Editor’s note: The following is an excerpt from an article published in the February 2017 issue of Dry Cargo International.
For bulk storage to be a lucrative business, companies have to find ways to get the biggest bang for their buck. And when it comes to property, that means using every square foot of real estate efficiently.
This is especially true for waterfront property. Oftentimes companies that buy land on a port have limited land availability, requiring them to make decisions on how to get the storage they need on a smaller parcel of land.
“If a port does not have height restrictions, which some do, the most efficient thing is to go vertical instead of horizontal, so domes or silos fit that,” Dome Technology sales manager Lane Roberts said, adding that these types of storage can store up to three times the product as a warehouse with the same footprint.
Because of its strength and height, a DomeSilo™ allows companies to stack product deeper, taking up less property at the site. In this taller version of a dome, the vertical DomeSiloTM wall lends itself to the ability to build up, rather than out, and the dome’s double curvature and construction materials provide strength at all points of the structure, even at the apex (the top of the dome). The entire interior of a dome, then, can be used to contain product.
The double curvature and structural engineering of the DomeSilo render it stronger than traditional structures, even traditional silos. Dome customers also have multiple foundation options; the most common are listed here:
- For sites with preferable or acceptable soil conditions, a ringbeam provides a shallow foundation alternative. Where applicable, the frost depth will determine the ringbeam’s depth, but usually the ringbeam is placed two to four feet in the ground.
- For sites where the top six to eight feet of ground is of less-than-ideal material, crews excavate the material, replacing it with controlled structural fill. This model allows for some settlement, but the amount will be within tolerable parameters for a dome.
- When the top 15 to 50 feet of soil is questionable, stone columns are a workable option. First, crews use an auger to remove earth in about a 30-inch diameter hole until a more stable, soil-bearing layer is reached. Rock then fills the hole and is compacted, even laterally so the soil around it is supportive.
For areas where deeper foundations are required, other systems are available:
- In a piled-raft system, steel or precast concrete piles are driven into the ground. A layer of crushed rock three feet thick is layered on top, along with a fabric geogrid, which stiffens the rock mat and adequately strengthens the soil for the structure to be built on top.
- Piles are driven and are topped with a heavily reinforced concrete pile cap; in this model, the system is designed to bear on those piles, so the structure is essentially supported by stilts although built at ground level.
- Soil mixing is an option when soil is questionable for as much as 30 feet of depth. An auger is used to mix the soil with cement and lime; the mixture is then compacted. For similar soil conditions, stone columns often cost less and can be installed faster.
- In sites with high water tables, a six-inch-wide piece of plastic called a wick drain provides a way for water to escape in areas of low permeability. A wick drain is driven vertically into the ground to the desired depth, and water flows to this strip, which acts as a channel that helps remove excess water. Consolidation of this soil can be expected within about three months with a surcharge loading.
- Dynamic compaction requires the use of a crane; a heavy weight is lifted and dropped repeatedly to densify soil.
Each of these methods requires different installation times and associated costs. Based on soil conditions, Dome Technology’s engineering team can identify the solutions most likely to work for a project. For a dome that doesn’t require deep foundations, customers can expect substantial savings.