Deep Foundation Pit Excavation Research Articles

Research on slope support control technology for deep foundation pit excavation in clay soil

Research on slope support control technology for deep foundation pit excavation in clay soil

Explainable deep learning-based dynamic prediction of surface settlement considering temporal characteristics during deep excavation

Accurate prediction of surface settlement (SS) induced by deep foundation pit (DFP) excavation is challenging considering the complicated soil distributions and uncertain construction situations. Therefore, a Recurrent Gated Unit (GRU) neural network model incorporated with Variation Mode Decomposition (VMD) was developed for SS prediction. By data denoising with VMD and hyperparameter tuning using Bayesian Optimization (BO), the proposed GRU model achieved dynamic and accurate prediction of SS caused by DFP excavation. Shapley Additive exPlanations (SHAP) analysis was then performed to enhance the interpretability of the GRU model. The presented GRU model was validated with a case study of Wuhan Metro Line 12 Shiqiao Station. The results indicate that: (1) The GRU models with VMD data denoising technique achieved accurate prediction with the average RMSE of 0.0244, MAE of 0.0189, MAPE of 0.0017, R2 of 0.9894, and VAF of 99.1206. (2) The GRU model outperformed the other five state-of-the-art models in predictive performance with robustness improvement of 13.5 %, 12.0 %, 50.0 %, 29.2 %, and 27.3 %, separately, compared to the other five models. (3) The historical values of the SS make the most significant contributions to the outcomes of the GRU models. In short, this study enhances the accurate and dynamic prediction of SS caused by DFP excavation, contributing to the safe execution of DFP projects.

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

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.

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 case study of the response of support structure and stratum deformation caused by deep foundation pit excavation in soft area

Investigating the spatial distribution and evolution patterns of deformations during foundation pit excavation is crucial for safeguarding the surrounding environment. This study focuses on a deep excavation case in Nanjing and discusses the strata deformation and the response of the retaining structure through the excavation phase, informed by on-site monitoring data. A three-dimensional finite element model of the excavation was developed, with comparisons between predicted values and on-site deformation monitoring data underscoring the accuracy of the numerical simulation results. This analysis delved into the deformation spatial distribution within the retaining structure and ground surface settlement throughout the excavation. Moreover, the three-dimensional deformation patterns of the diaphragm wall at various excavation depths were scrutinized, mapping the evolution pattern and spatial distribution of ground surface settlement around the foundation pit across different excavation stages. The findings reveal a pronounced spatial effect in both the diaphragm wall deformation and ground movements behind the wall, with the greatest deformation manifesting near the symmetric plane of the excavation center and markedly less deformation near the excavation corners. Furthermore, the deformation scope broadens with increasing excavation depth. These research outcomes aim to furnish a substantive reference for practical engineering implementations.

Study on the Influence of Adjacent Double Deep Foundation Pit Excavation Sequence on Existing Tunnel Deformation Based on HSS Constitutive Model

With the increase in the number of buildings along the subway, the impact of building construction on the adjacent subway tunnels has gradually come to the forefront and become an important problem to be solved in the engineering field. In particular, the excavation and unloading process of deep foundation pits will trigger an additional deformation of the subway structure, which may pose a serious threat to the safety and stability of subway tunnels. This article is based on a foundation pit project in the sub-center of Beijing, focusing on the form of a connected double foundation pit. Using the HSS constitutive model for soil materials, this study simulates the deformation response of adjacent existing subway tunnels under three excavation sequences: sequential excavation, simultaneous excavation, and the comprehensive excavation of the connected double foundation pits. The study shows that, from the point of view of the total displacement of the whole construction process, the impact of a synchronized excavation of double pits on the existing tunnel line is relatively large in the process, and the impact of sequential excavation is relatively small in the construction cycle. The result of the similarity of the excavation sequence is the similarity of the impact trend. The volume of excavated earth determines the value of displacement change for each excavation scenario in each working condition and is also responsible for the convergence of changes. The trend of total tunnel displacement is more consistent with that of vertical displacement, which is dominated by vertical displacement, with horizontal displacement having a relatively small influence. The maximum value of the total tunnel displacement occurs at the side of the tunnel near the excavation area, and the direction is inclined to the excavation area. The application of supporting structures, especially the center plate and the bottom plate, can suppress the vertical deformation of the tunnel bulge.

Research on ontology-based construction risk knowledge base development in deep foundation pit excavation

ABSTRACT Facing the massive amount of risk management data for deep foundation pit excavation (DFPE) construction, how to store and utilize these data to prevent the occurrence of risk events is an urgent problem that needs to be solved. The goal of this research is to build an ontology knowledge base aimed at standardizing and formalizing risk knowledge in the field of DFPE construction risk. The ontology knowledge base can promote construction risk identification and reduce the occurrence of risk events. A six-step method was applied to define the ontology classes and class hierarchy, determine objects and related data attributes. Ontology instances were created to further evaluate the integrity, correctness and consistency of the developed knowledge base. The case studies showed that through the formalization of knowledge and establishment of rule libraries, rule reasoning could intelligently identify potential risk events and provide risk prevention measures. This research contributed a new perspective to resolve problems of access and integration knowledge and information in DFPE risk management work. By structuring and standardizing knowledge and information, the ontology-based risk knowledge base can facilitate knowledge transfer, sharing and reuse among different project participants. The ontology knowledge base can provide decision support for managers to protect the on-site workers, building structures and the surrounding environments.

Numerical Simulation of Double-row Piles in Deep Foundation Pit Excavation

This paper aims to investigate the stress and deformation characteristics of double-row piles in deep foundation pit excavation by selecting representative strata in the Changchun area. The changes in bending moment, displacement, and earth pressure of double-row piles during the excavation are established using the FALC 3D software. The findings indicate that the deformation of the front pile is larger than that of the back pile, and the earth pressure distribution of the fornt pile deviates from the conventional Rankine earth pressure theory. Moreover, there are noticeable variations in earth pressure at the soil layer interface of the rear pile.

Effect of tempering on corrosion properties of mold steel

There are many strongly developed karsts in South China, which bring great uncertainty to the construction stability of underground projects. This paper takes the deep foundation pit project of a station in a sandy soil area as the background, simulates the deep foundation pit excavation process based on finite element software, and comparatively analyzes the influence of the existence of karst holes on the foundation pit support structure. The results show that the effective treatment of solution holes in the process of foundation pit excavation can reduce the risk of surface settlement around the foundation pit but has less influence on the lateral displacement of the foundation pit support structure. The cavity grouting reinforcement technology is also introduced in detail in the paper, which can provide a reference for the reinforcement of deep foundation pit projects in sandy soil stratum containing strong development of large cavities.

Multi-Stage and Multi-Parameter Influence Analysis of Deep Foundation Pit Excavation on Surrounding Environment

As urbanization accelerates, deep excavation projects have become increasingly vital in the construction of high-rise buildings and underground facilities. However, the potential risks to the surrounding environment and the inherent complexities involved necessitate thorough research to ensure the safety of those engineering projects with deep foundation pit excavation and to minimize their impact on adjacent structures. This study introduces a multi-stage and multi-parameter numerical simulation method to scrutinize the construction process of deep foundation pits. This approach not only investigates the influence of excavation activities on nearby buildings and roads but also enhances the fidelity of simulation models by establishing a three-dimensional finite element model integrated with on-site investigated geological information. Therefore, the proposed method can provide a more holistic and accurate analysis of the overall impacts of the pit excavation process. To examine the feasibility and effectiveness of the proposed method, this study adopts the multi-stage and multi-parameter influence analysis approach for a real practical engineering case to explore the impact of excavation on the foundation pit support structure, nearby buildings, and surrounding roads. The foundation pit support’s maximum displacement was 8.64 mm, well under the 25 mm standard limit. Anchor rod forces were about 10% below the standard limit. Building and road settlements were also minimal, at 10.33 mm and 16.44 mm, respectively, far below their respective limits of 200 mm and 300 mm. This study not only validates the feasibility of design and construction stability of deep foundation pits but also contributes theoretical and practical insights, serving as a valuable reference for future engineering projects of a similar scope.

Influence of Deep Foundation Pit Excavation on Adjacent Pipelines: A Case Study in Nanjing, China

To investigate the pipeline deformation pattern caused by the excavation of deep foundation pits in composite soil–rock strata, a comprehensive study integrating on-site monitoring and numerical simulation was conducted. This study centered on a deep foundation excavation project in the soft soil in Nanjing’s floodplain region. The analyses of pipeline settlement and deformation were performed based on field-measured data. This study investigated the impact of excavation on the mechanical properties of the surrounding soil that resulted in the progressive deformation of adjacent pipelines. Furthermore, numerical simulations were conducted using Plaxis 3D CONNECT Edition v22 finite element analysis software. This study elucidated the influence of factors such as pipeline–pit distance and burial depth on pipeline deformation, conducting a quantitative analysis of their effects. The results indicated that deformation primarily occurs unevenly near pit corners and is less pronounced in soil–rock strata than in single-type soil layers. This study established correlations between pipeline displacements and various factors, offering valuable insights for future excavation projects conducted under similar conditions.

Numerical Simulation and Monitoring Analysis of Deep Foundation Pit Excavation Based on Concrete Support Axial Force Servo Technology

Numerical Simulation and Monitoring Analysis of Deep Foundation Pit Excavation Based on Concrete Support Axial Force Servo Technology

Study on the influence of deep foundation pit excavation on the deformation of adjacent viaduct pile foundation

Study on the influence of deep foundation pit excavation on the deformation of adjacent viaduct pile foundation

Study on the influence of deep foundation pit excavation on the deformation of adjacent viaduct pile foundation

Study on the influence of deep foundation pit excavation on the deformation of adjacent viaduct pile foundation

Numerical Analysis of the Influence of Deep Excavation on Nearby Pile Foundation Building

In this paper, a numerical simulation is used to establish a three-dimensional model, which considers the height of buildings, the relative position between buildings, and foundation pits. These were studied in detail to investigate the changes in settlement of adjacent buildings and the displacement and internal force of piles caused by deep foundation pit excavation. The results indicate that the number of floors in the building, along with the angle and distance between the building and the excavation pit, have a significant impact on the settlement of the building and the deformation and internal force variation in the piles. For example, when D = 0.1 H, with the increase in the number of floors, the increase in the bending moment of pile 1 at the pile shaft is 62.63 kN·m, and the increase in the bending moment at the pile head is 224.72 kN·m. At this point, the maximum horizontal displacement of the pile shaft occurs at approximately 1.27 H. When θ = 45∘, the maximum difference between the maximum and minimum deformations of the building is 9.71 mm. When D ≤ 1.0 H, the majority of the building is in the primary influence range of surface settlement behind the wall, and the building undergoes a combined deformation of ‘upper convex’ and ‘concave’. When D > 1.0 H, the building predominantly resides in the secondary influence range, and the building undergoes a deformation of ‘upper convex’.

Deformation Characteristics of Pipelines Due to Adjacent Excavation in Riprap Reclamation Strata

The Shenzhen Ma Wan area has special geotechnical conditions, with more than 50% of the area being reclaimed rock formations. Riprap reclamation strata are particularly susceptible to significant deformation upon stress release. To comprehensively comprehend the reaction of existing pipelines to the excavation of an adjacent deep foundation pit within the riprap reclamation strata, an interaction of the soil–pipeline was conducted by encompassing both scaled model tests and numerical simulations based on a cross-sea channel project. Firstly, scaled model tests were performed on a soil–pipeline interaction caused by excavation. Subsequently, the numerical model was verified by comparing the numerical simulation results with the scaled model test results. Then, the internal force, strain of the pipeline, and soil surface deformation under the conditions of a soil layer with riprap were analyzed, and the results were compared with the case without riprap. Finally, the influence of the support structures was analyzed. The results indicated that the presence of the riprap in strata led to a 19% increase in vertical displacement of the ground surface and a 35% increase in the pipeline bending moment compared with the case without riprap in the same strata. The maximum internal force and strain occurred at an inclined angle of 45° in the pipeline section. Furthermore, it was found that the first lateral support after excavation played a pivotal role in controlling the overall deformation of the foundation pit. The changes in stiffness in the lateral support were more sensitive to the horizontal displacement than the vertical displacement of the pipeline. The results provide valuable insights for the design and safety evaluation of engineering projects in riprap reclamation strata.

Influences of Deep Foundation Pit Excavation on the Stability of Adjacent Ancient Buildings

The excavation of deep foundation pits has a significant impact on the stability of adjacent buildings. On the basis of a deep foundation pit project in Xi’an, China, the deformation of a diaphragm wall and the settlement and deformation of an adjacent ancient building with and without MJS (Metro Jet System) pile reinforcement were studied through onsite monitoring and numerical simulation. The influence of the building’s settlement difference on the shear strain of the building’s walls was analyzed, and then the effect of MJS pile reinforcement was verified. The research results show that (1) the settlement difference serves as the primary cause of the shear strain of the building, and the shear strain rises with increasing settlement difference; (2) the maximum shear strain of the building occurs on both sides of the building’s doors and windows and on the left and right corners of the building’s walls; (3) the shear strain and settlement of the building without MJS pile reinforcement are significantly greater than those with MJS pile reinforcement; and (4) MJS pile support exhibits a better reinforcement effect within one times the excavation depth of the foundation pit. These research results have a certain guiding significance for enhancing the stability of foundation pits and ensuring the safety of adjacent buildings.

Numerical Study on the Behavior of an Existing Tunnel during Excavating Adjacent Deep Foundation Pit

The excavation of a deep foundation pit adjacent to an existing tunnel may lead to the large deformation and induce damages in the tunnel structure. However, the influence on existing tunnel structure from nearby excavations has not been understood clearly, since it is affected by complex influencing factors of not only the geological and topographical conditions but also the construction method and positional relationship of the adjacent structures. This paper presents a numerical investigation into an existing underground rail transit line during the excavation of an adjacent deep foundation pit, in which the behavior of the existing tunnel structure from excavating the aforementioned foundation pit is clarified, and the effectiveness of the adopted three-dimensional model is confirmed by comparison between the numerically calculated and field-measured ground settlement of the monitoring point. The results demonstrate that the deformation of the existing tunnel structure is mostly induced by the excavation of the deep foundation pit. This study can provide a reference of deep excavations adjacent to existing infrastructures.