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Datum Installations

Deep Seated Datums are installed by drilling into the ground (usually at a 6m depth) using either our Restricted Access CFA rig or by hand. Once the depth is reached, the datum rod is installed. From this fixed datum point, level readings can be referenced.

The deep seated datum should be placed at the furthest point of any site influences.

Standpipes / Piezometers

Simple standpipes to measure the hydrostatic head of groundwater are formed in boreholes using 50mm diameter pipe. The details of individual installations are provided on borehole records. Typically the lower length is formed in slotted pipe, with the upper 1m un-slotted. The annulus between the riser pipe and the borehole wall is filled with clean granular material. Details of any bentonite seals or grouting are given on the borehole records. A removable gas tap is fitted where gas monitoring is required and standpipes typically have a metal access cover concreted in at ground level.

Standpipe piezometers are formed by using a Casagrande type piezometer tip at the base of the pipe, set in a granular response zone of sand or pea gravel. The response zone is isolated from the strata above and below by placing 500mm thick bentonite seals. The remaining annulus above the bentonite seal is filled with a cement bentonite grout or similar.

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