阶段空场嗣后充填体三维拱应力及强度需求模型

在地下厚大金属矿体的两步骤阶段空场嗣后充填采矿法中,合理平衡一步骤矿房采场胶结充填体的揭露稳定性及其强度需求对安全经济充填采矿影响重大。为获取该采矿法中胶结充填体强度需求的三维解析模型与方法,解决类似矿山确定充填体强度需求主要采用经验类比、缺乏科学合理计算方法的问题,本文借鉴土力学应力拱理论,分析了两步骤采充时序过程中的相邻采场充填体空间接触关系,分别研究了二步骤采场非胶结充填体、一步骤采场胶结充填体(揭露后)的应力分布模式,基于Marston拱应力二维模型,拓展建立了各采场充填体的三维拱应力解析模型,得出了非胶结充填体-胶结充填体-采场围岩之间的应力传递规律及接触力学边界解析方法,并通过FLAC^3D模拟的拱应力分布结果进行了三维拱应力解析模型的对比验证。进一步将提出的拱应力解析方法应用至Mitchell强度需求解析模型中,考虑了三维成拱作用下非胶结充填体对胶结充填体的侧向推力作用、采场上下盘围岩对胶结充填体的接触摩擦作用,以底部滑动面方向角、滑动体与围岩接触面摩擦力方向角的不同取值情况,定量表征了揭露后胶结充填体的潜在破坏模式,并据此提出了4种胶结充填体安全系数和强度需求的三维解析模型与方法。再利用FLAC^3D开展了不同采场尺寸(长度、宽度、高度)、不同充填体参数(容重、内摩擦角)等条件下的充填体强度需求数值解搜索计算,与4种解析方法计算的强度需求结果进行了对比验证,得出了当胶结充填体底部滑动面方向角α=45°+φc/2且滑动体与围岩接触面摩擦力方向角β=45°-φc/2时,胶结充填体强度需求的三维解析解和三维数值解吻合度最佳,最终获取了最优的一步骤采场胶结充填体强度需求三维解析模型与方法。

Models of three-dimensional arching stress and strength requirement for the backfill in open stoping with subsequent backfill mining

In two steps open stoping with subsequent backfill mining method for underground thick metal ore bodies,a reasonable balance between the stability and strength requirement of the exposed cemented backfill in primary stopes has significant effects on the safe and economic mining operations.In order to build a reasonable three-dimensional analytical model and method for estimating the strength requirement of cemented backfill in this mining method,and solve the problems that empirical analogy is usually applied to determine the required strength of backfill for the lack of scientific and reasonable calculation methods,the spatial contact properties of the backfills in adjacent stopes in the processes of excavating and filling have been analyzed based on the arching theory borrowed from soil mechanics.Stress distributions of the uncemented backfill in secondary stopes and the exposed cemented backfill in primary stopes have been investigated separately.Three-dimensional analytical models for the arching stress of these backfills have been developed from Marston two-dimensional arching stress model,to reveal the stress transfer laws and quantitative characterization methods of these contact boundaries among the uncemented backfill in secondary stopes,cemented backfill in primary stopes and surrounding rock.The analytical results of arching stress have been compared and verified against the numerical arching stress through FLAC3D simulations.The proposed analytical models of arching stress are further applied to Mitchell model of strength requirements evaluation.The three-dimensional arching lateral pressure from the uncemented backfill acting on the exposed cemented backfill,and the contact friction between the cemented backfill and surrounding rock masses have been considered.The potential failure modes of exposed cemented backfill are quantitatively characterized by the different values of direction angles of sliding plane and the frictional force along the interfaces between the cemented backfill and surrounding rock masses.Four kinds of three-dimensional analytical models and methods for the safety factor and strength requirement of cemented backfill are proposed based on these failure modes.Numerical solution search and calculation of backfill strength requirements have been carried with FLAC3D under different stope sizes (length,width,height) and different backfill parameters (bulk density,internal friction angle),to compare and verify the proposed four kinds of three-dimensional analytical solutions.The analytical and numerical solutions for the strength requirements of cemented backfill have the best consistency when the direction angle of the sliding plane α =45°+φc/2 and the direction angle of the frictional force along the interfaces between the cemented backfill and surrounding rock masses β=45°-φc/2.The optimal three-dimensional analytical model and method for the strength requirements of the cemented backfill in primary stopes have been obtained.