Field Monitoring And Centrifugal Model Test Of Prestressed Anchor Cable Piles Support Structure

In recent years, prestressed anchor pile has been widely adopted in deep foundation pit support structure, but its design and calculation theory is not mature. Therefore, it is necessary to study the stress and deformation rules of prestressed anchor cable piles. Based on the foundation pit engineering of Chaotianmen center in Yuzhong District of Chongqing City, this paper studies the stress and deformation law of prestressed anchor pile by field monitoring and centrifugal model test. The centrifugal test was divided into two groups, the first group is not anchored supporting pile, the second group is anchored supporting pile,put the model in 100g acceleration, The horizontal displacement of the pile top and the moment of the pile body under the 100g acceleration are collected statically, and the force and deformation rules of the support structure are obtained. The main conclusions of this paper are as follows:(1) The monitoring results of the support structure show: the monitoring data don't exceed design control value and are within a reasonable range.In addition, the prestress losses of anchor cable don't exceed the 30% of the design limit value can meet with code requirements; the anchor tension is small, deviated far from design value, some bolts may fail;(2) When the foundation pit is completed, the horizontal displacement of the top of the retaining structure is larger, and the first support structure is shifted with the second stage support structure;(3) The settlement of the top of the foundation pit mainly occurs in the excavation stage of the foundation pit. After the completion of the excavation, the settlement is basically stable, which shows that the settlement of the top is mainly due to the inclination of the supporting structure, and the settlement of the support pile is very small;(4) Two groups of centrifuge model tests have obtained the bending moment law of the support pile. When the first group is not supported by anchor cables, the bending moment of the first stage pile is approximately parabolic, and the bending moment of the second stage pile is opposite to the shape of the first stage pile. When the second groups are anchored with anchor cables, the bending moment distribution is basically the same as that of the first group. By comparing the results of the two sets of tests, it is found that the anchor reinforcement can reduce the maximum moment of the pile body and improve the stress state of the retaining pile;(5) The first group of centrifuge test, in the case without cable reinforcement, the displacement of the pile top is large, and the soil behind the pile is damaged; the second group of centrifugal test, in the conditions with anchor reinforcement, the displacement of the pile top is small, and the soil behind the pile was no significant deformation. Comparing the two groups of test pile top horizontal displacement, it can be found that anchoring force can decrease the deformation at the top of support pile and its effect is very good;(6) Comparing the field monitoring data and the horizontal displacement of the pile top of the second sets of centrifuge model tests, it is found that the data of the other three piles are different greatly except that the horizontal displacement of the top of the 7# pile is close to the field monitoring value. From the preliminary analysis, the main reason is that the test can not simulate the complicated geological conditions and construction conditions,and the mechanical parameters of the tested soil are different from those of the undisturbed soil.