Ground improvement is typically less expensive than piles or drilled shafts when one of the following is true: 

With these improvements in Geopier Technology, the applications for ground improvement have expanded.

Pile Replacement Example

Geopier rigid inclusions replaced a pile foundation on the Station 650 (Land Bay J) multi-family project in Alexandria, VA.  The soil conditions consisted of approximate 10 feet of contaminated urban debris fill overlying 8 feet of soft clay, 35 feet of loose to dense sands, underlain by very stiff Potomac Group clays. The original geotechnical report recommended 80-ton 14x73 steel H-Piles or 80-ton,  14-inch square-precast concrete piles driven 65 feet into very stiff Potomac Group clay.  The piles were replaced by 50-foot deep grouted Impact® Pier elements (Geopier rigid inclusions).  The Geopier rigid inclusions tested for the project deflected 0.04 inches at a load of 50 tons.  

By using Geopier ground improvement in lieu of piles on the Station 650 Project the owner was able to:

1. Take advantage of a faster installation schedule, which meant they could move in their first tenant earlier, and
2. Support the building on an engineered system that cost less money.  Some of the specific cost savings included:

• Use of spread footings vs. pile caps which meant less concrete
• Eliminated pile cutoffs which resulted in a quicker installation
• Geopier installation saved time on the construction schedule over piles 

Drilled Shaft Replacement Example

Geopier rigid inclusions were used on the Towson University Liberal Arts Building - Phase II in Towson, MD to replace a drilled shaft foundation system. The building was sited such that footings for the western section of the building could bear on decomposed rock with an allowable bearing pressure of 7.5 ksf, but fill soils and loose residual silty sands required a deep foundation system in the eastern section. The soil conditions for the eastern section consisted of approximate 10 feet of loose silty sand fill, overlying 25 feet of natural, loose to dense residual silty sands, which were underlain by decomposed rock and highly weathered to weathered gneiss bedrock. The original geotechnical report recommended that all shafts be a minimum of 36 inches in diameter, so that the bottom could be inspected to verify shafts were bearing on suitable material.  Due to the variability of the weathering in the bedrock profile, drilled shafts needed to be socketed into rock with an RQD (Rock Quality Designation) of at least 50%.  The shafts were designed for an allowable bearing pressure of 40 ksf.   

The general contractor, who was familiar with Geopier RAP elements, proposed an alternate of 30-inch diameter RAP elements.  The RAP elements supported spread footings designed for 6 ksf bearing and controlled settlement to less than 1 inch.  Having a designed system that was consistent with the spread footings used on the western section of the building simplified the design and construction sequencing for the GC and the owner. 

The Geopier alternative proved to be faster and eliminated the risk of potential overruns associated with variable drilled shaft lengths, rock socket depths, and rock testing to find rock with an RQD > 50%.  

Using ground improvement versus drilled shafts on the Towson Project provided the owner the assurance that the foundation would be completed on schedule with no cost overruns.  Specific benefits included:

• Ability to use spread footings for all the foundations
• Eliminating the requirement to socket piers into rock or case holes for inspection and testing
• Eliminating the risk of overruns due to encountering poor quality rock
• Generating fewer spoils saving time and haul-off costs

Bottom Line 

• Intermediate Foundations are your next best choice to natural soils.
• Owners and Contractors do not want to spend more money than necessary on the foundation system for any structure. 
• When fill soils or compressible natural soils and/or very high structural loads result in excessive unacceptable settlements your next choice is Geopier ground improvement.
• With a wide range of Geopier ground improvement tools available, a customized solution can be developed to solve most every foundation challenge.