Reproduction of stresses induced by traffic load to estimate ground settlement in soil element tests


Cracks and ruts (wheel tracks) on a road surface have become a big problem because loading against pavement is increasing through increases of traffic density and size of vehicles. These damages might be caused when bearing capacity of granular materials in roadbed and subgrade are insufficient. However, there is not enough data concerning deformation of the granular materials under the pavement.
This study was focused on the soil element deformed by the traffic load. For the purpose of reproduction of stresses induced by the traffic load, the hollow cylindrical torsional shear apparatus and its testing method were constructed with some improvements.
The traffic load was applied to the two types of the specimens, which are consolidated isotopically and anisotropically (K0 consolidation). The traffic load was reproduced with control of axial, lateral, and torsional stresses. The apparatus and the method were improved the following two points. First, the data logger was changed. The old data logger can obtain only one data per one second. That is too slow reading to achieve quick loading control. Then, the slow loading, which took long time for experiments, was necessary to obtain accurate stresses with motor control. Then, new data logger was selected to be readable once per 0.1 seconds. Second, booster of air pressure regulator was set in the apparatus because volume of the triaxial cell was so large that time lag occurred between the pressure applied and the reading of pressure in the cell.
As a result, a good agreement was achieved between calculated stresses and measured stresses for traffic loading. In comparison of the specimens between isotropic consolidation and anisotropic consolidation, larger increase of pore water pressure was observed in anisotropically consolidated specimen. However, the increased pore water pressure gradually decreased after about 600 cycles. Although vertical strain observed was very small in the isotropically consolidated specimen, larger vertical strain was observed and gradually increased even after 1000 cycles in the anisotropically consolidated specimen.

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