Dynamic response and failure process of horizontal-layered fractured structure rock slope under strong earthquake

Rock slope with horizontal-layered fractured structure(HLFS)has high stability in its natural state.However,a strong earthquake can induce rock fissure expansion,ultimately leading to slope failure.In this study,the dynamic response,failure mode,and spectral characteristics of rock slope with HLFS under strong earthquake conditions were investigated based on the large-scale shaking table model test.On this basis,multiple sets of numerical calculation models were further established by UDEC discrete element program.Five influencing factors were considered in the parametric study of numerical simulations,including slope height,slope angle,bedding-plane spacing and secondary joint spacing as well as bedrock dip angle.The results showed that the failure process of rock slope with HLFS under earthquake action is mainly divided into four phases,i.e.,the tensile crack of the slope shoulder joints and shear dislocation at the top bedding plane,the extension of vertical joint cracks and increase of shear displacement,the formation of step-through sliding surfaces and the instability,and finally collapse of fractured rock mass.The acceleration response of slopes exhibits elevation amplification effect and surface effect.Numerical simulations indicate that the seismic stability of slopes with HLFS exhibits a negative correlation with slope height and angle,but a positive correlation with bedding-plane spacing,joint spacing,and bedrock dip angle.The results of this study can provide a reference for seismic stability evaluation of weathered rock slopes.

Integrated simulation and monitoring to analyze failure mechanism of the anti-dip layered slope with soft and hard rock interbedding

The significant difference between the mechanical properties of soft rock and hard rock results in the complexity of the failure mode of the anti-dip layered slope with soft and hard rock interbedding.In order to reveal the landslide mechanism,taking the north slope of Fushun West Open-pit Mine as an example,this paper analyzed the failure mechanism of different landslides with monitoring and field surveys,and simulated the evolution of landslides.The study indicated that when the green mudstone(hard rock)of the anti-dip slope contains siltized intercalations(soft rock),the existence of weak layers not only aggravates the toppling deformation of anti-dip layered slope with high dip,but also causes the shear failure of anti-dip layered slope with stable low dip.The shear failure including subsidence induced sliding and wedge failure mainly exists in the unloading zone of the slope.Its failure depth and failure time were far less than that of toppling failure.In terms of the development characteristics of deformation,toppling deformation has the long-term and progressive characteristics,but shear failure deformation has the abrupt and transient characteristics.This study has deepened the understanding of such slope landslide mechanism,and can provide reference for similar engineering.

Groundwater monitoring of an open-pit limestone quarry:Water-rock interaction and mixing estimation within the rock layers by geochemical and statistical analyses

Water-rock interaction and groundwater mixing are important phenomena in understanding hydrogeological systems and the stability of rock slopes especially those consisting largely of moderately watersoluble minerals like calcite. In this study, the hydrogeological and geochemical evolutions of groundwater in a limestone quarry composed of three strata: limestone layer(covering), interbedded layer under the covering layer, and slaty greenstone layer(basement) were investigated. Water-rock interaction in the open-pit limestone quarry was evaluated using PHREEQC, while hierarchical cluster analysis(HCA)and principal component analysis(PCA) were used to classify and identify water sources responsible for possible groundwater mixing within rock layers. In addition, Geochemist's Workbench was applied to estimate the mixing fractions to clarify sensitive zones that may affect rock slope stability. The results showed that the changes in Ca2+and HCO3àconcentrations of several groundwater samples along the interbedded layer could be attributed to mixing groundwater from the limestone layer and that from slaty greenstone layer. Based on the HCA and PCA results, groundwaters were classified into several types depending on their origin:(1) groundwater from the limestone layer(LO),(2) mixed groundwater flowing along the interbedded layer(e.g., groundwater samples L-7, L-11, S-3 and S-4), and(3) groundwater originating from the slaty greenstone layer(SO). The mixing fractions of 41% LO: 59% SO, 64% LO: 36% SO, 43%LO: 57% SOand 25% LO: 75% SOon the normal days corresponded to groundwaters L-7, L-11, S-3 and S-4,respectively, while the mixing fractions of groundwaters L-7 and L-11(61% LO: 39% SOand 93% LO: 7% SO,respectively) on rainy days became the majority of groundwater originating from the limestone layer.These indicate that groundwater along the interbedded layer significantly affected the stability of rock slopes by enlarging multi-breaking zones in the layer through calcite dissolution and inducing high water pressure, tension cracks and potential sliding plane along this layer particularly during intense rainfall episodes.

Effect of the frozen layer on the stability of cut soil slopes during seasonal freezing and thawing

Research on the stability of soil slopes in seasonally frozen regions has mainly focused on slope failures during the thawing window.There are few studies on slope stability during the freezing window and its subsequent influence on slope failure in the next thawing window.In this paper,soil strength was tested during freezing and thawing to obtain temperature-dependent strength parameters for the simulation of slope stability.Then,the slope's temperature field over an entire year was accurately simulated so that characteristics of the frozen layer could be determined at any time.Based on the above results,the progressive failure modes of frozen soil slopes are discussed.The results show that:1)during the freezing window,depth of the frozen soil layer increases,as does the slope's safety factor,while a yield zone propagates towards the slope shoulder.(2)During the thawing window,the frozen soil layer shrinks in depth while the yield zone continuously expands,which decreases the safety factor.Comprehensive analysis of these results indicate that the frozen layer provides a“toe-locking effect”that increases the safety factor during the freezing window,while it also provides a“dragging effect”that propagates the yield zone towards the slope shoulder.During the thawing window,the“toe-locking effect”gradually diminishes;a continuous sliding surface is formed,which lead to a landslide.The frozen soil layer of the freezing window accelerates the slope sliding in the thawing window.

岩土成层条件下抗滑桩计算的改进有限差分法

滑坡治理工程中抗滑桩可能布置于层状土层、层状岩层,或岩、土成层等各种地质条件下,现行规范对于该问题建议将成层地基按加权平均法换算成等效的当量地基系数,但对于地层差异性较大的岩土成层地基其适用性有待研究。为解决这一问题,基于Euler-Bernoulli梁理论建立抗滑桩受荷段、嵌固段整体受荷分析模型,采用改进有限差分法提出抗滑桩全桩内力求解的统一矩阵运算式,避免常规有限差分方法将桩身分为受荷段和嵌固段及利用滑面处连续性条件求解的复杂迭代过程;基于2个边坡工程抗滑桩治理案例,证明改进有限差分法对岩土成层条件下抗滑桩分析的可靠性,计算用时仅需1.2 s左右,相比已有方法进一步提高抗滑桩分析设计的计算效率。

倾角变化条件下反倾层状斜坡倾倒变形演化研究

倾倒变形是反倾层状岩质边坡的一种典型破坏模式,为了研究不同岩层倾角对反倾层状岩质边坡倾倒变形的影响,以澜沧江上游古水水电站坝前倾倒变形体为原型,从岩层倾角变化的角度出发,利用大型土工离心机试验分析了反倾层状岩质边坡的失稳破坏过程、变形演化特征与最终失稳模式等。结果表明:①反倾层状斜坡的变形演化过程基本概括为岩层压密-坡脚压裂阶段、弯折面形成-部分失稳阶段和弯折面贯通-彻底失稳3个阶段,岩层倾角的改变并不会影响斜坡阶段性演化过程;②岩层倾角越大的斜坡,斜坡形成弯折面所需时间越短,失稳破坏发生后坡体贯通性倾倒破坏深度更大,对应的变形范围越大,折断岩层的破坏程度越剧烈;③岩层倾角变化会导致斜坡的倾倒变形过程与最终失稳模式存在一定差异。倾角较小的55°和70°模型斜坡前部岩层在重力作用下发生明显弯曲倾倒变形,最终以“倾倒-弯曲-滑移”的失稳模式发生破坏;倾角最大的85°斜坡岩层发生的弯曲变形较小,最终以“倾倒-折断-崩塌”的模式发生破坏。研究结果对大型工程项目的顺利开展具有一定指导意义。

多弱层顺倾软岩边坡控制开采技术

针对多弱层顺倾软岩边坡下部压煤问题,从边坡变形风险可控以及资源回收最大化角度出发,在分析地质资料和弱层层位的基础上,结合单一弱层的控制开采技术,提出了多弱层顺倾软岩边坡控制开采技术;以扎尼河露天矿北端帮边坡为工程背景,基于极限平衡理论,分析了北端帮边坡的稳定性,对多弱层控制的顺倾软岩边坡控制开采方案进行了研究。研究表明:通过多弱层顺倾软岩边坡控制开采技术的实施,可在采场深部增加内排物料形成“中间桥”工艺,对深部弱层形成“压覆”,对整体边坡形成“支撑”,保证边坡沿各弱层滑动均得以控制,实现多弱层顺倾软岩边坡煤炭高效回收以及蠕动形变的稳定性控制。

基于能量演化的反倾层状岩坡多级折断面深度计算模型

多级折断是反倾层状岩质斜坡倾倒过程中普遍发育的一种变形破坏现象。为准确定位反倾层状岩质斜坡倾倒变形过程中多级折断带的埋藏深度,首先从能量守恒角度出发,结合悬臂梁模型,利用外力做功吸收能量与板梁变形释放能量守恒关系推导单层板梁能量平衡方程;在此基础上,根据岩体弹性屈服和弯折破坏2种临界失稳状态,分别推导出2种板梁失稳折断计算模型,并通过改变岩层倾角、斜坡坡角、斜坡高度等参数建立反倾层状岩质斜坡多级折断面深度计算模型;最后,利用离心模型试验和实际工程案例对计算模型的可靠性进行验证。研究结果表明:离心模型试验能够充分揭示反倾层状岩质斜坡倾倒变形过程中存在多级折断现象,整个倾倒变形过程可分为后缘岩体倾倒变形、岩层折断面裂隙逐级形成贯通和斜坡岩体倾倒失稳3个阶段;反倾层状岩坡多级折断面深度计算模型结果与离心模型试验结果、云南某边坡工程案例中各级折断带的埋深相吻合,证明了提出的反倾层状岩坡多级折断面深度计算模型可对离心模型试验和实际工程案例进行较为准确的折断深度定位,且能够根据计算结果判别边坡变形破坏的主要失稳模式。研究成果对反倾层状岩质斜坡的稳定性评价研究及破坏机制分析具有一定的理论和实际意义。

岩体扰动对岩石边坡稳定性影响

在岩石边坡工程中,岩体内部应力的释放可能诱发断裂和扰动,尤其是在爆破作业期间,这种扰动效应尤为突出。考虑到岩体扰动的影响,采用Hoek-Brown破坏准则,通过有限元和极限解析法,系统评估了扰动因子和边坡坡度对边坡潜在滑动面及其稳定性的影响。结果表明:扰动因子和边坡角度显著影响岩石边坡的稳定性,特别是在岩质较差的边坡中,这一影响更加显著;扰动水平可能被视为常数或沿边坡呈线性变化,若在稳定性评估中忽视岩体扰动的影响,可能导致稳定系数的估值偏大;不同扰动因素情况下切岩边坡的上限塑性区域,均质边坡的破坏面(D=常数)更浅;破坏面的顶部从坡顶向斜面靠近,但破坏模式仍为边坡趾部破坏;仅降低边坡角度并不能确保边坡的稳定性,在岩体边坡稳定性评价中,必须全面考虑扰动因子的作用。

超厚中风化层高陡边坡稳定性研究

风化作用使岩石强度降低,进而导致边坡岩体的力学性能大幅度下降,因此露天矿山高陡边坡主要以微风化岩体为主,而以中风化岩体为主的边坡通常设计较为平缓,高度也多为30~50 m。对某钼矿完整性好的超厚中风化层高陡边坡稳定性进行研究,采用极限平衡法计算爆破振动力作用下的边坡安全系数,并根据计算结果对边坡参数进行优化,为下一步的设计提供技术支持。结果表明:边坡稳定性主要受到岩石强度和岩体完整性2个方面因素的影响,深部的中风化层如果节理裂隙发育减少,岩体完整性提升,边坡的稳定性也得到改善,完整性好的超厚中风化层也可以设计为高陡边坡。

某水电站2#倾倒体时效变形及失稳模式的离散元分析

为深入研究倾倒体变形破坏全过程特征,以某水电站消力塘左岸2#倾倒体为例,在野外调查基础上,利用离散元模拟,从模型时效变形及变形机理出发,分析该倾倒边坡在现状及地震作用下的失稳模式。结果表明:当边坡变形累积到一定程度,不稳定地质体将发生失稳,其位移表现为宏观的快速增加,若地质体的失稳是强震触发的,其位移还具有一定的“震荡”特征;倾倒边坡前期或前中期的变形破坏以沿结构面的剪切错动为主导,之后,随着拉张效应的逐渐积累,变形转为以沿结构面的拉张破裂为主;地震作用下,边坡中质点的水平速度及加速度均有高程放大效应,其中加速度放大系数大于速度放大系数,边坡破坏时,由于动力波的加速效应及岩体弹性应变能的释放将获得较大的水平加速度,表明岩体中的弱面对于岩质边坡的稳定性起控制作用;现状条件下,2#倾倒体整体稳定,其失稳模式以浅表层岩体的局部垮塌或沿小型山脊的滑塌为主,而遭受地震时则有整体失稳的可能,若整体失稳,其失稳过程应为:表层松动岩体率先垮塌、滚落→坡体震裂松弛→形成“滑移-拉裂”型滑坡。

露天煤矿非工作帮顺倾软岩边坡稳定性研究

为达到提高露天煤矿顺倾软岩边坡稳定性的目的,结合白音华二号露天煤矿非工作帮为典型顺倾软岩边坡的工程实际情况,采用岩土工程数值模拟软件FLAC^(3D),揭示边坡稳定性的形态效应与尺寸效应;建立了临界坡角与弱层暴露临界长度之间的关系曲线,最终设计了有利于稳定的白音华二号露天煤矿非工作帮边坡空间几何形态。研究结果表明:通过合理控制弱层的暴露长度以及开挖坡角等关键指标,可有效提高露天矿边坡的稳定性,最终确定的白音华二号露天煤矿非工作帮开挖坡角为45°,此时坑底弱层的临界暴露长度约为176 m,边坡即可满足安全要求。

Effect of crevice density on biological soil crust development on rock cut slope in mountainous regions,Sichuan,China

Background The rock cut slope(RCS)could cause damage to regional ecological functions and landscapes and requires recovery.Biological soil crusts(BSCs)are pioneer and dominant colonizers during the initial recovery stage.To accelerate the natural recovery of RCS,the development process and influencing agents of BSC should be revealed.Thus,the area index of crevices(IR),BSC coverage(COV)and biomass(BM),soil weight(SW),and major soil nutrients[organic carbon(OC),total nitrogen(TN)and total phosphorus(TP)]content,collected from 164 quadrats on 13 RCSs in the mountainous area of west Sichuan Province,China,were measured,to explore the effect of crevice of RCS on BSC development.Results Soil OC,TN and TP on RCSs ranged from 18.61 to 123.03 g kg^(-1),0.96 to 6.02 g kg^(-1)and 0.52 to 2.46 g kg^(-1),respectively,and were approximately to or higher than those on natural slopes.The OC,TN and TP contents in soils elevated unsystematically with recovery time of RCSs.BSCs on RCS distributed along crevices generally and firstly.During the first 13 years of natural recovery,COV,BM and SW ranged from 6.5 to 28.2%,14.43 to 67.25 g m^(-2),and 127.69 to 1277.74 g m^(-2),respectively.COV,BM and SW increased linearly with IR on RCSs.The positive correlation between COV and BM and IR was insignificantly impacted by bedrock,slope aspect and altitude within the recovery time less than 13 years.COV and BM on RCSs increased significantly when the recovery time is more than 27 years.Conclusions Crevice on RCSs could be a major environmental factor which is conducive to BSC development and soil accumulation through creating a space for water and soil particle.Furthermore,with the increase of recovery time of RCSs,BSCs may grow and reach a stable state with the promotion of soil nutrients,plant growth and microbial activity.These results provide a development process of BSC that from inside to outside the crevices on RCSs.In the areas with stable rock strata and a low risk of geological disasters,purposeful improvement in crevice density on RCS may effectively accelerate BSC development.

超深盾构工作井基坑施工技术研究——以甬舟铁路金塘海底隧道北仑工作井为例

近些年,大盾构被广泛用于铁路穿越江河湖海城工程,特别是越江、跨海地段,随之越来越深的盾构工作井应运而生。结合甬舟铁路金塘海底隧道北仑工作井施工案例,总结了高强岩层下超深基坑的多种围护结构体系设计,并对施工技术展开研究,同时结合监控量测数据探寻开挖循环进尺合理范围。相关施工技术对类似超深、高强度岩层、明挖逆作法基坑有一定的参考价值。

Simulation study of the void space gas effect on slope instability triggered by an earthquake

This study aims at exploring the void space gas effect of earthquake-triggered slope instability and providing a new method for studying the formation mechanism of earthquake-triggered landslides. We analysed the basic characteristics, kinematic characteristics, initiation mechanisms and physical mechanical parameters of the Daguangbao landslide, generalized a landslide prototype, and established a geological model and performed simulation tests. Based on the seismic wave propagation theory of rock-soil mass, rock fracture mechanics and the effective stress principle, we found that the void space gas effect is due to the occurrence of excess void space gas pressure when the dynamic response of seismic loads impacts the void space gas in weak intercalated layers of the slope. The excess void space gas pressure generated by the vibration(earthquake) damages the rock mass around the void space with a certain regularity. The model test results show that the effective shear strength of the rock mass can be reduced by 4.4% to 21.6% due to the void space gas effect.

双层近距离坚硬顶板切顶成巷围岩控制技术

针对双层近距离坚硬顶板下切顶参数不合理导致的沿空留巷围岩大变形问题,通过现场监测、理论分析和离散元模拟,以柏沟煤业090109运输巷道为工程背景,阐明双层近距离坚硬顶板沿空留巷矿压显现特征和机制,分析保持围岩稳定的必要条件,提出合理的切顶高度、角度和顶板强化支护技术。综合实际条件确定090109运输巷道切顶卸压高度和角度分别为6 m和15°;现场监测数据表明,结合顶板锚索强化支护技术后,顶底板与实体煤帮位移较原巷道围岩控制方案分别减少了35.3%和49.9%,围岩稳定时滞后工作面距离减少了55.2%。研究成果为双层近距离坚硬顶板下切顶留巷提供可行性依据。

露天矿薄层状岩质边坡顺层滑坡特征和形成机制

顺层滑坡是露天矿薄层状岩质边坡中常见的局部高频中小型地质灾害,在空间上遍布最终境界的整个顺倾边帮,在时间上贯穿矿山服务的全生命周期,严重影响矿山的安全生产。造成顺层滑坡的原因一方面是岩体本身不利的岩体组构,另一方面是受爆破开挖扰动及水的作用影响。本文从露天矿薄层状岩体的原岩地质成因和表生改造后的岩体结构特征出发,结合典型鞍山式沉积变质岩型铁矿的多个滑坡实例以及微震、应力计监测结果,分析了该类型滑坡的孕育条件、分布特征和演化规律。研究结果表明:(1)层理和片理结构是薄层状岩体中层状裂隙发育、岩层薄化的基础;(2)该类型滑坡以单台阶的楔形体或平面型滑坡为主,几何必要条件为台阶坡面上至少存在一侧暴露的层面自由边,诱发条件为爆破振动及强降雨;(3)滑坡运动方式以浅层的滑移-牵引为主,受局部断层影响易发生复合型多台阶滑坡。

复合多层顺倾岩质边坡最优锚固角研究

锚杆支护是一种加固边坡的有效方式,但目前针对复杂多层岩质边坡的锚杆最优锚固角研究较少,且未考虑中间主应力对锚固效果的影响。采用统一强度理论,以全长粘结型锚杆为对象,根据锚杆失效模式及锚固段与围岩的作用方式,推导出复合多层岩体中锚杆的极限抗拔力公式。通过计算不同岩层锚固段微元体的单位长度抗力比,提出了复合多层顺倾岩质边坡的锚杆最优锚固角模型与最优锚固角的确定方法。将该方法应用到三峡库区巴东县一公路边坡工程,结果表明模型计算所得最优锚固角与均匀试验方案确定的最优锚固角一致。新方法计算所得的边坡单位宽度锚杆总长与规范法计算结果相比减少约11.2%,与传统莫尔-库伦理论计算结果相比减少约8.9%。研究结果可为复合多层顺倾岩质边坡的锚固支护设计提供一定的参考和借鉴。

台阶式锯切开挖边坡岩体质量及稳定性评价

锯切法进行边坡开挖施工,开挖面平整光滑,对边坡岩体质量影响较小,利于提高边坡的开挖稳定性。目前采用锯切法开挖边坡的应用较少,缺少对切割岩体质量和应力应变特征的详细研究。本文对某抽水蓄能电站台阶式锯切开挖边坡进行研究,通过现场岩石回弹试验和波速测试,对切割开挖边坡的岩体质量进行研究,分析了切割开挖过程中岩体的应变特征。在此基础上,利用三维有限元模型,对锯切法开挖边坡的应力应变情况和稳定性特征进行了模拟。结果表明:台阶式锯切开挖对边坡的扰动较小,岩体质量几乎不受切割开挖影响;边坡开挖过程中的稳定性系数均大于3,边坡整体变形量较小,边坡稳定性较好;在开挖台阶上部会产生较大拉应力,容易引起局部拉裂或崩塌破坏,需要进行及时支护,边坡的锚杆支护深度建议在4.0m以上。

基于三维块体切割分析及块体理论的高陡硬岩边坡稳定性分析

硬岩边坡稳定问题通常表现为受结构面控制的块体失稳。采用三维块体切割和块体理论对某高陡硬岩边坡确定性结构面切割形成的定位块体问题、随机裂隙形成的不定位块体问题与确定性和随机结构面共同切割形成的半定位块体问题进行较为全面地计算分析。结果表明:当存在较多产状和位置变化复杂的确定性长大结构面时,采用传统块体理论方法进行组合并确定不同组合形成的关键块体,则工作量大,且块体形态特征难以确定。然而,三维块体切割分析可以快速搜索得到所有块体。在综合考虑结构面延伸为110 m,搜索得到体积大于100 m^(3)的可失稳块体有6个,但块体稳定性均较好,不需要采取支护措施;随机节理裂隙形成的不定位块体,在重力的作用下,不存在失稳问题;确定性与随机性结构面共同形成的半定位块体,只在少数断层旁边出现,其稳定性均满足设计要求。该边坡的岩体结构面切割形成的块体问题不突出,结构面组合特征对边坡的稳定性影响较小。