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 construction of diaphragm wall panels inevitably changes the initial stress condition and causes movements in the surrounding soil mass, which may also cause settlement and damages to adjacent buildings. Majority of current design and analyses of deep excavations assume that the diaphragm wall is wished-in-place, largely because of the complexities involved to consider the detailed wall installation process. Limited studies suggested that neglecting the wall installation effects would reduce the reliability of these analyses for both predictions and validations. This paper analyzes measured ground response and building settlements caused by diaphragm wall panel installation and highlights the importance of considering these installation effects in practical design. A realistic modeling procedure is then developed to incorporate the sequential diaphragm wall panel construction process in braced excavation analyses, to investigate the installation effects on adjacent ground and buildings. The computed results are consistent with those field measurements from different case studies. The benefits of the proposed approach are demonstrated though comparison with the conventional wished-in-place approach in the braced excavation analyses.

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.

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 use of envelope structures is crucial in enhancing the safety and stability of foundation pits. However, excavation activities in the foundation pit can result in deformations affecting the envelope structure. To investigate the impact of the excavation process on the envelope structure and surrounding soil, the Midas GTS NX 2022R1 (64-bit) finite element software was employed to model the excavation process of Nantong East Railway Station. The settlement of the soil around the envelope structure and the horizontal displacement of the underground diaphragm wall (UDW) were compared with field measurements. The analysis demonstrated that the numerical analysis results exhibited a similar trend to the data obtained from field monitoring. This comparison provided valuable insights for selecting an optimal excavation method for the foundation pit and offered guidance for addressing similar challenges in the future. Additionally, a new method using metamaterials as a frame to improve the stability of continuous walls is proposed. The method relies on the excellent mechanical properties of metamaterials, improves the integrity and stability of the underground diaphragm wall, and provides a new way to solve the stability problem of underground diaphragm walls.

The rigid and fixed diaphragm wall (RFD) is a novel strut-free retaining wall system. This system needs a rigid connection between diaphragm panels. However, in Indonesia, constructing the rigid connection between diaphragm wall panels is scarce. The main objective of this study is to investigate the effectiveness of the RFD system on lateral wall deflection and excavation stability considering anisotropic factors due to joints in the diaphragm wall panels. First, the soil and structure parameters of the three-dimensional finite element model were validated through a well-documented braced excavation case history, which is located in Central Jakarta. Then, the RFD system was introduced to the 3D model. Some parametric studies were also conducted by varying several parameters to understand their influence on safety factors and wall deflections. The analysis results indicate that the implementation of the RFD system yields positive outcomes in controlling lateral deformations. The length of buttress walls and the use of cap slabs significantly affect excavation deformations and safety factors, while the depth of cross walls and buttress walls has a less significant impact. The presence of joints in the diaphragm wall panels causes the wall to be anisotropic, resulting in a reduction in wall stiffness. The reduction in wall stiffness leads to an increase in lateral wall deformations and a decrease in the excavation safety factor.

In this paper, a seismic and vibration reduction measure of subway station is developed by setting a segmented isolation layer between the sidewall of structure and the diaphragm wall. The segmented isolation layer consists of a rigid layer and a flexible layer. The rigid layer is installed at the joint between the structural sidewall and slab, and the flexible layer is installed at the remaining sections. A diaphragm wall-segmented isolation layer-subway station structure system is constructed. Seismic and vibration control performance of the diaphragm wall-segmented isolation layer-subway station structure system is evaluated by the detailed numerical analysis. Firstly, a three-dimensional nonlinear time-history analysis is carried out to study the seismic response of the station structure by considering the effect of different earthquake motions and stiffness of segmented isolation layer. Subsequently, the vibration response of site under training loading is also studied by considering the influence of different train velocities and stiffness of the segmented isolation layer. Numerical results demonstrate that the diaphragm wall-segmented isolation layer-subway station structure system can not only effectively reduce the lateral deformation of station structure, but also reduce the tensile damage of the roof slab. On the other hand, the developed reduction measure can also significantly reduce the vertical peak displacements of site under training loading.

Most existing seismic behavior analyses of underground structures simply consider a single earthquake. Meanwhile, the diaphragm wall, as an enclosure structure, is regarded as a security reserve and is always ignored in current studies. Herein, the characteristics of a diaphragm wall-subway station system with different connection modes under earthquake sequences were investigated using numerical simulation. The damage degree of the structural component was calculated through quantitative analysis of the tensile damage picture. The seismic damage level of the station structure was evaluated to characterize the damage transition effect induced by the aftershock according to the inter-story drift angle. Moreover, an empirical model for predicting the inter-story drift angle with respect to different peak accelerations was proposed. The research results indicate that the effect of the connection mode between the sidewall and the diaphragm wall on the damage evolution and deformation behavior of the station structure is significant. Compared with that of the compound wall structure, the seismic damage to the sidewall of the composite wall structure is much less severe, but the slabs become more vulnerable and suffer more severe damage. The accumulative damage triggered by aftershocks aggravates the extent of structural damage and even leads to damage transition. The conclusions illustrated in this paper contribute to a better understanding of the seismic resistance design of diaphragm wall-subway station systems under earthquake sequences.

Diaphragm walls are commonly employed as a permanent support for the building of metro stations near urban valley, and in conjunction with the interior sidewalls of the station structure to withstand the pressure from surrounding soils. Despite their prevalent use, the effect of underground diaphragm walls on the seismic response of stations is not yet fully understood. In this paper, a series of 1-g shaking table tests is designed to investigate the seismic response of a near-valley station with underground diaphragm walls within the elastic range. Modeling the stratum-structure-diaphragm walls system is accomplished by employing granular concrete reinforced with galvanized steel wires and synthetic model soils, and a station without diaphragm walls is included, serving as a benchmark for comparative analysis to understand the influence of diaphragm walls on the seismic behavior of the station. The experiment was designed for three depth-to-width ratios (DWRs), i.e. 1/3, 1/4, and 1/8, of arc-shaped valley topography, as well as the seismic excitations for the test include actual seismic records with the amplitude of 0.2 g, 0.4 g, and 0.8 g, respectively. Results show that the underground diaphragm walls enhance the lateral stiffness of the near-valley station compared to structures without diaphragm walls, and thus significantly reducing the racking deformation of structure during earthquakes. The presence of diaphragm wall would decrease the amplification of dynamic earth pressure caused by valley effect at the structural sidewalls, and significantly reduce the lateral vibration and shear effect of the station near a valley with a larger DWR. Notably, bending moment response at the connection between the diaphragm walls and structural sidewalls are dramatically amplified under strong seismic loading, and such adverse effects gradually increase with the DWR of the valley.

Nodular diaphragm wall (NDW) is a novel foundation type with favorable engineering characteristics. In contrast to traditional diaphragm walls, the vertical bearing capacity of NDW is significantly enhanced by the existence of nodular sections. Currently, the application and research of NDW are limited, and further clarification is needed regarding its deformation properties and failure modes. This study employs particle image velocimetry (PIV) technology to analyze the displacement and failure mechanisms of the foundation under vertical uplift. The findings indicate that positioning end and middle nodular sections extend the influence range to both deep and shallow soil layers, while multiple nodular sections facilitate in mobilizing broader spectrum of soil. The failure pattens of NDW involve interconnected sliding planes, including vertical sliding planes, inverted pyramid-shaped, or tangent curves, and vase-shaped curves (referred to as curve sliding planes). Overall, compared to pile foundations, the failure surfaces of the retaining wall exhibit complexity, influenced by the number and arrangement of sections, with certain sliding plane orientations correlated with the soil's internal friction angle.