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Use Ground Improvement for Uncontrolled and
Contaminated Fill Sites
Uncontrolled Fills can be discovered during geotechnical investigations at urban brownfield
sites, suburban building pads, and even rural development sites. Fill materials can vary from
construction debris and contaminated or organic soils to reasonably good fill materials that
were dumped or placed without compaction control. All fill materials present unique
problems and significant risks to geotechnical and structural engineers, owners, and general
contractors planning to build a structure at a site underlain by uncontrolled fill soils.
Over the last 20 years engineers have moved from techniques such as over-excavation and
replacement or excavation and recompaction, to improving the fills in place by using Ground
Improvement techniques such as Geopier Rammed Aggregate Pier™ (RAP) System and
Rapid Impact Compaction (RIC).
In choosing a ground improvement technique a number of variables should be considered:
Cost Effectiveness - Rule of Thumb Cost Comparisons
Nature of Fill - Contaminated, Organics, Debris
Depth of Fill
Building Loads and Settlement Tolerances
Rules of Thumb for Cost Effectiveness
Typical applications where use of Ground Improvement is cost effective:
When Fill Depths are 5 Feet or Deeper
Contaminated Fill Soils of any Depth
Sites Where Shoring or Underpinning will be Required to Excavate Fills
Over-excavation of fill with shoring and dewatering vs Geopier RAP Ground
Improvement
At the pre-construction phase, the added site-specific costs that accompany a decision to
use over-excavation need to be considered. Just to be able to excavate to the known depth
of fill might require dewatering, support of excavation, and/or underpinning of adjacent
foundations. This coupled with the cost for placing the new fill and open-ended cost due to
unknown fill depths create risk for engineers, GC's and owners. The use of Geopier RAP
elements not only eliminates these risks but also can increase the soil bearing pressure
which can result in smaller footing sizes and savings in footing concrete. So the actual cost
comparison between over-excavation of fill soils and in-place ground improvement with RAP
elements should consider all the associated costs of each alternative.
Design Considerations
Go through the fill - Due to the variable nature and the non-uniform compressibility of fill
soils, the long term performance of fill soils cannot be interpreted through data commonly
obtained from geotechnical site investigations, such as Standard Penetration Test “N”
values. Likewise, without fill placement records, the variability of the fill between boring
locations in terms of soil type, N values, compressibility and consistency cannot be reliably
determined. Therefore, it is always recommended to install the Geopier RAP ground
improvement system through the fill layer. (See the Standard Geotechnical Report
Paragraph for Uncontrolled Fill for more information.)
Nature of Fill
Organic Soils – Fills with significant organics can be susceptible to settlement due to
longterm degradation of the organic matter. Depending on the organic content (generally over
10% is a concern) or soil classification (OL and OH Soils), the use of CTA Rammed
Aggregate Pier® elements (RAP) or grouted Impact® Pier elements can be used to span the
organic zone and transfer loads down to a stiffer layer. This was performed on a project for
a Costco Store in Wheaton MD where the geotechnical engineer identified an isolated area
where fill with unacceptable amounts of organics were present. The use of CTA RAP
elements on this project provided the owner and design team mitigation of settlement risk
due to long-term bulging in the organic layer. Conventional aggregate was used in the upper
portion of these RAP elements, below the fill to transition and dissipate the concentrated
stress from the CTA portion of the element. The conventional aggregate also allowed for the
design and construction of a traditional spread footing without the use of an engineered fill
pad (click here for more information within the December newsletter).
Contaminated Fill soils – When fill soils contain contamination those materials are
expensive to haul away and may cross-contaminate deeper soils or drinking water aquifers.
There are several design options including:
To eliminate spoils, the RAP elements can be installed using the Impact Pier
displacement method. Using this method the mandrel displaces the existing soils
during installation resulting in no spoils.
Piers can also be grouted to create impermeable zones to control the potential for
cross-contamination.
Examples of projects where Impact Pier elements have been used to reinforce contaminated
soils, while eliminating spoils, include:
Bakers Square Commercial Development - Philadelphia, PA
Sunrise at Cresskill Assisted Living - Cresskill NJ
Motiva Sewaren Terminal Expansion - Sewaren, NJ
Debris Fills
When debris fill soils are primarily granular with few fines (<15%), RIC has been used to
densify debris fills and contaminated soils for shallow foundation and floor slab support. RIC
is typically used for applications where fills are relatively shallow (15 to 20 feet) and for light
to moderate column loads (50 to 400 kips). One of the benefits of the RIC technique is that it
provides real time data such as deformation vs. number of blows. This data can be used as
a tool for the geotechnical engineer to identify soft zones which might require over
excavation or use of Ground improvement using RAP elements. It can also locate hard
zones like old concrete foundations which may need to be demolished. Recent RIC and
RIC/RAP projects include:
Target Store - Rochester, NY
Naval Square Biddle Hall Annex and Townhomes - Philadelphia, PA
Home Depot - Cherry Hill, NJ
Depth of Fill and Loading - RIC and Geopier RAP elements should be considered during
the pre-construction pricing stages for projects in which the fills are generally granular, the
column or floor loads are light to moderate, and the depth of fills are less than 20 feet.
Depending on the building layout a combination is often the optimal solution - Naval Square
Biddle Hall Annex and Townhomes - Philadelphia, PA and Home Depot project - Cherry Hill,
NJ are also example projects using combinations.
The Bottom Line...
Many solutions exist for "controlling" Uncontrolled Fills! Important considerations for
implementing these solutions include:
Install Geopier RAP elements through fills into natural ground.
Fills with high Organic Content that could lead to long-term degradation can be
stabilized through the use of CTA or grouted RAP elements to take the organics out of
play.
For granular fills, consider RIC as a solution for light to moderately loaded structures.
For contaminated fills, the use of Geopier RAP elements installed using the Impact
displacement system can eliminate spoils.
RAP elements can be installed to depths up to 65 feet, in caving soils, and below the
groundwater table to stabilize deep fills.
When fills are very variable and cannot be stiffened sufficiently in place, Geopier rigid
inclusions can bypass soft fills to transfer loads to stiffer materials to control
settlement.
Grounded Solutions February newsletter will discuss “ Geopier RAP Elements to
Replace Deep Foundations” .
Have questions about an upcoming project with uncontrolled fills?
Click the link below for a project assessment!
Project Assessement
OR CALL: 703-771-9844
Interested in scheduling a site visit?
Click here
News & Events
WACEL Luncheon on Rigid
Inclusions
February 26th - Maggiano's, Tysons
Corner, VA
Mr. Michael Cowell PE, President &
CEO of GeoStructures, will be speaking
about Geopier rigid inclusions and their
applicability to foundation ground
improvement at the upcoming WACEL
February Membership meeting.
Featured Projects
In Progress
Village at Valley Forge
King of Prussia, PA
The use of Cement Treated Aggregate
(CTA) was determined to be the most
effective ground improvement method
for the 363-unit apartment complex.
For more information contact Chris Worley at
[email protected] or 301-652-7925.
Completed
QA/QC Training
GeoStructures recently provided
Geopier Quality Assurance & Quality
Control Training in Pittsburgh, PA to
engineers and technicians. Firms
attended a presentation at their office
followed by jobsite training. If your firm is
interested in participating in a future
training please contact Shana Carroll
at [email protected] or 410458-0289.
Fairfax County Public Safety
Headquarters
Fairfax, VA
36-inch Geopier X1 elements
were installed at various depths.
Did You Know?
10 Weird and Wonderful Discoveries
Made During Construction!
Geotechnical Engineers from American
Geotechnical & Environmental Services at
The Yards at Three Crossings (Pittsburgh,
This list names 10 weird and wonderful
things that have delayed or shut down
construction projects around the world.
Read More
PA) site visit.
Previous newsletters can be viewed
on our website.
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