Study on the Variation Characteristics of the Anchor Cable Prestress Based on Field Monitoring in a Foundation Pit

Field monitoring was conducted on the variation of the tension in prestressed anchor cables used in a foundation pit engineering. Based on quite a few data obtained from in-site monitoring and other literature, the variation features of anchor tension were summarized concerning the install positions on a single anchor pile, anchoring strata, and locations on the plane of the foundation pit. The tension in selected anchor cables was monitored during the whole construction process from their locking to the completion of the whole construction. The results show that the anchor tension of anchor cables shows a three-stage variation. Anchor tension in cables decreases dramatically in a short period after the locking stage. Afterward, it fluctuates during the partial construction of the foundation pit which could mainly be attributed to the excavation of the subsoil close to the cables as well as the locking of the cables underneath. Finally, it tends to be stable after the completion of the whole construction. The strata condition of the cable anchored in and the position of the cable on the plane of the foundation pit would significantly affect the final anchor tension as the cables stabilized. The better the geological conditions of the anchoring strata and the closer the anchor cable is to the middle of the foundation pit slope, the greater the final anchor tension.