颗粒流细观强度参数与岩石断裂韧度之间的关系

 为研究岩石颗粒流分析模型中细观强度参数的物理意义,以接触黏结模型(CBM)中等效微梁的模型为基础,通过对2个黏结颗粒的拉伸和剪切状态进行分析,推导岩石颗粒流细观应力和断裂强度因子关系的理论公式,进而建立强度参数与岩石断裂韧度关系的理论模型。分析结果表明,岩石断裂韧度与细观强度呈线性关系。岩石颗粒最小粒径与颗粒半径比均对断裂强度因子有不利影响,且颗粒半径比的影响较大。以重庆地区砂岩为例,给出岩石断裂韧度与颗粒流细观强度之间的定量表达式,结果表明,岩石I型断裂韧度理论计算值范围与实测值较为相符。     

高温后高强混凝土剪切强度与细观结构

通过高温后高强混凝土(HSC)试件的push-off试验,研究了温度和混凝土抗压强度对HSC剪切强度的影响.基于剪切面细观结构的变化,分析了高温后HSC剪切强度变化的机理,研究了高温后HSC骨料断裂率与剪切强度的关系.结果表明:常温下HSC抗压强度为64.7,94.0 MPa时,200℃后HSC剪切强度较常温时分别略有减小和略有增大;超过200℃后,HSC剪切强度随温度的升高而降低;无论经历多高的温度,混凝土的抗压强度越高,则HSC剪切强度越大;HSC试件剪切面上的骨料断裂率随温度的升高而减小,随混凝土抗压强度的增加而增大.最后,建立了高温后HSC的骨料咬合模型.     

岩石断裂和损伤的研究现状

从岩石断裂和损伤力学角度以及细观角度对岩石的断裂和损伤理论的研究现状进行了综述分析,指出岩石强度理论的研究由经典强度理论向断裂强度理论、损伤强度理论发展。     

不同剪切速率下岩石节理的强度特性研究

不同剪切速率作用下岩石节理强度特性是研究地震荷载作用下岩体结构响应和安全的基本参数，通过RMT-150C电伺服试验机，利用人工浇铸的表面为锯齿状的混凝土岩石节理试样，研究不同剪切速率下各种岩石节理起伏角度岩石节理的强度特征。试验结果发现：（1）岩石节理面的峰值剪切强度随着剪切速率的增大而减小，减小幅度随着剪切速率的增大变小；（2）岩石节理面的峰值剪切强度随着起伏角度的增大而增大：（3）岩石节理面的峰值剪切强度随着法向应力的增大而增大，基本成线性关系。最后，基于试验的结果提出考虑不同剪切速率的岩石节理峰值强度模型。     

循环剪切荷载作用下岩石节理强度劣化规律试验模拟研究

 采用水泥砂浆为相似材料,制备5种起伏角度、3种岩壁强度的锯齿型节理试样。利用自行研制的节理循环剪切试验机,对制备的节理试样进行4种法向应力下的循环剪切试验。根据循环剪切试验过程和试验曲线,分析单个剪切循环中应力–位移曲线的峰值强度特点,以 来表示节理在第n个剪切循环中的峰值剪切强度;并进一步定义 = / 为剪切强度比,来表征节理在循环剪切荷载作用下经历一定剪切循环后峰值强度的劣化程度。基于多种条件下的节理循环剪切试验结果和定义的指标,分析峰值剪切强度 随循环剪切周期N的变化规律;并通过对比不同工况的试验结果,分析起伏角度、法向应力、岩壁强度对循环剪切荷载作用下节理强度劣化规律的影响。     

剪切破坏模式下岩石的强度准则

在对剪切破坏模式下岩石的变形和破坏局部化观察和本构模拟分析的基础上,提出了一个新的强度准则。该准则考虑了岩石材料的不均匀性及破坏局部化特性,定量地描述了岩石强度的尺寸效应。     

论岩石、混凝土离散–接触–断裂分析

阐述岩石、混凝土材料与结构的力学特征;综述当今岩石、混凝土离散–接触–断裂分析模型与数值方法;同时,对这一领域的前沿科学技术问题提出作者的见解;应用离散–接触–断裂分析模型,研究高坝与地基安全稳定问题,并给出若干工程实例;最后,展望岩石、混凝土力学未来的前景,指出构建连续–非连续介质统一数值模型,以研究细观损伤到宏观破坏失稳全过程机制是其主要发展方向。     

锚固方式对岩石节理宏细观剪切特性的影响及其机制研究

随着岩体工程规模的不断扩大和赋存环境的日趋复杂,岩石节理剪切滑移引起锚杆破断的现象日益突出。认清锚固节理的剪切特性及其抗剪机制对于岩体工程稳定性控制设计至关重要。通过开展锚固节理剪切试验与数值模拟,系统研究全锚和端锚2种方式对岩石节理宏细观剪切特性的影响及其机制。结果表明：全锚方式下锚固剂的存在会使锚杆迅速发挥其“销钉作用”,而端锚方式下在剪切位移超过钻孔与锚杆间的间隙后锚杆才开始发挥作用;在锚杆破断前,全锚方式相对于端锚方式的峰值剪切应力和破断剪切应力更大;相同剪切位移下相对于端锚,全锚条件下锚固节理的裂纹数量更多;全锚方式下裂纹集中在锚杆附近,尤其是锚杆与节理相交处,端锚方式下裂纹分布较为分散,在端头锚固处、锚杆与节理相交处以及垫片处均有分布;相同剪切位移条件下,全锚锚杆的剪切应力远大于端锚锚杆,但其轴向应力因受到锚固剂限制主要集中在节理面附近;端锚方式下锚杆轴向应力被充分调动,传递至垫片处后可有效增大节理的法向应力;端锚锚杆和全锚锚杆的变形范围均不断增大,但端锚锚杆的变形范围显著大于全锚锚杆。     

岩石节理剪切强度的J R C2JM C 新模型

 在应用Barton 的J RC2J CS 剪切强度准则时, 经常发现对于较不吻合的节理, 该准则往往过高地估测岩石节理的剪切强度。为了克服这一缺陷, 在实验结果的基础上提出形式为S= Rn tan [J R C JM C log10 (J CSöRn) + Ur] 的J RC2JM C 剪切强度准则。J RC2JM C 剪切强度准则考虑了节理表面粗糙度和吻合度的影响。J RC2JM C 准则能更好地描述节理的剪切实验结果, 并能更好地解释与估测各类岩石节理的特性, 特别是吻合程度较差的天然节理。     

岩石剪切破坏裂纹演化特征量化分析

 为深入研究岩石破坏过程表面裂纹演化规律,探讨表面裂纹与内部破裂之间的内在联系,对砂岩剪切过程中表面裂纹演化特征进行量化,分析砂岩剪切破坏表面裂纹演化模式,建立表面裂纹量化参数与应力状态和声发射特征之间的关系,并探讨含水状态对岩石剪切破坏表面裂纹量化参数的影响。研究结果表明：砂岩在剪切过程中伴随着表面雁行裂纹的形成与贯通,雁行裂纹宏观形态出现于破坏前的极短时间内,随后岩石发生剪切贯通;最大AE事件率总是出现在剪应力急剧下降来临之前极短时间内,且出现在表面裂纹非稳定快速扩展之前;饱水系数影响了表面裂纹出现的时间和相对于峰值剪应力的位置,随着饱水系数的增加,砂岩表面裂纹出现时间变早,最大瞬时贯通速度呈依次递减规律,贯通时间变长,表面裂纹快速扩展滞后时间呈明显增加趋势。     

Formulation of strain-dependent hydraulic conductivity for a fractured rock mass

By characterizing rock masses as anisotropic continua with one or multiple sets of critically oriented fractures, a methodology is developed in this paper to address the change in hydraulic conductivity resulted from engineering disturbance, material nonlinearity and anisotropy. An equivalent elastic–perfectly plastic constitutive model with non-associated flow rule and mobilized dilatancy is developed to describe the global nonlinear response of the rockmass under complex loading conditions. By separating the deformation of fractures from that of the equivalent medium, a strain-dependent hydraulic conductivity tensor is formulated. This not only considers the normal compressive deformation of the fractures, but also and more importantly, integrates the effect of material nonlinearity and post-peak shear dilatancy. Using this methodology, a closed-form solution is derived to describe the hydraulic behavior of a single fracture during combined normal and shear loading processes. The closed-form solution is validated by an existing coupled shear-flow test under wide ranges of normal and shear loads. Numerical simulations are performed to investigate the changes in hydraulic conductivities of a cubic block of fractured rock mass under triaxial compression and shear loading, as well as a circular underground excavation in a biaxial stress field at the Stripa mine, Sweden. The simulation results agree well with the in-situ experimental observations and an existing elastic strain-dependent analytical solution, respectively. The evaluation results clearly demonstrate that the proposed model is capable of predicting the changes in hydraulic properties of fractured rock masses under loading or excavation.     

短牛腿抗剪强度的敏感性因素分析

利用正交试验设计法对影响钢筋混凝土短牛腿抗剪承载力的各因素进行分析,考虑的因素包括混凝土抗压强度、剪跨比和钢筋屈服强度。通过分析可知剪跨比对短牛腿抗剪强度最为敏感,混凝土抗压强度和钢筋屈服强度次之。希望本文内容可作为进一步研究钢筋混凝土短牛腿受力性能的依据。     

Hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic and mechanical measurements

Hydromechanical coupled processes in a shallow fractured carbonate reservoir rock were investigated through field experiments coupled with analytical and numerical analyses. The experiments consist of hydraulic loading/unloading of a water reservoir in which fluid flow occurs mainly inside a heterogeneous fracture network made up of vertical faults and bedding planes. Hydromechanical response of the reservoir was measured using six pressure–normal displacement sensors located on discontinuities and two surface tiltmeters. A dual hydraulic behavior was characterized for low-permeability bedding planes well connected to high-permeability faults. Displacement responses show high-variability, nonlinear changes, sometimes with high-frequency oscillations, and a large scattering of magnitudes. Initial normal stiffnesses and effective normal stresses along fault planes were estimated in the field by interpreting pressure–normal displacement relations with a nonlinear function between effective normal stress and normal displacement. Two-dimensional discontinuum modeling with transient fluid flow was performed to fit measurements during hydraulic loading tests. Results show that the hydromechanical behavior of the reservoir is restored if a high stiffness contrast is allocated between low- and high-permeability discontinuities. Thus, a dual-permeability network of discontinuities will likely also be a contrasting stiffness network, in which the deformation of major flow-conducting discontinuities is significantly influenced by the stiffness of the surrounding less-permeable discontinuities.     

肋形纤维混凝土永久模板与新浇混凝土结合面抗剪强度试验研究

针对肋形混凝土永久性模板与结构新浇混凝土之间粘接问题,制作了与肋形模板原理相同的试件及对比试件共四种24个,用双面剪的方法对试块进行了新老混凝土的粘结面抗剪试验。试验结果表明,掺PVA纤维并带宽、高均为10mm肋的试件粘结面的抗剪强度是整体混凝土抗剪强度的85.78%,能够满足利用永久性模板浇筑的板、墙类构件抗剪要求。同时,对新老混凝土粘结面抗剪能力的计算方法进行了探讨。     

集中荷载作用下钢筋混凝土板的抗剪性能试验研究

根据多块板的试验资料 ,分析了宽跨比较大的板在集中荷载作用下的受剪承载力 ,建立了相应的计算公式 ;该公式具有形式简单、与试验结果符合性较好等特点。     

Experimental behaviour of a thermally restrained plate girder loaded in shear at elevated temperature

This paper outlines an experimental investigation of twelve simply supported steel plate girders subjected to shear loading at elevated temperature. Three different series of steel plate girders have been tested at three constant elevated temperature levels. Additional axial restraints were applied onto beams to simulate the thermal restraint effects of adjacent cooler parts of steel-framed structure in fire. Based on test results and observations, the pre- and post-buckling behaviours of plate girder web panels at high temperature were discussed. In addition, finite element modelling of the web panels was conducted and numerical models generally agreed well with test results. It was observed that the ultimate shear capacity decreased significantly under a thermal restraint effect.     

Numerical evaluation of strength and deformability of fractured rocks

Knowledge of the strength and deformability of fractured rocks is important for design, construction and stability evaluation of slopes, foundations and underground excavations in civil and mining engineering. However, laboratory tests of intact rock samples cannot provide information about the strength and deformation behaviors of fractured rock masses that include many fractures of varying sizes, orientations and locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costly and often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numerical predicting using discrete element methods(DEM) is a suitable approach for such modeling because of their advantages of explicit representations of both fractures system geometry and their constitutive behaviors of fractures, besides that of intact rock matrix. In this study, to generically determine the compressive strength of fractured rock masses, a series of numerical experiments were performed on two-dimensional discrete fracture network models based on the realistic geometrical and mechanical data of fracture systems from feld mapping. We used the UDEC code and a numerical servo-controlled program for controlling the progressive compressive loading process to avoid sudden violent failure of the models. The two loading conditions applied are similar to the standard laboratory testing for intact rock samples in order to check possible differences caused by such loading conditions. Numerical results show that the strength of fractured rocks increases with the increasing confning pressure, and that deformation behavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses and strains obtained from these numerical experiments were used to ft the well-known Mohr-Coulomb(MC) and Hoek-Brown(H-B) failure criteria, represented by equivalent material properties defning these two criteria. The results show that both criteria can provide fair estimates of the co     

Quantifying fractured rock hydraulic heterogeneity and groundwater inflow prediction in underground excavations: the heterogeneity index

This paper presents an approach to quantify the degree of heterogeneity of a fracture network starting from the information that is collected for a geomechanical classification of rock masses. Six synthetic experiments have been used to prove the existence of a correspondence between the variability in fracture properties and in the direction and magnitude of flow. Statistical analyses conducted using fracture data collected at a tunnel crossing the north-western Italian Alps have also shown that variability in fracture characteristics is indeed related to the magnitude of inflows. These findings have proved that it is reasonable to estimate the degree of heterogeneity of a fracture network by combining the variance of those fracture characteristics that regulate both flow and the geomechanical behavior of a rock mass. An index comprising a combination of variances of fracture parameters at different scales is presented. Its dependence on scale showed that the heterogeneity of fractured rock increases with scale up to a certain scale and then gradually decreases at large scales.     

Evaluation of shear strength of clayey soils by using their liquidity index

 It is well known that overconsolidated clays have higher shear strength than unconsolidated clays. The liquidity index makes possible an evaluation of the consolidation degree of clays. However, there is no empirical information about this relation. In this study, clayey soil samples have been collected from various locations and tested. The tests include the determination of liquidity index and shear strength. Obtained parameters were correlated and regression equations were established among liquidity index and undrained shear strength, presenting high coefficients of correlation (R=–0.93). So, an equation [c_u=e^{(0.026–1.21 IL)}] that makes possible a rough evaluation of the shear strength of clayey soils by using their liquidity index value is an improvement. Received: 10 December 1999 · Accepted: 4 April 2000