Full-Scale Field Test on Construction Mechanical Behaviors of Retaining Structure Enhanced with Soil Nails and Prestressed Anchors

Abstract

Soil nailing combined with prestressed anchors has a good workability and is relatively cheap in constraining the horizontal displacement. Current research on the technique, whether theoretical analyses, numerical simulations, or model tests, was conducted under ideal working conditions. However, in fact, external disturbances, such as tensioning-lagging of the anchor, are very common and play an important role on stress and displacement. Therefore, it is of great significance to carry out a field test considering the effects of external disturbances, which can obtain real and reliable data through real-time monitoring. In this paper, the impacts of the construction conditions on practical engineering are discussed based on in situ tests, and some reasonable suggestions for the upgrading of misbehaviors in the current construction situation are put forward. In particular, the influence features of soil predisturbance, excessive excavation, unloading on the surface of edges, tensioning-lagging of the anchor, and continuous rainfall on the stress–time curve of soil nails under practical working conditions are analyzed. Behaviors of three different retaining structures enhanced with (i) soil nails; (ii) soil nails and prestressed anchors without unbonded parts; and (iii) soil nails and prestressed anchors with a 2.5 m unbonded part were monitored during staged excavation to investigate the influences of (i) the prestressing force and (ii) the unbonded part of the prestressed anchors on the performance of the entire retaining system. Results show that (i) the prestressing force is the main factor affecting the stress and deformation of the composite retaining system, which is consistent with the existing literature; (ii) the variation of the magnitude and distribution of the soil nail force responding to the anchor prestressing force, however, showed no systematic trend; and (iii) the unbonded part of anchors, which was validated to be the main factor affecting the structural stability in dense materials in the existing literature, is found to have a minor influence in loose fill materials used in this study.

A Numerical Study of a Soil-Nail-Supported Excavation Pit Subjected to a Vertically Loaded Strip Footing at the Crest

“…Its apparent cohesion and internal friction angle are 20 kPa and 15 • , respectively; the Young's modulus and the Poisson's ratio of the soil are 12 MPa and 0.3, respectively. The nail reinforcement's diameter, yield strength, and elastic modulus were derived from [20]. In contrast, the elastic modulus of concrete and grout was similar to the values given in [19].…”

“…This study aims at extending the work performed by Gui and Rajak [9]. The simulated problem was a full-scale nail-supported excavation designed for excavating the foundation pit of a 20-story building [20]; the excavation face was inclined at an angle of 80 • from horizontal. Gui and Rajak [9] performed the analysis using the in situ soil conditions and studied the responses of the nailed facing of the excavation face.…”