LE LONG

Estimation of settlement of clayey and sandy ground induced by traffic load using soil element test

HIROFUMI TOYOTA

Cracks and ruts (wheel tracks) on a road surface have become an important problem because loading against pavement is becoming larger through increases of traffic density and size of vehicles. It is important that we grasp mechanism of road surface damages in order to attain the long lifetime of asphalt pavement. These damages are sometimes caused by deformation of the granular materials when bearing capacities of granular materials in roadbed and subgrade are insufficient. However, there is not enough data concerning them.

This study was focused on the soil element deformed by the traffic load. Soil element tests considering a reproduced traffic load was carried out using a hollow cylindrical torsional shear apparatus. From the results obtained, progresses of cohesive and sand ground settlements were estimated. Here, the traffic loading was applied to the specimens under undrained conditions for cohesive soil and under drained conditioned for sand.

As a result, vertical strain generated were different by the magnitude of loadings. They are roughly divided into two cases that are large deformation case (failure) and limited deformation case (no failure). In the failure case, larger progress of vertical strain was observed in relatively small number of cycles. In no failure case, progress of vertical strain was dampen with an increased number of cycles. The traffic load was reproduced with control of combination of three stresses; those are axial, lateral, and shear (torsional) stresses. Large difference in progress of vertical strain was observed by combination of three stresses. Therefore, vertical strain was significantly increased when axial stress and torsional stress are combined and applied to the specimen.

From the relations between the magnitude of loading and the number of cycles to reach a certain axial strain, a relational expression was obtained where the number of cycles showed the exponential increase when the magnitude of loading decreased. The relations between the magnitude of loading and axial strain at 3000 cycles also indicate exponential increase of vertical strain when the magnitude of loading increased. Moreover, the relations between vertical strain and excess pore water pressure in the cohesive soil demonstrated the same trend independent of the magnitude of loading. Although failure was observed at more than a certain load in the cohesive soil, failure was not observed in the sand even applying the load two times greater than that in the cohesive soil. Therefore, drainage conditions during loading are important factor to estimate ground settlement.