Challenge

A new boat dock was planned along the shoreline of a small manmade lake that formed within the limits of an abandoned gravel pit. The proposed dock would extend out into the lake from a stone paver terrace surrounded on three sides by poured concrete retaining walls and stepped walkways. The dock would be eight feet wide and 32 feet long and extend into water as deep as 12 feet. Helical piles were selected to support the dock by advancing through the soft and loose soils at the lake bottom to deeper, more competent materials below. Specific challenges of the project included accurate layout and installation of the piles, reaching out with the drive head to the proposed pile locations, and providing a stable working platform for the installation crew.

Solution

The hydraulic fluid system of a skid steer was used to power a Pengo 12K drive head fitted with a custom hanger and attached to the boom of a large rubber-tired forklift. The forklift had an extendable boom capable of reaching out 40 feet. The hydraulic connections were fitted with “leak kits” and wrapped with oil absorbing mats to prevent oil leaks from contaminating the lake. A 20-foot long pontoon boat ferried the pile materials to their proposed locations and provided a working platform for the installation crew. A three-point anchoring system was used on the pontoon boat to maintain stability during installation. A combination of a 100-foot vinyl measuring tape and a laser level were used to ensure accurate pier locations during installation. The two piles located farthest from the shore were driven first and were used as benchmarks to accurately locate the remaining piles. Eight Model 288 (2.875-inch OD by 0.276-inch wall) helical piles with an 8”-10”-12” triple-helix lead section were installed. The piles were advanced to depths ranging from 15 to 18 feet below the mud line and to torque-correlated ultimate capacities exceeding the design working load of ten kips by factors of safety greater than two. The pile components were hot-dip galvanized for corrosion protection. Despite the unique challenges associated with this project, the helical piles were installed in just two days.

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Project Summary

Architect: Design Workshop

Structural Engineer: KL&A, Inc.

Geotechnical Engineer: Hepworth-Pawlak Geotechnical, Inc.

General Contractor: Tenant Improvement Specialists, Inc.

Certified Pile Installer: Foundation Repair of Western Colorado

Products Installed: (8) Foundation Supportworks® Model 288 Helical Piles, 8”-10”-12” Lead Section, Installed to Depths of 15 to 18 feet Below Mud Line, Design Working Load of 10 kips