Excess Pore Water Pressure Generation, Distribution and Dissipation in Self-boring Pressuremeter Test: Numerical Analysis

Pore-water pressure is generated during the self-boring pressuremeter test (SBPT) in saturated fine-grained soils. The excess pore-water pressure (EPWP) generated during the expansion of the probe may also dissipate due to partial drainage and this affects the test results. The main objective of this paper is to present a numerical model to investigate the simultaneous effect of factors influencing the EPWP-response and to determine the drainage range for the interpretation of field data. The problem was simulated using coupled pseudo-static finite element analysis by assuming small-strain deformation. Probe expansion was investigated using the strain holding approach, and EPWP-generation and dissipation were monitored around the probe over time. The results of the numerical analysis were validated by the field, theoretical, and numerical data. The effects of the permeability coefficient (isotropic and non-isotropic) and constant and variable strain rates were simultaneously investigated. The results of parametric studies indicated that in the SBPT with probe geometry (L/D=6\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L/D = 6$$\end{document}) and conventional radial strain rate (1%/min), partial drainage occurs in the permeability coefficient range 10−6–10−11 m/s. Therefore, the assumption of undrained conditions in the cavity expansion stage under these states is incorrect. In addition, for different radial strain rates (0.01–100%/min), the variation in drainage behavior from drained to undrained conditions was noticeable. Therefore, for the normalized velocities in the range of 0.0001 to 1, considerations regarding partial drainage seem necessary. In addition, it was found that the dissipation curve is also affected if the strain rate is varied during the cavity expansion stage.