Experimental Study On Permeability And Influencing Factors Of Calcareous Sand

The groundwater,which is stored in the sand and gravel of the coral island reef,supported on the seawater,is collected by rainfall infiltration,and gradually weakened from the bottom to the top due to the density difference,is an important resource to support and maintain the island vegetation ecosystem.Permeability of reef sand is one of the important factors affecting the shape and reserves of freshwater bodies,and permeability is often affected by factors such as the shape of reef sand particles,the composition of concrete gradation,and porosity.In order to promote the rapid growth of plants on coral reef sands with irregular particle shape,wide concrete gradation,and loose salt,the red clay of cultivated soil is often used to provide early plant nutrition,which indirectly changes the permeability of the reef sand.Considering the important influence of reef sand permeability on the form and reserve of ground freshwater,the paper carried out permeation tests and analysis of morphological characteristics,coarse particle content and cultivated red clay content around reef sand permeability.The main conclusions are as follows:（1）after reef sand is mixed with cultivated red clay,its hydraulic conductivity decreases with the increase of cultivated red clay content and relative compaction,which has a negative correlation;the fitting formula of hydraulic conductivity and cultivated red clay content approximately obeys a quadratic function,and the relative compaction is approximately linearly negatively correlated.When the content of cultivated red clay is low,relative compaction is the main factor affecting hydraulic conductivity;when the content of cultivated red clay is high,the content of cultivated red clay is the main factor affecting hydraulic conductivity.Based on the test results,the Amer and Liu Jie hydraulic conductivity estimation models are improved.The improved model can be directly used to predict the hydraulic conductivity of calcareous sand-clay mixed soils.（2）the impact of coarse particle content on the hydraulic conductivity of reef sand has an inflection point.When the coarse particle content is less than the inflection point,the hydraulic conductivity of the reef sand decreases with the increase of the coarse particle content.When the coarse particle content exceeds the inflection point,the hydraulic conductivity increases with the increase of the coarse particle content.The penetration test also found that hydraulic conductivity was negatively correlated with coefficient of curvature,and positively correlated with coefficient of nonuniformity,F_L,d₁₀,d₃₀,and d₅₀.based on this,a hydraulic conductivity estimation model including particle shape factors was established.（3）for test materials with the same particle size and different morphological characteristics,the hydraulic conductivity increases with the increase of roundness and spherity,and decreases with the increase of concavity and aspect ratio;concrete gradation of calcareous sand hydraulic conductivity is positively correlated with concavity,spherity and roundness,and negatively correlated with concavity.The impact of particle size on permeability is greater than the impact of surface roughness（concavity,concavity）on permeability,and it is also greater than the impact of other topography parameters on hydraulic conductivity.The correlation between surface roughness and hydraulic conductivity is significant,and it is a key factor that cannot be ignored in terms of permeability.In addition,irregular particle shapes can reduce seepage failure.（4）the indoor experiment combined with the VG and Gardner models,theoretically deduced the conversion relationship between hydraulic conductivity and specific yield,and concluded that specific yield is positively correlated with matric suction.With reference to the published calcareous sand hydraulic conductivity and specific yield data,combined with laboratory tests and data analysis,a conversion formula for hydraulic conductivity and specific yield was established,and this formula reflects a positive correlation between hydraulic conductivity and specific yield.