# The Behavior of a Thread-Bar Grounded Anchor in Soils from Local Strain Monitoring
###### Abstract  
International standards discourage the use of grouted anchors with a fixed length exceeding 10 m. However, grouted anchors with a fixed length between 10 and 20 m are frequently used in Italy to transfer high loads to ground with poor geotechnical properties. This paper presents the results of investigation tests on an anchor with a length of 36 m, of which 18 m is fixed, sloping 40\({}^{\circ}\) from the horizontal; the anchor is comprised of a reinforced thread-bar which was instrumented with strain gauges and founded in nonhomogeneous ground, a sand deposit followed by marly clay. The test aimed at investigating the progressive mobilization of the shear strength along the foundation. The results indicate a very low shear strength offered by the sand, probably disturbed by the drilling, and an unusually fast mobilization of the shear strength in the marly clay at the deep end of the anchor. The results are particularly useful to identify the reasons for the observed poor performance of the grouted anchor. In particular, the study once again made it clear how important the influence of the execution details on reaching the expected load capacity may be, and likewise the practice of investigation tests on suitably instrumented test anchors. g _Applied_  
_Article_  
The Behavior of a Thread-Bar Grounded Anchor in Soils from Local Strain Monitoring  
[PERSON] _et al._ (2020), _et al._ (2020), _et al. of [PERSON] (1975) [4], [PERSON] (1978) [5] and [PERSON] (1985) [6] still represent the reference literature for this field. Recently, the development of the fiber optic technology allowed some detailed measurements of the strain distribution along the entire bar. [PERSON] and [PERSON], 2010 [7]; [PERSON] et al., 2013 [8]; [PERSON] et al., 2015 [9] and [PERSON] et al. (2019) [10] provided interesting analysis of fiber optic strain measurements during load tests on grouted anchors. It is worth noting that most of the monitored anchors had a short fixed length, usually not exceeding 10 m. This choice agrees with many recommendations that suggest limiting the fixed length of the anchor to avoid possible progressive failure phenomena due to the highly non-uniform mobilization of bond stress along the foundation length ([PERSON], 1997 [11]; [PERSON] and [PERSON], 1997 [12]). Precisely, such a non-uniform stress distribution corresponds to a progressively decreasing bond-strength with the increasing of the foundation length, along which the peak strength cannot be attained simultaneously. However, anchors with a fixed length between 10 and 20 m are frequently used when soils with low geotechnical properties are encountered, or high design loads have to be sustained. For example, to our experience, many quays of the Ravenna port (Italy) built between 20 and 40 years ago consist of anchored retaining walls with a fixed length of the anchors typically exceeding 15 m ([PERSON] et al., 2019 [13]; [PERSON] et al., 2020 [14]). All these anchors were designed by assuming a uniform shear strength along the bonded length; such structures are found to be fully operational even after decades of severe usage. Such a good performance of the anchors could possibly be related to a more uniform stress distribution along their fixed length, as observed in [PERSON] et al. (1999) [15] in weak rock and loose soil. Indeed, [PERSON] and [PERSON] (1970) [16], by studying stress distribution around a cylindrical anchorage in triaxial stress field using finite element methods, observed that non-uniform bond stress distribution is relevant when the ratio of the elastic modulus of the anchor material (EA) and the rock (ER) is less than 10 (EA/ER \(<\) 10), as commonly is the case for anchors in rocks. So far, the influence of such a stiffness ratio for grouted anchors in soils on the onset of progressive failure has not been thoroughly investigated in the literature.