The dual-purpose diaphragm wall, serving as both a temporary retaining structure and the permanent exterior wall of underground structures, has been extensively used for deep excavations in soft soil areas. Within some cases, soil mix panels are installed on both sides to enhance ground deformation suppression during excavation. Further research is essential to assess the effectiveness of this type of retaining structure in mitigating ground deformation caused by excavation in specialized soft soil areas. This paper utilized monitoring data to present a case study on the deformation characteristics of a 20.6-m-deep excavation supported by diaphragm walls supplemented by soil mix panels in soft soils, detailing its impact on adjacent pipelines and buildings. The findings revealed significant creep deformation properties of the surrounding ground. The diaphragm walls can effectively confine deformations caused by deep excavations to a limited extent. When supplemented with soil mix panels, greater deformation control efficacy can be achieved. Notably, the combined diaphragm and soil mix wall system exhibits maximum lateral displacements ranging from 0.07% to 0.22% of the excavation depth (H) and maximum ground surface settlements between 0.05%H and 0.25%H. The maximum surface settlement occurs within a region 0.5-1.5 times the maximum wall deflection. The region from 0 to 0.75 H distance from the retaining wall represents the maximum area of surface settlement, with the affected zone extending up to 4.0 H due to the influence of adjacent excavation construction. Significant spatial corner effects are displayed by the square excavation pit. Influenced by the pit's corner effects, pipelines and buildings near the midspan of the pit experience greater subsidence, resulting in an overall subsidence pattern with the most severe settlements occurring near the planview middle of the retaining system.

The under-consolidated state affects the deformation behavior of deep excavation in soft soil and poses potential risk to the safety of adjacent facilities. However, the deformation model of deep excavation in under-consolidated ground has not been well investigated yet. This study presents a series of numerical analyses on the deformation characteristics of deep excavations in under-consolidated and normally-consolidated ground, each of which is retained by diaphragm walls with rigid struts and a bottom improvement layer. Under-consolidated cases without excavation activities (i.e., simplified as Consolidate cases) were also included for comparison. The modelling results showed that, with the lateral constraint of inner rigid support system, the under-consolidated ground resulted in only a slight increase of lateral wall deformation but a significant increase in ground settlement as compared to normally-consolidated ground. The under-consolidated ground with lower initial average consolidation ratio, thicker surface fill, higher permeability, and longer construction period produced greater wall deformation and ground settlement during excavation. Besides, this study proposed an empirical method to estimate the settlement envelope for deep excavation in under-consolidated ground as the superposition of two parts: settlement induced by excavation activities, and settlement induced by residual consolidation with consideration of average consolidation ratios before and after excavation.

Significant movement of in-situ retaining walls is usually assumed to begin with bulk excavation. However, an increasing number of case studies show that lowering the pore water pressures inside a diaphragm wall-type basement enclosure prior to bulk excavation can cause wall movements in the order of some centimeters. This paper describes the results of a laboratory-scale experiment carried out to explore mechanisms of in situ retaining wall movement associated with dewatering inside the enclosure prior to bulk excavation. Dewatering reduces the pore water pressures inside the enclosure more than outside, resulting in the wall moving as an unpropped cantilever supported only by the soil. Lateral effective stresses in the shallow soil behind the wall are reduced, while lateral effective stresses in front of the wall increase. Although the associated lateral movement was small in the laboratory experiment, the movement could be proportionately larger in the field with a less stiff soil and a potentially greater dewatered depth. The implementation of a staged dewatering system, coupled with the potential for phased excavation and propping strategies, can effectively mitigate dewatering-induced wall and soil movements. This approach allows for enhanced stiffness of the wall support system, which can be dynamically adjusted based on real-time displacement monitoring data when necessary.

This paper uses the three-dimensional numerical simulation method to analyze the first deep foundation pit project directly above the operating subway in a certain area. The monitoring data were compared with the numerical results to verify the accuracy of the numerical model, and then a series of analyses were performed. The soil beneath the tunnel is the most direct object of tunnel deformation caused by the excavation of deep foundation pits above the tunnel. The rebound deformation of the soil beneath the tunnel forces the tunnel to produce an upward deformation cooperatively. Therefore, after comparing and analyzing the prevention criteria of traditional excavation measures, which were not sufficient for this project, a new method of fortification is proposed for the foundation pit above the tunnel, which is called the micro-disturbance drill pipe pre-reinforcement method (PRM) for the soil beneath the tunnel. The comprehensive parameter analysis of the PRM shows that the PRM can effectively reduce the uplift value of the tunnel, and the reinforcement effect is obvious.

Dewatering and excavation are fundamental processes influencing soil deformation in deep foundation pit construction. Excavation causes stress redistribution through unloading, while dewatering lowers the groundwater level, increases effective stress, and generates seepage forces and compressive deformation in the surrounding soil. To systematically investigate their combined influence, this study conducted a scaled physical model test under staged excavation and dewatering conditions within a layered multi-aquifer-aquitard system. Throughout the experiment, soil settlement, groundwater head, and pore water pressure were continuously monitored. Two dimensionless parameters were introduced to quantify the contributions of dewatering and excavation: the total dewatering settlement rate eta dw and the cyclic dewatering settlement rate eta dw,i. Under different experimental conditions, eta dw ranges from 0.35 to 0.63, while eta dw,i varies between 0.32 and 0.82. Both settlement rates decrease with increasing diaphragm wall insertion depth and increase with greater dewatering depth inside the pit and higher soil permeability. An analytical formula for dewatering-induced soil settlement was developed using a modified layered summation method that accounts for deformation coordination between soil layers and includes correction factors for unsaturated zones. Although this approach is limited by scale effects and simplified boundary conditions, the findings offer valuable insights into soil deformation mechanisms under the combined influence of excavation and dewatering. These results provide practical guidance for improving deformation control strategies in complex hydrogeological environments.

The soil disturbance caused by deep excavation of adjacent buildings will have adverse effects on building foundation. This will threaten the stability of superstructure and engineering safety. In this paper, a three-dimensional finite element model is established by taking the renovation project of underground parking garage near a hotel as an example. The calculated results of the model agree well with the measured data, which verifies the validity of the model. On this basis, the construction mechanical behavior of deep excavation of adjacent buildings is studied. The research content mainly includes the stress and deformation characteristics of soil and structural members. The results show that the stress and deformation characteristics of soil and structural members are sensitive to the excavation depth of deep excavation. It increases with the increase of excavation depth. The vertical displacement of soil at the bottom of deep excavation is mainly uplift. When the excavation is completed, the maximum uplift value is 26.9 mm. The displacement of strip foundation is mainly settlement. The maximum vertical displacement of the foundation of buildings A and B is - 5.2 mm and - 10.98 mm, respectively. In general, the vertical displacement of column foot shows the deformation law of slope. The maximum displacements of diaphragm wall 1 and 2 are 6.09 mm and - 6.56 mm respectively. The maximum values of XX direction stress and YY direction bending moment are - 494.2 kN/m and - 746.1 kN m/m, respectively. The axial force of the internal support is mainly pressure. The maximum value is - 1225.9 kN. The total maximum axial force shows a trend of increasing. When the excavation is completed, the total maximum axial force is - 2748.3 kN. The deformation and internal force distribution of soil and structural members at the bottom of deep excavation have obvious spatial characteristics. The closer to the center of the deep excavation, the greater the value. Therefore, attention should be focused and necessary measures should be taken.

This case study aims to evaluate the impact of deep excavation on the adjacent short floating pile and lateral deformation control strategies using capsule expansion technology (CET). Two control strategies, i.e., real-time control (RTC) and one-time control (OTC), were applied to control the lateral displacement of piles. In this case, the wall lateral deflections (delta hm) range between delta hm=0.075%He and delta hm=0.11%He, which are relatively small and less than the specified protection levels. Although the wall deflection was controlled to a relatively small level through reasonable excavation and support schemes, the maximum horizontal displacement of the short floating pile reached 13.2 mm (0.054%He). Therefore, reasonable deformation control measures are necessary. After three stages of RTC treatment, the maximum lateral displacement of P2 was reduced by 49.2%, while P1 was decreased by 22.7% treated by OTC. Meanwhile, multiple RTCs can always control the pile deformation within the cracking limit, which avoids the dilemma of protecting the pile after it has been damaged. It confirms the feasibility and efficiency of CET in controlling pile deformation in real-time. In addition, RTC for pile lateral displacement mainly includes two aspects: (1) expansion directly induces lateral displacement of piles; and (2) expansion compensates for the soil stress loss in front of the pile to reduce the impact of the next excavation on the pile. Therefore, as external influence sources have long-term adverse effects on adjacent piles, RTC as an efficient control method should be given priority consideration for controlling pile lateral displacement.

Deep excavations in silt strata can lead to large deformation problems, posing risks to both the excavation and adjacent structures. This study combines field monitoring with numerical simulation to investigate the underlying mechanisms and key aspects associated with large deformation problems induced by deep excavation in silt strata in Shenzhen, China. The monitoring results reveal that, due to the weak property and creep effect of the silt strata, the maximum wall deflection in the first excavated (Section 1) exceeds its controlled value at more than 93% of measurement points, reaching a peak value of 137.46 mm. Notably, the deformation exhibits prolonged development characteristics, with the diaphragm wall deflections contributing to 39% of the overall deformation magnitude during the construction of the base slab. Subsequently, numerical simulations are carried out to analyze and assess the primary factors influencing excavation-induced deformations, following the observation of large deformations. The simulations indicate that the low strength of the silt soil is a pivotal factor that results in significant deformations. Furthermore, the flexural stiffness of the diaphragm walls exerts a notable influence on the development of deformations. To address these concerns, an optimization study of potential treatment measures was performed during the subsequent excavation of Section 2. The combined treatment approach, which comprises the reinforcement of the silt layer within the excavation and the increase in the thickness of the diaphragm walls, has been demonstrated to offer an economically superior solution for the handling of thick silt strata. This approach has the effect of reducing the lateral wall displacement by 83.1% and the ground settlement by 70.8%, thereby ensuring the safe construction of the deep excavation. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The mechanical properties of soil, resulting from the weathering of rocks through physical and chemical processes, exhibit spatial variability. This variability introduces uncertainties in the design and characteristics of excavation projects. To address these uncertainties caused by soil spatial variability, safety factors are commonly used in excavation design. However, using the same safety factor for different indicators of soil spatial variability is illogical. Therefore, specialized research on the characteristics of deep excavations in the context of soil spatial variability is necessary, as it provides the theoretical basis for rational excavation design. In this study, we assumed that soil parameters follow a lognormal distribution, while spatial correlation adheres to a Gaussian function. We developed a random finite element algorithm for deep excavations, which incorporated Python programming and the ABAQUS computational platform. This algorithm was created within the framework of random field theory and Monte Carlo simulation. The results of our study indicate that, influenced by soil spatial variability, the lateral wall movements and ground surface settlements exhibit discrete distributions near the deterministic results. The maximum deformation of the excavation follows a normal distribution, while the pattern of ground surface settlements demonstrates diversity and chaotic characteristics. The extent to which soil spatial variability affects deep excavations is correlated with indicators of this variability. As the coefficient of soil spatial variability increases, the diversity and chaotic characteristics of ground surface settlements become more prominent. The locations of maximum ground surface settlement and maximum deformation becomes more scattered. Consequently, the probability of excavation failure increases, and the reliability index of the excavation decreases. In summary, soil spatial variability significantly impacts deformation prediction and safety control during the design and construction stages of deep excavations. Therefore, it is crucial to consider the influence of soil spatial variability when designing deep excavations, based on the variability indicators.

The issue of geotechnical hazards induced by excavation in soft soil areas has become increasingly prominent. However, the retaining structure and surface settlement deformation induced by the creep of soft soil and spatial effect of the excavation sequence are not fully considered where only elastic-plastic deformation is used in design. To understand the spatiotemporal effects of excavation-induced deformation in soft soil pits, a case study was performed with the Huaxi Park Station of the Suzhou Metro Line S1, Jiangsu Province, China, as an example. Field monitoring was conducted, and a three-dimensional numerical model was developed, taking into account the creep characteristics of mucky clay and spatiotemporal response of retaining structures induced by excavations. The spatiotemporal effects in retaining structures and ground settlement during excavation processes were analyzed. The results show that as the excavation depth increased, the horizontal displacement of the diaphragm walls increased linearly and tended to exhibit abrupt changes when approaching the bottom of the pit. The maximum horizontal displacement of the wall at the west end well was close to 70 mm, and the maximum displacement of the wall at the standard reached approximately 80 mm. The ground settlement on both pit sides showed a trough distribution pattern, peaking at about 12 m from the pit edge, with a settlement rate of -1.9 mm/m per meter of excavation depth. The excavation process directly led to the lateral deformation of the diaphragm walls, resulting in ground settlement, which prominently reflected the time-dependent deformation characteristics of mucky soft soil during the excavation process. These findings provide critical insights for similar deep excavation projects in mucky soft soil, particularly regarding excavation-induced deformations, by providing guidance on design standards and monitoring strategies for similar geological conditions.