This paper aims to investigate the tunnelling stability of underwater slurry pressure balance (SPB) shields and the formation and evolution mechanisms of ground collapse following face instability. A laboratory SPB shield machine was employed to simulate the entire tunnelling process. Multi-faceted monitoring revealed the responses of soil pressure, pore water pressure, and surface subsidence during both stable and unstable phases. The morphological evolution characteristics of surface collapse pits were analyzed using three-dimensional scanning technology. The experimental results indicate that: (1) The key to stable tunnelling is balancing the pressure in the slurry chamber with the tunnelling speed, which ensures the formation of a filter cake in front of the cutterhead. (2) The torque of the cutterhead, soil pressure, and surface subsidence respond significantly and synchronously when the tunnel face becomes unstable, while the soil and water pressures are relatively less noticeable. (3) Excavation disturbance results in a gentler angle of repose and a wider range of collapse in the longitudinal direction of the collapsed pit. (4) A formula for predicting the duration of collapse is proposed, which effectively integrates the evolution patterns of the collapse pit and has been well-validated through comparison with the experimental results. This study provides a reference for the safe construction of tunnel engineering in saturated sand.

The effective stresses in saturated soils are crucial for geotechnical engineering, particularly in the ocean environment, but no current transducers can directly measure both vertical and lateral effective stresses. Thus, a novel effective stress transducer based on fiber Bragg grating (FBG) technology is developed to directly measure three-dimensional (3D) effective stress in saturated soils. The design of the transducer ensures that pore water pressures inside and outside the transducer are balanced, allowing the strain to solely reflect the effective stress sustained by the soil skeleton. Two FBG sensing elements of the 3D effective stress transducer are designed to measure the vertical and lateral effective stresses by sensing the strain in the thin plate and the sensing cylindrical shell through the porous disk, respectively. Experimental results indicate that the transducer accurately captures the evolution of effective stress under complex static loads and precisely tracks cyclic stress variations under cyclic loadings. Compared to traditional transducers, the lateral earth pressure coefficient derived from the measurement data of the new effective stress transducer shows advanced accuracy and stability. Moreover, the FBG-based transducer effectively monitors effective stress changes during the excavation, capturing soil stress variations and enabling precise excavation stability assessments. The novel 3D FBG-based effective stress transducer offers a vital method for directly measuring the vertical and lateral effective stresses of saturated soils.

During pile installation, construction disturbances alter soil mechanical properties near the pile, significantly affecting the dynamic response of the pile. This paper develops a three-dimensional (3D) analytical model to investigate the vertical dynamic response (VDR) of a pile in radially inhomogeneous saturated soil. Firstly, by employing the separation variable method and incorporating the continuity and boundary conditions of the soilpile system, the exact solution of the whole system in the frequency domain was derived. Subsequently, the timedomain velocity response under semi-sinusoidal vertical excitation is obtained using Fourier inverse transform and the convolution theorem. The accuracy and superiority of the proposed solution were validated through comparison with previous analytical solutions. Finally, the developed solution is then used to examine the impact of parameters of saturated soil and pile on the VDR of a pile. The results demonstrate that the proposed saturated model better captures the VDR of a pile in radially inhomogeneous saturated soil compared to the single-phase model. The VDR of a pile is significantly influenced by the pore water, porosity, disturbed degree and range of the saturated soil, as well as the elastic modulus of the pile.

True triaxial tests were conducted on artificially frozen sand. The effects of the intermediate principal stress coefficient, temperature and confining pressure on the strength of frozen sand were studied. The stress-strain curves under different initial conditions indicated a strain hardening. In response to increases of either the intermediate principal stress coefficient or the confining pressure or to a decrease of temperature, the strength typically increased. Furthermore, a new strength criterion was proposed to describe the strength of artificially frozen sand under a constant b-value stress path, combining the strength function in the p-q and pi planes. Considering the low confining pressure, the strength criterion in the p-q plane fitted the linear relationship in the parabolic strength criterion well. The strength criterion in the pi plane was combined with stress invariants, and a new strength criterion was established. This criterion considers unequal tension and compression strength, and integrates temperature. Test results indicated its validity. All parameters of the strength criterion could be easily determined from the triaxial compression and triaxial tensile tests.

The raw-material mix ratio and preparation of similar materials are crucial for the success of physical model tests and for accurately reflecting prototype properties. In this study, an optimum similar material for plateau alluvial and lacustrine (PAL) round gravel was developed based on similarity theory. The similar materials were subjected to sensitivity factor analysis and microscopic analysis. Subsequently, the optimum similar material was applied to a three-dimensional (3D) physical model test of an ultradeep foundation pit (FP). The findings show that the similar material prepared with gypsum, LD, bentonite, water, barite powder, and DS at a ratio of 1:1:1.4:3.5:8.8:13.2 was the best for a 3D physical model test of the ultradeep FP in PAL round gravel strata. The sensitivity-factor analysis revealed that barite powder had the greatest impact on gamma, that c and phi were primarily affected by bentonite, and that the LD-gypsum ratio controlled E. A nonuniform particle-size distribution as well as the presence of edge-to-face contacts and small pores between particles constituted the microphysical factors affecting the mechanical properties of the optimum similar material. Using dolomite with a Mohs hardness of 3.5-4 instead of traditional quartz sand with a Mohs hardness of 7 as the raw material can produce a similar material for the target soil with mechanical parameters closer to those of the ideal similar material. The application of the optimum similar material in physical model tests has revealed the stress field response law of ultra deep foundation pit excavation. This study could provide reference and inspiration for the development of similar materials in gravel formations with weaker mechanical properties.

The influence of soil variability on the probabilistic bearing capacity of strip footings near slopes has been extensively studied, particularly under short-term undrained conditions. However, these investigations, predominantly based on the plane-strain assumption, fall short in accurately estimating the bearing capacity of square and rectangular footings and in capturing the spatial variability of soils. This study focuses on short-term undrained conditions and employs the random finite element method (RFEM) and Monte Carlo simulation (MCS) techniques to explore the effect of rotational anisotropy on the bearing capacity response and failure probability of a square and rectangular footing-cohesive slope system under a three-dimensional (3D) framework. The findings reveal that the rotation angles of soil strata significantly impact both the mean and coefficient of variation of the bearing capacity, with distinct variation patterns emerging for different footing orientations and aspect ratios. Typical failure patterns are identified, illustrating the correlation between the bearing capacity response, the footing orientations and aspect ratios, and the extension direction of plasticity. The probabilistic results are presented as probability density functions (PDF) and cumulative distribution functions (CDF) for various rotation angles around the x-axis and y-axis and for different L/B ratios of the footings. Additionally, detailed design tables, including failure probability results and corresponding safety factors for specific target failure probabilities, are provided to guide engineering applications.

The stress state is the fundamental for evaluating the soil strength and stability, playing a crucial role. However, during the stress testing, local damage and other uncertain factors may lead to partial sensor data missing, causing the existing three-dimensional stress calculation method to fail. To accurately restore the soil stress state during data missing, a three-dimensional stress calculation method was developed based on three-dimensional stress testing principles, incorporating axisymmetric and one-dimensional compression characteristics. The three-dimensional stress, principal stress , the first invariant of stress I-1, the second in variant of stress J(2) and stress Lode angle of a sandy soil foundation under one-dimensional compression conditions with different data missing were calculated and compared to results with complete data. The results show that the method is highly accurate; as the load increases, the relative error decreases and converges. The principal stresses, the first invariant of stress I-1, the second invariant of stress J(2) and the stress Lode angle align with one-dimensional compression response, suggesting that this calculation method supports advanced data mining. This study offers a novel approach and a practical method for fully utilizing the test data.

On June 11, 2016, a landslide occurred in Miaoling village, Jiujiang city, Jiangxi Province, China, following continuous rainfall. An engineering geological profile indicated that the landslide consisted of a stiff crust of residual Quaternary deposits overlying a water-sensitive gravelly clay layer with a soft-plastic consistency. A geotechnical field investigation and physical models of rainfall-induced landslides were carried out in situ and in the laboratory and included the use of a new sensors to develop a geotechnical model of the cut slope. During the rainfall process in the physical simulation experiments, automatic rainfall, three-dimensional scanning, and multiparameter monitoring were conducted to analyze the resulting landslides. The results showed that the increase in moisture and the generation of pore water pressure led to changes in soil pressure and the development of plastic deformation. An analysis performed after rainfall using a strain-softening behavior model showed the initiation and propagation of plastic zones, as well as the development of landslide cracks close to the observed ones. Therefore, it was proposed that the Miaoling-Jiujiang landslide could be explained by a progressive failure mechanism.

The existing research shows that the immersed tunnel is significantly affected by the earthquake, but the damage will cause serious casualties and property damage, and it is difficult to repair. However, the shaking table test of immersed tunnel including seabed and seawater site is difficult to realize at present, and numerical simulation is generally used for analysis. It has been found that seawater layer, seabed site conditions and soil-structure interaction have a large effect on the seismic response of immersed tunnels, but most of the existing studies have used two-dimensional models to analyze. In order to determine the influence of three-dimensional seabed site on the seismic response of immersed tunnel. Firstly, a three-dimensional layered site wave analysis program was established by using the coordinate system transformation and transfer matrix method, and combined with the finite element dynamic analysis software, a three-dimensional seismic wave analysis method of seawater and seabed immersed tunnel coupling was proposed. Besides, the correctness of the method is verified, and the influence of multi-dimensional site characteristics on seismic response of seabed site is analyzed. Finally, the immersed tunnel of Hong Kong-Zhuhai-Macao Bridge in China is taken as an engineering example, and the effects of tunnel longitudinal slope, incidence angle of ground motion, thickness of soft soil layer and water depth on seismic response analysis are studied. The results show that there is a great difference between twodimensional and three-dimensional seabed site model in seismic response. When considering the soft soil layer, the vertical seismic response of three-dimensional seabed site is significantly greater than that of twodimensional seabed site.Moreover, the silty soft soil layer also has a significant effect on the seismic response of the immersed tunnel, there is an obvious amplification effect on the tunnel horizontal seismic response. Besides, the horizontal seismic response of tunnel will be amplified with the increase of tunnel longitudinal slope and incidence angle, while the seismic response of tunnel will be inhibited with the increase of seawater depth.

Soil and rock mixture (SRM) is complex geological material that frequently leads to ground collapses, landslides, and debris flows. The mechanical and hydraulic properties of SRM have consistently attracted extensive attention. However, due to the presence of both large and small rock blocks, both experimental investigations and traditional mesh based numerical methods face significant challenges in the accurate evaluation of SRM mechanical properties. The numerical manifold method (NMM) is an excellent choice for this purpose as it effectively overcomes obstacles to mesh generation of complex SRM. Before exploring the hydraulic properties of SRM by NMM, it is necessary to construct a random preserved structure model of SRM, where the rock blocks are randomly distributed in space under a seismic load, which is a primary cause of structural changes in SRM. Using an explicit iterative scheme called the continuous-discontinuous element method (CDEM), we simulated the redistribution of rock blocks in SRM under artificial or natural seismic loads. Finally, we concentrated on determining the influences of some factors on SRM permeability using three-dimensional numerical manifold method (3D-NMM).