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.

Seismic Testing

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

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.

Soil, Water and Air Sampling and Monitoring Techniques

Sampling of Ground Water and Gas

The testing facility is equipped with ground water sampling and monitoring system. The system allows for quick, discrete sampling of both liquid and gas phases at specific depths. The sampling module can be inserted using the same apparatus used to push the cone penetrometers. The module is applicable for use in both saturated and unsaturated soil profiles.

After pushing the sampling probe to the required test depth, the push rods are then retracted by 200mm to expose the sampling screen from behind the sealed shield. An evacuated sample vial is lowered through the hollow centre of the push rods until the vial makes contact with a double ended needle which connects the vial and the filter tip. Any number of vial samples can be taken and recovered from a single test depth, to ensure adequate sample size and representation, before pushing to a new test depth.

All elements of the system, including the encapsulated samples, are hermetically sealed preventing loss of volatile components. A sealed shield protects the filter tip during delivery of the probe. This shield is retracted at the point of sampling to prevent cross contamination of samples during penetration.

Soil Pore Pressure Measurement

The BAT system can perform ground water pressure measurements. An electronic pressure transducer allows the BAT module to accurately measure both negative and positive ground water pressures at the position of the filter tip. Pressure measurements in the range from -10m to 150m can be determined to a resolution of 10mm of water column.

Soil Permeability Measurement

The system allows for routine testing of in-situ permeability. Testing involves measuring the rate of flow into or out of a sample container. Flow rates are computed by monitoring the pressure change in the container and using Boyle’s law to convert the pressure change to a volumetric change. Analysis of the time-pressure record yields the coefficient of permeability.