In order to investigate the frost-heaving characteristics of wintering foundation pits in the seasonal frozen ground area, an outdoor in-situ test of wintering foundation pits was carried out to study the changing rules of horizontal frost heave forces, vertical frost heave forces, vertical displacement, and horizontal displacement of the tops of the supporting piles under the effect of groundwater and natural winterization. Based on the monitoring condition data of the in-situ test and the data, a coupled numerical model integrating hydrothermal and mechanical interactions of the foundation pit, considering the groundwater level and phase change, was established and verified by numerical simulation. The research results show that in the silty clay-sandy soil strata with water replenishment conditions and the all-silty clay strata without water replenishment conditions, the horizontal frost heave force presents a distribution feature of being larger in the middle and smaller on both sides in the early stage of overwintering. With the extension of freezing time, the horizontal frost heave force distribution of silty clay-sand strata gradually changes from the initial form to the Z shape, while the all-silty clay strata maintain the original distribution characteristics unchanged. Meanwhile, the peak point of the horizontal frost heave force in the all-silty clay stratum will gradually shift downward during the overwintering process. This phenomenon corresponds to the stage when the horizontal displacement of the pile top enters a stable and fluctuating phase. Based on the monitoring conditions of the in-situ test, a numerical model of the hydro-thermo-mechanical coupling in the overwintering foundation pit was established, considering the effects of the groundwater level and ice-water phase change. The accuracy and reliability of the model were verified by comparison with the monitoring data of the in-situ test using FLAC3D finite element analysis software. The evolution of the horizontal frost heaving force of the overwintering foundation pit and the change rule of its distribution pattern under different groundwater level conditions are revealed. This research can provide a reference for the prevention of frost heave damage and safety design of foundation pit engineering in seasonal frozen soil areas.

With the widespread application of deep excavation projects, deformation control of diaphragm walls and management of surrounding soil displacement have become major challenges in the engineering field. To address these issues, this study proposes a prefabricated multi-limb composite concrete-filled steel tube (CFST) internal support system. The mechanical performance and deformation characteristics of the fixed ends of the system were systematically analyzed through axial compression tests and numerical simulations.First, based on the CFST stress-strain model, the constitutive model was modified to account for the effects of stiffening ribs, and a stress-strain relationship model for mold bag concrete was introduced. The simulation results demonstrate that the modified model can accurately predict the stress behavior of the fixed ends. Next, to characterize the overall mechanical response of the structure, a load-displacement relationship model was established. This model, which is closely related to the CFST strength grade, effectively captures changes in the structural performance.The results indicate that during loading, the CFST internal support system exhibits good stiffness and load-bearing capacity. With an increase in the concrete strength grade, the yield load increases by 12 %, and the ultimate strain decreases by 27.76 %, significantly enhancing the mechanical performance of the structure. This study not only deepens the understanding of the design principles for CFST internal support systems but also introduces new theoretical frameworks and calculation methods, providing strong support for engineering design with broad application prospects.

In soft soil regions, the construction of irregular-shaped excavations can readily disturb the underlying soft clay, leading to alterations in soil properties that, in turn, cause significant deformations of the excavation support structure. These deformations can compromise both the excavation's stability and the surrounding environment. Based on a large-scale, irregular-shaped excavation project for an underground interchange in a soft soil area, numerical simulations were performed using Midas GTS to analyze the overall foundation pit deformationn. The study explored the effects of groundwater lowering, excavation, and local seepage on the disturbance of surrounding soils and the resulting foundation pit deformationn. The findings reveal that the irregular-shaped excavation exhibits distinctive spatial deformation characteristics, with the arcuate retaining structure's arching effect reducing the diaphragm wall's horizontal displacement. Groundwater lowering exerts a stronger disturbance on shallow soils near the excavation and a weaker disturbance on deeper soils. Excavation-induced stress redistribution notably affects the soils above the excavation surface and those within the embedded region of the support structure. Local seepage primarily disturbs the soils surrounding the leakage point. Additionally, the weakening of soil parameters significantly influences the foundation pit deformationn. Combined disturbance (dewatering + excavation + leakage) induced 32%, 45%, and 58% greater displacements compared to individual factors, confirming the critical role of multi-factor coupling effects.

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.

Previous theoretical studies on the deformation of shield tunnels induced by foundation pit excavation generally consider the stratum as a linear elastic body, which seldom take the irregular construction boundary into account. Meanwhile, Curved beam theory and Timoshenko beam theory are less applied in the study of tunnels. This paper provides an analytical method to predict the displacements of small curved tunnels caused by deep excavation with time effects. Firstly, by introducing the fractional derivative Merchant model, a mechanical approach is proposed for analyzing the structural deformation of neighboring tunnels induced by foundation pit excavation. The parameters of viscoelastic soils are further derived in the Laplace domain based on time variability properties. Secondly, the additional stress field on existing small curvature tunnels is solved with theory of viscoelastic Mindlin solution and load reduction in foundation pits. Moreover, a deformation calculation model for curved shield tunnels is established by applying Pasternak foundation and Timoshenko beam theory. The time domain solutions for the radial and vertical deformations of small curvature tunnels are then derived by finite difference method along with Laplace positive and inverse transforms. In addition, the engineering measured data and three-dimensional numerical simulation solutions are compared with the analytical solution to verify relatively accuracy. Finally, sensitivity analyses are performed for parameters such as the buried depth of tunnels, minimum clear distance, fractional order, excavation method and creep time.

This paper addresses the issue of crack expansion in adjacent buildings caused by foundation pit construction and develops a predictive model using the response surface method. Nine factors, including the distance between the foundation pit and the building, soil elastic modulus, and density, were selected as independent variables, with the crack propagation area as the dependent variable. An orthogonal test of 32 conditions was conducted, and crack propagation was analyzed using the FEM-XFEM model. Results indicate that soil elastic modulus, Poisson's ratio, and distance between the pit and building significantly impact crack propagation. A predictive model was developed through ridge regression and validated with additional test conditions. Single-factor analysis showed that elastic modulus and Poisson's ratio of the silty clay layer, elastic modulus of sandy soil, and pit distance have near-linear effects on crack propagation. In contrast, cohesion, density, and Poisson's ratio of sandy soil exhibited extremum points, with certain factors showing high sensitivity in specific ranges. This study provides theoretical guidance for mitigating crack propagation in adjacent buildings during excavation.

In soft soil environments, deep foundation pit excavation often leads to significant surface settlement, lateral displacement of support structures, and uneven settlement of surrounding buildings due to the complex geotechnical conditions and the inherent characteristics of soft soil, such as high compressibility and low shear strength. This study systematically analyzes 23 deep foundation pit excavation cases from Ningbo city, located in a silty clay region, to examine the deformation behavior during excavation. The research focuses on the impact of key factors such as excavation depth, pit dimensions, support structure parameters, and soil characteristics on the deformation of diaphragm walls. The results show that the maximum lateral displacement of diaphragm walls ranges from 0.09 to 0.84% of the excavation depth, with an average value of 0.36%. Deeper excavations lead to greater lateral deformation due to increased soil pressure and pore water pressure, with the maximum displacement typically occurring at 1.0-1.3 times the excavation depth. Soft soil thickness significantly amplifies wall deformation, with the displacement ratio increasing linearly with the ratio of soft soil thickness to wall depth. Increased wall stiffness, embedment depth, and support system stiffness effectively reduce lateral displacement. These findings provide a quantitative basis for optimizing diaphragm wall design and support systems to mitigate deformation risks, offering valuable guidance for deep foundation pits in similar soft soil environments.

The excavation of the foundation pit impacts the safety, stability, and normal operational functionality of adjacent existing tunnels. With the increasing urban building density, it is becoming more common to conduct foundation pit excavation in close proximity to existing tunnels, which may result in deformation and damage to the tunnels. The impact of foundation pit excavation on adjacent existing tunnels was investigated using a transparent soil scale model and Particle Image Velocimetry technology. The horizontal and vertical distances between the foundation pit and tunnel, as well as the soil consolidation pressure, were individually examined to analyze their respective trends and magnitudes of impact on the maximum vertical deformation of adjacent existing tunnels. The findings suggest that as the excavation depth increases, the deformation of existing tunnels is increasingly impacted by the excavation of foundation pit. However, this impact decreases with greater horizontal or vertical distance between the foundation pit and tunnel. Furthermore, the impact of vertical distance between the tunnel and foundation pit on tunnel deformation is more significant. The pre-consolidation strength of the soil mass significantly impacts the deformation of the existing tunnel. In order to minimize tunnel deformation in practical engineering, constructive recommendations were proposed.

The development of underground spaces is crucial for modern urban environments, particularly in coastal cities with prevalent soft soil conditions. Deep foundation excavation works in such areas present technical challenges due to complex deformation phenomena including soil settlement and the lateral displacement of supporting structures. This study analyzes deformation patterns associated with deep foundation pit excavations in Ningbo's soft soil areas by examining 10 cases of subway station projects. This study evaluated the relationship between the maximum surface settlement and various engineering parameters using statistical and comparative analyses and also compared the results of each relationship with those of other regional studies. The results indicate that multiple coupled parameters-the excavation depth, diaphragm-wall-embedded depth ratio, support system stiffness, and pit aspect ratio-significantly shape the deformation patterns. The average ratio of the maximum surface settlement to the excavation depth is 0.64%, notably higher than in regions such as Hangzhou and Shanghai. The maximum lateral displacement in this study averaged 0.37% of the excavation depth. The maximum lateral displacement of the diaphragm walls in this study averaged 0.37% of the depth of excavation and, in addition, the average positive correlation between the depth at which the maximum lateral displacement occurred and the depth of pit excavation was h delta hmax=He + 1.46. A positive correlation also emerged between the maximum ground settlement and lateral displacement of the diaphragm walls. But the influence of the shape of the pit on the deformation will show different types of relationships depending on the area and geotechnical conditions, which need to be further investigated.

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.