岩石节理力学参数的非线性估计

通过建立一个多层神经网络模型ＮＮ（ｎ,ｈ１,ｈ２,１）,探讨了描述节理开度与剪切位移之间的非线性关系和尺度效应的新方法,由小尺度试件节理的实测数据建立的非线性模型可以推广地预测出较大一些尺度试件的节理开度值。对３７条现场实测的节理进行了分形特征研究,建立了分形维数与ＪＲＣ关系式,该关系式可用于ＪＲＣ值的近似分形预测     

一种用于计算JRC的节理面起伏形态表征方法

通过间隔取样的方式将Barton所提出的十条标准JRC曲线离散化,获取其离散数据点后尝试不同的函数形式对离散数据点进行拟合,探求能够描述节理面剖面线起伏形态的函数表达式。在获取节理剖面线的近似函数表达式后用其计算标准JRC曲线的节理参数。分析对比拟合结果与节理参数计算结果发现:节理面剖面线具有较强的三角函数特性,利用正弦函数逼近获取的近似函数表达式在形态上可以很好地表征节理面的起伏情况,并可以近似代替节理曲线对JRC值进行计算,其结果相比较于通过离散点得到的计算结果更为精确。这也为进一步利用JRC-JCS模型准确计算节理面剪切强度奠定了基础。     

新的岩石节理粗糙度指标研究

首先,基于节理轮廓线提出一个剪切粗糙度指标(SRI),新指标由3个粗糙度参数构成,描述节理平均起伏度、起伏的方向性、起伏分布特点以及粗糙的分形特性,并建立新指标与JRC之间的拟合关系。其次,基于三角形面积单元离散的三维节理面,将剪切粗糙度指标推广到三维形式,从而使得新指标能够描述节理的三维形貌特征。最后,以张拉型花岗岩节理作为算例,计算结果表明新指标能较好地反映节理的各向异性粗糙特性。新指标物理意义明确,计算方便,能够表征节理的主要粗糙特性,为进一步研究岩石节理的剪切力学特性奠定基础,具有重要的理论意义。     

Numerical simulation of a direct shear test on a rock joint using a bonded-particle model

Rock joints were numerically simulated, and an extensive series of direct shear tests were carried out using the code PFC3D. The feasibility of reproducing a rock joint using the contact bond model was demonstrated, and the effects of the geometrical features and the micro-properties of a joint on its shear behavior were examined. Asperity failure was observed from the micro-cracks and contact force distribution, as well as the stresses and displacements in shear and normal directions. A rough joint with a joint roughness coefficient (JRC) value ranging from 10 to 20 was produced in an intact sample by defining the joint-contacts along a predefined joint surface. To simulate a decrease in joint wall strength (JCS) caused by weathering and alterations, the bond strength between particles involved in the joint-contacts was reduced by up to 70%. The shear behavior and failure progress at a given stress corresponded well to those observed in laboratory tests. The friction coefficient was the most important factor governing the shear strength and dilation angle. The variation in joint roughness and contact bond strength had a larger effect on the cohesion than peak friction angle. In addition, a new approach to represent JRC and JCS values of a joint was proposed for practical use. A numerical 3D-profile scanning technique was developed to evaluate the actual JRC of the simulated joint, and the relationship between the JCS and the contact bond strength was investigated.     

Grasselli节理峰值抗剪强度公式再探

 确定节理峰值抗剪强度公式面临的首要问题是获取节理表面形貌并合理的评价其粗糙度。常用的方法是节理粗糙度系数(JRC)评价方法,但JRC的评价结果是基于二维剖面线获得的,该方法低估了节理面的粗糙度且具有较大的主观性。节理面形貌测试表明,节理面微元有效剪切倾角 与≥ 的微元面积的总和与节理总面积的比值呈高次抛物线关系。基于42组不同形貌节理的直剪试验结果,将节理的峰值剪胀角与形貌参数相联系,提出新的能够考虑剪胀效应的节理峰值抗剪强度公式。新峰值抗剪强度公式符合莫尔–库仑摩擦定律的形式,具有明确的物理含义。所需要的参数均由节理面形貌测试确定,因此能够预测节理的峰值抗剪强度。最后,对已有的节理峰值抗剪强度公式进行比优统计分析并建议公式的使用范围。     

深部花岗岩中天然开启节理剪切性能试验研究

针对取自中国高放废物地质处置首选预选区深部花岗岩中的天然开启节理,基于室内试验对其剪切性能进行了测试分析。首先开展了垂直于节理面的压应力循环加卸载测试,之后在不同压应力条件下开展了天然节理直剪试验。同时,借助三维激光扫描技术获得了剪切面精确面积,并实现了节理面粗糙度评价。测试结果表明:在对应的深部地应力条件下,天然开启节理处于压密状态,且压应力幅值的变化不会使得开启节理产生不可恢复的变形;同一条节理在室内试验尺度上的剪切性能具有一致性,不同深度处节理的剪切性能也具有相似性;节理粗糙系数(JRC)与剪切强度参数之间未发现明显的相关关系。上述研究结论以及获得的Mohr-Coulomb强度参数可以为后续现场试验和数值分析提供初步依据。     

岩体节理粗糙度系数与统计参数的相关关系研究

 测定节理粗糙度系数JRC的方法均基于10条标准剖面,其人为误差大,且未考虑采用不同取样长度离散节理剖面对各统计参数与JRC的影响。为避免对10条标准剖面JRC的测量误差,考虑JRC的取值范围及离散节理剖面时不同取样长度的影响,从数值模拟粗糙节理的角度出发,采用截断正态分布随机抽样得出节理凸起高度,由每段的凸起高度及取样长度形成凸起表面,叠加生成具有一定迹长的粗糙节理,根据Barton直边法测量其JRC,计算相应的统计参数,研究不同取样长度下各统计参数与JRC的回归关系。研究结果表明：JRC与均方根RMS和中线均值CLA呈线性关系,JRC与均方值MSV,均方根一阶导数Z2,粗糙剖面系数Rp和结构函数SF之间呈抛物线关系,且相关系数均较高;取样长度对统计参数、JRC及其回归关系式有较大影响,在数值模拟粗糙节理时应使取样长度与岩体粒径相近。由于MSV,RMS和CLA只能反映节理起伏高度的均值状况,不能反映各凸起高度所占权重对JRC的影响,因此,建议采用Z2,SF对JRC进行估算。     

砂岩劈裂裂隙多因素影响下可视化渗流规律研究

基于自主研发的可视化试验装置,应用颜色示踪技术,进行空间多角度砂岩裂隙渗流试验;通过采用图像不同灰度面积处理技术、裂隙面积分析方法,进行图像分区并统计其渗流面积,首次从可视化角度得出在不同法向应力、渗透压、倾角等多因素影响下渗流扩散面积比关系式,指出裂隙渗流加速汇集效应和优势扩散面积区域。并基于裂隙面三维形态测试数据,获得裂隙面粗糙度精确JRC值,利用该JRC值得到裂隙面二维粗糙度云图,并与渗流扩散面积图像相结合,从而确定渗流优势路径范围,指出低粗糙区域是渗流的主要过流路径,进而解释了渗流扩散区域会随倾角增大而减小原因,为隧道工程实践中的防渗封堵提供依据。     

模袋水泥土的界面粗糙度和抗剪强度的分形估算

基于分形几何理论,运用均方根坡度角法(ARMSS)对模袋水泥土的截面轮廓线进行了分形指标(β、A、D)的估算,测算出截面轮廓线的粗糙度系数JRC,并在此基础上结合JRC-JCS模型估算出模袋水泥土界面的抗剪强度,研究表明:ARMSS法能方便、快捷地推算出该类截面轮廓线的JRC,摆脱传统的带主观性和随意性的JRC判定方法...     

Nonlinear shear behavior of rock joints using a linearized implementation of the Barton-Bandis model

Experiments on rock joint behaviors have shown that joint surface roughness is mobilized under shearing,inducing dilation and resulting in nonlinear joint shear strength and shear stress vs.shear displacement behaviors.The Barton-Bandis(B-B) joint model provides the most realistic prediction for the nonlinear shear behavior of rock joints.The B-B model accounts for asperity roughness and strength through the joint roughness coefficient(JRC) and joint wall compressive strength(JCS) parameters.Nevertheless,many computer codes for rock engineering analysis still use the constant shear strength parameters from the linear Mohr-Coulomb(M-C) model,which is only appropriate for smooth and non-dilatant joints.This limitation prevents fractured rock models from capturing the nonlinearity of joint shear behavior.To bridge the B-B and the M C models,this paper aims to provide a linearized implementation of the B-B model using a tangential technique to obtain the equivalent M-C parameters that can satisfy the nonlinear shear behavior of rock joints.These equivalent parameters,namely the equivalent peak cohesion,friction angle,and dilation angle,are then converted into their mobilized forms to account for the mobilization and degradation of JRC under shearing.The conversion is done by expressing JRC in the equivalent peak parameters as functions of joint shear displacement using proposed hyperbolic and logarithmic functions at the pre-and post-peak regions of shear displacement,respectively.Likewise,the pre-and post-peak joint shear stiffnesses are derived so that a complete shear stress-shear displacement relationship can be established.Verifications of the linearized implementation of the B-B model show that the shear stress-shear displacement curves,the dilation behavior,and the shear strength envelopes of rock joints are consistent with available experimental and numerical results.     

考虑各向异性特征的三维岩体结构面峰值剪切强度研究

 由于岩体结构面形貌的复杂性,目前,所提出的峰值剪切强度模型不能够很好地体现其各向异性特征。鉴于此,综合考虑岩体结构面起伏角和起伏幅度,提出一个考虑各向异性特征的综合参数?表征岩体结构面粗糙度的新方法;?由某一方向的起伏角参数SRv和起伏幅度参数A表示;其中参数SRv表示结构面粗糙度的各向异性特征,用变异函数分析方法进行计算获得。然后,应用该法分析Barton十条标准轮廓线,拟合出JRC与参数SRv,A的关系表达式;结合Barton强度公式,给出考虑各向异性特征的岩体结构面峰值剪切强度模型。最后,基于ShapeMetriX3D三维形貌测量系统,在实验室开展类岩体结构面形貌的量测;并应用上述方法估算结构面4个方向上的峰值剪切强度。于此同时,开展该类岩体结构面各向异性的剪切力学试验,通过试验值与估测值的对比分析,验证了所提模型的正确性。研究结果为准确预测岩体结构面抗剪强度提供一种新方法。     

不同节理粗糙度系数单裂隙渗流特性试验研究

 实际岩石裂隙的裂隙面具有不同的粗糙度,难以满足立方定律的使用条件。根据N. Barton和V. Choubey(1977年)提出的10条节理粗糙度(JRC)标准剖面轮廓曲线,本试验运用数控电火花线切割技术,加工出具有不同节理粗糙度系数(JRC = 0～20)的10个钢模板,制作出10个包含不同JRC值单裂隙的圆柱形水泥试样(直径f 50 mm,高度100 mm),采用RCCP联测系统测试不同JRC值单裂隙在不同应力水平下的渗透性。试验结果表明：(1) 在低应力水平下,JRC值对单裂隙的渗流特性有较大影响;随应力水平的增大,JRC值对单裂隙渗流特性的影响迅速减小;(2) 不同JRC值单裂隙的渗透率与有效应力之间的关系可用负指数函数描述,并表现出明显的非线性特征,低有效应力阶段试样渗透率随有效应力的变化速度大于中高有效应力阶段的变化速度。     

基于数字图像处理技术的岩石节理分形描述

岩石节理的粗糙度对结构面的剪切强度起着重要的作用.分形维数对节理的次级细微粗糙结构能够进行很好的描述,而对节理的一级起伏结构体现并不明显.考虑了节理形态的层次性,用分形维数代表节理的次级精细结构,即节理的粗糙度;用起伏度表示节理的一级波状形态,据此提出用分形维数D和起伏度W_d两个指标来描述JRC(节理粗糙度系数),并给出相应的计算公式.另外,针对工程实践中分形维数准确快速量测存在的困难,本文以摄影测量为基础,借助数字图像处理技术,在VC++平台下开发了节理轮廓线分形维数计算程序,为分维较准确方便地应用于工程实践做了有益的探索.     

岩石模型结构面的取样代表性试验研究

岩石结构面的代表性取样是开展不同尺寸模型结构面直剪试验的前提条件,直接影响到结构面抗剪强度尺寸效应试验结果的有效性和可靠性。通过对取样尺寸为10 cm的18组岩石结构面粗糙度系数(JRC)的测量和统计分析,得到该尺寸岩石结构面试样的粗糙度系数分布规律,表明模型结构面取样代表性评价的必要性。基于结构面粗糙度系数非均一性分布特点,以及对简单随机取样法和分层取样法2种概率取样方法的比较分析,提出基于分层取样法的岩石模型结构面代表性取样方法,该方法采用JRC四分位法确定各层样本的数量比例,再利用分层取样公式计算样本的取样数量。通过岩体结构面抗剪强度的力学机制分析,对试样取样代表性和力学可靠性进行校验,结果表明,采用该取样方法能较好地代表该尺寸的表面形态分布,取样结果也较好地满足力学试验的统计精度要求。     

The effects of discontinuity surface roughness on the shear strength of weathered granite joints

Surface roughness is one of the most important parameters governing the shear strength of rock discontinuities. Roughness types may vary based on genesis, physico-mechanical, and mineralogical properties of rocks. In this study, granite samples representing three different weathering degrees were selected to evaluate the effects of surface roughness and weathering degree on shear strength. To this aim, we determined the profile roughness coefficient (PRC), profile roughness angle (PRA), and joint roughness coefficient (JRC) for the selected fresh and weathered granite joint samples. Values of PRC were in the range of about 1.043–1.073, and PRA and JRC varied in the ranges of 16.67–21.45 and 12–18, respectively. Weathering led to the increment of joint surface roughness of the selected granitic joints due to the higher resistance of quartz crystals in the weathered matrix. However, the increment in surface roughness did not result in an increase in the shear strength. On the contrary, the shear strength of discontinuities dramatically decreased.     

岩石节理吻合系数及其对节理特性的影响

根据节理表面的接触特性提出了一个节理几何特性的新参数──节理吻合系数 ＪＭＣ。实验显示，节理吻合系数是描述节理孔隙、形变、刚度、剪切强度和水渗导等特性的 重要指标。因此，将节理吻合系数和原有的节理粗糙系数相结合，可以更全面地描述节理的 几何特性，进一步估测岩石节理的水力特性。     

Joints in unsaturated rocks: Thermo-hydro-mechanical formulation and constitutive behaviour

A formulation for the coupled analysis of thermo-hydro-mechanical (THM) problems in joints is first presented. The work involves the establishment of equilibrium and mass and energy balance equations. Balance equations were formulated taking into account two phases: water and air. The joint element developed was implemented in a general purpose finite element computer code for THM analysis of porous media (Code_Bright). The program was then used to study a number of cases ranging from laboratory tests to large scale in situ tests. A numerical simulation of coupled hydraulic shear tests of rough granite joints is first presented. The tests as well as the model show the coupling between permeability and the deformation of the joints. The experimental investigation was focused on the effects of suction on the mechanical behaviour of rock joints. Laboratory tests were performed in a direct shear cell equipped with suction control. Suction was imposed using a vapour forced convection circuit connected to the cell and controlled by an air pump. Artificial joints of Lilla claystone were prepared. Joint roughness of varying intensity was created by carving the surfaces in contact in such a manner that rock ridges of different tip angles were formed. These angles ranged from 0° (smooth joint) to 45° (very rough joint profile). The geometric profiles of the two surfaces in contact were initially positioned in a “matching” situation. Several tests were performed for different values of suctions (200, 100, and 20 MPa) and for different values of vertical stresses (30, 60, and 150 kPa). A constitutive model including the effects of suction and joint roughness is proposed to simulate the unsaturated behaviour of rock joints. The new constitutive law was incorporated in the code and experimental results were numerically simulated.     

夯扩桩扩大头直径计算的试验研究

在人工均匀填筑的平潭标准砂中，针对不同密度，分别进行夯扩桩半模夯扩试验，生动地展示了扩大头的形成过程，其最终形状近似为椭球体，在此基础上，定义分项系数Ｆｃ和Ｆｒ，提出了扩大头计算直径的修正公式，此公式经兄弟单位全模试验及现场试验成果的检验表明，它比应用其他文献中的公式，计算结果更接近于实测值。