A series of problems, including large deformation of supporting structures, shotcrete peeling, and yielding of the steel frame, occurs constantly during tunnel construction in soft clay layers. These problems considerably raise the risk of tunnel construction. Thus, the deformation characteristics of soft clay around the tunnel during construction must be investigated to guarantee safety. In this research, a field test was conducted on 50 sections of a tunnel, which was built in high‐plasticity clay layers. Then, the deformation characteristics of surrounding rocks and influencing laws caused by burial depth, invasion thickness of soft clay, and atmospheric precipitation were discussed. Results indicated that surrounding rocks are most likely to undergo large deformation during tunnel construction when the burial depth of tunnel ranges from 1.5D to 2.5D (D is the tunnel excavation span). Tunnel deformation also increases rapidly when the invasion thickness exceeds 60% of the tunnel height. The ratio between clay thickness and burial depth of the tunnel is another crucial index that could cause a large tunnel deformation as it exceeds 0.25. In addition, a significant correlation was observed between tunnel deformation and rainfall during the construction period. The deformation of surrounding rocks increases rapidly with rainfall and will continually develop for 1‐2 weeks when the average daily rainfall is greater than 4 mm.

A systematic geometric algorithm is developed to generate particle packing with high density, controllable gradation, and uniform spatial distribution for discontinuous deformation analysis (DDA). The algorithm incorporates a lattice searching technique to expedite overlap detection and reduce computational costs during particle packing generation. Additionally, a Fourier transformation method is utilized to analytically handle overlap detections on arbitrary irregular boundaries. To evaluate the efficiency and accuracy of the proposed method, a series of comparisons are made between existing methods and the proposed approach. Numerical modelling of engineering problems is conducted using the proposed method and a self-developed numerical program called DDA. The modelling results demonstrate that the proposed particle generation method has wide applications in generating complex particle models for discontinuous numerical analysis. The algorithm exhibits excellent performance in both geometric and numerical analyses, further confirming its efficiency and accuracy.

When shield tunnelling is in a water‐rich sand stratum with poor bearing capacity, instability is easily generated, and even ground collapses may occur. The variation of pore water pressure in a water‐rich sand stratum during shield tunnelling was analyzed based on a large‐scale cross‐river shield tunnel in China, which was also investigated by a three‐dimensional fluid‐solid coupling finite element model. The results show that the influence range of the pore water pressure in front of the excavation face is approximately 2.0 times the excavation diameter and 1.5 times on both sides of the shield. The tunnelling steps would cause obvious variation in the pore water pressure and lead to great disturbance to the surrounding fine sand stratum. The quality of filter cake and the set of support pressure imposes an important impact on the nonlinear variation in the pore pressure, which could cause great disturbance to the stratum. To ensure the safety of the subsequent tunnelling in the fine sand layer, effective treatment should be taken.

This paper performs an extensive literature survey and example investigation on the stabilisation of slurry wall trenches during the construction of diaphragm wall panel trenches, and the failure modes of slurry wall trench instability, the stability theoretical analysis models and methods, the slurry formation and its protection mechanism, the influence of related factors on slurry wall trench stabilisation, and other related problems are summarized and analyzed emphatically. And then, based on the limit equilibrium analysis method, the mechanical models of the overall stability and local stability of the trench wall are established, respectively, and the design method of slurry unit weight is derived to ensure the stability of the trench wall. Furthermore, an example application shows that the established slurry unit weight design method is reliable. At last, this paper also proposes the focus and direction for follow‐up work, that is, to construct an accurate and effective theoretical analysis model of slurry wall trench instability considering the influence of multiple factors and the calculation method of the slurry cake and its mechanical or mathematical relationship with slurry quality.