Braced Excavation Research Articles

A Standard Penetration Test-Based Step-by-Step Inverse Method for the Constitutive Model Parameters of the Numerical Simulation of Braced Excavation

Numerical simulation is an essential method for predicting soil deformation caused by foundation pit excavation. Its accuracy relies on the constitutive model and its parameters. However, obtaining these parameters through lab tests has limitations like long durations, high costs, and potential errors. To improve the simplicity and accuracy of the selection of constitutive model parameters, this study proposes a step-by-step inverse analytical method. Using the braced excavation project in Hangzhou City, China as a case study, the proposed method firstly determines the ratio of the important constitutive parameters then the values of the key constitutive parameters. The results show that the reference secant stiffness (E50ref) and shear strain (γ0.7) of the hardening soil (HS) and hardening soil–small soil (HSS) models are the key constitutive parameters. The step-by-step inverse method not only reduces the number of parameters, but also improves the predicting accuracy. The established empirical relationship between the E50ref and standard penetration test (SPT) blow counts exhibits a good linear correlation. The parameter selection method proposed in this study is an accurate, practical, and efficient method, which can effectively predict the horizontal displacement and surface settlement of the retaining structure in multiple excavation stages.

A deep transfer learning model for the deformation of braced excavations with limited monitoring data

The current deep learning models for braced excavation cannot predict deformation from the beginning of excavation due to the need for a substantial corpus of sufficient historical data for training purposes. To address this issue, this study proposes a transfer learning model based on a sequence-to-sequence two-dimensional (2D) convolutional long short-term memory neural network (S2SCL2D). The model can use the existing data from other adjacent similar excavations to achieve wall deflection prediction once a limited amount of monitoring data from the target excavation has been recorded. In the absence of adjacent excavation data, numerical simulation data from the target project can be employed instead. A weight update strategy is proposed to improve the prediction accuracy by integrating the stochastic gradient masking with an early stopping mechanism. To illustrate the proposed methodology, an excavation project in Hangzhou, China is adopted. The proposed deep transfer learning model, which uses either adjacent excavation data or numerical simulation data as the source domain, shows a significant improvement in performance when compared to the non-transfer learning model. Using the simulation data from the target project even leads to better prediction performance than using the actual monitoring data from other adjacent excavations. The results demonstrate that the proposed model can reasonably predict the deformation with limited data from the target project.

Seismic response of braced excavation wall supporting deep sand layer using dynamic centrifuge tests

This paper presents the dynamic centrifuge model tests to investigate the seismic performance of a 24.8 m deep braced diaphragm wall supporting dry sand backfill soil at 40 g level acceleration. The model tests aim to determine the acceleration response of the backfill, seismic earth pressures acting on the wall, and the dynamic increment of the structure's inner force for sand backfills with different relative densities. Particularly, the horizontal seismic coefficient, earth pressure distribution, and dynamic thrust are analyzed in detail. Based on the experimental results, the dynamic thrust development is consistent for peak ground accelerations at bedrock less than 0.12 g and 0.10 g for relavitve densities of 78 % and 54 %, respectively. However, the dynamic thrust starts to increase when the bedrock acceleration exceeds this threshold. Moreover, the varying trend of dynamic thrusts under ground input motion employed during at the initial excitation differs from that of the succeeding input motions, likely due to the changes in relative density caused by backfill disturbance from sequential excitation. The increasing rate of increase on the dynamic thrusts among Northridge, Kobe, and artificial excitations was changed with the amplitude of the acceleration response. Lastly, the wall bending moment and strut axial force increase by up to 97.3 % and 12.9 % of the maximum value of member force on the at-rest condition due to earthquake loading.

Prediction of the undrained base heave and post uplift in braced excavation of a typical subway station in thick soft clay

Construction of a typical subway station usually involves a narrow long excavation with a width of approximately 20 m. An undrained base heave is a common problem in deep excavation areas with soft clay, which may induce considerable post uplift and damage the safety of the retaining system. Post uplift involves complex interactions between soil, pile post foundation, and supported struts, and an accurate prediction of post uplift is challenging. This paper aimed to establish a practical method for predicting the base heave and post uplift in the construction of typical subway stations in areas with thick soft clay. Series soil–water coupled finite element method (FEM) analysis was conducted to investigate the characteristics of the base heave with different soil properties and wall stiffnesses. The results showed that the calculated base heave can be fitted by a normalized function, regardless of large variations in soil properties and wall design parameters. The normalized function was then applied to a soil–post–strut interaction analysis model to predict the post uplift at different excavation depths. The application of the proposed method to a real subway station project showed that the predicted results were in good agreement with the field observations.

Effect of cross wall on the strut forces for braced excavations in clays

This study evaluates and estimates the effect of cross walls on the strut force for braced excavation in clays by using three-dimensional finite element analysis. A well-documented case history of a braced excavation with cross walls was utilized to validate the numerical analysis. Furthermore, a series of parametric studies were conducted to evaluate the distribution of strut force by considering different schematics of cross walls. The results revealed that implementing cross walls inside the excavation could significantly reduce the wall deformation and strut force along the wall section, particularly for the location near cross walls. In addition, a new empirical method was proposed to estimate the maximum strut force based on the apparent earth pressure for braced excavation with cross walls, which was verified through case histories. Finally, this study concluded that the existence of cross walls in braced excavations could ensure a safer bracing system and excavation design.

Evaluation of deformation for two-dimensional (2D) and three-dimensional (3D) braced excavation in clays with centrifuge modelling and numerical analysis

This study presents an improved in-flight strutting system for centrifuge modelling. Based on the centrifuge model test data, the mobilizable strength design (MSD) method was revised. The modified MSD method extends to the prediction of three-dimensional (3D) deformations in retaining walls due to excavation activities. Initially, an improved in-flight excavation tool used in centrifuge tests was employed to investigate the impacts of staged excavation on the characteristics of wall displacement and ground settlement in two-dimensional (2D) braced excavation. Subsequently, 2D and 3D finite element analyses, calibrated against the centrifuge test data and considering the small strain effect, were conducted to assess the performance of wall displacement, ground settlement, and movement of the underground soil induced by the braced excavation. Moreover, this research proposes a straightforward predictive model based on the modified MSD, specifically for calculating the deformation along the length of retaining walls in 3D braced excavations. The insights and the modified MSD method given in this study may facilitate the design of foundation pit projects, especially when the 3D effects are an essential detail to be considered in these projects.

Observed soil arching-induced ground deformation and stress redistribution behind braced excavation

This paper presents observed arching-induced ground deformation and stress redistribution behind braced excavation using the top-down construction method. The soil properties around the excavation were determined by laboratory and field tests. The ground deformation, soil displacement vector, strain path, principal strain, maximum shear strain, lateral earth pressure, pore water pressure, and effective stress path are presented based on the measured data. The majority of soil behind the wall is under volumetric expansion, indicating consolidation, creep behavior, or a combination of both. Besides, two periods of increases in pore pressure are observed, due to stress transfer from the lower to the upper parts (i.e., soil arching effect). The deep inward movement of the wall and the nearby soil accounts for the distribution of lateral earth pressure acting on the wall. The soil located behind the area of maximum wall deformation and adjacent to the wall, as well as the soil below the excavation base intersected by the shear plane, is in an active stress state. The lateral earth pressure at 5 m from the left excavation wall showed minimal changes, due to the combined effects of soil arching from lateral excavation and shield tunneling.

Influence of Ali Al -Gharbi Earthquake on Braced Excavation in Silty Clay Soil (Numerical Study)

The design of the braced excavation system is one of the important and necessary matters for the implementation of various projects. The braced excavation system is used to support excavations in temporary projects, so there are shortcomings in the study of this aspect, although sometimes there are many projects that take long periods of time especially the projects of underground tunnels and high buildings. This was the main reason for the study. Therefore, the possibility of exposing the drilling system to earthquakes is great, especially in seismically active areas. If the drilling system is exposed to an earthquake, it can cause great human and material losses, so it must be designed against earthquakes so that ensure complete collapse and failure does not occur. This study aims to investigate the behavior of braced excavations under the influence of the Ali Al-Gharbi earthquake in both x- and y- directions. A numerical study is carried out on braced excavation system of (14×6) m and depth 9m using software Plaxis 3D. The braced excavation system consists of three type of bracing system with three levels of strut and wales connected with sheet pile wall to support sides of excavation and prevent them from collapsing. The results of study showed that the horizontal displacement of braced excavation system is (100-155) % more than vertical displacement (settlement) with seismic time when system is subjected to Ali Al-Gharbi earthquake in both directions with the other factors remaining constant. The stiffness of sheet pile wall also play an important role increases and decreases lateral displacement in both direction. Also, the results showed that the movement of of braced excavation system depends on several factors like as type of soil, time acceleration and the direction of earthquake. Settlement of Ali Al-Gharbi earthquake in Y- direction is 13% more than in X-direction.

Deterministic and probabilistic analysis of great-depth braced excavations: A 32 m excavation case study in Paris

The Fort d’Issy-Vanves-Clamart (FIVC) braced excavation in France is analyzed to provide insights into the geotechnical serviceability assessment of excavations at great depth within deterministic and probabilistic frameworks. The FIVC excavation is excavated at 32 m below the ground surface in Parisian sedimentary basin and a plane-strain finite element analysis is implemented to examine the wall deflections and ground surface settlements. A stochastic finite element method based on the polynomial chaos Kriging metamodel (MSFEM) is then proposed for the probabilistic analyses. Comparisons with field measurements and former studies are carried out. Several academic cases are then conducted to investigate the great-depth excavation stability regarding the maximum horizontal wall deflection and maximum ground surface settlement. The results indicate that the proposed MSFEM is effective for probabilistic analyses and can provide useful insights for the excavation design and construction. A sensitivity analysis for seven considered random parameters is then implemented. The soil friction angle at the excavation bottom layer is the most significant one for design. The soil-wall interaction effects on the excavation stability are also given.

Review of recent developments in AI-based data processing and prediction for braced excavation design

Abstract This paper presents a review of the recent advances in the application of artificial intelligence (AI) techniques for data processing and prediction in the design and construction of braced excavation systems. It introduces various AI algorithms employed in addressing complex data processing and deformation prediction challenges in braced excavation. A pivotal development has been in the area of soil parameter and in situ monitoring data processing, which facilitates more reliable site characterization for efficient design. This paper delves into wall system and deformation predictions, showcasing AI’s ability to integrate multi-source data for real-time prediction. It also addresses spatiotemporal prediction, enhancing prediction accuracy by accounting for uncertainties. The significance of groundwater is highlighted by introducing predictive models that consider groundwater drawdown. Additionally, it discusses stability prediction based on the factor of safety of braced excavation, enabling proactive safety management for the retaining wall system and the surrounding environment. Furthermore, the paper discusses the challenges and opportunities associated with the use of generative AI and large language models, providing an overview of their significance, applications, and future directions in braced excavation.

Numerical analysis of one-strut failure in deep braced excavation considering anisotropic clay behavior

Numerical analysis of one-strut failure in deep braced excavation considering anisotropic clay behavior

The Behavior of Braced Excavation in Silty Clay Soil under El-Centro Seismic

The Behavior of Braced Excavation in Silty Clay Soil under El-Centro Seismic

Improved prediction of pile bending moment and deflection due to adjacent braced excavation

Improved prediction of pile bending moment and deflection due to adjacent braced excavation

Explainable boosted combining global and local feature multivariate regression model for deformation prediction during braced deep excavations

PurposeAn accurate prediction of the deformation of retaining structures is critical for ensuring the stability and safety of braced deep excavations, while the high nonlinear and complex nature of the deformation makes the prediction challenging. This paper proposes an explainable boosted combining global and local feature multivariate regression (EB-GLFMR) model with high accuracy, robustness and interpretability to predict the deformation of retaining structures during braced deep excavations.Design/methodology/approachDuring the model development, the time series of deformation data is decomposed using a locally weighted scatterplot smoothing technique into trend and residual terms. The trend terms are analyzed through multiple adaptive spline regressions. The residual terms are reconstructed in phase space to extract both global and local features, which are then fed into a gradient-boosting model for prediction.FindingsThe proposed model outperforms other established approaches in terms of accuracy and robustness, as demonstrated through analyzing two cases of braced deep excavations.Research limitations/implicationsThe model is designed for the prediction of the deformation of deep excavations with stepped, chaotic and fluctuating features. Further research needs to be conducted to expand the model applicability to other time series deformation data.Practical implicationsThe model provides an efficient, robust and transparent approach to predict deformation during braced deep excavations. It serves as an effective decision support tool for engineers to ensure the stability and safety of deep excavations.Originality/valueThe model captures the global and local features of time series deformation of retaining structures and provides explicit expressions and feature importance for deformation trends and residuals, making it an efficient and transparent approach for deformation prediction.

A parametric study on deformation behaviour for design of braced excavation in soft clay

ABSTRACT Adequate prediction of surrounding ground movement during braced excavation is critically important as excessive soil movement damages adjacent structures. The magnitudes and patterns of ground movement and wall deflection largely depend on excavation parameters like thickness of diaphragm wall, wall embedment depth, strut locations and soil parameters such as soil strength, compressibility and creep parameter. In the present paper a thorough, parametric study has been conducted using finite element (FE) analysis to address the influence of various parameters on deformation characteristics of braced excavation in soft clayey deposits. The importance of correct estimation of soil parameters for braced excavation design is also documented. The analysis of typical braced excavations in soft clay is carried out using PLAXIS 2D software where soft soil creep constitutive model is used. On the basis of numerical study a handy design guideline is recommended. Further multivariate regression models are developed incorporating various important excavation parameters for the adequate prediction of maximum wall and ground displacement along with wall and ground surface deformation profile. Here large numbers of data reported in case histories and generated artificially from FE analysis are used for formation of regression equations. The proposed model is validated comparing results from literatures not used for the development of the model.

Mechanism of Seismic Earth Pressure on Braced Excavation Wall Installed in Shallow Soil Depth by Dynamic Centrifuge Model Tests

Mechanism of Seismic Earth Pressure on Braced Excavation Wall Installed in Shallow Soil Depth by Dynamic Centrifuge Model Tests

An experimental study on time dependent ground settlement behind a braced excavation in soft clay using geotechnical centrifuge

An experimental study on time dependent ground settlement behind a braced excavation in soft clay using geotechnical centrifuge

Finite element analysis for a deep excavation in soft clay supported by lime-cement columns

The aim of the paper is to simulate the response of a deep excavation supported by sheet pile walls and lime-cement columns. The application of the deep mixing technique using lime-cement products in deep excavations changes the initial state of the natural soil and creates substantial displacements associated with the installation effects. In this paper, the influence of lime-cement stabilisation was investigated using the finite element method for an instrumented braced excavation. The 2D finite element analyses were performed with advanced constitutive models for both natural clay and stabilised soil, exploiting the laboratory test made on both field mixed and laboratory mixed stabilised clay samples. The numerical results show that taking account of installation effects provides realistic predictions of deformation, excess pore water pressure evolution, as well as the structural forces in the struts.

Failure Investigation of Braced Excavation in Soft Clays: Case Study on the Collapse of Nicoll Highway

Deep excavation in clay normally causes large soil movement, which may induce basal heave failure. In this study, the three-dimensional finite element analysis with the strength reduction method was employed to evaluate the typical failure mechanism of braced excavation in soft clays. The collapse of Nicoll Highway was selected as a failure case history and further conducted by considering the full elastoplastic structural behavior. The results showed that the computed wall displacements were successfully verified through the observation data. It was also found that the excavation failure was initiated by the yielding of the strut-waler connection, which was similar to that of the field observation. Finally, the proposed finite element model adopted in this study can be used as a design recommendation to evaluate the failure mechanism and further prevent possible braced excavation failure in soft clays.

Evaluation of a Braced Excavation by Numerical Method: A Case Study

Evaluation of a Braced Excavation by Numerical Method: A Case Study