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The complex variables boundary element method (CVBEM) is used to study interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane. A new complex hypersingular equation for piecewise homogeneous media with a circular opening is obtained. The equation is solved using the CVBEM technique with circular and straight boundary elements and polynomial approximations (with square root asymptotics for crack tip elements) for the unknown functions. The algorithm is verified through comparison with known semi‐analytical and numerical solutions that involve interaction between a circular opening and specific systems of cracks or other openings. New numerical results concerning the interaction of the circular opening with the cracks and circular inclusions are presented. The method is applied to an important problem in the petroleum industry: modelling propagation of hydraulic fractures in the vicinity of a borehole. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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地应力作用下的钻孔孔壁会发生一定程度的变形,导致钻孔横截面形状会发生变化,变形后的钻孔几何形态也反映了钻孔受力状态。在经典岩石力学理论的基础上,研究钻孔在平面二维应力作用下的几何形态,建立应力与变形后圆孔几何参数的关系,实现基于钻孔椭圆参数的应力解算,并提出钻孔椭圆参数的测量方法和测量技术,形成一种新的基于钻孔形态分析的地应力测量方法。结果表明,（1）在平面二维应力作用下圆孔变形后的几何形态为椭圆,推导了椭圆参数与应力的关系表达式;（2）利用3个不同方向的孔径值可以实现椭圆参数的解算,研发触头式显微光学孔径测量技术,实现了钻孔形态的测量,从原理上分析了技术实现的可行性,并就该技术进行地应力测量过程中可能存在的问题进行了探讨;（3）通过室内模拟试验,验证了技术原理的可行性,并通过误差分析和实例计算对该方法测量结果的准确性进行了讨论。 相似文献
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甘肃省关山隧道是一条受高地应力影响的大埋深硬脆性闪长岩铁路隧道,位于青藏高原东北缘,构造活跃,运动速率较大,且方向变化显著的六盘山挤压隆升构造区。在隧道开挖过程中围岩变形破坏现象明显,围岩等级低于前期岩体质量分级,表现出强烈的岩体质量劣化和各向异性。针对该问题,除了采用矿物成分和微结构分析寻找原因,还通过现场结构面统计分析对围岩质量劣化和各向异性进行描述,同时运用自行研发的钻孔电视进一步分析开挖前后一定时间间隔内围岩的渐进式变形和破坏。钻孔电视试验结果表明,尽管闪长岩作为一种硬脆性岩体,单轴抗压强度（UCS）高于现场地应力值,但其变形和破坏却普遍发生,开挖过程中新生裂隙迅速发育,原先在高地应力下闭合的裂隙也会重新张开和发展,围岩劣化,稳定性降低。为了进一步分析围岩的变形破坏过程,设计了变压力大小和方向的单轴抗压试验,试验中闪长岩的单轴压力值低于单轴抗压强度,试验结果与钻孔电视试验观测结果吻合,证明了在开挖引起的地应力剧烈变化条件下硬脆性闪长岩结构劣化,存在变形破坏的可能性。在大埋深高地应力条件下,除了岩体的各向异性,地应力的变化也是硬脆性围岩稳定性的重要考量因素。 相似文献
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A general analysis using an incremental elastic, perfectly plastic constitutive stress–strain relationship for poroelastoplastic materials is presented to simulate an opening in a low-permeability friable porous medium under non-isothermal conditions. Analytical solutions are obtained for the stresses and strains around a 2-D plane strain circular borehole. An expansion potential is introduced by combining the strains induced by temperature and pore pressure changes. Steady-state pressures and temperatures are considered, and a non-associated plastic flow rule is applied to calculate plastic strains. Focusing on stress distribution near a circular opening, the classic solutions for those stresses under dry and isothermal conditions are used to compare with the newly derived solution. The general poroelastoplastic effect and the thermal effect on sand production and borehole stability are addressed. We suggest that the knowledge of stress history is critical to achieve adequate solutions for displacement and stress in friable media such as clays, shales and oil sands. 相似文献
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柱状节理玄武岩在开挖卸荷条件下容易松弛与开裂,是白鹤滩水电站坝基稳定的主要挑战。以白鹤滩水电站左岸坝基柱状节理玄武岩试验区为工程背景,采用单孔声波、钻孔摄像等原位测试技术,研究了分梯段开挖及时间效应条件下Ⅲ1类和Ⅲ2类柱状节理玄武岩松弛深度、松弛程度的时空演化规律,探讨了坝基柱状节理岩体松弛特征的原因。分析结果表明：柱状节理玄武岩的松弛深度主要由开挖引起,临近开挖面岩体的松弛程度随时间呈负指数增长,其时效期不超过半年。柱状节理岩体松弛特征与岩体质量关系密切,两类岩体的松弛深度、松弛程度的时效性及松弛程度随孔深的分布规律差异较大。坝基柱状节理岩体时效松弛是由内部节理张开导致的岩体强度参数的时效劣化引起。该研究对认识柱状节理岩体卸荷力学行为及优化坝基柱状节理岩体开挖保护方案具有重要意义。 相似文献
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By applying the series expansion technique in the complex variable method established by Muskhelishvili, the plane elasticity problem for the stress and displacement field around a lined circular tunnel in conjunction with the consideration of misfit and interaction between the liner and the surrounding geomaterial is dealt with. The tunnel is assumed to be driven in a homogeneous and isotropic geomaterial. The coefficients in the Laurent series expansion of the stress functions are determined. The complex potentials in the liner and the surrounding geomaterial are explicitly derived, respectively. As an example, the case of a lined circular tunnel located in an isotropic initial stress field but subjected to uniform internal pressure is numerically considered. Numerical results indicate that the installation of tunnel liner can reduce the influences of the tunnel excavation on the in situ displacement and stress fields. However, the relative thickness and rigidity of the liner should be in an appropriate range. In addition, the effect of the tunnel excavation upon the displacement field is more significant than that upon the stress field. As far as the stress field in the surrounding geomaterial is concerned, when the ratio between the cover depth of tunnel and the tunnel radius is larger than 5, the results for the stress field in the paper are applicable. When the ratio between the tunnel depth and the tunnel radius is larger than 20, the results are applicable for the displacement field. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Excavation damaged zone, with significant irreversible deformations and nonnegligible changes in flow and transport properties generally occurs in indurated clay around underground structures. The stress perturbation around the excavation could lead to a significant increase of the permeability physically due to diffuse and/or localized microcracks growth in the material. In the present study, we investigate microcracks-induced damage processes together with the subsequent modification in permeability. The proposed approach is based on a homogenization-based upper bound extended to the context of microcracked media in presence of initial stress. Application of this approach is done on a borehole excavation problem related to the Selfrac in situ experiments on Opalinus Clay. Although, the model fails to quantitatively account for the in situ permeability change (which may also originated from existing macrofractures), its prediction shows a significant evolution of the material permeability around the borehole. This is in qualitative agreement with available data. 相似文献
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采用解析法研究穿越地表建筑物浅埋隧道开挖引起的地表沉降。由无建筑物时岩土体开挖引起的地表沉降公式及半无限平面在均布荷载下的相对沉陷,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,并通过实例验证了此方法的可行性。采用上述方法研究了地表建筑物的重量及其与浅埋隧道位置关系对地表沉降的影响,研究结果表明：浅埋隧道开挖引起的地表沉降随建筑物重量的增大而增大;建筑物中心到隧道轴线的水平距离是对地表沉降的一个重要影响因素,超过一定范围时建筑物的存在对地表沉降的影响可以忽略不计。研究结果可为类似隧道工程提供一定参考。 相似文献
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具有内支撑结构的围护系统在基坑边角处具有更大的系统刚度,使得基坑边角附近处土体的位移小于距离边角较远处土体的位移,即基坑的变形问题表现出空间特性。为了更好地研究L/He（L为沿基坑纵向方向上的距离;He为开挖深度）、开挖深度等因素对空间效应的影响,量测了两个狭长形地铁车站深基坑不同位置处土体的侧向位移、土体沉降等。通过对现场监测资料的分析发现,边角效应能够减小侧向位移的平面应变比,灌注桩围护结构、SMW工法桩围护结构和地下连续墙在边角附近处的平面应变比(PSR)分别为0.50、0.61和0.72。当平面应变比(PSR)接近于1.00时,对应的L/He值分别为2.50、6.00和4.00。随着L/He值的增大,土体的纵向最大沉降呈先增大后保持稳定的趋势。随开挖深度的增加,边角效应的影响范围呈增大的趋势。在基坑纵向沉降的空间效应中,灌注桩围护结构、SMW工法桩围护结构的土体最大沉降值达到稳定时对应的L/He值分别为2.50和5.20。土体沉降和侧向位移的空间效应有一定的相关性。 相似文献
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Fracture Length Estimation from Borehole Image Logs 总被引：1，自引：0，他引：1
Sait Ismail Özkaya 《Mathematical Geology》2003,35(6):737-753
We describe a method to estimate fracture length for circular fractures from borehole image logs. The relative frequency of fractures, which have complete circumference trace on image logs is related to fracture length. A simple functional relationship can be derived for the relative frequency of complete fracture traces in terms of average fracture inclination to borehole, borehole diameter and fracture length. This formulation however, tends to underestimate fracture length because a constant length is assumed. A more accurate length estimate can be obtained by assuming that fracture length is linearly correlated to fracture aperture or spacing. Cumulative frequency distribution of fracture aperture and spacing can be obtained from borehole image logs. The problem then transforms itself to finding the scaling factor between fracture length and aperture (or spacing) from the relative frequency of fractures with complete traces. The product of the scaling factor and average fracture spacing (or aperture) gives the average fracture length. 相似文献
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This paper presents time-dependent response of a cylindrical borehole in a poroelastic medium with an excavation disturbed zone. The general solutions are derived based on Biot’s theory of poroelasticity by employing Laplace and Fourier transforms. Both shear modulus and permeability coefficient are assumed to be changed from their original values in the disturbed zone. The general solutions are employed to formulate boundary value problems corresponding to a borehole subjected to axisymmetric loading applied at its surface, and contact problems of a rigid cylindrical plug in a borehole. Selected numerical results are presented to portray the influence of poroelastic effects and the excavation disturbed zone. 相似文献
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在既有公路下进行浅埋隧道开挖会引起地层产生位移,导致地表沉降。为了保证施工安全,快速精确地计算地层位移及应力,有效地控制地表沉降,对浅埋隧道的设计与施工均十分重要。在镜像法原理的基础上,引入等效模量当层法,推导出了在有上覆不同材料下浅埋圆形隧道开挖引起地层位移、应力及地表沉降的解析分布规律。计算结果表明,既有路基下开挖隧道引起地层产生的位移和应力解析解能够很好地体现上层高弹性模量路基对沉降及应力的扩散作用,可以求得隧道开挖后洞周地层包括上覆路基及下卧层中任意位置处的位移、应力以及地表沉降,为在双层地基材料中开挖浅埋隧道引起地层位移及地表沉降的计算提供了一种新的解析方法。 相似文献
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The overturning failure of a 13 storey residential building in Shanghai, China, has been investigated by plane strain finite element analysis (FEA). The results of the FEA indicate that ultimate failure of the building was probably initiated by the formation of tensile cracking in the reinforced concrete piles located under the side of the building adjacent to an excavation. This eventually led to complete structural failure of the piles located along the excavation side, which probably caused further settlement of the building, leading eventually to a toppling failure resulting in overturning of the entire building. Excessive tensile stress in the piles was probably caused by the combination of excavation of soil at one side of the building and the temporary dumping of the excavated soil on the opposite side of the building. It is likely that the effect of temporary dumping of the excavated soil adjacent to the building was either not considered or not properly taken into account in the foundation design nor the construction operations. A simple but important lesson to be draw from this failure is the need for engineers who design foundations in soft soil regions to consider not only the final loading conditions, but also any temporary and transient loading conditions during the construction process. 相似文献
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深埋洞室岩体开挖过程中,围岩应变能的聚集和释放是洞室发生灾变破坏的重要诱因。针对圆形洞室开挖,分析和比较初始地应力准静态和动态两种不同卸载方式下围岩应变能的调整过程,基于能量角度判定了围岩损伤范围。研究表明：伴随地下洞室的开挖,岩体能量靠径向应力做功的方式在围岩中由远及近传递,并导致近区围岩应变能聚集;初始地应力动态卸载诱发围岩应变能先减小后增大,先对靠近开挖面的相邻岩体通过径向应力做功的方式释放自身的应变能,随着卸载应力波的继续向前传播,远离开挖面的相邻岩体又通过径向应力对其做功的方式促使其应变能聚集;相比初始地应力准静态卸载,动态卸载条件下高应变能聚集程度导致围岩损伤破坏范围更大。 相似文献
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Laboratory and In Situ Simulation Tests of the Excavation Damaged Zone Around Galleries in Opalinus Clay 总被引：1，自引：0，他引：1
In the context of nuclear waste disposal in clay formations, laboratory and in situ simulation experiments were performed to study at reduced scale the excavation damaged zone (EDZ) around tunnels in the indurated Opalinus Clay at Mont Terri, Switzerland. In the laboratory, thick-walled hollow cylindrical specimens were subjected to a mechanical unloading mimicking a gallery excavation. In samples cored parallel to bedding, cracks sub-parallel to the bedding planes open and lead to a buckling failure in two regions that extend from the borehole in the direction normal to bedding. The behaviour is clearly anisotropic. On the other hand, in experiments performed on specimens cored perpendicular to bedding, there is no indication of failure around the hole and the response of the hollow cylinder sample is mainly isotropic. The in situ experiment at Mont Terri which consisted in the overcoring of a resin-injected borehole that follows the bedding strike of the Opalinus Clay showed a striking similarity between the induced damaged zone and the fracture pattern observed in the hollow cylinder tests on samples cored parallel to bedding and such a bedding controlled “Excavation” Damaged Zone is as well consistent with the distinct fracture patterns observed at Mont Terri depending on the orientation of holes/galleries with respect to the bedding planes. Interestingly, the damaged zone observed in the hollow cylinder tests on samples cored parallel to bedding and in situ around URL galleries is found to develop in reverse directions in Boom Clay (Mol) and in Opalinus Clay (Mont Terri). This most probably results from different failure mechanisms, i.e. shear failure along conjugated planes in the plastic Boom Clay, but bedding plane splitting and buckling in the indurated Opalinus Clay. 相似文献
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应变软化模拟与圆形隧道衬砌分析 总被引：1，自引：0，他引：1
在岩土工程中,有许多类岩体呈现应变软化特性。在应变软化过程中,如果多个材料强度参数分析发生变化,就很难给出软化问题的解析解。已有的文献研究表明,在经典的弹塑性理论框架下,模拟岩土介质的应变软化过程依然值得深入研究。利用应变软化材料强度参数随塑性应变增加而弱化的特点,提出了将应变软化过程简化为一系列的脆性应力跌落与塑性流动过程的思想,应变软化行为的模拟转化为一系列脆塑性过程的分析。将这种模拟应变软化过程的思想方法用于求解均匀初始应力场中应变软化介质内的圆形隧道开挖问题,研究了衬砌对减少岩土开挖扰动的作用以及考虑应变软化对衬砌内力的影响。数值结果表明,对于应变软化岩土材料,忽略其强度软化的行为是偏于危险的。 相似文献
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金丽温高速公路连拱隧道超挖预测及原因分析 总被引：3，自引：0，他引：3
通过对金丽温高速公路连拱隧道的地质特征进行现场调查,经分析得出隧道区岩体结构面的特征参数,利用分析出的结构面特征参数值,结合隧道超挖预测中的神经网络理论及结构面网络模拟理论,对连拱隧道的超挖情况进行预测。从分析结果看,超挖问题在连拱隧道的施工过程中不可避免,其产生部位主要集中在中导洞与隧道的连接部位,通过预测得出的结果与现场开挖情况进行对比分析说明,隧道的超挖预测理论预测结果与实际有较好的一致性,文中最后针对隧道的特点,分析了产生超挖的基本原因,为确保隧道开挖过程中减少超挖提供依据。 相似文献