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1.
The porosity and engineering properties of vesicular basalt in Saudi Arabia   总被引:2,自引:0,他引:2  
The presence of non-connected vesicles in extensive basalt flows in western Saudi Arabia greatly affects their engineering properties such as compressive strength, modulus of elasticity, Poisson's ratio and sonic velocities. In order to evaluate some of these properties, the density and/or the porosity of the material must be known. Using conventional methods to determine the porosity or the density of irregular lumps proved to be erroneous. An image analysis technique is suggested to estimate the porosity of the vesicular basalt. The estimated values were correlated against the calculated porosity values using core samples, and were found to have excellent correlation (R=0.99). The estimated porosity values were also correlated against the static and dynamic properties of the basalt and a good level of correlation (R=0.77) was obtained.  相似文献   

2.
Based on the particle simulation method, a thermo-mechanical coupling particle model is proposed for simulating thermally-induced rock damage. In this model, rock material is simulated as an assembly of particles, which are connected to each other through their bonds, in the case of simulating mechanical deformation, but connected to each other through thermal pipes in the case of simulating heat conduction. The main advantages of using this model are that: (1) microscopic parameters of this model can be directly determined from the related macroscopic ones; (2) the temperature-dependent elastic modulus and strength are considered in an explicit manner, so that thermally-induced rock damage can be realistically simulated in a thermo-mechanical coupling problem. The related simulation results from an application example have demonstrated that: (1) the proposed model can produce similar behaviors to those observed in experiments; (2) the final failure is initiated from the outer surface of the testing sample and propagates toward the borehole; (3) microscopic crack initiation and propagation processes can be reasonably simulated at the cooling stage.  相似文献   

3.
刘洋  赵明阶 《岩土力学》2009,30(Z1):47-52
建立单一微裂纹在单轴压缩荷载作用下的力学模型,采用宏观复合型断裂理论中的最大周向应力理论,求出单一微裂纹达到稳定时的形态尺寸.利用分形损伤理论,求出不同荷载阶段的分形维数;由分形维数的定义导出了不同荷载阶段的裂纹个数的变化情况;结合单一微裂纹的形态尺寸,求出不同荷载阶段中岩石孔隙率与荷载值之间的关系;利用目前被广泛采用的超声波纵波速度与孔隙率的关系式,最终导出单轴压缩荷载作用下岩石超声波纵波速度与应力的理论关系式.进行岩石声-应力的试验测试,根据试验成果作出声-应力曲线,并与理论声-应力曲线进行比对,结果表明,理论模型比较适合于反映岩石受载全过程中的后半部分的声-应力关系.  相似文献   

4.
This paper studies the depth variability of uniaxial compressive laboratory test results on intact Toki granite (i.e., sound rock without macroscopic fractures) from the Shobasama and Mizunami Construction Sites, Japan. Some of the depth variability observed in the laboratory results can be indirectly attributed to the high fracture frequency of the “upper highly fractured rock domain” from which some of the samples were taken. For samples taken from the “lower sparsely fractured rock domain,” however, the uniaxial compressive strength of the granite seems to be very strongly correlated to the level of in situ rock stress (i.e., maximum shear stress) determined by measurement results obtained from hydrofracturing tests. The correlation between the laboratory results and the level of in situ stress is explained by the damage due to the complex stress path that the cores undergo during drilling, besides the stress concentrations at the drill-bit/rock contact, which can also affect the microcracking of the samples. An attempt to adjust laboratory test results to estimate the in situ intact rock strength of Toki granite based on its correlation with in situ stresses was carried out.  相似文献   

5.
The fatigue damage behavior of granite under constant and variable amplitude loadings is studied. The experimental analysis reveals that there is a three‐stage law for the fatigue damage evolution as a function of absolute or relative cycle and the inverted‐S damage model proposed by the author, in this case, is capable of representing the damage behavior of rock. However, when the logarithmic cycle is considered, there are only two stages, i.e. steady and accelerated stages and the fatigue damage evolution greatly depends on the properties of rock and stress level. Accordingly, the fatigue damage evolution curves have been categorized into three types. Then, the effect of maximum stress, amplitude and fatigue initial damage on the damage evolution of rock is investigated. The analysis reveals that the damage evolution greatly depends on these influencing factors. The fatigue life decreases with the increase in the maximum stress, amplitude and fatigue initial damage due to the decrease in the proportion of the first stage to the whole fatigue process and the increase in the damage rate in the first stage. Meanwhile, a linear‐exponential formula is used to model the fatigue damage behavior of rock subjected to cyclic loading. This damage model is superior to the inverted‐S damage model in the convenience of establishment of critical instability point. The physical meanings of its constants have been illuminated and the applicability of this model to constant and variable amplitude cyclic loading explored. The fitting results for the test data show that this damage model can properly represent the fatigue damage behavior of rock. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

6.
This paper presents laboratory results regarding the shear behaviour of an artificial tensile fracture generated in granite. We used a direct shear rig to test fractures of different sizes (from 100 mm to 200 mm) under various shear displacements up to 20 mm and cyclic shear stresses with constant normal stress of 10 MPa. To determine the evolution of surface damage and aperture during shear, cyclic loading was performed at designated shear displacements. These changes in the surfaces topography were measured with a laser profilometer ‘non-contact surface profile measurement system’. In addition, changes were also measured directly by using pressure-sensitive film.

The results showed that the standard deviation (SD) of the initial aperture of the sheared fracture significantly increases with both shear displacement and size, which result in an increase in the non-linearity of the closure curve (since the matedness of the fracture surfaces decreases with shear displacement). Therefore, we concluded that shear dilation is not only governed by the surfaces sliding over each other, but is also strongly influenced by the non-linearity of closure with shear displacement. Furthermore, while the shear stiffness of the fracture during the initial stage decreases with fracture size, it increases with fracture size in the residual stage. This can be attributed to the fact that only small asperities with short wavelengths were mainly damaged by shearing. Moreover the result showed that the damaged zones enlarge and localise with shear displacement, and eventually tend to form perpendicular to the shear displacement.  相似文献   


7.
介绍了一种考虑地下洞室片帮、钻孔剥落等岩体应力型破坏特征为信息源,通过数值模拟智能反演方法预测高应力大型地下洞室群围岩局部应力场的新思路。该方法将地下洞室群片帮、钻孔剥落等应力型破坏的位置、深度或者宽度进行定量描述,以弹性模型计算获得的常偏应力大于岩体启裂强度的范围来表示应力型破坏范围,通过分析实测地应力数据约束部分地应力数量,然后采用智能数值反演方法得到其他的地应力分量。采用该方法预测了白鹤滩水电站右岸地下厂房0+76断面附近围岩地应力场,反演获得最大主应力在34 MPa左右。通过其他部位岩体破裂的数值模拟和观测结果对比,验证了地应力场预测的合理性。  相似文献   

8.
Existing models for predicting the small strain behaviour of unsaturated soil are not capable of predicting the initial shear stiffness during suction reduction under normally consolidated conditions. This problem has been addressed in the present study by combining an existing elastoplastic model and recent experimental data to provide a new model for the initial shear stiffness. The model, which is similar to that typically adopted for saturated soils, uses the average skeleton stress and an additional function of the degree of saturation. This new model not only captures the behaviour of the new experimental results, but it also describes a unique relationship between saturated and unsaturated soils.  相似文献   

9.
In the direct shear test (DST), an internal moment is distributed within the rock specimen by non‐coaxial shear loads applied to the specimen, which cause non‐uniform distributions of both the traction on the loading planes and the stress and deformation in the specimen. To examine the validity of the DST for a rock fracture and to clarify the effect of specimen height, both the stress and deformation in a fracture in the DST were analyzed for specimens with three different heights using a three‐dimensional finite element method with quadratic joint elements for a fracture model. The constitutive law of the fracture considers the dependence of the non‐linear behavior of closure on shear displacement and that of shear stiffness on normal stress and was implemented in simulation code to give a conceptional fracture with uniform mechanical properties to extract only the effect of non‐uniform traction on the stress and deformation in the fracture. The results showed that both normal and shear stresses are concentrated near the end edges of the fracture, and these stress concentrations decrease with a decrease in the specimen height according to the magnitude of the moment produced by the non‐coaxial shear loads. Furthermore, although closure is greater near the end edges of the fracture, where normal stress is concentrated, this concentration of closure is not so significant within the range of this study because of the non‐linear behavior of closure, that is, closure does not significantly increase with an increase in normal stress at large normal stresses. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

10.
张勇  项彦勇 《岩土力学》2016,37(12):3481-3490
针对高放射核废深地质处置库近场环境,建立分布热源作用下饱和裂隙岩体三维水流-传热过程中位移和应力的一种半解析计算方法:采用Goodier热弹性位移势和Laplace变换计算由温度梯度产生的温梯位移和应力;考虑单一裂隙的情况,利用经典弹性力学的Boussinesq解和Cerruti解计算为满足边界条件的约束位移和应力,与温梯位移和应力叠加,可得总体热位移和应力;把裂隙面离散为矩形单元集合,采用极坐标系下的解析法计算包含奇点的单元积分,采用数值法计算与分布热源有关和不含奇点的单元积分。与基于裂隙面法向一维热传导假设的一种解析解对比,结果表明,半解析法与解析法的计算结果基本一致,但由于半解析法考虑岩石的三维热传导,因温度时空分布和演变的不同而导致不同的温梯应力。针对一个假想单裂隙岩体三维水流-传热过程,计算温梯位移和应力、约束位移和应力、总体位移和应力;结果表明,裂隙水流-传热可能对位移和应力的分布和演变有显著影响,距离分布热源较近的岩石因升温膨胀受到约束而出现压应力,而距离分布热源较远的岩石则可能因协调收缩受到约束而出现拉应力。  相似文献   

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