【作者】 范雷；

【导师】 唐辉明；

【作者基本信息】 中国地质大学 ， 岩土工程， 2009， 博士

【摘要】 裂隙岩体是坝基、边坡、地下硐室等岩体工程中广泛遇到的一类复杂介质，它的变形、强度和地下水渗透性等力学特性将直接影响到各类岩体工程的设计与施工，以及工程运营期间的长期稳定性。而工程岩体又是工程地区地质体的组成部分，它存在于一定地质环境中，其形成和发展经过地质历史时期内各种外动力地质作用的改造和影响。因此岩体受各种结构面切割而具有一定的结构特征，并表现出强烈的非均质性、不连续性以及各向异性。岩体的变形、破坏等力学性状也受到岩体结构特征的制约。传统的均质、连续、各向同性的力学分析方法不再适用于裂隙岩体的评判。对岩体结构条件进行定量化研究，在考虑其结构特征的基础上研究其变形及破坏特性，是岩体力学的一个重要研究课题。岩体内部的结构面的产状、分布常常决定着整个岩体的力学特性。岩体的失稳和破坏最终都是通过岩体内部这些裂隙的张开、闭合和扩展进而形成的贯通破裂面所引起的。因此，从岩体中结构面分布状况入手进行研究，才能获得对裂隙岩体变形和强度特性的正确认识。在野外结构面测量的基础上，利用Monte-Carlo原理计算机再现岩体结构面网络，可以使模拟结果与岩体结构面实际分布在统计规律上一致，从而可以建立岩体结构模型，为进一步研究岩体的力学特性提供依据。由于裂隙岩体中结构面的大量存在，很难通过原位实验或室内实验确定岩体宏观力学参数。近年来，随着断裂理论、损伤理论、分形几何、模糊数学等非线性科学的发展，国内外专家学者提出了多种模型来估算岩体宏观力学参数。但岩体在不同应力状态下裂隙间的相互作用原理，复杂应力状态下裂隙岩体的变形及强度特征等仍是理论研究的难点，至今还没有很好地解决。随着数值模拟技术的日益强大，综合现场地质调查、结构面统计、室内小试件试验成果，模拟岩体裂隙，研究不同尺度的“岩体试件”力学行为的数值试验研究方法近来发展迅速，为探讨分析裂隙岩体力学特性、破坏机理及合理确定岩体的宏观力学参数开辟了一条新的途径。由于裂隙岩体的强度、变形及稳定性主要受结构面控制，因而对结构面的模拟成为这些数值分析方法的关键。基于牛顿运动第二定律的离散单元法是一种适于分析裂隙密集的岩体或离散体的力学行为的数值方法，可以较好的研究岩体等非连续介质的力学行为。但是，目前对它的研究还只是在探讨和实践阶段，还需要不断的应用、比较和改进。鄂西恩施地区属云贵高原的东延部分，地近四川盆地边缘，处于我国地形第二阶梯末端的大陆地形坡降带上，岩石边坡通常处于复杂的地质环境并具有复杂的地质结构。鄂西志留系砂岩在各种内外地质营力作用下，岩石结构构造易破坏，因而砂岩岩层中构造裂隙、节理发育密集。砂岩地层一旦出露地表，在外力的触发下岩体易产生变形破坏，引发崩塌、滑坡、泥石流等地质灾害。本课题在系统科学方法论的指导下，采用现场调研、工程地质分析、统计分析、室内试验、力学计算、计算机模拟相结合的综合研究方法，分析鄂西志留系砂岩结构面的地质历史成因、随机分布规律，概化建立典型砂岩岩体结构模型，采用计算机数值模拟方法对不同结构特征的裂隙砂岩进行不同尺度的数值试验，寻求鄂西志留系裂隙砂岩的变形特征及破坏模式，合理确定砂岩岩体变形参数及强度参数，指导工程实践。因而论文主要完成了下几个方面的工作：(1)裂隙砂岩岩体结构特征研究。鄂西恩施地区构造体系是经过印支运动、燕山运动和喜马拉雅运动长期演化发展而成的，志留系砂岩岩层先后经过N-S向压应力、N-S向扭动、NW-SE向压应力和E-S向压应力作用后，产生了以NW、NE、NNW与NEE向为优势方位的结构面。各组优势结构面倾向均服从正态分布，倾角除第三组服从负指数分布外，其它三组均服从对数正态分布，半迹长和隙宽一般服从负指数分布。在砂岩层面和随机分布结构面的互相交错切割下，裂隙砂岩岩体结构模型可概化为层状岩体结构，双组贯通裂隙岩体结构和耦合随机分布裂隙岩体结构三类模型。(2)通过砂岩室内试验，获取岩块弹性模量与泊松比分别为7．4GPa和0．25(均值)，抗剪强度参数内摩擦角为42．3°，内聚力为12．9MPa。(3)砂岩结构面本构模型及其力学参数研究。采用幂函数模型可较好的反映结构面闭合变形特性。对于法向循环加载试验，则提出了直线-圆弧型本构方程，分别用直线和圆弧线来拟合砂岩结构面的加载曲线和卸载曲线，以描述结构面法向循环加载过程中的回滞特性和整体现硬化特性。此外，还提出了半对数函数型式剪切变形本构模型反映结构面剪切变形特性。在中低法向应力作用下，采用物理意义明确的三参数Mohr-Coulomb抗剪强度准则即可较好的表示结构面抗剪强度特性。(4)砂岩岩块和结构面离散元数值试验研究。通过对砂岩岩块和结构面数值拟合试验，证明岩块数值压缩试验结果和结构面直剪数值试验结果与室内实物试验结果是一致的，说明采用离散单元数值试验方法研究岩体的力学行为是可靠的。(5)裂隙砂岩岩体变形特性及其变形参数研究。裂隙砂岩受压变形特性及等效变形参数与岩体结构模型、不同组系结构面间的交切情况、分析域的尺寸大小、岩块和结构面的变形参数等因素有关。层状砂岩宏观等效变形模量为3．91GPa～7．36GPa，等效泊松比为0．13～0．34；双组贯通裂隙砂岩宏观等效变形模量为3．25GPa～4．86GPa，等效泊松比为0．12～0．34；耦合随机分布裂隙砂岩宏观等效变形模量为1．68GPa～2．75GPa，等效泊松比为0．18～0．29。并且，层状砂岩和双组贯通裂隙砂岩变形参数关于层面方向和层面法向方向对称，而耦合随机分布裂隙砂岩变形参数仅关于层面方向对称。其中，层状砂岩等效变形参数的各向异性最明显，尺寸效应最不明显，耦合随机分布裂隙砂岩等效变形参数各向异性最不明显，尺寸效应最明显，双组贯通裂隙砂岩等效变形参数的各向异性和尺寸效应介于两者之间。(6)裂隙砂岩岩体破坏模式及其强度参数研究。裂隙砂岩受压破坏特征及其抗剪强度参数与岩体结构模型、不同组系结构面间的交切情况、分析域的尺寸大小、岩块和结构面的变形参数等因素有关。随着裂隙砂岩所含结构面的逐渐增加，岩体的抗剪强度参数逐渐减小。并且岩体所含结构面数量越多，其强度参数的各向异性越不明显，但其尺寸效应则越明显。层状砂岩内摩擦角为29．7°～42．3°，平均值为38．6°，内聚力为0．1～12．9MPa，平均值为7．2MPa；双组贯通裂隙砂岩内摩擦角为29．5°～42．1°，平均值为35°，内聚力为0．2～12．6MPa，平均值为6．1MPa；耦合随机分布裂隙砂岩内摩擦角为28．3°～38．1°，平均值为32．5°，内聚力为0．2～13．5 MPa，平均值为2．65MPa。层状砂岩的破坏模式与主应力方向密切相关，随着主应力方向与层面夹角的增大，岩体将产生三种不同的破坏模式：岩块材料的剪切破坏、岩块材料的剪切破坏联合沿层面的滑动破坏和沿层面的滑动破坏。对于双组贯通裂隙砂岩，当主应力与层面平行或夹角较小时，岩体产生由岩块材料的屈服而导致的整体破坏；当主应力与层面夹角逐渐增大时，岩体的破坏模式将转变为局部岩石块体的剪切屈服联合陡倾结构面形成贯通的联合破坏面的破坏模式；当主应力与层面夹角增大到45°到60°左右时，岩体以沿结构面的错动破坏为主。耦合随机分布裂隙砂岩的破坏路径不但与主应力方向有关，而且还与围压的大小、岩体模型的大小有关，但其最易发生破坏的路径为与最大主应力夹角在30°～45°之间的裂隙或岩块组成联合破坏面。(7)关于非贯通裂隙对砂岩岩体力学参数影响的探讨研究。对于应力状态较低的浅表岩体工程，岩体内部与主应力方向夹角较小的非贯通裂隙对岩体变形参数的影响是可以忽略的，对于与主应力方向夹角较大的非贯通裂隙则应根据实际工程对岩体整体变形的要求来考虑其对岩体变形参数的影响。但是，随着岩体非贯通裂隙的扩展开裂，其所需施加在岩体上的竖向压力越来越大，因此工程岩体应力水平较低时，在最大主应力增大到导致其中非贯通裂隙扩展开裂之前，岩体己经可能沿其包含的贯通裂隙组合而成的联通路径发生破坏。此时，非贯通裂隙对岩体破坏影响不大，岩体破坏主要受贯通裂隙的控制，非贯通裂隙对岩体强度的影响可以忽略不计。更多还原

【Abstract】 Fractured rockmass is a kind of complex medium which is existing in dam foundation engineering, slope engineering, underground chamber engineering and so on. Its mechanical characteristics, such as deformation, strength, and penetrability of groundwater, can affect the design, construction and the long term stability of rockmass engineering directly. The engineering rockmass is a part of the geologic body in the engineering area. It is existing in a certain geological environment. The formation and development of rockmass has been affected and changed by all kinds of external dynamic geological process in geological history period. So the rockmass has been cut by discontinuities, and has a certain of structure characteristic. The rockmass shows itself as heterogeneous, discontinuous and anisotropism strongly. The deformation and failure of rockmass are also controlled by its structure characteristics. The traditional mechanical analysis methods for homogeneous, continuous and isotropy medium will not be suitable to evaluate the fractured rockmass. The study of deformation and failure of rockmass based on quantitative analysis of its structure conditions is an important question for discussion of the rockmass mechanics.The mechanics of the whole rockmass is always defined by the orientations and distributing of the discontinuities in rockmass. The failure and breakage of rockmass are all begeted by the connected fracture planes which come into being of rupturing, closing and expanding of cracks in rockmass. So, the distributing of rockmass discontinuities should be studied first. And then the deformation and strength properties of fractured rockmass can be realized correctly. Based on surveing discontinuities in the field, the discontinuity network can be rebuilded on the computer with the Monte-Carlo theory. The simulation results can be consistent with the real distributing of rockmass discontinuities in a statistical rule. So we can set up the models of rockmass structure to provide a basis for the further study of the mechanics of fractured rockmass.Because of the large number of discontinuities existing in rockmass, it would be very hard to confirm the macromechanical parameters of rockmass by in-situ tests or lab tests. In recent years, with the development of nonlinear science of fracture theory, damage theory, fractal geometry, and fuzzy mathematics, many kinds of models have been adopted to estimate the macromechanical parameters of fractured rockmass. However, the reciprocity theory of discontinuities in different stress conditions and the deformation and strength properties of rockmass in complex stress conditions are still the theoretics research difficulties, and have not yet been solved very well.With the development of numerical simulation technique, numerical test method, which colligate the results of is-situ investigations, discontinuities statistic, lab tests with small samples, can simulate the rockmass fractrures and its mechanical behavior with different scales. It provides a new approach to study the mechanical properties, failure theory and confirm its macromechanical parameters of fractured rockmass. As the deformation, strength and stability of rockmass are mainly controlled by the discontinuities, the simulation of discontinuities is become the key problem of these numerical methods. Distinct Element Method, based on the Newton’s second law of motion, is especially adapted for discontinue deformation analysis of fractured rock mass. At present, the study of Distinct Element Method is still at the beginning phase, and much achievement need to be applied, compared and improved.The Enshi area in the west of Hubei Province, which locats on the end of the second ladder landform of China, is a part of the expend of Yunnan and Guizhou Plateau, and nearby the Szechwan basin. The rock slopes are often in a complex geological enviroment and have complicated geological structures. Because of all kinds of internal and external dynamic geological process, the structure of Silurian fractured sandstone rockmass can be destroied easily. Joints and fractures are very dense in these sandstone rockmasses. When the Silurian fractured sandstone stratum emerged on the ground, the fractured sandstone rockmasses can be deformed and breakaged by outside force. And the geological disasters of falling, sliding and debris flow may be induced.This study is under the guide of system science methodology. In-situ investigations, engineering geological analysis, statistic analysis, lab. tests, mechanic calculations and computer simulations are adopted for the research. The geological history cause of formation and stochastic distributing rule of the discontinuities in Silurian fractured sandstone rockmass have been analyzed. Numerical tests with different scale models of different structure characteristics of fractured sandstone rockmasses have been carried out in order to look for the deformation properties, failure modes, and estimate the defromation parameters and strength parameters. And they can be applied in engineering practice. So the main task completed in this paper are as follows:(1)Study on the structure characteristics of fractured sandstone rockmass in the west area of Hubei Province. The structural system in Enshi area in the west of Hubei province is come into being by Indosinian movement, Yanshan movement and Himalayan movement in a long term. The Silurian fractured sandstone stratum are effected by N-S compressive stress, N-S compressive-shear stress, NW-SE compressive stress, E-S compressive stress from early to late. And the NW, NE, NNW and NEE are the predominance directions of discontinuities. Each group of the discontinuities azimuth submits to normal distribution. The discontinuities obliquity of the third group submits to negative exponential distribution, and the others submit to logarithm normal distribution. The half trace length and aperature of the discontinuities submit to negative exponential distribution generally. With the intersection of sandstone layer and stochastic distributing discontinuities, the structural model of fractured sandstone rockmass can be generalized into three types: layered rockmass model, rockmass model contained fracturs attribute to two groups and rockmass model contained stochastic distributing discontinuities.(2)The mechanics of sandstone are obtained by lab tests. The average value of deformation modulus is 7.4GPa, the average Poisson’s ratio is 0.25, the shear strength parameter internal friction angle is 42.3°, and the cohesion is 12.9MPa.(3)Study on the constitutive model and mechanical parameters of sandstone discontinuities. The power function model can represent the deformation properties of discontinuities fairly well. According to the results of normal cyclic loading tests, a linear-arc curve model is adopted. The linear model is adopted to fit the loading curve and an arc curve model is adopted to fit the unloading curve. The linear-arc curve model not only represent the sclerotic properties during the normal cyclic loading process of discontinuities, but aslo reproduce the hysteresis loops in cyclic loading tests. Besides, a half-logarithm function model is adopted to represent the shear deformation curves of sandstone discontinuities. In the low stress conditions, the the three parameters in three-parameter Mohr-Coulomb strength criterion can represent the shear strength properties of the discontinuities.(4)Study on the numerical tests of rock blocks and discontiuities. Through the numerical tests of rock blocks and discontinuities, the results of numerical compress tests of rock blocks and shear tests of discontinuities are consistent with the lab tests. It shows that the study of rockmass mechanical actions by numerical tests with Distinct Element Mehtod is reliable.(5)Study on the deformation properties and its deformation parameters of fractured sandstone rockmass. The compressive defromation properties and equivalent deformation parameters have a close relation to these factors: structure model of rockmass, network of discontinuities, analysis scale of rockmass, deformation parameters of rock blocks and discontinuities and so on. The macro equivalent deformation modulus of layered sandstone rockmass change from 3.91GPa to 7.36GPa, the equivalent Poisson’s ratios change from 0.13 to 0.34; The macro equivalent deformation modulus of sandstone rockmass contained fractures attribute to two groups change from 3.25GPa to 4.86GPa, the equivalent Poisson’s ratios change from 0.12 to 0.34; The macro equivalent deformation modulus of sandstone rockmass contained stochastic distributing discontinuities change from 1.68GPa to 2.75GPa, the equivalent Poisson’s ratios change from 0.18 to 0.29. The deformation parameters of layered sandstone rockmass and sandstone rockmass contained fractures attribute to two groups are symmetrical with layer direction and its normal direction. The deformation parameters of sandstone rockmass contained stochastic distributing discontinuities are symmetrical with layer direction. Besides, the anisotropy of equivalent deformation parameters of layered sandstone rockmass is the most conspicuous of all, but its scale effect is the most unconspicuous; the anisotropy of equivalent deformation parameters of sandstone rockmass contained stochastic distributing discontinuities is the least conspicuous of all, but its scale effect is the most conspicuous; and the anisotropy and scale effect of sandstone rockmass contained fractures attribute to two groups are between the layered sandstone rockmass and sandstone rockmass contained stochastic distributing discontinuities.(6)Study on the failure modes and its strength parameters of fractured sandstone rockmasses. The failure properties and shear strength parameters have a close relation to these factors too, such as structure model of rockmass, network of discontinuities, analysis scale of rockmass, deformation parameters of rock blocks and discontinuities and so on. With the quantity of discontinuities increasing, the equivalent shear strength parameters of fractured rockmass will minish gradually. And the quantity of discontinuities is bigger, the anisotropy of the strength parameters is less conspicuous, but its scale effect will be more conspicuous. The shear strength parameter internal friction angles of layered sandstones change from 29.7°to 42.3°, and the average value is 38.6°; the cohesions change from 0.1 to 12.9MPa, and the average value is 7.2MPa. The shear strength parameter internal friction angles of sandstones contained fractures attribute to two groups change from 29.5°to 42.1°, and the average value is 35°; the cohesions change from 0.2 to 12.6MPa, and the average value is 6.1MPa. The shear strength parameter internal friction angles of sandstones contained stochastic distributing discontinuities change from 28.3°to 38.1°, and the average value is 32.5°; the cohesions change from 0.2 to 13.5MPa, and the average value is 2.65MPa. The failure mode of layered sandstone has a close relation to the principal stress directions. With the angles between the layer direction and the principal stress directions increasing, three different failure modes will happen: shear yield of rock block, mixed failure of rock block and disncontinuities and slide failure along the discontinuities. When the principal stress parallel to the layer of rockmass or the angle between them is on the small side, holistic failure caused by the yield of rock block material will happen in the fractured sandstone rockmass contained fractures attribute to two groups. When this angle become bigger, the failure mode will be changed to another one, combining failure surface of local rock block yield surface and discontinuities with steep dip angles. When this angle is between 45°and 60°more or less, the main failure mode is slide along the discontinuities. However, the failure modes of fractured rockmass contained stochastic distributing discontinuities not only have a relation to the principal directions, but also have a relation to the confining pressures and the scale of rockmass models. And the failure paths are mostly the combined surfaces of the discontinuities which have an angle of 30°to 45°to the maximum principal stress.(7)Discussion on the influences of the intermittent fractures to the mechanical parameters of rockmasses. For rockmass engineering in shallow surface, the influences of these intermittent fractures to the equivalent deformation parameters can be ignored, which have small angles with the principal stress directions. However, for these intermittent fractures, which have large angles with the principal stress directions, its influences should be considered with the deformation standard of the whole engineering rockmass. However, with the expanding and cracking of the intermittent fractures in sandstone rockmass, the vertical compressive stress inflicted on the rockmass should be more greater. So if the stress of engineering rockmass is low, before the intermittent fractures are cracked by the maximum principal stress, a failure along a combined path of transfixed discontinuities may happen in the fractured rockmass. In this condition, the intermittent fractures have little influence to the failure of rockmass. The failure of rockmass is controlled by the transfixed discontinuities, and the influence of the intermittent fractures to the strength parameters of fractured rockmass can be ignored.更多还原