To the aim of this paper is to study the structural and environmental deformation characteristics caused by the excavation of a very large deep foundation pit in the sandy soil area of Beijing. This paper is based on numerical simulation and field monitoring results and these results are compared with the deformation data of a soft soil foundation pit in the Shanghai area. The results show that the influence of the environment surrounding the super-large deep foundation pit project studied in this paper is obviously too great. With the progress of construction, the deformation rate and deformation amount of the column at the side of the foundation pit are obviously higher than that of the column in the middle area. Due to the hysteresis of stress transfer in the sand, the settlement of the roof of the north wall is delayed and the deformation range is smaller than that of the south wall. Compared with the conventional foundation pit, the influence area of the surrounding surface is larger, reaching 4 He (He is the depth of the foundation pit). Delta vmax (the maximum surface settlement) is between 0.2 similar to 2.3% He, and the relationship between delta vmax = 1.43% Vwm. Through orthogonal experiments and numerical simulation, it is concluded that the deformation of foundation pit structure and its surrounding environment is more sensitive to excavation unloading, precipitation amplitude, and column spacing. It is also concluded that the strong, medium, and weak influence areas of the bottom uplift after foundation pit construction are (0 similar to 0.07) x L, (0.07 similar to 0.14) x L, and (0.14 similar to 0.5) x L, respectively (L is the width of foundation pit). When the embedment ratio is between 1.8 similar to 2.4, the displacement mode of the parapet structure is T mode; when the embedment ratio is between 2.4 similar to 3.4, the displacement mode of the parapet structure is RB mode.

This paper is based on the construction of the underground Pile-Beam-Arch station at Beitaipingzhuang Station of Beijing Metro Line 12. It employs finite element software for three-dimensional numerical modeling, faithfully reproducing the entire station construction process. The results indicate that the excavation of the pilot tunnel and the stage of the secondary lining buckle arch are the main causes of surface deformation. Additionally, the construction of the secondary lining buckle arch is the primary factor inducing deformation in the middle column and side pile. On this basis, the paper investigates the influence of four crucial factors: the stagger distance of the pilot tunnel excavation, the sequence of the secondary lining buckle arch, the excavation sequence of the lower soil, and the excavation depth on the stress and deformation characteristics of the stratum and the station structure. The results suggest that when the distance between adjacent pilot tunnel faces is 1.5 to 3 times the diameter of the pilot tunnel, it has the greatest influence on surface settlement. When the first side is followed by the middle, closely aligning the second lining with the initial support, and simultaneously installing buckle arches on both sides minimizes deformation of the stratum and station structure. During excavation of the lower soil in the station, reducing the single excavation depth and prioritizing excavation on both sides help control deformation of the vertical bearing structure. The optimal construction scheme is derived through multi-criteria optimization and implemented in the field. Field monitoring results are in good agreement with simulation outcomes, offering valuable reference for the construction of stations under similar geological conditions.

In view of the safety of the construction of the long foundation pit of the new upper span to the existing subway under urban complex environment conditions, combined with the construction of the inter of the first line of the existing subway across the north-south Expressway in Shenyang, the mechanical properties during construction were studied by means of numerical simulation and on-site monitoring. The results showed that the general deformation characteristic of the existing metro tunnel was uplift first, then restrain. The local deformation characteristic was an unloading rebound in the cross region, and a compression deformation occurs outside the cross region. The index could be controlled in the range of the control value of the existing line protection by adopting the measures consisting of an uplift pile + capping beam balance, reinforcing the surrounding soil, the excavation of the foundation pit in sections, and the comprehensive construction.

The ground movement during the construction of shallow loess tunnels can easily cause deformation damage to surface buildings. Most the current studies focus on the damage soft soil and rock tunnels to independent buildings, and there are few studies on the case of building groups in loess areas. Using the new Xi 'Yan Railway Luochuan Tunnel as a case study, we conducted on -site testing to study building settlement and crack development characteristics. Three-dimensional numerical simulations were carried out to analyze settlement, flexure deformation, and main tensile strain distribution characteristics of the buildings at different buried depths. The study determines the extent of damage resulting from differential settlement and tension cracks. The results show that construction during the upper, middle, and lower bench stages results in significant ground volume loss, leading to a 'wide and steep ' settlement pattern with a maximum settlement value of 567 mm. Building cracks exhibit positive and inverted splayed shapes, with lengths ranging from 0.5 to 6.0 m and widths between 0 to 170 mm. As buried depth increases, maximum settlement, flexure deformation, and main tensile strain of buildings also increase. The severe damage range of buildings initially increases and then stabilizes, with the maximum range caused by differential settlement and tensile cracks being 34 m and 29 m from the tunnel axis, respectively. Based on the analysis of building damage characteristics, it was determined that a combination of surface measures and measures within the tunnel should be used to control building damage caused by tunnel construction. These research findings can serve as valuable references for similar projects.

A circular shaft is often used to access a working well for deep underground space utilization. As the depth of underground space increases, the excavation depth of the shaft increases. In this study, the deformation characteristics of a circular shaft with a depth of 56.3 m were presented and analysed. The main monitoring contents included: (1) wall deflection; (2) vertical wall movement; (3) horizontal soil movement; (4) vertical surface movement; and (5) basal heave. Horizontally, the maximum wall deflection was only 7.7 mm. Compared with the wall deflection data collected for another 29 circular excavations, the ratio of maximum wall deflection to excavation depth of this shaft was smaller due to a smaller ratio of diameter to excavation depth. The wall deflection underwent two stages of deformation: the first stage was mainly circumferential compression caused by the mutual extrusion of joints between walls, and the second stage was typical vertical deflection deformation. The horizontal soil movement outside the shaft was greater than the wall deflection and the deep soil caused great horizontal movement because of dewatering at confined water layers. Vertically, a basal heave of 203.8 mm occurred in the pit centre near the bottom. Meanwhile, the shaft was uplifted over time and showed 3 stages of vertical movement. The surface outside the shaft exhibited settlement and uplift deformation at different locations due to different effects. The basal heave caused by excavation was the dominant factor, driving the vertical movement of the shaft as well as the surrounding surface. The correlation between the wall deflection and the surface settlement outside the shaft was weak.

Disasters occurring at loess slopes in seasonal frozen regions are closely related to changes in the thermo-hydro-mechanical (THM) state in loess by freeze-thaw (FT) action. Current research on FT-induced soil slope failure focuses on frozen stagnant water effects, while the intrinsic connection between the FT-induced stagnant water effect and soil strength deterioration remains unclear. In this study, by taking the FT-induced loess slope failure as an example, field surveys, boreholes, exploratory wells, and 3D topographic mapping were used to reveal the landslide features and stratigraphic information; Furthermore, the temporal and spatial variation of water and heat in loess slope was revealed by on-site monitoring data; A THM coupled model of frozen soil was established using COMSOL Multiphysics simulation software to reconstruct the frozen stagnant water process of shallow loess slope, as well as the influence of THM field on loess landslide. The results show that the effects of FT in the seasonally frozen region occurred in the shallow layer of the loess slope. The water-ice phase transition during FT process broke the phase equilibrium of loess. Numerical calculations and field monitoring indicated a continuous migration of water to the freezing front, creating a water-enriched zone inside the loess. Both the impact of the frozen stagnant water and changes in the stress field led to the degradation of loess structure and reduced the strength properties, thus threatening the stability of the loess slope. The study results can contribute to an in-depth understanding of the mechanism underlying FT loess landslides in seasonal frozen regions, and provide a scientific basis for the evaluation and prevention of FT landslides. In the process of freezing and thawing, water migration occurs in the loess slope, resulting in the frozen stagnant water effect, which makes the water enriched in the slope. This makes the mechanical strength parameters of loess deteriorate. The effect of frost heave and thaw settlement destroys the soil structure and makes the soil particles rearrange. This threatens the stability of loess slope. image