节理岩体剪切试验的非连续变形方法分析

参照前人对含断续节理岩体所做剪切模型试验的结果,采用改进的非连续变形分析方法 (Discontinuous Deformation Analysis for Rock Failure,DDARF)对剪切试验进行数值模拟。从破裂现象看,仿真计算和模型试验结果相符良好。随后又对断续节理做雁形排列变化,研究对比了不同阶梯状排列裂隙的模型破裂现象及相应的模型峰值剪切强度。研究结果表明,裂隙扩展的过程始于预制裂隙两端的张力裂纹,随着张力裂隙的扩大在其附近生成许多细微裂纹,这些裂纹的贯通导致了模型的最终破坏。     

非贯通类节理岩体剪切变形规律分析

通过直剪条件下的模型试验研究具有相同连通率、含不同起伏角的共面闭合节理在不同法向应力作用下的剪切变形特征。试验结果表明：在达到峰值剪切强度前,剪切应力-位移曲线具有明显的线性段与非线性段;岩桥在法向与剪切荷载的共同作用下会产生一定程度的弱化,积累到一定程度时宏观表现为剪切应力软化。详细阐述了试验过程中裂纹发展的4个阶段并描述了剪切应力-剪切变形曲线变化的特征,提出一个能反映剪切应力-剪切变形曲线全过程的经验本构模型。新模型采用分段函数描述曲线变化特征。直剪试验数据分析表明,该模型能够拟合剪切应力-剪切变形变化发展趋势且具有较高的拟合精度,验证了模型的正确性。最后,对其存在的不足亦进行了简要分析     

Direct shear tests of artificial jointed rock specimens with parallel joints

Most previous studies focused on the performance of bedding rock slope under strong earthquakes, where limited publications involved bedding rock slope und     

类节理岩石直剪试验力学特性的数值模拟研究

节理岩体的剪切特性是主导岩体工程稳定性的关键因素。基于PFC2D离散元颗粒流程序,结合室内试验结果对比分析,选取合理的细观参数进行数值模拟,分别从细观角度研究了节理岩石的裂纹发展、能量转化及声发射现象等特性,从宏观角度研究了节理岩石的强度模型和破坏形态。结果表明：节理岩体主要呈现磨损和剪断两种破坏形态,不同的破坏形态对应不同的强度模型;随着剪切变形增加,岩体沿节理面发生破坏,弹性阶段以法向裂纹为主,而塑性阶段切向裂纹起主导作用,滑移区R、P裂纹贯通形成破碎带,节理面产生较大滑移;在应力达到峰值强度前,边界能主要转化为应变能,法向裂纹生成较多;越过峰值强度后,摩擦能快速增长,并伴随大量切向裂纹产生。与室内试验结果相比,PFC2D较好地模拟了节理岩体剪切力学特性,弥补了室内试验中无法进行细观特性研究的缺陷,对于节理岩体后期研究提供了一些参考。     

锚固方式对节理岩体剪切性能影响试验研究

分别采用预制混凝土块、45号钢螺杆、矿用化学浆液来模拟围岩、锚杆及锚固剂进行节理岩体室内剪切试验,研究在无锚、端锚和全锚3种情况下节理岩体抗剪特性及锚杆受力变形特征。研究结果表明:在不同锚固方式下节理岩体的剪力-位移曲线有显著的差异,无锚试件表现为脆性特征;端锚试件在调动锚杆抗剪强度时会有一剪力小幅下降的转折点,全锚试件与节理匹配性较好,可以承受更大的剪力;对于加锚试件,无论是端锚还是全锚锚杆,根据锚杆变形特点,均可分为拉伸区、剪拉区和压缩区。锚杆在剪力和拉力综合作用下破坏时即发生在剪拉区。锚固方式不同,剪切试验过程中锚杆轴力分布也不同,全锚锚杆主要分布于节理面附近,随着与节理距离增加,轴力迅速衰减。端锚锚杆轴力分布则相对均匀。     

加锚贯通节理岩体宏细观剪切破坏特性

为了研究加锚贯通节理岩体的剪切破坏特性,根据室内实验及数值模拟软件PFC2D,分析了不同法向应力及不同锚固角度作用下,加锚贯通节理岩体的抗剪性能及内部细观裂纹的演变过程。研究表明：（1）随着锚固倾角的增加,加锚节理岩体抗剪强度呈现先增大后减小的趋势,且在锚固角度为60°时,其抗剪强度最大,锚固效果最好。随着法向应力越大,加锚节理岩体抗剪强度越高,其抗剪性能越好。（2）随着剪切位移的不断增加,由初期阶段在锚杆和节理附近产生的少量裂纹通过不断的向外扩展,最终在锚杆和节理交界处聚集了大量的裂纹,其中裂纹以张拉裂纹为主。（3）锚固角度及法向应力对裂纹扩展影响显著,随着法向应力的增加,裂纹数也呈现了增加的趋势,且岩体破坏越严重。随着锚固角度的变化,加锚节理岩体破坏时形成的裂纹数量有先减小后增大的趋势,且在锚固角度为60°时,产生的裂纹最少。     

A portable shear box for testing rock joints

Rock Mechanics and Rock Engineering - The authors describe their early work on the development and operation of a portable shear box for testing rock joints. Experiences with sampling, roughness...     

基于3D打印的含复杂节理岩石直剪特性及破坏机制研究

岩体中节理的几何形态及力学特性是影响其剪切力学特性及破坏模式的重要因素之一。基于3D打印技术,建立了不同节理粗糙系数(JRC)的节理模型、几何形态节理模型和复杂裂隙网络物理模型,通过开展室内直接剪切试验分析了各组试件的剪切强度及破坏模式。结果表明节理模型的抗剪强度随JRC波动性较大,波动幅值越高,峰值剪切位移越低;平面形节理模型的峰值抗剪强度最低,矩形节理模型的峰值抗剪强度最高,正弦形和三角形节理试件的抗剪能力相近;离散裂隙网络模型和粗糙裂隙网络模型的峰值抗剪强度显著低于实心试件,考虑了节理粗糙性的裂隙网络模型抗剪强度高于直线型节理模型;实心试件破坏模式为典型脆性剪切破坏,裂隙网络模型的破坏模式相对复杂,沿着剪切方向主剪切裂面波动萌生,破断面由多个节理面的交叉点破坏与沿节理面的滑移构成。研究成果可以为3D打印技术的推广和复杂节理岩体剪切力学特性的室内试验研究提供参考。     

Stability of openings in jointed rock

The slide line approach is combined with the finite element method to represent the action of a removable block on a lined tunnel. The present paper examines the strength and ductility required of the tunnel liner to resist the forces imposed by a block when the surrounding rock mass is subjected to explosive loading. Key block theory developed by Goodman and Shi provides the conceptual framework for simplifying a general jointed domain to a manageable size for analysis with finite element models.     

Continuum modelling of jointed porous rock

Constitutive equations for the mechanical and hydraulic behaviour of saturated porous rock with joint sets of specified orientations are developed by superposing continuum representations for the mechanical and hydraulic properties of the intact rock and each of the joint sets. The resulting continuum theory allows for fluid diffusion through and between interconnected rock pores and joint sets of specified orientation, and also accounts for the anisotropy of the mechanical properties due to joint stiffnesses. The accuracy and reliability of this model are verified by finite element simulation of example problems. The first example considers joint orientation-dependent rock deformation in a hypothetical porous medium with one joint set of different dip angles. More realistic examples related to rock slope stability and reservoir-induced seismicity are also considered in which the constitutive law's utility for modelling time-dependent fluid pressures is illustrated.     

Undrained torsional shear tests on gravelly soils

Slope instability and landslides are frequently triggered during heavy rainfalls in mountainous areas. Geomaterials that are subject to this type of failure normally include coarse grains, which are made by weathering of mother rocks. These materials are called sandy gravel or gravelly sand in soil mechanics, depending upon the amount of gravelly components. This situation suggests a need for laboratory investigations that aim to understand the shear behavior of sand with gravel toward failure. Another feature of this type of failure is a quick rate of slope failure that is reasonably considered as an undrained process of shear distortion. Hence, the present study investigated by means of experiments the undrained shear behavior of sand with gravel. The torsion shear tests on hollow cylindrical specimens concerned the effects of gravel content on the undrained shear behavior. The tests revealed that the effect of gravel content is twofold. When the gravel content is relatively small, the effects of the sandy component are more important. Hence, the relative density of the sandy matrix among gravels has a predominant influence. In this situation, therefore, the overall relative density is a less important index to account for the shear behavior. In contrast, when the gravel content exceeds a threshold value, the amount of gravel comes to have a more predominant influence than the sandy matrix. This is probably because gravel particles start to have contact with each other to form a structural matrix of gravel grains that governs the overall stress–strain behavior. These results were summarized in three-dimensional diagrams that related the strength properties of gravelly sand varying with the density of sand matrix or the density of sand–gravel mixtures as well as the gravel content.     

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。     

节理岩体蠕变特性研究

在已知岩石和节理蠕变规律的前提下,推导了节理岩体蠕变模型的一般表达式。假定岩石体积变形和节理法向压缩变形为弹性变形,忽略节理的剪胀现象,认为只有岩石畸变和节理剪切滑移与时间有关,从而推导了含三组相交节理的岩体蠕变模型及其参数。根据反演出的岩石和节理蠕变模型,计算了含三组相交节理的岩体在单轴应力作用下一些节理参数对岩体单轴蠕变的影响。分析表明,节理间距、剪胀系数以及节理夹角都对岩体的单轴蠕变变形有明显影响。节理间距越大,剪胀系数越大,节理夹角越小,节理岩体的单轴蠕变柔量也就越小,岩体的蠕变变形也越小。     

Blast damage control in jointed rock mass

Highly jointed rocks often cause problems associated with blast damage and the stability of the back and/or walls of the excavation. A field study was performed to understand the role played by the joint parameters in inducing blast damage. The field work included blasting of small scale models, drift rounds and monitoring of blast damage at several operating mines. The damage was assessed by blast vibration monitoring, half cast factor, overbreak measurement and visual inspection.

The effect of spacing, orientation, aperture, condition, filling material and wall strength of joints on blast damage is described. The interaction between the joint planes and explosive energy has been discussed and the overbreak control measures have been suggested.     

Microplane damage model for jointed rock masses

The paper presents a new microplane constitutive model for the inelastic behavior of jointed rock masses that takes into account the mechanical behavior and geometric characteristics of cracks and joints. The basic idea is that the microplane modeling of rock masses under general triaxial loading, including compression, requires the isotropic rock matrix and the joints to be considered as two distinct phases coupled in parallel. A joint continuity factor is defined as a microplane damage variable to represent the stress‐carrying area fraction of the joint phase. Based on the assumption of parallel coupling between the rock joint and the rock matrix, the overall mechanical behavior of the rock is characterized by microplane constitutive laws for the rock matrix and for the rock joints, along with an evolution law for the microplane joint continuity factor. The inelastic response of the rock matrix and the rock joints is controlled on the microplane level by the stress–strain boundaries. Based on the arguments enunciated in developing the new microplane model M7 for concrete, the previously used volumetric–deviatoric splits of the elastic strains and of the tensile boundary are avoided. The boundaries are tensile normal, compressive normal, and shear. The numerical simulations demonstrate satisfactory fits of published triaxial test data on sandstone and on jointed plaster mortar, including quintessential features such as the strain softening and dilatancy under low confining pressure, as well as the brittle–ductile transition under higher confining pressure, and the decrease of jointed rock strength and Young's modulus with an increasing dip angle of the joint. Copyright © 2014 John Wiley & Sons, Ltd.     

一种新的节理裂隙岩体弹塑性模型

提出一种节理裂隙岩体弹塑性模型,将结构划分为块体单元和缝单元,其中缝单元可以是实际节理裂隙,也可以是人为缝单元。以块体单元形心的刚体位移和块体的平均应变作为基本未知量。该模型能充分考虑节理裂隙材料和块体材料的本构关系,计算量不大,是一种位移不协调单元。该模型特别适合节理裂隙岩体的数值分析。     

Shear resistance of jointed rock masses and stability calculation of rock slopes

Summary Based on an extension to a model originally proposed by Zhang (1990), a method for estimating the shear strength of a jointed rock mass containing two joint sets is developed. Compared to the original method in which only a single en-echelon joint set was considered, the new method has the following advantages: (1) it allows a much more realistic joint pattern to be incorporated; (2) the effects of joint connectivity and intersection angle between joint sets on shear strength are included. Use of the new method is demonstrated by application to the calculation of the stability of slopes in jointed rock. The importance of joint connectivity, joint persistence and joint set intersection angle on slope stability, as predicted by the model, is revealed.     

The transmission of compressional waves in jointed rock

Experiments have been carried out to determine the effect of joints on the propagation of P-waves in specimens of both weak and strong rocks; in particular the effect of normal stress on the transmission of P-waves in jointed rock was studied. These experiments were supported by measurements of seismic wave velocity carried out in tunnels driven in Lower Chalk and Carboniferous strata. The laboratory tests showed that relatively small normal stresses are sufficient to close joints acoustically and this was confirmed by the tunnel site observations. The results show that the interpretation of seismic data for the exploration of engineering sites may be improved by allowing for effects which result in the acoustic closure of joints.     

High lateral strain ratio in jointed rock masses

Rock masses encountered in the field are jointed and highly anisotropic. An important manifestation of this characteristic of rock masses is that the blocks, when slipping, separate and create voids in the mass resulting in high lateral strain even under low axial stress. It has been shown in this study that the ratio of lateral to axial strain may be very high, especially, if the joints are critically oriented. The assumption of isotropic linearly elastic material is not applicable in such situations. This observation is based on the outcome of an extensive laboratory testing programme, in which a large number of specimens of a jointed rock mass with various joint configurations were tested under uniaxial loading conditions. The trends of experimental results for both lateral strain ratio and rock mass strength have also been verified through distinct element modelling. The reason for high lateral strains has been attributed to the creation of voids and also to the fact that permanent deformations due to slip commence along rock joints right from the start of loading process. A simple mechanistic model has also been suggested to explain the high values of lateral strain for rough and dilatant rock joints. The lateral strains in such situations are important in the design of rock bolts. An example from a recently completed hydroelectric project has also been discussed where high lateral strain was found to be responsible for excessive wall closure and failure of rock bolts.