Hydraulic Properties Of Rock Mass Research Articles

Equivalent Continuum Coupling-Based Slope Stability Analysis of Zhouning Pumped Storage Power Station

A 3D equivalent continuum coupling analysis of the slope of the Zhouning pumped storage power station was proposed in this study. Firstly, the hydraulic properties of rock mass, groundwater, and deformation mechanism under high-frequency fluctuations of the water level are analyzed. Secondly, the three-dimensional Digital Terrain Model (DTM) with surface image information was established by digital photogrammetry technology for cataloging field fracture information. Third, stress-seepage coupling simulation using a hybrid grid approach and the FLAC3D equivalent continuum model was implemented. The results show that the permeability of rock mass is stress-dependent and anisotropic, and the direction of maximum principal permeability of both bank slopes is approximately parallel to the river. Slope deformations induced by impoundment during the operation period are the superposition results of two mechanisms, referred to as “mattress effect” and “swelling effect.” Attention should be paid to the tensile strength of the rock mass during operation.

Hydromechanical Coupling Characteristics of the Fractured Sandstone under Cyclic Loading-Unloading

The mechanical and hydraulic properties of rock mass play a crucial role in underground engineering. To study the effect of hydraulic pressure, confining pressure, and axial cyclic loading-unloading on variation of the deformation and permeability in fractured rock mass, the coupling triaxial experiment of sandstone was conducted. The concept of permeability recovery rate (PRR) and permeability enhancement reduction rate (PERR) was proposed to characterize the change in permeability. The results show that the permeability of fractured sandstone quadratically varies with the change of hydraulic pressure and confining stress. In detail, the permeability decreases with the decrease of hydraulic pressure and increases with the decrease of confining stress, respectively. Compared with the single-fracture permeability, the double-fracture permeability is more sensitive to the change of hydraulic pressure. Furthermore, the permeability of fractured sandstone is more dependent on the hydraulic pressure than the confining stress. With the performance of axial cyclic loading-unloading, the permeability spirals down, and both the axial and radial residual strains quadratically evolve. Following the first axial cyclic loading-unloading, an obvious deformation memory phenomenon characterized by a parallelogram shape in axial stress-strain curves was observed for the sandstone. The cumulative PRR of 85%-95% was maintained in double-fracture sandstone. On the contrary, a fluctuation of cumulative PRR characterized by “V shape” was observed for single-fracture sandstone. The enhancement effect of axial cyclic loading on the permeability was characterized by the decrease of PERR for double-fracture sandstone and increase of PERR with a greater gradient for single-fracture sandstone.

Prediction of mechanical and physical properties of some sedimentary rocks from ultrasonic velocities

In this study, density, porosity, void ratio, and ultrasonic P- and S-wave first arrival times were measured on limestone, sandstone, and siltstone samples obtained by using mechanical soundings in the city of Zonguldak. Turkey. Fracture and fissure indexes of rocks were calculated from ultrasonic P- (Vp) and S-wave (Vs) velocities. Multi-parameter relationships occurred between ultrasonic velocities with seismic fracture and fissure indexes and physical and mechanical properties of the rocks. Root mean squared error (RMSE = 0.5–0.8%) values correlated between measured densities and densities calculated from Vp and Vs. The correlation coefficients of experimental relations between densities, void ratio, and porosity with seismic velocities that were obtained ranged from 78, 86, 67, and 84%, respectively. Consequently, natural, water-saturated and grain densities, porosity, and void ratio values were determined from new multi-parameter relationships obtained from the combined use of Vp and Vs. In addition, the results of this study suggest that the rock quality may wrongly be determined using the only Vp, whereas it can be obtained more accurately by using Vp and Vs together. The reason for this is that the P wave spreads in solid, liquid, and gas media, while the S-wave spreads only in solid media. Therefore, S-waves will not be altered by fracture filling (gas or liquid), while P-waves are affected by fracture filling. In the present study, the use of Vp and Vs together in relationships was more useful in determining the strength and hydraulic properties of rock mass that the use of either Vp or Vs alone. Also, Rock Quality Designation (RQD) and Rock Mass Rating (RMR) values can be correctly calculated from the combined use of Vp and Vs. As a result, interpretation of crack fill and classification of the rocks can be quickly performed using seismic velocities.

Rock mass property evaluation based on the borehole wall images taken by using an ultrasonic scanner (USS)

Discontinuities, such as faults and fractures exist even in Neogene soft sedimentary rocks. These discontinuities play an important role for determination of physical, mechanical and hydraulic properties of rock mass. For geological disposal of high-level radioactive waste, these data should be obtained for designs of the layout of repository, engineered barrier system and safety assessment. Rock mass properties are important information for quantitative rock mass classification as well as for design and construction of underground facilities and assessment of safe waste disposal. Ultrasonic wave reflection intensity of the wall of the borehole drilled from bottom of East Access Shaft in Horonobe Underground Research Laboratory Center, Hokkaido, Japan, was obtained by using the ultrasonic scanner (USS). In this paper, we compared results of USS observation with core logging data including the core observation, the optical digital scanner (ODS) observation, and result of Needle Penetration Index (NPI) tests. These results indicated that ultrasonic wave reflection intensity had a good correlation with other observation results, and USS observation and NPI test are useful techniques for the determination of the detailed rock mass classification.

Multiscale hierarchical analysis of rock mass and prediction of its mechanical and hydraulic properties

Engineering geological and hydro-geological characteristics of foundation rock and surrounding rock mass are the main factors that affect the stability of underground engineering. This paper presents the concept of multiscale hierarchical digital rock mass models to describe the rock mass, including its structures in different scales and corresponding scale dependence. Four scales including regional scale, engineering scale, laboratory scale and microscale are determined, and the corresponding scale-dependent geological structures and their characterization methods are provided. Image analysis and processing method, geostatistics and Monte Carlo simulation technique are used to establish the multiscale hierarchical digital rock mass models, in which the main micro- and macro-structures of rock mass in different geological units and scales are reflected and connected. A computer code is developed for numerically analyzing the strength, fracture behavior and hydraulic conductivity of rock mass using the multiscale hierarchical digital models. Using the models and methods provided in this paper, the geological information of rock mass in different geological units and scales can be considered sufficiently, and the influence of downscale characteristics (such as meso-scale) on the upscale characteristics (such as engineering scale) can be calculated by considering the discrete geological structures in the downscale model as equivalent continuous media in the upscale model. Thus the mechanical and hydraulic properties of rock mass may be evaluated rationally and precisely. The multiscale hierarchical digital rock mass models and the corresponding methods proposed in this paper provide a unified and simple solution for determining the mechanical and hydraulic properties of rock mass in different scales.

Validation of 3D discrete fracture network model focusing on areal sampling methods-a case study on the powerhouse cavern of Rudbar Lorestan pumped storage power plant, Iran

. Discontinuities considerably affect the mechanical and hydraulic properties of rock mass. These properties of the rock mass are influenced by the geometry of the discontinuities to a great extent. This paper aims to render an account of the geometrical parameters of several discontinuity sets related to the surrounding rock mass of Rudbar Lorestan Pumped Storage Power Plant powerhouse cavern making use of the linear and areal (circular and rectangular) sampling methods. Taking into consideration quite a large quantity of scanline and the window samplings used in this research, it was realized that the areal sampling methods are more time consuming and cost-effective than the linear methods. Having corrected the biases of the geometrical properties of the discontinuities, density (areal and volumetric) as well as the linear, areal and volumetric intensity accompanied by the other properties related to four sets of discontinuities were computed. There is an acceptable difference among the mean trace lengths measured using two linear and areal methods for the two joint sets. A 3D discrete fracture network generation code (3DFAM) has been developed to model the fracture network based on the mapped data. The code has been validated on the basis of numerous geometrical characteristics computed by use of the linear, areal sampling methods and volumetric method. Results of the linear sampling method have significant variations. So, the areal and volumetric methods are more efficient than the linear method and they are more appropriate for validation of 3D DFN (Discrete Fracture Network) codes.

Comparison of methods for calculating geometrical characteristics of discontinuities in a cavern of the Rudbar Lorestan power plant

Discontinuities considerably affect the mechanical and hydraulic properties of rock mass. These properties of the rock mass are influenced by the geometry of the discontinuities to a great extent. This paper aims to render an account of the geometrical characteristics of discontinuities related to the rock mass around the powerhouse cavern of Rudbar Lorestan Pumped Storage Power Plant which is located in a extensional zone of an anticline measured based on linear and areal sampling (circular and rectangular) methods. These methods are used to calculate the geometrical properties of discontinuities at the Rudbar Lorestan powerhouse cavern. Quite a large quantity of scanlines and the window samplings used in this research indicated that the areal sampling methods are more time consuming and more cost-effective than the linear methods. Having corrected the biases of the geometrical properties of the discontinuities, their associated statistical distributions of function, density (areal and volumetric) as well as the linear, areal and volumetric intensity accompanied by the other properties are related to four sets of discontinuities that were computed. There is an acceptable difference between the mean trace length measured using two linear and areal methods for the two joint sets. Due to the fact that the region under study is highly tectonized, there is as well the surveying results of the discontinuities at different locations that have given rise to the performance having an equality of two for the multi means and variances test (ANOVA) for studying the homogeneity of the data. The dominant tectonic of the region as well as the genetic type of the discontinuities have caused their Fisher’s constant to be decreased, and the joint sets with uniform genetics have given rise to the same probability density function of the trace length and spacing. It is difficult to estimate the volumetric intensity of the study area. Review of the results depicts that the volumetric intensity of a joint set computed using different methods is different up to 38%. So, it is necessary to measure the geometrical characteristics of discontinuities by some methods, and taking into consideration correcting biases, do calculation of the areal and volumetric parameters of joint sets, studying the homogeneity and genetic type of discontinuities to generate the 3-D discrete fracture network.

Comprehensive characterization and clustering of orientation data: A case study from the Songta dam site, China

The quantitative description of orientation data in rock masses is fundamental for understanding the engineering geological properties of rock masses. However, the features of joint orientation distributions are still not easy to describe in practical projects. Orientation data are randomly distributed in a rock mass, and its poles are also randomly distributed on a stereonet. The delineation of orientation data on the stereonet is difficult, but the density of poles on the stereonet indicates some characteristics of joint geometric patterns, which will influence the mechanical and hydraulic properties of rock masses. Considering the nonlinear distribution of poles density, fractal geometry is introduced to describe the orientation data in this study. Accordingly, a framework combining the idea of fractal geometry, graphic display and the Schmidt upper-hemisphere equal-area projection plot is proposed for comprehensive characterization of orientation data. The monofractal and multifractal descriptions have been used to delineate the orientation data, and a fractal indicator is proposed for the dispersion of orientation data. In addition, the identification and delineation of joint sets with similar orientations are discussed, and the optimal method is recommended. Finally, the methods proposed in this study were further applied to a real data set collected from a survey at the dam site of the Songta hydropower station, China.

A discrete fracture network model for geometrical modeling of cylindrically folded rock layers

Geometrical characterization of discontinuities is a crucial step in determining the mechanical and hydraulic properties of rock masses. Discrete fracture network models are developed to model the geometric properties of discontinuities using the statistical distributions of these properties measured from core logging and outcrop mapping analyses. Among all of the discontinuity properties, shape is the most controversial. In previous discrete fracture network models, discontinuities have been considered to be limited or unlimited planes, but in reality curved discontinuities are also observed. Based on previous research, the planar assumption in rocks containing curved discontinuities leads to considerable errors in subsequent analyses. Curved discontinuities and reasons for their formation have not yet been specifically classified. However, it is obvious that there are several reasons for the creation of these types of discontinuities. Folding is the most common factor responsible for the generation of curved discontinuities. In this paper, a practical 3D geometric method is proposed to model folded rock layers. The method relies on Fourier analysis to model the folded layer and generates suitable input data for subsequent mechanical analysis via a purposely developed MATLAB script named RocFold. The applicability of the proposed model and script is tested by using an example of a typical folded structure in the Anjire mine, Iran.

A Multiscale Microstructural Model of Damage and Permeability in Fractured Solids

Deterioration of mechanical and hydraulic properties of rock masses and subsequent problems are closely related to changes in the stress state, formation of new cracks, and increase of permeability in porous media saturated with freely moving fluids. We describe a coupled approach to model damage induced by hydro-mechanical processes in low permeability solids. We consider the solid as an anisotropic brittle material where deterioration is characterized by the formation of nested microstructures in the form of equi-distant parallel faults characterized by distinct orientation and spacing. The particular geometry of the faults allows for the analytical derivation of the porosity and of the anisotropic permeability of the solid. The approach can be used for a wide range of engineering problems, including the prevention of water or gas outburst in underground mines and the prediction of the integrity of reservoirs for underground CO2 sequestration or hazardous waste storage.

Development of a new equation for joint roughness coefficient (JRC) with fractal dimension: a case study of Bakhtiary Dam site in Iran

The joint roughness has a significant effect on the shear behavior of rough joints, which control the shear strength of jointed rock mass. This index plays an important role in the mechanical and hydraulic properties of rock masses. There have been extensive studies in last a few decades. Joint roughness coefficient (JRC) and fractal dimension D are two well-studied and adopted parameters used in estimating the surface roughness of rock joints. This study proposed a new relation between JRC and D, and compared this relation with the previous studies by applying it on JRC profiles. This relation was also introduced into Barton’s empirical equation to assess the shear strength of rock joints, and its performance was estimated by applying it to more than 30 laboratory direct shear tests on natural rock joints from Bakhtiary Dam site. The advantage of this study, when compared to the previous works done by others, is using the results of more than 30 direct shear tests on natural rock joints for the evaluation of reliability of the proposed equation. Therefore, the new obtained relationship between JRC and D seems to capture well the roughness coefficient of natural rock joints.

Numerical study on the effects of unsaturated hydraulic properties of rock mass on stability of rock slope

Numerical study on the effects of unsaturated hydraulic properties of rock mass on stability of rock slope

Development and application of 3D spatial modeling techniques for characterizing regional mechanical and hydraulic properties of rock masses

Accurate spatial modeling of geologic structures and properties are crucial for mechanical and hydraulic characterizations of rock mass. This report presents several methods that are grouped into two categories depending on the natures of geologic data: type I for the data originated from plural populations and type II for the data that can be applied to the prerequisite of stationarity and have distinct spatial correlations. For the type I data, a spline-based method, its combination with stochastic simulation, and neural network method are demonstrated as effective, while geostatistics is certainly powerful tool for the type II data. As new approaches of geostatistics, an application to directional data such as fracture, multi-scale modeling that incorporates a scaling law, and space-time joint analysis for multivariate are reviewed briefly with case studies. These methods can contribute to Earth science and technology including rock engineering related to the problems such as repository of high-level nuclear waste and CCS (carbon dioxide capture and storage) which need the most comprehensive understandings of rock structures and properties.

Three-dimensional analysis of boreholes considering spatial variability of properties and poroelastoplasticity

In general, analysis of oil producing wells is carried out considering that both hydraulic and mechanical parameters of the rock mass are deterministic. Mechanical and hydraulic properties of rock masses and in particular sedimentary rock masses may show a considerable degree of spatial variability. This paper focuses on the evaluation of the three-dimensional borehole response, particularly of the plastic zone, taking into account the spatial variability of both hydraulic and mechanical properties. The analysis is performed with a developed finite element program that incorporates spatial variability, coupled fluid-mechanical effects and elastoplastic behavior of the rock mass. Examples are shown and conclusions are drawn regarding the effect of spatial variability on the three-dimensional borehole analysis.

Borehole stability analysis considering spatial variability and poroelastoplasticity

Typically, stability analysis of oil-producing wells is carried out considering that both the hydraulic and mechanical parameters of the rock mass are deterministic. When analyzing borehole stability, two failure mechanisms are generally considered, namely, failure due to either tensile or compressive (shear) stresses. These mechanisms are produced, respectively, by either too high or too low drilling fluid pressure. Mechanical and hydraulic properties of rock masses, and in particular sedimentary rock masses, may show a considerable degree of spatial variability. This paper focuses on the evaluation of the limits for the internal pressure associated with a target probability of failure, taking into account both the spatial variability of hydraulic and mechanical properties, and the simple variability of the initial pore pressure and in-situ stresses. The analysis is performed with a finite element program that incorporates coupled fluid-mechanical effects and elastoplastic behavior of the rock. In this way, the proposed borehole stability analysis can be set into a reliability-based framework described in the paper. Examples are shown, using stochastic data from the literature, and conclusions are drawn regarding the effect of spatial variability on the borehole stability.

Scale effects in the determination of hydraulic properties of rock masses : Carlsson, A; Gustafson, G; Lindblom, U; Olsson, T Proc 1st International Workshop on Scale Effects in Rock Masses, Loen, 7–8 June 1990P103–117. Publ Rotterdam: A A Balkema, 1990

Scale effects in the determination of hydraulic properties of rock masses : Carlsson, A; Gustafson, G; Lindblom, U; Olsson, T Proc 1st International Workshop on Scale Effects in Rock Masses, Loen, 7–8 June 1990P103–117. Publ Rotterdam: A A Balkema, 1990

Evaluation of hydraulic properties of rock masses. Symposium. In new horizons in rock mechanics : Sharp, JC Maini, YN, Univ. Calif. Berkeley, USA Brekke, TL, Univ. Calif. Berkeley, USA 9F, 10R. Proc. 14th symposium on rock mechanics, ASCE, New York, 1973, P481–500

Evaluation of hydraulic properties of rock masses. Symposium. In new horizons in rock mechanics : Sharp, JC Maini, YN, Univ. Calif. Berkeley, USA Brekke, TL, Univ. Calif. Berkeley, USA 9F, 10R. Proc. 14th symposium on rock mechanics, ASCE, New York, 1973, P481–500