The analysis provided allows the team to now draw conclusions on the four objectives that were set at the beginning of the project. For a brief recap the four objectives were: conduct a geotechnical report of Sterling Ranch soil, design Tella Firma foundations for 3 home layouts, conduct a cost comparison of Tella Firma and over-excavation, and provide insight on Tella Firma opportunities for improvement.
Geotechnical Report: The geotechnical report confirmed what was expected. The Sterling Ranch development is situated on extremely expansive clay soils that are inadequate for construction in their current state. Some solution is needed for any construction in the area, whether that be through remediation (over-excavation) or isolation (pier and beam or Tella Firma).
Tella Firma Design: The Tella Firma foundation system was found to be structurally sound and feasible for the three home types considered in this analysis. Since these home types represented a large range of sizes, it is safe to conclude that the Tella Firma foundation could be used for any size home that is expected to be built on the Sterling Ranch development.
Cost Comparison: In all three home cost comparisons, Tella Firma was found to be more cost effective than the incumbent over-excavation process. This was mainly due to a large savings in site preparation costs and schedule costs such as labor. A Tella Firma foundation can be completed months before an over-excavation foundation, which may be a bigger bonus than just the monetary value of time. It should be noted that the switching to the Tella Firma process from over-excavation would mean a large shift in equipment and construction methods. This could result in a learning curve that carries large inefficiencies until the process is mastered. Standards dictate that savings must be greater than 8% to consider implementation of a new construction strategy. This 8% is exceeded by the cost analysis performed on all three homes, indicating the technology could be cost effective.
This leaves the final objective: the discussion of future opportunities to improve the Tella Firma process.
Future Improvements
The team found that opportunities to make the Tella Firma process more efficient already exist but were not included in the analysis because they have not yet been widely accepted in practice. The two opportunities presented here are helical piers and multi-site pier drilling. Both of these improvements present an opportunity to save time and money on the Tella Firma process, especially for Sterling Ranch.
Helical piers are a newer product of the Tella Firma company. They are steel piers that are drilled into the ground and replace the poured cement piers that were considered in this report. Helical piers require no holes to be drilled or days for concrete to set, which can further reduce the time spent on a Tella Firma foundation. Helical piers can also save money by limiting the amount of concrete and rebar needed on a Tella Firma project. In the Trails Edge Duplex example, the piers made up 42% of the total concrete used, which comes out to a $3,000 expense. The helical piers are not free but there is an opportunity to save a lot of money with this switch. Helical piers do not create any further complications as the Tella Firma lifting devices can be installed as they were with the concrete piers. After the piers are placed, all construction proceeds as usual.
Another opportunity to improve the Tella Firma process is multi-site drilling, which takes advantage of building in bulk on a large development. Most Tella Firma projects have worked with single homes. Each contractor comes in, does their part on the foundation, and leaves. This is how the cost estimates were calculated. But at Sterling Ranch, there are tens of houses going up all at once. If the schedules could be coordinated, Sterling Ranch could create an assembly line of contractors that complete their task on all of the homes before leaving the site. This could be especially beneficial for the aspect of drilling holes for concrete piers. In the cost estimate, an auger was rented for an entire day to drill the holes for a single house; this cost $2542. This cost could be cut into a fraction of the estimated price by having the auger drill holes for multiple homes on the days that it is onsite. The ability to construction numerous houses at once provides Sterling Ranch with the opportunity to create its own bulk discount.
These opportunities are ways to sweeten the pot. Even without improvements, the Tella Firma technology is a feasible alternative with financial benefits. Even bigger than the money saved is the time that can be saved. By cutting nearly 200 days off the construction timeline, the Tella Firma foundation can greatly expedite the residential construction process and have houses ready for paying residents quicker than any other alternative.