Design and Installation of Helical Anchors and Tiebacks-PPT Presentation

PPT Presentation

Pdf Summary

The presentation outlines the design and installation of helical anchors and tiebacks. A typical system consists of a steel central shaft, one or more helical bearing plates, and a termination device; it is designed primarily to resist axial tension loads.<br /><br />Capacity may be estimated using the individual-bearing method, cylindrical-shear method, or torque-correlation method. The individual-bearing method sums the capacities of the helix plates, assumes no skin friction, and requires adequate spacing between helices. The torque-correlation method relates ultimate capacity to installation torque using an empirical factor that depends on shaft size. When installation torque is monitored, a factor of safety of 2.0 is typical.<br /><br />Applications include earth retention, guy-anchor support, seismic uplift restraint, and buoyancy control. Earth-retention uses include soldier-pile and lagging, sheet-pile, cantilever, and basement walls. Design considerations include axial capacity, embedment and helix spacing, torque criteria, batter angle, and locating the failure plane to identify the active zone. Connection options include threaded-rod adapters, waler systems, new-construction caps, lateral-restraint brackets, and boardwalk brackets.<br /><br />For retaining-wall systems, lateral loads can be converted into axial pile loads through either a statically determinate arrangement, where force lines intersect, or a moment-couple system using equally spaced vertical piles.<br /><br />Anchors may be installed with mini-excavators, skid steers, backhoes, or hand-held equipment. Testing can include pre-production testing in accordance with ASTM D3689, performance testing, and proof testing. The presentation concludes with a case study of an I-80 box culvert extension in Greenwood, Nebraska.

Keywords

helical anchors

tiebacks

axial tension

helical bearing plates

installation torque

individual-bearing method

earth retention

retaining walls

proof testing

ASTM D3689