Evolution of Soil Arching in Geosynthetic-Reinforced Pile-Supported Embankment of a High-Speed Railway under Long-Term Train Traffic Loading and Excessive Subsoil Settlement

Soil arching formed in geosynthetic-reinforced pile-supported (GRPS) embankments of high-speed railways plays an important role in transferring the forces within the embankments. In most cases of notable settlements and track irregularity of high-speed railways in China, excessive subsoil settlements and induced degradation of soil arching under long-term moving train loads are considered to be the primary causes. However, the evolution of soil arching remains unclear to date. Herein, a full-scale model of typical GRPS embankment of high-speed railways with dimensions of 5.5 (length)x15 (width)x6 m (height) was established in the laboratory. Firstly, pile efficacy was evaluated during model preparation, which increased with the filling height and stabilized at 89%, due to the normal differential settlement between piles and subsoil. Afterward, the evolution of soil arching under moving train loads applied for up to 500,000 carriages with axle loads ranging from 17 to 25 tons and speeds from 50 to 360 km/h was studied, followed by another comparative condition with excessive differential settlements up to 90 mm between piles and subsoil. The dynamic testing results indicated that the dynamic pile efficacy under normal conditions remained consistent regardless of variations in train speed and axle load. Nevertheless, it decreased by 13.4% under the excessive differential settlement condition when the speed was higher than 150 km/h but was nearly unchanged under variations in only axle load from 17 to 40 tons. Besides, the height of outer soil arching increased from 1.3 to 1.7 m as the differential settlement reached 90 mm, presenting a notable variation of arching shape. Two empirical formulas considering various train speeds and axle loads were then proposed to describe the dynamic soil stress and pile efficacy on the surface of piled system. From the long-term loading tests, both the static and dynamic pile efficacy in the normal case increased by 0.9% and 2.8%, respectively, while those in the case with excessive differential settlement decreased by 4.8% and 3.9%, respectively. These results would contribute to the long-term performance evaluation of soil arching within GRPS embankment of high-speed railways, especially above soft soil foundations.