Experimental Study On Bearing Charateristic Of CFG-Pile Composite Foundation Under Embankment Loading

High-speed railway construction is developing rapidly in our contry. CFG pile composite foundation is widely applied in high-speed railway subgrade for its high bearing capacity, small settlement, widespread applicable scope, fast construction speed, easy quality control, low project cost and so on. The theory system and design method of CFG pile composite foundation under rigid foundation is relatively consummate, and used to direct practice effectively. Relatively,that of CFG pile composite foundation under flexible foundation(subgrade for example) is immature now, and need further research.Field tests were taken out in wu-guang high-speed railway. Data were tested such as lateral displacement of foundation under toe of side slope, foundation settlement, foundation pressure, bar tension,pile strain and so on. Based on the data, bearing characteristics of CFG pile composite foundation were analyzed under embankment load. The main conclusions are as follows:(1)Pile cap set upon pile top can effectively decrease stress on pile top, bar tension on pile top, settlement difference between pile and soil and pile penetration into cushion.In filed tests, lm diameter pile caps were set partly. After setting pile caps, final test data indicate that:â‘ when pile spacing is 2.0m, stress on pile top was decreased by 80.8%, bar tension on pile top by 63.1%;â‘¡when pile spacing is 2.5m, stress on pile top was decreased by 37.2%, settlement difference by 41.9%;â‘¢when pile spacing is 3.0m,stress on pile top was decreased by 69.5%,bar tension on pile top by 73.2%, settlement difference by 83.5%, and lateral displacement under toe of side slope by 63.3%.(2)Coverage rate of pile cap influences bar tension on pile top. With the increase of coverage rate, bar tension on pile top and difference between bar tension on pile top and that on inter-pile soil decreases,. The maximum bar tension emerges on pile top not inter-pile soil.(3)The development degree of soil arching correlates closely to settlement difference between pile and soil. Date show that the larger the settlement difference, the larger the pile-soil loading ratio, and when settlement difference keep stable or increase slowly, the change of pile-soil loading ratio is small correspondingly.(4)The pile's lateral friction exert prior to the resistance of pile tip under embankment load. The development degree of pile-tip's resistance relates to the load on pile top. When the load on pile top is small, the later friction undertake mainly the load. With the increase of load on pile top, the resistance of pile tip develops gradually.