Rockburst criterion and evaluation method for potential rockburst pit depth considering excavation damage effect

Excavation-induced disturbances in deep tunnels will lead to deterioration of rock properties and formation of excavation damaged zone(EDZ).This excavation damage effect may affect the potential rockburst pit depth.Taking two diversion tunnels of Jinping II hydropower station for example,the relationship between rockburst pit depth and excavation damage effect is first surveyed.The results indicate that the rockburst pit depth in tunnels with severe damage to rock masses is relatively large.Subsequently,the excavation-induced damage effect is characterized by disturbance factor D based on the Hoek-Brown criterion and wave velocity method.It is found that the EDZ could be further divided into a high-damage zone(HDZ)with D=1 and weak-damage zone(WDZ),and D decays from one to zero linearly.For this,a quantitative evaluation method for potential rockburst pit depth is established by presenting a three-element rockburst criterion considering rock strength,geostress and disturbance factor.The evaluation results obtained by this method match well with actual observations.In addition,the weakening of rock mass strength promotes the formation and expansion of potential rockburst pits.The potential rockburst pit depth is positively correlated with HDZ and WDZ depths,and the HDZ depth has a significant contribution to the potential rockburst pit depth.

Dynamic analysis of fault rockburst based on gradient-dependent plasticity and energy criterion

Fault rockburst is treated as a strain localization problem under dynamicloading condition considering strain gradient and strain rate. As a kind of dynamic fracturephenomena, rockburst has characteristics of strain localization, which is considered as aone-dimensional shear problem subjected to normal compressive stress and tangential shear stress.The constitutive relation of rock material is bilinear (elastic and strain softening) and sensitiveto shear strain rate. The solutions proposed based on gradient-dependent plasticity show thatintense plastic strain is concentrated in fault band and the thickness of the band depends on thecharacteristic length of rock material. The post-peak stiffness of the fault band was determinedaccording to the constitutive parameters of rock material and shear strain rate. Fault bandundergoing strain softening and elastic rock mass outside the band constitute a system and theinstability criterion of the system was proposed based on energy theory. The criterion depends onthe constitutive relation of rock material, the structural size and the strain rate. The staticresult regardless of the strain rate is the special case of the present analytical solution. Highstrain rate can lead to instability of the system.

Theoretical verification of the rationality of strain energy storage index as rockburst criterion based on linear energy storage law

The rationality of using strain energy storage index(Wet)for evaluating rockburst proneness was theoretically verified based on linear energy storage(LES)law in this study.The LES law is defined as the linear relationship between the elastic strain energy stored inside the solid material and the input strain energy during loading.It is used to determine the elastic strain energy and dissipated strain energy of rock specimens at various loading/unloading stress levels.The results showed that the Wetvalue obtained from experiments was close to the corresponding theoretical one from the LES law.Furthermore,with an increase in the loading/unloading stress level,the ratio of elastic strain energy to dissipated strain energy converged to the peak-strength strain energy storage index(Wp et).This index is stable and can better reflect the relative magnitudes of the stored energy and the dissipated energy of rocks at the whole pre-peak stage than the strain energy storage index.The peak-strength strain energy storage index can replace the conventional strain energy storage index as a new index for evaluating rockburst proneness.

Rockburst proneness criteria for rock materials:Review and new insights

To review the rockburst proneness(or tendency)criteria of rock materials and compare the judgment accuracy of them,twenty criteria were summarized,and their judgment accuracy was evaluated and compared based on the laboratory tests on fourteen types of rocks.This study begins firstly by introducing the twenty rockburst proneness criteria,and their origins,definitions,calculation methods and grading standards were summarized in detail.Subsequently,to evaluate and compare the judgment accuracy of the twenty criteria,a series of laboratory tests were carried out on fourteen types of rocks,and the rockburst proneness judgment results of the twenty criteria for the fourteen types of rocks were obtained accordingly.Moreover,to provide a unified basis for the judgment accuracy evaluation of above criteria,a classification standard(obtained according to the actual failure results and phenomena of rock specimen)of rockburst proneness in laboratory tests was introduced.The judgment results of the twenty criteria were compared with the judgment results of this classification standard.The results show that the judgment results of the criterion based on residual elastic energy(REE)index are completely consistent with the actual rockburst proneness,and the other criteria have some inconsistent situations more or less.Moreover,the REE index is based on the linear energy storage law and defined in form of a difference value and considered the whole failure process,and these superior characteristics ensure its accuracy.It is believed that the criterion based on REE index is comparatively more accurate and scientific than other criteria,and it can be recommended to be applied to judge the rockburst proneness of rock materials.

基于隧道施工阶段地应力实测数据的岩爆判据研究

云南省蔓金高速草果山隧道属于深埋长隧道,隧道围岩坚硬完整且脆性较高,隧道施工阶段面临着岩爆发生的风险。因此,采用应力解除法进行地应力测量,并基于实测数据结合现场岩爆发生情况与国内外不同的强度判据进行对比,并对岩爆判据的适用性进行分析研究。最后,根据岩爆实际发生的情况和位置对岩爆判据进行验证分析,结果表明:岩爆预测标准除应力指标外,还应使用多因素指标进行综合判别;某种岩爆预测方法不能适用所有地下工程,应结合工程的具体情况,进行岩爆危险性评估,为工程提出岩爆防治措施。同时此研究成果为深埋完整硬岩的岩爆灾害分析预测和防控提供了参考依据。

不同应力路径下深部大理岩渐进破坏能量指标研究

为探究不同开挖扰动下深埋大理岩渐进破坏特征,利用RFPA3D对深部大理岩开展常规三轴加载、恒轴压卸围压、加轴压卸围压3种不同应力路径下的渐进破坏试验,提出基于能量指标的渐进破坏阶段划分方法,并分析其对应特征应力阈值、特征能量变化规律,最终完成岩爆指标Re、脆性指标Be的优化讨论,以期为深部地下工程勘察设计、地下能源开采提供一定的理论支撑。研究表明:不同应力路径下深部大理岩峰值强度、峰值应变虽有不同,但均随围压、卸荷应力水平增大而增大,弹性应变能从最初的线性增长到增长速率逐渐减小直至最后趋于稳定,耗散能则由缓慢增长向线性快速增长变化;引入弹性能增长率ke、耗散能增长率kd能够合理、准确界定深部大理岩渐进破坏4阶段;不同应力路径下,特征应力具有明显的围压效应,相同围压下,卸载特征应力均小于常规三轴加载;对应特征能量随围压、卸荷应力水平增大而增加,弹性能、耗散能的对应力路径敏感性存在差异;岩爆倾向性指标Re、脆性指标Be呈正相关性,且随着围压增大卸荷应力水平增高,岩爆发生的可能性随之递减。本研究可为相关研究提供参考。

Novel rockburst prediction criterion with enhanced explainability employing CatBoost and nature-inspired metaheuristic technique

Rockburst is a major challenge to hard rock engineering at great depth.Accurate and timely assessment of rockburst risk can avoid unnecessary casualties and property losses.Despite the existence of various methods for rockburst assessment,there remains an urgent need for a comprehensive and reliable criterion that is easy to both apply and interpret.Developing a new rockburst criterion based on simple parameters can potentially fill this gap.With its advantages,this criterion can facilitate a more effective and efficient prediction of rockburst potential,thereby contributing significantly to enhancing safety measures.In this paper,combined with the internal and external factors of rockburst,four control variables(i.e.,integrity index,stress index,brittleness index,and elastic energy index)were selected to be incorporated into a comprehensive rockburstability index(RBSI).Based on 116 sets of rockburst cases,the rockburst potential was accurately quantified and predicted using the categorical boosting(CatBoost)model and the nature-inspired metaheuristic African vultures optimization algorithm(AVOA).In its performance validation,the criterion achieved the highest accuracy of 90.48%,verifying the reliability and effectiveness of the proposed RBSI criterion.Additionally,an interpretive method was applied to analyze the variable influence on the criterion,facilitating the explanation of predictions and the analysis of the formula’s robustness under different conditions.In general,compared with existing criterion methods involving relevant indicators,the newly proposed RBSI criterion enhances the accuracy of rockburst potential prediction,and it can effectively and swiftly evaluate the preliminary risk of rockburst.Lastly,a graphical user interface was developed to provide a clear visualization of the assessment of rockburst potential.

一种新的岩爆等级评估指标及其在某超埋深矿井中的应用

现有多数岩爆指标判据考虑因素较为单一,对一些具体工程岩爆风险存在误判可能,不利于岩爆风险防控。在分析现有岩爆指标判据优缺点的基础上,提出了一种考虑岩爆发生内外因素的岩爆等级判别指标,该指标充分考虑了岩爆发生的充分必要条件即岩爆发生的外在驱动力(应力条件)和岩爆发生的内在条件(岩石固有的储能、耗能特性),弥补了多数岩爆判据只考虑内因或外因单一因素的不足,提高了判别结果的可靠性和稳定性,可更好地对潜在岩爆风险进行科学管控,实现地下工程的安全、高效开挖或开采。应用该指标判别了山东某超埋深金矿-1 480 m水平岩爆倾向性,判别结果经讨论分析认为可靠性较高,研究结果可为其他类似工程提供参考。

岩石脆性及描述岩爆倾向的脆性系数

在对岩石脆性进行分析的基础上 ,提出了利用岩石的单抗拉和抗压强度 ,峰值前、后应变值来计算岩石的脆性系数 ,认为该系数是衡量岩爆倾向性的一种尺度 。

地下工程岩爆研究现状综述

基于地下工程岩爆研究成果,系统总结了岩爆的定义、类型、烈度分级、影响因素、破坏机理、预测与防治方法。指出目前岩爆研究中存在的主要问题,即岩爆发生的机理不够明确,判据不够充分,工程适用性欠佳,预测手段单一等。提出岩爆综合预测的研究思路,建议将岩爆的预测划分为岩爆倾向性预测、岩爆趋势预测和岩爆现场监测3个阶段。

秦岭隧道岩爆的研究

概述了秦岭隧道岩爆的表现特征。通过对混合片麻岩变形破坏的试验研究,提出了岩爆发生的机理;分析了岩爆形成发生的条件,提出了岩爆发生的综合判据。

基于人工神经网络及非线性回归的岩爆判据

采用人工神经网络和非线性回归方法研究岩爆判据研究。首先利用人工神经网络对原始样本进行量化,然后对量化后的样本数据进行非线性回归分析,获得新的岩爆判据公式。研究结果表明:此岩爆判据公式具有较高的预测精度。

基于扰动响应判据的洞室岩爆分析

详细描述岩爆形成过程,总结其特点并对岩爆的影响因素作了系统分析,认为:岩石在具备大量弹性应变能又处在峰值强度以后,处于非稳定的平衡状态,此时再对其施加干扰性因素,则会失稳.在此基础上进一步将稳定性理论应用于岩爆判据分析.工程实例计算表明,该方法能较好地解释许多岩爆现象.

脆性岩石损伤力学分析与岩爆损伤能量指数

在大量试验研究和理论分析的基础上，建立起岩石弹脆性损伤力学模型，在此基础上分析了岩石能量储存、耗散以及转换过程。提出了岩爆损伤能量指数的概念。

基于剪切应变梯度塑性理论的断层岩爆失稳判据

应用应变梯度塑性理论及能量准则,提出了断层岩爆的失稳判据的解析解。断层带被视为一维剪切问题,断层带尺寸由岩石内部长度确定。断层带的一半及带外一侧的弹性岩石被视为一个系统。得到了依赖于断层带尺寸的断层带的耗散势能及峰后刚度表达式。应用能量准则,得到了断层带-围岩系统的失稳判据,它不仅与岩石材料的本构参数有关,也与岩石结构的几何尺寸有关,说明系统的稳定性具有尺寸效应。断层岩爆失稳判据与矿柱岩爆失稳判据具有类似性。目前的断层岩爆失稳判据的优越性在于:断层带的宽度、断层带的耗散势能、峰后刚度及失稳判据等都可以解析表示;而且,断层带内部具有不均匀的(塑性)剪切应变,这一点与有关的实际观测结果相符合。

采动支承压力引起应变型冲击地压能量判据研究

采动支承压力引起的能量积聚及其突发释放是导致应变型冲击地压发生的根源之一。在将工作面前方煤体划分为阻力区、驱动区和无明显影响区的基础上,把应变型冲击地压从孕育到发生全过程分为能量稳定积聚、能量平衡和能量非稳定释放3个阶段,并研究其发生的基本条件;建立了采动支承压力引起应变型冲击地压的能量判据,即认为力学平衡状态破坏时驱动区煤体释放的弹性应变能与阻力区煤体完全破坏消耗能量的比值大于1。从冲击地压防治角度出发,提出了阻力区临界宽度的概念,建立了以阻力区宽度为指标的应变型冲击地压发生判据。现场实测表明,本文所建立的能量判据和指标与实测结果相吻合。其研究成果可为采动支承压力引起应变型冲击地压的预测预报和防冲、减冲工作的实施提供依据。

滇藏铁路丽江玉峰寺隧道围岩岩爆刚度判据

从最小能量原理出发,探讨隧道围岩岩爆的刚度判据问题,并应用于滇藏铁路玉峰寺隧道工程。在滇藏铁路玉峰寺隧道代表性围岩岩样全应力应变刚压实验分析的基础上,结合地应力测量资料和数值模拟,分析玉峰寺隧道3种岩性不同围压条件下的变形破坏过程,得到隧道塑性破坏岩体和弹性岩体的刚度曲线,利用刚度判据,分析评价玉峰寺隧道3类岩体发生岩爆的危险性,玄武岩岩爆烈度最高,灰岩次之,砂岩最低,为隧道工程设计提供了参考依据。

基于矩张量的深埋隧洞岩爆机制分析

以锦屏二级水电站微震监测数据为基础,将矩张量引入到深埋隧洞岩爆机制分析研究中。对分析过程中遇到的2个关键问题提出了针对性的建议:①隧洞工程为线性工程,传感器布置空间有限,难以形成良性传感器阵列,矩张量分析结果的可靠性受到很大的影响,为此,提出了数值计算过程中的坐标系空间旋转法。该方法按最优路径旋转隧道坐标系,使对于同一个事件的每个传感器,源-传感器射线到新坐标系的3个方向余弦差值在10倍数值范围以内,在数值计算过程中,可以得到较理想的矩张量结果。②针对Ohtsu使用矩张量分解判断岩石破裂类型的方法中,提出的各分量比重计算公式,仅适用于各分量均为受拉的情况。考虑快速掘进条件下隧洞工程受力方向的不确定性,扩展其分量比重计算公式到更一般适用状态。在此基础上,建立了一套完整的岩爆孕育过程矩张量分析方法。利用该方法对锦屏二级水电站典型岩爆微震数据进行分析,结果表明,该方法可以较好地解释岩爆孕育过程岩石破裂演化机制。

弹性-脆性-损伤模型及其在岩石局部破坏研究中的应用

在弹性-脆性-损伤本构模型中,采用了由线性的莫尔-库仑剪切屈服函数和非线性的虎克-布朗屈服函数复合后的屈服函数,以适应高压应力条件下岩石变形及破坏规律的研究.为了考虑脆性岩石在应力突然跌落过程中的弹性模量的变化,引入了一个损伤因子,以描述损伤的程度.此外,还考虑了围压对弹性模量的增强作用.对平面应变压缩条件下的矩形岩样的破坏过程进行了计算,并与接近脆性的带拉伸截断的应变软化莫尔-库仑模型的结果进行了对比,发现了它们之间的差异.又对静水压力条件下的平面应变模型开挖圆形巷道之后的破坏区、轻微的剪切及拉伸岩爆区和体积模量的分布进行了计算.研究发现,当考虑围压对弹性模量的影响后,体积模量的高值区位于V形坑的尖端,而V形坑内部的损伤程度随着损伤因子的增加而增加.如果不考虑围压对弹性模量的影响,V形坑尺寸大、较钝.研究结果表明,不同岩石脆性破坏过程中的损伤程度及围压对弹性模量的影响程度不相同是导致V形坑形态差别的原因之一.

流变性岩层下矿柱岩爆的发生条件与滞后时间

针对厚层状粘弹性顶板下煤柱岩爆问题建立了一个简单力学模型，并据此讨论了岩爆的非稳定机制，建立了这种条件下岩爆发生的判别准则，对岩爆滞后现象给出了一种理论解释，并推出了岩爆滞后时间ｔｃ与岩爆最大滞后时间ｔｃｍａｘ的表达式。