Decoupling stresses from geosynthetic barrier systems, towards extended service life and safety
Mine structures, particularly heap leach pads, usually incorporate geocomposite barrier systems. These barrier systems are exposed to extreme stresses for the duration of the structure's service life. Tensile stress imposed on geomembranes may cause premature stress cracking, which can lead to the economic and environmental failure of the barrier system and subsequently the heap leach facility. Various studies have shown that barrier systems should ideally be designed and also performed without stress. They are simply intended to act as barriers. In this paper, two different scenarios of a typical liner system on a slope simulating the full and the partial mobilization of the interface friction angle are considered. The development of the acting forces in the geocomposite liners in the two scenarios is calculated and its effect on the stability and on the tensile load distribution between various geosynthetic barrier system components is analyzed. Finally, the influence of the deformations on the geomembrane's long-term serviceability is also discussed.
With the increased frequency of the utilization of geomembranes with regards to the lining system of critical structures such as Heap Leach facilities, so too does the understanding of the factors which impact the service life of these barriers increase. It is fundamentally important that a geomembrane barrier retains its intended key function, that of an environmental barrier, any stresses which could possibly be transferred to the geomembrane should be avoided and diverted to material solutions which are intended and designed for carrying loads, constantly. Towards this end, in this study two different scenarios of a typical liner system on slope are considered. The stability of the system was analyzed by taking into account the occurrence of a progressive failure i.e., peak and large displacement interface shear strength mobilization. The results show that in this case the factor of safety (FS) drops dramatically down from 1.5 to 0.8 and the slope stability is no more verified. Furthermore, the tensile force that might be transferred to the system is calculated by applying the analytical model proposed by Liu and Gilbert (2003, 2005) that maintains strain compatibility and force equilibrium of the system. The calculation shows that in case of progressive failure, the geomembrane will take the major part of the load that implies that it is acting as non-intentional reinforcement. The tensile force acting together with other degradation mechanisms can lead to a reduction in the service life of the geomembrane. Therefore, the means for decoupling loads from barrier systems should be evaluated in every case and where appropriate applied to ensure the responsible design and operation of lined structures these solutions.