Overcoming High Temperature Water Ingress in Deep Underground Mining

CIM Montreal 2015
Matthew T Swanson (Cementation USA), Tom M Goodell (Rio Tinto)
Resolution Copper Mining, along with mining contractor Cementation USA, are in the process of developing what is planned to become the largest copper-producing mine in North America. A project of this magnitude does not come without challenges, and No. 10 Shaft, the first of six record-breaking shafts, has presented many. An impressive feat of engineering, the project will eventually use block caving methods to mine approximately 1.7 billion metric tons of porphyry copper ore at rates of up to 120,000 metric tons per day. It will rely on the six 2,130 m deep shafts for ore extraction, ventilation, man access, and utilities.

This presentation will discuss the unique challenges faced during the sinking of No. 10 Shaft and the innovative thinking and engineering required to overcome them. These challenges included unexpected water ingress more than 1,950 m below surface. Within a 50 m section of shaft advance, water inflows increased from negligible amounts to totals in excess of 1,700 litres per minute at temperatures exceeding 80°C. Attempts to reduce water ingress by pressure grouting were unsuccessful due to the highly fractured nature of the rock and the high grouting pressures required at this depth. In order for shaft sinking to continue, the water had to be efficiently handled and removed from the shaft using inventive and relatively unproven methods.

Accompanying this water ingress was another unforeseen obstacle, a considerable heat load. Upon intersecting this high-temperature water, shaft air temperatures and humidity levels immediately began to rise and continued to increase until worker safety became a concern. The shaft was generating a heat load of 6.61 MW, easily overwhelming a cooling system designed to handle less than half of that amount. A complete overhaul of the shaft cooling and ventilation systems was required with just over 90 m of advance remaining to reach shaft bottom. This overhaul included the retrofitting of 610 m of 2 m diameter vent duct in the shaft as well as the installation of six massive cooling coil units underground, weighing nearly 5,900 kg each.

Lateral development work near the shaft bottom has faced similar yet unique challenges due to the high temperature water. Cooling the development headings and maintaining a high enough volume of airflow to combat the generation of dense fog was one of the more significant challenges. Additionally, water inflows were near the limit of what could be handled using the current dewatering system, requiring cautious advance and additional attempts at grouting.

Together, the water and heat forced the project to drastically modify the shaft sinking and development process. Pump box-outs, hanging sumps, concrete-embedded dewatering lines, and dewatering buckets are a few items that have become irreplaceable tools at The Resolution Copper Project. While remaining development work at the project will have the benefit of being better prepared to handle these obstacles, these exceptionally hot water inflows will never be considered routine. Numerous challenges remain for the project, challenges that will only be overcome by innovative thinking, adaptable operations, and “brute force engineering”

Keywords: Deep Mine Cooling, High Temperature, Ventilation, Underground Mining, Dewatering, Water Ingress
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