Integrated investigations on fracturing processes of highly stressed mine pillars

矿业对加拿大经济贡献巨大。根据加拿大矿业协会的数据，2015年采矿业在全国直接雇用了超过373，000名工人，为加拿大的国内生产总值（GDP）贡献了超过560亿美元。近年来，随着矿井向更深的深度（>1.5公里）发展，更加可靠和有效的界桩设计变得越来越重要。煤柱是指在两个或多个地下洞口之间留下的原地岩石柱。煤柱用于几乎所有地下采矿方法，为矿井开口提供支撑，并为矿井人员和设备保持安全稳定的环境。更好地了解支柱力学可以对矿山人员的安全以及矿山的经济效益产生重大影响。支柱可以具有不同的形状和大小。支柱的尺寸，通常表示为宽高比（W/H），是一个重要的设计标准。典型的支柱W/H比在0.5和2.5之间。*目前的煤柱设计工程方法包括基于现场煤柱性能数据的经验公式以及数值建模，其中使用经验破坏标准估计岩体强度。据推测，这些方法不能正确估计在很大深度的支柱强度（>1.5 km）由于以下原因：1）经验支柱强度方程来自不适合深井支柱设计的数据库; 2）常见的经验岩体强度估计方法往往低估大块至中等节性岩体的侧限强度;基于数值模拟的煤柱强度评价方法没有考虑采动应力变化及其对岩体渐进性破裂和强度退化的影响。拟议的研究计划的目的是开发方法，以提高目前的理解的断裂过程和破坏机制的高应力柱在大规模的中等节理岩体，受到采矿引起的应力变化和非均匀载荷条件。该研究计划包括两个主要组成部分：1）实验室规模的物理建模; 2）使用三维不连续建模方法的高级数值建模。这项研究计划的成果将为未来的工程师提供更可靠和更经济的深井煤柱设计工具。这将对加拿大矿业公司的财务和安全业绩产生直接影响，并将为培训高素质人员提供宝贵的机会。

Mining contributes significantly to Canadian economy. According to the Mining Association of Canada, mining industry directly employed over 373,000 workers across the country in 2015, and contributed over $56 billion to Canada's Gross Domestic Product (GDP). In recent years, as mines progress to deeper levels (>1.5 km), a more reliable and efficient design of pillars has become increasingly important. A pillar is defined as a column of in-situ rock left between two or more underground openings. Pillars are used in almost all underground mining methods to provide support to mine openings and maintain a safe and stable environment for mine personnel and equipment. A better understanding of pillar mechanics can have a significant impact on the safety of mine personnel as well as the financial benefits of the mines. Pillars can be of different shapes and sizes. The size of pillars, usually expressed as the width-to-height (W/H) ratio, serves as an important design criterion. Typical pillar W/H ratios range between 0.5 and 2.5.***Current engineering approaches for pillar design include empirical formulae from data based on in-situ pillar performances as well as numerical modeling, where the rock mass strength is estimated using empirical failure criteria. It is hypothesized that these approaches do not properly estimate the pillar strength at great depths (>1.5 km) due to the following reasons: 1) empirical pillar strength equations came from a database that is not appropriate for pillar design in deep mines; 2) common empirical rock mass strength estimation approaches tend to underestimate the confined strength of massive to moderately jointed rock masses; and 3) common pillar strength assessment approaches based on numerical modeling do not consider mining-induced stress changes, and their influences on progressive rock mass fracturing and strength degradation. The proposed research program aims at developing methods to improve the current understanding of fracturing processes and failure mechanisms of highly stressed pillars in massive to moderately jointed rock masses, subjected to mining-induced stress changes and non-uniform loading conditions. This research program consists of two main components: 1) laboratory-scale physical modeling; and 2) advanced numerical modeling using three-dimensional discontinuum modeling approaches. The outcome of this research program will provide future engineers with tools for a more reliable and economic pillar design in deep mines. This will have a direct impact on the financial and safety performance of Canadian mining companies, and will provide valuable opportunities for the training of Highly Qualified Personnel (HQP).*****