Laser Pipe Laying Control

LASER PIPE LAYING CONTROL Presented by: Tomas U. Ganiron Jr, MSCE •4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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Main Purpose:  define a visible laser line which can be interrupted anywhere  the centre of the spot taken as a reference point Incorporate:  own built-in self-levelling system OR  designed to fit into conventional surveying instrument tribrachs to enable levelling to be achieved •4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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used in conjunction with special targets on which the beam is viewed in order to check if there is any deviation from the designated direction Beam:  remains at a constant small diameter (10-20 mm) at any point along its working range OR  others have a lens system and need to be focused: 

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enables a smaller well-defined dot to be established at a particular location

if intercepted at other locations, beam diameter may not be usable and refocusing will be necessary

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•Author: Engr. Tomas U. Ganiron Jr

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the latter system is slightly more expensive to produce because of additional lens system required  used in any application requiring the setting out of line, level, slope or verticality In construction:  controlling pipelaying, pipejacking, tunnelling, rail alignment and dredging  most of them are purpose-built laser alignment equipment and have been developed to perform the particular task 

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•Author: Engr. Tomas U. Ganiron Jr

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most contractor tend to use purpose-built instruments which come under the general title of pipelasers used with targets fitted inside the pipe extremely robust and totally waterproof able to cope with adverse ground conditions and handling that they inevitably receive on construction site

Waterproof  not affected by flooding and will continue to function even if totally immersed  withstand pressure exerted by 10m head of water  can be used in a wide range of temperatures, (-25 to + 50°C)  diameter is about 10mm (varies with manufacturer)  low angular divergence (diameter increases very slowly with distance)  no focusing of the beam is required •4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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enables very long ranges to be achieved before divergence has too great an effect on the size of the laser spot (max. range 300m) Safety point of view:  most conform to Class 3A safety category  necessary when laying pipes in bright sunlight in order that the beam can be seen clearly on the target  so greater safety precautions must be taken 

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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Self Levelling 

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use electronic level-vial system manually operated level bubble which has to be centred initially to level the instrument roughly, then the automatic levelling system takes over instrument accurately levels itself in both the grade-axis and the crossaxis

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no danger of using the instrument when it is not level, since each incorporates some type of warning system which is activated while the self-levelling procedure is being carried out serves to notify the operator that the instrument is not yet ready to be use usually the beam flashes and, in some machine, a light also flashes on the display panel warning system also operates when the instrument is knocked-out of level during use

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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if possible, the instrument will re-level itself, but one must remember that it will not necessary re-level at the same height as before since it may have been moved in a vertical direction in addition, it will not necessary re-align itself on the target as a result, setting up on unstable ground must be checked regularly accuracy of the self-levelling system should also be checked regularly

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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incorporates motors which are activated by electronic circuitry within the instrument used to control the both the grade and line

Grade:  dialled in by turning a control knob  amount introduced is indicated on the instrument control panel, usually a LCD display  can be altered in increments of 0.002% over ranges from +30% to -10%

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for some machine, separate display panels are used to avoid confusion in indicating positive and negative grades required grade is calculated from:

height difference between manhole inverts grade (%)  100 horizontal disatance beteen manhole inverts 

a greater positive grade range is provided since pipes are usually laid uphill

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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Line:  controlled by simply turning a dial on the control panel  exact figures are not displayed since pipes are always laid with the aid of targets  the line is controlled by turning the dial until the beam hits the centre of the target

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•Author: Engr. Tomas U. Ganiron Jr

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besides manual mode, most lasers have a remote-control facility either by cable (12m) or wireless (80m)

Supports: 

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available to deal with any requirement, e.g. used inside or outside the pipe, above ground or in a manhole always used in conjunction with translucent targets beam is generated either exactly down or some known distance below its centreline, e.g. 15mm below the centreline of a 150mm diameter pipe

For larger-diameter pipes :  adjustable-length legs can be fitted to enable the beam to be projected either along the centreline or at some known height above the invert level For manhole locations:  adjustable cross-bracing is available to which the laser can be attached For above-ground work:  tripod mountings can be used •4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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Targets: 

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available in a variety of sizes and to fit into every size of pipe down to 150mm diameter ruggedly made and easy to read some are adjustable for centering in a range of pipe diameters and are fitted with 2 level vials to enable them to be levelled either right-side-up or upsidedown others are specially designed either self-centre or to fit exactly into pipes of a particular diameter

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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Refraction :  during pipelaying, laser beam may be refracted as it travels through the air in the pipe Occur :  when placing a warm pipe into a cold trench (or vice versa)  when a long stretch of pipe is left exposed in the trench such that it is heated by the sun on top and cooled by earth and possibly water on the bottom •4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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if there are pockets of hot and cold air present, a temperature gradient occurs the beam will be deviated from its intended straight path by the different densities

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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use special blowers to flush the pipe with air of a constant temperature while lasers is being used  

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mount laser higher up in the pipe 

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standardizes the density of the air within the pipe air circulation can be further improved if the blower nozzle is inserted into the pipe at a skew angle to create the corkscrew effect air temperature may be more constant

mount laser on top of the pipe 

•4.23/2000

pipelaying procedure being controlled externally •Author: Engr. Tomas U. Ganiron Jr

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amount of deflection of the beam increases exponentially as the target is moved further away the laser 

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move laser along the pipe as construction progresses and thus minimized the amount of deflection

backfilling the trench as soon as possible after the pipe has been laid can help to stabilize the air temperature inside the pipe

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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owner’s manuals normally give very detailed and easy-to-read descriptions of how the line of a pipe can be established Main Problem:  initial setting of the laser beam at the required direction along which the pipe is to run  the rest is simply moving the target to the next pipe being laid, which is adjusted in position and bedded in when the beam hits the centre of the target 

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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initial direction can be set in one of two ways, depending on the depth of the work Assume:  a ranging rod, peg or batter board has been placed on the surface at the next manhole location  a known level has been transferred into the bottom of the manhole or trench either by taping, vertical taping or some other suitable method 

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•Author: Engr. Tomas U. Ganiron Jr

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Shallow manholes and trenches: 

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with reference to the known level, the laser support is adjusted so that the beam is at the correct level in the excavation the required grade is set and the beam is aimed in the approximate direction

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a piece of cord is used as a sight line and is attached to a special hook which is usually fitted as standard carrying handle of the instrument the operator lines this in with the ranging rod at the next manhole, and adjusts the direction of the laser beam using the remote-control device until it is on the correct line

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•Author: Engr. Tomas U. Ganiron Jr

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Deep manholes and trenches: 

with reference to the known level, the laser support is adjusted until the beam is at the correct level at the bottom of the excavation or in the base of the manhole and at a point on the proposed line of the pipe

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a theodolite or special sighting telescope, which is usually available as an optional extra, si mopunted in such a position that it is directly above the laser done either by optical plumbing or by mounting the sight device on a lone vertical pole attached to the laser support

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sighting device is pointed at the ranging rod defining the next manhole location, and is used to control the line of the excavation once a short distance has been excavated, the sighting device is tilted downwards to give the line on the excavation wall the required grade is set on the laser and the beam direction is altered using the remotecontrol device until it is on the correct line as seen through the sighting device

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•Author: Engr. Tomas U. Ganiron Jr

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restricted to straight pipe runs curved section must usually be controlled by conventional techniques majority of pipelines run mainly in straight lines application of lasers to their control has many advantages over conventional methods

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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Eliminates the tools for conventional pipelaying control techniques   

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such as sight rails, profile boards and travellers awkward to use and have a tendency to be knocked over by site equipment lasers can be used in areas where surface conditions preclude the use of conventional techniques, e.g. in marshy and swampy ground

Speeds up work 

•4.23/2000

decreases the time required to do the job, up to 30pipe can be laid in the same time frame •Author: Engr. Tomas U. Ganiron Jr

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Materials costs are reduced 

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as is more accurate than conventional methods (better than ±10 mm in 100m), trench excavation can be to the minimum depth and width required estimated that approximately 15% of bed material costs can be saved as the laser prevents an excavator overdigging

Less shoring is needed  

•4.23/2000

the whole pipelaying activity is in a limited area safety is improved since backfilling can be carried out almost immediately •Author: Engr. Tomas U. Ganiron Jr

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Labour costs are reduced 

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elimination of sight rail-traveller technique means that fewer personnel are required for “eyeing-in” purposes no bankman is needed with an excavator to indicate when the correct level has been reached (may need for safety purpose)

Constant check during construction 

•4.23/2000

any movement or collapse will cause the beam either to move on the target or to be blocked completely.

•Author: Engr. Tomas U. Ganiron Jr

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Price, W.F. and J Uren (1989) Laser Surveying, Van Nostrand Reinhold (International) Co. Ltd., London Bannister, A & S. Raymond (1984) Surveying, 5th ed., ELBS/Pitman, Bath.

Jackson, J.E. (1977) Plane and Geodetic Surveying for Engineers, vol. 1, 6th ed., Constable & Co. Ltd. Schofield, W. (1993) Engineering Surveying, 4th ed., Butterworth-Heinemann Ltd., Oxford.

•4.23/2000

•Author: Engr. Tomas U. Ganiron Jr

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