Deep Foundation Pit Research Articles

Effects of the excavation of deep foundation pits on adjacent approach bridges: a case study of Nanjing Yangtze River Bridge

Effects of the excavation of deep foundation pits on adjacent approach bridges: a case study of Nanjing Yangtze River Bridge

Barrier Effect of Existing Building Pile on the Responses of Groundwater and Soil During Foundation Pit Dewatering

In regions with abundant groundwater resources, pre-excavation dewatering on deep foundation pits often leads to the deformation of the enclosure wall and settlement of the surrounding ground. Based on a series of engineering measurements, we conducted a series of numerical simulations to investigate the behaviors of wall and soil during pre-excavation dewatering with and without the existing pile foundations and under different distances between the existing pile foundations and foundation pits (D). Numerical results indicated that when the foundation pit is adjacent to existing building pile foundations, the soil was restricted by the pile foundations (i.e., soil-blocking effect). When D ≤ 40 m, the soil-blocking effect grows stronger as D gets smaller; while when D > 40 m, the soil-blocking effect is significantly weakened and the water-blocking effect (i.e., the blockage of groundwater seepage by the building pile foundation) gradually appears, which intensifies the ground surface settlement. The maximum settlement position of the soil behind the pile foundation of the existing building is farther away from the foundation pit as the soil-blocking effect becomes stronger. The coupling effect of soil-blocking and water-blocking on the ground deformation should be considered in the design of the foundation pit project to get a more reasonable support and dewatering scheme.

Impact of Excavation on Adjacent Elevated Bridges and Optimization Analysis of Deformation Control

Based on the deep foundation pit project of the TOD (Transit-Oriented Development) complex of the Shaoxing North High-speed Railway Station, the influence of different construction stages on the deformation and inclination rate of the adjacent elevated bridge and its variation law are studied through field measurement and numerical simulation. The construction process is optimized by the method of reinforcement outside the pit and adjustment of preloaded axial force, and the influence of distance on elevated bridges is summarized. The results show that with the excavation of the foundation pit, the deformation of the bridge pier and bridge pile foundation gradually increases, and the deformation of the bridge piers is larger than that of the bridge pile foundations. As the depth of soil reinforcement outside the pit and the preloaded axial force increases, the maximum vertical displacement of the bridge pier and bridge pile foundations gradually decreases. The deeper the depth of soil reinforcement, the better the displacement control effect on the elevated bridge. In actual construction, it is recommended that the depth of reinforcement be taken as the excavation depth of the pit. It is obvious that the preloaded axial force is subject to the pit angle effect, and the appropriate value of the preloaded axial force should be selected according to the site conditions. The deformation of the bridge pier and bridge pile foundation generally shows a decreasing trend with the increase in the distance between the elevated bridge and the foundation pit. When the elevated bridge is close to the foundation pit, it will be affected by the pit angle effect, and the fluctuation will decrease. The conclusions drawn in the article can serve as the basis and reference for design and construction, and provide reference for similar projects.

Stability analysis of deep foundation pit with a double-row cast-in-place piles and diagonal steel lattice braces under sloped excavation conditions

Existing deep foundation pit support structures are commonly composed of external earth-retaining structures, internal horizontal bracings, and vertical columns. A closed bracing system, often formed by a horizontal support through a bracket board, frequently impedes vertical excavation and soil removal operations in the foundation pit, and the processes of assembly and dismantling are complex and time-consuming. This study presents a combined support system and construction method consisting of cast-in-place piles and diagonal steel lattice braces. For sloped excavation, diagonal braces were constructed by slotting through the reserved soil, allowing the use of a single layer of support within the excavation depth. This approach significantly optimizes the construction process, reducing both project duration and overall cost. The field monitoring results indicated that the support method effectively controlled the lateral displacement of the pile bodies. Field monitoring results demonstrated that the proposed support system effectively controlled the lateral displacement of the pile bodies. The adoption of a support-first, excavation-second approach significantly controlled the settlement of the ground surface around the foundation pit, thereby preventing excessive increments in the axial force of the supports due to the large longitudinal depth excavation. The calculation results of the three-dimensional finite element model for foundation pit excavation and support indicate that the proposed support method results in a decreasing ratio of the maximum lateral deformation depth of the pile body, denoted as δh-m, to the excavation depth He as the excavation depth increases. This implied that the displacement of the pile body was strictly controlled. When the depth of the foundation pit excavation exceeded 10 m, the maximum lateral deformation occurred below 10 m along the pile shaft. The diagonal steel lattice braces transferred the load to the top of the cast-in-place piles at the bottom of the pit, where the stress concentration occurred. During construction, special attention must be paid to the strength of the connection between the pile top and the connecting beams.

Effects of the excavation of deep foundation pits on an adjacent double-curved arch bridge

The excavation of deep foundation pits can cause variations in the displacement and stress fields of surrounding soils, which hence induces adverse effects on adjacent structures. This study presents a two-stage method to quantify the impact of the excavation of a deep foundation pit on the adjacent double-curved arch bridge in the historical city of Nanjing, Southeastern China. The entire process of the foundation pit excavation was simulated and the induced deformation of the arch foot was obtained in the first stage by hardening soil model with small-strain stiffness. Then, the obtained deformation of the arch foot was applied to the bridge structure as a displacement boundary in the second stage to calculate the internal forces and deformations of the double-curved arch bridge structure. The tensile strength of concrete is taken as the limit value of the tensile stress of the double-curved arch bridge. The limit values of arch foot displacement under four evaluation conditions are obtained by step loading calculation. The present results provide construction guidance and safety warning for the process of foundation pit excavation adjacent to double-curved arch bridges for historical preservation.

Advanced Risk Assessment for Deep Excavation in Karst Regions Using Improved Dempster–Shafer and Dynamic Bayesian Networks

This study presents a novel risk-assessment methodology for deep foundation pit projects in karst regions, aimed at enhancing project safety and decision-making processes. This approach amalgamates fuzzy dynamic Bayesian networks with a refined Dempster–Shafer (DS) evidence theory to tackle the intricate uncertainties present in such contexts. A comprehensive risk index system, derived from historical accident cases, relevant standards, and the literature, encompasses environmental, design, construction, and management factors. Initial probabilities for each risk factor are determined through the integration of expert knowledge and fuzzy theory. The enhanced Dempster–Shafer theory is utilized to fuse diverse information sources, culminating in a robust and dynamic risk evaluation model. This model leverages real-time monitoring data to dynamically assess and adjust risk levels throughout the construction process. The validation of the proposed method is demonstrated through a detailed case study of the Guangzhou Tangxi Section 1 deep foundation pit project, which effectively identified critical risk factors and facilitated proactive construction strategy adjustments. To further evaluate the reliability of the methodology, comparisons were made with three alternative methods, and applications were conducted on three additional deep foundation pit projects. These comparative analyses confirm the superior reliability and applicability of the proposed methodology across varied scenarios.

A Multi-Objective Prediction XGBoost Model for Predicting Ground Settlement, Station Settlement, and Pit Deformation Induced by Ultra-Deep Foundation Construction

Building a deep foundation pit in urban centers frequently confronts issues such as closeness to structures, high excavation depths, and extended exposure durations, making monitoring and prediction of the settlement and deformation of neighboring buildings critical. Machine learning and deep learning models are more popular than physical models because they can handle dynamic process data. However, these models frequently fail to establish an appropriate balance between accuracy and generalization capacity when dealing with multi-objective prediction. This work proposes a multi-objective prediction model based on the XGBoost algorithm and introduces the Random Forest Bayesian Optimization method for hyperparameter self-optimization and self-adaptation in the prediction process. This model was trained with monitoring data from a deep foundation pit at Luomashi Station of Chengdu Metro Line 18, which are characterized by a sand and pebble stratum, cut-and-cover construction, and a depth of 45.5 m. Input data of the model included excavation rate, excavation depth, construction time, shutdown time, and dewatering; output data included settlement, ground settlement, and pit deformation at an operating metro station only 5.7 m adjacent to the ongoing pits. The training effectiveness of the model was validated through its high R2 scores in both training and test sets, and its generalization ability and transferability were evaluated through the R2 calculated by deploying it on adjacent monitoring data (new data). The multi-objective prediction model proposed in this paper will be promising for monitoring the data processing and prediction of settlement of surrounding buildings for ultra-deep foundation pit engineering.

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

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

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

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.

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

Study on Deformation Control of Road-Deep Foundation Pit Passing under Elevated Subway Bridge

This paper focuses on the application of pile foundation underpinning technology in a deep foundation pit of a subway Viaduct Project in Beijing. The study aims to address the engineering characteristics of the project, including a large number of new piles, a wide span of underpinning abutment, a long length of deep foundation pit, and a wide range of influences. This research utilizes field monitoring and numerical simulation methods to investigate the pile foundation underpinnings. The impact and management of road-deep foundation pit construction are considered, as well as their combined effect on subway viaducts and track structures. The primary accomplishments are as follows: (1) By analyzing the data from on-site deformation monitoring, it is evident that the pier exhibits maximum vertical deformation and maximum transverse deformation at the same location. The measuring locations are specifically situated on Pier 7# at the pile foundation underpinning. The maximum vertical and transverse deformations of the track are directly proportional to the maximum deformation of the pier. (2) By comparing the numerical simulation results with the field monitoring data, it is observed that although there is some discrepancy between the two, the deformation trend is largely consistent. This suggests that the numerical simulation analysis method is effective in reflecting the deformation of the bridge and track. (3) Through the numerical model and changing the values of the retaining structure parameters, the sensitivity of the pier deformation near the road foundation pit to the retaining structure parameters is systematically analyzed. The sensitivity of the pier deformation to the foundation pit parameters is as follows: the embedded depth insertion ratio of the retaining pile > the diameter of the retaining pile > the pile spacing.

Failure Mechanism and Control Mechanism of Intermittent Jointed Rock Bridge Based on Acoustic Emission (AE) and Digital Image Correlation (DIC).

Deep foundation pit excavation is an important way to develop underground space in congested urban areas. Rock bridges prevent the interconnection of joints and control the deformation and failure of the rock mass caused by excavation for foundation pits. However, few studies have considered the acoustic properties and strain field evolution of rock bridges. To investigate the control mechanisms of rock bridges in intermittent joints, jointed specimens with varying rock bridge length and angle were prepared and subjected to laboratory uniaxial compression tests, employing acoustic emission (AE) and digital image correlation (DIC) techniques. The results indicated a linear and positive correlation between uniaxial compressive strength and length, and a non-linear and negative correlation with angle. Moreover, AE counts and cumulative AE counts increased with loading, suggesting surges due to the propagation and coalescence of wing and macroscopic cracks. Analysis of RA-AF values revealed that shear microcracks dominated the failure, with the ratio of shear microcracks increasing as length decreased and angle increased. Notably, angle exerted a more significant impact on the damage form. As length diminished, the failure plane's transition across the rock bridge shifted from a complex coalescence of shear cracks to a direct merger of only coplanar shear cracks, reducing the number of tensile cracks required for failure initiation. The larger the angle, the higher the degree of coalescence of the rock bridge and, consequently, the fewer tensile cracks required for failure. The decrease of length and the increase of angle make rock mass more fragile. The more inclined the failure mode is to shear failure, the smaller the damage required for failure, and the more prone the areas is to rock mass disaster. These findings can provide theoretical guidance for the deformation and control of deep foundation pits.

Numerical Simulation Study on the Impact of Deep Foundation Pit Excavation on Adjacent Rail Transit Structures—A Case Study

Excavation in foundation pits can result in serious issues for nearby tunnel structures like deformation, differential settlement, and seepage damage, which profoundly impact project timelines and potentially endanger life and property safety. Therefore, it is imperative to investigate these impacts before and after construction and to facilitate timely adjustments of construction measures and reinforcement where possible. In this study, a foundation pit construction project near a rail transit line is employed as a case to comprehensive study the impact of on-site deep foundation pit excavation on adjacent rail transit structures by numerical simulation. A three-dimensional finite-element model of the foundation pit based on site geological characteristics and construction procedures is established to study the excavation and maintenance processes. Through analysis of key parameters including soil deformation, displacement, shear force, and bending moment of the tunnel structures, the designed protective structure is found to have effectively mitigated soil deformation, ensuring the stability of the foundation pit. As excavation progresses, lateral soil deformation and vertical uplift gradually increase but remain within specified control values. During various excavation stages, the maximum displacement of the tunnel structure gradually increases, with the increase rates of maximum settlement being 29.09%, 20.51%, and 6.45%, respectively. This indicates a gradual enhancement of the stability of the tunnel structure. Additionally, excavation of the foundation pit has a significant impact on the bending moment distribution of the tunnel structure but does not affect the axial force and shear force of the tunnel structure. The findings of this study offer crucial scientific insights for evaluating the safety and stability of construction near tunnel structures.

Prediction of Buildings’ Settlements Induced by Deep Foundation Pit Construction Based on LSTM-RA-ANN

In view of the shortcomings of existing methods for predicting the settlement of surrounding buildings caused by deep foundation pit construction, this study uses the monitoring data of a foundation pit project in Shanghai and divides the construction process of the pit into three working conditions, that is, enclosure construction, earthwork excavation, and basement support construction. The attention mechanism and residual update are integrated into the artificial neural network (ANN) model, and the root-mean-square error, average absolute error, and determination coefficient are used as the evaluation indices of the model. The artificial neural network prediction model LSTM-RA-ANN for building settlements in deep foundation pit construction was then established. The prediction performance of the model was also analysed under different working conditions, and the influences of the main factors (including the soil parameter, monitoring point location, activation function, hyperparameter, and input number) on the evaluation index was further explored. The results indicate that the performances of the established LSTM-RA-ANN model are closely related to the construction conditions, the predicted settlements agree well with the monitored ones in three working conditions with the greatest errors occurring at a later time of the working conditions, and the prediction accuracy of the great–small order corresponds to basement support, enclosure construction, and earthwork excavation respectively. The farther the monitoring point is from the edge of the pit, the better the model performance is. The activation function, initial learning rate, and maximum iteration batch have a great influence on the evaluation indices of the model, while the number of input points has little effect on the evaluation indices. These results may serve as a reference for the safe construction and normal operation of foundation pit engineering.

Research on a Calculation Method for the Horizontal Displacement of the Retaining Structure of Deep Foundation Pits

The precise calculation and effective control of the horizontal displacement of deep foundation pit retaining structures are critical for foundation pit support design and construction. Based on stress–strain linear elastomer theory and considering the deformation coordination between an enclosure wall and its internal support member, a formula for the redundant restraint force acting on the retaining wall was derived through the unit load method and the principle of elastic superposition. Moreover, a method for calculating the horizontal displacement of the retaining structure of a deep foundation pit was formulated, which is convenient for engineering applications. The method can also be used to calculate the horizontal displacement of cantilevered and anchored retaining structures when the loading conditions of the deep foundation pit and the relevant parameters of the enclosure structure are known. A case study was conducted on a standard section with an excavation width H of 19.3 m and an excavation depth h of 17.8 m. The structural parameters of the enclosure wall, along with the elastic support stiffness coefficient and soil layer parameters of the pit, were inputted into a MATLAB calculation code. Then, four internal support constraint forces Fi and the calculated values for the horizontal displacement of the enclosure wall were obtained after running the code. The calculated curve closely matched the curve of values measured in the field. The horizontal displacements of the top of the wall of several cement–soil gravity enclosure structures mentioned in the literature were also calculated. The results of these calculations were then compared with the measured data and corresponding data from the literature. The examples provided clear evidence demonstrating that the proposed method is highly reliable for calculating the horizontal displacement of deep foundation pit enclosure structures.

Development and Field Analysis of a Novel Servo Concrete Bracing System for Deep Foundation Pit Excavation

This study demonstrates the design and field implementation of an innovative servo concrete bracing system in foundation pit excavation. The bracing system comprises concrete struts, revised purlins, and hydraulic jacks, and its field performance is evaluated in a deep foundation pit project in Shanghai, China. The field measurements demonstrate that the servo bracing system effectively reduces the maximum lateral displacement of the retaining wall by up to 31%. Moreover, the servo jacks modify the wall’s flexural behavior by introducing local inflection points at certain depths and driving the displacement peak upward. Furthermore, the system’s performance varies with strut configuration, and servo forces influence not only the corresponding acting strut but also the adjacent struts’ behavior, implying that the monitoring scope should be expanded when applying the servo bracing system in actual engineering. This study provides a meaningful technical reference for future servo concrete bracing system applications in foundation pit engineering.

A method for predicting deformation field of deep foundation pit considering spatial effect

Urban underground spaces have experienced significant development and utilization due to the rapid progress of urban construction and continuous advancements in construction technology. The number of foundation-pit projects immediately adjacent to buildings, structures, and pipelines has been increasing. Ensuring the safety of construction and surrounding facilities, it is essential to predict deformation caused by foundation pit excavations. In this study, a simple calculation method was proposed for predicting deformation of an envelope structure and surface settlement caused by deep foundation excavation with spatial effects. Firstly, the principle of minimum potential energy was applied and the lateral displacement equation of the envelope structure was derived, considering spatial deformation effects. Secondly, based on linear elasticity theory, a surface settlement expression was formulated utilizing the plane strain boundary. Finally, the stratigraphic loss method was used to establish a connection between horizontal envelope deformation and surface settlement, allowing for calculations of surface settlement at any position behind the envelope structure. The effectiveness and practicability of the proposed method were demonstrated by comparison of two existing foundation-pit engineering examples.