Yu Tian

Conducting three‐dimensional (3D) numerical simulation is of great importance for accurately analyzing the stress and deformation of complex geotechnical structures. The transformed stress (TS) method provides an ingenious theory for the 3D generalization of soil constitutive models, but studies on its numerical implementation are limited. This paper first illustrates the basic idea of the TS method by showing how to obtain a 3D yield surface from the triaxial compression yield locus. According to the evolution trend of the Matsuoka‐Nakai yield locus on the deviatoric plane, a revised expression is proposed to determine the TS tensor when tensile stress appears. As an example, the Modified Cam‐clay model is generalized to be 3D, and its stress integration is implemented using the closest point projection method. Partial derivatives of the TS are efficiently calculated by the implicit differentiation method, while various singularity problems in special cases are overcome. Single‐element testing under different loading conditions and tunnel excavation simulation demonstrate that the proposed stress integration algorithm has high accuracy and strong convergence. Based on this work, the potential capability of the TS method in geotechnical structure analysis is displayed.

Blasting excavation can pose significant risks to adjacent structures, particularly during concrete pouring. Therefore, evaluating their safety is crucial. In addition, the influence of blasting vibration on the vibration of the foundation and the superstructure is different. Currently, there are only allowable vibration values in the time domain range affected by blasting construction on the foundation structure at vibration frequencies of 1–10 Hz and 50 Hz. There is a lack of allowable vibration values in the range of 10–50 Hz. Based on a liquefied natural gas (LNG) project in Zhejiang, China, this paper studies the safety evaluation index for the vibration of piles under the storage tank through in situ blasting tests and numerical simulations. The vibration velocity attenuation curve of the site, which can accurately predict the pile vibration velocity induced by blasting, is obtained by fitting the experimental results using Sodev’s formula. It is found that the vibration velocity gradually increases from the pile toe to the pile top. As the distance to the blasting source increases, the maximum vibration velocity of the pile top gradually decreases. The peak vibration velocity at the pile top is different from that at the ground surface around the pile. Their ratio, which can reach up to 1.33, gradually increases with the decreasing distance to the blasting source and the increasing concrete strength. The predominant frequency is greater than 10 Hz. For the pile whose concrete strength is lower than 50% of the design strength, blasting has little impact when the vibration velocity is less than 10.16 mm/s. The experimental results supplement the relevant experimental data within the range of 10–50 Hz. This study can provide references for similar projects.

In order to study the horizontal bearing characteristics of large-diameter rock-socketed rigid pile and flexible pile, two lateral loading tests in which the pile lengths are 5.2 m and 11.07 m were carried out. Unidirectional multi-cyclic loading was applied to the piles during the tests, with the maximum load reaching 3500 kN. The measured results are compared with the calculated results of Zhang’s method, m-method and the rigid pile method in the design codes. It is indicated that if the characteristic values of the horizontal bearing capacity of the large-diameter rock-socketed rigid pile and flexible pile are determined by the same horizontal displacement of the pile head, some risk will be brought to the design of the rigid pile. Compared with the rigid pile method, the m-method is more suitable for calculating the rotation angle of the pile head. In terms of the maximum bending moment of the large-diameter rock-socketed flexible pile under the critical load, the calculated result of Zhang’s method is less than the measured result, while the calculated result of the m-method is the largest. However, for the rigid pile, both Zhang’s method and m-method underestimate the maximum bending moment of the pile body. In summary, when a large-diameter rock-socketed pile is designed, reasonable calculation method and failure discrimination standard should be chosen according to the actual conditions.

The foundation pit area of Kunming International Comprehensive Transportation Hub is 56,800 m², and the excavation depth ranges from 18 m to 25 m. Because the surrounding environment is very complex, the foundation pit is supported by an underground continuous wall and three layers of internal support system with seven rings. The force of this internal support system is coupled integrally, and the number of rings is the highest in the world at present. In this work, a finite element model considering the interaction between soil and the retaining structure is established. The Hardening Soil model with small strain stiffness is used to simulate and analyze the whole excavation process of the foundation pit. Considering the ultra-large plane size of the foundation pit, we cannot ignore the temperature effect, so the deformation of the underground continuous wall and the force of the internal support system under seasonal temperature variation are investigated. By comparing numerical simulation results with field measurements, the deformation of the ultra-large seven-ring internal support system, the deformation of the surrounding soil, and the axial force of the supports are analyzed. The results show that the finite element simulation agrees well with the measured data. This work provides a reliable method for analyzing ultra-large deep foundation pits.

In order to consider the effect of fabric anisotropy in the analysis of geotechnical boundary value problems, this study proposes a modified model based on a fabric-based modified Cam-clay model, which can account for the anisotropic response of soil. The major modification of the original model aims to simplify the equations for numerical implementation by replacing the SMP strength criterion with the Lade’s strength criterion. This model comprehensively considers the inherent anisotropy, induced anisotropy, and three-dimensional strength characteristics of soil. The model is first numerically implemented using the elastic trial–plastic correction method, and then it is encapsulated into the FLAC^3D 6.0 software, and tested through conventional triaxial, embankment loading, and tunnel excavation experiments. Numerical simulation results indicate that considering anisotropy and three-dimensional strength in geotechnical engineering analysis is necessary. By accounting for the interaction between microstructure and macroscopic anisotropy, the model can more accurately represent soil behavior, providing significant advantages for geotechnical analysis.

The foundation pit area of Kunming International Comprehensive Transportation Hub is 56,000 m², and the excavation depth ranges from 18m to 25m. Because the surrounding environment is very complex, the foundation pit is supported by underground continuous wall and three layers of internal support system with seven rings. The force of this internal support system is coupled in-tegrally, and the number of rings is the most in the world at present. In this work, a finite element model considering the interaction between soil and retaining structure is established. Hardening Soil model with small strain stiffness is used to simulate and analyze the whole excavation process of the foundation pit. Considering the ultra-large plane size of the foundation pit, we cannot ignore the temperature effect, so that the deformation of the underground continuous wall and the force of the internal support system under seasonal temperature variation are investigated. By comparing numerical simulation results with field measurements, deformation of the ultra-large seven-ring internal support system, deformation of the surrounding soil and axial force of the supports are analyzed. The results show that the finite element simulation agrees well with the measured data. This work provides a reliable method for analyzing ultra-large deep foundation pit.

A multiscale method is presented to develop a constitutive model for anisotropic soils in a three-dimensional (3D) stress state. A fabric tensor and its evolution, which quantify the particle arrangement at the microscale, are adopted to describe the effects of the inherent and induced anisotropy on the mechanical behaviors at the macroscale. Using two steps of stress mapping, the deformation and failure of anisotropic soil under the 3D stress state are equivalent to those of isotropic soil under the triaxial compression stress state. A series of discrete element method (DEM) simulations are conducted to preliminarily verify this equivalence. Based on the above method, the obtained anisotropic yield surface is continuous and smooth. Then, a fabric evolution law is established according to the DEM simulation results. Compared with the rotational hardening law, the fabric evolution law can also make the yield surface rotate during the loading process, and it can grasp the microscopic mechanism of soil deformation. As an example, an anisotropic modified Cam-clay model is developed, and its performance validates the ability of the proposed method to account for the effect of soil anisotropy.