岩石裂隙渗流与法向应力耦合的复合单元模型

COMPOSITE ELEMENT MODEL OF SEEPAGE-NORMAL STRESS COUPLING FOR ROCK FRACTURES

首先,基于复合单元原理,建立渗流与法向应力耦合分析的复合单元模型,该模型前处理简便快捷,可含有一组或几组有明确定位的裂隙面,且可考虑裂隙面与相邻岩块的流量交换;然后,采用两场交叉迭代算法,对岩石裂隙的渗流场与应力场进行耦合分析。模型中视岩石裂隙为虚拟的"充填介质",采用"充填模型"将有充填和无充填的岩石裂隙统一处理,并进行裂隙面开度与其法向有效应力关系的推导。依据的耦合机制为:法向应力的作用导致裂隙面开度的变化,从而引起裂隙面导水系数的改变,以至渗流场的改变,从而反过来影响应力场。算例分析表明法向应力作用会引起裂隙岩体的渗透不均匀性:局部区域的渗透坡降、扬压力和渗透流速显著增大。研究结果表明在裂隙岩体中进行渗流与应力耦合分析的重要性。

Based on the principle of the composite element method（CEM）,the composite element model of seepage-normal stress coupling for rock fractures is built firstly,with the preprocessor being simple and convenient and containing one or more sets of fractures with specified orientations.The CEM model can further take into account the exchange of the flow rate between fracture and the adjacent rock masses.Secondly,the seepage-normal stress coupling analysis for rock fractures is realized by applying the iterative algorithm between the two fields.The rock fractures are assumed as a filled medium in the model,which enables to treat the rock fractures with or without fillings in a unified way.The relationship between the aperture and the normal effective stress is deduced.The coupling mechanism can be described as follows：in one hand,the normal stress leads to the change of the aperture,which further leads to the change of the conductivity of the rock fracture;on the other hand,the change of the conductivity of the rock fracture brings change of seepage field causing changes of the stress field correspondingly.The numerical example indicates that the normal stress results in the non-uniform hydraulic behavior of fractured rock massest：he hydraulic gradientt,he uplift,as well as the seepage speed in local area where the normal stress acts on increase remarkably.Therefore,the importance of the seepage-normal stress coupling analysis in fractured rock masses is emphasized.