Foundation Pit Research Articles

Numerical study on seismic performance of a prefabricated subway station considering the influence of construction process

In previous seismic analyses of cast-in-place stations, the importance of the construction process was typically not emphasized. Unlike cast-in-place stations, prefabricated subway stations feature innovative construction methods. The effect of ignoring the complete construction process on the seismic performance of prefabricated subway stations remains unclear, and this study aims to address this issue. In this research, a three-dimensional nonlinear numerical model considering soil-structure interaction (SSI) was established. First, the complete construction process of the station, including excavation of the foundation pit and structural assembly, was replicated. The initial state before dynamic loading was clearly defined. Subsequently, the seismic response mechanisms of the station, including deformation, SSI, acceleration, and internal forces, were thoroughly investigated, revealing the impact of structural type and construction method on seismic performance. The results indicate that neglecting the complete construction process leads to differences in the initial state before dynamic loading, resulting in variations in seismic response. Specifically, ignoring the assembly process causes an average bending moment error of 59 % and an axial force error of 35 % for each component. By comprehensively analyzing these findings, a deeper understanding of the intricate interplay between assembly techniques, structural behavior, and construction processes in seismic contexts can be attained, thereby informing more robust engineering practices.

Pipe piles and split-cables: reinforcing weak mine pits

To mitigate the instability problem of heavy equipment foundations in deep coal mine chambers under high geo-stress, this study proposes a combined reinforcement strategy for foundation pits, which are mainly composed of pipe piles and split-level vertical cables. The weak rock mass around the pit is reinforced using combined cables and grouting. The split-level-arranged cables with different lengths improve the tensional strength of the rock mass, whereas the pipe pile at the pit corner can enhance the shear strength. The overall performance of the structure in terms of bearing capacity can be significantly enhanced by pouring pipe piles to integrate them and the pump foundation to form a cohesive structure. Both the foundation integrity and foundation pit strength can be improved by stepwise support technology. Finally, an improved reinforcement strategy is implemented in a deep-pump chamber in the Huainan mining area. The monitoring results indicate that the foundation pit stability was successfully controlled and floor cracking and tilting of the pump foundation were avoided by using the improved support method.

Evaluation and Optimization of the Corner Effect of a Deep Foundation Pit Adjacent to a Subway Tunnel

Evaluation and Optimization of the Corner Effect of a Deep Foundation Pit Adjacent to a Subway Tunnel

An analytical solution for groundwater inflow of circle foundation pit with suspended waterproof curtains in the unconfined aquifer

An analytical solution for groundwater inflow of circle foundation pit with suspended waterproof curtains in the unconfined aquifer

Brief analysis of the innovation work in civil engineering technology

Under the new situation, the development process of urbanization is accelerating, the construction industry is developing well, the number and scale of civil engineering projects are gradually expanding, and the construction technology, as the core of the project construction, has always been the focus of people's attention. Because the construction quality will directly affect the safety of personnel, it is necessary to clarify the characteristics of construction technology and improve the existing civil engineering construction technology. Realize the technical innovation of foundation pit construction, prestressed construction, reinforced concrete construction and other links, improve the technical content of engineering construction under the premise of ensuring the construction quality, and extend the service life of the building as far as possible.

Analysis of factors affecting the groundwater level during foundation pit dewatering in the soft soil area: a review

Analysis of factors affecting the groundwater level during foundation pit dewatering in the soft soil area: a review

Intelligent analysis method for the global vertical displacement field of foundation pits in dense karst cave areas

Prior research on excavation in dense karst cave foundation pits has primarily concentrated on evaluating the localized spatio-temporal influence and isolated geological factors. Nonetheless, this approach oversimplifies modeling conditions, thereby limiting its ability to provide a comprehensive understanding of the vertical displacement field. Consequently, this oversimplification can inflate the safety factor and increase project costs. Therefore, we propose a feedforward neural network (FNN), updated with the loop nested optimal iterative method (LNOIM), which incorporates the spatiotemporal characteristics of monitoring points and geological factors to analyze the engineering sensitivity of karst caves. Ultimately, the global foundation pit vertical displacement field was obtained. Our method has been demonstrated to be effective in a foundation pit in South China ((P value) P > 0.050, Cohen's d < 0.200). Furthermore, it has been validated in other cases ((Root Mean Square Error) RMSE = 1.576–2.916). This work provides a new perspective on the accurate reflection of the global vertical displacement state of a foundation pit. Additionally, it enhances the ability to sensitively identify caves in dense karst cave areas, thereby improving the safety of foundation pit works.

An analytical model for permeability coefficient of soil-structure interface composed of different capillaries

The soil-structure interface, representing the contact surface between soil and structures such as buildings or rocks, assumes critical importance in water-related projects like earth dams, cut-off walls, side slopes, foundation pits, and water tunnels. Monitoring reports and studies consistently identify this interface as a vulnerable zone susceptible to seepage-related accidents. Despite this recognition, research on the topic has been limited, with a predominant focus on experimental methods that tend to underestimate permeability. This paper presents an analytical model, grounded in capillary theory, for calculating the permeability coefficient of the soil-structure interface. The study explores the differences in permeability between the interfacial soil and far-field soil. The study concludes that the higher porosity of the interfacial soil (porosity ≥ 0.48) compared to the far-field soil (porosity: 0.26–0.48) is a key factor in rendering the soil-structure interface susceptible to seepage. The calculated permeability coefficient of the interface, in relation to experimental values, exhibits a consistent ratio of 2.5–2.6 when the soil porosity is below 0.43, indicating reliable predictive utility. Moreover, the permeability coefficient of the interfacial soil proves to be at least 4.05–6.67 times larger than that of the far-field soil, potentially leading to the creation of preferential seepage channels at the interface.

Temporal-spatial-fusion-based risk assessment on the adjacent building during deep excavation

Foundation pit excavation will inevitably cause uneven ground settlement to pose potential risks to adjacent structures and infrastructures. To better perceive the risk status of adjacent buildings using multi-source information, a temporal-spatial-fusion-based risk assessment (TSFRA) model under the consideration of uncertainty and causality is developed by integrating FAHP (Fuzzy Analytic Hierarchy Process), DGDT (DAG-GNN, DEMATEL method, and topological analysis), and CM (cloud model). More specifically, FAHP handles temporal weights of excavation conditions based on expert knowledge. DGDT determines spatial weights for monitoring points, with DAG-GNN constructing causal graphs in a data-driven manner, DEMATEL handling global interactions, and topological analysis calculating node importance. CM can finally fuse the temporal (excavation conditions) and spatial (monitoring points) weights with settlement monitoring data, resulting in qualitative assessments of the overall risk status of adjacent buildings in uncertain environments. The proposed TSFRA is verified in the case of a Shanghai metro station construction project. Results indicate that the perceived risk of the project is at a relatively low level, consistent with the actual condition. High-risk excavation conditions and locations can be easily identified. There is a trend toward higher risk during the excavation of soft soil layers, and thus some risk control measures can be formulated to avoid potential risk events. In short, the weight determination and fusion method in TSFRA contribute to handling uncertainties in expert judgments and causalities in collected data, which can practically provide more reliable decision-making in excavation-induced risk assessment and control for ensuring the safety of adjacent buildings.

Numerical Investigation of the Influence of Foundation Pit Excavation on the Deformation of Underlying Tunnels Based on a Multi-Factor Orthogonal Test

The excavation of pits will induce the vertical displacement of tunnels and lead to engineering problems. The shape as well as size of a pit, and the complex spatial position relationship between the pit and tunnel will induce different deformation responses of tunnel structures; however, the degree to which each factor influences tunnel structure deformation is still unclear. This paper studied the impact of excavation on the deformation of tunnels via a combination of numerical simulation and orthogonal tests. The deformation of tunnels induced by excavation was studied using a numerical method, after which the sensitivity of influencing factors to tunnel deformation was studied by means of range and variance analyses through a four-factor and three-level orthogonal test. The results show that, for a foundation pit with a long side perpendicular to the tunnel longitude, the excavation has the least influence on tunnel deformation. Tunnel deformation increased with an increase in the excavation depth and decreased with an increase in tunnel–pit vertical and horizontal distance. As the plane shape of the foundation pit is 20 m × 45 m, the depth of excavation is 4 m, the pit tunnel vertical distance is 13 m, and the pit tunnel horizontal distance is 28 m, the tunnel has the least deformation. Based on the results of this study, the position relationship between the pit and the tunnel can be optimized in terms of design and construction, and the aim of controlling tunnel deformation can be achieved.

Study on the Impact of Deep Foundation Pit Construction on Nearby Elevated Structures—Case Study

Study on the Impact of Deep Foundation Pit Construction on Nearby Elevated Structures—Case Study

Effect of Steel Support Cross-Section and Preloaded Axial Force on the Stability of Deep Foundation Pits

Effect of Steel Support Cross-Section and Preloaded Axial Force on the Stability of Deep Foundation Pits

Prediction of the displacement in a foundation pit based on neural network model fusion error and variational modal decomposition methods

Prediction of foundation pit displacements is an important part of pit monitoring and early warning system, and accurate prediction of pit displacements can reduce pit disaster accidents. Herein, the Elman neural network model optimized by the mind evolutionary algorithm (MEA) is combined with the variational modal decomposition (VMD) and the fusion error method to accurately predict pit displacements at the top of the slope. Firstly, VMD is used to decompose the time series of pit displacements into trend, period, and random terms, and analyzed the rationality of the decomposition of the sub-displacement sequences; Secondly, the MEA-Elman model is used to predict the trend, period, and random terms and decomposition error in the decomposition of pit displacements, and finally the prediction results of the sub-displacements are superimposed to obtain the total displacement; The measured data of a pit in Qingdao, China, are used to verify the reliability of the model, and the calculated results show that the predictions are consistent with the measured data.

Deformation Effects of Deep Foundation Pit Excavation on Retaining Structures and Adjacent Subway Stations

Deformation Effects of Deep Foundation Pit Excavation on Retaining Structures and Adjacent Subway Stations

Mechanism mode and prevention and control measures of karst collapses induced by foundation pit excavation

Mechanism mode and prevention and control measures of karst collapses induced by foundation pit excavation

Numerical Investigation of Bedding Rock Slope Potential Failure Modes and Triggering Factors: A Case Study of a Bridge Anchorage Excavated Foundation Pit Slope

The analysis of slope failure modes is essential for understanding slope stability. This study investigated the failure modes and triggering factors of a rock slope using the limit equilibrium method, finite differences method, and exploratory factor analysis. First, the limit equilibrium method was used to identify potential sliding surfaces. Then, the finite differences method was employed to study deformation and failure features in a slope. Stability factors were calculated considering specific conditions such as rainfall, prestressing loss, and earthquakes using the strength reduction method. Finally, exploratory factor analysis was utilized to identify the triggering factors of each failure mode. The results revealed that failure modes were categorized into two types based on the positions of the sliding surface. The main triggering factors for Failure Mode 1 were rainfall and prestress loss, while for Failure Mode 2 they were earthquake loading and prestress loss. This study offers a comprehensive exploration of potential failure modes and their triggering factors from mechanical and statistical perspectives, enriching our understanding of potential failure modes in rock slopes.

Study on the coupling effect and construction deformation control of large deep foundation pit groups involving iron considering the coupling effect of seepage stress

Due to factors such as groundwater seepage and soil stress coupling effect, significant deformation and instability problems often occur during the construction process of super large deep excavation groups involving iron, seriously affecting the safety and stability of the project. This article aims to explore the coupling effect of super large deep excavation groups involving railways during the construction process, and how to effectively control construction deformation. This article combines theoretical analysis and numerical simulation to study the coupled effects of seepage and stress during the construction process of super deep excavation groups involving iron. With the help of finite element software, a numerical model of a large and deep excavation group involving iron was established, and the deformation and stress distribution at different construction stages were simulated. The research results indicate that the coupling effect of groundwater seepage and soil stress has a significant impact on the deformation and stability of the super deep excavation group involving iron. Therefore, reasonable construction measures and deformation control methods should be taken during the construction process.

Analysis of water inrush of a deep excavation triggered by river bank failure and its reconstruction

Many deep excavation projects are adjacent to river, and hence face the seepage risk. In this study, a through-wall seepage failure of a foundation pit adjacent to river is investigated. It is found that, the accident was initiated by the breakage of revetment along the construction joint and cracks of rubble stone masonry, which further caused the slope failure of river bank and the subsequent seepage of river water through the cold joint of waterproof curtain. The remedial works including construction of cofferdam in the river, backfill outside the foundation pit, reinforcement of cold joint, backfill inside the foundation pit, controllable dewatering outside the foundation pit and axial force adjustment of struts are designed. The monitoring results indicate effective implementation of the remedial works and the following successful reconstruction of the project. A summary of reported seepage failure cases adjacent to river is finally made to provide suggestions for the design and construction of future similar deep excavation projects.

Construction Mechanical Characteristics and Monitoring Analysis of the Existing Subway over the Newly Built Long Foundation Pit

Construction Mechanical Characteristics and Monitoring Analysis of the Existing Subway over the Newly Built Long Foundation Pit

Numerical Simulation of the Influence of a Deep Foundation Pit Adjacent to a Utility Tunnel: Case Study

Numerical Simulation of the Influence of a Deep Foundation Pit Adjacent to a Utility Tunnel: Case Study