水压力作用下三峡库区侏罗系软岩裂纹扩展规律及力学机制

三峡库区侏罗系地层滑坡发育广泛,研究该地层软岩夹层在不同水压力作用下的强度及变形破坏特性对库区岸坡的长期稳定性评价具有重要理论指导意义。以三峡库区侏罗系典型软岩——沙溪庙组泥质粉砂岩为例,对其进行了不同水压力下的力学试验系统(MTS)三轴压缩试验,并基于断裂力学与有效应力原理对水-力耦合效应下岩石的起裂及裂纹扩展机制进行了分析。研究结果表明：水压力的存在可降低岩石的峰值抗压强度,水压力越大岩石破坏后控制性裂纹的长度及倾角也总体随之增大,次生裂纹的数目也呈现出随之增多的趋势;原生裂纹的起裂及次生裂纹的扩展分别受控于K_Ⅱ、K_Ⅰ型应力强度因子,原生裂纹的起裂角最大为70.5°;次生裂纹的临界扩展长度随原生裂纹长度的增加而增大,当原生裂纹倾角约为45°时,在相同条件下次生裂纹的扩展长度最大;说明水压力的存在加剧了岩石裂纹的扩展,且使岩石的张拉破坏趋势更为明显,而原生裂纹形态特征对裂纹的扩展规律亦具有较大的影响。     

高应力区砂岩加卸载条件下能量变化规律及损伤分析

根据高应力区砂岩三轴压缩试验和峰前卸围压试验的结果,分析了砂岩在不同应力路径下的能量变化规律。试验结果表明,相同围压下,峰前卸围压试验的各能量指标(总吸收能、弹性应变能、耗散能)均小于三轴压缩试验,能量变化特征与其初始应力路径密切相关,且随围压的增大而增大。峰前储存的弹性应变能比耗散能多,耗散能只在临近峰值点处才迅速增加。能量的耗散会导致岩石产生损伤,并且使岩性劣化、丧失强度,从能量角度定义的损伤变量,可以得出结论:开始卸荷低围压下的损伤变量大于高围压下,临近破坏时高围压下的损伤变量大于低围压下;卸围压使岩样束缚减小,加速了损伤的发展,岩样所受的应力状态愈趋不平衡。因此,基于能量的角度来表征岩石的损伤演化更符合实际。      

基于声发射试验的红层砂岩损伤演化特性分析

红层砂岩在我国广泛分布,其特殊的工程地质特性对工程建设具有重要影响。对取自重庆万州龙驹坝地区的侏罗系红层砂岩样品进行了声发射试验,分析了其在单轴压缩条件下的损伤演化特性,得到了样品在单轴压缩条件下的应力－应变特征曲线,以及声发射参数在红层砂岩破裂过程中的响应特征。试验结果表明:样品在单轴受压条件下的损伤过程分为内部压密、弹性变形、塑性变形、破裂和残余变形５个阶段,各阶段声发射参数具有显著差异;不同类型样品的损伤量曲线与应力曲线具有同步性,且在弹性－塑性临界点开始出现损伤量的跳跃性
增长;对 ＡＥ振铃计数率参数的回归分析表明,样品在损伤破裂过程中的声发射参数序列存在分形特征,关 联 维数 Ｄ 可以较好地表征岩石内部损伤的发展规律。试验成果可为红层岩体失稳破坏的监测预警及风险评价提供数据支撑。      

模拟堆载作用的黄土边坡土体变形机理试验

通过固结不排水剪试验,研究了堆载作用下不同深度、含水量和围压的原状黄土的变形和破坏特征,并从黄土的微观结构角度分析了产生这一现象的原因,结合黄土边坡特殊的工程地质条件,分析了堆载作用下黄土边坡土体的变形破坏过程。试验结果表明,不同深度、含水量和围压的原状黄土的应力应变曲线和抗剪强度具有不同的特征;特殊的工程地质条件,使黄土坡体的某些部位形成了堆载作用下不利于黄土材料强度保持的含水量和围压的组合,导致了这些部位黄土的变形破坏,进而诱发坡体的变形破坏。     

基于损伤分区与统一强度理论的岩石本构模型

自然界中岩石内部均存在一定程度的损伤,损伤的持续演化过程对岩体的稳定性极为不利。为了研究岩石的损伤演化过程,将岩石分为未损伤部分、闭合裂隙部分与张开裂隙部分,采用统一强度理论与统计损伤理论分析岩石微元强度的分布,通过分析变形协调条件下各部分的应力-应变特征得到岩石的损伤本构模型与损伤演化模型,与巴东组紫红色泥岩三轴压缩试验结果对比验证后将模型应用于某反倾层状岩质边坡的破坏深度分析。分析结果表明:提出的损伤本构模型可以较好地模拟巴东组紫红色泥岩的三轴压缩应力-应变特性,提出的损伤演化模型可以较好地分析巴东组紫红色泥岩的损伤演化过程,且模型参数具有明确的物理意义;此外,根据基于损伤演化模型的反倾层状岩质边坡破坏深度修正模型计算得到的结果偏保守,用于岩土工程设计偏安全。      

单轴压缩条件下不同含水率黑云母二长花岗岩破坏特征与机制

花岗岩在不同含水率条件下的变形破坏特征和机制对此类工程岩体稳定性评价具有重要的意义。开展不同含水率黑云母二长花岗岩单轴压缩试验,分析破坏特征和应力-应变曲线特征,开展断口扫描电镜试验,分析微观形貌特征,研究破坏机制。试验结果表明:黑云母二长花岗岩具有明显的应变软化特征;随含水率增大,曲线上微裂隙压密阶段长度逐渐增加,稳定破裂阶段及非稳定破裂阶段长度均逐渐缩短,但所占比例增大,曲线上峰前阶段涨落交替现象加剧;饱和时单轴抗压强度和弹性模量相比干燥时分别降低了40.68%,20.3%;变形破坏过程可大致分为以下5个阶段:平静期、裂纹萌生期、裂纹扩展伴随颗粒弹射期、片状碎片剥落伴随颗粒弹射期及崩落式破坏期;随含水率增大,花岗岩破坏时的剧烈程度、发出的声响及脆性程度均逐渐降低;花岗岩破坏机制为拉-剪复合破坏,低含水率时以压致拉张破坏为主,随含水率增大呈现拉张破坏减少而剪切破坏增多的趋势,饱和时以剪破坏为主。研究结果可为黑云二长花岗岩与水之间的耦合模型构建提供理论支撑,对水-岩耦合环境下工程岩体稳定性分析具有重要科学意义。      

围压与轴压共同作用对恐龙化石应力场的影响

包括恐龙化石在内的古生物化石是重要的地质遗迹,是研究生物进化的最重要资料。该文从物理力学角度,通过数值试验模拟分析围压和轴压作用下对恐龙化石强度和破坏特性的影响效果。试验结果表明:不同埋深时围压对含有不同角度裂隙化石应力影响较大,随着埋深增加,含有裂隙化石的应力大幅增大。在围压与轴压共同作用时,埋深对开裂角的影响较小,而随埋深增大时极限载荷也随之增大。同时,在不同埋深下开裂角随裂隙角度的变化趋势一致,均随着裂隙角度的增大而减小;而极限载荷随裂隙角度的变化趋势一致。     

基于Hoek-Brown准则的节理岩体能量参数估算

岩体变形和破坏可以看作能量耗散和释放的过程.由于节理岩体结构复杂且难以开展室内试验,因此无法通过试验直接求取其能量学参数.基于Hoek-Brown准则和岩石能量理论,提出了节理岩体在临界状态能量学参数的估算方法.针对含贯通节理(或层面)岩体,通过修正岩块单轴抗压强度以体现贯通节理的方向效应.采用PFC3D分别模拟小尺寸岩样(Φ50mm×100mm)和大尺寸岩体(Φ2m×2m)的三轴压缩试验,通过岩石三轴试验结果拟合岩石数值模拟的细观参数并应用于节理岩体的模拟.根据节理岩体模拟得到应力应变曲线和能量流,验证了Hoek-Brown准则对节理岩体能量参数估算的合理性.     

泾河下游黄土台塬区侵蚀诱发滑坡机理

泾河下游黄土台塬区侵蚀诱发的黄土滑坡不仅威胁当地居民的生命财产安全,而且引发严重的水土流失及文物损毁等问题。以该类黄土滑坡为研究对象,在详细地质调查的基础上,取唐家村L2滑坡坡脚原状黄土进行减围压三轴剪切(RTC)试验,研究了饱和黄土的应力、孔压、围压特征以及剪切速率对土体力学行为的影响。结果表明,RTC应力路径下围压率达到0.55时,土体会因偏应力增大而引起塑性剪切破坏;同时,该应力路径下的饱和黄土内摩擦角很小,仅为10.7°;RTC应力路径下的破坏面,十分接近K 0状态面,说明天然斜坡坡脚饱和黄土在小幅水平应力降低条件下易于发生破坏,从而诱发滑坡失稳。     

不同受力状态下岩石破坏过程次声信号特征

采用室内试验方法,分别开展了岩石在压缩、剪切和拉伸状态下的破坏试验,利用高灵敏度的次声信号采集设备同步采集岩石破坏过程中的次声信号,对不同受力状态下岩石次声信号的特征差异进行了研究。结果表明:在压缩状态下,岩石次声信号发射主要在弹性和塑性变形阶段,次声信号的峰值频率在7Hz左右,在岩石临近破坏前,次声信号振幅和频率范围均有所增加;在剪切状态下,次声信号主要集中在峰值后应力逐步下降的阶段,信号功率分布集中程度较压缩试件略低,峰值频率在8Hz左右;在拉伸状态下,试件加载初始阶段便有次声信号发生,次声信号频率通常存在高、低两个中心,其中低频与压缩试件接近,高频则高出3Hz,拉伸试件内部裂隙的萌生和发展较压缩和剪切状态下更为迅速、有序,随着试件内部裂隙的发展,次声信号频率逐渐升高。以上特征的发现为不同受力状态下次声信号的识别以及岩体灾变预测提供了依据。     

三峡库区大型-特大型层状岩质滑坡成因模式及地质特征分析

三峡库区大型-特大型滑坡发育，尤以层状岩质滑坡的危害性大。因库区各段地质条件差异使得滑坡成因模式各不相同，这影响了滑坡的运动形式和岩土体解体程度。在收集三峡库区51处典型的大型-特大型层状岩质滑坡调查资料基础上，根据堆积岩体结构和区段地质条件反推该段滑坡破坏成因模式，而不同成因模式下的滑坡坡体渗透性不同，分析已有滑坡对库水位变动存在的复活响应差异，据此得出以下结论:①在成因模式上，除顺层滑移型滑坡在库区中均有分布外，从库首至库尾随着岩层倾角的逐渐减缓，滑坡成因模式从崩塌型、反倾弯曲型逐渐过渡到平推式；②在坡体渗透性上，成因模式造成的岩体结构变化与坡体中的泥质含量共同作用，导致顺层滑移型滑坡前后缘渗透性存在较大差异；反倾型滑坡渗透性则整体变化较小；③在库水位变动影响下，不同坡体渗透性与滑面形态共同决定了滑坡的复活变形差异。      

Experimental study of seepage characteristics of single rock fracture based on stress states and stress history

Through seepage tests under different loading and unloading confining pressures and different hydraulic gradients,the authors studied the effects of stress states and stress history on fracture permeability evolution for single granite fracture and sandstone fracture. The results show that there exists a linear relationship between the seepage discharge and osmotic pressure in sandstone fissure under each level of confining pressure. With the increasing in the confining pressure,the permeability of the fracture decreases,but the decreasing rate is changeing. During the unloading process,the fracture seepage velocity cannot be fully recovered to the size of the loading process. Therefore,in the unloading process of the confining pressure,the recovery of fracture permeability shows obvious hysteresis effects. The flow rate of the fracture remains unchanged during five cycles of loading and unloading processes of the confining pressure. In each cycle,the evolution character of the flow rate with the confining pressure remains unchanged. These experiments show that the seepage characteristics of sandstone and granite fractures are not the same under the same stress state.     

Slope reinforcement for housing in Three Gorges reservoir area

The Three Gorges Project of the Yangtze River is the largest hydropower-complex project under construction in the world. Under the largescale relocation projects, 2874 engineered slopes are formed along with the construction of new towns. In this paper, the cutting slopes are mainly soil slopes and rock slopes. Soil slopes include residual soil slopes, colluvial accumulation slopes, swelling soil slopes, and artificial earth fill slopes, etc. Rock slopes include blocky structure rock slopes, layer structure rock slopes, and clastic structure rock slopes, etc. Varied protection measures have been used for slope protection in the reservoir area including shotcrete concrete-anchor bars, frame beams, retaining walls, slope stabilizing piles, sheet-pile walls, anchorage anti-shear tunnels, flexible protection grids, and drainage, etc. Besides, slope deformation monitoring systems have been set up to monitor deformation failure and the stability state of slopes. The protection measures have guaranteed slope safety and maintained a harmony with the urban environment and surrounding landscape.     

Deformation and failure mechanism of phyllite under the effects of THM coupling and unloading

Although the study of TM(Thermo Mechanics),HM(Hydraulic-Mechanics) and THM(Thermo-Hydraulic-Mechanics) coupling under a loading test have been under development,rock failure analysis under THM coupling and unloading is an emerging topic.Based on a high temperature triaxial unloading seep test for phyllite,this paper discusses the deformation and failure mechanism of phyllites under the "H M,T→H,T→M" incomplete coupling model with unloading conditions.The results indicate that the elastic modulus and initial permeability decrease and the Poisson’s ratio increases with increasing temperature;the elastic modulus decreases and the Poisson’s ratio and initial permeability increase with increasing water pressure.During the unloading process,rock penetrability is small at the initial elastic deformation phase,but the penetrability increases near the end of the elastic deformation phase;mechanisms involving temperature and water pressure affect penetrability differently.Phyllite failure occurs from the initial thermal damage of the rock materials,splitting and softening(which is caused by pore water pressure),and the pressure difference which is formed from the loading axial pressure and unloading confining pressure.The phyllite failure mechanism is a transtensional(tension-shearing) failure.     

Effect of Freeze-Thaw Cycles on Mechanical Properties and Permeability of Red Sandstone under Triaxial Compression

Geological disasters will happen in cold regions because of the effects of freeze-thaw cycles on rocks or soils, so studying the effects of these cycles on the mechanical characteristics and permeability properties of rocks is very important. In this study,red sandstone samples were frozen and thawed with 0,4, 8 and 12 cycles, each cycle including 12 h of freezing and 12 h of thawing. The P-wave velocities of these samples were measured, and the mechanical properties and evolution of the steady-state permeabilities were investigated in a series of uniaxial and triaxial compression tests. Experimental results show that, with the increasing of cyclic freeze-thaw times, the P-wave velocity of the red sandstone decreases. The number of freeze-thaw cycles has a significant influence on the uniaxial compressive strength, elastic modulus, cohesion, and angle of internal friction. The evolution of permeability of the rock samples after cycles of freeze-thaw in a complete stress-strain process under triaxial compression is closely related to the variation of the microstructure in the rock. There is a highly corresponding relationship between volumetric strain and permeability with axial strain in all stages of the stress-strain behaviour.     

呷爬滑坡滑带土蠕变特性及其稳定性

水库滑坡变形破坏受其岩土体蠕变特性及环境因素的影响。当滑坡进入加速变形阶段后,变形骤然增大,失稳概率增加。为了研究滑坡岩土体蠕变特性及其稳定性,选取锦屏一级水电站呷爬滑坡为研究对象,采用坡表位移监测曲线分析与室内三轴蠕变试验相结合的方法,建立了Burgers蠕变模型结合FLAC3D软件进行了滑坡稳定性研究。分析坡表位移-时间曲线发现,坡体变形特征与一般滑坡土体的蠕变特征具有相似性,滑带土室内三轴蠕变试验结果表明,滑带土变形可划分为瞬时蠕变、减速蠕变与稳定蠕变3个阶段,同时其瞬时变形量、稳定蠕变速率均随围压以及应力水平的增大而增大。基于滑带土蠕变特性的Burgers蠕变模型的计算结果,对比了常规强度折减法与考虑蠕变的强度折减法的滑坡稳定性系数,计算结果表明呷爬滑坡目前处于稳定状态,在一个计算周期内考虑蠕变的强度折减法较常规强度折减法的稳定性系数下降了0.04,因此,揭示滑坡土体蠕变特性并在此基础上研究其稳定性具有实际意义。      

Temperature effects on the mechanical properties of slates in triaxial compression test

High geothermal temperatures appear to be unfavorable for the construction of tunnels in slate rocks with high overburden. To investigate the mechanical characteristics of slates at various levels of geothermal temperature, conventional triaxial compression tests at different levels of confining stress were carried out at 4 different temperatures from 20℃ to 120℃. The obtained results show high confining pressures weaken the thermal effects on rock mechanical characteristics while higher temperatures enhance the effect of confining pressure.At higher levels of confining stress the thermal effects on the rock strength characteristics decrease. The higher the temperature, the larger is the effect of confining pressure on the mechanical characteristics of the slate. Increase of temperature leads to a decrease of the peak strength but increases the deformability and ductility of the slate, the thermo effect on the peak strength and Poisson's ratio is larger than on the elastic modulus. Higher temperatures reduce the shear strength of slate, the decrease is mainly caused by a decrease of the cohesion. In general, the slate samples fail in shear failure.     

酸腐蚀作用下川渝红层砂岩蠕变特性试验研究

岩石蠕变特性对岩体工程的长期稳定有着重要影响, 尤其是在酸雨等水化学作用下, 岩石的细观结构遭到破坏, 蠕变特性及变形更为显著。以重庆二佛寺红层砂岩为研究对象, 通过开展室内三轴压缩分级蠕变试验, 研究了酸腐蚀状态下砂岩的蠕变特性。结果表明: 酸的腐蚀和浸泡会使砂岩内部孔隙增加, 导致砂岩在第一级荷载下会产生较大的瞬时应变和蠕变量, 之后瞬时应变量和蠕变量随着应力增加而增大; 岩样受到腐蚀软化, 蠕变破坏强度为抗压强度的76%, 长期强度仅为抗压强度的54%。为了描述蠕变全过程, 建立了一个损伤蠕变模型来拟合试验数据, 验证了其适用性, 可以为岩土工程建设的稳定性提供参考。      

Undrained behaviour of silt under static and cyclic loading

In this study, the undrained behaviour of silt under low stress level is studied. An effective preparation method for built—in silt samples in the triaxial test was firstly developed. By triaxial testing of samples at low confining pressures it was found that silt easily loses stability and liquefies. Loose silt may show temporary liquefaction under static loading, and develop full liquefaction under cyclic loading. The most important factors influencing the silt behaviour are porosity, confining pressure, consolidation state, cyclic loading level and number of cycles. The maximum obtainable shear stress is primarily a function of the confining pressure and the internal frictional angle. The actual structure of the silt material is the key factor in controlling its behaviour.