A study of the permeability of fractures with variable attitude in rock mass subjected to natural crustal stresses
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摘要:
为了研究天然地应力作用下裂隙产状等因素对深部岩体裂隙渗流特性的影响，基于单裂隙面渗透性服从负指数变化规律，建立了三维应力作用下不同产状裂隙的渗透系数计算公式，利用Lagrange乘子法分析裂隙面产状变化对其渗透性的影响，并分析了岩体裂隙有、无充填物对其渗透性的影响及敏感性；然后，以我国大陆地区地应力统计规律为例，分析了地表以下5000 m范围内在天然地应力作用下裂隙渗透性随深度、产状的变化规律。结果表明：裂隙产状的变化对其渗流特性有明显影响，对于浅层岩体，在大主应力大致呈水平方向分布时，随着裂隙面倾角的增加，裂隙渗透系数逐渐降低；但随着深度的增加，在裂隙深度超过约200 m和裂隙面走向与大或中主应力方向大致一致时，裂隙渗透性反而会随着裂隙面倾角的增加逐渐增加，在裂隙面走向与小主应力方向垂直时增加最为明显；对于深部岩体，裂隙的渗透性很小，裂隙面产状的变化对其渗透性影响很弱；对于有充填物裂隙，岩块与充填物的弹模比和充填物泊松比的变化对裂隙渗透性的影响很小。研究结果可为深入研究我国深部岩体渗透特性变化规律提供借鉴意义。
Abstract:In order to investigate the influence of fracture attitude variation on the permeability of fractures in deep rock mass under natural crustal stresses, based on the permeability law of a single fracture obeying the law of negative exponential change, the theoretical formula of coefficient of permeability of fractures with variable attitude subjected to 3D stresses is proposed. The Lagrange multiplier method is applied to analyze the change of variable attitude on fracture permeability, and influence factors and sensibility of fracture permeability with or without infillings are also analyzed. Statistic law of crustal stress in Chinese mainland is taken as an example, and the variable laws of the permeability of fractures in rock mass with depth and fracture attitude are analyzed. The results show that (1) the permeability of fractures in rock mass is obviously influenced by the attitude of fractures. For shallow rock mass, under the condition of the maximum principle stress distribution in the horizontal direction, the permeability of fractures gradually decreases with the increasing dip angle of fractures; but with the increasing depth, when the depth is more than 200 m and the strike of fracture is roughly consistent with the direction of large or medium principal stress, the permeability of fractures can increase with the increasing dip angle of fractures, especially the strike of fractures perpendicular to the direction of the minimum principle stress. For deep rock mass, the permeability of fracture is very weak, and the impact of fracture attitude change on its permeability is very slight. (2) For fractures with infillings, the change of elastic modulus ratio of rock block to infillings and Poisson’s ratio of infillings have little effect on fracture permeability. The conclusions can be used for reference for further investigating the variation of deep rock permeability characteristics.
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