Numerical Simulation And Experimental Research On Prestress Loss Of Anchor Cables In Foundation Pits

With the continuous development of prestressed anchor cable reinforcement technology which has been widely used in slope control and deep excavation projects in many projects such as water conservancy and hydropower,railway,mine and urban construction and other slope treatment and deep foundation pit projects.Most of the foundation pit support projects are temporary projects and the construction parties are generally reluctant to invest more funds in the actual implementation of the project.Therefore,accidents occur frequently in deep foundation pit support projects,which not only cause great economic losses to the society,but also delays the construction deadline,and caused huge adverse impacts on the construction of the project.Prestressed anchor cable has been widely used in improving the stress state of geotechnical media,improving the integrity of rock and soil and the stability of its bearing capacity.However,due to its complex mechanism of anchoring and influence of many other factors,the existing theoretical analysis compared with the practical engineering practice is still in the backward stage,and there is no systematic and in-depth theoretical research on the changing laws of the prestress value after the cable locked,especially in anchor stablization of the soil and weak rock mass in the foundation pit.The main contents of this paper are as follows:(1)Based on the relevant project of a project in Guiyang,the deep foundation pit is monitored by using advanced equipment and technology both at home and abroad.The monitoring mainly includes monitoring of supporting structure system,rock and soil system,hydraulic system and surrounding environment,and monitoring Information exchange platform is built as well.The monitoring experience under the condition of composite support is summarized.(2)According to the excavation of foundation pit,the construction process of anchor cable,the nature of rock and soil and the external environmental conditions,the main influence of prestress loss is determined according to the change and development process of anchor cable prestress and the long-term and short-term monitoring data of foundation pit.The variation rule of prestressing force under the interaction of anchor cable and foundation rock mass is analyzed.(3)Based on the existing predictive model of prestress loss and the optimization based on on-site monitoring data is conducted,the fitting formula of anchor cable stress under the influence of multiple factors is determined,and the revised prediction model is compared with the long-term monitoring data verification.Counter-proved the effectiveness of the anti-card model,made contrast and demonstration of the using effect of simulation results.(4)By using FLAC3D finite difference software,the paper analyzes the prestressing force and the distribution of it in the typical pile-anchor system of the nebula appliance city pit,and compares the result with the monitoring data and the predictive model.The results of this paper can provide reference for the design and construction of similar projects.