To assess the geotechnical properties of soil, the pressuremeter test has been widely employed since its introduction in 1955. This test is instrumental in determining key parameters such as the limit pressure (Pl), creep pressure (Pf), and modulus of deformation (EM). The fundamental principle of the test involves inserting a radially expandable probe into a borehole, which is subsequently expanded through incremental loading steps, with the resulting volume variation being measured. Traditionally, each loading step is maintained for a duration of 60 s according to European and American standards. In the scope of this study, an investigation was conducted to evaluate the impact of varying the loading time, specifically extending it from 60 to 120 s. These tests were carried out across diverse soil types at four sites in Tunisia. The findings revealed that beyond the 60-s loading period, the soils exhibited continued deformation. Notably, the limit pressure demonstrated a decrease with the prolonged loading time for most of the tested soils. This reduction, ranging from 2% to 30%, was particularly pronounced in soft and sandy clays. Furthermore, the creep pressure, representing the threshold of the soil's pseudoelastic behavior, also experienced a decline with the increased loading time. The pressuremeter modulus EM2, which is obtained for a loading step of Delta t = 120 s, exhibited a reduction across all soil types, with this reduction being more prominent in fine soils characterized by low consistency.

Self-boring pressuremeter (SBPM) tests are widely used in situ investigations, due to their distinct advantage to measure the shear stress-strain-strength properties of the surrounding soil with minimum disturbance. The measured pressuremeter curve can be interpreted using analytical solutions based on the long cylindrical cavity expansion/contraction theory with relatively simple constitutive models, to derive useful soil properties (e.g., undrained shear strength of clay, shear modulus, and friction angle of sand). However, the real soil behavior is more complex than the assumed constitutive relations, and the derived parameters may differ from those obtained using more reliable lab tests. In addition, SBPM tests can be affected by other well-known factors (e.g., installation disturbance, limited length/diameter ratio, and strain rate) that are not considered in the analytical solutions. In this paper, SBPM tests are evaluated using finite-element analysis and the MIT-S1 model, a unified constitutive model for soils, to consider complex soil behavior more realistically. SBPM tests in Boston Blue Clay and Toyoura sands are simulated in axial symmetric and plain strain conditions, and the computed results are interpreted following the suggested procedures by analytical solutions. The derived parameters are compared with those from the stress-strain relations to evaluate the reliability of SBMP tests for practical application.

The pressuremeter test is a widely used in-situ test method in geotechnical engineering for determining ground properties. It is applicable to all types of soil and weak rocks, it records soil deformation under loading conditions. This paper presents a literature review on the application of the pressuremeter test in evaluating the behavior of foundations under load. It explores the methods used to interpret pressuremeter test data in various soil types, reviews the different analytical models employed, and focuses on approaches for assessing the behavior of foundations using pressuremeter test results. The achievements and limitations of each method are presented and discussed. Despite the extensive literature on the applications, interpretation, and development of the pressuremeter test, its use in evaluating the behavior of foundations under load remains limited. This work seeks to address this research gap by identifying challenges in utilizing pressuremeter test data for such analyses and providing recommendations for future research. This work aims to encourage further investigation into the potential of pressuremeter tests for advancing the understanding of foundation behavior under loading conditions.

Many geotechnical scenarios involve cavity unloading from a loaded state, particularly in pressuremeter tests, and the unloading data of pressuremeter tests has exceptional attraction as it is less disturbed by the insertion process. However, the analyses for continuous cavity loading and unloading (i.e., cavity initially experiences expansion and then contracts) in critical state soils are rarely studied. To this end, a novel semi-analytical solution based on the unified state parameter model for clay and sand (CASM) is proposed for the whole expansion-contraction of spherical and cylindrical cavities under undrained conditions. The problem assumes that the cavity is unloaded after a monotonic loading stage, leading to plastic regions during both loading and unloading periods. The cavity response for the whole expansion-contraction process is investigated, with the total pressure and stress paths at the cavity wall presented and validated against numerical simulation. The developed solution is successfully implemented to interpret both loading and unloading data of pressuremeter tests. The undrained shear strength, in situ effective horizontal stress and initial overconsolidation ratio are back analyzed by using a curve fitting method based on the proposed solution.

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.

Accurate numerical analysis in geotechnical engineering heavily relies on the constitutive model and its parameters. The advanced constitutive model can describe the complex mechanical behaviors of soil that may involve a number of parameters. However, determining the values of constitutive parameters always relies on manual trial-and-error, which can be a time-consuming process and not conducive to widespread application. This paper presents an identification method that combines machine learning with search algorithm based on the laboratory and in-situ testing. Initially, the sensitivity of constitutive parameters was analyzed by investigating the effects of variations in soil overconsolidation and structural parameters on the results of triaxial and pressuremeter tests. Subsequently, the initial state parameter values and material control parameter ranges of the soil can be identified from the triaxial tests, this is achieved by using the neural network model. In order to accurately determine the parameters value, the numerical model was established based on in-situ pressuremeter test, and traversal algorithm was implemented to search for the optimal fit values within the range of material control parameters. Finally, the proposed identification method was applied to layers 3 - 5 of Shanghai clay, and the inverted parameters exhibited a good fit with the outcomes of triaxial tests and pressuremeter tests. The combination of laboratory and in-situ testing can enhance the reliability of obtaining constitutive parameters, and this method provides an insight into the parameters identification for advanced constitutive models.

In the last decade, a new multi-scale FEMxDEM approach has been developed using Finite Element Method (FEM) coupled with Discrete Element Method (DEM) as a constitutive law to account for the specificities of the mechanical behavior of granular materials. In FEMxDEM model, a DEM calculation is performed on a particle assembly (volume element-VE) at each Gauss point. Recent publications have demonstrated that FEMxDEM approach naturally captures the discrete and anisotropic nature of granular materials. Despite its advantages, FEMxDEM with classical FEM, suffers from mesh dependency, especially when material enters softening phase and exhibits strain localization. To overcome this limitation, FEMxDEM model has been enriched by incorporating a local second gradient model. Nevertheless, the existence of multiple possible solutions is observed. In this paper, we study the variability and loss of uniqueness of numerical solutions to a boundary value problem. Different VEs with equivalent mechanical properties are generated and used to model the pressuremeter tests by means of FEMxDEM. The modeling results show a great variability of the numerical results, both in shape of borehole and in different modes of shear bands. For the same VE, the loss of uniqueness of numerical solutions is evidenced by a slight modification of loading history at the level of the internal pressure applied to the borehole. Finally, we show that when a certain heterogeneity is introduced by using different VEs within the same BVP, even if the uniqueness of the solution is not guaranteed, the set of possible solutions seems more restrained.