Soil Testing Techniques
Cone Penetrometer Testing
The testing facility has available 5, 10 and 15 ton electric cones for penetrometer testing. The 5 ton cone is an electronic tension cone with very high resolution, well suited for investigation of soft and sensitive soils. The 10 and 15 ton cones offer high resolution with a more durable design. Typical 4 channel operation allows for measuring:
- Tip Resistance
- Sleeve Friction
- Pore Pressure
- Cone Inclination
The cone penetration test can be paused at any depth, at the clients request, to undertake pore pressure dissipation testing. The results of such tests can be used to determine consolidation and permeability parameters
The cone penetrometers are delivered by twin hydraulic rams capable of developing 200kN of down feed. The 5 ton cone has full scale operation limits of 50 MPa tip resistance, 1 MPa sleeve friction and 3450 kPa pore pressure, while the 10 and 15 ton cones have limits of 100 MPa tip resistance, 1 MPa sleeve friction and 3450 kPa pore pressure. Note that testing cannot safely continue beyond these limits without risk of damage to the cones.
An additional signal is incorporated into the system to allow for cone penetration testing to be undertaken simultaneously with electrical conductivity or seismic testing.
All test data from cone penetration testing is relayed to a field data acquisition system which allows for continuous monitoring, storing, interpretation and plotting of test data in the field.
The inclusion of a geophone in the seismic cone permits measurement of down hole shear wave velocities during cone sounding, for determining the dynamic shear modulus of a soil.
Seismic measurements are taken when the CPT has stopped. A shear wave is generated at the surface by striking a steel beam with a switched hammer.
The field computer measures the time taken by the shear wave to reach the geophone mounted in the cone.
Undertaking seismic tests at regular depth intervals allows a profile of shear wave velocity to be determined.
Performing seismic measurement during CPT soundings provides a quick, comprehensive and economical method of determining subsurface parameters.
Soil Conductivity Testing
An electronic conductivity module can be operated in conjunction with standard cone penetrometer testing. The combination of typical cone penetrometer parameters with electrical conductivity measurement provides a more comprehensive determination of subsurface parameters.
Conductivity measurements can be used to indicate the location of potential ground water problem such as corrosive soils, salt water intrusions or environmental contamination.
The conductivity module interfaces with the field data acquisition system which provides an auto-ranging technique to ensure accuracy over a range of 0 - 10,000 mS/m of conductivity.
Results of soil conductivity testing can be listed or plotted alongside standard cone penetration results, in terms of conductivity (Ms/m) or resistivity (ohm.m).
Pressuremeter testing can be undertaken in conjunction with typical cone penetrometer soundings. The pressuremeter is attached above the 15 ton penetrometer cone and the cone sounding is temporarily stopped desired pressuremeter test locations. The pressuremeter test provides a quick, easy measure of the in-situ stress-strain relationship of the soil which provides parameters such as the elastic modulus, creep pressure and the limiting creep.