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1.
Previous studies have shown that use of cross walls in deep excavations can reduce the wall deflection to a very small amount. However, design of cross walls is costly because the deflection behavior of the diaphragm wall with cross walls is in nature three dimensional. The objective of this study was to establish a simplified approach used as a first approximation to design cross walls such that the lateral wall deflection can satisfy a design criterion. A series of parametric studies using a three-dimensional numerical method was performed to obtain the influence factors on wall deflections, including excavation geometry, wall system stiffness, axial stiffness of strut, axial stiffness of the cross wall, normalized undrained shear strength of clay and the cross wall depth. Then, a simplified formula for predicting the wall deflection for excavations without and with cross walls was established using multivariate regression analysis, respectively. The formulas were validated through 36 excavation cases without cross walls and 12 cases with cross walls. The simplified formulas can be used to develop a spreadsheet that estimates the cross wall sizes and intervals based on the entered excavation geometry, material properties of retaining-strut system, in situ undrained shear strength and tolerable wall deflection. The estimated cross wall sizes and intervals should be verified by an appropriate full numerical analysis. 相似文献
2.
《地学前缘(英文版)》2022,13(2):101313
Deep excavation during the construction of underground systems can cause movement on the ground, especially in soft clay layers. At high levels, excessive ground movements can lead to severe damage to adjacent structures. In this study, finite element analyses (FEM) and the hardening small strain (HSS) model were performed to investigate the deflection of the diaphragm wall in the soft clay layer induced by braced excavations. Different geometric and mechanical properties of the wall were investigated to study the deflection behavior of the wall in soft clays. Accordingly, 1090 hypothetical cases were surveyed and simulated based on the HSS model and FEM to evaluate the wall deflection behavior. The results were then used to develop an intelligent model for predicting wall deflection using the functional linked neural network (FLNN) with different functional expansions and activation functions. Although the FLNN is a novel approach to predict wall deflection; however, in order to improve the accuracy of the FLNN model in predicting wall deflection, three swarm-based optimization algorithms, such as artificial bee colony (ABC), Harris’s hawk’s optimization (HHO), and hunger games search (HGS), were hybridized to the FLNN model to generate three novel intelligent models, namely ABC-FLNN, HHO-FLNN, HGS-FLNN. The results of the hybrid models were then compared with the basic FLNN and MLP models. They revealed that FLNN is a good solution for predicting wall deflection, and the application of different functional expansions and activation functions has a significant effect on the outcome predictions of the wall deflection. It is remarkably interesting that the performance of the FLNN model was better than the MLP model with a mean absolute error (MAE) of 19.971, root-mean-squared error (RMSE) of 24.574, and determination coefficient (R2) of 0.878. Meanwhile, the performance of the MLP model only obtained an MAE of 20.321, RMSE of 27.091, and R2 of 0.851. Furthermore, the results also indicated that the proposed hybrid models, i.e., ABC-FLNN, HHO-FLNN, HGS-FLNN, yielded more superior performances than those of the FLNN and MLP models in terms of the prediction of deflection behavior of diaphragm walls with an MAE in the range of 11.877 to 12.239, RMSE in the range of 15.821 to 16.045, and R2 in the range of 0.949 to 0.951. They can be used as an alternative tool to simulate diaphragm wall deflections under different conditions with a high degree of accuracy. 相似文献
3.
Several case studies have revealed that the installation of cross walls in excavations can effectively reduce the amount of wall deflection and ground settlement. However, the behaviour of the diaphragm wall due to the installation of the cross walls is still unclear. This study performed a series of 3D numerical studies of wall deflections for deep excavations with cross walls and studied the effects on the wall deflection of several parameters, including the number of cross walls, the distance to the cross wall, the cross wall interval, the cross wall height and the cross wall embedment. The results presented in this study can be used as a first approximation for cases in which cross walls are designed to reduce the wall deflection induced by deep excavation. 相似文献
4.
Installation of buttress walls against diaphragm walls has been used as an alternative measure for the protection of adjacent buildings during excavation, but their mechanism in reducing movements has not yet been fully understood. This study performs three-dimensional finite element analyses of two excavation case histories, one in clay with T-shape buttress walls and another in dominant sand with rectangular buttress walls, to establish analysis model. Then, a series of parametric study were performed by varying soil types, types and length of buttress walls based on the above-mentioned excavations. Results show that the mechanism of buttress walls in reducing wall deflections mainly came from the frictional resistance between the side surface of buttress wall and adjacent soil rather than from the combined bending stiffness from diaphragm and buttress walls. The buttress wall with a length <2.0 m had a poor effect in reducing the wall deflection because the soil adjacent to the buttress wall had almost the same amount of movement as the buttress wall, causing the frictional resistance little mobilized. Since the frictional resistance of buttress walls in a deep excavation has fully been mobilized prior to the final excavation depth, the efficiency of buttress walls in reducing the wall deflection in a deep excavation was much less than that in a shallow excavation. Rectangular shape of buttress walls was of a better effect than T-shape in the shallow excavation because frictional resistance between buttress walls and adjacent soil played a major role in reducing the wall deflection rather than bearing resistance of the flange. When the excavation went deeper, the difference in reducing the wall deflection between the R-shape and T-shape became small. 相似文献
5.
A series of two-dimensional (2D) and three-dimensional (3D) finite element analyses using the Hardening Soil (HS) model were carried out to investigate the influences of soil properties, wall stiffness, excavation length, excavation depth, clay thickness at the base of the excavation and wall embedment depth, on the maximum wall deflection induced by braced-excavation. The results show that the 3D maximum wall deflections are generally much smaller than those for 2D. Comparisons were also made with other commonly used semi-empirical charts. Based on the finite element results in this study, a simple wall deflection equation was developed for estimating the maximum wall deflection that takes the 3D effects into consideration through different ratios of excavation length over excavation width. 相似文献
6.
简述了某软土基坑复合土钉支护结构失稳过程,分析失稳原因,介绍工程治理措施.文中还对软土基坑与残积土基坑破坏机理进行探讨,提出了软土基坑按地层可分为双层软土基坑、三层软土基坑.三层软土基坑比双层软土基坑采用复合土钉支护结构能较优控制变形和提高稳定性.可供工程技术人员参考. 相似文献
7.
软土地区采用灌注桩围护的深基坑变形性状研究 总被引：14，自引：1，他引：13
根据上海软土地区80个钻孔灌注桩围护的深基坑工程案例有关数据,系统地分析了基坑开挖引致的灌注桩变形性状。所有基坑的灌注桩最大侧向位移介于0.1 %～1.0 %倍的开挖深度之间,平均值为开挖深度的0.44 %。钢筋混凝土支撑和钢支撑在控制墙体的变形上没有明显差别,最大侧向位移一般位于开挖面上下5 m的范围内。无量纲化最大侧向位移随着支撑系统刚度的增大而减小,随着墙底以上软土层厚度的增加而增大,但与灌注桩插入比及坑底抗隆起稳定系数之间并无明显的关系。墙顶侧向位移随着首道支撑位置深度的增加而呈现出指数增长的趋势,而灌注桩最大侧向位移与首道支撑的深度位置无明显关系。 相似文献
8.
Previous plane strain analysis of a case history has shown that cross walls in an excavation can effectively reduce movements induced by deep excavation. This study performed three-dimensional numerical analyses for 4 deep excavation cases with different installations of cross walls, including different excavation depths, cross wall intervals and cross wall depths. Both the observed and computed wall deflections for the 4 cases were compared with those of the same excavations that were assumed with no cross walls installed to demonstrate the effectiveness of cross walls in reducing lateral wall deflections. The results show that the cross wall also had a corner effect similar to that of the diaphragm wall. The deflection of the diaphragm wall was smallest at the location of the cross wall installed and then increased with the increasing distance from the cross wall, up to the midpoint between two cross walls. Many factors such as in situ soil properties, diaphragm wall properties, construction procedure, cross wall depth and so on may affect the amount of reduction in lateral wall deflections due to the installation of cross walls. Under the same condition, the amount of reduction was highly dependent on the depth of cross walls, distance to the cross walls and the cross wall interval. 相似文献
9.
Numerous studies have been devoted to the performance of excavations and adjacent facilities. In contrast, few studies have focused on retaining wall deflections induced by pre-excavation dewatering. However, considerable inward cantilever deflections were observed for a diaphragm wall in a pre-excavation dewatering test based on a long and narrow metro excavation, and the maximum deflection reached 10 mm (37.6% of the allowable wall deflection for the project). Based on the test results, a three-dimensional soil–fluid coupled finite element model was established and used to study the mechanism of the dewatering-induced diaphragm wall deflections. Numerical results indicated that the diaphragm wall deflection results from three factors: (1) the seepage force around the dewatering well and the soil–wall interaction caused the inward horizontal displacement of the soil inside the excavation; (2) the reduced total earth pressure on the excavated side of the diaphragm wall above approximately 1/2 of the maximum dewatering depth disequilibrated the original earth pressure on both sides of the diaphragm wall; and (3) the different negative friction on the excavated and retained sides of the diaphragm wall led to the rotation of the diaphragm wall into the excavation. 相似文献
10.
This paper presents an efficient Bayesian back-analysis procedure for braced excavations using wall deflection data at multiple points. Response surfaces obtained from finite element analyses are adopted to efficiently evaluate the wall responses. Deflection data for 49 wall sections from 11 case histories are collected to characterize the model error of the finite element method for evaluating the deflections at various points. A braced excavation project in Hang Zhou, China is chosen to illustrate the effectiveness of the proposed procedure. The results indicate that the soil parameters could be updated more significantly for the updating that uses the deflection data at multiple points than that only uses the maximum deflection data. The predicted deflections from the updated parameters agree fairly well with the field observations. The main significance of the proposed procedure is that it improves the updating efficiency of the soil parameters without adding monitoring effort compared with the traditional method that uses the maximum deflection data. 相似文献
11.
采用有限单元法研究了影响软土地区地下连续墙最大侧向变形的主要参数。针对基坑开挖深度H、基坑开挖宽度B、单位宽度地下连续墙系统刚度S、支撑结构的轴向刚度 及黏土归一化的不排水抗剪强度 为不排水抗剪强度, 为有效垂直应力）5个参数进行分析研究,通过回归分析研究结果,给出地下连续墙最大侧向变形的简易计算方法。利用简易计算方法,计算实际工程中基坑案例的地下连续墙最大侧向变形,并与现场监测结果进行对比,验证了计算方法的准确性,可为以后预估地下连续墙最大侧向变形及检查设计提供参考。 相似文献
12.
The influence of a diaphragm wall construction on the stress field in a soft clayey soil is investigated by the use of a three‐dimensional FE‐model of seven adjacent wall panels. The installation procedure comprises the excavation and the subsequent pouring of each panel taking into account the increasing stiffness of the placed fresh concrete. The soft clay deposit is described by a visco‐hypoplastic constitutive model considering the rheological properties and the small‐strain stiffness of the soil. The construction process considerably affects the effective earth and pore water pressures adjacent to the wall. Due to concreting, a high excess pore water pressure arises, which dissipates during the following construction steps. The earth pressure finally shows an oscillating, distinct three‐dimensional distribution along the retaining wall which depends on the installation sequence of the panels and the difference between the fresh concrete pressure and the total horizontal earth pressure at rest. In comparison to FE‐calculations adopting the earth pressure at rest as initial condition, greater wall deflections and surface ground settlements during the subsequent pit excavation can be expected, as the average stress level especially in the upper half of the wall is increased by the construction procedure of the retaining structure. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
13.
This paper adopts the NGI-ADP soil model to carry out finite element analysis,based on which the effects of soft clay anisotropy on the diaphragm wall deflections in the braced excavation were evaluated.More than one thousand finite element cases were numerically analyzed,followed by extensive parametric studies.Surrogate models were developed via ensemble learning methods(ELMs),including the e Xtreme Gradient Boosting(XGBoost),and Random Forest Regression(RFR)to predict the maximum lateral wall deformation(δhmax).Then the results of ELMs were compared with conventional soft computing methods such as Decision Tree Regression(DTR),Multilayer Perceptron Regression(MLPR),and Multivariate Adaptive Regression Splines(MARS).This study presents a cutting-edge application of ensemble learning in geotechnical engineering and a reasonable methodology that allows engineers to determine the wall deflection in a fast,alternative way. 相似文献
14.
Jamsawang Pitthaya Voottipruex Panich Tanseng Pornpot Jongpradist Pornkasem Bergado Dennes T. 《Acta Geotechnica》2019,14(1):225-246
This paper presents the observed and simulated effectiveness of deep cement mixing walls created using top-down (DCM-TD) construction techniques for a deep excavation in soft Bangkok clay. The wall system consisted of four rows of 0.7-m-diameter DCM columns, and the bracing system consisted of two 0.25-m-thick basement slabs and seven temporary struts. The effectiveness of the wall system compared to that of other wall systems was evaluated using the measured results of previous case studies. A 3D numerical analysis was performed to calculate forces in the basement slabs and bending moments in the DCM wall. Finally, series of parametric analyses of both DCM-TD and deep cement mixing walls created using bottom-up (DCM-BU) construction techniques were carried out, and their results were compared to highlight the effectiveness of DCM-TD and its applicability to excavations at greater depths. The field and numerical results show that DCM-TD is more effective than DCM-BU in terms of the limitations of lateral wall movement, the bending moment in a DCM wall and the thickness of a DCM wall for various depths because of a larger system stiffness. Therefore, DCM-TD is very effective and suitable for use in potential future deep excavations in urban areas.
相似文献15.
敏感环境下基坑数值分析中土体本构模型的选择 总被引：15，自引：1，他引：14
数值分析已成为敏感环境下基坑工程分析的最重要手段,其关键是选择合适的土体本构模型和计算参数。在分析了岩土数值分析中常用土体本构模型特点的基础上,通过算例较系统地对比了各类模型在基坑开挖数值分析中的适用性。敏感环境下的基坑工程需重点关注墙后土体的变形,从满足工程需要和方便实用的角度出发,建议采用能考虑黏土的塑性和应变硬化特征、能区分加荷和卸荷且刚度依赖于应力水平的硬化类弹塑性模型,如MCC模型和HS模型进行分析。具体工程实例的分析,表明了硬化类弹塑性模型在敏感环境下基坑开挖数值分析中的适用性。 相似文献
16.
Finite-element modeling of a complex deep excavation in Shanghai 总被引：2，自引：0，他引：2
The excavation of the north square underground shopping center of Shanghai South Railway Station is a complex deep excavation
using the top-down construction method. The excavation has a considerable size and is close to the operating Metro Lines.
In order to predict the performance of the excavation more accurately, 3D finite-element analyses are conducted to simulate
the construction of this complex excavation. The effects of the anisotropic soil stiffness, the adjacent excavation, and zone
excavation on the wall deformation are investigated. It is shown that the numerical simulation with anisotropic soil stiffness
yields a more reasonable prediction of the wall deflection than the case with isotropic soil stiffness. The deformation of
the shared diaphragm wall between two excavations is influenced by the construction sequence of the two excavations. The zoned
excavation can greatly reduce the diaphragm wall deformation. However, only the zoned excavation at the first excavation stage
affects the deformation of the walls significantly. When the depth of the excavation increases, the zoned excavation has minor
effect on the deformation of diaphragm walls. 相似文献
17.
预测和控制深基坑变形的抗隆起稳定系数法 总被引：1，自引：0，他引：1
本文讨论了在软土基坑工程设计施工中所涉及到的抗隆起稳定系数的合理计算方法；通过对大量上海深基坑工程的计算分析并结合现场实测数据论证了利用抗隆起稳定系数进行基坑变形预测和控制的合理性，并提出了适用稳定系数法控制基坑变形的设计计算预测公式：δh/H～Ks关系式。 相似文献
18.
A series of three-dimensional finite element analyses of deep excavations with the integrated system between buttress walls and diaphragm walls was conducted to investigate the effect of the buttress wall intervals, treatments, locations, height, and thickness on limiting deformations induced by deep excavation. The integrated retaining system was formed by maintaining buttress walls when soil was excavated. The wall deflection control mechanism of the integrated retaining system mainly came from the combined stiffness between the buttress wall and the diaphragm wall. In addition, the ground settlement control mechanism came from the combined stiffness between the buttress wall and the diaphragm wall, and the frictional resistance between the buttress wall and the surrounding soil. For achieving 50% reduction in the wall deflection and the ground surface settlement, the length and intervals of buttress walls that were applied to the integrated retaining system were at least 4 and 8 m, respectively. When the deflection at the diaphragm wall head was well restrained, for example, by the floor slab, the position of the buttress wall head could be located at a depth the diaphragm wall starts to bulge out. In such a case, the performance between the full height and limited height of buttress walls was quite close. Furthermore, a new well-documented excavation project was analyzed to verify the performance of the integrated retaining system. Results showed that the integrated retaining system worked excellently if the joints between buttress walls and diaphragm walls were constructed properly. 相似文献
19.
介绍了铁皮坑开挖中测斜仪监测和三维有限元反分析的结果。所研究的铁皮坑为深度27 m、总直径26 m的圆形深基坑,最终开挖面以上土层以砂土为主。每个开挖阶段采用腰梁加固的咬合桩作为挡土墙对基坑进行支护。采用硬化土模型作为土体本构模型,反分析结果表明,桩墙位移的趋势与测斜仪测量的结果接近,最大位移为5.1mm。案例中胶结土的有效黏聚力c′取决于胶结砂层的厚度,约为50～200kPa。NSPT为标准贯入试验中分离式取样器打入土体30cm的锤击数。模拟结果表明,砂土模量约为1 400NSPT～2 000NSPT（单位：k Pa）,而对于胶结砂,其模量为7 000NSPT。还研究了腰梁和外部荷载对咬合桩变形和受力的影响。结果表明,外部荷载对桩墙位移具有主导作用;同时,腰梁对减少桩墙位移没有明显作用。 相似文献
20.
Three-dimension finite element analyses of deep excavations with buttress walls were performed to evaluate the effect of buttress wall shapes on limiting movements induced by deep excavation. Results showed that a combination of the rectangular and the capital L-letter shapes (RL-shape) yielded the greatest performance in reducing wall deflections and ground surface settlements. The main deformation-control mechanism mainly came from the horizontal and vertical frictional resistances of buttress walls against adjacent soils which were pushed by wall deflections and the soil heave at the excavation bottom, respectively. Besides, the RL-shape buttress walls were successfully verified through a well-documented case history. 相似文献