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![Wall deflection and soil heave at the final excavation stage with different B values as He = 10.5 m, Hp/He = 2.6 and su/σv′\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$s_{\text{u}} /\sigma_{\text{v}}^{\prime }$$\end{document} = 0.22](publication/337753271/figure/fig2/AS:962240551321638@1606427433877/Wall-deflection-and-soil-heave-at-the-final-excavation-stage-with-different-B-values-as.png)
Wall deflection and soil heave at the final excavation stage with different B values as He = 10.5 m, Hp/He = 2.6 and su/σv′\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$s_{\text{u}} /\sigma_{\text{v}}^{\prime }$$\end{document} = 0.22
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This study investigates the stability of internally braced excavations in thick, saturated clay using a finite element method with reduced shear strength. The support system was fully modeled using elastoplastic structural elements, including struts, walls, and center posts. Effects of the ratio of the wall embedded depth to the excavation depth (H...
Citations
... However, there is a difference between the predicted displacement and the actual displacement during construction due to the fundamental problem that the methods proposed by conventional researches cannot properly describe the site conditions with various characteristics (Dmochowski and szolomicki 2021). The factors affecting the wall displacement during excavation are influenced by several parameters such as ground material properties, external influences such as groundwater level (GL) and surcharge load at the back and structure stiffness (Do and Ou, 2020;Zhang et al., 2020). ...
This study aims to identify and evaluate the significance of the key design factors that impact the stability of Earth retaining wall anchor-supported structures during excavations in urban areas. Although there are many previous studies on the deformation of Earth retaining walls during excavation, there is a lack of verification studies that quantitatively examine the stability of various influencing factors such as wall, ground characteristics, and external influencing factors. To this end, finite-element analyses were conducted, and their results were compared and validated with field measurements. These comparisons demonstrated that the numerical modeling technique employed in this study effectively simulates the wall’s behavior under excavation conditions. Subsequently, the impact of the main design factors, including ground properties, external conditions, and structural stiffness, on the behavior of the wall was quantitatively assessed by applying variation ratios. The findings indicate that the horizontal displacement of the wall, induced by excavation, is significantly dependent on the unit weight and shear strength of the soil. Conversely, the groundwater level location, surcharge load, and structural stiffness exhibit a relatively minor effect. Finally, the variability of the main design parameters was investigated, considering the specific ground layer where the wall is installed, revealing distinct influences of these variables across different ground layers. Consequently, it is expected that the importance of the influencing geotechnical factors will be selected and used for predicting the behavior of Earth retaining walls and actual design, which will help to efficient wall design.
... The soil profiles and index properties are shown in Fig. 2. Two-dimensional finite element analysis is currently a popular and reliable method for modeling excavation problems. The results these analyses have been verified through many case studies [21][22][23][24][25][26]. The first 4 layers were simulated using the soft soil model (SSM) [27], while the last 2 layers were modeled using the Mohr-Coulomb (MC) model. ...
The main objective of this article is to investigate the effectiveness of soil improvement methods, such as jet grouting and cement deep mixing, for a deep excavation in under-consolidated soil. A well-documented case history, located in Zhuhai, China, was used for analysis. The analyses were conducted using two-dimensional plane-strain finite element analysis. The studies included an examination of the effect of wall length on lateral wall deformation, the effect between the degree of consolidation and lateral wall deformation, and the influence of soil improvement on lateral deformation and settlement. The deformations induced by under consolidating states are greater than those caused by normally consolidated states. A similar trend was found with or without soil improvement. The greater the degree of consolidation is, the smaller the deflection of the wall. In this case, the retaining wall's length is well designed and stable, but the analysis results showed that the wall length can be shorter than the constructed length. Massive jet grouting was used behind the left wall to successfully reduce wall deflection and ground surface settlement. Finally, deep cement mixing has only a small effect on reducing wall deflection and ground surface settlement.
... Thus, other methods to determine the safety factor could be adopted, such as the strength reduction method. The strength reduction method is generally performed by reducing the soil strength until the failure occurs (i.e., divergence condition) [2,[12][13][14][15][16][17]. In this analysis, the corresponding strength reduction is defined as the factor of safety against basal heave (FSfem = SRmax). ...
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.
... Finite-element analysis is often used as a numerical approach to conducting the excavation stability with and without a supporting system (Do et al. 2016;Do and Ou 2020;Finno et al. 2007; Keawsawasvong and Ukritchon 2019;Li et al. 2020;Ukritchon et al. 2003Ukritchon et al. , 2020. In particular, the finite-element method (FEM) with the strength reduction method is generally adopted to assess the basal heave stability in deep excavations (Abdi and Ou 2022;Faheem et al. 2004;Goh et al. 2019). ...
... Hence, the elastic-perfectly plastic Mohr-Coulomb soil model with the total stress undrained analysis (ϕ ¼ 0) was used to perform the undrained behavior of the clay and soil strength characteristics near failure. Besides, many researchers have successfully used this soil model to analyze excavation stability (Abdi and Ou 2022;Do et al. 2013Do et al. , 2016Do and Ou 2020;Goh et al. 2019). A normally consolidated clay was considered in this study, where the undrained shear strength (s u ) and undrained elastic modulus (E u ) values are assumed to be increased linearly with the depth, following the typical soft clay in Taipei (Lim et al. 2010;Ou 2006). ...
The ground-improvement technique is commonly used to restrain the wall displacement induced by excavation and resist the basal
heave for deep excavations in soft clays. In this paper, a three-dimensional finite-element stability analysis was conducted to evaluate the
effect of different ground-improvement properties and patterns on enhancing the factor of safety against basal heave in deep excavations. The
results showed that a large downward movement of soil behind the wall could induce a large upward movement below the excavation, which
is mainly resisted by the weight of the interior soil mass and the frictional resistance acting on the contact surface area between the wall and
the soil inside the excavation. When the ground improvement was not contacted with the wall, the failure initially occurred on the wall
interface, causing the soil inside the excavation to move upward along with the ground improvement, which resulted in an insignificant
increase in the factor of safety. Hence, the ground improvement should be contacted to the wall to establish a higher basal heave resistance,
where the increase of the safety factor was governed by the amount of the ground improvement that contacted the wall. Furthermore,
a simplified method was proposed to calculate the factor of safety with and without ground improvement, which was validated by the results
from the finite-element method.
... However, to obtain the closed-form F s , a series of simplified assumptions such as no stress-strain relation, pre-specified failure surface shape, and relation of internal and external forces acting on slices between adjacent slices are used in LEM [36], which do not always produce realistic stress distributions. To overcome the limitations of LEM, the implementation of SRM through finite element analysis inherently incorporates the stress-strain relationship and eliminates the arbitrary assumptions on the shapes and positions of slip surface and inter-slices and associated forces [18]. Consequently, a more reliable stability analysis can be achieved through SRM. ...
After placement into underground mined-out voids (called stopes), a passive interface loading develops between cemented paste backfill (CPB, an artificially cemented soil) and surrounding rock mass, which results in the spatiotemporal changes in the geomechanical behavior and properties of CPB, and thus affects its field stability. In this study, meter-scale curing columns with rough inner surfaces were developed to investigate the effect of passive interface loading on the geome-chanical behavior and properties of CPB, and field-scale stability of CPB mass was conducted through a series of 3D numerical analyses. The obtained results discovered that the passive interface loading not only weakens the compressive and shear behaviors of CPB, but also leads to highly spatiotemporal changes in elastic modulus, unconfined compressive strength, cohesion, and angle of internal friction. Meanwhile, through the integration of the measured degradation in mechanical properties, the field-scale analysis reveals that consideration of stress arching and homogenous mechanical properties substantially overestimate the stability of CPB mass, especially in the narrow stopes with a relatively small height. The simultaneous consideration of stress arching and associated heterogeneous mechanical properties are required for the reliable and accurate assessment of the field stability of CPB mass and its safe engineering design.
... Many researchers Chen et al. 2015;Choosrithong and Schweiger 2020;Chowdhury et al. 2013;Do et al. 2013Do et al. , 2016Do and Ou 2020;Goh 1990;Goh et al. 2008Goh et al. , 2019Karlsrud and Andresen 2005;Ukritchon et al. 2003;Whittle et al. 2015) have studied the failure mechanism of braced excavations in recent years. Nevertheless, most of the previous studies focused on plane strain analysis to conduct the stability analysis in which elastic structural material was adopted and did not consider the actual geometry model in the FEM analysis. ...
This study aims to investigate the failure mechanism of structural support systems in braced excavations. The three-dimensional finite-element method (FEM) was used to model the complexity of real geometry by considering the elastoplastic structural support system. Because failure could occur at the connection between walls and struts, a new model of a strut–wall connection was considered in the analysis to represent the actual condition of excavation failure. Three failure case histories were studied to investigate the performance of strut–wall connections by calibrating their strength parameters until the factor of safety was close to unity. It was found that a good result of stability analysis could be obtained in the FEM by considering this model. The yielding of the strut–wall connection model initiated the collapse of the bracing system in all case histories, followed by the yield of struts and failure of soils. A robust failure mechanism was also obtained, in which the yielding of the structural support system at failure initially developed at the middle section toward the corner of excavation geometry.
... To protect the surrounding environment during excavation, an effective and efficient retaining technique is necessary to limit wall deflection and ground settlement [8,16,18,29]. Various retaining structures have been developed to control ground displacement and to protect surrounding facilities [4,15,17,19,22,26,27,31,36,39,42]. ...
A new excavation retaining structure, referred to as an outward inclined-vertical framed retaining wall (OIVFRW), has been developed and adopted in practice. This retaining structure can limit excavation-induced ground movement and protect adjacent infrastructures. A case history shows that it performs well in controlling wall deflection, but its retaining mechanism and the factors influencing its performance are not fully understood. Therefore, this paper aims to investigate the behaviour of an OIVFRW to provide a better understanding of the retaining mechanism of this newly developed retaining structure. A case history of an OIVFRW in soft soil is first introduced, and a finite element model is then established. Parametric studies are carried out to investigate the relationship between influencing factors and the performance of an OIVFRW. Subsequently, the location of the neutral plane, the mobilization of the skin friction and the distribution of the axial force are analysed. Moreover, the retaining mechanism of this structure is discussed on the basis of the parametric investigation, and the contribution of pile length to the retaining mechanism is investigated. The results show that an OIVFRW structure performs well in limiting deformation, and the length of the vertical pile and the inclination angle show significant contributions to limit the structure movement. Moreover, the axial force of the vertical pile, which stems from the relative displacement between the soil and vertical pile, acting on the head of the inclined pile is beneficial to resist the deformation of the OIVFRW.
... Estimating the basal heave stability of braced excavation is quite significant for design. Up to the present, it can be performed by using the limit equilibrium method (LEM) [2,[8][9][10][11][12][13][14][15][16][17][18][19], limit analysis method [9,[20][21][22][23][24], probabilistic method [2,10,[25][26][27][28][29][30][31][32], and finite element method (FEM) with shear strength reduction technique (SSRT) [2,10,15,20,[33][34][35][36][37][38][39][40]. e limit equilibrium method can be divided into two categories [15,19,21,24]: the bearing capacity method [8,9,13,16,17] and the slip circle method (SCM) [11,16,18,19]. ...
... Naturally, with the continuous development of computer and numerical methods, FEM with SSRT has been widely applied to geotechnical engineering and has gradually become the mainstream numerical method and effective means for the analysis of complex engineering problems. In this way, many scholars [2,10,20,33,[35][36][37][38][39] evaluated the basal heave factors of safety for excavations and analyzed the influence of various factors. e current design codes [13,16] consider that excavations with different widths have the same basal heave factors of safety, resulting in huge design waste. ...
... In comparison to conventional methods, the most significant advantage of FEM with SSRT is that the failure surface and factor of safety emerge naturally without the user hypothesizing a particular failure mechanism in advance [15,20,[33][34][35][36]. To explore the basal heave failure mechanism of narrow excavation, this section will perform numerical simulation through the FEM with SSRT. ...
Engineering practices indicate that narrow braced excavation exhibits a clear size effect. However, the slip circle method in the design codes fails to consider the effect of excavation width on basal heave stability, causing waste for narrow excavation. In this paper, numerical simulation for basal heave failure of excavation with different widths was performed by FEM with SSRT (shear strength reduction technique). The results revealed that the failure mechanism of narrow excavation is different from the complete slip circle mode. In addition, the safety factor decreases increasingly slowly as the excavation widens and stabilizes when approaching the critical width. Subsequently, the corresponding computation model was presented, and an improved SCM (slip circle method) was further developed. Finally, the engineering case illustrated that it can effectively optimize the design, which exhibits clear superiority.
... Mode3: Due to multiple struts in the upper part of the wall, the depth reaching the static balance can be deeper. However, when the excavation reaches a certain depth, the weight of the soil column outside the pit exceeds the foundation bearing capacity below the bottom of the foundation pit and the plastic equilibrium was broken (Do and Ou, 2020). In addition, the phenomena of top subsidence, bottom uplifting as well as sidewall soil sliding will occur. ...
The instability or destruction of diaphragm walls in underground engineering will cause significant economic losses and casualties. The distributed and high-precision monitoring of diaphragm wall deformation can provide reliable and detail data for disaster early-warning as well as economical design. However, recording continuous deformation of the diaphragm wall using traditional monitoring technologies remain challenging. Moreover, the basement movement of diaphragm wall is rarely considered in previous studies. In order to overcome the shortcomings of the current displacement monitoring methods and deal with the basement boundary issues, a new base boundary reconstruction (BR) was proposed and the ultra-weak Fiber Bragg grating (UWFBG) technology was adopted to monitor the displacement of the diaphragm wall. For validation, a laboratory test based on ultra-weak FBG was carried out and the feasibility of the BR method was demonstrated. Subsequently, the ultra-weak FBG and the BR method were applied to Shanghai metro line 18. The results showed that the monitoring technology and analysis method proposed in this paper can obtain detailed deformation information of the diaphragm wall in real-time, which not only provides an advanced monitoring method for the deep deformation of diaphragm wall, but also solves the deformation calculation issue with the base boundary condition changes involved.
... Some of these programs are capable of transmitting information about the minimum necessary system parameters to the user, for example, the Wall-3 program gives the value of the retaining structure fixed end length, which is necessary to ensure the stability of the system, but the user is given the freedom to change it. The supporting structures themselves are selected from design experience or simply by selection, and then, based on the calculation results, the user evaluates the received forces in the elements [3][4][5]. Typically, for struts made of steel pipes, the axial force N, kN is of greatest importance, since such elements are designed for compression work. Based on the calculated design forces, the stresses arising in the sections of the elements are determined and the strength and stability calculation is also performed. ...
Currently, there is a rapid compaction of urban areas, which inevitably leads to the need for more active and integrated use of the underground space. In conditions of dense urban development, for the construction of underground structures or underground parts of buildings, it is necessary to design and realize deep excavations with vertical walls under the protective of the retaining structures, including supporting systems. The most common support is a system of metal elements -distribution beams and pipes (struts). The article deals with the calculation of the real excavations, taking into account the elastic and elastoplastic behavior of the support elements, the influence of this factor on the resulting internal forces and the stability of entire retaining system. Questions about the correctness of calculations by elastic models for structural elements used in geotechnics, are raised.
