Based on typical water‐rich sandy gravel strata in Beijing, in order to explore the application of the artificial ground freezing method (AGF) in urban large‐scale underground engineering, the formation and development of freezing body were analyzed when multirow freezing pipes were working together, and the group effect exhibited during the freezing process was also revealed in this paper. On this basis, the basin‐shaped freezing method (BFM) is put forward as an application of AGF used in underground engineering. BFM structure consists of two parts: the frozen curtain (basin wall) around the excavation scope and the horizontal frozen body (basin bottom) at the bottom of the station. Physical model test and numerical simulation were conducted to study temperature field expansion of BFM under two different conditions. The results show the following: (1) The group effect refers to the cooling effect of different freezing pipes influencing each other during freezing process. Under the condition of still water, the group effect expands the freezing area, and it shows the gradual development of freezing from back water surface to front water surface under seepage condition. (2) BFM can effectively play the role of water proofing, and although different parts of basin structure show different frozen order under different conditions, both basin wall and basin bottom can form an effective thickness during the freezing process.

Sandy gravel stratum is very common in tunnels and underground engineering projects. The accurate determination of mechanical parameters is crucial for engineering design and construction. The Hardening Soil (HS) Model, which accounts for both shear hardening and compression hardening, has demonstrated advantages in numerical simulations. This study conducts large-scale mechanical experiments, including triaxial drained shear tests, loading-unloading tests, and standard consolidation tests, on sandy gravel specimens. The results reveal that the ratio of the three stiffness parameters in the HS Model, namely Young’s modulus under triaxial loading (E₅₀), oedometric loading (E_oed), and unloading-reloading (E_ur) is 1:1:4.3. The validity of the established stiffness ratio relationship is verified through numerical simulations of a foundation pit project and comparison with field monitoring data, demonstrating a consistent agreement between the simulation results and actual monitoring values.

The contact is a typical non-linear problem that exists in various projects. For traditional three-node triangular mesh and four-node quadrilateral mesh, the accuracy and convergence of the calculation results are affected by the quality of the mesh. The test space and trial space in the virtual element method (VEM) do not need to be accurately calculated, avoiding mesh dependence. In this paper, the formulation of linear elasticity and the formulation of the frictionless node-to-segment (NTS) contact model via VEM are shown. There are four numerical simulations. The sensitivity of the virtual element method to mesh distortion is studied in the first numerical simulation. The exactness and convergence of the algorithm are investigated by the second numerical example. The second numerical example simultaneously explores the penalty factor’s effect on the results. The third example investigated the impact of mesh shape and number of Voronoi mesh elements on the results by comparing normal contact stresses. The fourth numerical example studies the application of the method to engineering. Those numerical examples show that the virtual element method is insensitive to mesh distortion and could solve the joint contact in engineering.