Subsurface Investigation

Subsurface conditions below a site are explored using various methods.

These include:

Hand auger drilling

Hand auger drilling is the simplest method of subsurface conditions. It is hand operated and creates a borehole approximately 50mm diameter. A hand auger penetrates the surface soils and can go to a maximum depth of 5m. Shear vane testing is undertaken in hand auger boreholes to give an indication of soil strength.

Machine Boreholes

Where deeper ground information is required or where information about the underlying rock is needed, machine boreholes are used. The drilling is undertaken by a 3rd party drilling contractor under the supervision of KGA. The recovered core is collected for logging and laboratory testing. In situ testing via standard penetration tests (SPT) are carried out at regular intervals to give an indication of soil strength. At the end of drilling, the area is reinstated, as required.

Cone Penetration Testing (CPT)

CPT testing involves pushing an instrumented cone tip into the ground to measure soil properties. It is a relatively quick method of testing and can penetrate deeper than hand auger boreholes. Samples are not recovered, however the testing can indicate the type of soil, soil strength and liquefaction assessment.

Dilatometer (DMT) and Seismic Dilatometer testing (DMT and SDMT)
DMT and SDMT tests involve pushing an instrumented flat plate into the ground using a CPT rig. This test provides information about the geotechnical properties of the soil which can be used for settlement analyses, liquefaction assessments and foundation design.

Test Pits

Where it is necessary to see a greater exposure of the soil profile than a hand auger or machine borehole allows, test pits are undertaken. These involve a digger excavating into the ground to create a pit or trench. The depth varies depending on the application, but a large digger can excavate to approximately 5m depth. Test pits enable a geologist to see how the soil is lying in situ and can pick up the presence of shear surfaces or other abnormalities. They also locate transition zones between different types of materials.

Groundwater Monitoring

Piezometer standpipes can be installed the boreholes for groundwater monitoring and groundwater measurements can then be undertaken through the life of a project. Where required, data loggers can be installed in piezometers to provide continuous groundwater monitoring.