Study On Fine Particle Migration And Hydrogeological Significance Of Calcareous Sand Reclamation Islands And Reefs

In order to explore the migration law of fine calcareous sand particles in hydraulic fill coral island stratum,a detachable soil column seepage device was designed.The effects of formation gradation,dry density,hydraulic gradient and initial concentration of fine particles on the migration and deposition of fine particles are studied by the laboratory soil column seepage test.The influence of fine particle migration on permeability of different parts of soil column in the process of seepage is studied.The results show that in the process of clear water seepage,under the same water head difference and dry density,the increase range of permeability coefficient is: Gravel > Coarse Sand > medium sand,and the concentration of exudate under stable state is: Medium Sand > Coarse Sand > Gravel sand;when the dry density of each layer is fixed,the greater the seepage speed is,the greater the peak concentration of particles in the exudate is;when the water head difference is fixed,the dry density of each layer is fixed The larger the degree is,the smaller the increase rate of permeability coefficient is,and the smaller the peak value of exudate concentration is;the permeability of most samples in the initial stage of seepage appears a short-term decline phenomenon,because in the configured model soil,a large number of fine particles are not attached to the surface of coarse particles,they will preferentially lose,deposit and block the seepage channel during the seepage process;before and after the comparative test,the upper,middle and lower model soil mass It is found that there are more fine particles in the upper and lower soil mass and the least in the middle soil mass,because the middle soil mass is the sedimentary layer of the upper soil mass,and the lower soil mass lacks the sedimentary layer.In the process of suspension seepage,the fine particles first deposit in the upper part of the three groups of samples and block the seepage channel,resulting in the decrease of the upper permeability coefficient;the larger the particle size of the formation and the smaller the dry density,the easier the fine particles enter the deep part of the formation and change the particle size characteristics of the larger depth,resulting in the decrease of the permeability coefficient of this part;the infiltrated suspended particles are distributed in each position of the soil column However,it is mainly deposited in the upper part,and the fine particles deposited in each layer decrease with the increase of depth.The position of the relative aquiclude which may be formed during the formation of the freshwater lens is analyzed and determined;the minimum time required for the formation of the relative aquiclude is estimated;the design proposal of the aquiclude which is most conducive to the freshwater conservation process of the reclamation coral island is put forward.There are 49 figures,15 tables and 83 references in this paper.