Mechanisms of longitudinal cracks along pavement shoulder in ...

laboratory tests as shown in Figure 6. The dryingpath was chosen since it was the evaporation processthat was to be simulated. The saturated permeability,k s , was determined for undisturbed sample (38mmdiameter) using the constant head method in a triaxialapparatus. As for the hydraulic properties ofpavement surface materials (i.e. base, subbase andsand cushion), the parameters were assumed basedon the particle size distribution of crushed rock subbaseas well as the void ratio observed in the fieldusing Arya & Paris (1982) approach. The permeabilityvariations with suction for all materials were estimatedbased on Jackson (1972) approach as shownin Figure 9b.from the drying test which corresponds to the inverseof slope in Figure 6a. It should also be notedthat for the suction range of zero to 2000 kPa, thesoil is still nearly fully saturated (Sr >90%) (seeFigure 6). Thus, the soil remained nearly saturatedfor most of the drying path obtained from the seepageanalysis. In such case, the principle of effectivestress and the expression H=E/(1-2ν) would stillhold true. The value of Young’s modulus, E is thencalculated based on this expression. Since no totalvertical stress change was imposed in this analysis,the conventional characterization of the Young’smodulus using triaxial tests was not relevant and notused here.Volumetric water contentq = 0q = 5E-5 m/daya)k (m/sec)0.40.35a)0.30.25Clay-Subgrade0.2Pavement - Crushed rock0.150.10.0500.01 0.1 1 10 100 1000 10000 100000Suction, kPa0.01 0.1 1 10 100 1000 10000 1000001.E-021.E-04Clay Subgrade1.E-061.E-08Pavement-Crushed rock1.E-101.E-12b)1.E-141.E-161.E-18Section-1b)Suction,kPaFigure 9. SWCC and Permeability functions used in the analysisA transient analysis was performed with upwardflux rate of 5E-5 m/day imposed on the slope sidebut not on the road top surface where no flow conditionwas prescribed. The initial pore water pressurecondition is hydrostatic but assuming a maximumsuction of 10kPa within the subgrade zone aboveground water. The finite element mesh and the resultantpore water pressure contour after 150 days ofevaporation are shown in Figure 10. The suction inclay subgrade increased to about 150 kPa while inthe pavement material the suction appeared to increaseto about 1,500 kPa due to the high contrast inthe SWCC of the two materials.Fredlund & Rahardjo (1993) proposed a simplifiedelastic equation for incremental stress-strain relationship,accounting for change in suction asshown in Equation 3 (Geo-slope international,2008). The modulus with respect to suction, H, usedhere was obtained from drying test results as shownin Figure 6a using the Equation 4. Figure 11 showsthe variation of secant H with suction as obtainedElevation, mDay zeroDay 150-2000 -1500 -1000 -500 0Pore water pressure, kPa13.512.511.510.510Figure 10. a) Finite Element Mesh; b) Pore-water pressure contour(unit in kPa) after 150 day of drying; c) Pore water pressuredistribution at the shoulder edge (Section-1) from numericalseepage simulation at day zero and day 150c)14131211703