10% C. 20% D. 30% 31. What is the proper way to correct an error in field notes? A. Erase the error B. Blot out the error C. Draw a line through the error and enter the correct information above D. Circle and initial the error 32. In which of the following ratios does the length of the sides indicate that the triangle is a right triangle? A. 10:15:20 B. 18:24:30 C. 20:30:40 D. 30:40:50 33. Computing the size of an angle by the chord method involves the partial solution of a triangle in which the only known values are which of the following measurements? A. The size of two angles B. The length of the sides C. The seize of two angles and length of one side D. The lengths of two sides and the size of one angle 34. Reading a tape upside down and obtaining, for example, 69 instead of 96 and leaving out an entire tape length are samples of what? A. Natural errors B. Instrumental errors C. Personal errors D. Mistakes 13-48 35. In caring for and maintaining steel tapes, a chainman should make it a practice to take which of the following steps? A. Inspect all tapes weekly B. Wipe them dry before storing them C. Coat them from time to time with light rust-resistant oil D. All of the above 36. What is the proper sequence of steps in splicing a broken steel tape? 1. Align and rivet the repair stock at one end of the break. 2. Insert one rivet at a time and arrange the rivets in a triangular pattern 3. Place the repair stock on the face of the other section of the tape, using the calibration section as a measure for the break splice. 4. Use a three-edge file to partially cut through the surplus stock A. 1, 2, 3, 4 B. 1, 3, 2, 4 C. 3, 1, 2, 4 D. 4, 2, 1, 3 37. In which of the following ways are microwave and light wave EDM devices the same? A. Both have interchangeable transmitters and receivers B. Both require the application of correction for atmospheric conditions C. Both are used for the direct measurement of distances D. Both should be used for only short distances of less than 600 feet 38. What symptom is usually the first to be noticed by someone who has come in contact with poison ivy or poison oak? A. A cluster of large blisters B. A deep red rash C. An extreme itching D. A cluster of small blisters 39. Poisonous sumac can be distinguished from nonpoisonous sumac in what way? A. It bears red berries B. It has more leaves C. It bears white fruit D. It grows closer to the ground 40. The first-aid procedure for plant poisoning of the skin consists of which of the following steps? A. Soaping and rinsing frequently B. Applying a light coat of oil C. Obtaining immediate medical care D. Soaping with an alkaline laundry soap and not rinsing it off 13-49 41. While surveying, the members of a field party must work on and near a heavily traveled highway that they are forced to cross several times a day. They can reduce the danger of being struck by a moving vehicle by taking which of the following precautions? A. Wearing brightly colored outer clothing B. Detouring traffic away from the field party C. Erecting conspicuous signs and barriers D. All of the above