In-situ soaking test on composite loess foundation with down-hole dynamic compaction (DDC)
Kong Yang1,2 Ruan Huaining1,2 Huang Xuefeng3,4
1. Key Laboratory of the Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098, China;
2. Jiangsu Research Center for Geotechnical Engineering Technology, Hohai University, Nanjing 210098, China;
3. Lanzhou University of Technology, Lanzhou 730050, China;
4. Logistical Engineering University of PLA, Chongqing 401331, China
Abstract：Due to the fact that less research is focused on the soaking load test in loess area, a 137-day large-scale in-situ soaking test on the composite foundation treated by the down-hole dynamic compaction (DDC) method was carried out in loess area with 36.5m collapsible thickness in Peace Town, Lanzhou City. Several essential testing stages, such as ground humidification on leveled foundation, foundation treatment by the DDC method under different working conditions and field soaking below the cap were carried out in the test. Given the constant pile length, the relation of average compacting coefficient λac and pile spacing L of points between three piles can be represented by the Holliday formula. The time-varying curve of total settlement of concrete tap shows a clear “stair” shape, and the sharply increasing state is related to several collapses of the loess around and under the pile caused by water infiltration. The time-varying curve of total settlement for the concrete tap can be divided into 4 parts, i.e., the rapidly increasing stage, the constant stage, the gradually increasing stage and the tending to steady stage. The inflection point of each stage can be regarded as the characteristic point of the vertical movement study of water. The difference of the growth curve of the settlement at each stage is related to the occurrence of the remnant collapsible settlement. The surface swell around the cap is more obvious than the surface settlement, so, the position and time of the sharply increasing of surface swell point can be used to study the lateral movement of water. The reasonable pile spacing of the DDC method and pile length are suggested as 1.1m and 20m, respectively.
