Experimental study on bearing characteristics of micro steel tube piles in loess fill foundation

The researches on the performance of micro steel tube piles for the loess fill foundation are very scarce. Based on a practical reinforcement and slant rectification project, three micro steel tube piles are used as the test piles in the loess fill site. The single-pile static load tests with concrete strain gauges arranged on concrete of test piles are performed. The results show that: (1) In some cases, especially in the narrow construction site under complicated engineering conditions, the micro steel tube pile can be used for reinforcement and slant rectification of foundation of high load-support and has higher bearing capacity. (2) The Q-s curve of the micro steel tube piles slowly changes in loess fill site. Under the maximum load, there is no obvious downward bending section. (3) The bearing capacity of micro steel pipe piles in the loess fill foundation is between the material damage and the unstable failure, about 62% of the material damage and 1.76 times the unstable failure. The settlement caused by pile deflection is the uppermost reason for the failure of the test piles. (4) When defining the vertical ultimate bearing capacity of single pile of the micro steel tube piles 30~40 meters in length in loess fill foundation, it is recommended to combine the Q-s curve and the s-lgt curve, and to consider the settlement value of pile top, and it is more reasonable.