Our Products At Work in the Field

Concrete Cloth™ GCCM: Foundation Installation

San Francisco, CA
November 26, 2018

Project Overview
The San Francisco Bay Area presents difficult challenges with respect to foundation design and construction because of the range of mud layers, ground water table and the design for earthquake loads on the structures. A typical method used to stabilize a temporary excavation for foundation installation is to stair step the excavation, which is a passive system. A passive system is preferred because it is less likely to be out of stormwater compliance over a 24-hour period. When using a stair step method, the excavation must not slide and cause a disruption at the excavation site. Truebeck Construction, in Redwood City, CA, was working on a site that had both shallow and deep foundations, which called for stair stepping and mechanical shoring during the installation.

If the stair stepping slope crumbles over time, the crumbling could cause potential slope
stability issues for the excavation site. This risk is common when working with silt or clay
material, which tends to dry out from the sun or wind and cause shrink cracks. Signs of
crumbling or the slope drying out can be a larger issue if precipitation occurs during the time of the project because it could destabilize the excavation.

Truebeck was motivated by the asset owner to:

(a) save time and ultimately cost
(b) reduce material usage
(c) exceed stormwater runoff quality requirements
(d) prevent over-excavation
(e) minimize delays when precipitation events did occur

Muller Construction Supply from San Jose, CA, discussed Concrete Cloth™ GCCM with
Truebeck for armoring the excavation walls. These requirements prompted Truebeck to decide to use a combination approach for armoring the stair step excavation with geotextiles, slurry concrete and Concrete Cloth GCCM.

“Concrete Cloth GCCM came highly recommended from Muller,” said Mike Currier,
Superintendent for Truebeck. “We visited some sites that had used the material and decided to go with it because the time of year meant we needed a reliable solution for supporting foundations during the winter.”

Truebeck established a process for selecting the appropriate material (geotextile, Concrete Cloth GCCM, mud mats, steel sheet pile and other shoring devices) to be used for the armoring protection at each excavation for the foundation construction as well as the installation methods. When using Concrete Cloth GCCM, the process for rapidly deploying was streamlined to precut the sizes needed per vertical wall, hydrated the material within a tub and then hung and secured it to the vertical surface with spikes.

As expected, during the construction of the foundation for this site, the winter rains came and filled up the pile cap excavation that was armored with Concrete Cloth GCCM, which acted as a miniature water basin. Because of the armoring provided by Concrete Cloth GCCM, all that Truebeck had to do was pump the water out, which was much lower in Nephelometric Turbidity Units (NTUs) compared an excavation that was not armored, helping to exceed requirements for stormwater quality. The water was pumped out to its temporary holding basin and the team was back to work installing the rebar the very next day.

Brian McGovern, President of Muller, explained that the “Concrete Cloth material has ideal characteristics to be used in unconventional ways that lead to completing successful projects and eliminating costly risks.”

If Concrete Cloth GCCM was not used, Truebeck would have been excavating out soils, making the excavation bigger than required, treating higher NTU water and waiting for the soils to dry out before work could resume, which could take one to two weeks. This delay would have affected the entire construction schedule and cost.

“The material worked really well with no failures,” said Currier. “We would use it again for
projects during the rainy season.”