Additional CPT Testing

GEONOR H10 VANE

The Geonor H10 vane is used to measure, ‘in situ’ the undrained shear strength and the re-moulded shear strength in clays. The system is used predominantly in soft clay material.

The system is designed to be pushed into the soil using a CPT rig, to reduce the potential soil

disturbance associated with drilling. The vane comprises of a number of different parts; the vane itself sits on a number of 1m long inner rods. The inner rods run up inside the 1m long outer rods. At the base of the outer rods is the vane housing shoe in to which the vane is located when being pushed through the ground; finally, at the top of the vane is the calibrated torsion head.

MOSTAP SOIL SAMPLER

The MOSTAP soil sampler is a relatively ‘undisturbed’ pushed soil sampler. The sampler provides good samples of soil for identification and classification purpose. The samples may also be used for classification lab testing and triaxial and odometer lab tests.

The main advantage of this system is the ability to take samples at discreet depths. The system is pushed in to the ground with the cone tip in place. When the depth of the required sample is reached a ‘fishing tool’ is lowered down, releasing the cone tip to reveal the cutting shoe. The system is then pushed a further meter in order to take the sample.

The sampler goes inside a stockinet (to reduce the side friction) and then inside a plastic sample tube and it takes a 1m long 65mm sample.

 

SEISMIC MARCHETTI DILATOMETER

The dilatometer is a tool used to estimate settlement and operative moduli in both sands and clays, and also the shear strength in clay.

A dilatometer test consists of pushing a flat blade located at the end of a series of rods, into the ground. Once at the testing depth, a circular steel membrane located on one side of the blade is expanded horizontally into the soil. The pressure is recorded at specific intervals during the test. The blade is then advanced to the next test depth.

The seismic dilatometer has the added module behind it of duel seismic receivers. The seismic receivers allow the measuring of shear wave velocity (Vs). The seismic source is obtained by a swinging hammer hitting horizontally onto a metal plate. The shear wave velocity is the ratio between the difference of distance between the energy source and the two receivers and the measured delay time of the pulse from the upper to the lower receiver. Vs may be converted into the initial shear modulus G0.

The two measured pressures (p0 and p1) from the dilatometer are used to obtain the three index parameter:
Id – Material Index
Kd – Horizontal Stress Index
Ed – Dilatometer Modulus

By means of correlations the index parameters are used to interpret the following parameters:
M – Oedometer modulus (both in cohesive and cohesionless soils)
cu – Undrained shear strength (cohesive soils)
Ko – In situ earth pressure coefficient (cohesive soils)
OCR – Overconsolidation ratio (cohesive soils)
? – Friction angle (cohesionless soils)