Foundation Pit Excavation Research Articles

Mechanics and permeability properties of ecological concrete mixed with recycled engineering muck particles

The excavation of construction foundation pits, tunnels, channels, and other projects generates a significant volume of engineering muck, posing challenges in management. Prolonged accumulation of this muck can lead to environmental pollution. The effective recycling of this type of construction waste is crucial for the advancement of a circular economy, necessitating immediate attention to research and solutions. In this study, a novel method is introduced for the preparation of low-carbon and environmentally friendly ecological concrete. This method involves the utilization of recycled engineering muck particles to substitute a portion of the natural aggregate and enables the comprehensive recycling of engineering muck. Subsequently, the mechanical and permeability properties of ecological concrete under varying muck particle content and porosity conditions are analyzed through experiments, taking into account the impact of relative average pore diameter and pore tortuosity. A predictive model has been developed for the tortuosity of pore channels in ecological concrete, taking into account effective porosity and average pore diameter. The enhanced Kozney-Carman model is employed to describe the correlation between pore properties and hydraulic conductivity. The findings indicate that a composite curing agent is formed by combining ordinary Portland cement with a hydrophilic polyurethane solution. This composite curing agent demonstrates superior performance compared to pure cement in the solidification of engineering muck. As the replacement rate of unsintered recycled residue particles increases, the porosity of concrete may increase by up to 29.7 %. This results in enhanced permeability characteristics but a decrease in compressive strength. In contrast to lightweight aggregates manufactured through the sintering process, the carbon emissions of unsintered recycled residue particles are reduced by 57.7 %. This study provides suggestions for the repurposing of construction waste and contributes to the advancement of sustainable practices within the concrete production sector.

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.

Strategy and analysis of the deformation of subway tunnel caused by pre-dewatering under water-rich sand

Pre-dewatering is an essential step in deep foundation pits with water-rich sand, and its impact on the surrounding environment has attracted increasing attention. To study the impact of pre-dewatering on the tunnel, we selected a typical foundation pit project in Shanghai to conduct in situ pre-dewatering tests and comprehensively record the soil stress, horizontal displacement, and tunnel deformation around the foundation pit during pre-dewatering. The data showed a strong correlation between the displacement and stress changes in the surrounding soil and the locations of the pre-dewatered soil layers. Based on the changes in the water-earth pressure and displacement, the deformation mechanism of the adjacent subway tunnel caused by pre-dewatering before foundation pit excavation was analyzed. Combined with existing research results, strategies such as increasing the stiffness of the ground wall, improving the anti-deformation ability of the soil in the passive area, and on-demand dewatering were proposed, and the findings can be used as reference for similar projects.

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.

Performance of Diaphragm Walls during Ultra-Deep Excavations in Karst Areas: Field Monitoring Analysis

Deep foundation pit excavations have become more extensive for the construction of underground spaces with rapid urbanization. Diaphragm walls are commonly used to support deep excavations. However, due to the complex geological conditions in karst areas, construction accidents frequently occur during the excavation of foundation pits. This study aims to investigate the performance of diaphragm walls in karst areas through field monitoring analysis. A kick-in deformation mode of the diaphragm wall is revealed during the foundation pit excavation. Furthermore, the results show that the diaphragm walls present multiple deformation modes rather than a single mode. Additionally, this study proposes a method to calculate the lateral displacement of the diaphragm walls at different depths. It is found that the karst caves have a considerable impact on the stability of diaphragm walls, as demonstrated by their lateral displacement. The hidden karst caves reduce the bearing capacity of the bedrock, rendering it insufficient to resist the active earth pressure. As a result, the bottom of the diaphragm wall is kicked into the foundation pit, causing significant lateral displacement and posing risks during excavation. The findings of this study contribute to the design and construction of similar excavations in karst areas.

Numerical Simulation of Double-Row Retaining System with Different Piers

With the rapid expansion of foundation pit excavation areas due to the burgeoning underground transportation networks in large cities, spatial combined double-row retaining structures have become indispensable for ensuring stability and minimizing deformation. Integrating piers into these structures enhances stiffness; however, the research on this topic is limited. This study investigates the Chisha Metro project, which utilizes a double-row support structure with added support piers to improve overall stiffness. Numerical simulations are employed to model the foundation pit and analyze the stress distribution and deformation of double-row retaining systems with T-shaped, cross-shaped, or square-shaped piers. The results demonstrate that the retaining system, after the introduction of piers, exhibits reduced maximum horizontal displacement and surface settlement of soil, and indicates spatial characteristics and the transformation from a planar problem to a spatial problem. Furthermore, in specific geological conditions, the T-shaped support pier proves to be more effective in connecting the front and rear support structures compared to the cross-shaped and square-shaped support piers, which mainly reinforce the soil without connecting the support structures. This research provides valuable insights for improving design and construction practices in foundation pit engineering.

Ground settlement and estimation of maximum settlement value in adjacent foundation pit excavation

The excavation of adjacent pits following the initial foundation pit excavation can significantly influence ground settlement. Using a foundation pit excavation project in Changzhou as a prototype, this study employed the numerical simulation method in conjunction with the HSS model to analyze the settlement deformation characteristics of the original excavation and compare them with the recorded monitoring values. In this study, the analysis focused on the ground settlement between two pits by varying the spacing between them at different excavation depths. The findings revealed that the ground settlement does not exhibit a significant increase when the new pit is excavated at a shallow depth. However, it rapidly increases when the excavation depth of the new pit surpasses that of the existing pit. Furthermore, an increase in the distance between the two pits causes the maximum settlement position to shift towards the edge of the new pit. The maximum ground settlement is found to have a linear relationship with both the maximum horizontal displacement of the two pits and the spacing between them.

Inverse Analysis of Strata in Seepage Field Based on Regularization Method and Geostatistics Theory

During the construction of underground engineering, the prediction of groundwater distribution and rock body permeability is essential for evaluating the safety of the project and guiding subsequent design and construction. This article proposes an objective function that solves an underdetermined inverse analysis problem based on the least-squares theory and regularization method and uses geostatistics theory and the variogram function to describe the spatial characteristics of the actual engineering system. It also establishes an optimization model of the analysis stratum seepage field and puts forward the method of using on-site test observation data to solve the stratum penetration coefficient. Relying on the foundation pit project of the Lingshanwei Station of Qingdao Metro, the on-site pumping and packer permeability test was conducted for different strata venues in the foundation pit, and the on-site water-head observation value was obtained. Physical detection of the influence area of foundation pit excavation confirms the correctness of the model from the region and verifies the accuracy of the model on the value through the on-site pumping test. Results show that the accuracy of the use of this objective function to solve the underdetermined inverse problem is above 85%, which proves the effectiveness of the method. The stratigraphic geological information obtained by the inverse analysis model provides an important basis for engineering design and security construction.

Experimental study on stress and deformation characteristics of foundation pit considering excavation width using 3D printing technology

A sophisticated model of the foundation pit support structure was developed via a model test that incorporated 3D printing technology. A meticulously scaled-down simulation of foundation pit excavation was conducted, utilizing the excavation width of the foundation pit as the sole variable, to evaluate and compare the impact of various foundation pit widths on the force and deformation characteristics of the foundation pit following layer-by-layer excavation. The findings indicate that the stress and deformation characteristics of the retaining structure shift from the “cantilever” mode to a composite mode of “internally convex” or “concave-convex” as the pit is excavated and internal support is installed. The change in pit width has minimal influence on the mechanical response law of the support structure during excavation. Nonetheless, the alteration in the pit width had a direct effect on both the internal force and deformation of the support structure, as well as the change in surface settlement value. In the experiment, wider pits had monitoring values that increased multiple times compared to narrower pits. The width of the foundation pit has a considerable impact on the mechanical response and stability of the pit, which is evident in the relatively lower lateral earth pressure on the outside of the retaining structure in narrower pits. This results in less stress and deformation of the pit structure. Moreover, the decrease in the passive zone of the pit contributes to better stability, indicating that the lower lateral earth pressure on the outside of the retaining structure is an innate reason for the excellent stability of narrower pits.

A Theoretical Solution of Deformation and Stress Calculation of the Underlying Tunnel Caused by Foundation Pit Excavation

A Theoretical Solution of Deformation and Stress Calculation of the Underlying Tunnel Caused by Foundation Pit Excavation

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.

Theoretical Study on Diaphragm Wall and Surface Deformation Due to Foundation Excavation Based on Three-Parameter Kerr Model

To calculate the horizontal displacement of the diaphragm wall and surface settlement caused by foundation pit excavation, the three-parameter Kerr foundation model was applied to a diaphragm wall and derived the flexural differential equations of the diaphragm wall and calculated the horizontal displacement of the diaphragm wall using the finite difference calculation method. The boundary element method combined with the Mindlin displacement solution was then used to invert the additional horizontal stress near the diaphragm wall. Lastly, the Mindlin solution was used to calculate the surface settlement. The effectiveness of the proposed calculation method was verified by comparing the horizontal displacement of the diaphragm wall and the surface settlement between the theoretical calculation and the actual project. The theory proves that there is a certain connection between the horizontal displacement of the diaphragm wall and the surface settlement, and the horizontal displacement of the diaphragm wall is larger than the surface settlement. Using this theory to further analyze the foundation pit construction parameters, the greater the thickness and elasticity modulus of the diaphragm wall, and the greater the diameter and number of internal supports, the smaller the horizontal displacement of the diaphragm wall and the surface settlement. The theory can accurately predict the horizontal displacement of the diaphragm wall and surface settlement and provides guidance for the construction of foundation pit projects.

Structural displacement and deformation of adjacent shield tunnel induced by foundation pit excavation

Excavating a foundation pit close to a tunnel will unavoidably impact the nearby soil, causing the tunnel to shift and deform. Examining the longitudinal displacement and convergence deformation of a nearby shield tunnel during foundation pit excavation is crucial for maintaining safe operations. Nevertheless, most of the current research primarily focuses on the effects of a single foundation pit excavation on existing tunnels. This study examines and analyzes the effects of multiple foundation pit excavations on the displacement and deformation of pre-existing tunnels, using a project at a subway station as a case study. By employing the PLAXIS three-dimensional finite element software, a large-scale computational model based on the HS model is established, and then five dangerous working conditions are selected for simulation analysis. The research findings delineate that: (i) The displacement of the tunnel is affected by various factors. These encompass the magnitude of the foundation pit excavation, the positioning of the foundation pit excavation in relation to the tunnel, and the closeness of the tunnel to the foundation pit. (ii) The deformation encountered by the tunnel is largely influenced by external loads, where the scale of the unloading load primarily determines the deformation characteristics of the tunnel.

Influence of foundation pit excavation on the internal force of adjacent shield segment structure

As subway line density increases, excavation of foundation pits around tunnels unavoidably triggers soil disturbance. This consequently alters the on-site strain and distortion fields of the soil, resulting in internal force modifications in the tunnel shield segment and joint failure. To maintain tunnelling structure safety through numerous foundation pit diggings, this study uses a real-world project as its model. Leveraging the tunnel convergent deformation results derived from prior analyses with PLAXIS 3D software, the Midas GTS software is utilized to explore the alterations in internal forces and joint failure patterns of the tunnel subjected to convergent deformations of 4cm and 5cm. The findings are as follows: (i) Under the effect of a vertical load, the segment deformation takes on a transverse elliptical shape. (ii) The majority of joint failure is primarily focused around the foundation pit excavation area, where the base of the arch opens inwardly, and the midsection of the arch expands outwardly. (iii) The stress on the structure escalates as the extent of foundation pit excavation increases.

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.

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.

Study on Influence of Tension Height of Steel Strand on Displacement of Foundation Pit Supported by Fish-bellied beams

The steel support system of prestressed fish-bellied beams can reliably control the deformation of foundation pit and provide open excavation space for foundation pit excavation, in which the triangle plate plays an important role in the fish-bellied beams system. But the deformation of the triangle plate and the steel strand is too large is a common problem in the foundation pit support, through the analysis of the stability of the triangle plate, it is found that the tension point height is an important factor leading to the deformation of too large. Through MIDAS/GEN analysis, it is found that the increase of the tension point height of the strand is conducive to the control of the displacement of the connecting part, and with the increase of the tension point of the strand, the anti-impact stability of the fish-bellied beams system is gradually enhanced. Therefore, by changing the tension height of the steel strand, the supporting system of the fish-bellied beams is optimized.

Application of a Hot Melt Recoverable Anchor Cable in Foundation Pit Support

With the continuous development of the social economy, the depth of foundation pit excavation of proposed construction projects in various places gradually increases, which is closer to the building red line, and the surrounding environment is relatively complex; therefore, there are few supporting schemes for foundation pit selection. Based on the Vanke B-6 plot of a real estate development project, the project has close neighboring buildings. If we use a normal anchor cable, underground cut line problems are possible, and so we choose the hot melt-type recoverable anchor; with three element dispersion pressure, the anchor cable can minimize broken sections of brush slope excavation and has advantages of a simplified construction process and good seismic performance. Except for the cable barrel, the other parts and all steel strands can be recycled, and recycled parts can be reused. The recyclable bolt (cable) overcomes the disadvantages of the conventional bolt (cable) as a temporary support, such as pollution of the underground environment, encroachment on the underground space of adjacent buildings, and becoming an underground obstacle in follow-up projects. It accords with the characteristics of the times of environmental protection and sustainable development, and has achieved good economic and social benefits.

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.

Analysis of deformation law of an airport foundation pit monitoring in loess area

This paper takes an airport foundation pit project in northwest loess area as the research object, and introduces the key method technology of support, construction and monitoring of this foundation pit project. The scope of this foundation pit project is widely distributed, there are no buildings in the surrounding area, and there is less restriction on the construction space, so the GRF01 green assembled support method of Slope release with soil nail wall is adopted, which controls the deformation of the foundation pit well and at the same time, plays the role of green environmental protection and reduces the cost. The analysis of the pit monitoring data shows that the pit engineering support design scheme effectively controls the deformation of the pit, and all monitoring data did not reach the alarm value, which ensures the safety of pit excavation and in-pit operation, and achieves the dual goals of economy and environmental protection. It can provide reference for the design and construction of similar large-scale foundation pit excavation and support in loess area.