Study On Variability Of Physical And Chemical Properties Of Sandy Soil After Coal Mining Subsidence

In order to provide theoretical reference for the ecological restoration and construction in windy desert area affected by coal mining subsidence,the variability of physical and chemical properties of sandy soil in the area subsided in 2005 and the area subsided in 2004 in Bulianta mining area of southeast Mu Us Sandy Land after mining subsiding were studied in this paper.The conclusions are as follows:1,In 2 subsidence areas,bulk density reduced significantly(p＜0.05) while soil porosity increased significantly(p＜0.05) 1～2 years after mining subsidence.2～3 years after subsiding,bulk density and hardness is significantly lower than the control area while soil porosity is still higher than the control area in the subsidence area subsided in 2005, however,bulk density,hardness and soil porosity of the subsidence area subsided in 2004 showed no significant difference with the control area and displayed a recovering tendency. The slope position that subsidence caused most intense porosity disturbance is the top of the slope where soil layer ruptured severely,while the second-intense porosity disturbance occorred at the mid of the slope and the porosity disturbance showed correspondingly slight at the bottom of the slope and the lowland.Affected by freezing and covered by snow,the shortage Of soil water in the subsidence area was significantly restrained.The soil water content of subsidence area reduced significantly when the soil was not freezing (P＜0.01),however,there was no significantly difference of soil water content between each subsidence area and control area when the soil was freezing(P＞0.05).After the soil thawing,the shortage of soil water started earlier and showed more seriously at the positions that are not propitious to freeze and the dissipation of the soil water in 0～50cm layer showed severely in the subsidence area.2,1～2 years after subsiding,the porosity of correspondingly outcropping side of the caving cracks were significantly higher than that of the correspondingly subsiding side(P＜0.05),while 2～3 years after subsiding,there were no significant difference of both sides of the caving cracks(P＞0.05).The subsidence caused significantly bigger porosity disturbance in mid-height and high-height(30～90cm) caving position,while caused significantly smaller porosity disturbance in low-height(10～13cm) caving position.The porosity disturbance in mid-height(30～40cm) caving position is the biggest in number. During 1～3 years after subsiding,the soil water of correspondingly outcropping side of the caving cracks were significantly lower than that of the correspondingly subsiding side in (P＜0.05) in subsidence area. 3,The infiltration depth,average infiltration rate and initial infiltration rate exceeded the average level of the control area,but not always increased significantly(P＜0.05).The simulation of infiltration rate to Horton formula showed that,compared with the control area,the infiltration rate at lowland of subsidence area increased in the earlier stage of infiltration while decreased in the later stage,and the infiltration rate at top of slope in subsidence area always increased in the whole stage of infiltration.The phenomenon that infiltration depth of correspondingly subsiding side exceeded the outcropping side of the caving cracks showed universally(with the proportion of 81.8%).The difference value of infiltration depth to both sides of the caving cracks randomly increased following with the increasing of the height to the caving soil mass.4,2～3 years after subsiding,total N and total P decreased significantly(total N—P＜0.01,total P—P＜0.05),carbon-nitrogen ratio(C.N) increased significantly(P＜0.05), while Total K and Organic matter didn't vary significantly(P＞0.05) at unitary level.Total N and total P decreased universally and significantly(P＜0.05) in the lowland of each subsidence area where cracks exposed largely.5,2～3 years after subsiding,canonical discriminant analysis showed that there was a significant difference of multivariate mean vector between subsidence areas and control area and there was also a differentiation among the influencing directions cansed by coal mining subsidence to each subsidence area.Principal component analysis synthetically showed that the principal component that reflects synthetical soil quality decreased in each subsidence area.At the soil layer below 60cm of each subsidence area,synthetical soil quality decreased most seriously.The principal component that reflects soil porosity property was relatively large in the subsidence area subsided in 2005.Factor analysis showed that coal mining subsidence caused the biggest effect to soil synthetic quality factor and caused the second major effect to soil structure factor while caused no obvious effect to stable matter factor.