| Soil organic reconstitution is one of the main measures to realize the resource utilization of sludge soil,save land,protect the environment,and prevent mudflow induced by piling.In this paper,to address the resource utilization of sludge soil with waste primary minerals from the sand and gravel processing system of Lava hydropower station in the dry and hot valley region of southwest China,based on the evaluation of heavy metals and organic nutrients of sludge soil,we selected local widely distributed river sand and straw（ammonia treatment）,and implemented tests of unsaturated/saturated infiltration,water retention test,substrate suction test,and agglomerate structure culture after organic reconstitution in a certain proportion,and The infiltration and water retention characteristics of the organically reconstituted soil samples were analyzed,with emphasis on the mechanism of the influence of straw morphology and quantity on the hydrological properties of the reconstituted soil.The details and research results are as follows:（1）Through the indoor test of heavy metals and nitrogen,phosphorus and potassium elements,the evaluation results according to the norms show that the content of metal elements in sludge soil and river sand is low,and the evaluation levels are all above grade II,so no special treatment is needed.According to the fertility standard of farmland,the evaluation of soil fertility elements required for plant growth are all at level 6,and the content is seriously insufficient,which is not conducive to plant growth.（2）The unsaturated infiltration and saturation infiltration tests of the soil column with constant head of various ratios of organic reconstituted soils formed by sludge soil,river sand and straw showed that the movement rate of the wetting front of the soil column was larger in the early stage,but gradually decreased and slowed down in the later stage;meanwhile,the movement rate of the wetting front increased step by step with the increase of the river sand mixture;a small amount of straw could significantly accelerate the movement rate of the wetting front,but the movement rate of the wetting front did not increase with the increase of the straw mixture.However,the rate of wetting front movement did not increase with the increase of straw incorporation.The saturated permeability coefficient of organic heavy soil mixture can be increased by incorporating river sand,and the saturated permeability coefficient reaches the maximum when the river sand content is 66.7%;the saturated permeability coefficient of organic heavy soil can be increased by incorporating a small amount of straw,and the saturated permeability coefficient is the maximum when the straw content is 0.5%,but too much straw will reduce its saturated permeability coefficient.（3）The results of the experimental study on water retention of organic reconstituted soil showed that when the mass of sludge soil accounted for more,the increase of river sand admixture would continuously weaken the water retention capacity of reconstituted soil.The water retention capacity of the reconstituted soil is weakened and the rate of water loss is increased after mixing river sand with a small amount of straw in the sludge soil,which is due to the increase of porosity and the more open channels for water dissipation inside the soil body.The increase of straw will significantly prolong the change of volumetric water content,which means that the increase of straw can significantly increase the water retention of the reconstituted soil,the main reason is that after the reconstituted soil is fully immersed in water,the straw also fully absorbs water,and its water absorption process is equivalent to"capillary",the water dissipation channel of the reconstituted soil depends on the size of the pore ratio and its connectivity,and the straw The water dissipation channel of reconstituted soil depends on the size of pore ratio and its connectivity,while straw is equivalent to the water storage body in reconstituted soil,and its water dissipation is mainly through the opening of two sections of"capillary".（4）Will be crushed straw in the sludge soil for horizontal and vertical placement of infiltration tests show that the permeability coefficient of reconstituted soil is mainly above10-4cm/s,straw horizontal placement form has a catalytic effect on infiltration,but increase the number of straw has an inhibitory effect on infiltration,the main reason is that a small amount of straw increases the permeability of the seepage channel（soil-straw wall）,the increase in the number of straw reduces but reduces the interface The main reason for this is that the increase in the number of straws reduces the effective pore ratio of the interface,forming the bottleneck effect of the seepage interface;a small amount of straws in the form of vertical placement of straws has a catalytic effect on infiltration,but with the increase in the number of straws gradually inhibits infiltration,the main reason for this is that in the case of the same test soil,the insertion of too many straws will crowd the perimeter of the soil,showing the bottleneck effect of seepage.（5）The results of agglomerate incubation tests show that river sand can promote the formation of small agglomerates and inhibit the aggregation of large agglomerates;a small amount of straw promotes the binding of microagglomerates and increases the content of large agglomerates,while a large amount of straw promotes the stabilization of small microagglomerates and reduces the content of large agglomerates.Wet and dry cycles can promote soil particle linkage,but too many wet and dry cycles will reduce the content of large agglomerates. |
