液氮冻结对岩石抗拉及抗压强度影响试验研究

液氮温度极低（?195.8℃）,当与储层岩石接触时,能够改变岩石物性并对岩石结构产生损伤致裂,因此,可用于储层压裂改造。为了研究液氮压裂时低温对岩石力学性能的影响,分别对不同含水状态（干燥与饱和）的不同类型（大理岩、砂岩和花岗岩）岩石进行液氮冻结处理,并对冻结前、后岩样进行抗拉及单轴抗压强度对比测试。结果表明,经液氮冻结后,岩石的单轴抗压强度、抗拉强度和弹性模量都降低;岩石在干燥状态下,液氮冻结对大理石强度的影响大于对红砂岩的影响;岩石饱和水状态下,液氮冻结对红砂岩强度的影响大于对大理岩的影响;饱和水状态岩石经液氮冻结后,其应力-轴应变曲线在弹性变形阶段出现一个拐点;对于同种类型岩石,饱和水状态能加剧液氮冻结并对岩石损伤,岩石强度影响显著;对3种岩样微观结构进行了电镜扫描（以大理岩为例进行分析）,发现经液氮冻结后在矿物颗粒之间生成了微裂隙。研究结果可为进一步研究液氮压裂机制提供试验依据。     

对称和非对称载荷下声发射特征的数值模拟研究

利用自行开发的岩石破裂过程分析RFPA^2D系统，研究了对称载荷和非对称载荷下岩样的破坏过程以及破坏过程中所呈现的声发射特征。数值模拟结果演示两种条件下由微破裂诱致宏观破坏的演化过程以及和微破裂相关的声发射事件源的空间分布特征和事件序列特征。数值模拟结果指出，和对称载荷压缩实验相比，两者的最大区别在于在非对称载荷压缩实验中局部的剪切破坏的发生以及一个更加局部化的声发射事件源分布。从物理意义上讲非对称载荷实验提供了在预定破裂路径下研究脆性破坏的方法，从声发射研究方面来说非对称实验比对称实验能更好地观察声发射事件源的局部化。     

A comparative assessment of indirect methods for estimating the uniaxial compressive and tensile strength of rocks

Arabian Journal of Geosciences - The uniaxial compressive and tensile strength of rocks are crucial parameters in the design stage of geotechnical structures. However, direct determination of these...     

Discrete element model for quasi‐brittle rupture under tensile and compressive loading

In the absence of initial cracks, the material behavior is limited by its strength, usually defined in homogeneous conditions (of stress and strain). Beyond this limit, in quasi‐brittle case, cracks may propagate and the material behavior tends to be well described by fracture mechanics. Discrete element approaches show consistent results dealing with this transition during rupture. However, the calibration of the parameters of the numerical models (i.e., stiffness, strength, and toughness) may be quite complex and sometimes only approximative. Based on a brittle rupture criterion, we analyze the biaxial response of uncracked samples. Thus, tensile and compressive strengths are analytically identified and become direct parameters of our discrete model. Furthermore, a physically reliable crack initiation (and subsequent propagation) is shown to be induced during rupture and verified by the simulation of three‐point bending and diametral compression tests. Copyright © 2016 John Wiley & Sons, Ltd.     

砂土中群桩的压拔加载试验研究

进行砂土的单桩和2×2群桩的压、拔试验,测定桩身轴力、桩顶荷载、位移以及桩端阻力。试验研究结果表明,群桩的抗压群桩效应系数 >1,最优桩间距为4D(D为直径),对应的 约为1.2;桩端阻力群桩效应系数 大于桩侧摩阻力群桩效应系数 ,其最优桩间距为5D,对应的 值约为1.3;桩侧摩阻力群桩效应系数在3D时约为1.2,但随桩间距的增大而减小。与前人理论分析的结果不同,由于砂土的挤密效应,试验测得抗拔群桩效应系数也大于1,最优桩间距在4D～5D之间,系数约为1.2。桩间距为7D时压、拔群桩效应系数均趋近于1,可基本忽略群桩效应。     

Statistical prediction formula for compressive strength of a rock

SummaryStatistical Prediction Formula for Compressive Strength of a Rock Compressive strength of a rock, amongst its other mechanical properties, is known to be related to its water absorbing capacity which is thus appropriately termed its quality index. Mapping of foundation areas and the acceptance of stones in masonry could be based on this relationship. However, the existing literature on rock mechanics does not give any prediction formula for compressive strength of a rock in terms of its quality index. Such prediction formulae for the basalt and the sandstone rocks at two sites have been developed and presented in this paper. The 95% confidence belts for the estimated compressive strengths have also been worked out. The locus of the lower confidence limit for the estimated compressive strength enables determination of the maximum permissible quality index.

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ZusammenfassungStatistische Formeln zur Abschätzung der Druckfestigkeit eines Gesteins Die Druckfestigkeit eines Gesteins kann, wie bekannt, neben anderen Eigenschaften, auch zum Wasseraufnahmevermögen in Beziehung gesetzt werden, weshalb es als Quality Index bezeichnet wird. Planungsunterlagen und die Entscheidungen über die Verwendungsfähigkeit als Baustoff könnten auf dieser Beziehung basieren. In der Literatur findet sich jedoch keine Formel für die Abschätzung der Druckfestigkeit von Gesteinen in Abhängigkeit vom Quality Index. Solche Formeln wurden für einen Basalt und einen Sandstein entwickelt. Ebenso wurden die 95%-Vertrauensbereiche für die geschätzten Druckfestigkeiten ermittelt. Der Verlauf der unteren Vertrauensgrenze ermöglicht die Bestimmung des höchstzulässigen Quality Index.

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RésuméFormule pour la prédiction statistique de la résistance de compression d'une roche On sait que la résistance de compression d'une roche, entre ses autres qualités mécaniques, est allié à sa capacité d'absorption d'eau qui est désignée convenablement son indice de qualité.On peut fonder la formation d'une carte des régions de fondation et l'acceptation des pierres en maçonnerie sur cette relation. Pourtant, la littérature existante sur la mécanique des roches ne présente pas la formule de prédiction pour la résistance de compression d'une roche au moyen de son indice de qualité. On a développé telle formule pour les roches basalte et grès en deux sites laquelle se présente ici.De même façon on a calculé les zones de confidence de 95% pour les résistances de compression estimées.Le lieu de limite inférique de confidence pour la résistance de compression estimée facilite la détermination de l'indice de qualité maximum possible.

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With 2 Figures     

单轴拉伸条件下岩石本构理论研究

利用损伤力学理论研究了细观非均匀性岩石拉伸应力应变关系,包括:线弹性阶段、非线性强化阶段、应力降阶段、应变软化阶段。所用的模型分析了岩石的细观各向异性对全过程应力应变关系的影响,分析了产生应力跌落和应变软化的主要原因是损伤和变形局部化,将损伤和变形局部化引入本构模型是和以往模型的重要区别。通过与实验成果对比分析验证了模型的正确性和有效性。     

动水压力作用下碳酸盐岩溶蚀作用模拟实验研究

为研究岩溶地区水库蓄水不同条件下动水压力驱动下的碳酸盐岩溶蚀作用机制。以乌江流域某水电站坝前地区碳酸盐岩为研究对象,利用自行研制的开放体系压力溶蚀实验系统,对不同动水压力（0～2.0 MPa）条件下CO2水溶液溶蚀碳酸盐岩的过程进行实验模拟,其结果显示,动水压力增大会引起碳酸盐岩的溶蚀作用加剧,溶解速率曲线随动水压力的变化而发生显著改变;随动水压力的增大,岩石的化学溶解量和机械破坏量同时增大,两者的比值随着压力增大逐渐趋于1：1,两者之间存在耦合关系。采用扫描电镜与压汞试验相结合的方法进行微观研究发现,动水压力对碳酸盐岩的溶蚀作用不仅发生于岩石表面,使表面溶孔增大并加深,产生次生孔隙和次生矿物,同时还改变着岩石的内部孔隙结构,降低其渗透性并弱化结构面的连接。     

静动荷载下桩网结构路基模型试验研究

通过室内模型试验测试了桩网结构路基各部分在动静两种荷载下的桩-土应力、格栅拉力,研究了土拱效应的发展演化机制以及土工格栅拉膜效应的发展特点。试验结果表明：桩-土应力以及格栅拉力的分布都是路基横截面方向上大于其纵向延伸方向,这与路基的梯形截面设计相关;空间土拱效应要强于平面土拱效应,空间土拱效应的极限状态出现在桩-土应力比为3.8时,平面土拱效应的极限状态出现在桩-土应力比为2.2时;动荷载下土拱效应较静载有一定的衰减,且静载下土拱效应越强的部位在动载的下衰减程度越大,桩间土压力随振次的发展趋势类似N型,与桩顶土压力的变化趋势正好相反。     

A prediction method using grey model for cumulative plastic deformation under cyclic loads

Being able to predict cumulative plastic deformation of soil under cyclic loading has been quite a popular subject for researchers both in the past and at present. In this paper, a non-equal interval non-homogeneous exponential grey model NNGM (1, 1) for cumulative plastic deformation has been put forward by improving the traditional grey model GM (1, 1). The proposed model was evaluated by numerous experimental data of existing literatures and found to be valid for a wide range of soils. It is also valid for predicting long-term settlement of subgrade under subway loads and has a better performance than the traditional model GM (1, 1) as well as non-homogeneous exponential model NEM.     

Developing new equations for TBM performance prediction in carbonate-argillaceous rocks: a case history of Nowsood water conveyance tunnel

Nowsood water conveyance tunnel is 49 km long and has been designed for transferring 70 m³/s water from Sirvan river southward to Dashte Zahab plain in the west of Iran. This long tunnel has been divided into three sections, namely 1A, 1B and 2. By April 2008, about 5.3 km of the lot 2 of this project, with a total length of 26 km, were excavated by a double-shield TBM. The bored section of tunnel passed through different geological units of three main formations of the Zagross mountain ranges which mainly consist of weak to moderately strong argillaceous-carbonate rocks. This paper will offer an overview of the project, concentrating on the TBM operation, and review the results of the field performance of the machine. Also results of statistical analyses to evaluate correlation of TBM performance parameters with rock mass characteristics will be discussed. The results of machine performance analysis indicated that there are strong relationships between geomechanical parameters and TBM performance parameters in this particular project. In this research some empirical equations and a chart have been developed to estimate TBM performance parameters in similar cases based on common rock mass properties.     

Discovery of marine Upper Jurassic-Lower Cretaceous rocks in Uttaradit Province: a new approach for paleoenvironment and tectonic settings

The sedimentary rocks exposed in the study area, the Cham Bon reservoir and nearby area in Phichai District, Uttaradit Province, Thailand were grouped as non-marine Jurassic Phra Wihan Formation of the Khorat Group. After the previous reconnaissance by geologists of Department of Mineral Resources of Thailand, marine bivalves have been newly discovered in this area. This made us eagerly to examine the sedimentology, stratigraphy and geotectonic evolution of this region. The purpose of this research is to study in detail the sedimentary rocks in order to reconstruct the depositional environment. Two sections, the Cham Bon section and another section at 58 km-stone of Highway no.11, have been measured and 25 samples were petrographically examined. The Cham Bon sec-tion, which is 252 m thick, can be lithologically di-vided into 3 parts: the lower, middle and upper parts. The lower part is characterized by thick-bedded and massive quartz arenite.     

Correlation between point load index and compressive strength for quartzite rocks

Summary The relationship of the point load test with uniaxial compressive strength was examined using quartzite rocks to substantiate the existing correlations.     

Homeostatic representation for risk decision making: a novel multi-method simulation approach for evacuation under volcanic eruption

Natural Hazards - All decision-making processes are complex and include a high number of variables. Particularly, decisions related to disaster risk reduction despite having an inherent...     

A tensile damage model for rocks: Application to blast induced damage assessment

In this paper, an experimental methodology is presented using digital image techniques to assess the internal microcracks and to quantify the rock damage within rock cores. The second part of the work is devoted to the numerical estimation of the tensile blast induced damage evolution law. The set up methodology is then applied to a set of limestone cores which were sampled before and after a real field blast round. The image analysis algorithm which was developed during the present work is based on a segmentation technique that uses a particular thresholding. Petrographic parameters, such as crack number, orientation, extension, centroid position were computed as a first step aiming at a fine characterization of the cracked medium. The most important estimated parameter is the specific crack area which is defined as the ratio between the crack area and the total image area. This parameter was taken as the rock internal damage. A dynamic tensile damage ordinary partial differential equation is numerically solved and calibrated with the obtained data in order to derive a general blast induced damage evaluation law within the muckpile blocks. The application of the numerical algorithm to cores coming from sampled blocks before and after real field blasts allowed the estimation of damage parameter and dynamic stress evolution histories as well as an estimation of the microfracturing activation and growth energies used during the blast.     

Ultimate bearing capacity of a foundation reinforced by columns or cross trenches under inclined loads: a homogenization approach

This paper addresses the geotechnical engineering problem of evaluating the ultimate bearing capacity of a strip foundation resting upon a reinforced soil, by means of the yield design homogenization approach. The analysis is notably focused on the determination of the macroscopic strength criterion of such reinforced soils, where both constituents are purely cohesive, which can be conveniently expressed through the notion of anisotropic cohesion. A comprehensive comparison is made between the classical configuration of reinforcing columns and the more original one of orthogonal reinforcing trenches. Among the most outstanding results of the analysis is the conclusion that the cross trench configuration is notably more efficient in terms of load bearing capacity than the reinforcement by columns, notably when significantly inclined loading is concerned. Copyright © 2014 John Wiley & Sons, Ltd.     

Random field characterization of uniaxial compressive strength and elastic modulus for intact rocks

Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of geotechnical structures in rock engineering, the spatial variability of rock properties is rarely quantified. Hence, this study characterizes the autocorrelation structures and scales of fluctuation of two important parameters of intact rocks, i.e. uniaxial compressive strength(UCS) and elastic modulus(EM).UCS and EM data for sedimentary and igneous rocks are collected. The autocorrelation structures are selected using a Bayesian model class selection approach and the scales of fluctuation for these two parameters are estimated using a Bayesian updating method. The results show that the autocorrelation structures for UCS and EM could be best described by a single exponential autocorrelation function. The scales of fluctuation for UCS and EM respectively range from 0.3 m to 8.0 m and from 0.3 m to 8.4 m.These results serve as guidelines for selecting proper autocorrelation functions and autocorrelation distances for rock properties in reliability analyses and could also be used as prior information for quantifying the spatial variability of rock properties in a Bayesian framework.     

车辆载重与动荷载对X形桩桩-网复合地基动力特性影响的试验研究

基于大比例模型试验,采用半正弦波模拟移动车辆荷载,通过开展不同车辆载重和动荷载作用下X形桩桩-网复合地基的动力特性模型试验,分析桩身动应力、土拱效应、动土压力、垫层应力传递系数、格栅动应变等的变化规律,初步揭示了车辆载重和动荷载对X形桩桩-网复合地基的影响机制。试验结果表明,车辆动荷载对X形桩桩身动应力的影响深度约为2 m;车辆载重和动荷载的增加会导致桩间土承受更多的动应力,并且会降低路肩处土工格栅的作用;但是,路基中心的垫层应力传递系数几乎保持不变;土工格栅的动应变比超过0.048时,格栅累积变形会随着车辆载重和动荷载的增加迅速增大。     

动静组合作用下刀具破岩机制数值分析

基于细观损伤有限元方法,模拟分析了刀具在单一动载、动静联合荷载、静态围压条件下动静联合荷载3种情况下岩体破碎的全过程。模型采用黏弹性人工边界剔除了边界应力波反射对模拟结果准确性的影响。数值模拟结果表明：在弹性情况下,静压的存在对岩体内部最小主应力值影响不大,却显著提高了材料内部最大主应力水平,增大了剪应力的大小,导致剪切破坏可能性增加;当有围压存在时,岩体内部受拉区域减少,岩体强度有所提高。单一动载和动静联合荷载破岩时,岩体内部除刀头附近呈现少量压破坏外,破坏均以拉破坏为主;而围压条件下,岩体破碎面积相对减小,裂纹在围压的作用下向两侧自由面延伸,岩体内部破坏形式则趋于多样化,压破坏比重明显增大,整体表现为拉压复合作用。模拟结果还表明,刀头侵入量主要受动载力大小影响,在相同幅值增量下,动载力增加导致的刀头侵入量远大于静压增加所导致的侵入量。相对单一动载和静压作用下的岩石破碎机制来说,动静组合加载破岩的研究还需更为深入的探讨。研究结果可望对岩体破坏机制以及地下工程作业等实际应用提供一定的参考。