层状岩体磷矿床采空区失稳风险定量评价方法研究

Study on a Quantitative Evaluation Method of Goaf Instability Risk of Phosphate Deposits in Layered Rock Mass

现有层状岩体磷矿床采空区失稳分析方法很少考虑岩体力学参数的空间变异性。以杉树垭磷矿为研究背景,构建了能够表征岩体力学参数自相关性、互相关性及非高斯性的随机场,以层状岩体破坏接近度(FAI)为评价指标,建立了岩体单元破坏的极限状态方程,并借助Hermite随机多项式建立了随机岩体力学参数输入场与网格单元FAI输出场间的显式函数表达式。最后,采用蒙特卡洛法计算磷矿采空区网格单元破坏概率,实现了磷矿采空区失稳风险的定量评价。结果表明:参数随机场能够很好表征岩体力学参数的空间变异性,采空区失稳高风险区域(破坏概率≥70%)位于矿柱高度的中间部位,矿柱表面的破坏深度在2m以内,与实际矿柱破坏位置与破坏深度相吻合。常规数值计算因计算结果指标分布差异,常面临难以判定磷矿采空区是否失稳的问题,而本文数值计算方法既考虑了层状岩体力学参数自相关性、互相关性及非高斯性的客观空间变异性特征,又实现了基于破坏概率的磷矿采空区失稳风险定量评价。

Goaf instability accidents such as roof falling,rib spalling,or pillar spalling often occur during the room-pillar mining process in layered phosphate deposits,severely affecting mine production safety.Considering that the spatial variability of rock mass mechanical parameters is rarely incorporated into goaf instability analysis methods,a database for rock mass matrix cohesion(c)and internal friction angle(ϕ_(j))is first established in the Shanshuya phosphate deposit using the displacement inversion method.Then,the spatial variability characteristic parameters of c andϕ_(j)are fitted based on geostatistical principles.Random fields are constructed using the Karhunen-Loeve(K-L)series expansion method and assigned to the FLAC3D grid model through element traversal to represent the autocorrelation,cross-correlation,and non-Gaussian properties of c andϕ_(j)during numerical calculations.The limit state equation for rock mass failure is then established,using layered rock mass's failure approach index(FAI)as the evaluation index.The Hermite random polynomial coefficients between the input field of c andϕ_(j)and the output field of the FAI are solved by the probability collocation method,establishing an explicit function expression between the probability collocation point and the FAI.Finally,the FAI for each element is calculated using the cross-correlation standard random variables instead of the probabilistic collocation points.Hence,the element failure probability of the phosphate mine goaf is determined by the Monte Carlo method,which reveals a quantitative evaluation of the goaf instability risk.The results showed that the random field assigned to the FLAC3D grid model effectively characterizes the spatial variability of rock mass mechanical parameters.The high instability risk area of the goaf(failure probability≥70%)is located in the middle of the pillar within 2 meters,consistent with the actual pillar failure location and depth.Compared to conventional numerical calculations,the mechanical parameters of layered rock mass in this study exhibit objective spatial variability characteristics such as autocorrelation,cross-correlation,and non-Gaussian properties,and the calculated failure probability achieves a more specific and comprehensive quantitative evaluation of the instability risk of phosphate mine goaf.This addresses the difficulty in determining whether the phosphate mine goaf is unstable due to the varying distribution of maximum displacement,maximum and minimum principal stresses,and the FAI.The research results can provide a technical reference for stability analysis and support optimization of similar underground engineering projects in layered rock mass.