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R.k. Goel - One of the best experts on this subject based on the ideXlab platform.
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Rock Mass Rating
Engineering Rock Mass Classification, 2011Co-Authors: Bhawani Singh, R.k. GoelAbstract:Publisher Summary The geomechanics classification or the Rock mass rating (RMR) system was initially developed at the South African Council of Scientific and Industrial Research (CSIR) on the basis of experiences in shallow tunnels in sedimentary Rocks. This chapter provides an overview on RMR with discussion on estimation, application, and precaution of RMR. To apply the geomechanics classification system, a given site is divided into a number of geological structural units in such a way that each type of Rock mass is represented by a separate geological structural unit. The following six parameters are determined for each structural unit: Uniaxial compressive strength (UCS) of Intact Rock Material, Rock quality designation (RQD), joint or discontinuity spacing, joint condition, groundwater condition, and joint orientation. RQD is determined from Rock cores or volumetric joint count; it is the percentage of Rock cores in one meter of drill run. RMR is determined as an algebraic sum of ratings for all of the parameters. On the basis of RMR values for a given engineering structure, the Rock mass is sorted into five classes: very good (RMR 100–81), good (80–61), fair (60–41), poor (40–21), and very poor (
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Rock Mass Number
Engineering Rock Mass Classification, 2011Co-Authors: Bhawani Singh, R.k. GoelAbstract:Rock mass number, denoted by “N,” is stress-free Rock mass quality “Q.” Stress effect is considered indirectly in the form of overburden height “H.” Rock condition rating is defined as Rock Mass Rating (RMR), without ratings for the crushing strength of the Intact Rock Material and the adjustment of joint orientation Rock condition rating (RCR). Therefore, it is free from the crushing strength, which is a parameter sometimes difficult to obtain at the site. Moreover, parameter wise, N, and RCR have become equivalent and can be used for the purpose of interrelation. RCR and Rock mass number N from 63 cases were used to obtain a new inter-relation. Furthermore, two sets of empirical correlations for estimating support pressure for tunnel sections under non-squeezing and squeezing ground conditions are developed using N and the measured values of support pressures, the tunnel depth H, the tunnel radius a , and the expected tunnel closure u a from 25 tunnel sections.
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Bolt length requirement in underground openings
International Journal of Rock Mechanics and Mining Sciences, 2007Co-Authors: R.k. Goel, Anil Swarup, P.r. SheoreyAbstract:Abstract A parametric study has been carried out using the numerical analysis code FLAC 3D to obtain the influence of various shapes of underground openings on the maximum induced boundary stress. Five shapes—viz. circular, horseshoe, rectangular, elongated D-shape and elliptical—have been considered. For each shape, four tunnel depths and five horizontal in situ stress models have been taken for the study of induced boundary stresses. The values of maximum and minimum induced boundary stresses in the roof and wall have been obtained from the analyses. This data has subsequently been used to develop correlations to estimate the normalized maximum and minimum boundary stresses, which have been subsequently compared with the strength of the Rock mass obtained from the Sheorey's non-linear failure criterion for three Rock masses represented by three values of Bieniawski's RMR and three values of crushing strength of Intact Rock Material. The values of minimum factor of safety at the roof and the wall have been collected from all the plots. Using these data sets, different correlations have been developed to estimate the minimum factor of safety ( f min ) in the roof and wall. Since the bolt length should be normalized with the opening size, some more computer models have been run with varying tunnel width of 5 and 20 m besides the earlier 10 m size to obtain the correlations for estimating the bolt length. The depth of factor of safety contour of 1.5 from the opening periphery has been picked up from all these models and the correlations have been developed for estimating the roof and wall bolt length for the five shapes of underground openings. The correlations for bolt length show that in addition to the shape of underground openings and in situ stress, the bolt length also varies with the Rock mass type. These correlations have been verified for field cases of elongated D-shape openings.
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Effect of shape of underground openings on boundary stresses
2004Co-Authors: R.k. GoelAbstract:As soon as an underground excavation is made, the in situ stresses within the Rock mass gets disturbed and redistribution of stresses takes place. As such, the stresses around an underground opening would be different from the pre-excavation stresses, i.e., in situ stresses. A zone of disturbed stresses is formed around an opening and generally known as 'zone of influence'. The extent of zone varies from Rock to Rock. For a very good and strong Rock this zone is small, where as for weak Rocks it is large. In other words, if the induced stresses due to tunnelling do not exceed the in situ strength of the Rock mass, the surrounding Rock mass remains in an elastic state and the zone of influence is limited. However, when the induced stress is more than the strength of the Rock mass, the Rock fails and the condition is popularly known as squeezing ground condition. The boundary stresses around an underground opening govern the stability of underground opening. It has been studied by Hoek and Brown (1982) that the shape of underground opening does affect the boundary stresses around an underground opening. To carry forward the work, a Research Project was awarded to the author by Ministry of Water Resources, Government of India. Parametric study has been carried out to obtain the influence of shape of underground openings on maximum boundary stress. In addition to five different shapes of the opening, various other parameters used for the study are tunnel depth, in situ stresses, uniaxial crushing strength of Intact Rock Material, and Bieniawski's Rock mass rating. The analyses for various values of all these parameters have been performed using numerical analysis code FALC3D. The maximum boundary stresses at the roof have been obtained and simple equations are developed for estimating the maximum boundary stresses. The analysis shows that the curves for horse-shoe and circular shapes are almost superimposing indicating that the roof stresses at the centre of the opening in these two shapes are almost same. Using the equations, maximum boundary stress can be estimated. Using the failure criterion of Sheorey (1997), safety factor contours for all the models have been plotted and the minimum safety factor values (fmin) at the roof have been obtained. Using fmin, in situ stress ratio k, depth of underground opening, Rock mass rating RMR and laboratory crushing strength, rc, finally different equations have been developed for each shape to estimate the minimum factor of safety value in the roof of the opening. (A) "Reprinted with permission from Elsevier". For the covering abstract see ITRD E124500.
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Rock mass rating (RMR)
Rock Mass Classification, 1999Co-Authors: Bhawani Singh, R.k. GoelAbstract:To apply the geomechanics classification system, a given site should be divided into a number of geological structural units in such a way that each type of Rock mass is represented by a separate geological structural unit. There are six parameters of structural unit. Out of these six, three are considered: (1) uniaxial compressive strength of Intact Rock Material, (2) Rock quality designation Rock Quality Designation (RQD), and (3) joint or discontinuity spacing. Engineering properties of Rock masses are obtained using Rock Mass Rating (RMR). If the Rock mass rating lies within a given range, the value of engineering properties is interpolated among the recommended range of properties. Thus, this chapter briefly explains the applications of RMR.
Bhawani Singh - One of the best experts on this subject based on the ideXlab platform.
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Rock Mass Number
Engineering Rock Mass Classification, 2011Co-Authors: Bhawani Singh, R.k. GoelAbstract:Rock mass number, denoted by “N,” is stress-free Rock mass quality “Q.” Stress effect is considered indirectly in the form of overburden height “H.” Rock condition rating is defined as Rock Mass Rating (RMR), without ratings for the crushing strength of the Intact Rock Material and the adjustment of joint orientation Rock condition rating (RCR). Therefore, it is free from the crushing strength, which is a parameter sometimes difficult to obtain at the site. Moreover, parameter wise, N, and RCR have become equivalent and can be used for the purpose of interrelation. RCR and Rock mass number N from 63 cases were used to obtain a new inter-relation. Furthermore, two sets of empirical correlations for estimating support pressure for tunnel sections under non-squeezing and squeezing ground conditions are developed using N and the measured values of support pressures, the tunnel depth H, the tunnel radius a , and the expected tunnel closure u a from 25 tunnel sections.
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Rock Mass Rating
Engineering Rock Mass Classification, 2011Co-Authors: Bhawani Singh, R.k. GoelAbstract:Publisher Summary The geomechanics classification or the Rock mass rating (RMR) system was initially developed at the South African Council of Scientific and Industrial Research (CSIR) on the basis of experiences in shallow tunnels in sedimentary Rocks. This chapter provides an overview on RMR with discussion on estimation, application, and precaution of RMR. To apply the geomechanics classification system, a given site is divided into a number of geological structural units in such a way that each type of Rock mass is represented by a separate geological structural unit. The following six parameters are determined for each structural unit: Uniaxial compressive strength (UCS) of Intact Rock Material, Rock quality designation (RQD), joint or discontinuity spacing, joint condition, groundwater condition, and joint orientation. RQD is determined from Rock cores or volumetric joint count; it is the percentage of Rock cores in one meter of drill run. RMR is determined as an algebraic sum of ratings for all of the parameters. On the basis of RMR values for a given engineering structure, the Rock mass is sorted into five classes: very good (RMR 100–81), good (80–61), fair (60–41), poor (40–21), and very poor (
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Rock mass rating (RMR)
Rock Mass Classification, 1999Co-Authors: Bhawani Singh, R.k. GoelAbstract:To apply the geomechanics classification system, a given site should be divided into a number of geological structural units in such a way that each type of Rock mass is represented by a separate geological structural unit. There are six parameters of structural unit. Out of these six, three are considered: (1) uniaxial compressive strength of Intact Rock Material, (2) Rock quality designation Rock Quality Designation (RQD), and (3) joint or discontinuity spacing. Engineering properties of Rock masses are obtained using Rock Mass Rating (RMR). If the Rock mass rating lies within a given range, the value of engineering properties is interpolated among the recommended range of properties. Thus, this chapter briefly explains the applications of RMR.
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Chapter-9 – Rock mass number
Rock Mass Classification, 1999Co-Authors: Bhawani SinghAbstract:Publisher Summary Rock mass number, denoted by “N,” is stress-free Rock mass quality “Q.” Stress effect is considered indirectly in the form of overburden height “H.” Rock condition rating is defined as Rock Mass Rating (RMR), without ratings for the crushing strength of the Intact Rock Material and the adjustment of joint orientation Rock condition rating (RCR). Therefore, it is free from the crushing strength, which is a parameter sometimes difficult to obtain at the site. Moreover, parameter wise, N, and RCR have become equivalent and can be used for the purpose of interrelation. RCR and Rock mass number N from 63 cases were used to obtain a new inter-relation. Furthermore, two sets of empirical correlations for estimating support pressure for tunnel sections under non-squeezing and squeezing ground conditions are developed using N and the measured values of support pressures, the tunnel depth H, the tunnel radius a, and the expected tunnel closure ua from 25 tunnel sections.
Amir Sagy - One of the best experts on this subject based on the ideXlab platform.
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Geometrical evolution of interlocked rough slip surfaces: The role of normal stress
Earth and Planetary Science Letters, 2016Co-Authors: Nir Badt, Renaud Toussaint, Yossef H. Hatzor, Amir SagyAbstract:Abstract We study the evolution of slip surface topography using direct shear tests of perfectly mating surfaces. The tests are performed under imposed constant normal stress and constant slip rate conditions, to a sliding distance comparable to the roughness scale of the studied surfaces. Prismatic limestone blocks are fractured in tension using four-point bending and the generated surface topographies are measured using a laser profilometer. The initially rough fracture interfaces are tested in direct shear while ensuring a perfectly mating configuration at the beginning of each test. The predetermined sliding distance in all tests is 10 mm and the sliding velocity is 0.05 mm/s. A constant normal stress is maintained throughout the tests using closed loop servo control. The range of normal stresses applied is between 2 MPa and 15 MPa. After shearing, the surface topographies are re-scanned and the geometrical evolution is analyzed. We find that surface roughness increases with increasing normal stress: under normal stresses below 5 MPa the surfaces become smoother compared to the original geometry, whereas under normal stresses between 7.5 MPa and 15 MPa the surfaces clearly become rougher following shear. Statistical spectral analyses of the roughness profiles indicate that roughness increases with length-scale. Power spectral density values parallel to the slip orientation are fitted by power-law with typical power value of 2.6, corresponding to a Hurst exponent of 0.8, assuming self-affine roughness. This power value is consistent for the post-sheared surfaces and is obtained even when the original surface roughness does not follow initially a power-law form. The value of the scaling-law prefactor however increases with increasing normal stress. We find that the deformation associated with shearing initially rough interlocked surfaces extends beyond the immediate tested surface, further into the Intact Rock Material. The intensity of the damage and its spatial distribution clearly increase with increasing normal stress. Wear loss is measured by subtracting the post-shear surface from the pre-shear surface matrices using known reference points. Our measurements indicate that wear loss and roughness evolution are both positively correlated with the mechanical shear work applied during the experiments. We argue, therefore, that normal stress plays a significant role in the evolution of interlocked surfaces, such as geological faults, and strongly affects the energy partitioning during slip.
Louis Ngai Yuen Wong - One of the best experts on this subject based on the ideXlab platform.
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Numerical study on coalescence of two pre-existing coplanar flaws in Rock
International Journal of Solids and Structures, 2013Co-Authors: Louis Ngai Yuen WongAbstract:Abstract Crack propagation and coalescence processes are the fundamental mechanisms leading to progressive failure processes in Rock masses, in which parallel non-persistent Rock joints are commonly involved. The coalescence behavior of the latter, which are represented as pre-existing coplanar flaws (cracks), is numerically investigated in the present study. By using AUTODYN as the numerical tool, the present study systematically simulates the coalescence of two pre-existing coplanar flaws in Rock under compression. The cumulative damage failure criterion is adopted in the numerical models to simulate the cumulative damage process in the crack initiation and propagation. The crack types (shear or tensile) are identified by analyzing the mechanics information associated with the crack initiation and propagation processes. The simulation results, which are generally in a good accordance with physical experimental results, indicate that the ligament length and the flaw inclination angle have a great influence on the coalescence pattern. The coalescence pattern is relatively simple for the flaw arrangements with a short ligament length, which becomes more complicated for those with a long ligament length. The coalescence trajectory is composed of shear cracks only when the flaw inclination angle is small (such as β ⩽ 30°). When the pre-existing flaws are steep (such as β ⩾ 75°), the coalescence trajectory is composed of tensile cracks as well as shear cracks. When the inclination angle is close to the failure angle of the corresponding Intact Rock Material, and the ligament length is not long (such as L ⩽ 2a), the direct shear coalescence is the more favorable coalescence pattern. In the special case that the two pre-existing flaws are vertical, the model will have a direct tensile coalescence pattern when the ligament length is short (L ⩽ a), while the coalescence between the two inner flaw tips is not easy to achieve if the ligament length is long (L ⩾ 2a).
Nicholas Vlachopoulos - One of the best experts on this subject based on the ideXlab platform.
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Refined Approaches for Estimating the Strength of Rock Blocks
Geotechnical and Geological Engineering, 2019Co-Authors: Anastasios Stavrou, Ioannis Vazaios, William Murphy, Nicholas VlachopoulosAbstract:Micro-discrete fracture networks (μDFNs) have been integrated into grain-based models (GBMs) within the numerical software UDEC to assess Rock block strength through a series of unconfined compressive strength (UCS) tests of progressively larger in size numerical specimens. GBMs were generated by utilizing a Voronoi tessellation scheme to capture the crack evolution processes within the Intact Rock Material, and μDFNs were separately created and embedded into the GBMs to simulate the effect of pre-existing defects. Various μDFNs realisations were generated stochastically within the software FracMan to assess the combined impact of defect intensity, persistence, strength and specimen size. The resulting synthetic Rock block models were used to assess the “flawed” Material strength at block scale through a rigorous sensitivity numerical analysis. The acquired results predict a progressive strength reduction with decreasing Intact Rock quality and certain trends are captured when Rock block strength is expressed as a function of a newly proposed “Defect Intensity× Persistence” factor. This allow us to standardise the data along specific strength reduction envelopes and to propose generic relationships that cover a wide range of defect geometrical combinations, defect strengths and sample sizes. Accordingly, an attempt is undertaken to refine two existing empirical approaches that consider the effect of scale and micro-defects explicitly for predicting the UCS of Rock blocks.