# The Behavior of a Thread-Bar Grounded Anchor in Soils from Local Strain Monitoring
## 2 Materials and Methods
### Installation of the Ground Anchor  
The test anchor was built with the same geometrical and structural characteristics of the working ones. It slopes 40\({}^{\circ}\) to horizontal, has a total length of 36 m with 18 m of free length and 18 m of bonded length. It is made of a fully threatened Gewi steel bar, 63.5 mm diameter, with a yield load of 1758 kN and ultimate resistance of 2217 kN.  
The test anchor was instrumented with 12 welded vibrating-wire strain gauges to allow the monitoring of the load-transfer process. For redundancy, two mutually opposite strain-gauges were welded at each position, so that the deformations were detected at 6 different locations along the anchor. In Figure 2, two pictures showing the installation process of a pair of strain-gauges on the bar are shown. Note that after welding, the sensors were encapsulated by a protection cover to avoid damage during installation into the borehole's casing.  
Figure 1: Cross-section of the quay with the upgrading work. Note the location of the ground anchor (modified from [13]).  
Figure 2: Picture of a pair of strain-gouges welded on the bar in mutually opposite position and detail of the cover plate adopted to protect the sensors.  
The chosen strain gauges, manufactured by Gestecno (Gestecno S.r.l., Castelraimondo, Italy), have a measurements range of 3000 \(\upmu\varepsilon\), an average resolution of 1 \(\upmu\varepsilon\), a working temperature between \(-20\) and \(+60\)\({}^{\circ}\)C, an active gauge length of 153 mm, external dimensions of \(165\times 25\times 25\) mm and a gauge factor equal to \(3.618\times 10^{-3}\)\(\upmu\)e/Hz\({}^{2}\).  
As shown in Figure 3, 2 strain-gauges were placed in the middle of the free length segment and 10 in the fixed length segment of the anchor. Moreover, a toroidal load cell at the head provides the actual value of the applied force. The soil stratigraphy recorded for the tested anchor indicates that of the 18 m of fixed length, 14 m are in the dense fine sand and 4 m are in the marly-clay deposits.  
Because the test anchor had a temporary and experimental purpose, no corrosion protection was provided. In addition, differently from working anchors, the free length of the bar for the tested anchors was not encased in a debonding sleeve. This was imposed by the lack of free space between the borehole casing and the bar for the heavy wiring of the strain-gauges.  
A casing was necessary for the entire borehole length. Two different casing diameters were used: 220 mm for the 18 m free length and 178 mm for the bonded length.  
A post-grouting injection was also planned but it could not be carried out due to difficulties of the opening of the manchette valves. Therefore, the preliminary test was carried out on an anchor with the primary grouting only.  
The grout used for the injection has a water/cement ratio equal to 0.45; a free flow grout additive was also used. The effective length of the anchor foundation is relevant for assessing the performance of the system and it should be as compliant as possible with the designed length. However, it is practically impossible to evaluate the real volume of the drilling cylinder. Recommendations suggest setting the injected volume of the grout between the nominal volume and 1.5 times the nominal volume of the fixed length segment, depending on the soil and drilling technology. For the considered anchor, 0.70 m\({}^{3}\) of grout was injected, corresponding to 1.5 times the nominal volume of the foundation cylindrical segment.  
Note that an excess of the injected grout volume could produce a foundation segment in the backfill and the consequent reduction in the anchor free length. However, the very poor geotechnical properties of the backfill ensure that the above shortcomings could not significantly affect the pull-out test response.