Investigation On Permeability Of Sands With Different Particle Size

Sand is a type of cohesionless soil in which the mass of gravel is less than50%ofthe total mass. Its particle size ranges from0.075mm to2mm. Sand soils are widelydistributed in river and the desert region. The main component of natural sand is sandgrains of different particle size and a small amount of silt and clay. The granularcomposition makes sand soil has a larger compression modulus and higher shearstrength. In the aspect of structure, compared to other soil, sand has a smaller specificsurface area and larger void size, which leads to good permeability of it. Owing to thegood mechanical properties and hydraulic performance, sand soils are used in manyengineering fields, such as building engineering and hydraulic engineering. However,many negative effects also come with its good permeability in practical engineeringprojects, such as piping and quicksand in the foundation excavation process, andseepage stability problem in the design of earth-rock dam, and so on. Therefore,investigations on the permeability of sand are of great significance.Domestic and foreign researchers have studied a lot about the permeability ofcohesionless soil. The influencing factors of permeability were discussed in the aspectsof engineering practice, experimental study and theoretical analysis. Theoretical orempirical formulas were derived for calculating the permeability of cohesionless soil.The most popular of them are the Kozeny–Carman formula and the Liu Jie formulafrom Nanjing Hydraulic Research Institute. All of these studies are of great importancefor both development of seepage and permeability research and engineering practice.Based on previous investigations, the theoretical formula is derived based on thetraditional percolation model in this paper. After that, the influencing factors of the permeability of sand soil with single particle size fractions were investigated. Theauthor firstly takes the sand soil with single particle size fractions as the object to studythe related influencing factors by constant head permeability tests. Based on this,influence of gradation on the permeability of multi-particle-size sand soil wasinvestigated to extend the results from single particle size fraction to natural sand.Linear regression analysis was carried out on the test results, and a new permeabilitymodel is developed considering all of the factors for the engineering practice. The mainconclusions are as follows:(1) As for the single-particle-size sand soil, the coefficient of permeabilityincreases linearly with the increase in the porosity and square of average particle size.The linear correlation for the two parameters is good.(2) As for the natural sand soil, four factors have certain influence on thecoefficient of permeability, which are the equivalent particle size, porosity, curvaturecoefficient, and nonuniform coefficient. Among these four factors, influence of theequivalent particle size is more significance, the change in which leads to change inorder of magnitude of the coefficient of permeability. All of the four parameters havegood linear correlation with the coefficient of permeability.(3) An empirical equation considering all of the four factors was developed forengineering practice and the compounding sand soil of specific permeability by linearregression analysis. The empirical equation is:K=C·(n~3)/((1-n)~2)·d_a~2C_u·C_c...