ABSTRACT: Corrugated dual-walled polyethylene pipes are commonly used in the solution collection system of heap leaching facilities. Under load, these pipes tend to deflect, thereby developing passive soil support at the sides of the pipe. At the same time, the vertical deflection of the pipe generates vertical movement of the ore column above the pipe, inducing an arching action which relieves the pipe of the major portion of the vertical load. The deflection of the pipe creates stress redistribution near the solution collection pipe with a significant reduction in stress immediately below the pipe and an increase in stress along the sides of the pipe. The zone of stress increase extends to about four pipe diameters to each side of the pipe. There are some instances when the designer specifies two adjacent pipes, with same or different diameters, to have a horizontal separation keeping the second pipe away from the overstressed zone. This specification is founded on the belief that the arching effect of one pipe will increase the stress on top of the adjacent pipe causing excessive deflection. This paper presents the results of a series of finite element models, which were calibrated with published laboratory tests, to evaluate the effects of stress redistribution on adjacent pipes. Four cases were evaluated: a single pipe, two pipes separated by five-pipe diameters, two pipes separated by one pipe diameter, and two pipes with different diameters separated by one pipe diameter. The results indicate that the arching action of one pipe does not substantially increase the stress on top of the adjacent pipe. The calculated deflection of a single pipe is somewhat similar to the deflection of two adjacent pipes. Adjacent pipes deflect due to the weight of the ore developing their own arching effect and redistributing the stresses on the adjacent zones, in between the pipes and outside the pipes. The overstress generated in the zone between the pipes is larger than that outside the pipes. The results of this paper will help regulators and designers understand the stress redistribution of adjacent flexible pipes in heap leaching facilities and make decisions regarding the proper separation of adjacent solution collection pipes and the adequate geomembrane protection in the overstressed zones.
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