Development of prestressed geotextile-reinforced soil

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Since late 1980's, geotextile-reinforced soil method has been widely used for important structures as reraining walls and bridge abutments for reilways or highways in Jpana, resulting from its cost-performance ratio superior to that of conventional method using reinforced concrete (RC) structures supported by pile foundations. To make the new method spread more widely, however, it is necessary to make reinforced soil structures much stiffer against vertical compressive load and to give them high stability and stiffness not significantly lower than those of RC structures. For that purpose, a new method called 'preloaded and prestressed (PLPS) reinforced soil method' was invented. In the method, a well compacted geotextile-reinforced soil embankment using well graded gravel as the backfill is vertically compressed on its reinforced area by using several tie rods. First, the reinforced backfill is preloaded at the load level about twice as large as that of the design load to be deformed b … More y creep. Second, the backfill is unloaded to the load level about the same as the design load. Finally the top ends of the tie rods are fixed to the reaction block on the top of the backfill to make the system in a prestressed condition. The structure is used as a bridge abutment or pier under that condition.In this study, loading tests and detailed measurements were performed on a full scale model embankment and a prototype railway bridge pier, which were constructed by the PLPS reinforced soil method. In addition, large scale triaxial compression teats were preformed on the fill materials (well graded gravels). The feasibility and mechanisms were examined based on the results, and the method for quantitative prediction of the deformation and the design method for PLPS reinforced soil structures were developed. The major conclusions are as follows.a) Large prcload can be applied because the soil is reinforced. The preloading makes the soil nearly elastic and stiff. In addition, preloading on the soil introduces tensile prestress in the geptextile arranged horizontally, which confines the backfill in the horizontal direction.b) High vettical prestress gives the backfill higher, vertical and compressive stress condition, therefore the soil shows higher stiffness against vertical load.c) Sufficinet creep deformation which occurs during preloading results in a suppression both of the creep deformation and the decrease in the tie rod tension when a vertical load lower than the preload level is applied.d) When vertical compressive load is applied on top of the structure, the amount of increase in the load which works on the backfill decrease because the tie rod tension decreases by compression of the backfill. Less