Study On The Improvement And Application Of Clay And Polyacrylamide Content On The Water Physical Properties Of Plant Pore Matrix Soil

Planting hole technology is a kind of ecological restoration technology based on ground mirror reconstruction method,which is widely used in high and steep rock slope greening.It has the advantages of simple construction,low cost and quick effect.Because the planting hole provides a narrow cylindrical growth space for plant growth,there are problems such as large hole depth,poor permeability,small catchment area and low rainwater utilization rate.Therefore,the water physical properties(permeability,water holding capacity and water retention)of the planting pore matrix soil are more demanding.In this thesis,the matrix soil mixed with low liquid limit silt,low liquid limit clay and nutrients is taken as the research object,and a commonly used soil structure modifier-anionic polyacrylamide is selected as an additive.By means of theoretical analysis,laboratory test and mathematical statistics analysis,the influence law and improvement mechanism of clay and polyacrylamide content on the water physical properties of plant pore matrix soil are studied by changing soil ratio and polyacrylamide content,and good results are obtained in engineering application.The research results of this thesis provide a scientific basis for the improvement of the water physical properties of the planting pore matrix soil(hereinafter referred to as " Planting hole matrix soil ")by clay and polyacrylamide,and have important engineering practical significance for improving the ecological environment restoration effect of the high and steep rock slope in the north.The main research contents and conclusions of this thesis are as following:(1)The effects of clay and polyacrylamide content on the water physical properties of plant pore matrix soil were studied and revealed:With the increase of clay and polyacrylamide content,the permeability and water holding capacity of the matrix soil increased first and then decreased,and then increased again and decreased again.The relationship was in accordance with the binary quadratic equation.When the clay mass percentage content is constant and only the polyacryl amide content is changed,the water physical properties of the matrix soil are better when the polyacrylamide content is 0.025%～0.05%.When the mass perc entage of polyacrylamide is constant and only the clay content is changed,the permeability of the planting hole matrix soil decreases rapidly first and then de creases slowly with the increase of the clay content.The permeability coefficie nt is negatively correlated with the clay content in a power function.The wate r holding capacity of the planting hole matrix soil increases rapidly first and t hen increases slowly with the increase of the clay content.The saturated water holding capacity and capillary water holding capacity are positively correlated with the clay content in an exponential function.The water retention of the planting pore matrix soil has no obvious rule with the change of clay and polyacrylamide content.However,when the clay content is 12.1%and the polyacrylamide content is 0.05%,the water content attenuation rate of the planting pore matrix soil is lower and the water retention is better.(2)The formation mechanism of aggregates and the improvement mechanism of soil water physical properties were studied and revealed.The results showed that:Soil particles first form micro-aggregates under the cementation of clay and polyacrylamide,and micro-aggregates further form multi-stage composite aggregates under the cementation of clay and polyacrylamide.When the clay content is less than 12% and the polyacrylamide content is less than0.025%,the aggregate content in the soil is low,the number of intergranular pores is large,the diameter is large,the number of intragranular pores is small,the permeability of the soil is good,and the water holding capacity and water holding capacity are poor.When the clay content was 12% ～ 14% and the polyacrylamide content was 0.025%～ 0.05%,the content of aggregates with a particle size of 10～0.25 mm in the planting soil was higher,and the water physical properties of the planting soil were better.When the clay content is greater than 14% and the polyacrylamide content is greater than 0.05%,the content of large aggregates with particle size >10mm in the planting soil is extremely high,the number of intergranular pores is small and the diameter is small,the number of intragranular pores is large and the diameter is large,and the permeability and water holding capacity of the planting soil are poor.Due to the layered structure formed in the planting pores after the cementation of aggregates with soil particles and polyacrylamide,the water holding capacity of the planting soil is better.(3)According to the growth habit of drought-tolerant plant bermudagrass and based on the above research results,the best planting soil with better water physical properties was screened.Under the condition of planting bermudagrass,through the comparison of plant growth status and drought stress test with the matrix soil commonly used in the plant hole greening project,it was found that when the clay content was 12%～14% and the polyacrylamide content was 0.025%～0.05%,the water physical properties of the planting soil were better and could effectively improve the germination rate and survival rate of bermudagrass.