Abstract: In order to study the evolution of internal force and the load characteristics on pile-anchor retaining structure of complex, large and deep foundation, based on the deep foundation of which the total area is about 160 000 m2 and the maximum excavation depth reaches 26 m, we have monitored the internal forces of the pile and anchor respectively in the process of foundation pit excavation, pile head with lateral loaded and different working conditions of the bolt drawing by embedded bar gauge on the retaining pile and anchor reinforcement. The results show that: (1) during the cantilever pile stage, as the foundation pit excavation the lateral pile body stress of three retaining piles presents “tension-compression-tension” and the inside pile body stress exhibits “compression-tension”. The same point stress increases. Max stress position moves down slightly. The stress-zero appearance varies depending on the length of pile. During single-fulcrum stage, along with increasing exposure time of foundation excavations, the exposed pile stress increases. The peak stress of pile appears in the near excavation area. Excavation of pile body stress tends to complex and the zero-stress point arise earlier than the cantilever pile stage. During two-fulcrum stage, pile’s reinforcing stress tends to be more complicated. Main reasons are that the excavation time of foundation excavations and the impact of factors such as tension locking of prestressed anchor. (2) structural bolting design needs to consider the maximum deformation; After meeting the threshold length of anchorage, the longer the free section, the better anchoring effect, the shorter anchoring section, the more economical. (3) without pulling force or during different tensile force, redistribution occurs in bolt stress, which is different from the those in soil or rock excavation. (4) the appearance and movement of the neutral point of lateral friction force in anchor arm are in consistence with those of the potential slip surface. Therefore, the location of slip surface and anchor arm threshold length in a deep excavation can be determined.

Key words: deep foundation, pile-anchor retaining structure, in-situ test, internal force, dynamic evolution, bearing behavior