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1.
为了揭示斜坡效应和循环弱化效应共同影响下的斜坡桩水平循环特性,进行了不同循环次数、荷载幅值及坡度下的单向水平循环加载试验,并将水平静载试验作为对照,揭示了桩顶位移、桩身弯矩及地基反力等变化规律。综合考虑二阶效应及桩-土相互作用的影响,对单元刚度矩阵进行了改进,提出了有限杆单元解。将理论预测曲线等与实测曲线及幂级数法计算结果进行了对比,验证了有限杆单元解的合理性。结果表明：桩身弯矩及位移均随循环次数非线性增加,最大弯矩位置逐渐从无量纲深度zα=1.25下移到zα=1.75;桩顶无量纲位移y0,α与循环次数n之间的关系符合幂函数y0,α=An0.11;当荷载幅值由20 N增加到40 N时,最大无量纲弯矩由0.010增加到0.029,位置均保持在zα=1.7附近;当坡度由30°增加到60°时,最大无量纲弯矩由0.011(zα=1)增加到0.025(zα=2.5)。 相似文献
2.
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
3.
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
4.
提出了基于子集模拟的边坡风险评估的高效随机有限元法（RFEM）,推导了基于子集模拟的边坡失效概率和失效风险的计算公式,并给出了基于高效RFEM的边坡可靠度分析和风险评估流程图。采用一个边坡算例验证了所提方法的有效性。结果表明,基于子集模拟的高效RFEM可以视为是对基于蒙特卡洛模拟的传统RFEM的改进,显著地提高了失效概率和失效风险的计算效率以及失效样本的产生能力,非常适用于分析小失效概率的可靠度问题,极大地增强了RFEM在边坡可靠度分析和风险评估中的实用性。高效RFEM将边坡的整体失效风险分解为对应不同概率水平的边坡失效风险,并量化了它们对整体风险的相对贡献度。在该方法中,边坡可靠度分析和风险评估与确定性边坡有限元分析互不耦合,极大地简化了它们的计算过程。此外,土体不排水抗剪强度的竖向空间变异性对边坡失效风险具有显著的影响。 相似文献
5.
Enhancement of random finite element method in reliability analysis and risk assessment of soil slopes using Subset Simulation 总被引：4，自引：2，他引：2
Random finite element method (RFEM) provides a rigorous tool to incorporate spatial variability of soil properties into reliability analysis and risk assessment of slope stability. However, it suffers from a common criticism of requiring extensive computational efforts and a lack of efficiency, particularly at small probability levels (e.g., slope failure probability P f ?<?0.001). To address this problem, this study integrates RFEM with an advanced Monte Carlo Simulation (MCS) method called “Subset Simulation (SS)” to develop an efficient RFEM (i.e., SS-based RFEM) for reliability analysis and risk assessment of soil slopes. The proposed SS-based RFEM expresses the overall risk of slope failure as a weighed aggregation of slope failure risk at different probability levels and quantifies the relative contributions of slope failure risk at different probability levels to the overall risk of slope failure. Equations are derived for integrating SS with RFEM to evaluate the probability (P f ) and risk (R) of slope failure. These equations are illustrated using a soil slope example. It is shown that the P f and R are evaluated properly using the proposed approach. Compared with the original RFEM with direct MCS, the SS-based RFEM improves, significantly, the computational efficiency of evaluating P f and R. This enhances the applications of RFEM in the reliability analysis and risk assessment of slope stability. With the aid of improved computational efficiency, a sensitivity study is also performed to explore effects of vertical spatial variability of soil properties on R. It is found that the vertical spatial variability affects the slope failure risk significantly. 相似文献
6.
Sina Javankhoshdel Ning Luo 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2017,11(3):231-246
The 2D random finite element method and the one-dimensional and 2D random limit equilibrium method are used to investigate the influence of spatial variability of soil strength parameters on the probability of failure of simple soil slopes with cohesive undrained shear strength. The combined influence of spatial variability of soil properties and cross-correlation between undrained soil strength and unit weight on the computed probability of failure is explored. The paper identifies conditions where numerical outcomes are similar and where they are not. The limitations of each analysis method are described and implications to analysis and design are identified.Abbreviations: FEM: finite element method; LEM: limit equilibrium method; RFEM: random finite element method; RLEM: random limit equilibrium method 相似文献
7.
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
8.
R. Nishanthan D. S. Liyanapathirana C. J. Leo 《Geotechnical and Geological Engineering》2018,36(6):3375-3389
Deep cement mixed (DCM) walls are widely used in supporting excavations in many parts of the world. In this paper, a case study of an excavation supported by a DCM wall with steel inclusions is analysed using a three-dimensional finite element model and based on the coupled theory of nonlinear porous media. The DCM wall is constructed with wide flange steel inclusions. The stress–strain behaviour of the DCM wall section is simulated using an extended version of the Mohr–Coulomb model, which considers the strain-softening behaviour of DCM columns beyond yield. The computed lateral deformations are compared with the field measurements to validate the numerical modelling procedure. Using the same case study, the internal stability of the wall against bending and shear failure modes is investigated. In addition, the lateral pressure distribution along the wall length is investigated because in practice design is carried out considering a uniform pressure distribution assuming rigid wall movements. A parametric study was carried out to investigate the viability of DCM walls in supporting excavations by varying the spacing between steel inclusions, wall thickness and initial lateral earth pressure. Based on the results of the parametric study, guidelines are proposed to select the most efficient geometric arrangement of steel inclusions within DCM walls. 相似文献
9.
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
10.
围护结构最大侧移所在深度是衡量基坑变形的重要指标之一,而目前鲜有关于其对周边环境变形影响的研究。基于工程实测数据分析和有限元数值模拟,系统地研究了基坑围护结构最大侧移深度对邻近桩基础建筑物不均匀沉降和坑外深层土体位移场的影响。经研究发现：围护结构最大侧移的下移会导致坑外土体位移场扩大,进而降低相应区域的桩基础承载力,导致邻近桩基础建筑物发生显著的不均匀沉降。不同深度的土体经历复杂的竖向位移,且位移形态与围护结构最大侧移深度密切相关。随围护结构最大侧移深度的逐渐下移,坑外土体位移场向深层土体发展,且主要影响范围相应地扩大。在实际工程中,根据基坑周边环境合理地控制围护结构最大侧移所在深度,可有效降低基坑开挖对周边环境的不利影响。 相似文献
11.
《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(3-4):207-217
The present study comprises Monte-Carlo simulation assisted analysis of foundations resting on reinforced earth beds using the concept of beams on an elastic foundation, treating the modulus of subgrade reaction (MSR) as a stationary stochastic field characterised by mean, variance, autocorrelation function (ACF) and the autocorrelation distance (ACD). Realisations of the MSR, generated by solving a stochastic differential equation, are fed to a deterministic distributed parameter model to generate realisations of two dependent stochastic fields, namely deflection and bending moment in the foundation beam, and two random variables, namely the location of occurrence of maximum deflection and the bending moment. Subsequently these realisations are analysed to evolve probability distribution functions, variance and ACF of the dependent stochastic fields and the random variables. It is revealed that the ACF of these fields is independent of the ACF of the MSR. Further, variance of deflection is found to increase as the ACD of the MSR increases, implying requirement of a larger factor of safety when random soils display low frequency (macro level) variations. On the other hand, variance of the bending moment is larger at smaller ACDs of the MSR, indicating that for bending moments a larger factor of safety is required when the random soils display high frequency (micro level) variations. 相似文献
12.
软土地层中当桩顶水平荷载较大时,采用传统m法计算容易低估桩身弯矩与挠曲变形,有必要针对该问题提出相关计算方法。将地基土体简化为理想弹塑性体,假定桩身某一深度处存在土体的弹塑性变形临界点,临界点以上的土体进入塑性变形状态,而临界点以下的土体仍处于弹性变形状态,分段建立桩身挠曲微分控制方程,得到水平受荷单桩简明弹塑性计算方法。现场单桩实测和参数敏感性分析结果表明：采用简明弹塑性计算方法得到的桩身最大弯矩较传统m法计算精度提高38.1%;桩身最大水平位移计算精度提高22.3%;桩顶边界条件对桩身水平位移与弯矩沿桩身的分布规律影响显著;桩身最大弯矩和水平位移对土体的极限抗力系数及其形状参数较敏感,设计中宜按下限值选取。 相似文献
13.
约束随机场下的边坡可靠度随机有限元分析方法 总被引：2，自引：1，他引：1
目前边坡可靠度中常用的简化分析方法,不考虑边坡土体的空间变异性,每次计算整个边坡都取用相同的强度参数,由离散点试样试验得到的土体参数统计特性只能反映点特性,而边坡的稳定性受滑面上平均抗剪强度特性控制,因此,需要考虑空间范围内的平均特性。描述空间变异性的随机场理论对变异性较高的土体,实际上高估了其空间变异性。把随机场理论和地质统计中的区域化变量理论结合起来,建立约束随机场,并在此基础上进行Monte-Carlo随机有限元分析。计算实例表明,在高变异性条件下约束随机场能有效降低完全随机场的模拟方差,得到更低的破坏概率。对比了随机有限元和简化法的计算结果表明,简化法在土体强度变异性很高时其结果并非偏于保守。另外也指出了可靠度分析中存在的边坡尺度效应和简化法的适用条件。 相似文献
14.
Reliability analysis of bearing capacity of a strip footing at the crest of a simple slope with cohesive soil was carried out using the random finite element method (RFEM). Analyses showed that the coefficient of variation and the spatial correlation length of soil cohesion can have a large influence on footing bearing capacity, particularly for slopes with large height to footing width ratios. The paper demonstrates cases where a footing satisfies a deterministic design factor of safety of 3 but the probability of design failure is unacceptably high. Isotropic and anisotropic spatial variability of the soil strength was also considered. 相似文献
15.
In the present study an analytical procedure based on finite element technique is proposed to investigate the influence of vertical load on deflection and bending moment of a laterally loaded pile embedded in liquefiable soil, subjected to permanent ground displacement. The degradation of subgrade modulus due to soil liquefaction and effect of nonlinearity are also considered. A free headed vertical concrete elastic nonyielding pile with a floating tip subjected to vertical compressive loading, lateral load, and permanent ground displacement due to earthquake motions, in liquefiable soil underlain by nonliquefiable stratum, is considered. The input seismic motions, having varying range of ground motion parameters, considered here include 1989 Loma Gilroy, 1995 Kobe, 2001 Bhuj, and 2011 Sikkim motions. It is calculated that maximum bending moment occurred at the interface of liquefiable and nonliquefiable soil layers and when thickness of liquefiable soil layer is around 60% of total pile length. Maximum bending moment of 1210 kNm and pile head deflection of 110 cm is observed because of 1995 Kobe motion, while 2001 Bhuj and 2011 Sikkim motions amplify the pile head deflection by 14.2 and 14.4 times and bending moment approximately by 4 times, when compared to nonliquefiable soil. Further, the presence of inertial load at the pile head increases bending moment and deflection by approximately 52% when subjected to 1995 Kobe motion. Thus, it is necessary to have a proper assessment of both kinematic and inertial interactions due to free field seismic motions and vertical loads for evaluating pile response in liquefiable soil. 相似文献
16.
Lei Wang Zhe Luo Junhua Xiao C. Hsein Juang 《Geotechnical and Geological Engineering》2014,32(2):273-285
This paper presents an approach for the probabilistic inverse analysis of braced excavations based on the maximum likelihood formulation. Here, the soil parameters are updated using the observations of the maximum ground settlement and/or the maximum wall deflection measured in a staged excavation. The updated soil parameters are then used to refine the predicted wall and ground responses in the subsequent excavation stages, as well as to assess the building damage potential at the final excavation stage. Case study shows that the proposed approach is effective in improving the predictions of the excavation-induced wall and ground responses. More-accurate predictions of the wall and ground responses, in turn, lead to a more accurate assessment of the damage potential of buildings adjacent to the excavation. The proposed approach offers an effective means for a probabilistic inverse analysis of braced excavations. 相似文献
17.
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
18.
水平荷载作用下PCC桩复合地基工作性状 总被引：5，自引：1，他引：4
利用河海大学岩土所自行研制开发的大型试验模型槽进行PCC桩水平承载足尺试验,实测得到了水平荷载作用下桩身弯矩分布。利用三维弹塑性有限元方法,研究了PCC单桩与等截面实心圆桩、PCC桩复合地基与等截面实心圆桩复合地基在水平荷载作用下的工作性状,对其桩身弯矩和水平位移的分布规律进行了比较,分析了竖向荷载、褥垫层厚度、基础埋深和置换率对PCC桩复合地基桩身性状的影响。研究表明,PCC桩复合地基在水平荷载作用下,随着竖向荷载、褥垫层厚度、基础埋深和置换率的增加,其桩身弯矩和水平位移随之减小。因此,在PCC桩复合地基设计时可以通过适度调整这些影响参数来减小水平荷载作用下的桩身弯矩和水平位移,确保桩身的安全。 相似文献
19.
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20.
FRP复合板桩弹性模量较低,在使用过程中易产生较大的变形而导致结构无法正常使用,因此设计时要考虑其变形特性。FRP复合板桩的变形包括弯曲变形和剪切变形两部分。通过一种简化的计算FRP板桩变形的方法,使FRP复合板桩设计更为方便。运用该法计算出的最大变形与有限元计算结果较为接近,表明该法具有一定的可靠性。 相似文献