Written by CHANCE Foundation Solutions on August 18, 2022
Soil borings are important! Borings revealed that site had a soft layer of sand for the first 10-15 ft. and below that was approximately 20 ft. of extremely dense clay. Mason Frascona, with Mason Grady Foundations, shared, “(The density) was enough to almost max out the SS225 material which is why we had to go with the larger material to get through that layer and the soft layer below, reaching the 75 ft. depth. There wouldn’t have been another way to penetrate that dense layer.”
They were also working with a high water table at approximately 4 ft., which combined with weather, could create a large excavation full of water and delay the whole project.
CHANCE Helical Pulldown Micropiles (HPM) provided the best solution for this project. This deep foundation solution constructs a grout column around the shaft of a standard helical pile foundation system. This time- and labor-saving product is installed directly into soil. A lead displacement plate eliminates the need for excavation and spoil removal from the job, allowing for 40-50 piles to be installed per day with smaller crews and equipment. The grout column results in a higher capacity pile system (greater than 100 tons possible) that is ideal for weak soil sites with limited access.
Ideal for projects where increasing capacity and providing predictable results is a must. The HPM provides a stiff pile that resists buckling in weak soils while also providing corrosion protection in aggressive soils and high water tables. A proven engineered system, bearing and side resistance is combined to bring a no pre-drill solution to a wide variety of applications for new construction, remedial repair, and limited access areas with minimal site disturbance.
A load test was conducted prior to the installation of production piles to verify the pile capabilities. Even at 200 kips, pile movement was less than 1/2 in. During the project, the piles were installed with a 28,000 lb. excavator and 30,000 ft-lb Digga drive head. There was limited access to the site, and the excavator entered the work area through a 10 ft. wide by 18 ft. high opening. The working load was as high as 97 kips in compression and 54 kips in tension. They installed SS225 piles with a 8/10/12/14 helix and a 7 in. grout column to a depth of approximately 75 ft. and torque values from 10,000 ft-lbs. to 20,000 ft-lbs. Torque was monitored during the installation using a CHANCE torque indicator.
The General Contractor wanted to minimize the amount of time needed work around the pool excavation. Therefore, they installed the pool foundation piles near the end of the project, after the roof was complete.
The contractor estimates the time saved to be six to eight weeks on production and prevented project delays due to weather. The pile installation was the third Helical Pulldown Micropile project that the installers completed, and they found the piles easy to work with. Ultimately, the lesson they learned from this project is to make sure the piece of equipment that is being used is appropriate for the size drive-head and material being used, to ensure that the proper penetration rate and crowd can be maintained during installation. In total, there were 36 CHANCE Helical Pulldown Micropiles installed across the two YMCA pool locations and the installation took only eight days to complete.
Penetration through dense soil count
Easy to use
Low to no vibration/noise
Standard equipment for installation
Immediate proof testing and loading
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