Leon County Drainage Easement
The Problem:
An existing concrete retaining wall along a county-owned drainage easement was in need of repair in Leon County, FL. A steel sheet pile retaining wall was to be installed in its
An existing concrete retaining wall along a county-owned drainage easement was in need of repair in Leon County, FL. A steel sheet pile retaining wall was to be installed in its place but would need to be tied back to prevent buckling. The county-owned easement, however, only extended approximately 20' from where the rear of the wall was to be located. A tieback system with predictable capacities, that could be designed to achieve those capacities within the 20' easement, and that could be installed in a limited access area was needed.
The Solution:
The CHANCE Helical Anchor system was chosen to tieback the steel sheets because various sizes and numbers of helical bearing plates can be used on the central shaft of the anchor to aid in generating more torque, and therefore, increase the capacity of the anchor. The CHANCE Helical Design Software Program, HeliCap, was used to determine the number, and size of the helical bearing plates that were needed to achieve the design capacities, given the current soil conditions. The challenge was using an anchor with the appropriate helix configuration, and correct length, so that the bearing plates were beyond the failure plane of the wall, but the anchor tip was still within the easement.
Technical Description
Product:
(15) CHANCE Model SS5 Square Shaft Helical Anchors (1-1/2”, 70 KSI) were installed at a 30-degree batter. A 10712714716" helix configuration was used. Anchors were installed with a John Deere 50G Mini-Excavator to overall lengths of 21-23’, and installation torques of3,000 - 4,000 ft.-lbs. as averaged over the final three feet of installation. A performance test was conducted on one anchor prior to production anchor installation. Each anchor was then proof tested, and locked off at 75% of the design load. A steel plate, beveled washer, and hex nut were used to lock the anchor rod against the steel sheet. A concrete cap was poured on top of the wall to tie the sheets together, and encapsulate the end of the anchors. The anchor installation and testing took three (3) days to complete. The concrete cap was formed and poured immediately after final anchor testing to prevent project delays.
