Experimental and numerical analysis of desiccation of a mining waste

Abstract

The paper presents an analysis of the desiccation process in mining materials, based on physical laws. Due to the process complexity, most of the previous approaches used have an empirical basis. In this case, however, a formulation using coupled hydromechanical equations has been considered. To show the capabilities of the theoretical framework, several laboratory tests were performed, and afterwards a numerical simulation of the measured variables was attempted. The material tested was a metallurgical waste in tailings form and it was exposed to atmospheric desiccation. Further cracking will eventually change its properties, and this may have an environmental impact. Some of the experiments were devoted to material characterization, including the water retention curve, the hydraulic conductivity, and the tensile strength. In addition, laboratory drying tests open to the atmosphere or in hermetically closed containers were also performed. The numerical analyses carried out attempted to simulate some of these tests. One of the main outcomes of the analyses was the prediction of the time and the location of crack initiation. Finally, it should be pointed out that good agreement between the experiments and numerical simulations indicates that the formulation is taking into account the fundamental mechanisms involved in the desiccation process

Observations on the desiccation and cracking of clay layers

“…Tang et al (2008), Tang et al (2010a) and Costa et al (2013) were able to show that there was an influence of the desiccation rate in the amount of cracks produced. Rodríguez et al (2007) observed that the effects of soil thickness on the cracking water content were not noticeable for very thin soil layers. Peron et al (2009) looked at free and constrained desiccation, and crack patterns.…”

“…Abu-Hejleh and Znidarčić (1995) described the cracking process in terms of the consolidation and shrinkage of the desiccating material. Rodríguez et al (2007) presented a general approach, introducing coupled hydro-mechanical behavior of the soil in unsaturated conditions to simulate the cracking in their laboratory experiments on mine tailings. Shin and Santamarina (2011) utilized an effective stress approach and explained the crack initiation process using the evolution of the air-water interface membrane as the soil dries.…”

Some investigations about the tensile strength and the desiccation process of unsaturated clay

“…The results show that the tensile strength-suction evolution depends strongly on both drying and compaction paths. These results are compared with recent published results by [2]. In parallel, the clayey soil is studied by a mercury porosimetry test to characterize the pore distribution network.…”

Cracking in desiccating soils

“…Most recent works dealing with cracking in drying soils consider the tensile strength as failure criterion to define whether a crack initiates or not in a particular point of the soil mass ( [10], [15], [16], [22]). This failure criterion, however, has been criticised as too simplistic ( [21]).…”

“…While the soil is a continuous medium, the conventional coupled HM formulations used for porous media may apply. Therefore, soil drying up to the crack initiation can be simulated numerically by using standard finite element codes solving HM equations in unsaturated conditions [10].…”