| With the planning of national road network and the construction of Dawan District in Guangdong,Hong Kong and Macao,a large number of water bridges have been constructed in the Pearl River Delta.During the construction of pile foundation of water bridge,because of the instability of soil,it is often necessary to place steel barrel to stabilize the bored hole wall.It forms a composite pile foundation with the pile body.Concrete filled steel tube composite pile has better mechanical characteristics than reinforced concrete pile.Under the same working conditions,the safety reserve of composite pile is much higher than that of reinforced concrete pile.In practical application,steel sheath is usually regarded as a basic safety factor,which is obviously unreasonable design.Based on the field practice of Guangzhongjiang Expressway,through field investigation,centrifugal model test and numerical simulation calculation,the transverse and axial bearing characteristics of concrete filled steel tubular composite piles are studied in this paper.The results are as follows:(1)Compared with ordinary reinforced concrete piles,the transverse and axial ultimate bearing capacity of concrete filled steel tubular piles increases slightly.The composite pile foundation with steel tube buried depth greater than 12 cm(prototype is 12 m)is defined as concrete filled steel tubular composite pile.(2)Steel pipe has changed the distribution law of soil resistance along pile length.With the increase of the buried depth of the steel pipe,the maximum value of soil resistance on the side of the pile decreases gradually,and the position of the first zero point of soil resistance moves downward;with the increase of soil modulus in the area of soil compaction on the side of the pile,the maximum value of soil resistance on the side of the pile increases,and the position of the first zero point of soil resistance moves up.(3)Under the action of transverse axial load,the lateral bearing capacity of CFST composite pile is mainly provided by the rock and soil around the pile and the material of the pile.With the increase of the buried depth of the steel pipe,the maximum bending moment of the pile body increases gradually,and the position of the section of the maximum bending moment moves downward.The position changes within 8cm~10cm below the ground,which is consistent with the variation law of lateral soil resistance.(4)The influence of buried depth of steel tube and soil compaction effect on the transverse axial bearing characteristics of concrete filled steel tube is further verified by numerical simulation,and the influence law of pile length,pile diameter and steel tube wall thickness is increased,which makes up for the deficiency of the above three points not considered in centrifugal model test. |
