Roughness characterization and shearing dislocation failure for rock-backfill interface

Shearing dislocation is a common failure type for rock–backfill interfaces because of backfill sedimentation and rock strata movement in backfill mining goaf.This paper designed a test method for rock–backfill shearing dislocation.Using digital image techno-logy and three-dimensional(3D)laser morphology scanning techniques,a set of 3D models with rough joint surfaces was established.Further,the mechanical behavior of rock–backfill shearing dislocation was investigated using a direct shear test.The effects of interface roughness on the shear–displacement curve and failure characteristics of rock–backfill specimens were considered.The 3D fractal dimen-sion,profile line joint roughness coefficient(JRC),profile line two-dimensional fractal dimension,and the surface curvature of the frac-tures were obtained.The correlation characterization of surface roughness was then analyzed,and the shear strength could be measured and calculated using JRC.The results showed the following:there were three failure threshold value points in rock–backfill shearing dis-location:30%–50%displacement before the peak,70%–90%displacement before the peak,and 100%displacement before the peak to post-peak,which could be a sign for rock–backfill shearing dislocation failure.The surface JRC could be used to judge the rock–backfill shearing dislocation failure,including post-peak sliding,uniform variations,and gradient change,corresponding to rock–backfill disloca-tion failure on the field site.The research reveals the damage mechanism for rock–backfill complexes based on the free joint surface,fills the gap of existing shearing theoretical systems for isomerism complexes,and provides a theoretical basis for the prevention and control of possible disasters in backfill mining.

Resilient performance of self-centering hybrid rocking walls with curved interface under pseudo-static loading

Frame and rocking wall(FRW)structures have excellent resilient performance during earthquakes.However,the concrete at interfacial corners of rocking walls(RWs)is easily crushed due to local extreme compression during the rocking process.An innovative RW with a curved interface is proposed to prevent interfacial corners from producing local damage,enhancing its earthquake resilient performance(ERP).The precast wall panel with a curved interface is assembled into an integral self-centering hybrid rocking wall(SCRW)by two post-tensioned unbonded prestressed tendons.Moreover,two ordinary energy dissipation steel rebars and two shear reinforcements are arranged to increase the energy dissipation capacity and lateral resistance.Two SCRW specimens and one monolithic reinforced concrete(RC)shear wall(SW)were tested under pseudo-static loading to compare the ERPs of the proposed SCRW and the SW,focusing on studying the effect of the curved interface on the SCRW.The key resilient performance of rocking effects,failure modes,and hysteretic properties of the SCRW were explored.The results show that nonlinear deformations of the SCRW are concentrated along the interface between the SCRW and the foundation,avoiding damage within the SCRW.The restoring force provided by the prestressed tendons can effectively realize self-centering capacity with small residual deformation,and the resilient performance of the SCRW is better than that of monolithic SW.In addition,the curved interface of the SCRW makes the rocking center change and move inward,partially relieving the stress concentration and crush of concrete.The rocking range of the rocking center is about 41.4%of the width of the SCRW.

Fracture behaviors of columnar jointed rock mass using interface mechanics theorem

For a special geological structure of columnar jointed rock mass(CJRM),its mechanical properties are strongly affected by the columnar joints.To describe the fracture behaviors of CJRM using the basic theories of interface mechanics for composite materials,the interface stresses of the vertical and horizontal joints,which are the two primary joints in the CJRM under triaxial compression,are studied,and their mathematical expressions are derived based on the superposition principle.Based on the obtained interface stresses of the vertical and horizontal joints in the CJRM,the crack initiation of the joint interface in the CJRM is studied using the maximum circumferential stress theory in fracture mechanics.Moreover,based on this investigation,the fracture behaviors of CJRM are analyzed.According to the results of similar material physical model tests for the CJRM,the theoretical study is verified.Finally,the influence of the mechanical parameters of the CJRM on the joint interface stress is discussed comprehensively.

Attenuation of rock blasting induced ground vibration in rock-soil interface

Blasting has been widely used in mining and construction industries for rock breaking.This paper presents the results of a series of field tests conducted to investigate the ground wave propagation through mixed geological media.The tests were conducted at a site in the northwestern part of Singapore composed of residual soil and granitic rock.The field test aims to provide measurement data to better understand the stress wave propagation in soil/rock and along their interface.Triaxial accelerometers were used for the free field vibration monitoring.The measured results are presented and discussed,and empirical formulae for predicting peak particle velocity (PPV) attenuation along the ground surface and in soil/rock were derived from the measured data.Also,the ground vibration attenuation across the soil-rock interface was carefully examined,and it was found that the PPV of ground vibration was decreased by 37.2% when it travels from rock to soil in the vertical direction.

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.

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.

A novel radial cable for restraining tensile failure in steep fill–rock interfaces

It is quite common for fill slopes such as embankments and airport foundations to be constructed in mountainous areas.Steep fill–rock interfaces in such areas undergo tensile failure owing to differences in the stiffness values and tensile strengths of the soil and hard rock.In this study,a new anchor system,termed“radial cable,”is proposed to increase the pullout capacity of cables in the fill;this in turn helps control tensile deformation in the fill slope along the interface.In a radial cable,the steel ropes of a conventional cable are equally and symmetrically separated into three sub-cables(a central sub-cable and two branch sub-cables)with a radial distribution starting from the position of the interface.Moreover,each of the sub-cables is fixed in the fill using short U-shaped rigid rods along the cable length and a rigid baffle at its end to further increase pullout resistance.Experimental and numerical uplift tests were conducted to analyze the pullout capacity and anchoring behavior of the radial cables in soil to study the effect of branching.The reinforcement effect of the radial cables was also examined using a case study.

STUDY ON THE COAL-ROCK INTERFACE RECOGNITION METHOD BASED ON MULTI-SENSOR DATA FUSION TECHNIQUE

The coal-rock interface recognition method based on multi-sensor data fusiontechnique is put forward because of the localization of single type sensor recognition method. Themeasuring theory based on multi-sensor data fusion technique is analyzed, and hereby the testplatform of recognition system is manufactured. The advantage of data fusion with the fuzzy neuralnetwork (FNN) technique has been probed. The two-level FNN is constructed and data fusion is carriedout. The experiments show that in various conditions the method can always acquire a much higherrecognition rate than normal ones.

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.

Interaction mechanism of the interface between a deep buried sand and a paleo-weathered rock mass using a high normal stress direct shear apparatus

In order to evaluate the feasibility of safe mining close to the contact zone under reduced security coal pillar conditions at a coal mine in eastern China, the interaction mechanism of the interface between deep buried sand and a paleo-weathered rock mass was investigated in the laboratory by direct shear testing. A DRS-1 high pressure soil shear testing machine and orthogonal design method were used in the direct shear tests. Variance and range methods were applied to analyze the sensitivity of each factor that has an influence on the mechanical characters of the interface. The test results show that the normal pressure is the main influencing factor for mechanical characteristics of the interface, while the lithological characters and roughness are minor factors; the shear stress against shear displacement curve for the interface shows an overall hyperbola relationship, no obvious peak stress and dilatancy was observed.When the normal pressure is 6 MPa, the shear strengths of interfaces with different roughness are basically the same, and when the normal pressure is more than 8 MPa, the larger the roughness of the interface, the larger will be the shear strength; the shear strength has a better linear relationship with the normal pressure, which can be described by a linear Mohr–Coulomb criterion.

Failure characterization of fully grouted rock bolts under triaxial testing

Confining stresses serve as a pivotal determinant in shaping the behavior of grouted rock bolts.Nonetheless,prior investigations have oversimplified the three-dimensional stress state,primarily assuming hydrostatic stress conditions.Under these conditions,it is assumed that the intermediate principal stress(σ_(2))equals the minimum principal stress(σ_(3)).This assumption overlooks the potential variations in magnitudes of in situ stress conditions along all three directions near an underground opening where a rock bolt is installed.In this study,a series of push tests was meticulously conducted under triaxial conditions.These tests involved applying non-uniform confining stresses(σ_(2)≠σ_(3))to cubic specimens,aiming to unveil the previously overlooked influence of intermediate principal stresses on the strength properties of rock bolts.The results show that as the confining stresses increase from zero to higher levels,the pre-failure behavior changes from linear to nonlinear forms,resulting in an increase in initial stiffness from 2.08 kN/mm to 32.51 kN/mm.The load-displacement curves further illuminate distinct post-failure behavior at elevated levels of confining stresses,characterized by enhanced stiffness.Notably,the peak load capacity ranged from 27.9 kN to 46.5 kN as confining stresses advanced from σ_(2)=σ_(3)=0 to σ_(2)=20 MPa and σ_(3)=10 MPa.Additionally,the outcomes highlight an influence of confining stress on the lateral deformation of samples.Lower levels of confinement prompt overall dilation in lateral deformation,while higher confinements maintain a state of shrinkage.Furthermore,diverse failure modes have been identified,intricately tied to the arrangement of confining stresses.Lower confinements tend to induce a splitting mode of failure,whereas higher loads bring about a shift towards a pure interfacial shear-off and shear-crushed failure mechanism.

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.

Design principle for parameters and interferences of tungsten carbide insert interface on roller bits

The lifetime of roll-bits with inserted tooth will be obviously decreased while drilling in strata and the tungsten carbide can be integrally separated from the roll-cone,which will need more trip out time to replace the roller bit.This study provides an entire analysis on stress as well as strength for teeth and tooth holes in loaded conditions.Qualities of tooth drop from matrix within roller bit.The optimized interferences of teeth inserted into the bit can be reasonably obtained by the critical interference derived from some relevant influence factors on the tooth-fixing quality of roller bits.

Interface模型模拟断续节理洞群渗流效应的数值分析

采用三维有限差分FLAC3D程序,以二滩工程地下洞群的结构形式为背景,提出interface界面模型模拟断续节理的力学效应,考虑与不考虑节理岩体静水渗流对围岩稳定性进行了大量计算工况的准三维数值模拟。通过系统分析得出相应的结论,为大型地下工程围岩稳定分析提供了有益的参考。

The shear strength of the interface between artificial rock and printed concrete at super-early ages

3D concrete printing has the potential to replace shotcrete for construction of linings of tunnels in hard rock.The shear strength of the interface between rock and printed concrete is vital,especially at super-early ages.However,traditional methods for testing the shear strength of the interface,e.g.,the direct shear test,are time-consuming and result in a high variability for fast-hardening printed concrete.In this paper,a new fast bond shear test is proposed.Each test can be completed in 1 min,with another 2 min for preparing the next test.The influence of the matrix composition,the age of the printed matrices,and the interface roughness of the artificial rock substrate on the shear strength of the interface was experimentally studied.The tests were conducted at the age of the matrices at the 1st,the 4th,the 8th,the 16th,the 32nd,and the 64th min after its final setting.A dimensionless formula was established to calculate the shear strength,accounting for the age of the printed matrices,the interface roughness,and the shear failure modes.It was validated by comparing the calculated results and the experimental results of one group of samples.

A new diamond bit for extra-hard, compact and nonabrasive rock formation

A new impregnated diamond bit was designed to solve the slipping problem when impregnated diamond bit was used for extra-hard, compact, and nonabrasive rock formation. Adding Si C grits into matrix, Si C grits can easily be exfoliated from the surface of the matrix due to weak holding-force with matrix, which made the surface non-smooth. Three Ф36/24 mm laboratorial bits were manufactured to conduct a laboratory drilling test on zirconiacorundum refractory brick. The laboratory drilling test indicates that the abrasive resistance of the bit work layer is proportional to the Si C concentation. The higher the concentration, the weaker the abrasive resistance of matrix. The new impregnated diamond bit was applied to a mining area drilling construction in Jiangxi province, China. Field drilling application indicates that the ROP(rate of penetration) of the new bit is approximately two to three times that of the common bits. Compared with the common bits, the surface of the new bit has typical abrasive wear characteristics,and the metabolic rate of the diamond can be well matched to the wear rate of the matrix.

The Principle of the Drilling by Impregnated Diamond Bits and the Classification of Rocks

Recently impregnated diamond bits have been widely applied in drilling hard and medium - hard formations in the world . It is quite necessary to study the fracturing mecha-nism of the impregnated diamond bit and the classification of rocks , which can realize optimum drilling . Using multi - parameter rotary test stand can monitor and print nine parameters . The diamond size and concentration for experiment are various and there are nearly 200 types of samples , numbering over 1000 pieces . The results of laboratory are the same as those in the field . Besides , this paper expresses that the diamond concentration of impregnated diamond bits effect the bonding strength of diamond imbedded in ma-trix . During drilling by impregnated diamond bits three ways are used to cool the bits . The contact area between impregnated diamond layer and flow , and the drilling flow through annulus carrying away heat with conduction form can be shown by equations . It is impossible to classify the rock drillability only by using single factor . The best method is to use main factors to analyse the drillability of rocks. Only in this way , the results can be applied to practice .

THREE DIMENSIONAL DYNAMIC ELASTICPLASTIC ANALYSIS OF THE INTERACTION OF A SET OF PERCUSSION BITS WITH ROCK MASSES

A three dimensional dynamic elastic-plastic finite element analysis of the interaction of percussion bits with rock masses is presented. The dynamic contact problem was investigated with the numerical method developed for high velocity impact calculations[1]. The numerical analysis was carried out for three simultaneously loaded percussion bits arranged on a straight line on the rock surface, the loading time was kept constant throughout this work. The numerical calculation for various strengths of the dynamic load tm the percussion bits shows that a critical minimum dynamic load exists for the generation of plastic deformations in the rock. For this critical value of the load the maximum normal stress of the longitudinal wave in the percussion bit exceeds the yield stress of the rock mass.

Impact of evolution of cathode electrolyte interface of Li(Ni0.8Co0.1Mn0.1)O2 on electrochemical performance during high voltage cycling process

In this work, the electrochemical performance of LiNi0.8Co0.1Mn0.1O2(NCM811) has been investigated after cycling with various upper cutoff voltages. Noteworthily, electrochemical impedance of NCM811 declined with the increasing cycle number to high voltages. It was found that the decline of charge transfer impedance could be related to the structural and compositional change of cathode electrolyte interphase(CEI) of NCM811 when charging to high voltages, based on the characterization of electrochemical impedance spectroscopy(EIS), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The corresponding mechanism has also been proposed in this study. Specifically, due to the increasing roughness of cathode surface, the bottom of CEI film and cubic phase on cathode surface form a transition region mainly at high voltages, leading to the nonobvious boundary. This newly formed transition region at high voltages could promote the Li ion diffusion from electrolyte to cathode, then reducing charge transfer impedance. Additionally, the decrease of Li F on the surface of the cathode could also make a contribution to lower the interface impedance. This study delivers a different evolution of CEI on NCM811, and the impact of CEI evolution on electrochemical performance when charging to a high voltage.

Research on Lubrication Model of Rock Bit Bearings with Non-Newtonian Medium

Lubrication media of rock bit journal bearing is non-Newtonian fluid, and because of structure limitations, lubricant supply is only from the inside track and its rheological properties are relatively complex. In general studies, the non- Newtonianism of lubrication media of rock bit journal bearing is neglected to simplify the research process. Based on the universal Reynolds equation of non-Newton media, the mathematical model of lubrication analysis was suitable for the rock bit bearing working conditions was established. Then according to the experimental results of rheological properties of RB-type lubricating grease, the equivalent viscosity of the model was established and this model can be solved by the method used in solving the Reynolds equation of Newton fluid.