Analysis of Load Transfer Law of Short Pile-Net Composite Foundation for High-Speed Railway

Abstract

Although pile-net composite foundation has been widely used in the construction of high-speed railway, load transfer characteristics of its structural system during the filling of roadbed are seldom studied, so field studies are conducted in the Gan-Long (Ganzhou-Longyan) high-speed railway DK86 + 998.0–DK87 + 191.2 test section, aiming to explore the bearing characteristics of a short pile-net composite foundation over low to medium compressible soil. The study encompasses a field measurement of Earth pressure and pore water pressure which lasted almost two years, and a systematic analysis of variation law of soil pressure between piles and their tops and that of pore pressure in reinforcement zone and retaining layer in medium and low compressibility soil area. The results suggest that the soil in the test section bears the characteristic of a low water content, low porosity ratio, and high liquid limit, with compression factor being approximately 0.25, and test values of the natural soil pressure and the lateral distribution are close to the theoretical values. Soil pressure at the top of the piles is higher than that between the piles by approximately 2.4 times because of the differences in pile-net rigidity. Besides, the soil pressure of the pile-net composite foundation follows the pattern of “jagged” in the transverse direction of the roadbed. The filling load of the composite foundation soil arch is 80 kPa and the composite foundation reaction coefficient is 6.4 kN/m3 when the filling is stable. The pile-soil stress ratio at the shoulder and the center of the line is 3.2 and 2.8, respectively. The change of the hole pressure at the pile end point is larger than that at the reinforcement area, and the side verification short pile can effectively transmit the additional stress of the upper part to the pile end soil layer.