查看更多>>摘要：It has become an inevitable trend of human development to seek resources from the deep underground.However,rock encountered in deep underground engineering is usually in an anisotropic stress state(σ1＞σ＞σ3)due to the influences of geological structures and engineering disturbances.It is therefore essential to study the mechanical,seepage,and dynamic disaster behaviors of deep rock under true tri-axial stress to ensure the safe operation of deep rock engineering and the efficient exploitation of deep resources.In recent years,experimental techniques and research on true triaxial rock mechanics have achieved fruitful results that have promoted the rapid development of deep rock mechanics;thus,it is necessary to systematically review and summarize these developments.This work first introduced sev-eral typical true triaxial testing apparatus and then reviewed the corresponding research progress on rock deformation,strength,failure mode,brittleness,and energy as well as the 3D volumetric fracturing(dy-namic disaster)properties of deep rocks under true triaxial stress.Then,several commonly used true tri-axial rock strength criteria and their applicability,the permeability characteristics and mathematical models of deep reservoir rocks,and the disaster-causing processes and mechanisms of disturbed volu-metric fracturing(rockburst,compound dynamic disasters)in deep rock engineering were described.This work may provide an essential reference for addressing the true triaxial rock mechanics issues involved in deep rock engineering,especially regarding the stability of surrounding rock at depth,disaster prevention and control,and oil and gas exploitation.
查看更多>>摘要：In recent years,the mine tunneling method and the new Austrian tunneling method have been consid-ered the main theories of tunneling approaches in China.It is difficult for the traditional technique to overcome the large deformation problems imposed by complex geological conditions of mountain soft rock tunneling.Hence,the compensation excavation method has been proposed to solve this issue under the consideration that all damage in tunneling originates from the excavation.It uses supportive strate-gies to counteract the excavation effects successfully.This paper provides an overview of the fundamen-tal ideas of the compensation excavation method,methodologies,and field applications.The scientific validity and feasibility of the compensation excavation method were investigated through the practical engineering study of the Muzhailing and Changning tunnels.
查看更多>>摘要：Several derivative disasters such as ground pressure disasters and methane explosions can be caused by the hard roof in coal mines.For limestone roofs with fine integrity and extreme hardness,collapse is dif-ficult and the effect of conventional roof control methods is limited.Acidizing reformation is an effective way to weaken the strength of roof strata based on acid-rock reaction.In this study,the rock strength damage law and acid reaction characteristics were tested by the limestone acidification experiment.Besides,the strength degradation mechanism of limestone under the acidity effect was analyzed.The results show that the acid corrosion characteristics of limestone are obvious,as numerous mineral grains generate voids under the effects of acid corrosion,and more defects are formed inside.The acid-rock reac-tion is the most intense at the early stage and then gradually reaches dynamic equilibrium,and the acid corrosion rate of limestone is 4.24％(10％HCl,360 min).The hard limestone is damaged after acidification.Furthermore,the internal cracks can be induced to rapid initiation and unstable propagation under load,which reduces the strain required for rock failure by 33.33％.The failure morphology is more complicated,and the uniaxial compressive strength and elastic modulus decrease by 52.42％and 34.44％respectively.The strength weakening of hard roof after acidification is due to the defects such as intergranular cracking caused by the corrosion of rock crystals under acidity effect,which accelerate the initiation and propaga-tion of internal cracks with external force.Macroscopically,acidification induced the deterioration of rock mechanical properties by reforming the roof structure.The feasibility of acidizing reformation method to control hard roof is confirmed in this study.
查看更多>>摘要：This paper presented a novel bond-slip model to better reveal the mechanical behavior of the bolt-grout interface for fully-grouted rockbolts under tensile loads by considering the non-linear response in the softening stage.The exponential decay function is adopted for describing the non-linear response in the softening stage.Based on the improved bond-slip model,the corresponding analytical solutions for the interfacial shear stress and the axial force of the bolt under different loading stages are solved.Then,the validity of this proposed model was verified by comparing with the experimental results.The results show that compared with the linear softening model,the proposed model is more suitable for predicting the mechanical performance of fully-grouted rockbolts.Finally,a series of parametric stud-ies are conducted to explore the effect of model parameters on the mechanical properties of fully-grouted rockbolts.The results indicate that compared with the anchor length,the bolt diameter and the bond strength of the bolt-grout interface have a significance influence on the ultimate load of bolt,especially for the elastic and softening stage.Moreover,it can be found that using the linear softening model maybe overestimates the supporting performance of grouted bolt,resulting in an unsafe design for bolt.
查看更多>>摘要：Traditional explosives have characteristics of high risk,large vibration,and poor directional fracturing.Consequently,an instantaneous expander with a single crack surface(IESCS),which is a novel non-explosive directional rock-breaking technique,has been developed.The directional roof-cutting mecha-nism of the IESCS method,driven by high-pressure gas,was theoretically analyzed.Laboratory experi-ments and numerical simulations proved the directional slitting effect of the IESCS method to be excellent.Compared with shaped-charge blasting,the charge of IESCS was reduced by 8.9％,but the crack rate increased by 9％in field tests.After IESCS pre-splitting,the roof directionally collapsed along the cut-ting line,and the gangue filled the goaf.Moreover,the directional roof cutting by the IESCS could decrease roadway stress.The average pressure of hydraulic supports on the cutting side of the roof was 31％lower than that on the non-cutting side of the roof after pre-splitting.After the self-formed road-way constructed by the IESCS was stabilized,the final relative displacement of the roof and floor was 157.3 mm,meeting the required standard of the next working face.Thus,the IESCS was effectively applied to directional roof pre-splitting.The results demonstrate the promising potential of IESCS in the mining and geotechnical fields.
查看更多>>摘要：It's a universal engineering problem to seal micro-cracks of low-permeability argillaceous rock mass by grouting in the fields of civil engineering and mining.This paper achieved the grouting sealing of low-permeability artificial rocks with the permeability of 0.1-40 mD by adopting silica sol imbibition grout-ing.The variation characteristics of particle size,viscosity,and contact angle of silica sol during solidifi-cation and the pore size distribution of low-permeability artificial rocks were measured,and spontaneous imbibition tests of the artificial rocks were carried out.Finally,combined with the imbibition theory,per-colation theory,and fracture medium grouting principle,the silica sol imbibition mechanism of low-permeability rocks and soil was discussed.The results show that:(1)Silica sol can be injected into arti-ficial rocks with the minimum permeability of 0.1 mD through spontaneous imbibition;(2)The particle size increase of silica sol leads to decreased wettability,affinity,and injectability in grouting materials;and(3)In the range of 0.1-40 mD,the grout absorption first increases and then decreases with increased permeability.The number of large pores and fractures in the rock mass is related to injectability,and the number of small and medium pores is related to the internal driving force of imbibition.This study pro-vides a theoretical basis for silica sol grouting sealing of low-permeability argillaceous rocks and is,there-fore,an important reference for application.
查看更多>>摘要：Borehole breakout is a widely utilised phenomenon in horizontal stress orientation determination,and breakout geometrical parameters,such as width and depth,have been used to estimate both horizontal stress magnitudes.However,the accuracy of minimum horizontal stress estimation from borehole break-out remains relatively low in comparison to maximum horizontal stress estimation.This paper aims to compare and improve the minimum horizontal stress estimation via a number of machine learning(ML)regression techniques,including parametric and non-parametric models,which have rarely been explored.ML models were trained based on 79 laboratory data from published literature and validated against 23 field data.A systematic bias was observed in the prediction for the validation dataset when-ever the horizontal stress value exceeded the maximum value in the training data.Nevertheless,the pat-tern was captured,and the removal of systematic bias showed that the artificial neural network is capable of predicting the minimum horizontal stress with an average error rate of 10.16％and a root mean square error of 3.87 MPa when compared to actual values obtained through conventional in-situ mea-surement techniques.This is a meaningful improvement considering the importance of in-situ stress knowledge for underground operations and the availability of borehole breakout data.
查看更多>>摘要：In order to control the large deformation of tunnel surrounding rock,a new energy-absorbing bolt is developed.This bolt can be transformed into a rigid support when the deformation of the surrounding rock reaches the length of the sleeve tube,thus preventing the surrounding rock from continuing to deform.Moreover,this bolt has a simple structure and is easy to manufacture and assemble.Then the static tensile test is conducted on the bolt specimen to test its working performance.The test results show that when the cone angle of the cone block is small,the load-displacement curve of the bolt con-tains three stages;when the cone angle is large,the load-displacement curve contains only two stages.Meanwhile,both the average constant resistance and the maximum absorbed energy increase linearly with the increase of cone angle.On this basis,ignoring the influence of shear stress,and it is supposed that the thickness of the sleeve tube is constant,then the theoretical calculation formula of constant resistance for the new bolt is derived,and the rationality of the formula is verified using the static tensile test results.It is found that the error of the calculated result is less than 15％when the cone angle does not exceed 15°.At last,the numerical simulation method is used to analyze the performance of the new bolt.The simulation results indicate that the generation of shear stress and the change of tube thickness dur-ing the movement of the cone block are two important factors that cause theoretical errors.
查看更多>>摘要：The effectiveness of rock bolting in ground control has been extensively investigated,mainly for resin based systems.Alternative coupling materials are needed to have good mechanical performance and to reduce the economic impact.This study proposed a new bolting system exploiting steel particles as coupling material.The applicability of this system was assessed by laboratory and field pullout tests,assisted by digital imaging correlation(DIC),infrared thermography(IRT)and acoustic emission(AE).The results indicated that,for a 20 mm diameter bolt,the suitable steel particle size and corresponding inner diameter of borehole were 1.4 and 28 mm,respectively.For bolts installed in steel tubes,the par-ticles improved the loading capacity compared to the resin bonded ones.Additional pullout tests on cement blocks indicated that steel particles can be effective for hard rock,whilst resin was a better choice for bolting of soft rock.Similar understanding was obtained by pullout tests in engineering fields,which demonstrated that the steel particles coupled bolts can provide favorable effects in hard rock mass,while the effects were negligible when installed in extremely soft coal mass.The wide set of multi-technique measurements helped to understand the mechanisms involved in the performance of the bolting system with coupling steel particles.
查看更多>>摘要：The anchoring eccentricity of the bolt and cable bolt is a common problem in geotechnical support engi-neering and affects the ability of the bolt and cable bolt to control the rock mass to a certain extent.This paper reports on numerical simulation and laboratory experiments conducted to clarify the effect of eccentricity on the anchoring quality of the bolt and cable bolt,and to establish an effective solution strategy.The results reveal that the anchoring eccentricity causes unbalanced stress distribution and the uncoordinated deformation of the resin layer,which results in higher stress and greater deformation of the resin layer at the near side of the rod body.Additionally,as the degree of anchoring eccentricity increases,the effect becomes more significant,and the resin layer of the anchoring system becomes more likely to undergo preferential failure locally,which weakens the load-bearing performance of the anchor-ing system.This paper develops an innovative bolt anchoring rectifying device(B-ARD)and cable bolt anchoring rectifying device(C-ARD)on the basis of the structural characteristics of the bolt and cable bolt to better ensure the anchoring effect of them.The working effects of these two devices were verified in detailed experiments and analysis.The experimental results show that the anchoring rectifying devices(ARD)improve and ensure the anchoring concentricity of the bolt and cable bolt,which will help improve the supporting performance of them.The paper provides a convenient and effective method for improv-ing the anchoring concentricity of the bolt and cable bolt,and provides a concept and reference for tech-nical research on improving the effect of roof bolting.
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