Influence of Construction Sequence on the Force Characteristics of Foundation Pit Support Structure

The construction process is often different from the ideal process in the design scheme. To investigate the effect of construction sequence on the force of the pile-anchor support structure in foundation pit, the internal force of the pile-anchor support structure under two different construction sequences was monitored and analyzed based on a deep foundation pit project in Lanzhou, China, and the internal force change law of the pile-anchor support structure under different construction sequences was obtained and further verified and analyzed using finite element method. The results show that there are many differences in the internal forces of anchor cables under different construction sequences, and the time to apply prestress to anchor cables has an important influence on the internal force distribution of the support piles. When the first anchor cable is prestressed and the second and third anchor cables are not prestressed, the pile is actively stressed and the pile moment is distributed in an "S" shape, with the negative moment at the top and the positive moment at the bottom. When the upper three anchor cables are not prestressed at the same time, the support pile is in a passive stress state and the pile bending moment is negative. If the anchor cables are not tensioned in time after construction, the excavation will cause irreversible changes in the bearing state of the support piles, and the maximum displacement of the support piles will increase about 26% and the maximum bending moment of the support piles will increase about 42.8% compared with the normal working condition, which is not conducive to the safety of the foundation pit. Therefore, the principle of "soil should be excavated in layers and anchor cables should be tensioned in time" should be strictly followed during construction.