Research On Hydraulic Of Stalk Composite Pipe Under The Constrain Of Ditch-soil

Stalk subsurface irrigation is a new type of water-saving irrigation technology with stalk composite pipe(SCP)as the core.The SCP is made of stalk and soil as the main raw materials,and has the functions of water seepage and water conveyance at the same time.When applied,it is shallowly buried subsurface to complete irrigation.The SCP can be directly returned to the field after completing the irrigation task for one year or one season,which can be completely decomposed into the soil,which can improve the physical and chemical properties of the soil,and can also solve the problem of difficult capillary recycling in other irrigation technologies.Subsurface stalk irrigation is the product of the combination and optimization of the two technologies of irrigation and stalk returning,which has certain significance for the realization of farmland irrigation technology and the treatment of agricultural waste resources.Whether the stalk subsurface irrigation can be successfully applied depends on its hydraulic performance and irrigation effect after it is buried in the ground.In this paper,based on the buried test of SCP,the water permeability under free outflow condition,hydraulic performance and irrigation effect under buried condition were investigated.In view of the influence of working pressure,pressure increasing and decreasing process and drying time on the water permeability of SCP,a free outflow test was carried out.In view of the effects of trenching parameters(depth and width)and backfill soil bulk density on the hydraulic performance and irrigation effect of SCP,the subsurface outflow test was carried out.The main conclusions are as follows:(1)Under the condition of free outflow,when the working pressure is 10-50 cm,the seepage amount of the SCP is between 0.6-3.6 L/(m·h);the cumulative seepage amount and seepage time are a power function.The water seepage rate gradually decreased with the increase of water seepage time,and gradually became stable after 1h;the whole water seepage process of the SCP conformed to the Philip infiltration model.(2)In the process of lifting and lowering pressure,the effect of the pressure reduction process on the water seepage of the SCP is greater than that of the pressure increase process.The interaction between drying time and working pressure has a direct impact on the water seepage of the SCP.Increasing the drying time can increase the water seepage amount of the SCP and reduce its water seepage stability.In the production and application,it should be considered to reduce the drying time of the SCP to realize on-site production and burial.(3)Under the condition of buried outflow,the cumulative infiltration amount of the SCP increases gradually with the increase of infiltration time;the depth of the pre-embedded trench has the greatest influence on the cumulative infiltration amount of the SCP,and the bulk density of the backfill soil Second,the effect of the embedded trench width is the smallest.The soil wetting body formed by the infiltration of the SCP is approximately an ellipsoid,with the short axis in the horizontal direction and the long axis in the vertical direction,and the wetting range is between 32 and 46 cm.(4)Through the relationship between the experimental factors and the wetting front migration distance,the established wetting front migration model can well predict the soil wetting front migration law of the SCP.The ditch-soil confinement process occurred within 30 minutes before infiltration,and the water migration was mainly affected by the soil water potential gradient.Decrease and eventually tend to be stable;the water transport rate in the vertical downward direction is larger in the early stage,and then gradually decreases with the extension of time in the later stage.(5)The distribution of water in the soil wet body is directly related to the burial depth,and the position of the moisture peak is consistent with the burial depth of the SCP;through the comprehensive analysis of the three indicators of irrigation water utilization coefficient,irrigation water uniformity coefficient and soil moisture ratio,it was concluded that when the depth of pre-embedded ditch was 20 cm,the width of pre-embedded ditch was 25 cm,and the bulk density of backfill soil was 1.2 g/cm~3,the comprehensive irrigation effect of straw underground irrigation was the best.