Study On The Characteristics And Contact Parameters Of Ecological Detention Pond Filler Improved By Biochar

With the influence of global climate change and human activities,the occurrence of ecological damage and extreme rainfall events are gradually increasing in hilly mountain areas.The hilly mountain area in our country is large,and the terrain is complex.It has the problem of many potential hazards and great difficulty in defense.Flood control is becoming a difficult and weak point in the hilly mountains,so exploring effective flood control engineering measures has become an urgent need for it.Traditional flood control projects are characterized by large project scale,high construction costs,and extensive floor space.They have high requirements for engineering construction conditions and site location,and have the drawback of not being able to handle and control rainwater runoff at the source.The ecological detention pond is a new type of flood control facility that has a good effect on reducing rainwater runoff from the source.Under the background of new rural construction,it is necessary to explore the ecological retention pond suitable for the construction of the hilly mountainous area,to realize flood control and improve agricultural production.At present,ecological detention pond is widely used in urban stormwater treatment,but there are still some problems,such as poor mechanical properties,heavy nutrient loss,and single effect.Therefore,based on the existing problems of the ecological detention pond,this paper conducts research from the perspective of flood control and plant cultivation in the hilly mountains.To obtain the optimum improved filler and contact parameters for the ecological retention pond,various characteristics of ecological retention pond filler improved by biochar were investigated in this paper.The main research contents and results are as follows:(1)Single application and mixed application of biochar were used in the experiment.The effect of rice husk charcoal and bamboo charcoal on the compression properties of purple soil was studied by the method of labeled consolidation test.The results show that the application of biochar to purple soils reduces the compressibility of the soil and changes it from highly compressive to moderately compressive soil.The soil compaction coefficient of a single application of biochar decreased with increasing biochar content.When the amount of rice husk charcoal and bamboo charcoal applied alone was 7%,the compression coefficient decreased by 82.08%and 83.96%compared to the control group(without biochar),respectively.When the mixture of 4.5%rice husk charcoal and 4.5%bamboo charcoal was applied,the compression coefficient of the improved soil was the lowest,which decreased by 84.91%compared with the control group.(2)The relative application amount of rice husk charcoal,depth of improvement,and layered structure were used as the test factors.The wetting front bottoming time and cumulative infiltration amount were used as test indicators.The infiltration characteristics of ecological detention pond filler improved by biochar were investigated by indoor soil column tests.The results show that the relationship between the wetting front migration distance and the infiltration time of the improved filler follows a power function law.When 7%rice husk charcoal and 2%bamboo charcoal were mixed into the purple soil with a surface depth of 18cm,and only purple soil was filled in the middle and bottom layers,the wet front bottom time of the improved filler was 77 minutes,which was 56.98%less compared to the control group.Its cumulative infiltration was 39.3cm,an increase of 11.97%compared to the control.The Horton model was the most suitable for modeling the water infiltration process,followed by the Kostiakov model,while the Phillip model was not suitable for modeling the process.(3)The Cumulative leakage,cumulative loss of total nitrogen,and cumulative loss of total phosphorus were used as test indicators.The leakage and nutrient loss characteristics of ecological detention pond filler improved by biochar were investigated through orthogonal tests under normal field irrigation and fertilizer application conditions.The optimal combination of improved filler proportions was searched for by combining the extreme difference analysis method,analysis of variance,and the integrated equilibrium method.The results showed that the comprehensive effect of the improved filler was optimal when 4.5%rice husk charcoal and 4.5%bamboo charcoal were mixed into purple soil with a surface layer of 18 cm depth and without biochar applied in the middle and bottom soil layers.At this point,the cumulative leakage of filler was measured to be 1.76L and the cumulative loss of total nitrogen was 48.76mg,an increase of 79.59%and 18.38%respectively compared to the control group.The cumulative loss of total phosphorus was 0.16mg,which was a decrease of 11.11%compared to the control group.It was used as the optimum improved filler for the ecological retention pond.(4)Based on the JKR contact model,the contact parameters of the optimum improved filler for the ecological retention pond were calibrated using the discrete element method,the response surface optimization method,the RealityCapture modeling technique,and image processing techniques through the steepest climb test,the PlackettBurman test and the Box-Behnken test.The results show that the static friction coefficient between rice husk charcoal and steel plate is 0.4,the rolling friction coefficient is 0.175 and the collision recovery coefficient is 0.3;the static friction coefficient between bamboo charcoal and steel plate is 0.425,the rolling friction coefficient is 0.119 and the collision recovery coefficient is 0.4;the static friction coefficient between mixed filler is 0.6,the rolling friction coefficient is 0.051 and the collision recovery coefficient is 0.226;the mixed filler between JKR surface energy is 0.131J·m-2.