Deformation Behavior Of Rock Research Articles

Microfabrics-Based Approach to Predict Uniaxial Compressive Strength of Selected Amphibolites Schists Using Fuzzy Inference and Linear Multiple Regression Techniques

In this paper, we established the prediction capability for uniaxial compressive strength (UCS) from microfabric characterization of banded amphibolite schists using fuzzy inference system (FIS) and multiple linear regression (MLR) techniques. In this study, the method of semi-automatic petrographic image analysis (PIA) was adopted to calculate and measure the microfabric parameters. Based on statistical analysis, more influential microfabrics parameters that affect the UCS more than the others have been selected to predict UCS, which include grain size, shape factor, and quartz content. Multi-variate regression relations were established using the same input variables as the FIS model. To assess the performance of both models, some performance indices such as correlation coefficient (R), variance accounted for (VAF), and root mean square error (RMSE) were calculated and compared for the two models. The results show that both models reliably predict the UCS, with the multiple regression model being better based on the performance indices criteria. One of the most significant findings to emerge from this study is that the microfabrics-based PIA approach can be easily extended to the modeling of strength and deformation behavior of rocks in the absence of adequate geological information or abundant data.

Empirical relations between compressive strength and microfabric properties of amphibolites using multivariate regression, fuzzy inference and neural networks: A comparative study

In this paper, microfabric properties including grain size, shape factor and quartz content are tailored to the specific evaluation of UCS of banded amphibolite rocks. However, the predicting capabilities of Artificial Neural Networks (ANNs) and Fuzzy Inference System (FIS) as well as the Multivariate Regression (MR) techniques have been evaluated and compared using the same input variables. To assess the model performances, some performance indices such as correlation coefficient (R), variance account for (VAF) and root mean square error (RMSE) were calculated and compared for the three models. The study revealed that even though the developed three models are reliable to predict the UCS, the presented ANN method displays an obvious potential for the reliable assessment of UCS according to model performance criterion. However, the outcomes of this study are quite satisfactory, which may serve microfabric characterization to be easily extended to the modeling of strength and deformation behavior of rocks in the absence of adequate budget and facility of testing UCS.

Experimental Investigation on Creep Deformation Behavior of Medium-strength Marble Rock

The creep deformation behavior of rocks has significant effect on the stability of underground structures. This study presents the short-term and creep deformation behavior of medium-strength marble rock using a conventional uniaxial compression testing machine and a servo-controlled rheology testing machine. The uniaxial compressive strength is obtained by the uniaxial compression testing machine. During the creep behavior test, two types of rock specimens (dry and water-saturated) are specified to be used to perform the uniaxial creep tests. Two rheological failure modes and the relationship curves between axial/circumferential strain and stress levels of marble specimens are also obtained from the creep test results. Eventually, the creep deformation behaviors are compared with those of typical soft rocks. These creep curves combined with a given creep constitutive model would provide accurate parameters for long-term stability analyses of actual projects.

The importance of stress percolation patterns in rocks and other polycrystalline materials

A new framework for thinking about the deformation behavior of rocks and other heterogeneous polycrystalline materials is proposed, based on understanding the patterns of stress transmission through these materials. Here, using finite element models, I show that stress percolates through polycrystalline materials that have heterogeneous elastic and plastic properties of the same order as those found in rocks. The pattern of stress percolation is related to the degree of heterogeneity in and statistical distribution of the elastic and plastic properties of the constituent grains in the aggregate. The development of these stress patterns leads directly to shear localization, and their existence provides insight into the formation of rhythmic features such as compositional banding and foliation in rocks that are reacting or dissolving while being deformed. In addition, this framework provides a foundation for understanding and predicting the macroscopic rheology of polycrystalline materials based on single-crystal elastic and plastic mechanical properties.

Analysis of Surrounding Rock Deformation Behavior and Supporting Measures in High-Level Strata Pressure Tunnel

According to geological investigation and monitoring results, this paper analyzed the reasons for large deformation in Baozhen Tunnel, discussed the deformation characteristics and presented the corresponding supporting measures.

Effect of volume changes on complete deformation behavior of rocks

For the purpose of describing the deformation characteristics of rocks, the effect of volume changes on mechanical properties of rocks should be taken into account with relation to the development of constitutive model. Firstly, rocks are divided into three parts, i.e., voids, a damaged part and an undamaged part in the course of loading. The void ratio was applied to describing the changes of voids or pores during the deformation process. Then, using statistical damage theory, a constitutive model was developed for rocks to describe their strain softening and hardening on the basis of investigating the relationship between the net stress and apparent stress, in which the influence of volume changes on rock behavior was correctly taken into account, such as the initial phase of compaction and the latter stage of dilation. Thirdly, a method of determining model parameters was also presented. Finally, this model was used to compare the theoretical results with those observed from experiments under conventional triaxial loading conditions.

A mobilized dilation angle model for rocks

Experimental and field observations of rock failure show that the failure process is closely associated with rock dilation, an indicator of volumetric increase during rock deformation. The most common concept used to describe dilation is the dilation angle. The conventional Mohr–Coulomb model considering strain-softening often makes an assumption of constant dilation, but it is observed that the approach is not successful in characterizing the nonlinear deformation behavior of rocks. In the present study, based on published data acquired from modified triaxial compression tests with volumetric strain measurement, a mobilized dilation angle model considering the influence of both confining stress and plastic shear strain is established. Based on the model response and in combination with the grain size description and the uniaxial compressive strength, the model parameters for four rock types (coarse-grained hard rock, medium-grained hard rock, fine-medium-grained soft rock, and fine-grained soft rock) are suggested. For coal and quartzite representing fine-grained soft rock, and coarse-grained hard rock, respectively, the dilation angle model is used to predict the volumetric-axial strain relationships, and the predictions are found to be in good agreement with experimental results.

Time-dependent deformation behaviors of weak sandstones

Time-dependent deformation behavior of rocks has a significant impact on the stability of rock slopes or underground constructions. This paper presents systematic experimental data regarding time-dependent deformation of a typical weak sandstone, known as the Mushan sandstone. The observed deformations are further separated to distinguish elastic and viscoplastic behaviors of the weak sandstone through the use of multi-staged loading–creep-unloading–reloading tests. The stress path is designed to be a purely hydrostatic loading followed by a pure shear, so that the deformations induced by these two types of stresses can be distinguished. For elastic behavior, although the nonlinear stress–strain relations vary according to the applied hydrostatic stress, these stress–strain relations can be normalized by the applied hydrostatic stress or the bulk modulus and converted into a single consistent stress–strain curve. Inelastic behavior is then obtained by subtracting the elastic deformation from the total deformation. As a result, the characteristics of the viscoplastic deformation are that: (1) the direction of the viscoplastic flow is time independent, and (2) it has a similar direction to the conventionally defined plastic flow. As such, the viscoplastic potential has a similar shape to the plastic potential, but the size of the former changes with time, while the latter has a size that is time independent. Meanwhile, through the calculation of irreversible work, direct evidence of orthogonality between the yield surface and the plastic flow, as well as the viscoplastic flow, is observed. Thus, it is reasonable to assert that the yield surface, the plastic potential, and the viscoplastic potential all have the same geometry. Consequently, the associated flow rules are applicable to modeling the time-dependent deformational behavior of weak sandstones.

The stress-strain behaviour of rock material related to fracture under compression

Fracture is the main reason for the non-linear behaviour of hard rocks. The fracture mechanics of rock is studied in this article by analysis of the fracture process under compression. A constitutive model that describes the relationship between the macro deformation of rock and the micro fracture within rock is developed. The propagation of microcracks, the non-linearity of deformation, the loading-and-unloading hysteresis and the variation of the apparent Young's modulus and Poisson's ratio are studied using the developed model. The model simulations demonstrate that: (1) the fracture toughness, initial crack length, crack density, and Young's modulus are four crucially important parameters that affect the deformation behaviour of rock; (2) the elastic parameters ( E and v) of the rock matrix should be measured in triaxial tests. If they are measured in uniaxial tests, the upper straight unloading portion of the stress-strain curve is suggested to be used for the purpose, unless the closure effect of open cracks will be included in the estimations. In addition (3), the slope of the reloading stress-strain curve is a measure of the damage in material.

Deformation Behaviour of Rock around a Borehole Filled with an Expansive Cement

إن استخدام الاسمنت المتوافر والقابل للتمدد كعامل لهدم وتكسير الصخور في المناطق الآهلة بالسكان ، وكذلك أماكن وجود أحجار البناء هو في زيادة مستمرة . وهذا الاسمنت يستخدم بكثرة في المملكة العربية السعودية لتكسير الصخور في المناطق الآهلة بالسكان وفي محاجر الجراني والرخام . إن المقال الحالي هو محاولة لدراسة سلوك التشوه وانشقاق الصخور الصلبة ، مثل الجرانيت، عندما تتعرض لضغط متزايد داخل ثقب حفر مملوء بالاسمنت القابل للتمدد، وذلك عن طريق قياس الانفعالات عند نقاط مماسة لثقب الحفر حوله. وقد تم أيضا دراسة تأثير الحمولة ( أقصر مسافة إلى الثقب من أقرب حافة ) وقطر الثقب في هذا البحث .

Shear strength and deformation behaviour of rock with weak planes: Kim, K J; Lee, C I; Kim, Z K Proc International Symposium on Engineering in Complex Rock Formations, Beijing, 3–7 November, 1986P271–277. Publ Beijing: Science Press, 1986

Shear strength and deformation behaviour of rock with weak planes: Kim, K J; Lee, C I; Kim, Z K Proc International Symposium on Engineering in Complex Rock Formations, Beijing, 3–7 November, 1986P271–277. Publ Beijing: Science Press, 1986

岩石のぜい性破壊特性と鉱柱の山はねの機構に関す一考察

岩石のぜい性破壊特性と鉱柱の山はねの機構に関す一考察

Analysis and Measurements of Behaviors of Rock around Under-ground Cavity in the Process of Excavation

This paper deals with the results of studies on the theoretical analysis of the deformation behavior of rocks, and the actual measurements made during the underground cavity excavation at Okutataragi Pumped-Storage Hydro Project.To initiate the studies, the material properties of rock were obtained by repeated in-situ tests at the proposed location for the projects to define the initial ground stress, rock shear strength, modulus of elasticity, creep deformation ratio, retardation ratio, Poisson's ratio, and rock compressive strength. The material properties thus obtained were used to analyze the extent of rock loose zone, the rock displacement and other fundamental factors for each step of the excavation work by means of a two- or three-dimensional elastic finite element method.To compare the measured data with the analytical calculations, the rock deformeters were installed in such an arrangement as to observe changes with the time of the rock displacement at the cavity arch and side walls, and several concrete strain gauges and reinforcing bar strain meters were also buried in the arch concrete to measure the loads on the arch concrete.The comparison of the calculations and these measurements disclosed the followings;(1) The results or calculations of the analysis could be adequately utilized for designing the rock walls anchored by prestressed steel bars and for maintaining the safety or security control during the construction.(2) The three-dimensional analysis and the results of measurements confirmed that the rock strut or rock mass support method could confine the displacement to about 70 percent of the estimated values of displacement for the construction method without rock strut support. As proposed and adopted at Okutataragi Project, the rock strut was arranged to come in the center of the cavity to house the underground power station and to provide the space for assembling the power equipment, machinery and tools.(3) The horizontal displacement, which was most carefully studied, was 12 to 14mm at the measurement as against 11mm arrived at by the analysis. It follows that the analysis calculation proved to be fairly precise.(4) It is understood that the loads on the arch concrete comes primarily from the horizontal forced displacement arising out of the loose side walls, but not from the ground pressure in the upper direction as has otherwise been assumed. This was proved by the measurement of the maximum concrete compressive stress of 120 to 130kg/cm2 and the calculated estimate of 140kg/cm2 maximum.The estimations and the measurements carried out for this project have proved quite satisfactory. However, several problems have been raised for further reviews and analyses to improve the safety or security of large underground power station structures, such as;(1) Decrease of the rock strength in the loose zones.(2) A method or methods to estimate the effects of rock bolts of prestressed steel bars.(3) Development of more accurate and efficient devices or methods for measuring the initial ground pressure.(4) Improved excavation methods to prevent the rock loose zone from developing or expanding.