| Coal is the main energy resource in China.At present,China is still in the period of rapid economic development,and the main energy status of coal will not change.The exploitation of coal resources has inevitably caused land subsidence while making great contributions to the development of the national economy.About 85%of the subsided land was cultivated land.The eastern mining area of China is an important grain production area and a high-water coal production base.Land subsidence causes large areas of water accumulation,resulting in the loss of cultivation capacity of large-scale cultivated land.The mining subsidence area is growing at a rate of 70,000 hectares per year.The loss of cultivated land caused by subsidence will continue to increase,which makes the contradiction between large population and small land become more prominent.It is imperative to reclaim the cultivated land which has lost the ability of cultivated land due to coal mining subsidence,and filling reclamation technology is an effective way to solve this problem.Because of low reclamation efficiency,shortage of filling materials and potential pollution problems,the previous technologies such as deep-digging,coal gangue filling and fly ash filling are difficult to solve the contradiction between mine and farmers caused by coal mining subsidence in eastern China.Utilizing the advantage of subsidence land close to the Yellow River and filling the subsidence land with Yellow River sediment can not only solve the problem of silt in the Yellow River channel,but also solve the problem of shortage of filling materials.Based on the existing researchs,this dissertation firstly analyzed the technology of the filling reclamation with Yellow River sediment,pointed out the problems existing in the traditional one-time filling process without strips and one-time filling process with alternating strips,and analyzed the principle,advantages and technology of the multi-times multilayer filling reclamation with alternating strips.The time cohesion model of alternating filling between strips and the mathematical conceptual model of the number of strips in synchronous alternating filling were given.The laboratory and field experiments were conducted using the knowledge of sediment movement mechanics,soil science,soil mechanics,fluid mechanics,pedology and agronomy.Combining with field filling reclamation experiment,the sediment silt volume and drainage consolidation time of the Yellow River were calculated,and the numerical simulation of the filling reclamation with Yellow River sediment was carried out by means of fluid mechanics.In order to optimize the best drainage way,indoor drainage simulation test is carried out.Field planting experiments were carried out to verify the effect of multi-times multilayer filling reclamation by continuously monitoring of wheat and maize yield,1000-grain weight,and soil moisture and nutrient content of reclaimed soil profile.The main results were as follows:(1)The traditional filling reclamation technology with Yellow River sediment has the problems of small scope of application and poor quality of reclaimed soil.The key of the multi-times multilayer filling technology with alternating strips is to solve the coupling between soil stripping and stockpiling,multiple backfilling and filling.The aim is to construct a high-quality interlayer soil profile construction under the condition of continuous filling.How to achieve continuous filling i5 the focus of research.The key technology of alternating multi-layer filling with in Yellow River sediment refers to the time connection of continuous filling,sediment deposition and enhanced drainage technology.(2)The key of multi-times multilayer filling is how to achieve continuous backfilling.The coupling mechanism betAveen multiple soil backfilling and multiple filling needs to be solved.In this paper,taking the case of intercalating a layer of subsoil and intercalating two layers of subsoil in Yellow River sediment layer as an example,the time model for realizing continuous filling and the mathematical conceptual model of the number of simultaneous alternating filling strips for continuous filling were given,and the key problems of continuous filling were theoretically solved.(3)The settlement rule of filling sediment and the calculation of consolidation time are of great practical significance for guiding the filling and realizing continuous filling,saving reclamation time and cost.Combining theoretical research with field filling reclamation experiment,the sediment settlement law and the calculation of consolidation time were discussed.?The particle size of sediment is closely related to the hydraulic characteristics of sediment.The particle size of sediment is an important factor affecting its starting,stopping,settling and suspension.The theoretical formulas of sediment vertical line and distribution along the process,the rate of sediment deposition,sedimentation and sediment consolidation in the filling process are listed respectively.?A field filling reclamation experiment was carried out.The hydraulic parameters and settlement of each calculation section in the filling process were calculated,including Chezy's coefficient,average hydraulic gradient,flow frictional velocity,restoring saturation coefficient,sediment content in the upper and lower sections of the filling strip,sedimentation rate,siltation volume and siltation thickness.The settlement thickness of obtained by theoretical calculation and experimental data were basically consistent.?According to the calculation of drainage consolidation time,the consolidation coefficient was 0.025656 mZ/d,the time factor Tv of sediment consolidation is 0.575,and the consolidation time in this experiment was 9.18 days.Drainage mode has a significant effect on drainage consolidation time.Rational layout of drainage mode is of great significance for accelerating the drainage consolidation of sediments.?The numerical simulation of filling reclamation with Yellow River sediment was carried out by means of Euler model of fluid mechanies.The results of numerieal simulation showed that the coarse sediment was settled earlier than the fine sediment,It conformed to the rule of sediment transport and the numerical simulation results were good.(4)The laboratory simulation experiment of enhanced drainage was carried out.The reclamation effects of the five treatments(sediment concentration of drainage,sediment particle size of drainage,surface sediment particle size of filling layer),water content change in different layers of profile after the first filling and the second filling.The best enhanced drainage mode was selected.According to the analysis of the test results,the geotextile had a good sediment-trapping effect,and the sediment can be intercepted in the glass trough;the flocculant was beneficial to the rapid sedimentation of the fine-grained sediment and reduces the discharge;the drainage effect of the underground pipe treatment was better.(5)Field planting experiments were earried out to verify the effect of muti-times multilayer filling reclamation with altermating strips.By analyzing the 1000-grain weight and yield of wheat in June 2016,maize in September 2016,wheat in June 2017,maize in September 2017 and wheat in June 2018,it was found that for the same soil thickness,the inter-layers soil profile construction formed by multi-times multilayer filling was larger in 1000-grain weight and yield than the double-layer soil profile construction.Different interlayer soil profile construction had certain effects on crop 1000-grain weight and yield.The number of filling layers,the thickness of filling layers and the thickness of subsoil layers are all important factors affecting the reclamation effect.Even the crop 1000-grain weight and yield of some interlayer soil profiles were larger than the control.Compared with the double-layer soil profile,the soil layer of the interlayer soil profile construction was conducive to retaining more water,and it is easier to preserve organic matter,total nitrogen,available phosphorus and available potassium in the surface soil.The interlayer soil profile configuration is conducive to retaining total nitrogen and available potassium in the profile.In this paper,the key technologies of multi-times multilayer filling reclamation the coal mining subsidence with Yellow River sediment were explored and studied.According to analysis,the multi-times multilayer filling reclamation was technically feasible and the reclamation effect was relatively good,but there are still many deficiencies,which need further study.Because there were many uncertainties in the process of field filling reclamation,field filling and drainage experiments can be carried out in the future to further verify the results of laboratory experiment.In this paper,the effect of filling reclamation was analyzed only from 1000-grain weight,crop yield,water content and nutrient content of soil profile.The method was relatively simple,and its reclamation effect can be analyzed from comprehensive benefits in the future. |
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