Study On The Permanent Deformation Prediction Model Of Sand Through Tests And Simulations

The paper is supported by National Natural Science Foundation Project (No.50608007), Western Transportation construction Science and Technology Project of Ministry of Communications(No.2004 318 000 04) and China's postdoctoral Foundation Project (No.20060400673) .Rutting is one of the most common distresses of asphalt pavement which affects the comfort and safety of vehicle driving. Foreign asphalt pavement design uses two methods to control the excess rutting of pavement. One is to control the compressive strain on the top of subgrade be less than the allowable values. The other is to compute the rutting on the pavement surface through layer wise summation method. Both of the methods need subgrade soils permanent deformation prediction model.The sand permanent deformation test scheme was developed by referring to foreign subgrade soils permanent deformation and resilient modulus test scheme and Chinese regulations of compactness and moisture content for subgrade soils. The diameter and height of specimen was 100 mm and 200 mm respectively; the compactness was 91% and 96%, and the moisture content was 105%, 110% and 120% of OMC; the type of loading was haversine, the frequency was 1 HZ, the loading time was 0.2s and the interval time was 0.8s, he number of load applications was10000; the confining pressure was 28 kPa, the deviator stress was28 kPa, 48 kPa and 69 kPa.Repeated load triaxial tests were conducted to sand on a universal testing machine-100 (UTM-100).The permanent deformation developmental curves of sand were got, the basic relationship between the plastic strain and the loading times was found, the regression formula between the coefficients in the models and moisture content and resilient modulus were found with the least square method, and reliability analysis was conducted to the regression formula above. When the loading times were 10000, the minimum and maximum of the relative difference between the measured permanent deformation and the calculated permanent deformation from the existing model was 52% and 376% respectively; the minimum and average of the square of the correlative coefficient of the regression formula of the coefficients in the models was 0.31 and 0.41 respectively which were greater than the critical value of 0.28; and the square of the correlative coefficient between the calculated and measured permanent deformation was as high as 0.99. Results show that the regression formula between the coefficients in the existing models and moisture content or resilient modulus can not be used directly; the permanent deformation prediction model for sand founded has high reliability.At last, the repeated load triaxial tests to sand were simulated by the finite element software ABAQUS and a 2D finite element model was adopted. Extended Drunker-Prager model was used to sand for the high nonlinear characteristics of the constitutive relation of sand. Results showed that the permanent deformation curve from simulation was similar with that from the repeated load triaxial tests.