Performance evaluation of standard grouted anchors versus expanded anchors

ABSTRACT: Foundations and tiebacks with expanded elements have been used in the past, namely soil anchors, driven, vibrated and bored piles. This paper presents a test program conducted at a site in Ottawa, Ontario, Canada, comparing the performance of conventional tiebacks (strand anchor with gravity grouting) to shorter tiebacks with an expanded anchor. The conventional tiebacks (strand anchors) were 150 mm in diameter and were constructed to a depth of 28 m:18.0 m of unbonded length and 10 m bonded in dense sands with gravity grout. Tiebacks anchored with expanded elements were installed in a 228 mm diameter hole to a depth of 7 m and were expanded in loose to compact sands. The expanded element was initially 1.2 m long and about 0.95 m long after expansion. The remainder of the tieback was unbonded. The results of the tension tests conducted on both types of tiebacks showed that the tiebacks with expanded elements provided on average about three times the resistance measured for conventional anchors, even in less competent soils.