Comparison of undrained shear strength by pressure

Authors: Nihat Sinan Isik Resat Ulusay Vedat Doyuran

Publish Date: 2014/07/24

Volume: 74, Issue: 3, Pages: 685-695

PDF Link

Abstract

There is a wide body of research reported in the literature which compare the undrained shear strength determined from various field and laboratory tests The pressuremeter testing equipment and the related design techniques have been continuously refined However the undrained shear strength S u determined from the pressuremeter test PMT is generally higher than that obtained from other field or laboratory tests In this study numerical methods to consider the effects of length to diameter ratio L/D of the pressuremeter probe and the procedural implications of soil disturbance and testing depth on the undrained shear strength determined from the PMT were investigated and possible correction factors depending on L/D ratio were established In addition in order to compare the variations in undrained shear strength of a clayey material with depth and testing method a lightly overconsolidated and highly plastic clay called “Eymir Lake clay” near Ankara Turkey was selected as the material of the study and its values of undrained shear strength S u which were determined by PMT field vane shear FVT conic penetration test CPT and laboratory tests were compared Based on the numerical analysis results the correction factors depending on the L/D ratio of the conventional probes were suggested The correction factors ranged from 083 to 096 for L/D ratios of 53 to 11 respectively and they were determined to be independent of the rigidity values ranging from 25 to 200 It was also shown that overestimation of S u is independent of depth In addition due to very low permeability values of the Eymir Lake clay it is concluded that for soils with coefficients of permeability lower than 10−10 m/s partial drainage around the pressuremeter probe is unlikely Based on the comparison among the results from laboratory and different field tests the values of S u determined from the theoretical Palmer’s solution are higher than those from CPT FVT and CU tests If the correction for L/D ratio is applied to the values of S u determined from the Palmer’s solution S u from pressuremeter approaches S u obtained from FVT however there is still a slight overestimation in S u obtained from PMT This overestimation is probably due to the differences in the mode of failure and the presence of a disturbed zone around the pressuremeter probe However S u determined from the PMT by empirical methods is close to those determined from CPT FVT and CU testsThe support provided by Zemar Corporation through the cone penetration tests is gratefully acknowledged The authors also acknowledge the anonymous reviewers for their critical and constructive comments that lead to significant improvements in the article

Keywords: