Anchorage Behavior of Shaft Anchors in Alluvial Soil

Based on the full-scale test results of 29 shaft anchors installed in the silty alluvial soil of the Taipei basin, the anchorage behaviors of anchors having two different types of tendon assemblies, namely the singly anchored type and the multiple anchored type, are evaluated in this paper. Test results indicate that the benefits of the multiple anchored anchor system is not obvious in terms of the residual movement and the ultimate anchorage capacity when compared with the traditional singly anchored anchor. A critical fixed length of 20 m is observed regarding the ultimate anchorage capacity for both singly anchored tension anchors and triply anchored compression anchors. This critical fixed length is considerably longer than the upper fixed length limit proposed by the major anchorage specifications. For those anchors with fixed length shorter than the critical length, the anchorage capacity increases linearly with the fixed length. However, if the fixed length is extended beyond this critical length, up to 70% falloff in anchorage resistance per unit fixed length increment was found.