Abstract
This research focused on the impact of mining on the permeability of key aquifuge (N2 laterite) that is widespread in the arid and semi-arid areas of northwestern China and is critical for preserving water resources. The impact of mining stress recovery on the permeability of cracked N2 laterite was assessed for parts of northwestern China that included the Jingle laterite and Baode laterite. The mineral compositions and swelling properties of the laterite at both locations were examined, and analytical results showed that the laterite contained abundant clay minerals. The Baode laterite exhibited higher expansibility than Jingle laterite. The triaxial creep permeability performance of laterite specimens with a prefabricated crack width of 1.0, 1.5, and 2.5 mm were tested. The results indicated that strain of cracked laterite all exhibited transient creep following each level of loading, and then unstable creep and stable creep. With the increase of loading, the transient creep deformation corresponding to each level of loading decreased, the unstable creep deformation produced by identical loading gradually and incrementally increased. The nonlinear power function equation was selected to fit creep grading curves which have high precision. The cracks within the laterite gradually closed with the stress recovery, and permeability gradually recovered. During the stress recovery, the narrower cracks exhibited a smaller change in permeability. However, for narrow cracks in mining soil, permeability recovered after mining stress when permeability was closer to initial permeability, and the Baode laterite showed greater recovery than that of the Jingle laterite.
Highlights
Coal occupies a dominant position in China’s energy structure and is an important primary energy source for China
The impact of mining stress recovery on the permeability of cracked N2 laterite was assessed for parts of northwestern China that included the Jingle laterite and Baode laterite
In situ permeability test showed that cracks in Jingle laterite and Baode laterite did not develop under natural conditions, and after contact with water the montmorillonite minerals expanded to fill the internal cracks of soil and resulted in an aquifuge effect
Summary
Coal occupies a dominant position in China’s energy structure and is an important primary energy source for China. When the regional topography and ground conditions are suitable, shallow groundwater supplies are very valuable water resources, and have great significance for maintaining the ecological environment of the overall region (Xu et al 2004; Li et al 2017; Zhang et al 2017). These are represented by the upper Pleistocene Salawusu group (Q3s) sand aquifer which has a large distribution as the Maowusu desert beach, runoff water formed by rainfall at loess ravine region, lakes and reservoir water (Fig. 1).
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