Selection of Optimal Threshold of Generalised Rock Quality Designation Based on Modified Blockiness Index

Chen, Qingfa; Yin, Tingchang; Jia, Hangyu

doi:10.1155/2019/1340549

Cited by 6 publications

(3 citation statements)

References 24 publications

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“…First, the "threshold value of 10 cm" is used as the only criterion for judging rock quality. Whether this threshold can be used as the most reasonable threshold value for distinguishing rock mass has been questioned by many scholars [15][16][17][18][19]. Second, due to the geological survey level and engineering cost, the value of RQD can be different for a given location when measured from cores with different drilling orientations [20,21].…”

Section: Introductionmentioning

confidence: 99%

Characteristics Analysis of Generalized Rock Quality Designation (RQD) Based on Degree of Joint Development

Sha

Gao

et al. 2021

Advances in Civil Engineering

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Rock quality designation (RQD) is widely adopted as a fundamental tool in characterizing rock masses since it was devised in 1964. Since the conventional RQD calculation is limited due to its dependence on the selected threshold, previous research introduced generalized RQD to adequately reflect the anisotropy and scale effect of RQD. However, the influence of the joint development inside rock mass on generalized RQD remains unclear. The objective of this work is to investigate characteristics of the generalized RQD in view of different development degrees of discontinuities in rock mass, including spacing (density) and trace length. Three-dimensional fracture network modelling is employed to simulate the actual rock mass of open-pit iron mine in China. Virtual scanlines are set to obtain RQD values in different directions. The results primarily show that the generalized RQD should be introduced to calculate the RQD with different thresholds to fully reflect the anisotropy of rock mass. The optimal threshold can be obtained based on an anisotropic coefficient, which is defined by (RQDmax-RQDmin). It is also indicated that the fracture spacing has a great influence on both the anisotropy of RQD and the selection of the optimal threshold. The optimal threshold of the generalized RQD increases with the increase in the fracture spacing. In addition, the scale effect of RQD in different models is discussed by changing the length of the scanlines. The longer the scanlines we set, the more stable RQD value can be obtained in the model. It is recommended to fit much longer scanline to get realistic RQD in heavily fractured rock mass.

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Section: Introductionmentioning

confidence: 99%

Characteristics Analysis of Generalized Rock Quality Designation (RQD) Based on Degree of Joint Development

Sha

Gao

et al. 2021

Advances in Civil Engineering

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“…Furthermore, the quantitative evaluation method of this index was discussed. Chen et al [21] introduced to generalised RQD. Based on the modified block index (MBI), the optimum threshold of the generalised RQD was determined.…”

Section: Introductionmentioning

confidence: 99%

State Judgement Model of the Coal and Rock Medium and Its Engineering Application

Zhu

Wang

Han

2020

Advances in Civil Engineering

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In the loading and failure process of the coal and rock medium, with the increasing of the damaging and failure extent, the medium state gradually changed from the continuous, the quasicontinuous, and the discontinuous to the loose successively. To evaluate the damaging failure extent of the coal and rock mass and distinguish the state of the coal and rock mass medium, first, the medium state index was defined based on the acoustic wave propagation model. Then, based on the coal mass in the working face 8512 in the Chenjiagou Coal Mine in China, the acoustic character and the mechanical character experiments were conducted. Through experiments, the variation law of the ultrasonic wave velocity and the medium state index of the coal mass with the strain under the compressive state were acquired; with the increasing of the strain, the medium state indexes successively experienced the variation process including stabilising around 0, slow increasing, dramatic increasing, and stabilising around 1. Then, based on the variation law of the medium state index, the coal and rock mass medium state judgement model was constructed. This model was applied to judge the coal mass medium state. After it, the mudstones in the roof of the same working face were regarded as the research object, the mudstone medium state was divided into 4 types according to the medium state judgement model, namely, continuous, quasicontinuous, discontinuous, and bulk solid, and the mudstone failure state was basically consistent with the continuous, quasicontinuous, discontinuous, and bulk solid state. The adaptability and rationality of the judgement model was verified. Finally, engineering application of the judgement model was conducted. The distribution law of the top coal with different medium state was acquired. In the top coal that was 186 m away from the working face, it belonged to the continuous medium state. As for the top coal that was 6 m to 186 m far away from the working face, it was under the quasicontinuous medium state. For the top coal that was 3 m to 6 m far away from the working face, it was under the discontinuous medium state. For the top coal that was less than 3 m far away from the working face and behind the working face, it belonged to the bulk solid medium state. The state judgement model can successfully distinguish the medium state of the coal seam and mudstones in the roof in the working face 8512. This provided a new approach to evaluate the damaging failure extent of the coal and rock medium in the Chenjiagou Coal Mine.

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“…Some researchers have investigated the rock mass structure and presented several measurements for the degree of rock mass fracturing. Chen (1979) presented the concept of a twodimensional blockiness modulus that characterizes the rock mass intactness degree based on the two-dimensional discontinuity data measured on rock mass outcrops. Sen and Eissa (1991) proposed the concept of volumetric RQD estimated from the volumetric joint count (Jv).…”

Section: Introductionmentioning

confidence: 99%

Archives of Mining Sciences

Chen¹,

Yin²,

Niu³

2018

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The evaluation accuracies of rock mass structures based on the ratings of the Rock Quality Designation (RQD) and discontinuity spacing (S) in the Rock Mass Rating (RMR) system are very limited due to the inherent restrictions of RQD and S. This study presents an improvement that replaces these two parameters with the modified blockiness index (B z ) in the RMR system. Before proceeding with this replacement, it is necessary for theoretical model building to make an assumption that the discontinuity network contains three sets of mutually orthogonal disc-shaped discontinuities with the same diameter and spacing of discontinuities. Then, a total of 35 types of theoretical DFN (Discrete Fracture Network) models possessing the different structures were built based on the International Society for Rock Mechanics (ISRM) discontinuity classification (ISRM, 1978). In addition, the RQD values of each model were measured by setting the scanlines in the models, and the B z values were computed following the modified blockiness evaluation method. Correlations between the three indices (i.e., B z , RQD and S) were explored, and the reliability of the substitution was subsequently verified. Finally, RMR systems based on the proposed method and the standard approach were applied to real cases, and comparisons between the two methods were performed. This study reveals that RQD is well correlated with S but is difficult to relate to the discontinuity diameter (D), and B z has a good correlation with RQD/S. Additionally, the ratings of RQD and S are always far from the actual rock mass structure, and the B z ratings are found to give better characterizations of rock mass structures. This substitution in the RMR system was found to be acceptable and practical.

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Selection of Optimal Threshold of Generalised Rock Quality Designation Based on Modified Blockiness Index

Cited by 6 publications

References 24 publications

Characteristics Analysis of Generalized Rock Quality Designation (RQD) Based on Degree of Joint Development

Characteristics Analysis of Generalized Rock Quality Designation (RQD) Based on Degree of Joint Development

State Judgement Model of the Coal and Rock Medium and Its Engineering Application

Archives of Mining Sciences

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