Geometrical heterogeneity of the joint roughness coefficient revealed by 3D laser scanning
TL;DR: In this paper, the joint roughness coefficient (JRC) is an important indicator that characterizes the physical and mechanical behaviors of a jointed rock mass, and the effects of sampling interval on JRC were assessed during the JRC calculation process.
About: This article is published in Engineering Geology.The article was published on 2020-02-01. It has received 39 citations till now.
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TL;DR: In this paper, the authors used NMR and polarizing light microscopy to detect pore structure characteristics of red sandstone, and then, the pore situation can be obtained, and finally, the influence of temperature on the porosity and internal grain structure do not change significantly.
Abstract: High temperatures affect the physical properties of red sandstone seriously, especially the pores. Understanding its mechanism is of great significance in coal mining following underground gasification, geothermal energy utilization, and the deep burial of nuclear waste. Nuclear magnetic resonance (NMR) was used to detect pore structure characteristics, and scanning electron microscopy (SEM) and polarizing light microscopy (PLM) were used to mechanism of change. The transverse relaxation time (T2) and signal strengths of red sandstone treated at various temperatures were observed by NMR, and then, the pore situation can be obtained, and finally, the influence of temperature on the pore structure of red sandstone can be obtained. Microscopic photographs of the pores of red sandstone were obtained by SEM and PLM to assist in explaining the process of microstructural change, especially the influences of temperature on pore characteristics and grain morphology and distribution. The researches indicate that after the heat treatment of red sandstone at 25–1300 °C, the pore and strength characteristics change in well-defined stages. Before 500 °C, the pore diameters and distribution range increase, but the porosity and internal grain structure do not change significantly. At 500–1000 °C, red sandstone micropores contract, mesopores and macropores develop, and strength decreases. After 1000 °C, the grains that comprise sandstone melt and fill many of the pores, decreasing porosity. The proportion of micropores decreases, while mesopores and macropores increase. In addition, a large number of bubbly holes appear in and on the sandstone, presumably caused by gases such as CO2, and water vapor from dehydrating grains. The changes in pore and cementation states with temperature are the main factors affecting the tensile strength of red sandstone.
26 citations
TL;DR: In this article, the statistical mechanics of rock masses (SMRM) theory was proposed to analyze the structural properties of rock mass structures and to provide fast and precise solutions for parameter estimations, such as full-direction rock quality designation (RQD), elastic modulus, Coulomb compressive strength, and Poisson ratio and shear strength.
Abstract: To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses, a theoretical and methodological system called the statistical mechanics of rock masses (SMRM) was developed in the past three decades. In SMRM, equivalent continuum models of stress–strain relationship, strength and failure probability for jointed rock masses were established, which were based on the geometric probability models characterising the rock mass structure. This follows the statistical physics, the continuum mechanics, the fracture mechanics and the weakest link hypothesis. A general constitutive model and complete stress–strain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory. An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses, such as full-direction rock quality designation (RQD), elastic modulus, Coulomb compressive strength, rock mass quality rating, and Poisson’s ratio and shear strength. The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses. It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses. Examples of engineering applications of SMRM were presented, including a rock mass at QBT hydropower station in northwestern China, a dam slope of Zongo II hydropower station in D.R. Congo, an open-pit mine in Dexing, China, an underground powerhouse of Jinping I hydropower station in southwestern China, and a typical circular tunnel in Lanzhou-Chongqing railway, China. These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.
25 citations
TL;DR: Wang et al. as discussed by the authors proposed a time-dependency model for evaluating the evolution of the excavation heavily damaged zone (EHDZ), which can be used to predict EHDZ depths at different times after rock mass excavation.
24 citations
TL;DR: Based on the statistical parameters of the fracture network of rock mass and combining them with the strain energy theory from continuum and fracture mechanics, the elastic stress-strain relationship of fractured rock mass is derived and its elastic modulus is derived.
18 citations
TL;DR: In this paper, the initial climbing angle was defined and used to characterize the micro-slope distribution of the ascent section of joint profile, and a new method was proposed for calculating the morphology parameter, M, which embodies anisotropy, and the values of M for all profile lines, which are selected on the same joint at equal intervals in one direction, are log-normally distributed.
16 citations
References
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01 Dec 1977
TL;DR: In this paper, the authors describe an empirical law of friction for rock joints, which can be used both for extrapolating and predicting shear strength data, and demonstrate that it can be estimated to within ± 1° for any one of the eight rock types investigated.
Abstract: The paper describes an empirical law of friction for rock joints which can be used both for extrapolating and predicting shear strength data. The equation is based on three index parameters; the joint roughness coefficientJRC, the joint wall compressive strengthJCS, and the residual friction angleφ
r
. All these index values can be measured in the laboratory. They can also be measured in the field. Index tests and subsequent shear box tests on more than 100 joint samples have demonstrated thatφ
r
can be estimated to within ± 1° for any one of the eight rock types investigated. The mean value of the peak shear strength angle (arctanτ/σ
n
) for the same 100 joints was estimated to within 1/2°. The exceptionally close prediction of peak strength is made possible by performing self-weight (low stress) sliding tests on blocks with throughgoing joints. The total friction angle (arctanτ/σ
n
) at which sliding occurs provides an estimate of the joint roughness coefficientJRC. The latter is constant over a range of effective normal stress of at least four orders of magnitude. However, it is found that bothJRC andJCS reduce with increasing joint length. Increasing the length of joint therefore reduces not only the peak shear strength, but also the peak dilation angle and the peak shear stiffness. These important scale effects can be predicted at a fraction of the cost of performing large scale in situ direct shear tests.
2,139 citations
TL;DR: In this paper, a sliding scale of roughness is proposed for estimating the shear strength of rough joints, and the curvature of the proposed strength envelopes reduces as the roughness coefficient reduces, and also varies with the strength of the weathered joint wall or unweathered rock.
1,168 citations
TL;DR: In this paper, a relation between the Rock Quality Designation (RQD∗) and mean discontinuity frequency per metre (λ) was established: RQD ∗ = 100 e − 0.1λ (0.1 ε + 1).
599 citations
TL;DR: In this article, a grain-based UDC model was developed to generate a deformable polygonal grain-like structure to simulate the microstructure of brittle rock, which takes into account grain-scale heterogeneity including microgeometric heterogeneity, grainscale elastic heterogeneity, and microcontact heterogeneity.
Abstract: A grain-based Universal Distinct Element Code model was developed to generate a deformable polygonal grain-like structure to simulate the microstructure of brittle rock. It takes into account grain-scale heterogeneity including microgeometric heterogeneity, grain-scale elastic heterogeneity, and microcontact heterogeneity. The microgeometric heterogeneity can be used to match the grain size distribution of the rock. The discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy. The modeling approach was evaluated using Lac du Bonnet granite and A "Aspo" Diorite. The microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading. The crack-initiation stress was found to be controlled primarily by the microscale geometric heterogeneity, while the microcontact heterogeneity controlled the strength characteristics. The effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined.
360 citations
TL;DR: In this paper, the authors used the discrete element software PFC3D to investigate the effect of geometric parameters of joints on the rock mass failure mechanism, unconfined compressive strength and deformation modulus.
266 citations