下向分层进路充填采矿法中预留阶段顶柱力学行为分析

基于下向分层进路充填采矿法,针对下分层开采或回采过程中遇到开挖进路帮部一侧为胶结充填体、另一侧为矿体的情况,将胶结充填体假设为弹簧支撑件,把采场预留顶柱简化为平面问题的“固定端超静定悬臂梁”力学模型,并将半逆解法引入预留顶柱力学分析中,推导出均布荷载下“固定端超静定悬臂梁”应力分量,揭示了顶柱稳定性的主要影响应力为水平拉应力σ_x和剪应力τ_xy。理论分析表明:影响σ_x和τ_xy分布变化的主要因素,既包括采场结构参数顶柱厚度和跨度,也包括了充填参数充填体弹性模量。以某铁矿为例,采用控制变量法研究了顶柱在不同采场结构参数和充填参数条件下σ_x和τ_xy的变化规律,结果表明,当顶柱厚度不小于5 m、跨度选取5~7 m、胶结充填体强度1~3 MPa时可有效减小顶柱上部的水平拉应力和剪应力,避免了顶柱处于悬臂梁状态和顶柱下部出现较大拉应力。

Mechanical Behavior of Preset Cap Pillar in Underhand Cut and Fill Mining

During underhand cut and fill mining or stoping mining, a roadway in the advancement was found to be with a cemented filling body on one side and orebody on the other side. In view of such situation, the cemented backfill was assumed to be a spring supporting part and the preset cap pillar was simplified as a mechanical model of “a fixed-end hyperstatic structure sketch of cantilever beam” in the study. And semi-inverse method was introduced into the mechanical analysis of cap pillar, with the stress component of a fixed-end hyperstatic structure sketch of cantilever beam under a uniform load deducted, which revealed that tensile stress σ_x and shear stress τ_xy primarily brought influence on the stability of cap pillar. Theoretical analysis showed the primary factors contributed to the change in the distribution of σ_x and τ_xy included the stope structure parameters of stope pillar thickness and width, as well as filling parameters of elastic modulus of backfill. With an iron mine for example, the variation rule for σ_x  and τ_xy of the cap pillar with different stope structure parameters and filling parameters was investigated by using the control variable. It is found that with the thickness of cap pillar less than 5 m, span within the range of 5~7 m, the strength of cemented backfill at 1~3 MPa, the horizontal tensile stress and shear stress of the upper part of cap pillar can be effectively reduced, thus the cantilever state of pillar and tensile stress at the bottom of pillar can be avoided.