Experimental Study On Factors Influencing The Specific Yield Of Coral Sand Stratum

The groundwater desalination of islands and reefs plays an important role in promoting the construction of the ecological environment.The analysis of groundwater movement is an important step in the desalination of groundwater of islands and reefs,and specific yield is an important hydrogeological parameter that affects the analysis results of groundwater movement.In this paper,systematic research work was carried out on reef sand specific yield and its influencing factors.Gradation analysis and water content test were carried out on different depth reef sand layer of an reclaimed coral reef island,to grasp the distribution of water content and particle size characteristics.Borehole pumping tests were carried out to understand the characteristics of specific yield in different reef sand formations and the relationship between specific yield and soil particle size grading.The specific gravity of calcareous sand was obtained based on different determination methods,and the suitability of the test method was analyzed;Designed a specific yield test device independently,the specific yield test of the coral sand stratum under a large number of different initial conditions was carried out by changing the water level drawdown,water depth,single grain group size,dry density,solution salinity and material,to obtain the coral sand permeability coefficient and specific yield,analyzing the influence of these factors on specific yield by combining with the measured water content distribution in different parts of the seepage path of coral sand column.PartAn3 D Maxi scanning equipment was used to obtain the size parameters and total surface area of the soil particles of a single particle size group,and quantitative analysis was carried out in conjunction with specific yield.The water release process is decomposed into two water release stages: saturated seepage and unsaturated seepage,and the relationship between specific yield and time in the water release process is studied.The main conclusions are as follows:1.The specific gravity of calcareous sand was determined by the true density meter.The closed porosity of each grain group is different,and the recommended specific gravity value is 2.81.The two field tests calculated that the specific yield value is 0.168 and 0.196 respectively,which match the grain size.The grain size of reef sand stratum could be roughly judged by the water supply value.The grain size of reef sand stratum could be roughly judged by the specific yield.2.The test results of coral sand column under different initial conditions show that: 1)the specific yield of reef sand in the medium density state is smaller than that of medium sand measured by Fetter.As the water level drops or the initial water level is buried deeper,the specific yield of reef sand also increases and gradually tends to a certain value.2)The specific yield of reef sand decreases rapidly with the increase of dry density,and the greater the density,the faster the specific yield decreases;he water release is rapid in the saturated seepage drainage stage,and the water release can reach more than 60% of the total water release;3)The effect of salinity on the specific yield of reef sand is weak.The specific yield first increases and then decreases with the increase of salinity,and reaches the maximum value at the salinity of 20g/Lat the stage of saturated seepage water release;The water release rate is inversely related to the salinity.when the salinity is between 0 and 20g/L,the water release rate changes little.While when the salinity is greater than 20g/L,the impact of salinity on the water release rate increases.4)when the porosity is 0.4662,the specific yield of quartz sandwith a particle size of 0.1-0.25 mm is about twice that of calcareous sand;The water release rate of calcareous sand in the saturated seepage stage is much lower than that of quartz sand,and the calcareous sand and quartz sand are respectively 59.9% and 78.47% of their total water release at the "inflection point" of water release.3.The combined analysis of soil sample particle shape,total surface area parameters of soil column particles obtained by Part An3 D Maxi and specific yield shows that Da,Dp,V,and SA have a positive correlation with the specific yield,and the variation trend is consistent when Da increases in the range of 0.325 ? 2.421 mm,the specific yield increases rapidly when Da is greater than 2.421 mm,the specific yield increases slowly.The specific yield decreases with the increase of the total surface area of soil column particles,and has a good linear relationship with the logarithm of the total surface area.