Model test research on bearing behavior of pile-net composite foundation on oversized deep soft soil

Based on the foundation treatments of Xiamen-Shenzhen railway Chaoshan station and in-situ distribution of soft soil layers, two laboratory models of pile-net composite foundation with different pile spacings are designed to study the load transfer mechanism, pile load sharing ratio, pile-soil stress ratio and settlement laws. The results show that the axial force of pile shaft increases first down along pile shaft to a certain depth, then gradually reduces. With the increment of pile spacing, the bearing pattern tends to be ending-bearing form; and the neutral point and the position of maximum negative skin friction move down. The pile spacing has obvious effect on pile-soil stress ratio, but minor influence on pile load sharing ratio. The differential settlement of center soil between piles and pile top is smaller for double pile than that of four piles. Tensile strain of geogrid rises gradually as the embankment filling load increasing; tensile strain curve is initially smooth, then steepening gradually; the rising rate of curve is slow at first then becomes fast afterwards.