Anisotropic characteristics of layered backfill:Mechanical properties and energy dissipation

Layered backfill is commonly used in mining operations,and its mechanical behavior is strongly influenced by delamination parameters.In this study,13 specimens with different numbers of delamination and delamination angle were prepared to investigate the anisotropic mechanical behavior,energy dissipation characteristics and crack development of backfill.P-wave velocity,uniaxial compression,scanning electron microscope(SEM),and acoustic emission(AE)experiments were conducted.The results indicate that:(1)The P-wave velocity has linear and elliptical relationships with the number of delamination surface and delamination angle,respectively;the strength,delamination parameters and P-wave velocity show a high degree of coincidence in terms of their function relationship,which can realize the rapid prediction of strength.(2)The microstructure of the delaminated surface is looser than that of the matrix,leading to a decrease in strength and an increase at the pore-fissure compaction stage.The number and angle of delamination increase linearly with the anisotropy coefficient.(3)The energy evolution in angle-cut backfill can be divided into four stages,with a decrease in the proportion of elastic energy at the initiation stress and peak stress with increasing number of delamination planes and delamination angle.(4)Crack development increases with the number of delamination surface and delamination angle,resulting in a decrease in energy dissipation coefficient and peak AE energy.These findings provide valuable insights for the design of filling materials and processes in mining operations.

Dynamic mechanical properties and instability behavior of layered backfill under intermediate strain rates

To obtain dynamic mechanical properties and failure rule of layered backfill under strain rates from10to80s-1,impactloading test on layered backfill specimens(LBS)was conducted by using split Hopkinson pressure bar system.The results indicatethat positive correlation can be found between dynamic compressive strength and strain rate,as well as between strength increasefactor and strain rate.Dynamic compressive strength of LBS gets higher as the arithmetic average cement-sand ratio increases.Compared with static compressive strength,dynamic compressive strength of LBS is enhanced by11%to163%.In addition,theenergy dissipating rate of LBS lies between that of corresponding single specimens,and it decreases as the average cement contentincreases.Deformation of LBS shows obvious discontinuity,deformation degree of lower strength part of LBS is generally higherthan that of higher strength part.A revised brittle fracture criterion based on the Stenerding-Lehnigk criterion is applied to analyzingthe fracture status of LBS,and the average relevant errors of the3groups between the test results and calculation results are4.80%,3.89%and4.66%,respectively.

Enhanced Phase Change Heat Storage of Layered Backfill Body under Different Boundary Conditions

In view of the high temperature problem faced by mining activities,the coordinated mining of ore deposit and geothermal energy is a solution in line with the concept of green mining.The layered backfill body with finned double-pipe heat exchanger continuously exchanges heat with the surrounding thermal environment,which plays an effective role in gathering geothermal energy.In this paper,the heat storage process of each layered backfill body under different boundary conditions is simulated by Fluent.The results show the heat storage characteristic of layered backfill body can be significantly improved by adding fins to the double-pipe heat exchanger.On the whole,the heat storage effect of bottom layer backfill body(BLBB)is the best.The total heat storage capacity of top layer backfill body(TLBB),middle layer backfill body(MLBB)and BLBB with the finned double-pipe heat exchanger is 666.3 kJ,662.2 kJ,1003.0 kJ;1639.0 kJ,1760.8 kJ,1911.2 kJ and 1731.1 kJ,1953.3 kJ,1962.8 kJ respectively at 1 h,8 h and 24 h.This study explores the law of heat storage of layered backfill body under different boundary conditions and also expands the idea for layered backfill body to efficiently accumulate geothermal energy.

Axi-symmetric Active Earth Pressure for Layered Backfills Obtained by the Slip Line Method

The axi-symmetric active earth pressure for layered backfills was investigated using the slip line method. Due to different soil properties, the interfaces of the soil layers were considered as discontinuity surface. Accordingly, the change of the major principal direction was obtained and a new computation scheme was proposed to deal with the discontinuity in the calculation, finally the slip line method was extended to layered backfills. Results indicate that, the major principal direction, as well as the earth pressure, has a finite jump on passing the soil interfaces. The magnitude of the jump depends on the soil properties mainly. Generally, the active earth pressure when a strong layer is overlying a weak layer is much larger than that when the weak layer is lying on the strong layer. The present solution can be reduced to plane strain case and it has been compared with Rankine's and Coulomb's results, and a good agreement is observed.