The contraction behavior of monotonically expanded cavities is intriguing as it offers insights into certain geotechnical scenarios, especially for pressuremeter tests, where the unloading data is equally informative as the loading data. Despite many solutions for cavity expansion, attempts for the analyses of cavity contraction from an expanded state were rarely made. To extend previous solutions to include contraction, this paper presents a novel semianalytical solution for drained contraction of spherical and cylindrical cavities from an initially expanded state in soils characterized by a unified state parameter model for clay and sand (CASM). Given the nonself-similar nature of the contraction after expansion problems, the hybrid Eulerian-Lagrangian (HEL) approach is employed to derive distributions and evolutions of stresses and strains around the cavities during the unloading process. Combined with the previous expansion solution, the complete loading-unloading cavity pressure curves and stress paths at the cavity wall are presented and verified against numerical simulations. Following validation through comparisons with calibration chamber pressuremeter tests conducted in Stockton Beach sand, a new method for the interpretation of pressuremeter testing data is developed based on the proposed solution. This method demonstrates its capability in the back-calculation of the effective horizontal stresses and state parameters for four distinct types of sands.

The expansion of a thick-walled hollow cylinder in soil is of non -self -similar nature that the stress/ deformation paths are not the same for different soil material points. As a result, this problem cannot be solved by the common self -similar -based similarity techniques. This paper proposes a novel, exact solution for rigorous drained expansion analysis of a hollow cylinder of critical state soils. Considering stress -dependent elastic moduli of soils, new analytical stress and displacement solutions for the nonself -similar problem are developed taking the small strain assumption in the elastic zone. In the plastic zone, the cavity expansion response is formulated into a set of first -order partial differential equations (PDEs) with the combination use of Eulerian and Lagrangian descriptions, and a novel solution algorithm is developed to ef ficiently solve this complex boundary value problem. The solution is presented in a general form and thus can be useful for a wide range of soils. With the new solution, the non -self -similar nature induced by the finite outer boundary is clearly demonstrated and highlighted, which is found to be greatly different to the behaviour of cavity expansion in in finite soil mass. The present solution may serve as a benchmark for verifying the performance of advanced numerical techniques with critical state soil models and be used to capture the finite boundary effect for pressuremeter tests in small -sized calibration chambers. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).