Experimental and Numerical Study on Anchorage Strength and Deformation Properties of Blocky Rock Mass

This study experimentally and numerically investigated the anchorage properties,bolt force evolution,deformation and stress fields of blocky rock mass with various dip angles of joint surfaces under an applied axial load.The results show that due to bolt reinforcement,the axial stress-strain curves of anchorage blocky rock mass show typical strain-hardening characteristics,and comparedwithmodels without anchorage,the peak strength and elastic modulus increase by 21.56%and 20.0%,respectively.With an increase in axial stress,the lateral strain continuously increases,and restriction effects of bolts reduce the overall deformation of model surfaces.The axial stressstrain curves of anchorage blocky rock mass in the simulations present a“double peak strength”phenomenon due to bolt reinforcement,and the peak strength,second peak strength,residual strength,surface displacement field,as well as the principal stress fields all depend on the dip angles of joint surfaces.As a result of the bolt reinforcement effects,cone-shaped compression zones are produced in the models,and compression zones of adjacent bolts superimpose with each other to form anchorage belts,improving the overall bearing capacity of anchorage models.Obvious stress concentration can be observed at both bolt end and anchorage section.Not only the role of bolt support transfers the blocky rock mass to be a three-dimensional stress state through compression effects,but also it improves both tensile strength and shear resistance of both joint surfaces and the overall blocky rock mass.

Stress arch bunch and its formation mechanism in blocky stratified rock masses

Stress arch is a common phenomenon occurring in continuous materials and has also l：een proved to have great influences on the self-stabilization of soils or rock masses after excavation. In this paper, based on UDEC simulation, stress redistribution after excavation is investigated for a kind of special discontinuous material, i.e. blocky stratified rock mass. A layered stress arch system is observed with each stress arch lying over another. This special phenomenon is defined herein as ＂stress arch bunch＂. Effects of dip angle of bedding plane, lateral pressure and joint offset on this stress arch bunch are studied. Its formation mechanism is also discussed based on voussoir beam theory.

Simulation and Experimental Study on Improving Electrochemical Machining Stability of Highly Convex Structures on Casing Surfaces Using Backwater Pressure

Casing parts are regarded as key components of aero-engines.Most casing parts are attached to convex structures of diferent shapes,whose heights range from hundreds of microns to tens of millimeters.Using profling blocky electrodes for electrochemical machining(ECM)of casing parts is a commonly adopted method,especially when highly convex structures.However,with an increase in the convex structure height,the fow felds of the machining areas become more complex,and short circuits may occur at any time.In this study,a method to improve the fow feld characteristics within a machining area by adjusting the backwater pressure is proposed and validated through simulation and experiment analyses.The simulation results demonstrated that the back-pressure method can signifcantly improve the uniformity of the fow feld around the convex structure compared with the extraction and open outlet modes.Subsequently,the back-pressure value was optimized at 0.5 MPa according to the simulation results.The experimental results showed that using the optimized back-pressure parameters,the cathode feed-rate increased from 0.6 to 0.7 mm/min,and a 16.1 mm tall convex structure was successfully machined.This indicates that the back-pressure method is suitable and efective for electrochemical machining of highly convex structures with blocky electrodes.In this study,we propose a method to improve the electrochemical machining stability of a convex structure on a casing surface using backwater pressure,which has achieved remarkable results.

Influence of degree of interlock on confined strength of jointed hard rock masses

The strength of jointed rock mass is strongly controlled by the degree of interlock between its constituent rock blocks.The degree of interlock constrains the kinematic freedom of individual rock blocks to rotate and slide along the block forming joints.The HoekeBrown(HB)failure criterion and the geological strength index(GSI)were developed based on experiences from mine slopes and tunneling projects in moderately to poorly interlocked jointed rock masses.It has since then been demonstrated that the approach to estimate the HB strength parameters based on the GSI strength scaling equations(called the‘GSI strength equations’)tends to underestimate the confined peak strength of highly interlocked jointed rock masses(i.e.GSI>65),where the rock mass is often non-persistently jointed,and the intact rock blocks are strong and brittle.The estimation of the confined strength of such rock masses is relevant when designing mine pillars and abutments at great depths,where the confining pressure is high enough to prevent block rotation and free sliding on block boundaries.In this article,a grain-based distinct element modeling approach is used to simulate jointed rock masses of various degrees of interlock and to investigate the influences of block shape,joint persistence and joint surface condition on the confined peak strengths.The focus is on non-persistently jointed and blocky(persistently jointed)rock masses,consisting of hard and homogeneous rock blocks devoid of any strength degrading defects such as veins.The results from this investigation confirm that the GSI strength equations underestimate the confined strength of highly interlocked and non-persistently jointed rock masses.Moreover,the GSI strength equations are found to be valid to estimate the confined strength of persistently jointed rock masses with smooth and non-dilatant joint surfaces.

Nonlinear amplitude versus angle inversion for transversely isotropic media with vertical symmetry axis using new weak anisotropy approximation equations

In VTI media,the conventional inversion methods based on the existing approximation formulas are difficult to accurately estimate the anisotropic parameters of reservoirs,even more so for unconventional reservoirs with strong seismic anisotropy.Theoretically,the above problems can be solved by utilizing the exact reflection coefficients equations.However,their complicated expression increases the difficulty in calculating the Jacobian matrix when applying them to the Bayesian deterministic inversion.Therefore,the new reduced approximation equations starting from the exact equations are derived here by linearizing the slowness expressions.The relatively simple form and satisfactory calculation accuracy make the reduced equations easy to apply for inversion while ensuring the accuracy of the inversion results.In addition,the blockiness constraint,which follows the differentiable Laplace distribution,is added to the prior model to improve contrasts between layers.Then,the concept of GLI and an iterative reweighted least-squares algorithm is combined to solve the objective function.Lastly,we obtain the iterative solution expression of the elastic parameters and anisotropy parameters and achieve nonlinear AVA inversion based on the reduced equations.The test results of synthetic data and field data show that the proposed method can accurately obtain the VTI parameters from prestack AVA seismic data.

Pepper variome reveals the history and key loci associated with fruit domestication and diversification

Pepper(Capsicum spp.)is an important vegetable crop that provides a unique pungent sensation when eaten.Through construction of a pepper variome map,we examined the main groups that emerged during domestication and breeding of C.annuum,their relationships and temporal succession,and the molecular events underlying the main transitions.The results showed that the initial differentiation in fruit shape and pungency,increase in fruit weight,and transition from erect to pendent fruits,as well as the recent appearance of large,blocky,sweet fruits(bell peppers),were accompanied by strong selection/fixation of key alleles and introgressions in two large genomic regions.Furthermore,we identified Up,which encodes a BIG GRAIN protein involved in auxin transport,as a key domestication gene that controls erect vs pendent fruit orientation.The up mutation gained increased expression especially in the fruit pedicel through a 579-bp sequence deletion in its 5′upstream region,resulting in the phenotype of pendent fruit.The function of Up was confirmed by virus-induced gene silencing.Taken together,these findings constitute a cornerstone for understanding the domestication and differentiation of a key horticultural crop.