The Behavior of a Thread-Bar Grouted Anchor in Soils from Local Strain Monitoring

Paolo Ruggeri,Viviene M E Fruzzetti,Giuseppe Scarpelli

doi:10.3390/app10207194

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° 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.

Highlights

Grouted anchors in soils are common geotechnical structures able to transfer tensile load to the soil
Grouted anchors are geotechnical structures that are very efficient for transferring tension loads to soil
Their performance depends on several construction details which are very difficult to anticipate by the designer

Summary

Introduction

Grouted anchors in soils are common geotechnical structures able to transfer tensile load to the soil. The importance of the details on the behavior of these geotechnical structures is clearly indicated by the results of investigations on failures that occurred in some cases (Littlejohn and Mothersille, 2008 [2]; Ruggeri et al, 2013 [3]) For these reasons, common practice and standards require testing of all ground anchors before going to service. Eurocode 7 part 3 (prEN1997-3), EN 1537:2013 and ISO 22477-5:2018, the three coordinated standards respectively assessing the design, execution and testing of grouted anchors in Europe, establish three types of test: investigation tests, suitability tests and acceptance tests All these tests are oriented to evaluate the global performance of the anchors by making external measurements (e.g., applied force, elongations, creep). The investigation test is a load test aimed at evaluating the geotechnical ultimate resistance of the anchor and its behavior at working loads

Methods

Results

Conclusion