SAMPLE DISTURBANCE EFFECTS IN SOFT LOW PLASTIC NORWEGIAN CLAY

The Sherbrooke block sampler has been used at several clay sites in Norway. Samples down to 22 m (72 ft) below ground level have successfully been obtained. Standard piston sampling with the 54 mm (2.12 in) NGI sampler have been obtained at the same sites. 75 mm (29.5 in) and 95 mm (27.4 in) piston samples have been obtained in some cases. Piezocone test results are also available. Subsequent laboratory testing (CAUC triaxial and CRS oedometer tests) clearly show the superior quality of the block samples compared to the piston samples; this is at least the conclusion to a depth of 16 m (48 ft) where comparative results are available. The effects of sample disturbance are especially dramatic for low plasticity clays. The results are described in detail and the soil parameters that are most affected by sample disturbance are identified. The results are used to develop a new criteria for evaluation of sample disturbance. It is also stressed that results of CAUC and CRS tests on piston samples should be corrected to reduce the effects of sample disturbance. Soil parameters as measured on the block samples are used as reference parameters for a new generation of correlations for interpreting CPTU results.