Beaches + Dense Coralline Gravel = Stable Foundation

Hanalei Weke Road is nestled between Hanalei Bay and mountains and nature preserves on the beautiful island of Kauai in Hawaii. Challenging soil conditions prompted the engineers at Kelikai, Inc. of Honolulu to call on Chance distributor Structural Systems, Inc. to help them design and build a reliable foundation for a new home construction.

In order to provide the best design based on the local soil conditions, Kokua Geotech LLC performed soil borings at the jobsite. Per the geotechnical report, the surface soils underlying the project site are classified as beache sands and mokuleia fine sandy loam. This soil has a low to moderate swell potential and slight to rapid permeability making it not structurally sound for the home to be built on. It was determined that the piles would need to be installed from 60 to 80 feet deep, allowing sufficient depth for the sandy mokuleia to transition into a medium-dense coralline gravel.

Engineers relied on HeliCAP® helical capacity design software to design the new construction foundation for the 5,466 square foot home using Chance helical piles. The software allows the soil parameters to be custom input into a profile. Then the user adds piles and the program calculates the torque and capacity to be expected during installation.

Product Selection

By using Chance products, engineers and installers had some key advantages due to the decades of innovation and experience that come by working with the world’s first earth anchoring company. In this foundation design, assisted by the Hubbell team, engineers specified:

1. ROCK-IT Lead Section – manufactured from grade 80 structural steel with a half-inch thick helix with a sharpened leading edge, the ROCK-IT was able to penetrate the dense coralline gravel. Due to its carbide tip on an easier-to-install square shaft pile, ROCK-IT makes tough installations possible, even on Earth’s toughest soils.
The geotechnical report specified 10”/12”/14” flights with extension of 65’, all galvanized, on a 1.75” steel square shaft to achieve an allowable compression load capacity of 15 kips with a factor of safety of 2. 

2. Combination “Combo” Pile – a Combo pile combines a square shaft lead section followed by round pipe shaft extensions. As discussed, the square shaft lead was needed to combat difficult installation conditions and to allow embedment in the coralline gravel. A cast transition coupler between the lead and the first round shaft extension provides the change from square to larger round shaft, thus providing lateral stiffness at the top of the pile.

Helical Pile Installation

Transportation logistics was a key factor because the construction crew and engineers were based in Honolulu. Young Brothers, Hawaii’s foremost inter-island freight handling and transportation company, transported all of the equipment to Kauai and the piles direct to the jobsite. The crew stayed at a local Airbnb Monday through Friday and came home over the weekend until the job was complete. The piles were installed with a Komatsu PC88 excavator rented from Bacon Universal on the Island.

The jobsite crew found the beach sand was almost like standing in quicksand when it was dry! So, the general contractor watered down the work area constantly to keep the sand denser and more walkable, giving the excavator and crew better conditions to work on.

Once the torque and depth achieved the target capacity of 15 kips, the installation was terminated. As anticipated from the HeliCAP designs, the helical piles were installed to depths of 60 to 80 feet and topped off with a new construction cap.

Rebar cages for footings were installed around the helical caps and a 12” thick footing was poured; followed by a 4’x 8” concrete wall poured on top of the footings. all of the structure load would be transferred to the dense coralline gravel via the helical piles rather than to the sandy mokuleia at the surface.

The structural integrity of the home was achieved, and construction could commence! The owners were pleased that the crew finished the work ahead of schedule, working twenty 10-hour days, creating a solid foundation that would stand the test of time.

Incorporated in Hawaii in 1985, Structural Systems is a Hawaii Licensed “A” General Engineering Contractor, License #AC-13555. Focusing and specializing in new and remedial foundation construction, commercial and residential drilling, concrete restoration, and premium railing systems, Structural Systems is recognized for expertise in value-engineered solutions to construction problems.