Devereaux Commons HOA

Situation

The Home Owners Association was experiencing slope failure of an embankment at one of the detention ponds within their community. Inspection revealed soft soils on the slope suggesting improper compaction of the site. At the base of the 10-ft slope was a weir and drain structure designed to handle the detention pond. Continued subsidence of the embankment would have dramatic impact on the structure and road at the top of the slope.

Scope of Work

A retaining wall system was recommended to stabilize the slope, preventing the threat of future damage and wasted expenses. An 8' poured in place wall was designed to stabilize a 50-ft section of the slope. Excavation to the designed wall footing elevation, approximately 2-ft below the drain structure, took place with the spoils being stock piled at the top of the slope. This allowed clean up of the pond basin, which had been left unattended since construction in 2000. A soil compaction test was performed using both a helical probe and Dynamic Cone Penetrometer (DCP), which confirmed insufficient soil bearing pressure to support a wall footing. Cantsink Helical Piles were installed for the cantilevered wall design to include two rows of piles spaced 6' on center, staggered. Pile depth ranged from 17.5-ft to 24.5-ft with one pile extending to a depth of 28-ft. A 5,500-ft.-lb hydraulic drive head mounted to a Bobcat S250 skid steer loader was used to install the piles. A 15-ft boom on the end of the loader allowed installation from the top side of the slope.

Soil Conditions

Sandy silt with high content of organic debris. "N" value to 5-ft depth - 3

Piling System

2.5-inch schedule 40 pipe, (3-inch nominal), to include 7-ft lead sections with a single flight 14-inch diameter helix. 7-ft and 10.5-ft extensions were used as required to meet load requirements. Pile cap used for each pile was a 8 x 8-inch x 3/16-inch plate sleeved into top of pile.

Design Load

Working Load per pile - 16 Kips.

Results

16 piles were installed within 4 hours allowing no delays in construction of footing. Since the project was located at a detention pond, weather conditions come into play. There was a high concentration of sub-surface drainage in the area requiring time management in completing the footing. The use of Cantsink Helical Piles eliminated glitches in both design and construction, allowing for a permanent wall structure.