Effect of Bonding Surface Roughness on The Strength of Backfill Based on 3D Printing Technology

The discontinuous filling and the fluctuation of slurry mass concentration are easy to lead to the stratification of the backfill. In this paper, four kinds of moulds with different roughness structural planes (R1, R2, R3, R4) were prepared by 3D printing technology. Through uniaxial compression experiment and PFC2D numerical simulation method, the mass concentration was 68%, 70%, 72%, 74%, and the ratio of gray to sand was 1:4, 1:6, 1:8, 1: 10. The influence of layer roughness on the uniaxial compressive strength of the backfill body under the conditions of 12 h, 24 h, 36 h and 48 h filling interval. The research results show that: (1) the compressive strength of the backfill body increases with the increase of the cemented surface roughness; The uniaxial compressive strength of the backfill presents a quadratic polynomial function relationship with the coupling effects of two factors (mass concentration and roughness, lime sand ratio and roughness, filling interval time and roughness). The compressive strength increases with the increase of roughness and mass concentration, with the increase of roughness to lime sand ratio, with the increase of roughness and the decrease of filling interval time. (2) By introducing the strength enhancement coefficient r of the backfill body to analyze the growth law of cemented surface roughness on the strength of the backfill body, it is found that when the cemented surface roughness is constant, the increase of the mass concentration and the ratio of lime to sand has an increase effect on the growth coefficient of the strength of the cemented surface roughness, and the r value is positively correlated with the mass concentration and the ratio of lime to sand. The shorter the filling interval, the more obvious the effect of the cemented surface roughness against the compressive strength, and the R-value is negatively correlated with the filling interval time. (3) The failure form of the stratified backfill body is mainly the whole through-tension failure form, and the cracks of the stratified backfill body gradually initiation, expansion and penetration eventually lead to the failure of the sample, and the failure is mainly concentrated at the stratified structural plane. With the increase of roughness, a large number of tensile failures and long cracks through the stratified surface appear gradually in the backfill. The damage morphology of the numerical model of the backfill body is similar to the experimental results, which also verifies that the mechanical properties also increase with the increase of roughness.