| The rapid development of human urbanization has stripped away the original vegetation surface layer and replaced it with a large number of "grey" water-proof infrastructure surface.The city underlay layer becomes a piece of dense nearly impermeable "baffle",which becomes the interface to block the rain water from natural infiltration.In addition,the compaction of soil mass by various loads on the upper part of the urban ground destroys the hydraulic channel in the original natural state,and the low-lying areas of the city are easy to form waterlogging in the rainy season.The concept of "sponge city" has been a hot topic of research since it was put forward.Scholars are committed to solving urban problems around the six-character principle of "infiltration,stagnation,storage,cleanness,utilization and discharge",and promote the process of modern urbanization by means of facilities such as permeable pavement.Based on the transformation concept of low impact on the natural environment,we envisage the improvement of soil seepage characteristics,so as to realize the natural infiltration of water amount based on the ability of the environment to some extent.As a green and environmentally friendly porous material,biochar has a variety of organic functional groups attached to its surface(or adsorbable).It has a strong ion exchange capacity and strong water absorption.It is mainly used to absorb harmful gases,absorb heavy metal ions in soil,retain water and fertilizer in crop soil,and adjust soil p H value.Using biochar to improve cohesive soil,the following corresponding results were obtained through the experiment:(1)The effects of biochar on the physical properties of clay such as bulk density,maximum moisture content,liquid and plastic limits and free expans ion rate were studied through geotechnical experiments.The influence of biochar on particle gradation and specific surface area of viscous soil was investigated with the laser particle size analyzer,and it was found that biochar could optimize partic le gradation and increase permeable channel to some extent.All the above results are the basis for the follow-up experiments.(2)Through indoor soil column model test,it was found that biochar had a significant effect on the early infiltration rate and cumulative infiltration amount of soil,and could accelerate the early infiltration rate of soil,and had a greater effect on red and ordinary clay than expansive soil.In addition,in terms of cumulative infiltration amount,it had the greatest influence on ordinary clay and was positively correlated with biochar content.Group C(30%)was 63.8% higher than group CK(0).Red clay was next,and also positively correlated with biochar content.Group C(30%)was 33.4% higher than group CK(0).(3)By using the variable head method,it was found that biochar had a significant effect on the saturated permeability coeffic ients of the three soils,and the overall trend increased with the increase of biochar content.The influence of red and ordinary c lay was greater,with a maximum increase of 343.99%.The variation law of expansive soil is complicated.(4)The soil column water holding test showed that the maximum soil water holding capacity of biochar changed significantly.With the increase of biochar content,the maximum soil water holding capacity of all three types decreased first and then increased.Heat lamp was used to simulate sunshine to conduct evaporation test on soil samples at high temperature.It was found that most of the results were contrary to the assumption.In high temperature environment,biochar did not play a role in water retention,but accelerated the evaporation rate of water.Moreover,the data obtained are relatively discrete,but the 10% content has an obvious "water-lock" effect on ordinary clay. |
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