Numerical simulation of CPT in dry and saturated soils using CFD–DEM

Can foam always reduce sandy soil’s permeability? CFD-DEM insights and a gradation-dependent threshold for EPB shield tunneling

Assessing the Potential of Numerical CPTs to Improve the Geotechnical Characterization of Offshore Sites: Case of the Italian Sea

The paper presents the results of large deformation finite element analyses of laboratory and site cone penetration tests (CPTs) in sand. The numerical model implements the Arbitrary Lagrangian-Eulerian formulation and hypoplastic constitutive model to reproduce the soil response. Available laboratory CPTs conducted in dense sand within a large-scale testing facility were used to calibrate the model and to assess its ability to reproduce the cone penetration mechanisms and to explore the effect of variation in the cone size. The approach, as validated, was then applied to reproduce CPT tests carried out in the Italian offshore. Within the scope, new parameters were identified for the soil model using routine test data. The model was shown to successfully reproduce the profiles of cone resistance as collected on-site, also in the presence of local variation of soil density, assessing the modeling procedure as a whole and providing the basis for broader applications related to the study of large deformation problems in the offshore environment, such as those concerning foundation installation. The model also allows for verifying the consistency of CPT-based empirical correlations, such as the relative density and the peak friction angle, improving confidence in their use in design. The outcomes of the work also show how geotechnical site information collected in the past can be turned into a practical tool to support the geotechnical design of new offshore developments, supporting, in a practical way, the transfer of knowledge from the oil and gas to the renewable energy market.

Numerical Investigation of Key Parameters Influencing Stone Column Behavior and the Impact of Column Arrangement on Liquefaction Mitigation in Sandy Soils

One of the most critical challenges faced by geotechnical engineers is soil liquefaction and its associated damage. When saturated soil is subjected to seismic vibrations, its static equilibrium is disrupted due to irregular dynamic forces, leading to the occurrence of liquefaction. This study first validates the numerical model using the results of VELACS physical modeling. Subsequently, a 3D numerical analysis is conducted using FLAC 3D to perform a parametric study on the factors influencing the pore water pressure generation, such as ground acceleration, soil compaction, and stone column dimensions. The results indicate that an increase in the stone column diameter consistently reduces settlement and horizontal displacement. However, this trend diminishes for diameters exceeding 0.8 m. With an increase in peak ground acceleration, soil mass displacement increases in all earthquake scenarios. A nearly linear relationship is observed between acceleration increase and excess pore water pressure at distances of 3.5 and 5 m. On the other hand, higher soil compaction reduces displacement but has a limited effect on decreasing excess pore water pressure within the soil mass. The findings reveal that the effective influence range of stone columns extends up to 1.5 m in all directions, beyond which the impact on liquefaction mitigation is minimal. Therefore, it is recommended to install stone columns at a maximum center-to-center spacing of 3 m. A configuration involving multiple stone columns demonstrated superior performance in dissipating pore water pressure and limiting deformations, especially at larger distances and depths. The results contribute to a more robust understanding of stone column behavior under dynamic loading and offer a practical framework for their effective implementation in earthquake-prone regions.

Discrete Element Method-Based Mesoscopic Insight into Effect of Soil Mechanical Properties on Shield Tunnel Deformation

Excessive deformations and associated structural defects in urban metro shield tunnels are often observed because of the surcharge load and other disturbances in soft soil areas, threatening the serviceability and even safety of metro systems. However, the quantitative effect of soil mechanical properties on shield tunnel deformation remains unclear. This paper aims to characterize the development pattern of tunnel deformation under increasing surcharge load, considering the effect of random migration and the mechanical properties of the tunnel-surrounding soil. Therefore, a discrete element model is developed to simulate the macro and mesomechanical behaviors of the soil–tunnel interaction system. The numerical simulation results show that tunnel transversal convergence develops with a nonlinear growth trend with the increase in surcharge load. This trend is accompanied by a certain degree of dispersion because of the random movement of granular soil. A 20% reduction in soil elastic modulus increases tunnel convergence by 24% under 0.14 MPa surcharge, while a 20% increase in soil internal friction coefficient reduces convergence variability by 28%. Based on the simulation results, a mathematical model for the quantitative prediction of tunnel transversal convergence is proposed, which incorporates the effects of surcharge magnitude and soil properties. The results from the mathematical model are compared with real data and show the promising possibilities of the model to predict tunnel deformation under varying load conditions.

Numerical Analysis of Axisymmetric Consolidation Around Jacked Piles Considering Permeability Reduction in the Disturbed Soil Zone

The installation of jacked piles inevitably disturbs the surrounding soil, leading to a significant reduction in its radial permeability, which in turn retards the dissipation of excess pore water pressure. This study develops an enhanced axisymmetric consolidation theory that explicitly incorporates this installation‐induced disturbance. The soil around the pile is conceptually divided into a disturbed zone and an undisturbed zone, with three distinct modes of permeability variation within the disturbed zone being investigated, namely Pattern A (linear decay), Pattern B (nonlinear decay, modeled as a quadratic function), and Pattern C (abrupt decay). The governing partial differential equations are solved using an alternating implicit finite difference scheme to obtain the distribution in space and time of excess pore water pressure. The proposed numerical results are validated through comparisons with existing theoretical solutions and field measurements. A key finding reveals that Pattern A and Pattern B provide the closest agreement with in‐situ data, while Pattern C model overestimates the disturbance effect and shows a significant deviation from field observations, highlighting the importance of a realistically transition in permeability.

Review of Numerical Modeling Studies and the Influence of Compaction, Moisture, and Particle Size on Slope Stability