Study On Development Of Mining Cracks In N₂ Laterite Aquiclude

The Neogene N2 laterite in the large coal base in Northwest China is widely covered,and it is easy to produce downward tensile cracks under the influence of mining.The research on the crack closing characteristics of laterite mining cracks to carry out research on the development law of mining cracks in the N2 laterite aquifer is of great significance to the realization of surface diving and ecological environment protection in mining areas.This thesis takes the N2 laterite of a mine in Yushen mining area as the research object.It has passed laboratory experiments such as clay mineral composition test(XRD ray diffraction test),N2 laterite crack closing test and physical similarity simulation,combined with theoretical analysis(including probability integral theory and elastoplasticity theory).And use the mining damage prediction software to conduct a systematic study on the development law of mining cracks in the N2 laterite aquiclude.The main research results are as follows:(1)The XRD ray diffraction test shows that the content of montmorillonite in the clay minerals of N2 laterite is relatively high,which is one of the main factors affecting the swellability of N2 laterite;the test of the swellability of N2 laterite shows that the content of montmorillonite accounts for laterite minerals.When the ratio of the total amount increases from 7.3%to 12.3%,the expansion rate increases from 10.97%to 15.31%,and the expansion rate increases linearly with the increase in the content of montmorillonite.Through a similar material ratio test,it was.determined that the sand-soil ratio 1:5,oil-soil ratio 1:6 and montmorillonite powder with 8%of the total mass of sand added were the best similar ratios of N2 laterite under similar conditions of 1:200.(2)Using the self-designed physical similarity simulation test bench,a similar simulation of the development of cracks in the N2 laterite was carried out The simulation results showed that the N2 laterite in the stretched area outside the goaf produced permanent boundary cracks,and the crack development process experienced.There are three stages of "generation?expansion?stabilization".The fractures generated inside the goaf(neutral zone and compression zone)have gone through the four stages of "generation?expansion?closure?stabilization".(3)The N2 laterite crack closing test shows that when the crack width is 2mm and the montmorillonite content increases from 7.3%to 12.3%,the corresponding closing rate increases from 26.65%to 33.2%,when the montmorillonite content is a fixed value of 8.9%,when the crack width increases from 1mm to 5mm,the corresponding closing rate decreases from 39.2%to 18.15%(in a word,the closing ability of N2 laterite increases with the increase of montmorillonite content,and gradually weakens with the increase of crack width).N2 laterite mining crack closing experiments show that permanent cracks at the edge of the mining tension zone are only bridged by water expansion,while the internal(neutral and compression areas)cracks in the goaf area(neutral zone and compression zone)cause compression deformation and N2 laterite.Under the combined action of water swelling,the middle clay minerals are bridged,and the degree of closure is greater than the former(4)Theoretical analysis gave a formula for predicting the development depth of cracks in N2 laterite mining,and it was concluded that the crack depth was positively correlated with mining height and horizontal deformation,and negatively correlated with the ultimate tensile deformation of N2 laterite itself;the closing capacity increased with cracks.The width increases continuously decreases,and continuously strengthens with the increase of montmorillonite content;the order of the degree of crack closure in the N2 laterite in different areas affected by mining is:compression zone inside the goaf>neutral zone inside the goaf>extension zone outside the goaf The conclusion.The reliability of the formula for predicting the depth of mining cracks in the N2 laterite aquiclude was found with the help of actual examples.The research results can provide reference and experience for the realization of water-preserving mining and green mining in mining areas.