# The Behavior of a Thread-Bar Grounded Anchor in Soils from Local Strain Monitoring
## 4 Discussion
### Lesson Learnt from the Investigation Test Results  
The rare opportunity to have local strain measurements along the anchor thread-bar allowed an explanation of the anchor performance below the expectation.  
In particular, the analysis of the local measurements pointed out two aspects:  
* the segment of the foundation in sand did not perform well;
* shear strength mobilization along the foundation of the anchor was unusual for a tension grouted anchor.  
The shear strength mobilized in sand was anomalous not only in terms of its limit value (less than 1/3 of the expected) but also in terms of the very low stiffness and absence of a peak in the load transfer curves. These results are in contrast with the geotechnical properties of the deposit and have to be related with the construction process. It has already been indicated that the planned post-grouting injection could not be executed due to the very quick concrete hardening that impeded the opening of the mancheture valves. This fact could explain the low limit skin friction, but cannot justify the very soft behavior shown by the transfer curves. It seems possible to relate this behavior to the decay of the original density of the sand around the borehole, due to the use of air flushing during the drilling operations.  
Moreover, the local measurements revealed a particular distribution of the shear strength along the foundation. Different from expected, the shear strength mobilization was very significant at the deep end of the grouted body, probably due to the minor installation damage suffered by the maryl clay in comparison with the sand. In summary, the relatively high stiffness and resistance of the grout-maryl clay interface and the very low stiffness and resistance of the grout-sand interface caused an unusual progression of the skin friction mobilization with a large amount of the tensile load quickly transferred to the deeper stratum. It is interesting to note that this load-transfer distribution resembles that observed by [PERSON] (2003) [18] for the so-called compression anchors, which are anchors in which the tendon is bonded to the soil only in its deeper segment.  
Figure 9: Comparison between obtained transfer curves of anchor T1 and typical transfer curves of side resistance for (**a**) granular and (**b**) fine soils.  
The information collected by carrying out an investigation test on an instrumented anchor allowed us to fulfill design requirements by adapting the technological process. In particular:  
* taking into account the susceptibility of the dense sand to the use of air, the entire drilling of the working anchors was executed by using water flush only;
* the post-grouted injection was always executed within 6-8 h from the completion of the primary injection, so that a large part of the manchettes valves opened and allowed a correct execution of the high-pressure injection.  
Moreover, some general conclusions can be outlined from such testing:  
* the high stiffness of the bar compared with the soil stiffness properties allowed a rapid mobilization of the shear strain along the entire foundation, so that a progressive failure of the foundation does not apply for the examined anchor;
* the presence of a layered soil deposit in which the deep soils are stiffer than the shallow ones does not allow the progressive transfer of the anchor loads to the ground, as should occur with long anchor foundations.