Download - Engineering Surveyor

River works: sheet pilesMethod of installationAs on land, sheet piles are driven in ‘panels’, using a pair of walings as a guide. Pairs of temporary piles are drivenat ‘panel’ intervals either side of the sheet pile centre-line. A crosshead, located on a pair of temporary piles, supportsthe ‘leading’ end of the walings. The ‘trailing’ end is supported on the end pile of the panel of sheet piles previouslydriven. Thus it is necessary to check the line of the leading end of the waling before each panel is driven.Note: Temporary piles are often later used to support falsework.Line of piles at angle to shoreFor sheet piles at an angle to a river bank:set up theodolite or total station on line offset to centre-line of piles; fix offset targets at each end of walingsight along offset centre-line and align both ends of walingafter driving first panel of piles, set trailing end of waling against last pile driven and align leading end.Line of piles roughly parallel to river bankSet up a baseline along the river bank and use bearing and distance or two bearings to set up the walings asdescribed previously. Alternatively, sighting marks could be set up on temporary piles.Driving piles to levelTo drive piles to required level with fair accuracy in reasonably calm water: set up staff gauge to be read from piling rig (staff gauge indicates tide/river level relative to the leveldatum) mark required level on pile drive pile until mark on pile and same level on staff gauge are same distance above water level.Underwater concretingHaving constructed a sheet pile cofferdam, it may be necessary to concrete a base underwater. If formwork isrequired, it must be positioned by divers. Within reasonable limits of accuracy, this can be achieved as follows: set out each locating point from the shore stations fix plywood sheets (or timbers) to the upper walings drill small holes through ply and suspend plumb-bobs from piano wires passed through the holes when divers have located formwork by plumb-bobs, use weighted tape to define required concreting level.CIRIA C709107