New criterion for rock joints based on three-dimensional roughness parameters

The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.

Numerical investigation for anisotropy of compressive strength of rock mass with multiple natural joints

Based on Rock Failure Process Analysis model RFPA2D, the evolutionary proc- esses of failure process of rock mass with multiple natural joints were simulated. Numeri- cal simulations show that anisotropy of compressive strength of jointed rock mass varies with the number of natural joints and inclination of natural joints. As the number of natural joints in rock mass increases, the anisotropy becomes less and less. It is justifiable to treat approximately rock mass containing six or more natural joints instead of four or more joints that was described in literature of Hoek and Brown as isotropy.

Method for visualizing the shear process of rock joints using 3D laser scanning and 3D printing techniques

This study presents a visualized approach for tracking joint surface morphology.Three-dimensional laser scanning(3DLS)and 3D printing(3DP)techniques are adopted to record progressive failure during rock joint shearing.The 3DP resin is used to create transparent specimens to reproduce the surface morphology of a natural joint precisely.The freezing method is employed to enhance the mechanical properties of the 3DP specimens to reproduce the properties of hard rock more accurately.A video camera containing a charge-coupled device(CCD)camera is utilized to record the evolution of damaged area of joint surface during the direct shear test.The optimal shooting distance and shooting angle are recommended to be 800 mm and 40?,respectively.The images captured by the CCD camera are corrected to quantitatively describe the damaged area on the joint surface.Verification indicates that this method can accurately describe the total sheared areas at different shear stages.These findings may contribute to elucidating the shear behavior of rock joints.

A novel method for geometric quality assurance of rock joint replicas in direct shear testing-Part 1:Derivation of quality assurance parameters and geometric reproducibility

Since each rock joint is unique by nature,the utilization of replicas in direct shear testing is required to carry out experimental parameter studies.However,information about the ability of the replicas to simulate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.With the aim to facilitate generation of high-quality direct shear test data from replicas,a novel component in the testing procedure is introduced by presenting two parameters for geometric quality assurance.The parameters are derived from surface comparisons of three-dimensional(3D)scanning data of the rock joint and its replicas.The first parameter,smf,captures morphological deviations between the replica and the rock joint surfaces.smf is derived as the standard deviation of the deviations between the coordinate points of the replica and the rock joint.Four sources of errors introduced in the replica manufacturing process employed in this study could be identified.These errors could be minimized,yielding replicas with smf
0.06 mm.The second parameter is a vector,VHp100,which describes deviations with respect to the shear direction.It is the projection of the 100 mm long normal vector of the best-fit plane of the replica joint surface to the corresponding plane of the rock joint.

VHp100

was found to be less than or equal to 0.36 mm in this study.Application of these two geometric quality assurance parameters demonstrates that it is possible to manufacture replicas with high geometric similarity to the rock joint.In a subsequent paper(part 2),smf and VHp100 are incorporated in a novel quality assurance method,in which the parameters shall be evaluated prior to direct shear testing.Replicas having parameter values below established thresholds shall have a known and narrow dispersion and imitate the shear mechanical behavior of the rock joint.

A novel method for geometric quality assurance of rock joint replicas in direct shear testing-Part 2:Validation and mechanical replicability

Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.In this study,a novel method is presented for geometric quality assurance of replicas.The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results.In Part 1 of this study,two quality assurance parameters,smf and V_(Hp100),are derived and their usefulness for evaluation of geometric deviations,i.e.geometric reproducibility,is shown.In Part 2,the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior,which qualifies the parameters for usage in the quality assurance method.Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σ_(mf)<0.06 mm and
|V_(Hp100)|
<0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength.The wear in these replicas,which have similar morphology as the rock joint,is in the same areas as in the rock joint.The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties,possibly from differences in toughness.It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics,which makes them useful in parameter studies.

Investigation of long-wavelength elastic wave propagation through wet bentonite-filled rock joints

The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system.Therefore,the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal.This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test.Jointed rock specimens with different joint conditions(i.e.joint surface saturation and bentonite filling)were prepared using granite rock discs sampled from the Korea Underground Research Tunnel(KURT)and Gyeongju bentonite.The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels.A Hertzian-type power model was used to fit the wave velocities,and the relationship between the two fitted parameters provided the trend of joint conditions.Numerical simulations using three-dimensional distinct element code(3DEC)were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.

An approach to measure infill matric suction of irregular infilled rock joints under constant normal stiffness shearing

Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers(HCTs) during direct shear of infilled joints under constant normal stiffness(CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using threedimensional(3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients(JRCs) of 8-10 and 18-20 with the ratios of infill thickness to asperity height(t/a)equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness.

软弱夹层结构面剪切特性各向异性试验研究

【目的】研究不同剪切方向下软弱夹层结构面剪切特性的差异。【方法】选取各向异性特征明显的天然三维结构面形貌,制作了具有不同充填度的含淤泥质黏土结构面试样;基于自主研发的软弱夹层岩石结构面各向异性直剪仪,开展了不同充填度下含有软弱夹层岩石结构面各向异性直剪试验,分析了软弱夹层结构面剪切特性的各向异性规律。【结果】1)不同剪切方向下无充填结构面剪应力剪切位移曲线具有峰前硬化和峰后软化特征,其法向与剪切位移曲线表现出先剪缩后剪胀的变化趋势;2)相同充填度不同剪切方向下软弱夹层结构面剪应力剪切位移变化规律存在差异,且剪应力与剪切位移的峰后软化特征随着充填度的增大逐渐消失;3)同一充填度下结构面峰值抗剪强度随着剪切方向的变化呈现差异;各向异性程度随着充填度增大呈现出先增大后减小的规律;4)同一充填度下软弱夹层结构面法向与剪切位移曲线随剪切方向差异呈现不同的变化规律,剪切特性随充填度增大由剪胀转变为剪缩,各向异性程度降低。【结论】本试验结果对研究岩体滑坡的破坏机理具有一定的参考价值。

含节理大理岩变形和强度特性的试验研究

锦屏二级水电站处于高地应力区域,引水隧洞开挖后岩体变形和稳定问题十分突出。从辅助洞取样制备含节理试件,采用MTS815.03岩石三轴试验机,开展了含天然节理大理岩试件的常规三轴压缩试验。试验中,节理面与最大主应力夹角θ为29.3°～56.0°,围压为5～40 MPa。通过试验结果分析,主要得到如下结论:(1)试件共有两类破坏形式:穿切节理面破坏和沿节理面滑移。试件破坏形式主要取决于节理面与最大主应力夹角大小。在试验围压范围内,围压高低对试件破坏形式没有影响。(2)试件变形特征取决于节理面与最大主应力夹角的大小,并受围压高低影响。(3)试件轴向变形曲线均具有较好的线性段,但其轴向等效弹性模量均显著低于完整岩石弹性模量。(4)试件强度首先取决于θ的大小,θ>40.0°的试件破坏强度与完整岩石相当;θ<40.0°的试件破坏强度较完整岩石有显著降低,不同节理强度差异是导致不同试件破坏强度差异的主要原因。

岩体性质与爆破效果的灰关联度分析

利用灰关联度理论分析了岩体性质与爆破效果的相关程度，指出了由于岩体地质构造的差异，在不同爆区，岩体性质对爆破效果的影响作用也有所不同，其结果对实际生产有一定的指导意义。

节理岩体爆破的研究现状

描述了目前国内外学者对节理岩体爆破的研究进展，分析了常用的一些数学模型，阐述了人们对爆破块度的测定及预报情况以及计算机模型模拟及其应用。节理岩体本身的特性较一般工程材料更复杂、更特殊，因此在爆破作用中，节理对爆破效果的影响有时比岩体本县物理力学性质的影响更显著，所以研究更有理论意义和实际意义。文章提出了节理岩体爆破的研究工作中今后需要解决的一些问题。

岩石节理粗糙面的分形几何特性与剪切强度关系的实验研究

自然形成的岩石节理面的表面形状具有分形特性,利用分形理论来描述岩石节理的粗糙特性,并确立与岩石节理面的剪切力学特性间的关系对于指导岩体工程设计、施工和管理具有重要意义。本研究利用开发设计的三维激光测距仪在精确测定岩石节理面的表面形状的基础上,依据变量图法建立了新的岩石节理面的分形几何模型,模型中的两个分形参数(振幅B和分形维数D)分别定量表述了岩石节理面表面形状的两个几何特性(一级倾斜度和高级次起伏度),在此基础上,进一步提出了由这两个分形参数组合得出的代表岩石节理面表面粗糙特性的平均粗糙角U的概念和计算方法。其次,在岩石节理面剪切强度实验基础上,应用新的分形模型,建立了剪切强度和分形参数及平均粗糙角U的定量关系。

岩石天然块度预测的计算模型

为了对岩石天然块度作出合理正确的预测,分析讨论了岩体结构面的分形特征,提出了 一种利用分形分布、节理密度、岩石质量指标R_(Q,D)和结构面间距分布形式的联系来预测岩石天然块度。研究表明,此模型可以作为岩石天然块度的预测模型。

不同围压下含天然贯通节理岩石卸载破坏机理研究

二郎山特长高速公路隧道断裂带较多,受此影响,隧道开挖后岩爆灾害十分严重.从此隧道中取样制备成含天然贯通节理试件,进行常规单轴压缩室内试验,获取基本力学参数和破坏模式.本文以室内实验结果为依据,确定数值试验时所采用的岩石和节理的力学参数,利用RFPA软件开展数值试验,研究了不同围压同轴向荷载下卸掉围压诱发岩石失稳破坏机理.试验结果表明,五种不同围压(5、10、15、20、25 MPa)卸载后应力—应变曲线均呈"断崖式"跌落,试样均突然破坏,与现场岩爆情况吻合;受贯通节理影响,不同围压试样的具体破坏形态、声发射数量最大值出现时刻有所差异;在卸载阶段五种试样声发射累积数量都突然急剧增大.

松辽盆地深层区域地质特征及有利勘探方向

松辽盆地深层东部断陷区徐家围子断陷天然气勘探实现跨越,徐深1井等取得重大发现,提交探明储量超千亿方。作为松辽盆地深层天然气重要接替的西部断陷区,古龙—长岭断陷在地层、构造、沉积等方面与徐家围子断陷具有类似的特征。古龙—长岭断陷烃源岩厚度大于1000m的面积为10692km2,最厚为1400m,总资源量为9435×108m3,勘探前景十分广阔。2005年9月25日长深1井在营城组火山岩中获日产气46×104m3,无阻流量超百万方。长深1井的重大突破和松北徐家围子的勘探成果形成了南北相映的场面,揭示了松辽盆地深层天然气勘探的巨大潜力。

天然充填岩石节理抗剪强度模型研究进展

系统总结了目前关于天然充填岩石节理抗剪强度模型的最新研究成果:现有天然充填岩石节理抗剪强度模型大多以粘性土充填规则锯齿状模拟岩石节理直剪试验结果为基础,考虑充填介质对岩石节理抗剪强度的弱化作用,将抗剪强度分为岩石节理强度和充填介质强度两部分,再考虑充填介质固结度和饱和度影响,得到相应的抗剪强度模型;分析了现有抗剪强度模型研究方法和理论中的不足,探讨了今后充填岩石节理抗剪强度模型研究的新方向,即:以天然岩石节理为研究对象,从充填节理制样技术、抗剪强度细观力学机理、剪胀效应等方面开展深入研究,建立与天然充填岩石节理更一致的抗剪强度模型。

3D打印技术在岩体物理模型力学试验研究中的应用研究与展望

含内部三维缺陷的试样和含复杂地质结构的物理模型制作一直是制约岩石力学试验发展的主要原因之一,鉴于3D打印(3D Printing,3DP)技术可以便捷地制作含复杂结构的三维实体,将3DP技术引入到岩体/岩石力学试验的研究中。以粉末性石膏为打印材料制作了含内部多孔洞结构和预制裂隙结构的模型试样,力学试验表明,这2种打印试样的变形特征、破坏特征、强度特征以及裂隙扩展过程与岩石类材料较为一致;利用粉末性石膏和PLA材料为打印材料,制作出了含单断层和含锚杆衬砌支护工程的隧道物理模型,试验证明了断层的存在降低了隧道的稳定性,而锚杆衬砌支护系统可以有效地提高洞室的承载能力,而且3DP隧道模型的变形破坏过程与其他岩石类材料的物理模型试验结果和工程现场观测现象较为一致。同时,将3D光学面扫描技术和3DP技术相结合建立一种含自然节理面模型的制作方法,试验测试表明该方法能够较好地复制出节理面的形貌特征,并且试样的剪切力学性质和破坏特征具有很好的稳定性和一致性。通过上述3DP试样的初步力学试验测试表明该技术在岩体力学试验研究中的可行性。最后,进一步了探讨和挖掘了3D打印技术在岩石力学和岩体工程研究中的应用潜力。