Analysis of pressuremeter geometry effects in clay using critical state models

Abstract

SUMMARYThe conventional interpretation methods of pressuremeter testing effectively approximate pressuremeter membranes as infinitely long. As a result, the effects of the two-dimensional geometry of pressuremeters are ignored, leading to an overestimation of soil shear strength by pressuremeter testing, as demonstrated in several previous studies. This paper presents results of a numerical study of two-dimensional geometry effects on self-boring pressuremeter tests in undrained clay. The results are obtained using critical state soil models with an effective stress formulation. This is in contrast to most (if not all) existing studies on pressuremeter geometry effects, which were based on perfectly plastic soil models (e.g. Yu (Cavity expansion theory and its application to the analysis of pressuremeters. DPhil Thesis, The University of Oxford, 1990), Yeung and Carter (Proc. 3rd Int. Symp. on Pressuremeters, 1990), and Houlsby and Carter (Ge´otechnique, 1993; 43 (4):567-576)). The present study suggests that the overestimation of soil strength due to the neglect of finite pressuremeter length is significantly affected by the soil model used in the calculations. It is found that for clays with a high overconsolidation ratio (OCR) the strength overestimation predicted using critical state soil models could be considerably smaller than that predicted using perfectly plastic soil models. The main conclusion of this numerical study is that care must be exercised before directly applying any numerically determined pressuremeter geometry correction factors in practice.

A combined neural network/gradient‐based approach for the identification of constitutive model parameters using self‐boring pressuremeter tests

“…The numerically optimized values of R p may also sustain the geometry effect since all of the analyses were carried out with the simplified numerical mesh representing a unit of pressuremeter membrane. As reported by Yu et al [31], the effect of geometry in lightly consolidated soil may have an influence on the derived [60] are higher than those derived numerically, which can be attributed to the assumed undrained conditions.…”

“…The FE mesh was built with the full awareness of the existing analyses of the L/D geometry effect (e.g. [31]). It was also assumed that the expansion takes place in a fully saturated medium.…”

Relationship between small and large strain solutions for general cavity expansion problems in elasto-plastic soils

“…The second example considers a self-boring pressuremeter with length to diameter ratio of 6. It should be emphasized that intention here is not to study the effect of pressuremeter geometry on the interpretation of test results (for such investigations see Houlsby & Carter [27], Shuttle & Jefferies [28], Yu et al [29]), but to verify the accuracy of the derived relationship in a typical cavity expansion problem with rotating principal directions. Therefore, a simple numerical model of the finite length self-boring pressuremeter is used (Fig.…”

Undrained cavity expansion analysis with a unified state parameter model for clay and sand

“…In addition to classical cavity expansion solutions in elastic materials, a range of analytical solutions have been proposed using more sophisticated constitutive soil models, from elastic-perfectly plastic soils (Vesic, 1972;Carter et al, 1986;Yu & Houlsby, 1991;Mo et al, 2014) to elasticplastic strain hardening soils (Palmer & Mitchell, 1971;Collins & Yu, 1996;Chen & Abousleiman, 2012, 2013. Although numerical simulations are gaining popularity for boundary value problems when sophisticated soil models are employed (Carter, 1978;Yu, 1990;Yu et al, 2005), analytical solutions remain highly useful both for validation of numerical simulations and providing insight into the relative importance of various soil parameters.…”