节理岩体动态破坏的SHPB相似材料试验研究

采用相似材料模型试验对不同节理倾角、节理贯通度、节理条数、载荷应变率、节理充填物厚度、节理充填物类型及试件长径比等7种工况下的节理岩体动态强度及破坏模式进行了分离式Hopkinson压杆(SHPB)试验研究。结果表明：节理岩体动态破坏模式及强度与节理构造形态密切相关。对于单节理岩体,其强度及破坏特征在很大程度上受节理倾角控制,节理倾角0°、90°试件动强度分别为完整试件的90%和71%,且其破坏形式均为张拉破坏;倾角60°试件动强度几乎为0;倾角30°、45°试件的动强度分别为完整试件的50%和18%,且其破坏以剪切破坏为主,兼有张拉破坏。中心1/4、1/2、4/5及全贯通节理试件的峰值强度分别为完整试件的95%、74% 、28%和17%,即随节理贯通度增加,试件动强度逐渐降低。含1~3条节理的试件动强度分别为完整试件的54%、23%和10%,即随节理条数增加,试件动强度随之有较大幅度降低,但节理条数的增加并没有改变其破坏模式。随着节理充填物厚度增加及节理充填物强度降低,试件强度依次递减,但破坏模式并没有改变。完整试件和节理试件的动强度均随着载荷应变率的增加而变大,且前者对载荷应变率的敏感性要远远高于后者,相应地试件的破坏模式也变得更加复杂。两类试件的动强度均随着试件长径比的增加先增大后减小,即存在一个最佳长径比。     

基于广义Hoek-Brown准则强度折减法的岩坡稳定性分析

针对岩质高边坡的稳定性分析问题,开展了基于广义Hoek-Brown破坏准则强度折减法的研究。提出了判别强度折减法合理性的两个基本标准：与Mohr-Coulomb准则强度折减法的一致性和能否体现节理岩体的真实破坏特征。基于以上标准,对比了3种不同的基于广义Hoek-Brown破坏准则的强度折减方法：σci、mi,σci、GSI和mi、GSI均同比折减,理论分析表明：mi、GSI同比折减更符合前述标准。最后,通过对工程实例的对比研究,验证了这一结论,并提出mi、GSI同比折减更能体现节理岩体的真实破坏特征,因而其安全系数的计算结果也更加真实可靠。     

A Simplified Failure Criterion for Intact Rocks Based on Rock Type and Uniaxial Compressive Strength

The uniaxial compressive strength (UCS) of intact rock, which can be estimated using relatively straightforward and cost-effective techniques, is one of the most practical rock properties used in rock engineering. Thus, constitutive laws to represent the strength and behavior of (intact) rock frequently use it, along with additional intrinsic rock properties. Although triaxial tests can be employed to obtain best-fit failure criterion parameters that provide best strength predictions, they are more expensive and require time-consuming procedures; as a consequence, they are often not readily available at early stages of a project. Based on the analysis of an extensive triaxial test database for intact rocks, we propose a simplified empirical failure criterion in which rock strength at failure is expressed in terms of confining stress and UCS, with a new parameter which can be directly estimated from the UCS for a specified rock type in the absence of triaxial test data. Performance of the proposed failure criterion is then tested for validation against experimental data for eight rock types. The results show that strengths of intact rock estimated by the proposed failure criterion are in good agreement with experimental test data, with small discrepancies between estimated and measurements strengths. Therefore, the proposed criterion can be useful for preliminary (triaxial) strength estimation of intact rocks when triaxial tests data are not available.     

基于巴西劈裂试验的页岩强度与破坏模式研究

为了研究页岩横观各向同性性质对劈裂强度及破坏模式的影响,对7组不同倾角下的试样进行了巴西劈裂和声发射测试。研究表明：层理的方向对试样的劈裂强度和最终破坏模式有着重要的影响。随着层面倾角 的增加,页岩试样的劈裂强度逐渐减小。在不同倾角下的破坏模式可分为直线形（ 0°、90°）、月牙形（ 15°）和曲弧形（ 30°、45°、60°、75°）。通过分析不同倾角下圆盘中心点沿层理分解得到的正应力和剪应力,当 0°时,试样的破坏方式为基质的拉伸破坏;当 90°时,试样的破坏方式为层理的拉伸破坏,当15° 75°时,试样的破坏为复合型破坏。观察声发射空间累计定位演化分布情况,直线型的声发射点较均匀地分布在试样中轴线的两侧;曲弧型的声发射点在圆盘的一端较密而另一端较稀疏;月牙型则在试样的中部和一端都累积了部分声发射点;分布特征与宏观破坏方式具有相似性。分形维数D可以较好地反映试样的破坏模式,从倒V形的变化趋势可知,直线形试样D值接近于2,而月牙形和曲弧形试样D值介于2.2～2.7。因此,D值越大,说明裂纹的曲率半径越大;相反D值越小,裂纹越趋于一条直线,破裂形态也就越简单。     

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。     

Back analysis of an excavated slope failure in highly fractured rock mass: the case study of Kargar slope failure (Iran)

This paper examines the failure of Kargar cut slope located at the south part of Esfahan subway using analytical and numerical back analysis methods. The excavated trench has 27 m depth with near vertical walls due to the space limitation around it. The geology of the area comprises weathered and heavily jointed shale and sandstone overlaid by alluvium deposits. Despite the slope being supported by shotcrete and fully grouted rock bolts, a catastrophic failure occurred at the east wall. Due to the uncertainty about the causes of failure initiation, back analyses have been performed via both the limit equilibrium and numerical method for considering various probable mechanisms. In the back analysis with limit equilibrium method, the rock mass is assumed as an equivalent continuum and Hoek–Brown failure criterion and geological strength index (GSI) are applied to calculate the shear strength parameters. The results show that GSI value was 33 in the failed mass. In the numerical back analysis, the distinct element method is applied to study the contribution of rock joints to the failure and progressive rock mass strength degradation until failure. The results show that threshold values of joint cohesion and friction were 0.2 MPa and 30°, respectively. Also the modeled slip surface being step-shaped agrees with the observed one.     

广义非线性强度理论形状参数研究

姚仰平等提出的广义非线性强度理论,将各种摩擦材料的非线性强度理论统一起来,使统一后的非线性强度理论能够合理地反映各类摩擦材料的强度特性。在广义非线性强度理论体系中,形状参数?是影响在?平面上破坏曲线形状的重要因素之一,因此,需要对形状参数进行如下研究：（1）将广义非线性理论应用于各类砂土中,根据其在?平面上破坏曲线特性,在判断该破坏曲线凹凸的基础上,得到砂土形状参数?临界值与破坏应力比参数Mf之间的关系;（2）通过对几个经典砂土真三轴试验结果的整理,验证广义非线性强度理论对砂土破坏特性的预测能力,并在此基础上建立该理论中形状参数?和破坏应力比参数Mf的线性关系。因此,在实际应用时,仅通过三轴压缩试验即可得到三维应力条件下的强度包线。     

Tensile strength and its anisotropy measured by point and line-loading of sandstone

Tensile fracture is an ubiquitous feature of rock failure ranging in size from microfracture around Griffith cracks to the large-scale explosive failure accompanying rock bursts in underground cavities. Hence the resistance of rock to failure in tension, the tensile strength, is one of the fundamental parameters of rock strength. The tensile strength of rock is, however, a most elusive parameter which is difficult to measure and to define.

The tensile strength, and its variation with direction, was determined by the pointloading and the line-loading (Brazilian test) methods for nine rocks from five sandstone formations in New Brunswick, Canada. Altogether 319 double point-load and 357 line-load tests were conducted on discs having a diameter of 22.9 mm and thickness of 7.9 mm.

The tensile strength determined by the point-load test and as calculated by the Frocht formula was found to be consistently lower than that obtained by the line-loading technique. To some extent, the difference is due to the fact that most of the sandstones are anisotropic with respect to tensile strength and that the constraints in the point-load test are such that fracture occurs along the plane of minimum tensile strength; the computed tensile strength therefore represents a minimum value. To a greater extent, the lower tensile strength calculated from the point-load test is due to the difference in the states of stress induced by the two techniques. When correction is made for the anisotropy, the tensile strength from the Brazilian test is still 3.76 times larger than the one obtained from the point-load test.

The Brazilian test seems to yield a more accurate definition of both the tensile strength and its variation with direction. The point-load test is more suitable for the determination of the minimum value of tensile strength and the direction of the preferred fracture plane.     

不同节理表面形貌下非贯通节理岩体强度特性直剪试验研究

通过直剪模型试验,研究节理表面形貌下非贯通节理岩体扩展贯通强度特性。非贯通节理岩体的扩展贯通过程分为4个阶段：初裂前阶段、稳定扩展阶段、非稳定扩展阶段和摩擦阶段。结合试验现象和切向变形曲线,研究了非贯通节理岩体的初裂强度、临界强度、贯通破坏强度、残余强度等特性。在相同的法向应力下,节理表面越粗糙,不仅非贯通节理岩体的贯通破坏强度越大,而且初裂强度、临界强度、残余强度也越大。在不同的节理表面形貌下,初裂强度与贯通破坏强度的比值约为70%;临界强度与贯通破坏强度的比值约为90%;不过,残余强度与贯通破坏强度的比值变化较大,约为50%～90%。试验为进一步研究非贯通节理岩体破坏理论提供试验验证。     

Interpretation of shear strength uncertainty and reliability analyses of slopes

The variance of the friction angle or friction coefficient (tan ?) is often considered in geotechnical reliability analyses, which implies that the variance of the shear strength as defined by a Mohr-Coulomb envelope increases as the normal stress on the shearing surface increases. However, shear strength data sometimes has approximately constant variance, and most simple regression techniques assume constant variance. Four effective stress shear strength data sets are evaluated using both the constant variance (homoscedastic) and constant coefficient of variation (heteroscedastic) interpretations. The impact of the variance interpretation on slope stability is evaluated using infinite slope, homogeneous dam, and zoned dam examples. For relatively shallow infinite slope surfaces, the reliability index for the heteroscedastic interpretation of shear strength variance was about twice the reliability index obtained using the homoscedastic approach. In the dam examples, the difference in the reliability indices resulting from the heteroscedastic and homoscedastic interpretations was about one, indicating a tenfold increase in the probability of failure. The typical assumption of constant coefficient of variation of shear strength may result in unconservative estimates of the reliability of shallow failure surfaces and overly conservative results for deeper failure surfaces.     

预制节理岩体试件强度及破坏模式的试验研究

采用相似材料模型试验对不同节理倾角、节理贯通度、节理组数、载荷应变率、试件长径比、节理充填物厚度及类型等7种工况下的预制节理岩体在单轴压缩下的峰值强度及破坏模式进行了研究。结果表明：节理岩体的破坏模式及峰值强度与节理构造形态密切相关。贯通节理岩体将产生沿节理面的剪切破坏或穿切节理面破坏,且与第1种破坏模式对应的岩体峰值强度更低。非贯通节理岩体的强度介于完整岩体和贯通节理岩体之间。随着平行节理组数的增加,岩体峰值强度逐渐下降。随着载荷应变率的增加,岩体峰值强度逐渐增大,相应地试件的破坏模式也变得更加复杂。试件长径比基本没有改变其破坏模式,完整试件仍主要是以张拉破坏为主,而节理试件仍以剪切破坏为主。随着长径比增加,试件峰值强度逐渐增大。随着节理充填物厚度增加,试件峰值强度降低。不同节理填充物对试件峰值强度也有一定影响。     

基于统计岩体力学的岩体强度特征分析

结构面的存在改变了岩体力学性质,影响了岩体强度特征。基于统计岩体力学强度判据,结合摩尔-库仑准则,得到了含单组结构面岩体破坏的4种不同方式和相应的结构面倾角范围,推导了岩体强度由结构面控制转化为应力控制的临界围压表达式。在此基础上,根据岩石和结构面参数之间的关系,将含单组结构面岩体分为4类,并探讨了可能破坏方式和发生破坏的条件。最后,举例分析了含单组结构面闪长岩的强度特征,结果表明,该岩体属于第I类岩体,在垂向受压时先沿结构面后沿岩块破坏,临界围压为9.12 MPa;从全空间分析,该岩体强度各向异性显著,围压增大可使岩体在一些方向上受力时强度由结构控制转化为应力控制。     

Stability analysis of laterally confined slope lying on inclined bedding plane

A stability analysis of a laterally confined slope model, lying on an inclined bedding plane, was presented to evaluate the lateral shear resistance by considering the loading paths and failure envelopes. Two slope models were prepared on a bedding plane by compaction, one with and one without lateral confinement. The compacted models are related to the geological conditions at shallow depths where brittle deformation can occur and an excavation can induce horizontal field stress that significantly influences the stability of the slope. Three distinct loading paths, controlled by either tilting the angles or increasing the surcharge loads, were applied to achieve the failure of the slope models. Rankine’s passive earth pressure due to compaction was reduced by the shear strength reduction ratio. The shear strength reduction ratio was estimated through the least-squares fitting method based on the results of model tests at failure when the loading paths intersected the failure envelope. Provided that the effect of lateral confinement in a rock mass can be described by the shear strength reduction ratio, the proposed equations will be beneficial for slope stability analyses of laterally confined slopes on bedding planes. A case study of an undercut pit wall in an open-pit mine was demonstrated by showing that the unknown shear strength reduction ratio can be back-analyzed from the rainfall-induced landslide case. Therefore, the design of other undercut slopes with different geometries and groundwater conditions in the rock mass, which have undergone the same geological process as the back-analyzed case, is possible.

     

四川盆地焦石坝区块深部页岩力学特性试验研究

为深入研究不同埋深页岩储层的力学性质,对四川盆地焦石坝区块五峰-龙马溪组平行层理取心试样进行单轴压缩试验,总结了取样区段页岩试样的力学特性、强度规律以及破坏特征。实验及分析结果表明:该区块页岩呈现典型的脆性破坏特征,破坏形式以劈裂破坏为主、伴随部分或局部剪切破坏,并细分5种单轴压缩条件下的基本破坏形式;页岩抗压强度随埋深增加整体上呈现出两端低中间高的现象;随取心角度的增大,变形参数和抗压强度总体上均呈现出先增大后减小的趋势;对比分析了页岩试样力学参数的横向和纵向异性度,弹性模量和泊松比的横向及纵向异性度均在1.50附近,抗压强度的异性度显著高于弹性模量和泊松比的异性度;层理的影响是导致页岩强度及破坏方式差异性的主要原因之一,层理面在一定程度可以决定岩体的强度及破坏方式;水力压裂过程中,横向异性度大的层理面首先被打开,导致压裂通道沿层理面扩展,难以形成复杂裂缝网络,达不到理想的压裂效果,在施工过程中要避免此类层理面被打开。     

A relation between safety factors with respect to strength and height of slopes

Conventional slope stability analysis is usually based on the linear Mohr–Coulomb failure criterion utilizing the notion of safety factors with respect to shear strength, and one of the available slice methods. Failure criteria of most soils are not linear, and it is possible to show that this non-linearity has a very significant effect on calculated safety factors. The present work is based on a non-linear failure criterion, which appears to fit the experimental information better than Mohr–Coulomb. All slice methods utilize various kinematical and static assumptions, which cannot be rationally justified. The present work is based on rigorous variational approach to slope stability analysis, which does not employ any kinematical and static assumptions. Safety factors with respect to shear strength are useful abstractions, but physical significance of results based on them is clear only at failure when they are equal to 1 (at any other value of the safety factor with respect to strength results of the analysis correspond to fictitious material with a modified shear strength function). In the present note, we use the variational analysis in order to establish a simple analytical relation between safety factors with respect to strength and height. These two safety factors provide alternative measures for the stability of a given slope; but the safety factor with respect to height appears to have clearer physical interpretation.     

绿泥石片岩各向异性特性研究

为研究十堰地区片岩的各向异性特性,开展了武当群绿泥石片岩长方体试样的单轴压缩和圆盘试样的间接拉伸试验,探讨了试样各向异性的力学特性和在不同受力状态下的变形破裂特性,揭示了不同变形破裂的力学机制。研究表明,武当群绿泥石片岩具有明显的各向异性性质,平行片理方向强度高,垂直片理方向强度低。该片岩特殊的定向排列片束状构造和片理间的弱胶结作用,致使不同方向上的破坏特征具有明显差异,其力学机制也不相同。在压应力作用下,泊松效应容易引起平行片理面的张拉劈裂和压杆失稳,垂直片理方向容易发生片理面间的剪切破坏。在同一方向上强度具有一致性,即平行片理面抗压和抗拉强度均较垂直片理面强度大。由于片理面间的抗拉承载力极低,在小角度劈裂荷载下,容易发生张拉劈裂和拉剪破坏,因此,实际工程中应尽可能避免片理面间的受拉破坏和沿片理的拉剪破坏。研究结果可以为隧道、边坡支护加固和防水处理提供参考。     

基于流固耦合理论某尾矿坝失稳特性及稳定性分析

选用典型的尾矿库工程实例,采用流固耦合和强度折减法相结合对其尾矿坝进行稳定性分析,确定尾矿库渗流场分布及浸润线的位置,该浸润线位置与实测浸润线位置吻合较好。建议强度折减过程中尾矿坝的失稳准则,计算安全系数,确定潜在滑裂面的位置,并与极限平衡法计算出的安全系数及临界滑裂面位置进行比较,表明强度折减法得出的结果与Bishop法结果接近,流固耦合-强度折减法在尾矿库稳定性分析的可行性。在该基础上研究尾矿坝潜在的失稳模式,将尾矿坝潜在的失稳模式分为局部失稳和整体性失稳两种,局部失稳为尾矿坝的部分坝面发生滑移,整体失稳为整个尾矿坝坝体发生失稳,并分析导致该尾矿坝两种失稳模式的主要因素,认为浸润线埋深过浅是导致局部失稳的主要原因。     

非贯通节理岩体直剪试验研究进展

基于典型的直剪试验,国内外学者提出了非贯通节理岩体贯通破坏机理,并建立了相应的强度准则,如Jennings方法,即加权平均强度理论和强度准则、Lajtai岩桥破坏理论和强度准则、断裂力学的II型破坏理论和强度准则,拉剪复合破坏和强度准则。然而,非贯通节理岩体破坏机理目前还没有完全弄清楚,已建立的强度准则所包含的重要参数还需深入研究,如：如节理面的传压系数、传剪系数、弱化了的岩桥内摩擦力和内摩擦角等;非贯通节理岩体节理闭合和剪切的本构关系有待建立;不共面非贯通节理岩体全过程最大抗剪强度需进一步研究。伺服直剪试验机、静态应变测试仪、声发射仪、X射线测量等无损检测技术能够为进一步研究非贯通节理岩体的破坏机理,提出新的理论和建立新的强度准则提供强有力的技术支持。     

Effects of confining pressure and loading path on deformation and strength of cohesive granular materials: a three-dimensional DEM analysis

This paper is devoted to numerical analysis of strength and deformation of cohesive granular materials. The emphasis is put on the study of effects of confining pressure and loading path. To this end, the three-dimensional discrete element method is used. A nonlinear failure criterion for inter-granular interface bonding is proposed, and it is able to account for both tensile and shear failure for a large range of normal stress. This criterion is implemented in the particles flow code. The proposed failure model is calibrated from triaxial compression tests performed on representative sandstone. Numerical results are in good agreement with experimental data. In particular, the effect of confining pressure on compressive strength and failure pattern is well described by the proposed model. Furthermore, numerical predictions are studied, respectively, for compression and extension tests with a constant mean stress. It is shown that the failure strength and deformation process are clearly affected by loading path. Finally, a series of numerical simulations are performed on cubic samples with three independent principal stresses. It is found that the strength and failure mode are strongly influenced by the intermediate principal stress.

     

多层边坡破坏机制数值模拟研究

通过大量的多层边坡算例来分析FLAC3D强度折减法在不同强度、坡比和层厚的情况下所得安全系数与滑动面位置的变化规律,并与极限平衡法进行对比,探究强度折减法和极限平衡法所得结果产生差异的原因,揭示多层边坡的破坏机制。数值模拟计算结果表明:①对于上层土体强度较软的边坡,当上下层强度相差到一定程度,表现为上层破坏,强度折减法与极限平衡法的安全系数相对差值最大,达5%~7%;上层土体厚度h增加时,安全系数逐渐减小;上层土体位于地表以下时,滑动面通过坡趾,安全系数保持不变。②对于下层土体强度较软的边坡,当上下层强度相差到一定程度,强度折减法所得安全系数基本保持不变,但极限平衡法仍保持增长趋势,最大相对差值可达12%;上层土体厚度h增加时,安全系数也相应增大,h位于9~12 m,边坡表现为深层破坏;而h=12 m时,极限平衡法的滑动面却通过坡趾,但安全系数相差很小。当h的变化范围在3~5 m,两种方法的安全系数相对差值最大,达6%~10%。破坏区分布分析表明,边坡呈拉伸-剪切复合破坏,对于下层土体强度较软的边坡,复合破坏模式更显著,与单一剪切破坏模式相比,最大有10%左右的相对差值。