Developing Innovative Shotcrete as Rock Support for Underground Mining in Canada's North

喷射混凝土是指一种以水泥为基础的混合物，以气动的方式向目标基材高速喷射。喷射混凝土作为岩石支护已广泛应用于地下矿山；然而，永久冻土对喷射混凝土的设计和使用提出了重大挑战，因为喷射混凝土混合物在冻结基质上的缓慢水化会导致岩石支护系统硬化不足和故障。这是不安全的，因为硬化不足可能导致落石和随后的伤害甚至矿工死亡。对于北方地区，必须加快喷射混凝土的水化速度，以保证足够的岩石支护强度；然而，喷射混凝土水化产生的过量热量和矿井内的暖风导致了周围永久冻土的融化。解冻是一个严重的问题，因为它会引发温室气体排放（即甲烷），威胁全球气候，并破坏地面的稳定，使地下作业变得不安全。

Shotcrete refers to a cement-based mixture projected pneumatically at high velocity towards the target substrate. Shotcrete has been widely used in underground mines as rock support; however, permafrost poses significant challenges to the design and use of shotcrete to support freshly excavated frozen rock/permafrost because the slow hydration of shotcrete mixture on frozen substrates leads to insufficient hardening and malfunctioning of the rock support system. This is unsafe as insufficient hardening may result in rockfalls and subsequent injuries or even fatalities of mine workers. For northern applications, the hydration of shotcrete must be accelerated to ensure adequate strength for rock support; however, excessive heat produced by shotcrete hydration and warm ventilation air within the mine causes thawing of the surrounding permafrost. Thawing is a serious problem because it triggers greenhouse gas emissions (i.e., methane) threatening global climate and it destabilizes the ground making underground operations unsafe. As mining in colder environments increases in Canada and abroad, innovative shotcrete and rock support systems will be needed for subsurface mine workings excavated in permafrost. However, very limited work has been conducted in this research area. In the next five years, I propose to develop an innovative shotcrete system that can be used as rock support for underground mining in Canada's North and other permafrost regions. Moreover, fundamental research will be conducted on the heat transfer process in shotcrete and shotcrete-permafrost thermal interactions. The long-term goal of the proposed research program is to establish a framework that includes guidelines and software for the design of underground support systems in Canada's North. Mining in Canada's North plays an indispensable role in the economic and social growth of northern regions and communities; mining accounts for over 20% of the GDP of Canada's North; it is also the largest private sector employer of aboriginal Canadians. The proposed research program directly contributes to the development, characterization, and understanding of innovative shotcrete for the use as underground rock support in Canada's North. It will also pave the way for further investigations on the fundamental theory and a framework for underground rock support system design in Canada's North and other permafrost regions. Finally, this research program will train eight highly qualified Northern mining engineers who can apply their knowledge and academic abilities to mineral resource development in Canada's North.