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.
Highlights
Soil nailed retaining structures are widely used in slope supporting, tunnel retaining, and as bracing structure for foundation pits to limit deformation and improve safety
The soil nail force is transferred to the surrounding soils through soil–grout interface friction, which arises from the relative displacement between the soil and the grout
According to the superposition principle, the nail force affected by compressive stress will decrease, while the stresses of soil nails which are adjacent to the tensile stress zone will increase [27–29]
Summary
Soil nailed retaining structures are widely used in slope supporting, tunnel retaining, and as bracing structure for foundation pits to limit deformation and improve safety. Soil nails have a high ratio of circumference to cross-section area, and rely essentially on friction resistance for the load transfer. The shear strain required to mobilize the nail force is very small; soil nails usually start to function soon after the excavation when deformation occurs. Soil nailing is one of the in situ soil reinforcement techniques which are widely utilized by civil engineers in underground construction, slope stability, housing construction on. Sci. 2021, 11, 7928 required to mobilize the nail force is very small; soil nails usually start to function soon after the excavation when deformation occurs. The research presented in this paper is useful for the rational design and serviceability analysis of composite retaining structures
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