Laser Method of Laying PipeFigure 10-20.—Setting sewer line to grade.subtract the specified cut from 10 feet. At station 8 +50, for example, the height of the top of the batter boardabove the top of the hub would be 10 – 5.55, or4.45 feet.The offset is measured off from a point directlyabove the hub along the batter board; a mark here isdirectly over the center of the pipeline. Battens arenailed on the batter board to indicate sewer center-linealignment. A string is stretched and tacked alongthese battens; this string indicates the horizontal loca-tion of the line and follows the gradient of the line, butat a distance of 10 feet above the invert. The amountof cut required to be taken out at any point along theline can be determined by setting a measuring polealongside the string. If the string indicates 8.5 feet, forexample, another 1.5 feet of cut must be taken out.Corners of rectangular manhole boxes are stakedout much as building corners are staked out. For a boxlocated where a line changes direction, it may be desiredthat the center line of the box bisect the angle betweenthe lines. The box for a curb inlet must be exactlylocated with respect to a street curb to be constructed inthe future; therefore, curb inlets are usually staked outwith reference to the street plan, rather than with refer-ence to the sewer plan.Another useful device for controlling pipelineexcavations and laying pipe is the laser. So manyapplications are being found for the laser that it mayeventually be the only tool needed for the layout andcontrol of construction projects. It can be quickly,accurately, and economically used for purposes suchas distance measurement, alignment for tunnelborings, setting of pipes with desired grades, andsetting of line and grade for many types ofconstruction.The laser is an intense light beam that can beconcentrated into a narrow ray, containing only onecolor (red) or wavelength of light. The resulting beamcan be projected for short or long distances and isclearly visible as an illuminated spot on a target. It isnot disturbed by wind or rain, but it will not penetratefog. A laser can be set up on a bracket or even attachedto a transit telescope. The beam is aligned in the properdirection at the desired grade and can be left relativelyunattended.Today, instead of using batter boards and strings,lasers can be used to control the alignment for excavat-ing trench and setting a pipe. The laser can be set so thatit shines on the boom of a backhoe so that the equipmentoperator can clearly see the illuminated spot. By itsposition, the operator can closely control the depth ofdigging. For laying the pipe, the laser is set in the properdirection at the desired distance above the pipe invert.With the aid of the L-shaped pole or templet, as shownin figure 10-21, the workmen can control the invertelevation. It may also be possible to direct the laserbeam from the inside of manholes through the pipesbeing laid and to control the grade without any interfer-ence from the backill operations. This can be done evenif the pipes are too small for human access.Underground Duct System LayoutThe stakeout for an underground power line issimilar to that for a sewer. For the ducts, cuts areFigure 10-21.—Pipe laying with a laser.10-21
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