| Longitudinal crack is a common road disease,and temperature is a important factor that effect its formation. In order to Omni-directionally study temperature’s effect on asphalt road longitudinal crack formation and development in cold area, investigation and analysis had done to some highway of longitudinal crack disease in Heilongjiang province. Select the test sections and do investigations on its shallow layer geological and hydrological situation, monitor the temperature on test road subgrade and pavement and deformation and moisture content of subgrade. We could see the internal temperature changes of subgrade based on the monitoring datas, and comparatively analyzed the effect of subgrade’s freeze-thaw deformation on road longitudinal crack formation. Build numerical simulation of layer-structure on the basis of road surface temperature datas, analyze the internal force and displacement caused by temperature changes and the effect of internal force on road longitudinal cracks.Through the investigation we got that development of longitudinal cracks on the road sections was serious, the crack locations were mainly concentrated on the middle ground of the road panel. From monitoring temperature data we could see maximum frozen deep were2.4m, and2.7m and1.4m respectively for road shoulder, driveway and natural foundation of sections in2009～2010, the freeze and thaw of subgrade soil below the pavement plate were earlier than road shoulder. And the entire freeze period of subgrade was longer than thaw period. Water ratio of subgrade soil near the frost line in the freeze period rise along with water migration and accumulation. The water cannot timely discharge in the thaw period afer the melt of the frozen subgrade, which caused water ratio of soil body rise. Through the analysis of variation of subgrade section freezing-thawing region and monitoring of the subgrade deformation we could get that the deformation of subgrade freeze-thaw damaged the mechanical balance of the upper layer, and caused extremum shear and bending moment occuring in the middle of the panel structure or in the vicinity of driveway which prompted a longitudinal crack occurred at that location. Through the simulation of temperature stress of pavement test section structure we could get that the inside of low-temperature period base mainly showed level tensile stresses which decrease from the middle to both ends, and the lower the temperature,the bigger the tensile stress, the maximum value is about0.44MPa in the design temperature range. And in the period of high temperature test section of base structures mainly showed pressure stress, the maximum compressive stress was about0.12Mpa. The maximum tensile stress of base exceeded the minimum value of the range allowed in low temperature winter, resulting in long vertical cracks appear in the section of the road because of low strength. By calculation and simulation we could get that the low temperature construction could efficiently reduce the maximum tensile stress of base at low temperature, and if the molding temperature drop10℃the tensile stress would reduce0.14MPa down to permissible stress; on the condition of1cm wide longitudinal crack run through in the middle of the base site and taking no measures of the direct of paving asphalt pavement, through the simulation and analysis we could get low-temperature tensile stress was much larger than permissible stress value in low temperature, and reflective crack will appear in asphalt surface layer. |
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