临近基坑开挖复合地基侧向力学性状离心试验研究

临近基坑开挖引起复合地基CFG桩变形和内力改变,现有理论缺乏对该问题的研究。通过开展离心模型试验,对临近基坑开挖条件下,复合地基变形、CFG桩内力和变形、土压力等分布和变化规律进行深入分析。结果表明：开挖引起CFG桩弯矩增大,近基坑桩增幅明显|开挖引起桩土不同步沉降,导致CFG桩上刺入褥垫层,桩受到褥垫层的“嵌固拉结”作用,同时远基坑桩、褥垫层、加载气囊一起提供了“摩擦拉结”作用,从而在近基坑桩上出现负弯矩|而远基坑处不均匀沉降小,“嵌固拉结”作用小,且“摩擦拉结”作用是利于正弯矩产生,桩上未出现负弯矩|开挖引起支护背后土压力分为增长区和减小区两部分,在上部土体中,土体卸荷,土压力减小,而下部土体受支护挤压,土压力有所增大|开挖引起地表沉降呈指数形式,临近基坑地表沉降最大,在显著变形区域内,支护水平位移基本呈直线形式,各阶段最大水平位移均出现在支护顶端|开挖引起的CFG桩水平变形大小和范围随距基坑边距离的增大而减小。     

Subsurface ground movements due to circular shaft construction

The rapid development of modern metropolises has led to a shortage of surface space and, in response, engineers have pursued alternatives below ground level. Shafts are commonly used to provide temporary access to the subsurface for tunnelling and, as permanent works, are utilised for lifts or ventilation purposes. The construction sequence of axisymmetric shafts makes them a dramatically simple solution. In addition, circular shafts are inherently stiffer than other plan geometries. Those are perhaps the reasons why circular shafts are preferred in situations of restricted space or unfavourable ground conditions. However, due to the lack of case histories reporting ground movements induced by shaft construction, no empirical prediction method for subsurface soil displacements exists. The work presented here seeks to provide clearer insights into surface and subsurface soil displacements induced by circular shaft construction by means of an analysis of measurements obtained from centrifuge tests and available field data. Novel empirical equations and procedures are then suggested for practical use.     

辅助坑道开挖隧道出砟及衬砌混凝土概算编制

通过对铁建设〔2010〕223号发布的新版《铁路隧道预算定额》和《高速铁路路基、桥梁、隧道、无砟轨道工程补充定额》学习,提出了客运专线利用无轨辅助坑道开挖正洞隧道出砟及衬砌混凝土概算编制方法,以期为类似项目概算编制提供指导。     

平行隧道开挖引起上方既有隧道的纵向变形研究

城市地铁隧道大多数采用平行双洞的布置形式作为隧道设计施工方案,根据不同的地层条件等因素采用盾构法或暗挖法施工。由于城市地下空间变的越来越拥挤,研究新建平行双洞隧道施工过程中对邻近既有隧道的影响程度问题显得尤为重要。本文基于两阶段分析方法研究预测平行双洞隧道开挖引起上方已建隧道的纵向变形的简化解析方法。首先,采用两高斯曲线叠加,计算新建平行双洞隧道施工引起的作用在既有隧道上的附加荷载。然后,将既有隧道考虑为Winkler 地基上的Timoshenko梁,建立既有隧道纵向变形的基本微分方程,并基于Galerkin 法进行求解。将本文提出的简化解析方法得到的结果与工程沉降实测数据进行对比以验证本文提出的预测方法的合理性。最后,进行了参数敏感性分析,研究了不同隧道相互位置、地层损失率、相对抗弯刚度和地层土性参数等对结果的影响规律。     

Influence of deep excavation induced ground movements on adjacent piles

In urban areas, excavations for cut-and-cover tunnels and basement construction cause detrimental effects on adjacent existing piles. Hence quantifying the excavation induced lateral deformations and bending moments on piles are important to ensure the stability of structures. In this paper, behaviour of a single pile subjected to excavation induced ground movements is analysed using the finite element method, which has the ability to simulate the construction sequence comprising soil excavation, deformations due to dewatering within the excavation and installation of struts. A fully coupled analysis is carried out based on the effective stress principle. The numerical model was verified using the centrifuge test data found in the literature. A parametric study was carried out to establish the excavation induced pile behaviour varying the depth of the excavation, soil properties, wall support system, pile fixity conditions and pile location with respect to the excavation. Increasing axial load does not have a significant influence on the pile behaviour. However, pile head fixity condition, and stiffness and spacing of the wall support system have a significant influence on the pile behaviour adjacent to the excavation. Finally, based on the parametric study, a set of design charts are developed to predict the pile behaviour by taking into account the depth of excavation, undrained shear strength, width of the pile, spring stiffness, spacing of vertical supports, and unsupported depth of the excavation. The capability of the proposed design charts are demonstrated using a three-dimensional finite element analysis, a case study from the literature and a previously published simplified analysis procedure.     

Shanghai center project excavation induced ground surface movements and deformations

Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of the Shanghai Center involved excavations in excess of 33-m-deep using the top-down method at a site underlain by thick deposits of marine soft clay. A retaining system was achieved by 50-m-deep diaphragm walls with six levels of struts. During construction, a comprehensive instrumentation program lasting 14 months was conducted to monitor the behaviors of this deep circular excavation. The following main items related to ground surface movements and deformations were collected: (1) walls and circumferential soils lateral movements; (2) peripheral soil deflection in layers and ground settlements; and (3) pit basal heave. The results from the field instrumentation showed that deflections of the site were strictly controlled and had no large movements that might lead to damage to the stability of the foundation pit. The field performance of another 21cylindrical excavations in top-down method were collected to compare with this case through statistical analysis. In addition, numerical analyses were conducted to compare with the observed data. The extensively monitored data are characterized and analyzed in this paper.     

Fuzzy genetic programming method for analysis of ground movements due to underground mining

The prediction of ground surface movements is an important problem in rock and soil mechanics in the excavation activities especially the coal and metal mining. Based on results of the statistical analysis of a large amount of measured data in underground excavation engineering, the fuzzy genetic programming method (FGPM) of ground surface movements is given by using the theory of fuzzy probability measures and genetic programming (GP). And genetic programming approach is proposed to determine the parameter of ground surface movements due to underground mining of coal in this paper. Genetic programming is trained by used practical mining induced surface movement data. The agreement of the theoretical results with the field measurements shows that the FGPM is satisfactory and the formulae obtained are valid and thus can be effectively used for predicting the ground surface movements due to underground mining, especially the mining of coal and metal.     

基坑施工对下卧地铁隧道上抬变形影响的简化理论分析

为了合理地分析基坑施工对下卧已建地铁隧道上抬变形的影响,首先,将软土地基考虑为三参量H-K黏–弹性体,推导了自由边界半无限黏–弹性空间体在内部集中荷载作用下的Mindlin时域解,并采用积分、叠加的方法,提出了一种用于计算基坑开挖及工程降水所引起的邻近隧道附加应力的方法;然后,将已建隧道视为Pasternak黏–弹性地基上的欧拉伯努利长梁,建立了隧道在附加荷载作用下的平衡微分方程,求得了隧道纵向附加变形和内力的表达式;最后,将所提方法运用于某近接既有地铁隧道的基坑工程中,并与三维数值模拟流变分析结果和现场实测结果进行了对比分析。研究发现:提出方法能较好地反映软土隧道变形随时间的发展趋势;隧道纵向附加变形、曲率和弯矩的解析解与数值解基本一致,且上抬变形的解析解与实测值能较好地吻合;成果可为基坑施工对邻近隧道的影响分析及保护措施的制定提供一定的理论依据。     

穿越地表建筑物浅埋隧道开挖引起的地表沉降

采用解析法研究穿越地表建筑物浅埋隧道开挖对地表沉降的影响,推导出了穿越地表建筑物浅埋隧道施工引起的地表沉降公式,依托广州地铁五号线右线区庄区间隧道穿越地表建筑物工程实例,验证了此方法的可行性,可为类似穿越已有建筑物隧道工程提供一定指导。     

上海基坑开挖引起地面沉降估算经验系数探讨

对地面沉降估算实用方法与上海同济启明星科技发展有限公司开发的基坑开挖环境影响分析软件JK3E进行简单的介绍。基于分析软件JK3E,采用上海地区5个工程的6个工况实测数据,对软件中估算地面沉降分布的同济启明星曲线法的沉降经验系数γ和位置经验系数η进行了计算研究。计算研究结果表明:用于调整地面沉降量值大小的沉降调整系数γ介于0.90与1.25之间;用于调整各基本模式下最大沉降点位置的位置调整系数η介于0.20与0.50之间。研究结果为JK3E软件更好地服务于上海地区基坑工程实际中提供了重要的参数取值参考,并有利于积累工程经验。     

地铁交汇站施工上部结构不均匀变形分析

通过多方案数值计算并与现场实测对比的分析方式,对暗挖段施工引起上部结构不均匀变形的产生原因进行了详细深入的探讨,得到了有实用价值的结论,成功指导了现场进一步的施工工作,并最终使上部结构不均匀变形得以控制。     

隧道开挖不均匀收敛引起地层位移的预测模型

在隧道施工引起的地层位移预测中,随机介质理论法是在我国应用较为广泛的实用方法之一。在目前的随机介质理论法中,均假定地层位移是由于隧道开挖断面的均匀收敛变形引起,本文认为隧道收敛模式一般为不均匀,推导了各类断面在不均匀收敛模式下的计算公式,并补充推导了矩形、马蹄形断面的计算公式。通过算例的比较,认为均匀与不均匀收敛这两种情况对于埋深越浅的隧道,计算结果差别越大,建议在工程中适当考虑隧道断面收敛形式以考虑实际位移情况或隧道施工工法等的影响。     

Microseismicity-based method for the dynamic estimation of the potential rockburst scale during tunnel excavation

Bulletin of Engineering Geology and the Environment - The severity and harmfulness of a rockburst event are significantly correlated with the scale of rock mass ejection, especially when the rock...     

A multi-dimensional approach to the assessment of tunnel excavation methods

Selection of tunnel excavation method in rock calls for an exact assessment of engineering geology as well as geotechnical conditions of the tunnel strike. Moreover, uncertainties related to properties of engineering geology of rock often trigger complexity. In order to select the best possible excavation technique, one needs to take into account numerous operational, economic, environmental factors, and so forth. Using a hybrid methodology, including multiple attributes decision-making techniques and fuzzy set theory, the present study aims to evaluate the excavation methods of tunnels. The proposed approach is based on fuzzy-AHP and TOPSIS methods where the fuzzy-AHP determines weights of the criteria by decision makers in uncertain environment and TOPSIS concludes rankings of the excavation methods. Finally, a case study of Ghomroud project in Iran is presented to demonstrate the result of the proposed methodology.     

临近地铁隧道的软土深基坑施工影响分析

以杭州某临近地铁隧道的软土深基坑工程为背景,运用有限元方法动态模拟基坑开挖过程,分析基坑变形以及对地铁隧道的影响,并对不同计算模型进行对比分析.研究结果表明:HSS模型考虑了地下水及时空效应的影响,较HS硬化模型能更好地模拟基坑施工过程;为控制基坑开挖对邻近地铁隧道的影响,需辅助其他措施,如分块开挖、基坑降水等;地下连续墙成槽过程无法模拟,施工中应尽量减小成槽对周边土体和隧道的影响.研究结论可为类似工程提供借鉴与参考.     

不同直径盾构隧道地层损失率的对比研究

地层损失率是引起地面沉降最主要的因素之一。因此,收集了国内盾构隧道地面最大沉降实测数据,利用Peck公式反推得到地层损失率的取值,研究大直径(D10m)与中小直径盾构隧道地层损失率的分布规律及主要影响因素。结果表明:(1)中小直径、大直径盾构隧道施工引起的地层损失率分别有93.19%在0%～2.0%、近70%在0%～0.5%之间,大直径盾构隧道施工引起的地层损失率数值更小,分布更集中;(2)中小直径、大直径盾构隧道引起的地层损失率分别随着地层条件变好、地层渗透性的变小而减小;(3)两种直径盾构隧道的地面最大沉降与地层损失率均具有一定的线性相关性;(4)隧道覆土深度比与地层损失率的相关性较弱;(5)中小直径盾构隧道引起的地层损失率随着地层黏聚力、内摩擦角以及弹性模量的增大而逐渐减小。研究成果可为今后相关地区类似隧道工程施工诱发的地面沉降预测和施工控制提供科学参考。     

改进离散灰色模型在基坑周围地面沉降预测中的应用

离散灰色模型解决了常规灰色模型从离散形式到连续形式直接跳跃的问题,该模型估计模型参数时采用最小二乘法,而在模型检验时常采用平均相对误差指标,因此导致建模与模型检验的脱节。鉴此,本文基于平均相对误差最小准则,利用果蝇算法的快速全局优化能力对模型参数进行优化,从而提高离散灰色模型的建模与预测精度。将本文提出的果蝇算法优化离散灰色模型应用到工程实例,结果表明该模型具有较好的有效性和可行性。     

考虑隧道剪切效应的基坑开挖对邻近隧道纵向变形分析

 基坑施工将打破周围地层已平衡的应力场,引起应力释放,对既有下卧地铁隧道产生不利的影响。针对既有研究的不足,提出考虑隧道剪切效应的基坑开挖对下卧隧道影响的解析解。既有隧道简化为搁置于Winkler地基上的Timoshenko梁。通过两阶段分析法,考虑基坑卸荷作用下已建隧道的响应。首先基于Timoshenko梁理论,建立考虑隧道剪切效应的隧道纵向变形微分方程,然后将由Mindlin弹性解计算得到附加荷载施加于既有隧道上,最后通过有限差分法得到在附加荷载作用下隧道的纵向变形解答。收集3个已发表工程实例的实测数据,并与本文方法及Euler-Bernoulli梁法的计算结果进行对比分析,发现实测结果与2种方法得计算结果有较好的一致性。然而,在内力分析上,相对比于本文方法,Euler-Bernoulli梁法明显高估基坑卸荷引起的隧道弯矩与剪力。由于本文方法可有效模拟既有隧道剪切效应,因而可进一步给出1在卸荷作用下隧道管片间错台量。研究成果可为合理预测邻近基坑施工对既有隧道的影响提供一定的理论支持。