CHARACTERIZING SPATIAL VARIABILITY OF A CLAY BY GEOSTATISTICS

This paper presents a characterization of the variability of a lightly overconsolidated and highly sensitive clay deposit located near Saint -Hilaire, 50 km east of Montreal. The geotechnical investigation consi sted of in situ and laboratory tests. The variability of the in situ t est results is the subject of this paper. The working hypothesis assum es that piezocone and vane test results may be modelled by a random fu nction. This is done on the basis of a geostatistical approach. In sit u vane and piezocone tests are found to increase with depth following a linear trend. This is a nonstationary problem and inference of the a utocorrelation function must be made through the estimation of a gener alized covariance. Results for both types of tests give the same shape of generalized covariance. Measurements made with both testing device s yield the same 2 m autocorrelation distance but the standard deviati ons are different. The standard deviations for the piezocone cone resi stance, pore pressure behind the cone tip, and sleeve friction are 74, 34, and 2.1 kPa, respectively. Vane measurements have a standard devi ation of 4.9 kPa. Results are also presented for the estimation of the vertical linear trend and for the statistical distributions of fluctu ations.