Analysis And Experimental Investigation Of Mesoscopic Seepage Characteristics Of Pavement And Subgrade Based On Lattice Boltzmann Method

The water damage problem of highway pavement and subgrade is very serious in southern China where is rainy,hot and damp.The most basic problem among all is to obtain the accurate seepage characteristics of pavement and subgrade materials as well as the infiltration rate of pavement surface water,so as to design,construct and maintain the waterproof and drainage structure of pavement and subgrade economically and reasonably.Previous studies were mostly based on macroscopic angle and traditional computational fluid dynamics（CFD）method,but limited studies have used the seepage law based on mesoscopic structure.In this dissertation,the Lattice Boltzmann method（LBM）was first introduced into the design and analysis of the drainage of pavement and subgrade.To begin with,use X-ray CT and Scanning Electron Microscope（SEM）to study mesoscopic structure of different pavement and subgrade materials.Furthermore,employ saturated monophasic flow to simulate and calculate the seepage characteristics of pavement asphalt mixtures and subgrade granite residual soil filler,and then the laboratory tests are carried out to verify.In addition,utilizing the specialty and advantage of LB method,the general characteristics and influence factors of mesoscopic seepage in porous media and crack are further discussed.And then,based on the above research results,the infiltration rates of pavement surface water in the whole structure of pavement and subgrade are analyzed.Finally,according to the in-situ long-term and systematic monitoring of the moisture content within subgrade under different pavement structure and conditions in the rainy area of southern China,the conclusions of the study on the mesoscopic seepage characteristics of pavement and subgrade material are verified.The main works and innovations of this dissertation can be listed as:1.Through indoor molding and field coring,4 typical types of asphalt mixture samples（AC-13C,SMA-13,GAC-16C,OGFC-13）are conducted with X-ray CT technology to study their characteristic parameters of internal void structure,including porosity,void connectivity,void volume,average diameter and curvature of voids,etc.2.Based on the SEM method,the undisturbed samples and the internal void structure parameters（porosity,pore diameter,shape coefficient and fractal box dimension）of a typical subgrade filler-Granite residual soil-are studied.3.The permeability of asphalt mixture is an important index to measure the quality of pavement.However,there are many defects in the present indoor and field seepage test methods.Therefore,a permeability coefficient tester with applicable confining pressure side rubber membrane is developed,whose test theory is rigorous,operation is simple,and results are reliable.4.The X-ray CT images are used to reconstruct the 3-D model of the asphalt mixture,and the Lattice Boltzmann method is used to calculate its permeability coefficients in three directions(k_xx、k_yy、k_zz)and permeability coefficient bias(k_xz、k_yz).5.Based on the SEM image of granite residual soil,the characteristics of mesoscopic pore structure are analyzed,and 3-D reconstruction was carried out by using Quartet Structure Generation Set（QSGS）.In addition,the Lattice Boltzmann is used to study its undisturbed sample and permeability coefficient k_zz(=k_xx=k_yy)under different compaction degree.Finally,the results are compared and analyzed through laboratory tests.6.Lattice Boltzmann method is very convenient for processing the complex boundary conditions.Therefore,the influences of pipe diameter,bending degree and shape coefficient on the seepage characteristics of a single pipeline and the general regularity of 3-D mesoscopic seepage in porous media are discussed.7.The influences of roughness,crack width variation and bending degree on seepage characteristics of pavement and subgrade cracks are studied and the general regularity of mesoscopic seepage in complex cracks is discussed.8.Taking whole pavement and subgrade as the research object,this dissertation deduces the formula for calculating the infiltration rate of pavement water,obtains the accurate calculation method for seepage and drainage amounts of pavement water,and modifies the suggested value of the pavement seepage rate in current drainage specification.9.The subgrade moisture contents under two typical pavements in the rainy area of southern China are long-term monitored in-situ,so the accuracy of the calculation,analysis and test of the seepage characteristics of pavement and subgrade as well as infiltration rate of pavement.It provides valuable reference for the future design and construction of pavement and subgrade drainage.