围岩松动圈理论计算方法的评述与展望

Overview on theoretical calculation method of broken rock zone

研究围岩松动圈的目的是指导地下工程的设计与施工,相比于现场实测和数值模拟分析,理论计算围岩松动圈更为方便快捷。综述了2种主要的松动圈理论计算方法——强度准则法和数学模型法。强度准则法以Mohr-Coulomb准则、Hoek-Brown准则和Druker-Prager准则为主,普遍经塑性区半径推导、松动区与塑性区界分和岩石强度参数修正可得到较准确的松动圈半径,其关键在于松动区的边界条件和岩石软化方法,并建议以应力梯度作为边界条件和以参数反演修正岩石参数进行计算,同时也简要评述了以动静力学思路和统一强度准则为基础的松动圈计算。数学模型法主要是基于对松动圈影响因素的研究,常采用神经网络模型和支持向量机模型,以及未确知聚类模型和多元回归函数拟合等,其关键在于松动圈影响因素的选择和建模选型。松动圈影响因素选择的重点在于次要因素,而建模选型在于引入其他模型对原有模型的核心元素进行寻优。建议应因地制宜地选择影响因素或引入灰色预测模型,同时必须经本地数据库训练修正后使模型达到最佳。实际工程中,由于强度准则法基于均质岩体中静水应力作用下的圆形巷道模型,巷道半径和侧应力系数取值及岩性不均一将会严重影响计算精度;数学模型法受制于影响因素考虑不足及现有数据库噪声等条件而难以提高预测精度。结合围岩松动圈实测技术,由于受众多因素影响,巷道同一横断面内、同一巷道相邻地段的松动圈均在一定范围内波动,故任何非实测方法均不能精确预测松动圈厚度。在工程应用中,不主张在难以符合强度准则法的假设条件或者数学模型中未知的次要因素影响较大的条件下采用计算的方法确定松动圈厚度。后续研究可从新强度准则推导或多个单预测模型相结合与数据等维等方面进行,同时应关注在深部多种地质条件下松动圈的理论计算以及矩形和其它非规则形状巷道松动圈的理论计算,并提高预测精度。

The purpose of theoretical calculation of broken rock zone is to guide the design and construction of underground engineering project.Compared with the field measurement method and numerical simulation analysis,the theoretical calculation of broken rock zone is more convenient and faster.Two main theoretical calculation methods of broken rock zone are systematically summarized,which are the strength criterion method and the mathematical model method.The strength criterion method is mainly based on Mohr-Coulomb,Hoek-Brown and Druker-Prager theory.Usually,it can get a more accurate radius of broken rock zone by deriving the plastic zone radius,differentiating the boundary between broken rock zone and plastic zone,and modifying the parameter of rocks’strength.The key is the boundary conditions of broken rock zone and the method to soften rocks.It also recommends that the calculation should be done by setting the stress gradient as the boundary condition,and adjusting the parameter of rocks by parametric inversion.Furthermore,the fundamental calculation of broken rock zone based on the dynamic and static mechanics ideas and the unified strength criterion is also briefly reviewed.The mathematical model method is based on the study of influencing factors of broken rock zone.Neural network models,support vector machine models,unascertained clustering models and multiple regression function fitting are commonly used in this method.The key is to determine the influencing factors,model selection and modeling.The focus of influencing factors selection is the secondary factors while the focus of model selection and modeling is to introduce other models to optimize the core elements of the original model.It recommends that the influencing factors should be selected according to local conditions,or the gray prediction model should be introduced,and then the model must be optimized by local database training and correction.In actual engineering project,as the strength criterion method is based on the circular roadway model under hydrostatic stress in homogeneous rock mass,the roadway radius,lateral stress coefficient and heterogeneous lithology will significantly affect the accuracy of calculation.On the other hand,the mathematical model method is restricted by insufficient consideration around influential factors and the existing database noise,which makes it difficult to improve the prediction accuracy.Combining with the field measurement technology,the size of broken rock zone fluctuates within a certain range within one cross section of the roadway and adjacent sections of the same roadway due to many factors,so any non-field-measured method cannot accurately predict the size of broken rock zone.In engineering applications,it is not advocated to determine the size of broken rock zone by theoretical calculation under the conditions that it is difficult to meet the assumptions of strength criterion method,or the unknown secondary factors have a significant influence on broken rock zone in mathematical model method.Future studies can be carried out from the perspectives of new strength criterion derivation,a combination of multiple single prediction models and data iso-dimensional.Furthermore,the theoretical calculation of broken rock zone on various geological conditions in deep mine,and the rectangular or other irregular shape roadway should be focused on as well,under the condition of improving the prediction accuracy.