Investigation of asphalt pavement failure due to sub-base and subgrade soil properties: a case study of kemmise – dessie road

Abstract

In this study an attempt was made to investigate the causes of failure due to sub base and subgrade soil properties and remedial measures of damaged pavement. The study focused on performing laboratory tests, taking representative pavement material samples (i.e sub-base and selected fill) from different portions of the road and making the necessary laboratory tests on the collected samples. Additional natural subgrade samples from left and right hand side of the road were also taken for laboratory testing. The case study road pavement was damaged in different stations were seen during field observation. From field investigation in the study area was observed several type of pavement damaged such as; Raveled, transverse cracked, patched, differential settlement/depression, rutting, shoved/corrugation, and potholes/debonding layers of damaged. To find out the real cause of pavement damaged related to soil pavement layer properties was conduct different laboratory test. Such as; sieve analysis (Wet method) to check the soil layer grain size distribution, Atterberg limit (LL and PL test) to find out the plasticity index of their soil, Compaction test (Modified) to get Maximum Dry Density and Optimum Moisture Content of the soil and finally California Bearing Ratio test to check the soil strength and stability. The laboratory results showed that the soil materials used along the road have high percentage clayey material for half of the natural subgrade soil sample (rated as fair to poor materials for road use) and low percentages of clayey and silt/gravel/sand materials of sub-base and selected fill soil samples. The OMC are almost high for all the soil samples the exception of few samples. The MDD values were ranged from 1.33 kg/m³ to 2.25 kg/m³ for the soil materials. The Plasticity Indices and Liquid limits are very high for all Sub-base, selected fill and natural subgrade soil samples with the exception of few samples. Most of CBR values for the selected fill soil materials almost meet specification requirements while that of Sub-base and natural Subgrade soil - materials almost did not meet the specification requirements with the exception of few samples. Conclusively, the pavement failure may necessarily be due to weak/ poor soil pavement layer performance in the different failed location. Finally, a different remedial measure (i.e Patching, Sealing, Digging out and replace good soil and structural or non-structural overlay) was made with respect to their different type of pavement damaged in the study road.