# Study on the Effect of Anchor Cable Prestress Loss on Foundation Stability
## 5 Conclusions and Prospect  
For a soil-rock combination foundation pit project in Qingdao City, through the comparison of field measurement and numerical simulation results, the deformation and stress of supporting structures in the process of foundation pit excavation and the influence of prestress loss on the stability of the foundation pit were analyzed, and are summarized as follows:  
1. The loss of prestress reduces the deformation restraint effect of the supporting structure on the rock and soil mass outside the pit. When the excavation depth is shallow, the loss of prestress has little influence on the settlement of the rock and soil mass. With the increase in the excavation depth, when the excavation reaches the soil-rock interface and below, the deformation of the rock and soil mass outside the pit increases significantly and is greatly affected by the prestress loss. 2. The horizontal displacement of the retaining pile increases with the increase in excavation depth, and the maximum displacement point gradually approaches the soil-rock interface. The maximum horizontal displacement of the pile increases linearly with the increase in the prestress loss rate under each working condition, and the increase rate is obviously smaller in shallow soil than in deep rock. The maximum axial force of the anchor cable and support increases with the increase in excavation depth. When the excavation is near the soil-rock interface, the maximum axial force of anchor cable and support increases significantly, and then the growth rate decreases gradually with the progress of the excavation. Under the same excavation depth, the maximum axial force of the anchor cable and support gradually decreases with the increase in the loss rate. The maximum axial force of the support increases gradually with the increase in the prestress loss rate. 3. When the excavation is near the soil-rock interface, the deformation of the whole system, such as the rock and soil mass and supporting structure, changes significantly. This means that in future similar engineering practices, in order to ensure the quality and safety of the project, it is necessary to improve the monitoring project at this stage in advance. 4. Through the comparison of field measurement and numerical simulation, it can be seen that the support structure of bored pile + first concrete support + anchor cable can meet the needs of soil-rock combined foundation pit construction. Meanwhile, the control of prestress loss can effectively control the surface settlement and the stress and deformation of the retaining structure. The loss of prestress can be controlled by selecting different types of anchorage cementing materials. At present, the cost of  
Figure 14: Comparison of the measured axial force and the calculated maximum axial force. resin anchoring agents and high strength fast-setting cement anchoring materials for this purpose is generally high, which restricts their application in engineering practice. * Different stress forms of anchor cables will lead to different support effects. At present, the mainstream stress forms of anchor cables mainly include tension type, pressure type, tension distributed type, pressure distributed type, etc. Combined with practical projects, it is very valuable to study the ultimate bearing capacities and stress distributions of different types of anchor cables, which can be conducive to the subsequent application and promotion of pile and anchor foundation pits. Conceptualization, T.X. and H.L. ; methodology, T.X. and H.L. ; software, X.Y. and H.P. ; validation, X.Y. ; formal analysis, X.Y. and Y.L. ; investigation, J.Z. ; resources, J.Z. ; data curation, T.X., H.L. and Y.L. ; writing--original draft, T.X. and H.L. ; writing--review and editing, Y.L. ; visualization, H.P. All authors have read and agreed to the published version of the manuscript. National Natural Science Foundation of China (42277139, U2006213). Not applicable. The data used to support the findings of this study are included within the article.