查看更多>>摘要：A blasting experiment was conducted on iron ore samples by considering multiple coupling charge coef-ficients.The resulting internal fracture and damage characteristics were quantitatively analyzed via com-puterized tomography(CT),scanning,and three-dimensional(3D)model reconstruction.The results show that the iron ore primarily displayed radial and circumferential cracks along the blast hole under an explosive load.When the decoupling coefficient was small,the crack surface was dominated by trans-granular fractures in the form of intracrystalline fractures.As the uncoupling coefficient increased,the crack surface exhibited transgranular and intergranular coupled fracture modes.Using fractal theory to analyze crack distribution characteristics,as the decoupled coefficient increased,the body fractal dimen-sion tended to decrease,and the degree of damage gradually decreased.The degree of damage reached a turning point when the decoupling charge coefficient was approximately 1.33.A numerical simulation suggested that the explosion energy transmitted to the iron ore and the effective stress decrease sharply when the decoupling coefficient exceeds 1.33.In some optimal uncoupling coefficient range,excessive fragmentation of the ore body is prevented,thereby allowing full use of the explosive energy.
查看更多>>摘要：Recently a new grout material called water inflow sealing(WIS)was invented for sealing water inflow in tunneling and underground constructions.In this study,a special experimental method called intubated counter grouting(ICG)was proposed to investigate the influence of water dispersion on the rheological properties of the grout during the grouting process,and to testify the sealing performance of the grout,such as instant gelling ability(IGA)and anti-dispersion ability(ADA).In the experiment,dispersion was restricted in the downstream of the channel with a high turbulence intensity.The influences of ADA and IGA were therefore decoupled and evaluated separately.Experimental results revealed two distinctive sealing mechanisms of WIS.For a low initial velocity of water,WIS turned the shear flow of water into an overall movement of a plug by absorbing water into the particles.For a high initial velocity and the situation that the particles reached the outlet before sufficiently expanding,WIS modified the rheology of the water in the channel and reduced its velocity till the static state.The distinctive feature of WIS brings a reformation on the sealing mechanism and provides an effective way to control water inflow with high pressure and velocity.
查看更多>>摘要：As underground excavations are getting deeper and field stresses increase,the behavior of intact rock blocks plays an increasingly important role in understanding and estimating the overall rock mass strength.To model the brittle behavior of intact rock blocks,the stress-strain curve is usually idealized considering a linear strength mobilization approach(cohesion-weakening-friction-strengthening,CWFS),however,it is well recognized that rock presents a nonlinear behavior in terms of the confining stress.This study extends the strength mobilization in brittle failure of rock using nonlinear criteria.To deter-mine the model parameters,a standard statistical method that uses the complete laboratory stress-strain curves of the intact rock is employed.Several hypotheses of linear and nonlinear models are statistically compared for different types of rock and confining stress levels.Results demonstrate that the best approach to model the brittle failure of rock is to consider a nonlinear strength envelope,such as the Hoek-Brown criterion assuming a residual uniaxial compressive strength different from zero and a mi parameter that increases,both with simultaneous mobilization.This model helps to recreate high-confining conditions and a more realistic transition between peak and post-peak strength.The obtained parameters are discussed and compared with literature values to verify the validity and to develop guide-lines for the estimation of parameters,providing an objective mobilization criterion.Finally,the nonlin-ear model was applied to a finite element code and extended to a tunnel scale in the brittle rock under high-stress conditions.A reasonable fit between the simulations and the in-situ overbreak measurements was found.
查看更多>>摘要：This paper develops a model that only requires two sets of small-size rock specimens with the ratio of the structural geometry parameter maximum to minimum ae,max:ae,min≥3:1 to determine the rock fracture and strength parameters without size effect and predict the actual structural performance of rock.Regardless of three-point-bending,four-point-bending,or a combination of the above two specimen types,fracture toughness KIc and tensile strength ft of rock were determined using only two sets of spec-imens with ae,max:ae.miin≥3:1.The values KIc and ft were consistent with those determined using multiple sets of specimens.The full structural failure curve constructed by two sets of small-size specimens with ae.max:ae.min≥3:1 can accurately predict large-size specimens fracture failure,and±10％upper and lower limits of the curve can encompass the test results of large-size specimens.The peak load prediction curve was constructed by two sets of specimens with ae,max:ae,min≥3:1,and±15％upper and lower limits of the peak load prediction curve can cover the small-size specimen tests data.The model and method proposed in this paper require only two sets of small-size specimens,and their selection is unaffected by the spec-imen type,geometry,and initial crack length.
查看更多>>摘要：To investigate the deformation mechanisms of rock under hydrostatic stress,destructive experiments were conducted on sandstone under different levels of hydrostatic stress and stress Lode angles.The results reveal that the shape of the strength envelope on the π plane gradually changes from the shape of the Lade criterion to the shape of the Drucker-Prage criterion with an increase in hydrostatic stress.Normally,there exists a deviation between the strain and stress paths for porous rocks on the k plane,and the deviation decreases with an increase in stress Lode angle and hydrostatic stress.A rock failure hypothesis based on the rock porous structure was proposed to investigate the reasons for the above-mentioned phenomena.It was found that the shear expansion in the minimum principal stress direction is the dominant factor affecting the Lode angle effect(LAE);the magnitude of the hydrostatic stress induces the variation of the porous structure and influences the shear expansion.Therefore,the hydro-static stress state affects the LAE.The failure hypothesis proposed in this paper can clarify the hydrostatic stress effect,LAE,and the variation of the rock strength envelope shape.
查看更多>>摘要：Rock joints exhibit hysteresis shearing behavior and produce energy dissipation under shear cyclic loads,which however cannot be accurately depicted by existing constitutive models.This paper establishes a constitutive model for hysteresis shearing and associated energy dissipation of rock joints.Analytical expressions of the model during cyclic shearing processes are derived.Derivation of the model indicates no energy dissipation in the elastic stage.When the shear load exceeds elastic boundary,nonlinear energy dissipation takes place.Validations with experiments show that the proposed model provides good conformities with direct shear curves and hysteresis loops,and can predict the energy dissipation characteristics of rock joints under different working conditions.Compared to the constitutive models using Weibull's distribution,the proposed one is smooth at the elastic boundary and can accurately cap-ture the maximum shear stress.Unlike the existing incremental-type models,the proposed one provides clear and direct analytical expressions for both shear stress and energy dissipation during the whole dis-placement domain,which is more convenient in application.
查看更多>>摘要：The constant mi in the Hoek-Brown(H-B)criterion is a fundamental parameter required for determining the compressive strength of rock.In this paper,drilling parameters provide a new basis for determining the constant mi.An analytical relationship between the drilling parameters and constant mi is established in consideration of the contact response between the drilling bit and the cut rock in the crushed zone.New models are developed to predict the triaxial compressive strength(TCS),internal friction angle ?and cohesion c of rock.Drilling tests are carried out on 6 rock types to study the correlation between ? and mi.A comparison between the predicted values of rock mechanical properties and the measured values from the laboratory is performed to verify the accuracy of the proposed model(yielding an error less than 10％).The TCSs and constant mi values of fifteen rocks are cited to validate the accuracy of the proposed model.The result shows that the proposed model predicts the TCS and constant mrii within a maximum error of 20％.The method can be conveniently applied to the rock mechanical properties.
查看更多>>摘要：The surrounding rock in tunnelling engineering and coal mining will sometimes be exposed to high tem-perature.Rock failure is the result of energy dissipation,and the study of the evolution and transforma-tion behavior of energy is of great significance for the in-depth understanding of the deformation and failure of rock after high temperature.This study analyzed the intrinsic connection between mechanical properties and acoustic emission(AE)energy under temperature effect.Based on the energy dissipation and release theory,the distribution and transformation of energy was analyzed,and the energy self-incentive and self-inhibition(EIi)model was further established.The main findings are that temperature effect affects the confidence interval trend and the value of AE energy rate,which is related to the change in mechanical properties.The ability of sandstone to store elastic strain energy after exposure to high temperature is independent of the mechanical properties.In this study,the ratio of dissipated energy to elastic energy is used to characterize the stable state of the sandstone system,which can be used as the energy indicator of rock failure precursor.During the absorption,storage,and release of energy before the peak stress,there exists self-incentive and self-inhibition of energy(control behavior).
查看更多>>摘要：Due to the complexity of the real engineering environment,the arrival measurement inevitably contains outliers and leads to serious location errors.In order to eliminate the influence of the outliers effectively,this paper proposes a novel robust AE/MS source localization method using optimized M-estimate con-sensus sample.First,a sample subset is selected from the entire arrival set to obtain fitting model and its parameters.Second,consensus set is determined by checking the arrivals with the fitting model instan-tiated by the estimated model parameters.Third,optimization process is performed to further optimize the consensus set.The above steps are iterated,and the final source coordinates are obtained by using all the elements in the optimal consensus set.The novel method is validated by a pencil-lead breaks exper-iment.The results indicate that the novel method has better location accuracy of less than 5 mm com-pared to existing methods,regardless of the presence or absence of outliers.With the increase of outlier scale and outlier ratio,the location result of the proposed method is always more stable and accu-rate than that of the existing methods.Mine blasting experiments further demonstrate that the new method holds good prospects for engineering applications.
查看更多>>摘要：Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering.In this study,a series of impact tests were performed using a split Hopkinson pressure bar system with high-speed photography to investigate the effect of interlayer strength on the wave propagation and fracturing process in composite rock-mortar specimens.The results indicate that the transmission coefficient,nominal dynamic strength,interlayer closure,and specific normal stiffness generally increase linearly with increasing interlayer stiffness.The cement mor-tar layer can serve as a buffer during the deformation of composite specimens.The digital images show that tensile cracks are typically initiated at the rock-mortar interface,propagate along the loading direc-tion,and eventually result in a tensile failure regardless of the interlayer properties.However,when a relatively weaker layer is sandwiched between the rock matrix,an increasing amount of cement mortar is violently ejected and slight slabbing occurs near the rock-mortar interface.
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