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1.
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
2.
通过大量的人工冻结黏土蠕变试验研究,获得在高偏应力下人工冻结黏土具有显著的蠕变特性：当应力水平较低时,人工冻土发生黏弹性蠕变变性;当应力水平较高时,人工冻土发生黏塑性蠕变变性。因此,以西原模型为基础,增加一个黏弹性元件项和用抛物线屈服函数代替塑性屈服项,构建了高应力下抛物线型黏弹塑性蠕变本构模型。改进的西原模型可以较好描述人工冻土剪切蠕变特性。基于小生境技术的遗传算法和人工冻土黏弹塑性模型有限元理论,在FEPG（有限元程序生成器）自动生成平台上研发了位移反分析程序。利用现场实测数据对深井冻结井筒开挖过程进行了位移反分析,获得了与试验相一致的冻土本构力学模型参数,数值分析结果与实测数据之间的误差在6%以内,反演结果验证了模型的可行性。冻结井筒开挖过程的位移反分析获得的人工冻土本构模型参数,能反映冻结壁施工过程和有效冻结范围内冻土本构参数平均值,因而具有广泛的代表性,对冻结壁应力场、位移场和稳定性预测具有重要工程意义。 相似文献
3.
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
4.
5.
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
6.
Youssef M.A. Hashash Séverine Levasseur Abdolreza Osouli Richard Finno Yann Malecot 《Computers and Geotechnics》2010
Performance observation is a necessary part of the design and construction process in geotechnical engineering. For deep urban excavations, empirical and numerical methods are used to predict potential deformations and their impacts on surrounding structures. Two inverse analysis approaches are described and compared for an excavation project in downtown Chicago. The first approach is a parameter optimization approach based on genetic algorithm (GA). GA is a stochastic global search technique for optimizing an objective function with linear or non-linear constraints. The second approach, self-learning simulations (SelfSim), is an inverse analysis technique that combines finite element method, continuously evolving material models, and field measurements. The optimization based on genetic algorithm approach identifies material properties of an existing soil model, and SelfSim approach extracts the underlying soil behavior unconstrained by a specific assumption on soil constitutive behavior. The two inverse analysis approaches capture well lateral wall deflections and maximum surface settlements. The GA optimization approach tends to overpredict surface settlements at some distance from the excavation as it is constrained by a specific form of the material constitutive model (i.e. hardening soil model); while the surface settlements computed using SelfSim approach match the observed ones due to its ability to learn small strain non-linearity of soil implied in the measured settlements. 相似文献
7.
鲁中小官庄铁矿由于埋藏深、地压大、矿体倾角比较缓、矿岩破碎,是国内有名的难采矿山之一。进路开挖以后支护巷道破坏严重,其围岩变形为无收敛变形,也是国内支护较难的矿山之一。针对小官庄铁矿情况,为掌握其地压活动规律,应用东北大学岩石破裂过程分析系统（RFPA）,模拟其采用无底柱分段崩落法进路开挖过程,对进路开挖过程巷道围岩应力变化进行数值分析。发现随着进路开挖,导致进路出现片帮、底鼓、顶板下沉等现象,并且在矿岩接触带出现高应力集中,导致两进路之间的间柱破坏严重,并随着进路开挖应力逐步向新开挖两进路之间的间柱转移,开挖顺序造成边界矿体出现高应力集中,导致边界矿体难采。数值分析结果可以看出：进路的开挖顺序是导致小官庄铁矿进路围岩破坏的一个主要原因。 相似文献
8.
This study back analyzed deformation parameters of in situ sand through two excavation case histories in Kaohsiung, Taiwan. Two main features are highlighted; deformation prediction based on monitoring data at the first excavation stage and in situ Young’s modulus evaluation for sand considering monitoring data at the overall excavation stages. The former tends to establish a reliable method to predict the wall deflection at the critical stage based on the data at the first stage and the latter to enrich the limited database of Young’s modulus correlation for sand, specifically applicable for deep excavations analysis. The two constitutive models, linear elastic perfectly plastic and non-linear stress–strain constitutive models, were selected. The stiffness parameters of the models were discretely distributed along the subdivided soil body mesh to reflect the effect of overburden pressure on the in situ soil. In addition, relationship between Standard Penetration Test value (SPT-N value) and Young’s modulus and relationships for estimating the in situ Young’s modulus of the Kaohsiung sand as a function of depth were evaluated. The results greatly enhanced a framework for estimating the in situ Young’s modulus of sand. 相似文献
9.
The full-scale mine-by (MB) test conducted in 2008 in the Mont Terri underground rock laboratory (Switzerland) investigated the deformation and the coupled hydro-mechanical behavior of the Opalinus Clay in response to tunnel excavations. The Opalinus Clay is currently under investigation in Switzerland as a potential host rock for geologic disposal of high-level radioactive waste. To further improve the understanding and modeling of the coupled processes and their impact on the performance of a geologic repository in Opalinus Clay, a newly developed two-part Hooke’s model (TPHM) was implemented into a geomechanical simulator. A three-dimensional simulation model based on the TPHM was then developed to predict the deformation and pore pressure responses in the near field of the MB Niche 2 test at the Mont Terri Site. The usefulness and validity of the TPHM are demonstrated by the consistency between simulation results and field observations. Simulation results show that the pore pressure disturbance becomes visible at about 11 m ahead of the mine-by excavation advancing face (along the longitudinal direction of the MB Niche). The results also demonstrate that there exists a good correlation between the excavation damage zone (EDZ) and the pore-pressure evolution, which may have important practical implications for monitoring EDZ evolution with pore-pressure sensors. The simulation results, which are sensitive to the constitutive relationships used in the model, capture both the observed displacements and the size of the damage zone, whereas the approach based on the conventional Hooke’s law underestimates both. The comparison between simulated and observed results also indicates that laboratory-measured mechanical properties can be used to accurately predict field-scale mechanical deformations, as long as valid constitutive relationships are employed. 相似文献
10.
Numerical studies of anchored sheet pile wall behavior constructed in cut and fill conditions 总被引：1，自引：0，他引：1
The construction of sheet pile walls may involve either excavation of soils in front or backfilling of soils behind the wall. These construction procedures generate different loading conditions in the soil and therefore different wall behavior should also be expected. The conventional methods, which are based on limit equilibrium approach, commonly used in the design of anchored sheet pile walls do not consider the method of construction. However, continuum mechanics numerical methods, such as finite element method, make it possible to incorporate the construction method during the analyses and design of sheet pile walls. The effect of wall construction type for varying soil conditions and wall heights were investigated using finite element modeling and analysis. The influence of construction method on soil behavior, wall deformations, wall bending moments, and anchor forces were investigated. The study results indicate that walls constructed by backfill method yield significantly higher bending moments and wall deformations. This paper presents the results of the numerical parametric study performed and comparative analyses of the anchored sheet pile walls constructed by different construction methods. 相似文献
11.
上海地区基坑开挖数值分析中土体 HS-Small模型参数的研究 总被引：6，自引：0，他引：6
数值分析方法已成为分析敏感环境下基坑开挖对环境影响的最重要手段,其关键是选择合适的土体本构模型和计算参数。HS-Small模型可以同时考虑土体剪切硬化和压缩硬化,而且还可以考虑土体剪切模量在微小应变范围内随应变衰减的行为,因此,HS-Small模型在基坑开挖数值分析中具有很好的适用性。但HS-Small模型的参数较多,不仅包含了HS模型的参数,还包含了小应变参数,因此,获取完整的HS-Small模型参数存在一定困难。通过上海地区5个基坑开挖数值分析的实例对基于室内试验得出的上海典型土层HS模型参数进行了检验。通过参数的敏感性分析,对HS-Small模型的部分参数的确定方法进行了修正。在此基础上,采用反分析法确定了敏感性最强的小应变参数,从而初步完整地获取了上海典型土层土体HS-Small模型参数。采用文中确定的上海典型土层HS-Small模型参数对该地区若干典型基坑工程实例进行计算,结果表明,计算值与实测值吻合得较好,从而验证了确定的上海典型土层HS-Small模型参数的适用性。 相似文献
12.
Coupled THM processes in EDZ of crystalline rocks using an elasto-plastic cellular automaton 总被引：5，自引：0，他引：5
Peng-Zhi Pan Xia-Ting Feng Xiao-Hua Huang Qiang Cui Hui Zhou 《Environmental Geology》2009,57(6):1299-1311
This paper aims at a numerical study of coupled thermal, hydrological and mechanical processes in the excavation disturbed
zones (EDZ) around nuclear waste emplacement drifts in fractured crystalline rocks. The study was conducted for two model
domains close to an emplacement tunnel; (1) a near-field domain and (2) a smaller wall-block domain. Goodman element and weak
element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto-visco-plastic
material. Mohr–Coulomb criterion and a non-associated plastic flow rule were adopted to consider the viscoplastic deformation
in the EDZ. A relation between volumetric strain and permeability was established. Using a self-developed EPCA2D code, the elastic, elasto-plastic and creep analyses to study the evolution of stress and deformations, as well as failure
and permeability evolution in the EDZ were conducted. Results indicate a strong impact of fractures, plastic deformation and
time effects on the behavior of EDZ especially the evolution of permeability around the drift. 相似文献
13.
重塑超固结上海软土力学特性及弹塑性模拟 总被引：1，自引：0，他引：1
对典型上海软土重塑样进行了围压不变和平均主应力不变的三轴排水剪切试验,得到重塑上海软土在不同初始超固结比和围压条件下的应力-应变关系,弄清了超固结比、围压以及应力路径对重塑上海软土的变形和强度特性的影响;根据土体的应力-应变曲线得到重塑上海软土的临界状态应力比及内摩擦角。采用姚仰平等建议的基于伏斯列夫面的超固结土本构模型,并根据等向压缩及三轴排水剪切试验确定其模型参数,对保持围压和平均主应力不变的三轴压缩试验进行了模型预测。预测结果表明,此超固结土本构模型能较好地反映重塑超固结上海软土的变形和强度特性。 相似文献
14.
土蠕变性质及其模型研究综述与讨论 总被引：3，自引：0，他引：3
对土的蠕变性质及其本构模型研究进行了系统地总结,主要内容包括：时间和应力对土蠕变性质的影响、土蠕变破坏准则、蠕变势和塑性势关系、蠕变微观机制、宏观和微观本构模型等。此外,基于上述总结,提出了土等效变形过程的概念,探讨了土蠕变模型中时间效应的表述方式,提出了一种可加快土蠕变试验的方法。 相似文献
15.
软硬相接岩层在长时间跨度内的蠕变变形可能极为不协调,这对开挖工程安全稳定造成严重威胁。对某水电站引水隧洞同一开挖断面内砂质泥岩和泥质砂岩两种软硬相差较大的岩石进行卸荷条件下的蠕变试验和数值模拟,结果表明：在卸围压条件下,试样侧向蠕变变形较轴向发展更为迅速,呈现出显著的侧向扩容;初始围压水平较高时,试样卸荷蠕变破坏的侧向扩容效应更加显著;泥质砂岩在稳态蠕变阶段变形速率比砂质泥岩更慢,蠕变破坏时的应变值均比砂质泥岩蠕变破坏时的应变值要小,征兆性更弱。基于Burgers模型,引入损伤变量,建立带损伤的蠕变本构模型,模型曲线较好地描述了岩石破坏偏应力水平之前的线性蠕变特征和破坏偏应力水平下的非线性加速蠕变特征;软硬相接岩层蠕变数值模拟表明,蠕变变形初期,软硬相接点变形差别幅度不大,随着时间增长,在交接面处发生层间错动,对围岩整体稳定十分不利,工程实践中应予以足够关注。 相似文献
16.
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
17.
工程岩体开挖会遇到各种复杂应力条件，岩体在荷载作用下随时间会产生流变现象，这种“累进性破坏”导致工程岩体常出现滑坡、塌方、大变形和支护困难等问题.为解释天然岩体结构面的流变现象，以天然红砂岩结构面为研究对象，基于结构面三维形貌扫描试验、结构面分级加载剪切蠕变试验，对天然岩体结构面的剪切蠕变特性进行系统研究.研究发现，岩体结构面蠕变变形量与蠕变应力和结构面三维形貌特征指标正相关；岩体结构面蠕变曲线可分为3个阶段，即过渡蠕变、稳态蠕变和加速蠕变阶段，当法向应力一定时，结构面三维形貌特征指标越大，发生的蠕变破坏越剧烈；基于结构面剪切蠕变曲线与剪切蠕变速率曲线特征，建立了参数物理意义明确的岩体结构面剪切蠕变经验模型. 相似文献
18.
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
19.
岩土工程数值计算中粗粒土常采用邓肯-张本构模型,为了验证该模型在轴向加载、卸载、侧向加载等复杂应力路径条件下的适用性,进行了粗粒土的三轴试验获取其力学特性及本构模型参数;根据相似性原理制作了堆石坝的离心模型试样,并采用与三轴试验同样级配与粒径的粗粒土进行复杂应力路径的堆石坝离心模型试验,试验中通过改变离心加速度模拟加载、卸载,利用上游蓄水模拟坝体的侧向加载;采用ABAQUS对离心模型试验进行三维数值模拟,并研究了模型箱侧壁摩擦系数与土体的初始应力对数值结果的影响。通过比较离心模型试验与数值模拟成果,表明土体的初始弹性模量对计算结果影响较大,初始应力应选择自重作用下的应力场;邓肯-张本构模型能较好地描述堆石坝的加载应力路径,而模拟卸载应力路径有一定的差异,需要改进邓肯-张本构模型中卸载模量的确定方法。 相似文献
20.
新型预应力路基技术可用于整治路基病害或强化既有线路基,研究其预应力损失规律对保障预应力路基工程的长期安全具有重要意义。基于弹性理论提出了预应力路基侧压力板与路基边坡接触面中心点后方水平路径上附加应力的计算方法,分析表明该特征路径上水平附加应力随距板−土接触面中心点距离的增加呈现良好的指数函数衰减关系。基于水平附加应力的指数函数扩散规律及路基土的蠕变行为,推导了路基土的蠕变变形计算公式。进一步基于蠕变变形与预应力钢筋回缩变形的协调性,建立了路基预应力的损失模型和计算方法,并结合FLAC3D数值仿真开展了对比分析。研究表明：钢筋预拉力损失的理论预测曲线与数值仿真曲线吻合良好,二者偏差不足5%,论证了路基预应力损失模型的有效性;钢筋预拉力可在锚固后的60 d内达到稳定,且预拉力的稳定值可达其初始值的85%～90%,说明新型预应力路基技术可为路基土提供相当可观的稳定附加围压,从而通过改善路基土的应力状态达到强化路基的目的。 相似文献