Investigation of long-wavelength elastic wave propagation through wet bentonite-filled rock joints

The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system.Therefore,the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal.This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test.Jointed rock specimens with different joint conditions(i.e.joint surface saturation and bentonite filling)were prepared using granite rock discs sampled from the Korea Underground Research Tunnel(KURT)and Gyeongju bentonite.The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels.A Hertzian-type power model was used to fit the wave velocities,and the relationship between the two fitted parameters provided the trend of joint conditions.Numerical simulations using three-dimensional distinct element code(3DEC)were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.

FREEZE PROFILE AND HEAT BALANCE CALCULATION OF THE 160kA DRAINED CELL

A 2D full cell thermo-electric model of 160kA drained cell was set up using finiteelement code to calculate its freeze profile, then the drained cell model was modifiedaccording to the freeze profile computed and its heat balance was calculated. Comparedwith that of a 160kA conventional Hall-Heroult cell (H-H cell), though the melts vol-ume of the drained cell reduced greatly, the whole heat loss from it didn't drop downapparently, and an analysis was presented in the paper. On the other hand, the anode-cathode distance (ACD) of a drained cell was much less than that of a H-H cell, sothe voltage drop on it and heat produced decreased too, steps should be taken to keepa workable heat balance on a drained cell.

Prediction of strength and deformability of an interlocked blocky rock mass using UDEC

The accurate prediction of strength and deformability characteristics of rock mass is a challenging issue.In practice,properties of a rock mass are often estimated from available empirical relationships based on the uniaxial compressive strength(UCS).However,UCS does not always give a good indication of in situ rock mass strength and deformability.The aim of this paper is to present a methodology to predict the strength and deformability of a jointed rock mass using UDEC(universal distinct element code).In the study,the rock mass is modelled as an assemblage of deformable blocks that can yield as an intact material and/or slide along predefined joints within the rock mass.A range of numerical simulations of uniaxial and triaxial tests was conducted on rock mass samples in order to predict the equivalent mechanical properties for the rock mass under different loading directions.Finally,results are compared with the deformability parameters obtained by analytical methods.

Failure mechanism and control technology of deep soft-rock roadways:Numerical simulation and field study

Large deformations such as roof subsidence,floor heave,and two-sided deformations occur frequently in deep soft-rock roadways.The deformation becomes more severe under the combined effect of high in-situ and mining-induced stresses,which detrimentally affect the safe mining of coal.Based on the geological conditions and roadway failure characteristics of the Nanyaotou coal mine in Shanxi province,China,we used comprehensive numerical simulations and field observations to study roadway deformation and failure.The deformation mechanism of deep soft-rock roadways under dynamic pressures is described,and the corresponding control measures are proposed.The deformation and fracture development characteristics of roadways surrounding rocks were explored with a primary support scheme,and its effects were evaluated.The radius of the plastic zone and the displacement deformation of the roadway were studied by using theoretical analysis,and a combined-support design of‘‘anchor bolt+anchor cable+shotcrete+deep and shallow borehole grouting+inverted arch”was proposed to limit deformations and relieve the stress in the surrounding rocks.Numerical simulations and field monitoring showed that the combined support scheme can effectively mitigate the large deformations of ventilation roadways and provide guidance for the stable control of deep soft-rock roadways.