Integrated investigations on fracturing processes of highly stressed mine pillars

矿业对加拿大经济的贡献很大。根据加拿大矿业协会的数据，2015年，采矿业在全国直接雇佣了超过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，随着矿山向深部发展（约1.5公里），更可靠、更高效的矿柱设计变得越来越重要。矿柱被定义为在两个或多个地下洞口之间留下的原位岩柱。矿柱几乎在所有的地下开采方法中都有使用，为矿井开孔提供支撑，维护矿井人员和设备的安全稳定环境。更好地了解矿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。柱子可以有不同的形状和大小。柱的尺寸通常表示为宽高比（W/H），是重要的设计准则。典型的矿柱W/H比值在0.5 ~ 2.5之间。目前矿柱设计的工程方法包括基于原位矿柱性能数据的经验公式以及数值模拟，其中使用经验破坏准则估计岩体强度。假设这些方法不能很好地估计大深度（>1.5 km）矿柱强度，原因如下：1)经验矿柱强度方程来自数据库，不适合深部矿柱设计；2)常用的经验岩体强度估计方法往往低估了块状至中等节理岩体的约束强度；3)基于数值模拟的矿柱强度评价方法未考虑采动引起的应力变化及其对岩体渐进破裂和强度退化的影响。提出的研究计划旨在开发方法，以提高目前对块状至中等节理岩体中受采动应力变化和非均匀加载条件影响的高应力矿柱的破裂过程和破坏机制的理解。本研究计划包括两个主要部分：1)实验室规模的物理建模；2)采用三维非连续介质模拟方法进行高级数值模拟。该研究项目的成果将为未来的工程师提供更可靠、更经济的深部矿柱设计工具。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).