中间主应力对岩石强度的影响程度和规律

本文根据普通三轴试验中随着围压的增加岩石的变形和破坏特性的变化,划分出低围压,中等围压及高围压的界限。通过分析国内外学者的岩石真三轴试验结果,总结出了中等围压下中间主应力对不同岩石强度的影响程度和规律,并指出了莫尔(Molr)准则的适用范围。     

空心圆柱砂岩真三轴试验研究

利用岩石空心圆柱扭剪试验系统针对灰砂岩进行真三轴试验研究,分别开展控制（σ2-σ3）（σ2为中间主应力,σ3为最小主应力）条件压缩试验和恒σ3、变σ2条件压缩试验,对灰砂岩的应力-应变规律、强度特性及破坏特征进行详细分析,并进一步探讨了中间主应力效应,最小主应力效应,应力洛德角效应以及强度准则的适用性。研究结果表明：岩石空心圆柱扭剪试验系统能够实现真三轴应力状态的模拟,相较于常规的实现方式,该方法可避免端部摩擦的影响;内外围压的压差对岩石强度有很大影响,尤其是在高围压下,较大的压差使得岩石强度迅速弱化导致剧烈破坏;中间主应力对岩石强度影响显著且具有区间效应,最小主应力对岩石强度有强化作用,该特点对于实际工程开挖岩体的高效及时支护具有重要的指导意义;进一步地,根据所获试验结果对现阶段用于描述岩石力学特性的强度准则进行分析,认为采用指数强度准则能合理反映岩石真三轴应力状态,具有较好的适用性,可用来评价实际工程中岩石的强度特征。     

陆内裂陷盆地构造动力学分析

陆内裂陷盆地区形成和演化过程中的构造力包括4方面：（1）地幔对流由岩石圈板块底面边界施加到岩石圈板块内部的构造力F1;（2）板块相对运动通过岩石圈板块侧面边界施加到岩石圈板块内部的构造力F2;（3）岩石圈受热膨胀和冷却收缩在地壳内部产生的构造力F3;（4）地壳质量在地壳内部产生的围压F4。地壳中的应力是这4方面的构造力的函数S(Fi),其中,F1和 F2的大小和方向对三轴应力状态的主应力大小和方向起决定作用。地壳发育正断层的条件是应力状态方程S（Fi）中σ2 σ3主应力平面大致处于水平面状态、σ1近直立。当F1和F2的方向一致且F1＞F2或F1和F2的作用方向相互垂直的情况下,F1和F2合成的应力场中的最小主应力方向与X轴方向一致,地壳发生正向裂陷作用。在F1和F2的方向既不平行也不垂直的情况下, F1和F2叠加产生最小主应力（σ3）的方向与X轴方向不一致,地壳发生斜向裂陷作用。当地幔对流从岩石圈底部对岩石圈产生的引张作用力减小、板块之间相对运动从岩石圈侧面边界对岩石圈产生的挤压作用力增强的情形下,地壳应力状态S（Fi）在X轴和Y轴构成的水平面上的最大主应力可能超过Z轴方向的主应力,使σZ相当于三轴应力状态的σ2,裂陷盆地发生走滑构造变形。如果地壳应力状态S（Fi）在X轴和Y轴构成的水平面上的最小主应力也超过Z轴方向的主应力,则σZ相当于三轴应力状态的σ3,裂陷盆地发生收缩构造变形,可能发育逆冲断层或使早期的正断层发生反转位移。随着裂陷作用的渐进发展,不同时期F1和F2的大小和方向的变化导致地壳应力场的主应力轴方向也相应发生变化,使裂陷盆地在不同演化阶段表现出不同的构造变形特征。     

三维应力作用下岩体层面效应分析

为得到层状岩体在真三轴压缩情况下的强度变形特征,利用数值分析方法建立计算模型,得到不同结构面倾角? 下试样的应力和变形响应,结果表明,(1) 加载初期,结构面倾角? = 0°和? = 90°试样对应的初始弹性模量最大;随着试样变形的增大,对应的弹性模量以? = 90°、60°、0°的顺序逐渐减小;? = 90°和? = 0°试样发生破坏的脆性特征比较明显;(2) 随着围压? 3 = σ2的增大,压缩强度? 1不断增大;围压对强度极值发生的位置影响不大;(3) 最小主应力与结构面走向平行情况下,随着中间主应力? 2的增大,试样压缩强度呈现先增大后减小的趋势;随着最小主应力? 3的增大,? 1逐渐增大;当? 3较小时,二者符合线性关系;随着? 3的增大,二者的关系逐渐呈现非线性特征;并且结构面滑移破坏型试样的非线性特征更加明显;(4) 最小主应力与结构面走向垂直的情况下层状岩体的压缩强度与中间主应力和最小主应力的关系均呈现显著的线性特征。     

人造多晶冰三轴压缩强度特性试验研究

为研究冰的三轴强度特性,对人造宏观各向同性冰进行了不同温度和不同围压下的恒定加载速率三轴压缩试验,得到多晶冰三轴压缩的应力-应变曲线、抗压强度与温度之间的关系,利用莫尔-库仑强度准则分析了温度和围压对强度参数的影响.结果表明：轴向应变加载速率为1.67×10-4 s-1时,不同温度、不同围压下冰的应力-应变曲线均为应变...     

粗粒料大型三轴试验的尺寸效应研究

采用大型三轴仪,对双江口高土石坝的砂岩过渡料进行试验研究。通过对不同试样直径D和不同最大粒径dmax的过渡料进行等?3应力路径试验,分析了D、dmax对应力-应变-强度特性的影响,研究了室内试验存在的尺寸效应。结果表明,对同一种级配试样,破坏主应力差、内摩擦角和初始切线模量随试样直径的减小而增大;在低围压下破坏主应力差和内摩擦角的增大趋势明显,但随围压增大,增大幅度减小;对同样的试样直径,最大粒径增大,破坏主应力差和内摩擦角增大,同样这种增大趋势在低围压下明显。     

考虑主应力轴偏转角影响的饱和软粘土路基长期沉降分析

基于循环三轴试验基础上的交通荷载路基沉降计算模型未能反映主应力轴偏转现象,而建立在不同围压的饱和软粘土恒定主应力轴偏转角的不排水循环加载试验基础上的循环累应变显式模型、累积孔压显式模型能考虑主应力轴偏转的现象。基于拟静力有限元计算、恒定主应力轴偏转角循环累积塑性变形及累积孔压显式模型相结合的思路,提出了考虑主应力轴偏转角影响的交通荷载作用下软土地基长期运营沉降的实用分析方法,并应用于高速公路工程的长期沉降预测。     

堆石料应力-应变特性大型三轴试验研究

通过对水布垭筑坝堆石料进行0.2~3.5 MPa围压下的大型三轴固结排水剪(CD)试验,分析了不同围压下堆石料的偏应力-轴应变关系及体应变-轴应变关系的变化规律;引入破坏强度和体变与围压的关系,采用临界偏应力σ_(cre)和临界体应变ε_(vcre)作为归一化因子对不同围压下的应力-应变关系试验结果进行归一化处理,建立了不同围压下的应力-应变关系表达式,并将计算预测与试验结果进行对比验证。研究表明:对于颗粒级配确定的密实堆石料,初始变形期存在一定的弹性增长阶段,且该直线段的斜率受围压的影响较大;低围压时表现为应变软化,先剪缩后剪胀为主的力学特性,且围压越低,剪胀效应越明显;高围压(0.8 MPa≤σ_3≤3.0 MPa)时表现为应变硬化、剪缩为主的特性;剪胀消失的临界围压处于0.45~0.8 MPa之间;超高围压(σ_33.0 MPa)条件下,虽表现为应变软化、剪缩的特性,但其应变软化的机制与低围压下不同;分析认为,超高围压下剪切过程中颗粒的相对破碎率达15%以上,颗粒破碎引起的堆石料强度降低大于围压的增大对堆石料强度的提高。峰值主应力比随围压的增大而降低,且随轴应变的增大而趋于一致。堆石料的破坏强度与围压呈线性相关。最后,通过计算预测结果证明了该应力-应变关系表达式的正确性。     

绿片岩三轴流变力学特性的研究(Ⅰ):试验结果

为了解锦屏一级水电站坝基绿片岩的流变力学特性，采用岩石全自动流变伺服仪对绿片岩进行了三轴压缩流变试验。基于试验结果，研究了绿片岩在不同围压作用下的轴向应变以及侧向应变随时间的变化规律，讨论了流变特性对岩石应力一应变曲线的影响，探讨了不同应力水平下的轴向以及侧向流变速率变化趋势，分析了不同围压下流变的破裂机制，掌握了绿片岩三轴流变的基本规律，从而为该水电站工程流变数值分析时参数的辨识提供了可靠的依据。     

动态围压下空心圆柱扭剪仪模拟主应力轴旋转应力路径能力分析

针对英国GDS公司动态空心圆柱扭剪仪（HCA）在主应力轴旋转试验中能够实现三向动态加载（轴力、扭矩、内围压或外围压）的功能,通过严格的数学推导,提出了3种易于实现又与实际工程背景相符合的应力路径加载方式。当三向动载满足相应的条件时,可以实现（1）平均主应力p和剪应力幅值q保持恒定的应力路径（应力路径1）;（2）中主应力参数b = 0.5、剪应力幅值q为常数的应力路径（应力路径2）;（3）平均应力p保持不变、主应力旋转角90º突变的应力路径（应力路径3）,其中应力路径1、2为模拟海洋波浪荷载作用下的应力路径试验提供了理论依据,应力路径3可用于模拟地震荷载作用下的土体动力特性。以上3种应力路径均不能在两向动态HCA仪中实现     

Mechanical Properties of Weak Porous Sandstone Under General Triaxial Stress States

The mechanical properties of weak porous sandstone with uniaxial compressive strength of about 300kg/cm2 , porosity as high as 27% and bulk density 1.85 g/cm3 , were investigated experimentally by using Mogil’s true triaxial compressive apparatus. The properties of deformation and failure, in the whole process from brittleness to ductility, were observed by bringing confining pressure up to 500 kg/cm2 under room temperature . The intermediate principal stress was successfully brought up from the lowest limit. σ2=σ3 to the highest limit , σ2=σ1 under constant confining pressure, 50 and 100 kg/cm2 respectively. The whole process that the strength increases gradually to a maximum and then decreases gradually with increasing of intermediate principal stress under constant σ3 was observed . Failure and flow were effecfed not due to volume dilatancy but rather du to compression of volume under constant confining stress of 100 kg/cm 2 and a general triaxial stress state of σ3 =100 kg/cm2 , σ2=295kg/cm2 . For hard rocks , this behavior can be observed possibly only under higher temperatures and pressures. The experimental result shows that the ductility and coefficient of strain hardening are increased in proportion to the intermediate stress σ2 under constant σ3 . This is different from the behavior of hard rocks.     

一般三轴压缩下岩石的流动和破坏

引言在天然条件下,岩石的破坏和流动是在复杂的组合应力下产生的.应力状态的影响在岩石力学里是个基本课题之一.为了研究这一影响,在各种组合应力状态下,进行了许多岩石变形的室内实验。     

FLOW AND FRACTURE OF ROCKS UNDER GENERAL TRIAXIAL COMPRESSION

Recent laboratory studies of the flow and fracture of rocks under general triaxial compression are reviewed .New Developments in laboratory techniques have made it possible to measure three principal stresses and strains under general triaxial stress states ,in which all three principal stresses are different . Strength and ductility of isotropic rocks are markedly affected not only by the least compression σ3 ,although these two effects are rather additional in strength ,but opposite in ductility .The experimental results show that dilatancy is highly anisotropic rocks have been also measured under the general triaxial compression .In this case ,the effect of the intermediate compression markedly depends on the orientations of the weak planes.     

Q3砂黄土真三轴强度变形特性研究

为了研究Q3砂黄土强度变形特性,以甘肃永靖黑方台Q3砂黄土为研究对象,利用西安理工大学研制的真三轴仪,进行了3个围压（50、100 kPa 和200 kPa）、3个b值（0、0.25和0.5）和3个含水率（5%、10%和15%）不同工况试样破坏情况的真三轴试验。试验结果发现：（1）真三轴条件下Q3砂黄土剪切破坏方式以侧胀破坏、单缝剪切破坏为主,其次少数土样发生锥形破坏、双缝剪切破坏和T型缝剪切破坏。（2）相同围压和含水率、不同中主应力比（b）的情况下,Q3砂黄土的主应力差随中主应力比增大而增大,应力-应变关系曲线为强硬化型,剪胀现象明显;中主应力比对广义剪应力和广义剪应变之间关系有一定影响,随b值增加,曲线依次增加;随b值的增加,强度降低,广义剪应力与平均球应力比（q/p）与主应变关系曲线逐渐变缓,且曲线依次降低。（3）随含水率增加,Q3砂黄土由固态向半固态转化过程中,不同中主应力比时黏聚力均出现明显降低,但内摩擦角则出现微小增加。     

Effect of fluid pressure on rock compressive failure in a nearly impermeable crystalline rock: Implication on mechanism of borehole breakouts

We conducted laboratory true triaxial experiments in the nearly impermeable Pohang rhyolite to investigate failure mechanisms under ‘dry’ and ‘wet’ rock conditions. Under ‘dry’ conditions prismatic specimens were jacketed all around to prevent confining fluid penetration. Under ‘wet’ conditions one pair of the specimen faces was left unjacketed and in direct contact with the confining fluid (kerosene) applying the least principal stress in an attempt to simulate the case of an unlined borehole wall. In both testing setups the true triaxial compressive strength for a given least principal stress increases significantly as the intermediate principal stress rises. The unjacketed rhyolite strength is, however, only 60 to 85% of the strength under dry conditions, depending on the magnitude of the intermediate principal stress. In dry rhyolite the failure process begins upon dilatancy onset, followed by microcrack localization, and ending in a steeply dipping shear fracture. On the other hand, brittle fracture in wet specimens occurs almost immediately after the onset of dilatancy by the development of one or more through-going extensile fractures subparallel and adjacent to one of the unjacketed faces, resembling the extensile cracks leading to borehole breakouts in crystalline rocks. We infer that upon dilatancy the confining fluid intrudes and quickly propagates newly opened stress-induced microcracks subparallel to the unjacketed faces, leading to ‘early’ failure.     

岩体裂隙三轴应力渗透规律的试验研究

利用三轴应力渗透仪分别对煤矿底板的硬岩和软岩进行三轴应力渗透试验 ,观测渗水量、围压、轴压及水压的变化。     

高应力下砾质心墙料切线模量研究

使用高压大型三轴仪,对某300 m级土石坝的砾质土心墙料进行了最高围压5 MPa的三轴试验。试验结果表明砾质土的应力-应变关系符合双曲线关系,抗剪强度包络线呈非线性。根据参数的物理意义,初始模量Ei应在尽可能小的应变范围内取值,最大主应力差 应在大应变范围内取值,且实际工程的应变在1 %左右,建议在?a= 0 %～3 %下取Ei值,在?a = 5 %～15 %下取 值,数据拟合表明建议取值法比传统取值法拟合度高。由于试验的围压范围较大,提出把围压分0.2～1.0 MPa,1.5～3.0 MPa,3.5～5.0 MPa三段分别取切线模量,通过回归证明拟合较好。     

Considerations on strength of intact sedimentary rocks

This study presents the results of laboratory testing of sedimentary rocks under point loading as well as in uniaxial and triaxial compression. From the statistical analysis of the data, different conversion factors relating uniaxial compressive and point loading strength were determined for soft to strong rocks. Additionally, the material constant m_i, an input parameter for the Hoek and Brown failure criterion, was also estimated for different limestone samples by analysing the results from a series of triaxial compression tests under different confining pressures. The uniaxial compressive strength (UCS) of intact rocks, as estimated from the point load index using conversion factors, together with the Hoek–Brown constant m_i, and the Geological Strength Index (GSI) constitute the parameters for the calculation of the strength and deformability of rock masses.     

Influence of Loading Rate on Deformability and Compressive Strength of Three Thai Sandstones

Uniaxial and triaxial compressive strength tests have been performed using a polyaxial load frame to assess the influence of loading rate on the strength and deformability of three Thai sandstones. The applied axial stresses are controlled at constant rates of 0.001, 0.01, 0.1, 1.0 and 10 MPa/s. The confining pressures are maintained constant at 0, 3, 7 and 12 MPa. The sandstone strengths and elastic moduli tend to increase exponentially with the loading rates. The effects seem to be independent of the confining pressures. An empirical loading rate dependent formulation of both deformability and shear strength is developed for the elastic and isotropic rocks. It is based on the assumption of constant distortional strain energy of the rock at failure under a given mean normal stress. The proposed multiaxial criterion well describes the sandstone strengths within the range of the loading rates used here. It seems reasonable that the derived loading rate dependent equations for deformability and shear strength are transferable to similar brittle isotropic intact rocks.     

锦屏二级水电站大理岩复杂加卸载应力路径力学特性研究

地下洞室开挖围岩经历典型径向卸载、环向加载应力路径,由此引起的岩体强度、变形特征和破坏机制也不尽相同。针对锦屏二级水电站高地应力赋存环境,对施工排水洞大理岩开展常规单轴全应变、三轴压缩、卸围压、卸围压-加载轴压等4种不同应力路径力学试验,得到应力-应变全过程曲线、变形破坏特征和极限储能变化规律。试验研究结果表明, （1）锦屏二级水电站大理岩破坏时轴向应变一般较小,为硬脆性材料,卸荷应力路径下该脆性特征更为明显;（2）卸围压同时加载轴压试验峰值强度对应轴向应变、环向应变及体积应变值一般高于单纯的卸围压值,而对应峰值强度则一般低于卸围压值;（3）卸荷速率较大时,变形模量越大,大理岩峰值强度越低。加载速率越大,变形模量越小,峰值强度越高。初始围压越高,变形模量值越低,峰值强度越高;（4）无侧限作用时试件主要为张拉破坏,低侧限作用时为剪切破坏为主,局部存在张拉破坏,较高侧限时,剪切面为典型X或Y型;（5）岩石试件具有极限储能值,该值受多种因素的影响。一般情况下试件破坏对应围压越高,极限储能值越高,卸载速率越大,极限储能值越小。研究结果对于岩爆孕育发生机制解释以及工程实际问题的解决均有参考价值。