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1.
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2.
This article presents the observed and simulated lateral movements and strut forces induced in deep cement mixing walls under deep excavation using top-down construction techniques in soft Bangkok clay. The walls are supported laterally by permanent concrete slabs and temporary struts. A three-dimensional numerical model is first calibrated with observed data from a case study. Then, a parametric study is performed to compare this construction method with the bottom-up method and investigate the influence of the DCM wall thickness on lateral movements and strut forces of the wall. 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.
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
5.
掌握高速铁路陡坡地基条件下路肩桩板墙力学特性是路堤侧向变形控制的关键。以贵广高速铁路某陡坡地基路肩桩板墙为试验工点,对墙背土压力、桩身内力与变形进行了900余天现场长期观测,讨论了墙后路堤分层填筑引起的墙土侧向变形形态差异及机械碾压残余应力对土压力分布的影响。结果表明：适应高速铁路小变形要求的强约束、深锚固路肩桩板墙能有效控制陡坡地基路堤侧向变形,桩体仅呈0.94‰的近似刚性转动,填筑完成后变形约占30%,且1.0～1.5 a趋于稳定;经碾压密实的墙后粗粒土填料,即使在小变形下依然能达到主动土压力状态;分层填筑引起墙后填土侧向变形呈现的“上小下大”分布形态与墙体位移相反,是墙背土压力呈现出中部大、两端小抛物线分布模式的重要因素;基于适筋梁受力状态及平截面假定,分别结合实测钢筋应力与混凝土应变换算得到的桩身弯矩具有良好的一致性,与极限地基反力法的理论计算吻合。 相似文献
6.
One important consideration in the design of a braced excavation system is to ensure that the structural bracing system is designed both safely and economically. The forces acting on the struts are often determined using empirical methods such as the Apparent Pressure Diagram (APD) method developed by Peck (1969). Most of these empirical methods that were developed from either numerical analysis or field studies have been for excavations with flexible wall types such as sheetpile walls. There have been only limited studies on the excavation performance for stiffer wall systems such as diaphragm walls and bored piles. In this paper, both 2D and 3D finite element analyses were carried out to study the forces acting on the struts for braced excavations in clays, with focus on the performance for the stiffer wall systems. Subsequently, based on this numerical study as well as field measurements from a number of reported case histories, empirical charts have been proposed for determining strut loads for excavations in stiff wall systems. 相似文献
7.
One of the most important factors in optimized design of non-yielding retaining walls like basement walls and bridge abutments is to determine the exact variation of earth pressure acting on such walls. In this paper, the distribution of at rest earth pressure behind a laboratory model of a fixed and rigid retaining wall with a cohesionless dry backfill is measured under the effect of static and repeated loads. The same conditions of the experimental model are then simulated numerically with a two-dimensional finite-difference analysis computer code. For the purpose of model verification, the results of numerical model are compared to the results of the experimental model, which is similar in geometrical and geomechanical properties. Cyclic surcharges with different amplitudes and frequencies are applied in different distances from the wall, and the earth pressure distribution, the resultant force, and its point of application are investigated. The effect of soil and loading parameters on the at rest earth pressure is also evaluated, and a parametric study has been carried out. The results of model show a significant increase in the earth pressure due to cyclic loading compared to static loading, especially in the initial cycles of loading. It indicates that the effect of cycling nature of loading should be essentially taken into account in the design of retaining walls. 相似文献
8.
狭窄基坑平动模式刚性挡墙被动土压力分析 总被引：2，自引：0，他引：2
对于地铁车站、地下管道沟槽等狭窄基坑,其被动区土体宽度有限,不满足半无限体的假定,采用经典的库仑、朗肯土压力理论计算挡墙被动土压力是不合适的。首先建立了无黏性土中狭窄基坑刚性挡墙的有限元分析模型,研究了挡墙相对平移时不同宽度土体的被动滑裂面的分布规律;借鉴库仑平面土楔假定,建立了狭窄基坑刚性平动挡墙被动土压力的理论计算模型,推导了被动极限状态下滑裂面倾角及被动土压力系数的解析公式;再采用水平薄层单元法,得到了被动土压力分布、土压力合力作用点高度的理论公式。结合算例,深入研究了这种工程背景下挡墙被动滑裂面倾角的影响因素,以及被动土压力合力、土压力分布及合力作用点位置与经典库仑土压力理论的差别,与数值计算结果的对比验证了该理论方法的合理性。研究发现,当被动区土体宽度小于满足半无限体的临界值、且墙土摩擦角大于0时,被动滑裂面倾角大于传统库仑被动滑裂面倾角,被动土压力大于经典库仑解,合力作用点高度则小于库仑解,且基坑越窄,墙土摩擦角越大,其差别越大。 相似文献
9.
In India, soil nail walls are being extensively used for supporting vertical excavations below ground level to accommodate construction of one-or two-storied basements. Generally, the depth of excavations for basement construction ranges from 10 m to 15 m. For such large depth of excavation, variability of in-situ soil properties has significant influence on the stability of the soil nail walls. In the present study, using reliability analysis, an attempt is made to study the influence of variability of in-situ soil properties on the stability of soil nail walls. For better understanding, a case of 10 m high soil nail wall constructed to support a vertical cut is considered for the study and its stability is evaluated for various failure modes. Additionally, the influence of correlation among soil parameters on soil nail wall stability is assessed. In-situ soil friction angle and correlation between in-situ soil cohesion and angle of friction are found to influence soil nail wall stability significantly. In general, reliability analysis provided a better insight into the assessment of stability of soil nail wall. 相似文献
10.
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
11.
Kourosh Ghaffari Irdmoosa 《Geomechanics and Geoengineering》2019,14(2):71-84
The current study was undertaken to study the effect of soil arching on active earth pressure distribution in retaining walls with c–φ backfill. An analytical approach is presented to develop a general solution considering the effects of surcharge, backfill soil cohesion and slip surface inclination. The magnitude and height of the application of lateral active force is also derived. The results from the proposed equation corresponded to the measured results from a full-scale test, shows non-linear pressure distribution with zero pressure at wall base and less pressure in deeper heights compared to Coulomb’s method. According to the results of parametric analysis, the proposed equation predicts the active earth thrust nearly equal to that of the Coulomb’s equation, however, the surcharge-induced soil pressure is obtained approximately 50% greater than the conventional equation. Moreover, the height of application of active thrust is located at the height of 0.4H from the wall base. These indicate that using the Coulomb’s active equation for retaining walls design, is not in the safe side. 相似文献
12.
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
13.
Deep excavations particularly in deep deposits of soft clay can cause excessive ground movements and result in damage to adjacent buildings. Extensive plane strain finite element analyses considering the small strain effect have been carried out to examine the wall deflections for excavations in soft clay deposits supported by retaining walls and bracing. The excavation geometry, soil strength and stiffness properties, and the wall stiffness were varied to study the wall deflection behavior. Based on these results, a simple Polynomial Regression (PR) model was developed for estimating the maximum wall deflection. Wall deflections computed by this method compare favorably with a number of field and published records. 相似文献
14.
地震液化条件下重力式码头的变形破坏机理 总被引：3，自引：0，他引：3
现场调查发现在神户地震期间重力式码头破坏时都发生了相当大的侧向位移，因此，阐明挡土墙有变形机理对于改善抗震设计具有十分重要的意义。为此，根据相似原理设计了重力式码头的地基模型，进行了一系列的振动台试验。试验结果表明：基底土的强度降低和局部液化是挡土墙变形破坏的主导因素。墙后动土压力的增加为挡土墙的运动提供了条件。在液化条件下重力式码头地基的运动以侧向位移为主。重力作用是地基侧向运动的主要影响因素。减少作用于挡土墙上的动土压力和充分填实基底下的砂土是增加重力式码头抗震稳定性的重要措施。 相似文献
15.
The influence of vertical spatial variability of sands on the excavation-induced lateral wall deflection and bending moment of excavations supported by cantilever retaining walls is investigated in this paper. Herein, the random finite element method (RFEM) is adopted to explicitly study the effect of one-dimensional spatial variability of internal friction angle of sands on the predicted wall and ground responses. The RFEM analysis consists of three components: (1) finite element method for analyzing lateral wall deflection and bending moment, (2) random field theory implemented with Monte Carlo simulation (MCS), and (3) statistical interpretation of MCS results through confidence intervals. This study reveals the importance of random field modeling in coping with the spatial variability of sands in the problem of supported excavations: (1) neglecting spatial variability of soil property will cause an overestimation of the variation in the predicted wall deflection and bending moment; (2) the estimated probability of failure based on a well-established serviceability limit state may be overestimated or underestimated depending on the chosen limiting lateral wall deflection. This study further investigates the effect of the number of MCS on the confidence intervals of the predicted statistics of the maximum lateral wall deflection and the maximum bending moment. The results also demonstrate that the confidence interval analysis of the predicted statistics of the maximum lateral wall deflection and the maximum bending moment provides a rational tool for interpreting the statistical data from RFEM. 相似文献
16.
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
17.
While the evolution with time of the factor of safety against slope failure is well understood for excavations performed under fully saturated conditions, this evolution has not been extensively studied for excavations carried out in unsaturated soils. The objective of this paper is to investigate the relationship between the factor of safety and time for an excavation performed in an unsaturated silty soil, employing the finite element method. A hypothetical boundary value problem is considered and two types of analyses performed; in the first one, unsaturated soil behaviour is modelled through appropriate constitutive and soil–water retention curve models, whereas in the second one full saturation is assumed. The effect that the saturated soil permeability, its variation with suction, the increase of apparent cohesion due to suction, the depth of the groundwater table and the hydraulic hysteresis have on the results of the unsaturated analysis is examined in a parametric study. The analyses results demonstrate that for unsaturated soils the factor of safety may increase with time, in contrast to what is commonly accepted to be the case in fully saturated soils. Furthermore, it is not possible to know in advance which one of the two types of analysis performed (i.e. the saturated or the unsaturated) will produce conservative results. It is, therefore, advisable to perform unsaturated analysis in geotechnical practice, when dealing with excavations in such soils. 相似文献
18.
钢板桩挡墙主动土压力分布的形状效应 总被引：1，自引：0，他引：1
采用有限元数值试验,研究帽型钢板桩的截面形状对墙后主动土压力分布规律的影响。首先,对室内缩尺模型试验进行数值模拟,对比实测数据验证数值模型的有效性;然后,建立钢板桩挡墙数值模型,模拟该挡墙在不同位移模式下土压力变化和分布的规律,与平板挡墙计算结果进行对比,分析钢板桩截面形状对土压力分布的影响,进一步探讨形状效应的可能影响因素及机制。分析结果表明,钢板桩的截面形状影响墙后主动土压力的分布形式,影响程度与位移模式有关;墙体平动和绕墙底转动情况下,钢板桩挡墙凸出部分的主动土压力值大于凹处,但墙体绕墙顶转动情况下差异不明显;主动土压力的形状效应由土拱效应引起,截面高宽比对其影响显著,墙土摩擦角影响有限。 相似文献
19.
A 3D numerical model for mechanised excavations is presented, which is capable of simulating the overall process of excavation and construction of a tunnel when a TBM EPB (Tunnel Boring Machine–Earth Pressure Balance) is used.The main construction aspects of a mechanised excavation are modelled. Their influence on calculated ground displacements are investigated by means of a series of parametric analyses.With the aim of testing the performance of the proposed 3D numerical model, a series of 25 Class C predictions has been carried out. Case Histories related to the construction of the 1995–2003 Madrid Metro Extension Project were considered for this purpose.As a general rule, the results obtained with the Modified Cam–Clay model closely fit in situ measurements. When the Linear-Elastic or the Mohr–Coulomb models are used, it is not as easy to summarise the results obtained, as higher fluctuations are observed around in situ measured data. A good agreement is also shown when the distribution of horizontal displacements along depth is considered.For some sections, the mechanised excavation model is not capable of reproducing the high values of the surface settlements measured in situ. A closer look at the results shows that mixed face conditions are found for these cases, with the TBM excavating through layered soil formations having sharply different mechanical behaviour. 相似文献
20.
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