Suitability Evaluation Of Land Reclamation And Evolution Of Soil Physical Properties Of Nonmetal Mines In Xinjiang

There are vast non-metallic mineral resources at the northern foothills of the Tianshan Mountains in Xinjiang,and exploration of nonmetallic mineral resources in Xinjiang is conducive to the economic construction of Belt and Road Initiative.It is necessary to carry out the work of land reclamation because the large-scale exploitation of mineral resources is bound to cause irreversible damage to the fragile geological environment and ecological environment in this region.This dissertation focuses on the scientific problems of feasibility of reclamation,physical properties' evolution and law of water transport in reconstructing soil.Firstly,a land reclamation suitability evaluation indexes system and evaluation model for non-metallic mines in Xinjiang was established in this dissertation.Secondly,the effects of reclamation machinery on the physical properties of surface reconstructing soil were studied by static load test,laboratory geotechnical experiment and numerical simulation,and the hydraulic parameters of reconstructing soil were obtained.Finally,in-situ test,dynamic monitoring and numerical simulation were used to analyze the variation of water content and matix potential of reconstructing soil,revealing the soil hydrodynamic model of aerated zone under the condition of sudden change of layered structure interface.The research results are as follows.(1)This dissertation proposes a suitability evaluation index system and model for land reclamation of non-metallic mines in Xinjiang.Using 21 non-metallic mines as research objects,nine factors were chosen as classification indexes.The 149 samples were trained using a discriminant analysis method to establish the land reclamation suitability evaluation model.The tests showed that the correct rate has reached 98.7%.The evaluation model is applied in practice and the evaluation result is satisfactory.The evaluation model developed here can serve as a powerful complement to the evaluation of land reclamation suitability in Xinjiang.The evaluation index system and model can be used to determine the direction of land reclamation in non-metallic mines in Xinjiang,that is,whether it is necessary to cover soil.(2)This dissertation studies the variation of physical properties of reconstructing soil.The variation of physical properties of reconstructing soil under different reclamation thickness and compaction and after one-year management period was obtained.1)Both the compaction times and the thickness of the reconstructing soil are significant factors affecting the density of the reconstructing soil,and the mutual interaction between the two factors have an impact on the density of the reconstructing soil.There is significant difference of the compaction effect to the reconstructing soil between noncompaction and three-time compaction by the reclamation machine.With the increasing times of compaction,the effect of every additional single compaction is weakened.The thicker the topsoil is,the less effective the compaction effect would be.2)The reclamation machine shows variable compaction effects at different depths of the reconstructing soil.It has the most significant compaction effect on the superficial part of the reconstructing soil(at the 10 cm depth).3)There are seepage and capillary transportation of water in the reconstructing soil due to irrigation during the one-year maintenance period.These factors affect the density of the reconstructing soil.4)The sampling depth of reconstructing soil has a significant influence on the granulometric composition of reconstructing soil.5)The fine particle content affects the physical properties such as the homogeneity,porosity and water content;the overall change is that the coarser the particles are,the more uniform the soil particles,the higher the water content and the larger the porosity will be.(3)Water movement in reconstructing soil with different thickness under uncompacted and one compacted was obtained by studying water movement in reconstructing soil.The results show that: 1)for one compacted or uncompressed soil,the soil water content at the depth of 10 cm is obviously affected by meteorological factors,and its water content is less than that at other depths of the reconstructing soil.The water content at the depth of 30 cm is higher than that at other depths of the reconstructing soil.2)The response time of soil water content and matix potential to primary irrigation infiltration is different due to the thickness and compaction of overlying soil.3)The thicker the soil layer is,the weaker the infiltration recharge capacity is.The overall infiltration capacity of uncompacted soil is greater than that of one compacted reconstructing soil.The evaporation capacity of uncompacted reconstructing soil is also greater than that of compacted reconstructing soil.5)It is recommended that the thickness of reconstructing soil should not be less than 50 cm.(4)In this dissertation,a reconstructing soil hydrodynamic model was proposed,and a numerical simulation of water movement in reconstructing soil was carried out.The results show that: 1)The evaporation loss,bottom discharge flux and internal water consumption of compacted soil are less than those of uncompressed soil under the condition of 30 cm soil cover,and the compaction effect is obvious.2)The amount of evaporation loss in 50 cm and 70 cm thickness reconstructing soil is the same because soil water loss was mainly leached under gravel layer during reclamation.3)Comparing with the results of physical experiment and numerical simulation,the loss of soil moisture in 50 cm thick compacted soil is the smallest,which means that it can be used as a scheme for reclamation.4)Based on the meteorological data for non-freezing period during a 20-year span,the inversion parameters of 50 cm compacted soil numerical simulation are analyzed.The results show that the consumption of precipitation and evaporation is basically the same.The consumption of vegetation after reclamation is mainly supplied by irrigation recharge,and the effect of irrigation is prominent.There are 116 figures,36 tables and 190 references in this dissertation.