| Tibet is located in a high-altitude area with a large number of glaciers,complex geological structure and uneven distribution of rainfall in space and time.Natural disasters caused by rainfall,such as mudslides,landslides and landslides,have great destructive power.Infiltration damage is the main factor causing geological disasters,so it is of great significance to study the seepage characteristics and permeability mechanism of soils and calculation methods.Coarse-grained soil is widely used as a high-rise building filler,dam(shell)material,anti-seepage material,etc.for roads,slope engineering,earth and rockfill dam,water conservancy project because of its strong water permeability,low impermeability and small settlement deformation.At the same time,there are many engineering safety problems caused by penetration.The correct choice of permeability parameters and the rationality of the control design have important scientific value for the safety and stability of the project.Combined with the soil conditions in Tibet,the research on the saturated permeability of coarse-grained soil and the unsaturated infiltration of rainfall are carried out.Reliable empirical formula of permeability coefficient or theoretical theory of seepage mechanism can not only provide a strong reference for the actual instability of rock and soil engineering,but also provide a theoretical basis for geological disasters caused by osmotic damage in southeastern Tibet.In this paper,a saturated infiltration test device and a rainfall infiltration test device were designed and manufactured to study the seepage of coarse soil,the infiltration tests of coarse soil with different single particle size groups and two gradations of coarse soil with saturated state,and rainfall infiltration test under continuous rainfall and intermittent rainfall,and the following conclusions were obtained:(1)The results of the permeability test of coarse-grained soils of six single-size groups show that the seepage velocity v measured by the permeability test of each single-particle group is linear with the hydraulic gradient J,which is consistent with Darcy’s law.The permeability coefficient increases with the increase of the particle size.The permeability coefficient of the smallest particle size is different from the permeability coefficient of the largest particle size by 4 orders of magnitude.The particle size of the soil particles in the soil is an important factor affecting the permeability coefficient.(2)According to the mesoscopic mechanism of laminar flow head loss,a calculation model of permeability coefficient is established,and the superposition coefficient is introduced.The calculation formula of permeability coefficient based on porosity and equivalent particle size is derived.Through 6 kinds of single particle group of coarse grained soil permeability test,fitting the composite coefficient of empirical formula,used for calculating the coefficient of permeability of coarse-grained soil.(3)The permeability test of two-stage coarse-grained soil shows that the permeability coefficient decreases with the increase of the percentage of filler particles,and the permeability coefficient increases with the increase of the particle size of the filler particles.The correlation of permeability coefficient with porosity,equivalent particle size and percentage of filled particles was analyzed.It was found that these three parameters have a good correlation with the permeability coefficient.And through the regression analysis,the relationship between the permeability coefficient and the percentage of filled particles is obtained.(4)The results of rainfall infiltration infiltration test show that under the two rainfall conditions,the changes of mass water content,matrix suction,pressure and other parameters are the same,and the fluctuation of air pressure under intermittent multiple rainfall conditions is more obvious.Under the condition of different rainfall intensity,with the increase of rainfall intensity,the faster the wetting peak depth increases,the faster the mass water content increases,the matrix suction changes with the change of water content.Under the condition of different particle sizes,with the increase of particle size,the diameter of the pore channel larger,easier for rainwater infiltration,moist peak shorter the time required to reach the same depth,the interfacial tension of two phase flow of water is not obvious,the less pressure fluctuation change. |
