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... layer originated by the alteration of Val Gardena Sandstone. Up to a depth of 20-30 m from the ground surface, a bedrock of low to medium altered phyllite was found. At the landslide toe, below the first 5 m of backfill clay, a strongly altered phyllite in a reddish silty clay matrix exists, but Sandstone or Bellerophon layers are not noticed (Fig. ...
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... Geosciences 2019, 9, 240 2 of 21 began researching the development and performance-cost evaluation of an innovative technique for landslide stabilisation, named 'composite anchors' [3][4][5][6]. ...
... Composite anchors can be applied to various geotechnical works and offer the most considerable advantages in landslide stabilisation, where large stabilising forces are needed. In this case, their use follows the approach of the so-called 'floating anchor' [5,6]. This type of anchor consists in installing passive sub-horizontal reinforcements in order to increase the forces that contrast the sliding. ...
... Since the interactions between the soil-bar and strand-bar are the most important aspects on which depend both the design of these reinforcements and the assessment of their efficiency on the stabilization of an existing (or potential) landslide, this research group is engaged in evaluating these interactions by means of laboratory tests and on-site measurements. After a first attempt, in which Bisson et al. [5] used strain gauges with not completely satisfactory results, we applied distributed fibre optic sensors (DFOSs) [12,13] to better measure the strain of composite anchors. ...
Composite anchors are special passive sub-horizontal reinforcements recently developed for remediation of unstable slopes. They are composed of a hollow steel bar, installed by a self-drilling technique in the soil, coupled with tendons cemented in the inner hole to increase the global anchor tensile strength. The anchors are primarily intended to stabilise medium to deep landslides, both in soils or weathered rock masses. Among the valuable advantages of composite anchors are their low cost, ease of installation, and flexibility in execution, as testified by a rapid increase in their use in recent years. The bond strength at the soil-anchor interface is the main parameter for both the design of these reinforcements and the evaluation of their long-term effects for landslide stabilisation. After a brief description of the composite anchor technology, this paper presents a novel methodology for monitoring the strain and stress accumulated in the anchors over time when installed in an unstable slope. The new monitoring system is composed of a distributed fibre optic sensing system, exploiting the optical frequency domain reflectometry (OFDR) technique, to measure the strain exerted on the optical fibre cable embedded with the tendons inside the bar. The system permits an evaluation of the axial force distribution in the anchor and the soil-anchor interface actions with a spatial resolution of up to some millimetres. Therefore, it allows determination of the stabilising capability associated with the specific hydrogeological conditions of the site. Furthermore, upon an extensive validation, the system may become part of a standard practice to be applied in this type of intervention, aimed at evaluating the effectiveness of the anchor installation and its evolution over time.
