Compaction Characteristics Of Reclaimed Soil And Its Effects On Soil Environment In Coal Mining Subsidence Land

Coal mining area with high ground-water level in east China is both a national coal energy base and a main food production area,which means that coal mining subsidence in this area will significantly threaten ecological environment as well as arable land resources and food security.In this area,coal mining subsidence reclamation is the main way to increase arable field area,ease human-land contradiction and protect food security.However,in the process of agricultural utilization of reclaimed soil,soil compaction has become the most important reason that affects soil productivity.This study aims to discuss the effects of mechanical use on soil compaction and the resulting soil environmental effects during reclamation.On the one hand,study the changes of soil compaction,soil particle composition,soil macropores,and microbial activity after turbulent disturbance by reclaiming machinery through combined methods,including observing samples from the construction site,simulating compaction tests,geostatistical theory,fractal theory and CT scanning techniques;on the other hand,study the differences in soil thermal conductivity and inorganic phosphorus distribution at different reclamation areas,and also analyze the relationship between them and soil compactness,through observing samples drawn from typical reclamation areas.The main findings are as follows.?1?The mechanism of mechanical compaction of reclaimed soil is preliminarily proved.By observing samples from the construction site,we found that the mechanical compaction during reclaiming significantly increased the compaction of reclaimed soil.When the soil has a mass moisture content of 16%to 18%,each time after the TD80B-type crawler dozer grind,the average compaction of the reclaimed soil increased,the backfilling topsoil layer?0-20 cm?,backfilling subsoil layer?20-40 cm?and packing layer?40-60 cm?respectively increased by53.586 kPa,57.791 kPa,and 16.100 kPa.According to the geostatistical characteristics,after three-times compaction,the compaction of the reclaimed soil in all three layers exceeded1000 kPa,which will inhibit crop growth.The use of crawler bulldozer during construction greatly disturbed the reclaimed soil layer.The particle composition of the soil in the surface layer?0-20cm?gradually converged with that of the packing layer,and the distribution of soil particles?D?0??becomed smaller,the asymmetry??f?increased,varying between centralizd-dispersed”?D?1??and“even-uneven”????.In addition,the use of crawler bulldozer also compressed the soil while disturb the soil layer,making it smaller of the area???,quantity and size of reclaimed soil pores,while increasing the circularity?C?of macropores.?2?The effect of soil compaction on soil microorganism is revealed.Through compaction test to simulate different soils under different mechanical compaction times,we found that the microbial activity in the surface layer?0-20 cm?is different after natural ripening for 3 years.We simulated the compaction of crawler bulldozer and the dump truck separately.From 1 to 9times,the number of bacteria,fungi and actinomycetes,soil respiration rate,and content of urinary enzyme and acid phosphatase showed inverted“V”changes.Microbial activity is best after 3 or 5 times crawler bulldozer compaction.?3?The relationships between soil compactness and soil thermal conductivity,soil inorganic phosphorus morphology in reclamation area are analyzed.Soil thermal conductivity under different reclamation types varied,Soil thermal conductivity under"Digging deep to fill shallow reclamation","Filling reclamation"and"Beforehand reclamation"were all smaller than that of the control land,which was related to the texture and compaction degree of the reclaimed soil,when the soil bulk density is 1.205-1.593 g/cm³,the sandy content is the main factor,when the soil bulk density is 1.604-1.813 g/cm³,the bulk density is the main factor.Content of various forms of inorganic phosphorus in the reclaimed soil varied when different materials were used to refill,among which,the inorganic phosphorus content and phosphorus effectiveness were higher when lake silt was used as refilling material.In addition,the compaction degree of the reclaimed soil showed a significant negative correlation with the total content of inorganic phosphorus,Ca₈-P and Ca₁₀-P in the reclaimed soil.The correlation coefficient r was-0.611*,-0.498*,and-0.509*,respectively?P<0.05?.The results above indicated that controlling the number of compaction times during the construction of reclamation could reduce the disturbance and squeezing of soil by mechanical use,and could avoid the reduction of soil microbial activity caused by excessive compaction.In the reclamation area,it could effectively increase reclaimed soil thermal conductivity when reducing the degree of soil compaction and increasing the sand content.Filling material would affect the distribution of various forms of inorganic phosphorus in reclaimed soil,but to a certain extent,reducing the compaction degree of reclaimed soil could increase the effectiveness of soil phosphorus.The research results may provide theoretical knowledge and data support for the innovation of reclamation techniques and the formulation of reclamation standards.