An optimization strategy for evaluating modified Cam clay parameters using self-boring pressuremeter test data

Abstract

This paper presents an efficient, practical, and automated strategy for deriving modified Cam clay parameters from undrained self-boring pressuremeter (SBPM) data. A mixed approach involving a parametric sweep and numerical optimization is used, with a focus on parameter groups that dominate the modified Cam clay response in undrained cavity expansion. The proposed technique is illustrated using data from SBPM tests carried out in soft estuarine clay. The resulting parameters are used to back-analyse large-scale foundation load tests and are shown to provide an excellent match to the measured foundation response.

Insights from a shallow foundation load-settlement prediction exercise

“…A shear modulus profile was also derived using a numerical optimisation technique to match the modified Cam clay model to undrained self-boring pressuremeter data. Full details of this process are presented by Gaone et al (2017a). The resulting match of the optimised modified Cam clay model to the pressuremeter data is shown in Figure 12b.…”

Large-scale shallow foundation load tests on soft clay – At the National Field Testing Facility (NFTF), Ballina, NSW, Australia

“…The secant shear modulus of the triaxial data, G10 and G50 were interpreted using two different points on the curve of the total change in deviatoric stress (10% and 50% of the total change in deviatoric stress). Interpretation of the shear modulus from SBPM tests were performed using an inverse analysis (GIA) method [18] and from the slope of unload-reload loops (GUR).…”

“…The crust was modelled as an elastic perfectly plastic material as in the analysis of the UU test. The Modified Cam Clay (MCC) model was adopted to represent the soil response of the soft clay with parameters derived through an optimization analysis of undrained self-boring pressuremeter tests [18]. The optimization method focused on matching the undrained shear strength and stress strain response from the self-boring pressuremeter and focused on matching composite parameters Λ, (where Λ=1 -κ/λ) and κ* (where κ* = κ/(1 + e), where κ is the slope of the unload reload line; λ is the slope of the normal compression line.…”

“…Based on the information given in Figure 4 the permeability k was taken as 1.0E-08 m/s and the vertical stress profile for the FEA was determined based on the soil unit weight. An average value of coefficient of earth pressure at rest, K0 = 1.0 was based on the inverse analysis of 21 SBPM tests over the depth of interest according to a numerical optimization procedure set out in the literature [18].…”

“…MCC parameters could alternatively be derived through a programme of element tests [13], but this does not necessarily result in a consistent set of parameters relevant to the boundary value problem that the parameters are then applied to. The philosophy and process of the inverse analysis method for deriving an optimized and consistent set of soil parameters is discussed in detail in the literature [18]. The sequence of the key activities modelled replicated the site activities for test CU1 and included:…”