In September 2014, Concrete Cloth (CC) was used to remediate a drainage ditch at the base of a slope at the Pogo mine in Alaska. The ditch is needed to prevent surface and storm water coming into contact with the adjacent mining tailings field. The Pogo mine is owned and operated by Sumitomo Metal Mining. Due to the mine location and surrounding terrain, there are challenges with storm and surface water management.
Relining the ditch with shotcrete was considered; however, 2 miles of shotcrete-lined ditches had been installed in the previous two years, and the results proved this was not a long-term solution. Storm water had undermined the ditch, which, when coupled with freeze-thaw weathering and heavy spring rains, had caused extensive cracking of the shotcrete, leading to failure.
CC allowed the installation to be undertaken in September, when temperatures in the area are already near freezing and there is regularly frost in the mornings – conditions that prevent the use of conventional concrete. Additionally, CC negates the costly maintenance requirements associated with other drainage solutions.
Installation
Thirty-three bulk rolls of CC5 and five bulk rolls of CC8 were delivered to the Pogo mine. The existing shotcrete ditch was cleaned of debris such as rock and vegetation to ensure intimate contact between the CC and the incumbent shotcrete lining. An anchor trench was created at the crest of the ditch adjacent to the slope, above the level of the existing shotcrete, to prevent runoff water from the slope infiltrating under the CC. The opposite side of the ditch is located next to a road, for which the bank was graded and the ditch was re-profiled using a Volvo EC360C and a Caterpillar 320C excavator.
The CC was mounted onto a Caterpillar small-wheel loader with a spreader beam, unrolled and cut to a specific profile length with a utility knife to avoid wastage. The mine staff then laid the CC transversely, overlapping layers in the direction of water flow. The outer edges on the side adjacent to the slope were fixed with 305-mm galvanized Ardox spikes into the previously created anchor trench. The overlaps were screwed every 300 mm with 20-mm truss-head stainless steel full-thread screws. The roadside edge of the CC was then sealed with a bead of Sikaflex 1A and fixed into the existing shotcrete liner with 15-mm-by-10-mm steel mushroom anchors. The material was hydrated via a water truck with a 50-mm adjustable nozzle.
Applying and securing Concrete Cloth is simple.
Summary
The 7,225 sq m of CC was installed in 11 days at rate of up to 1,000 sq m a day by a team of six in low temperatures. The installation was deemed a success due to the speed of install and cost savings of 90%.
