Study On The Depth Of Subgrade Work Area Of Grade Road Under Excess Traffic Load

Subgrade and foundation are the basis of pavement structure. In the plain areas, because of the serious constraints of land resources, generally low elevation of the road subgrade becomes common with the subgrade fill of 1m or so, or even lower. Recently, with increasing overloading of vehicles, heavy road traffic level has been becoming increasingly serious.In the traditional structure and the existing pavement subgrade compaction standards, when overloading the subgrade work area is 3 to 5 meters below the natural foundation, which makes much of foundation work in the scope of subgrade work area. After repeated traffic load, a large rutting and non-uniform settlement will occur. Moreover, the pavement layer is thinner and the premature damage due to the deficient subgrade bearing is more serious. Therefore, it is very important and realistic for the pavement engineering to investigate the subgrade work area depth and its impact factors and the effect on the pavement structure.Based on one grade highway rebuilding in the south of Shandong province, this research analyzed the mechanism of damage in this district by in-place survey and inspect and in-lab experiments. One new method to divide the subgrade work area is proposed from the viewpoint of that subgrade material is one elastic-plastic material. This research analyzed the subgrade work area depth and accumulative settlement at different load axle in the present subgrade compaction standards and traditional pavement structure respectively. Also this research investigated the effect of different subgrade treatment methods on the subgrade work area depth and subgrade accumulative settlement and some measures are suggested on how to reduce the subgrade work area depth and accumulative settlement and increase the subgrade bearing of foundation.This research suggests that in the condition of heavy traffic,before the subgrade and foundation were treated, the subgrade work area depth is over 4m and a large scope below the foundation is in the subgrade work area; when the accumulative subgrade settlement is more than 30cm, rutting will occurs easily, resulting in cracking of the pavement structure which shows that the bearing of subgrade is not enough seriously. After compaction of natural foundation and treatment of subgrade by limestone, the subgrade work area depth and accumulative settlement decrease and the pavement structure improves greatly, which show that the treatment method is satisfactory and feasible.