Coal–rock interface detection on the basis of image texture features

Based on the stability and inequality of texture features between coal and rock,this study used the digital image analysis technique to propose a coal–rock interface detection method.By using gray level co-occurrence matrix,twenty-two texture features were extracted from the images of coal and rock.Data dimension of the feature space reduced to four by feature selection,which was according to a separability criterion based on inter-class mean difference and within-class scatter.The experimental results show that the optimized features were effective in improving the separability of the samples and reducing the time complexity of the algorithm.In the optimized low-dimensional feature space,the coal–rock classifer was set up using the fsher discriminant method.Using the 10-fold cross-validation technique,the performance of the classifer was evaluated,and an average recognition rate of 94.12%was obtained.The results of comparative experiments show that the identifcation performance of the proposed method was superior to the texture description method based on gray histogram and gradient histogram.

Application of wavelet packet decomposition and its energy spectrum on the coal-rock interface identification

The theory and method of wavelet packet decomposition and its energy spectrum dealing with the coal rock Interface Identification are presented in the paper. The characteristic frequency band of the coal rock signal could be identified by wavelet packet decomposition and its energy spectrum conveniently, at the same time, quantification analysis were performed. The result demonstrates that this method is more advantageous and of practical value than traditional Fourier analysis method.

Numerical investigation on the tensile fracturing behavior of rock-shotcrete interface based on discrete element method

Four groups of numerical models of Brazilian tests on rock-shotcrete interfaces were successfully conducted by PFC2D. The tensile strength and Young’s modulus of shotcrete were considered. Six different undulations of rock-shotcrete interface were set up. The influences of multiple parameters on the bearing characteristics of the rock-shotcrete interface were studied. The results showed that a better support performance can be obtained by increasing the Young’s modulus of shotcrete rather than the tensile strength of shotcrete. For different tensile strength and Young’s modulus, the increase of sawtooth height has different effects on the support performance. The failure mechanism of the rock-shotcrete interfaces was analysed in detail. The stress shielding effect and stress concentration effect caused by the shape characteristics of rock-shotcrete interface were observed. The influence of these parameters on the overall support performance should be fully considered in a reasonable support design.

Stress wave propagation and incompatible deformation mechanisms in rock discontinuity interfaces in deep-buried tunnels

Complex weak structural planes and fault zones induce significant heterogeneity,discontinuity,and nonlinear characteristics of a rock mass.When an earthquake occurs,these characteristics lead to extremely complex seismic wave propagation and vibrational behaviors and thus pose a huge threat to the safety and stability of deep buried tunnels.To investigate the wave propagation in a rock mass with different structural planes and fault zones,this study first introduced the theory of elastic wave propagation and elastodynamic principles and used the Zoeppritz equation to describe wave field decomposition and develop a seismic wave response model accordingly.Then,a physical wave propagation model was constructed to investigate seismic waves passing through a fault,and dynamic damage was analyzed by using shaking table tests.Finally,stress wave attenuation and dynamic incompatible deformation mechanisms in a rock mass with fault zones were explored.The results indicate that under the action of weak structural planes,stress waves appear as a complex wave field decomposition phenomenon.When a stress wave spreads to a weak structural plane,its scattering may transform into a tensile wave,generating tensile stress and destabilizing the rock mass;wave dynamic energy is absorbed by a low-strength rock through wave scattering,which significantly weakens the seismic load.Wave propagation accelerates the initiation and expansion of internal defects in the rock mass and leads to a dynamic incompatible deformation.This is one of the main causes for large deformation and even instability within rock masses.These findings provide an important reference and guide with respect to stability analysis of rock mass with weak structural planes and fault zones.

Influence of interface morphology on dynamic behavior and energy dissipation of bi-material discs

To investigate the dynamic behavior and energy dissipation of the rock−concrete interface,dynamic splitting tests on bi-material discs were conducted by using the split Hopkinson pressure bar.The test results reveal that with the change of the interface inclination angles(θ),the influence of interface groove width on the bearing capacity of specimens also varies.Whenθincreases from 0°to 30°,the bearing capacity of the specimen increases first and then decreases with the rise of the interface groove width;the optimal groove width on the rock surface in this range of interface inclination angles is 5 mm.Whenθincreases from 45°to 90°,the bearing capacity of the specimen has no obvious change.Moreover,whenθincreases from 0°to 45°,the dissipated energy of the specimens rises obviously at first and then tends to be stable as the width of the interface groove increases.

Mechanical Behaviors of Anchorage Interfaces in Layered Rocks with Fractures under Axial Loads

Rock bolts are widely employed as an effective and efficient reinforcement method in geotechnical engineering.Sandwich composite structures formed by hard rock and weak rock are often encountered in practical projects.Furthermore,the spatial structure of the rock mass has a direct influence on the effect of the anchorage support.To investigate the impact of rock mass structure on the mechanical characteristics of anchorage interfaces,pull-out tests on reinforced specimens with different mudstone thicknesses and fracture dip angles are conducted.The experimental results indicate that the percentage of mudstone content and fracture dip angle have a significant influence on the pullout load of the samples.A weaker surrounding rock results in a lower peak load and a longer critical anchorage length,and vice versa.The results also show that 70%mudstone content can be considered a critical condition for impacting the peak load.Specifically,the percentage of mudstone content has a limited influence on the variation in the peak load when it exceeds 70%.Optical fiber deformation results show that compared to the rock mass with fracture dip angles of 0°and 60°,the rock mass with a fracture dip angle of 30°has a more uniformly distributed force at the anchorage interface.When the fracture dip angle exceeds 60°,the dip angle is no longer a key indicator of peak load.The accuracy of the experimentally obtained load-displacement curves is further verified although numerical simulation using the discrete element method.

Practical configured microtremor array measurements(MAMs)for the geological investigation of underground space

Underground space utilization is becoming increasingly essential for modern metropolitan cities such as Singapore.Mapping a soil/rock interface using traditional borehole investigation methods is expensive and difficult,owing to the numerous physical constraints within a built-up city.Boreholes are often far apart,resulting in many unforeseen ground conditions during subsequent excavation.Geophysical methods are sometimes employed as possible alternatives for fast,economical,and efficient bedrock surveys.The goal of this study is to investigate the practical details of applying microtremor array measurement(MAM)as a non-invasive surface wave survey for mapping soil/rock interfaces in Singapore.Critical configurations in field data acquisition are examined,and practical recommendations for array construction are provided.In addition,30 in situ MAM tests are carried out for two major geological formations in Singapore.From the results,a standard shear wave velocity(V_(s))of 500 m/s is found to be suitable for interpreting the soil/rock interface,for the Bukit Timah Granite and Jurong formations.However,the method does not predict well when soft Kallang formation deposits are present.Other limitations are also discussed in the later parts of this paper.Conclusions and practical recommendations are discussed,providing constructive guidance to the industry.The proposed Vs-based method and associated guidelines and limitations can be used to create a digital geological database and are especially useful for rock profiling in an urban environment.

Latest advances in discontinuous deformation analysis method

Discontinuous deformation analysis （DDA） method, proposed firstly by Shi [1] in 1988, is a novel numerical approach to simulate the discontinuous deformation behaviors of blocky rock structures. In DDA, the domain of interest is represented as an assemblage of discrete blocks and the joints are treated as interfaces between blocks. The governing equations of DDA are derived from Newton’s Second Law of Motion and the Principle of Minimum Potential Energy.