基于三维形貌的岩石节理抗剪强度计算模型

JRC-JCS模型在岩土工程领域被广泛应用,但也存在一定缺陷：其一,粗糙度系数JRC的二维性不能综合表征节理表面形貌的各向异性;其二,抗压强度系数JCS不能全面反映材料属性对节理剪切力学行为的影响。借助三维激光扫描和3D打印技术,浇筑具有自然节理形貌的人工节理试样,对其进行常法向应力下的剪切试验。将试验结果和理论推导相结合,建立了含有三维形貌参数和抗拉强度参数的抗剪强度模型。通过室内试验以及模型对比,分析了法向应力和三维形貌特征对岩石节理的抗剪强度以及剪胀角的影响。结果表明：节理剪切是以张拉为主导的破坏模式,而不是单纯的压缩破坏。不同的三维形貌特征会得到不同的初始剪胀角。随着法向应力的增大,峰值剪胀角减小,通过研究剪胀效应中峰值剪胀角的变化规律,可用于计算岩石节理的抗剪强度。     

基于节理面三维形貌的岩石节理抗剪强度计算模型

JRC-JCS模型在岩土工程领域被广泛应用,但也存在一定缺陷:其一,粗糙度系数(JRC)的二维性不能综合表征节理表面形貌的各向异性;其二,抗压强度系数(JCS)不能全面反映材料属性对节理剪切力学行为的影响。借助三维激光扫描和3D打印技术,浇筑具有自然节理形貌的人工节理试样,对其进行常法向应力下的剪切试验。将试验结果和理论推导相结合,建立了含有三维形貌参数和抗拉强度参数的抗剪强度模型。通过室内试验以及模型对比,分析了法向应力和三维形貌特征对岩石节理的抗剪强度以及剪胀角的影响。结果表明,节理剪切是以张拉为主导的破坏模式,而不是单纯的压缩破坏。不同的三维形貌特征会得到不同的初始剪胀角。随着法向应力的增大,峰值剪胀角减小,通过研究剪胀效应中峰值剪胀角的变化规律,可用于计算岩石节理的抗剪强度。     

确定岩石节理Maksimovic峰值抗剪强度准则中“粗糙度角Δφ”的新方法

岩石节理的非线性Maksimovic峰值抗剪强度准则,采用双曲线函数描述不同法向应力作用下剪胀角的变化,参数物理含义明确、适用的法向应力范围广且形式简洁。采用的参量"粗糙度角??"反映节理的粗糙程度,但由至少3组直剪试验数据回归分析确定,因此,不能采用该准则估算节理的峰值抗剪强度。通过等价关系,由已有的峰值抗剪强度准则得到用三维形貌参数表示的"粗糙度角??",提出含三维形貌参数的Maksimovic峰值抗剪强度准则。采用不同形貌节理的直剪试验数据对准则进行了验证,结果表明,计算值与试验值吻合较好,验证了公式的正确性;同时,亦与经典的Barton准则进行了对比。可用该准则预估节理的峰值抗剪强度。     

岩桥直剪细观破坏特征与剪胀效应研究

节理岩体的剪切贯通机制影响着边坡的稳定性。为揭示锁固段型非贯通节理岩体在不同连通率和法向应力下的破坏特征,在室内直剪试验中结合高速摄影与AE特征参数分析其剪切全过程及剪胀效应。结果表明:节理岩体直剪试验中,法向应力的增大及节理连通率的下降会致使峰值剪切应力及峰值剪切位移增大;节理连通率与法向应力对其破坏特征具显著影响,表现为节理连通率较高且法向应力较小时呈直接剪断的特性,节理连通率降低后呈拉剪复合破坏,出现剪胀现象,而法向应力的增大使得剪胀效应呈波动现象;AE特征与岩桥贯通过程一致,事件数峰值随节理连通率的降低及法向应力的增大而增大且位于峰后。试验得到的岩桥细观破坏特征与剪胀效应对研究锁固段型岩质边坡的贯通破坏机制具指导意义。     

砂土充填大理岩节理的剪切强度经验公式

为研究砂土充填对节理抗剪强度的影响,利用GCTS（RDS?200型）岩石剪切测试系统对4种不同摩擦系数砂土充填的粉晶大理岩节理进行了直剪试验。结果表明：相同法向应力下,未充填节理的峰值剪切应力大于充填节理的峰值剪切应力,说明砂土的存在降低了节理的剪切强度;由节理面三维形貌参数最大谷深 表征节理面粗糙程度,得到了未充填节理的峰值剪切强度公式,公式预测值与试验值基本吻合;得到了用充填砂土摩擦系数表达的充填节理峰值剪切强度公式,公式预测值与试验值较为吻合。研究结论对充填节理岩体稳定性评价具有一定指导意义。     

不同边界条件下剪切速率对类岩石节理剪切力学特性的影响

为研究不同边界条件下剪切速率对岩石节理剪切力学特性的影响,采用RDS-200型岩石节理剪切试验系统对人工浇筑的具有相同节理形貌的不规则水泥节理试样进行了常法向应力和常法向刚度2种边界条件下5种剪切速率的直剪试验。结果表明：（1）常法向应力边界条件下,随剪切速率增大,相同法向应力下的类岩石节理峰前剪切刚度减速增大,峰值剪切强度和残余剪切强度呈对数降低;随剪切速率增大,类岩石节理黏聚力减速增大,内摩擦角呈对数降低。（2）常法向刚度边界条件下,随剪切速率增大,相同法向应力的类岩石节理峰前剪切刚度减速增大,峰值剪切强度呈对数降低,较高法向应力下的残余剪切强度先增大后减小;随剪切速率增大,类岩石节理黏聚力呈对数降低,内摩擦角减速增大。（3）与常法向应力边界条件相比,常法向刚度条件下,节理黏聚力平均增加了115.85%,内摩擦角平均降低了8.44%;相同初始法向应力和剪切速率下,峰前剪切刚度、峰值剪切强度和残余剪切强度分别平均增加了11.96%、19.47%和32.32%,峰值法向位移平均降低了40.12%。该研究结论可为不同剪切速率下地表和地下工程岩体节理的剪切失稳评价提供一定参考。     

循环剪切荷载作用下岩石节理变形特性试验研究

以水泥砂浆为相似材料,制备3种岩壁强度、5种起伏角度的锯齿型节理试样;利用试验设备,进行了在4种法向应力下的循环剪切试验。根据试验结果,结合循环剪切试验特点,定义剪胀角来表征节理循环剪切的法向变形特性,以及剪切刚度来表征节理循环剪切的切向变形特性。基于不同起伏角、不同强度等级和不同法向应力下的节理试样循环剪切试验结果,分析了循环剪切过程中剪胀角和剪切刚度的变化规律;并利用不同条件下的试验结果,对比分析初始起伏角度、法向应力、岩壁强度对节理循环剪切变形特性的影响规律。研究发现：剪胀角、剪切刚度均随着剪切循环次数的增加而呈现先快、后慢的降低趋势,并且中低起伏角度节理的剪胀角、剪切刚度的降低趋势随着初始起伏角度、法向应力的增加而加快,随着岩壁强度增加而变慢,高起伏角度节理的剪胀角、剪切刚度的降低趋势基本保持不变。     

峰前循环剪切作用下岩石节理剪切力学特性

微震、工程爆破等低应力循环剪切荷载作用对节理岩体工程失稳破坏具有重要影响。为研究峰前循环剪切加卸载作用下岩石节理剪切力学特性,采用RDS-200型岩石节理剪切试验系统对人工劈裂黄砂岩节理进行了峰前循环剪切下的直剪试验。通过与未进行峰前循环剪切加卸载时岩石节理力学参数预测值对比,得到峰前循环剪切加卸载作用对峰前剪切刚度、峰值剪切强度、峰值剪切位移与残余剪切强度的影响。结果表明：（1）峰前循环剪切加卸载后,当法向应力为2 MPa时,岩石节理峰前剪切刚度增大,当法向应力为4～10 MPa时,岩石节理峰前剪切刚度在循环剪切应力幅值范围内增大,在超出循环剪切应力幅值时减小;（2）峰前循环剪切加卸载后,峰值剪切强度降低了10%～20%,降低百分比随法向应力增大整体呈对数函数增大;峰值剪切位移增加了2%～40%,增加百分比随法向应力增大整体呈对数函数减小;（3）峰前循环剪切加卸载后,岩石节理残余剪切强度无明显变化,峰值剪切强度与残余剪切强度差值减小,峰后剪切应力做功损失百分比降低。     

锚杆锚固对节理岩体剪切性能影响试验研究及机制分析

为研究锚杆锚固对节理岩体剪切性能的影响规律及锚杆抗剪作用机制,开展不同锚杆倾角及不同法向应力作用下加锚节理岩体室内剪切试验研究,探究加锚节理岩体在法向力及剪切力作用下的变形和受力特征,对比分析节理岩体锚固前与锚固后的剪切变形规律,讨论锚杆倾角、节理面法向应力等因素对节理岩体抗剪性能的影响。试验结果表明,锚杆锚固能够有效地增加节理面的黏聚力和内摩擦角,提高节理岩体的抗剪强度;锚杆倾角对加锚节理岩体的抗剪强度及剪切变形规律有重大影响,较大的锚杆倾角有利于发挥锚杆的"销钉"抗剪作用;节理岩体施加锚杆后其剪力–位移曲线存在弹性阶段、屈服阶段及塑性变形阶段3个区段;在锚杆倾角相同的条件下加锚节理岩体的抗剪强度随节理面法向应力的增加而增大。分析试验后试件破坏形态可知,加锚节理岩体中锚杆的屈服破坏主要发生在节理面附近的区段,岩体材料由于锚杆横向的挤压作用,也会在节理面附近发生局部破坏现象。     

节理峰值剪切位移及其影响因素分析

根据Barton-Bandis节理峰值剪切强度准则,分析了节理峰值剪切位移与法向应力之间的变化关系,并以此为基础总结了Barton峰值剪切位移公式的不足。通过室内直剪试验验证了节理粗糙度与法向应力是影响结构面峰值剪切位移的两个主要因素。试验结果表明,峰值剪切位移与节理粗糙度成反变化关系,与法向应力成正变化关系。建立了考虑节理粗糙度与法向应力的节理峰值剪切位移计算新公式。克服了Barton经验公式只考虑节理粗糙度,而不考虑法向应力作用的局限。新公式能很好地拟合试验数据,表明其合理性。     

New Peak Shear Strength Criterion of Rock Joints Based on Quantified Surface Description

The prime objective of this work is to improve our understanding of the shear behavior of rock joints. Attempts are made to relate the peak shear strength of rock joints with its three-dimensional surface morphology parameters. Three groups of tensile joint replicas with different surface morphology are tested with direct shear tests under constant normal load (CNL) conditions. Firstly, the three-dimensional surface characterization of these joints is evaluated by an improved roughness parameter before being tested. Then, a new empirical criterion is proposed for these joints expressed by three-dimensional quantified surface roughness parameters without any averaging variables in such a way that a rational dilatancy angle function is used instead of ${\text{JRC}} \cdot \log_{10} \left( {{{\text{JCS}} \mathord{\left/ {\vphantom {{\text{JCS}} {\sigma_{\text{n}} }}} \right. \kern-0em} {\sigma_{\text{n}} }}} \right)$ by satisfying the new peak dilatancy angle boundary conditions under zero and critical-state normal stress (not physical infinite normal stress). The proposed criterion has the capability of estimating the peak shear strength at the laboratory scale and the required roughness parameters can be easily measured. Finally, a comparison among the proposed criterion, Grasselli’s criterion, and Barton’s criterion are made from the perspective of both the rationality of the formula and the prediction accuracy for the three groups of joints. The limitations of Grasselli’s criterion are analyzed in detail. Another 37 experimental data points of fresh rock joints by Grasselli are used to further verify the proposed criterion. Although both the proposed criterion and Grasselli’s criterion have almost equal accuracy of predicting the peak shear strength of rock joints, the proposed criterion is easier and more intuitive from an engineering point of view because of its Mohr–Coulomb type of formulation.     

Empirical Formula of Shear Strength of Rock Fractures Based on 3D Morphology Parameters

The prime objective of this work is to provide a reference to predict the peak shear strength of rock fractures. The paper studied some shear properties of rock fractures and proposed an empirical formula for the peak shear strength of rock fractures based on 3D morphology parameters. The rock fractures were induced in cylindrical sandstone and marble specimens by means of indirect tension. A rock direct shear apparatus (RDS-200) was adopted to conduct direct shear tests on five groups of rock fractures under different levels of normal load. Before the direct shear test, 3D morphology parameters of rock fracture surfaces were obtained using a 3D optical scanner. By analyses of direct shear test data, the relationships between peak shear strength, peak shear displacement, peak dilatancy angle, residual friction coefficient and peak normal stress were found. According to the evolution trends of peak shear strength and peak dilatancy angle along with the normal stress, an empirical formula was proposed to predict the peak shear strength of rock fractures in both sliding and cutting failure modes considering the 3D morphology parameters of rock fracture surfaces. The empirical formula could be commonly used for different types (sandstone and marble) and grain sizes (powder-grained, fine-grained, medium-grained and coarse-grained) of rock fractures.     

估算异性岩石不连续面峰值剪切强度的经验公式

长江三峡库区广泛发育着两侧岩性不同的不连续面（称为异性不连续面）,研究其峰值剪切强度可为相关岩体的稳定性分析和评价提供理论依据。采用高强石膏浇注3组不同形貌且上、下壁面强度不同的不连续面试件,并在不同常法向应力下进行剪切试验。引入不连续面壁组合系数λ来综合量化不连续面壁的抗压强度和基本摩擦角对异性不连续面峰值剪切强度的影响,λ越小,上、下不连续面壁强度差异越大。异性不连续面的峰值剪切强度随λ的增加呈非线性增加,且在高法向应力下更为显著。在Barton公式的基础上,通过多元回归分析建立了估算异性不连续面峰值剪切强度的经验公式。采用天然和人工锯齿形异性不连续面的直剪试验结果对新公式做了进一步验证,试验剪切强度与新公式预测值吻合较好。简要分析了新公式在软硬互层岩质边坡稳定性评价中的应用。最后,讨论了Wu公式的适用性以及新公式的优点和不足。     

基于统一强度理论深埋圆形隧道围岩的剪胀分析

基于连续介质理论中岩体的剪胀角与围压和塑性剪切应变密切相关,隧洞周边岩体的应力状态因开挖卸荷而发生应力重分布,迫使其围压由原地应力逐渐衰减,塑性剪切应变不断增加,引起剪胀效应呈非线性变化。首先,基于统一强度理论和非关联流动法则,将潜在塑性区围岩按等围压释放划分为若干同心圆,提出了考虑中间主应力和非线性剪胀性的有限差分法,计算应变软化围岩的力学问题,并以实例验证其正确性。其次,通过参数分析,研究塑性区内岩体的剪胀角受中间主应力、临界软化系数和支护力的影响规律。研究结果表明,中间主应力主要影响剪胀角的峰值,随着中间主应力效应增加,剪胀峰值增加;临界软化系数主要影响剪胀角的变化率,随着临界软化系数的增加,剪胀角变化缓慢;中间主应力和临界软化系数共同影响塑性区剪胀角的变化;随着支护力的增加,洞壁处的剪胀角增加;双剪强度理论计算的位移值较小,应谨慎采用,同时采用Mohr-Coulomb强度准则时可以适当考虑围岩的承载潜力。     

Friction and degradation of rock joint surfaces under shear loads

The morpho‐mechanical behaviour of one artificial granite joint with hammered surfaces, one artificial regularly undulated joint and one natural schist joint was studied. The hammered granite joints underwent 5 cycles of direct shear under 3 normal stress levels ranging between 0.3 and 4 MPa. The regularly undulated joint underwent 10 cycles of shear under 6 normal stress levels ranging between 0.5 and 5 MPa and the natural schist replicas underwent a monotonics shear under 5 normal stress levels ranging between 0.4 and 2.4 MPa. These direct shear tests were performed using a new computer‐controlled 3D‐shear apparatus. To characterize the morphology evolution of the sheared joints, a laser sensor profilometer was used to perform surface data measurements prior to and after each shear test. Based on a new characterization of joint surface roughness viewed as a combination of primary and secondary roughness and termed by the joint surface roughness, SR_s, one parameter termed ‘joint surface degradation’, D_w, has been defined to quantify the degradation of the sheared joints. Examinations of SR_s and D_w prior to and after shearing indicate that the hammered surfaces are more damaged than the two other surfaces. The peak strength of hammered joint with zero‐dilatancy, therefore, significantly differs from the classical formulation of dilatant joint strength. An attempt has been made to model the peak strength of hammered joint surfaces and dilatant joints with regard to their surface degradation in the course of shearing and two peak strength criteria are proposed. Input parameters are initial morphology and initial surface roughness. For the hammered surfaces, the degradation mechanism is dominant over the phenomenon of dilatancy, whereas for a dilatant joint both mechanisms are present. A comparison between the proposed models and the experimental results indicates a relatively good agreement. In particular, compared to the well‐known shear strength criteria of Ladanyi and Archambault or Saeb, these classical criteria significantly underestimate and overestimate the observed peak strength, respectively, under low and high normal stress levels. In addition and based on our experimental investigations, we put forward a model to predict the evolution of joint morphology and the degree of degradation during the course of shearing. Degradations of the artificial undulated joint and the natural schist joint enable us to verify the proposed model with a relatively good agreement. Finally, the model of Ladanyi and Archambault dealing with the proportion of total joint area sheared through asperities, a_s, once again, tends to underestimate the observed degradation. Copyright © 2001 John Wiley & Sons, Ltd.     

剪切过程中锚杆的轴向和横向作用分析

为了分析锚杆轴向力和横向剪切力分别换算的结构面抗剪强度大小规律,依据最小势能原理的变分法,并考虑结构面剪胀特性,建立加锚结构面抗剪强度计算公式。通过加锚结构面直剪试验验证理论计算的有效性,结合理论计算公式,分析了在不同锚杆倾角下围岩强度、锚杆直径和法向应力对锚杆轴向力和横向剪切力换算的抗剪强度影响规律,以及预应力对抗剪强度的影响。结果表明：加锚结构面抗剪强度计算结果与试验结果吻合较好;当锚杆倾角逐渐增大时,锚杆轴向力发挥的抗剪强度逐渐降低,横向剪切力发挥抗剪效能逐渐增大,当锚杆倾角为120°～150°时,轴向力换算的抗剪强度基本为0,而横向剪切力换算的抗剪强度最大;随着围岩强度或法向应力的增大,锚杆轴向力换算的结构面抗剪强度减小,但随锚杆直径或预应力的增大,锚杆轴向力换算的结构面抗剪强度增大;当围岩强度和锚杆直径增大,锚杆横向剪切力换算的抗剪强度会明显增大,而预应力增大会使锚杆横向剪切力换算的抗剪强度呈现降低趋势。     

含二阶起伏体的模拟岩体节理试样剪切特性试验研究

利用规则的小尺寸锯齿构造二阶起伏体,对不同二阶起伏体高度的人工节理进行常法向应力下的直剪试验,研究了节理剪切力学特性。对节理的剪切强度、变形特征进行了分析,并对破坏特征做出解释。试验结果表明：二阶起伏体对节理剪切力学特性有重要影响,含二阶起伏体节理的剪切力学特性与只含有一阶起伏体节理的剪切力学特性不同,只含一阶起伏体的节理剪应力只有一个峰值,含二阶起伏体的节理会出现波浪状的剪胀曲线和多峰值剪应力,且峰值剪应力随剪切位移增大依次出现并逐个减小;随着二阶起伏体高度增大,节理峰值剪切强度增大,节理依次出现磨损破坏、多次性剪断破坏、一次性剪断破坏。