【作者】 苏生瑞；

【导师】 王士天；

【作者基本信息】 成都理工学院 ， 地质工程， 2001， 博士

【摘要】 地应力是地质环境和地壳稳定性评价、地质工程设计和施工的重要基础资料之一。本文通过对大量实测地应力资料的深入分析和对云南丽江地区、川西北岷江上游地区等地区的现场地质调查,结合系统的数值模拟分析,进行了断裂构造对地应力场的影响及其工程意义的研究:(1)以相关领域的最新研究成果,系统研究了地应力的形成因素和影响因素,阐明了断裂在地应力场形成中的作用;(2)通过对国内外大量实测地应力资料的分析,分别研究了活动断裂和非活动断裂对地应力场的影响;(3)通过深入的现场调查和综合分析,研究了云南丽江地区和川西北岷江上游地区的断裂构造格架、主要断裂的现今活动性及其对应力场的影响;(4)通过应用离散元方法进行系统的数值模拟分析,研究了断裂引起附近应力场变化的规律及其机理;(5)通过工程实例的研究阐明了断裂构造对地应力场影响的工程意义。通过上述研究,本文取得了如下进展和新认识: (1)重力作用和地质构造运动是形成地应力的两个最基本的因素,地质构造、地形、岩性等则是影响地应力重要因素,而断裂构造是造成地壳岩体中应力发生复杂变化的主要因素之一。(2)不论是单一活动断裂还是复合活动断裂,均对岩体中的应力场有明显的影响。活动断裂附近的主应力方位和量值均不同程度地发生变化,而这种变化主要限于断裂附近一定距离内,远离断裂,逐渐趋于与区域应力场一致。同一条断裂不同段具有不同的应力状态,表现在最大主应力方向和量值都不同。活动断裂附近的应力是随时间而变化的,特别是在地震活动区。复合活动断裂能造成在断裂复合部位的局部应力集中,产生地震和其它高地应力现象。(3)非活动断裂对其附近的应力场也有明显的影响。在断裂附近,应力方位发生转向,旋转角度可从十几度到近90°度。断裂组成地应力局部分区的界面,断层的上盘与下盘应力大小和方向都有差别。断裂发育的复杂程度与地应力的变化的幅度密切相关。(4)本文首次用离散元方法对断裂构造对地应力场的影响进行了全面系统的模拟分析,揭示了断裂构造对地应力场的影响的规律及其机理。通过模拟分析可知,断层附近应力方位变化的幅度和发生变化的范围因断层的力学性质、围岩的物理力学性质及边界条件等的不同而不同。断层的内摩擦角(φ)和边界应力比值(K_b)及断层方向与边界最大主应力方向之间的夹角(α)对断层附近应力方位发生变化的范围和幅度影响最大。发生变化的范围随着断层的内摩擦角的增大而减小,随着边界应力比值的增大而增大。在影响断层附近应力方位的因素中,断层的内摩擦角是最重要的因素。(5)通过使用Kulatilake 等提出的起到完整岩石作用的假节理(或断裂)(fictitious joints)的方法成功地模拟分析了断层端部的应力状态。(6)现场调查和数值模拟分析结果表明,云南丽江地区和四川岷江上游地区的地应力场以及地震活动等受断裂的复合的影响。更多还原

【Abstract】 Knowledge of the in situ stress in the Earth’s crust is very important for many problems in civil, mining and petroleum engineering as well as in geology and geophysics. Despite the importance of in situ stress and the development of a variety of methods to determine in situ stresses in rock masses, rock stress has not been well understood. Fracture is one of the most important factors affecting rock stresses and results of site measurements indicate that there exist reorientation and magnitude variation of stresses in the vicinity of fractures. This thesis is intended to study the effect of fractures by site measurement analysis, field geological survey and numerical modeling. It consists of five parts: (1) By studying current results in rock stress and its measurement, the factors in generating and affecting rock stresses is analyzed and the role of fractures in disturbing in situ rock stresses is documented; (2) By carefully studying the in situ stress measurement results over the world, the general features of the effect of both active faults and inactive faults on rock stresses are concluded; (3) The geological structural characteristics and the modern activities of major active faults in Lijiang region of Yunnan Province and upper stream of Minjiang River in Sichuan Province of West China and their effect on rock stresses are studied through site investigation and laboratory tests. (4) By systematic numerical modeling by the distinct element method with UDEC code, the features of rock stress perturbation caused by the existence of fractures ( both single fracture and compound fractures) and the mechanism are analyzed; (5) The significance of rock stress perturbation produced by fractures in geological engineering is discussed on the basis of engineering practice both in regional crustal stability and rock mass stability. The main conclusions drawn from this study are as follows: (1)Gravitation and tectonic movement are the fundamental causes for producing rock stresses. While factors that may influence rock stresses are various, such as geological structures, topography, rock types and the so on. However, the effect of fractures on rock stresses is very common, and the existence of fracture is one reason of the complicated variations of rock stresses in the Earth’s crust. (2)Both a single active fault and compound active faults can perturb stresses in rock masses, Compared with regional stress, the orientation and magnitude of stresses around active faults changes in different extent, and most of this kind of change occurs in a certain range around the fault. However, the orientation of principal stresses trends to be in line with regional stress far from the fault. The variation of stress magnitude around active faults is a little bit complex, that is, stresses may be increased or be decreased. The decrease in stress magnitude is manifested by being lowered near the fault, increasing with the distance from the fault and becoming constant at certain distance from the fault. Increase or decrease of stress magnitude is determined by the geometry of the fault and the angle relations between the orientation of regional stress and that of fault, and the magnitude of variation largely depends on the scale of faults concerned. There are different stress regime in different sections along a fault, both in the orientation and magnitude of principal stresses. Stress regime in the vicinity of active faults changes with time, especially in the seismically active region. Compound active faults can lead to local stress concentration near the fault, generating earthquakes and high-stress phenomena. The effect of compound fault on stresses is strongly controlled by the geometry of the fault. The geometry of any single fault among the compound faults may influence the stress regime. (3) Non-active faults also have an effect on the stress field near fractures. Near fractures, the stress may reorients in an angle as large as 90°. Fractures make up local interface of stress regime, and both magnitude and orientation may be different at the two sides of a fault. The density and intersection of fractures determine the magnitude of stress variation. (4)Numerical modeling by the distinct element method demonstrate much information about stress variation caused by the existence of fractures. It is found from modeling that the variation stresses in the vicinity of fractures depends on the mechanical and strength properties of both fractures and rock masses as well as boundary conditions. The range of stress variation is strongly determined by the friction angle (φ) of the fault, the boundary stress ratio (Kb=σ1/σ2) and the angle (α) between the fault and the direction of regional maximum principal stress. Among the mechanical properties of faults influencing the stresses around a fault, the friction angle is the most important of those studied. (5) By employing the technique that uses fictitious joints behaving as intact rock, the stress state at fault ends is successfully modeled. (6) Site investigation and numerical modeling indicate that the stress field and seismic activity in Lijiang region of Yunnan Province and the upper stream of Minjiang River are controlled by the compounding of active faults. (7) The stress field in ?sp? area of Sweden is much dependent on the development of fractures and their combination. (8) The effect of fractures on rock stresses may be successfully applied to solve the problems concerned with geological engineering like regional crustal stability and rock mass stability. (9) The study of this thesis is a contribution to understand rock stresses in the Earth’s crust and provides theoretical evidence for the evaluation of crustal stability and design of rock engineering.更多还原