Tensar® Biaxial (BX) Geogrids Roll Over Lime in Texas Developments

Tensar Earth Technologies, Inc.
Issue 13.2 — summer 2003
Tensar Biaxial (BX) Geogrids Roll
Over Lime in Texas Developments
®
geo
Geosynthetics Applications Newsletter
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Austin, Texas can claim a number of well-known assets — among them, the University of
Texas Longhorns, authentic Tex-Mex cooking, and a highly plastic (expansive) clay subgrade.
Highly expansive clay soil is especially prevalent in southeast Austin, site of the gleaming
Austin-Bergstrom International Airport. Opened just four years ago, the facility has triggered
a residential and commercial construction boom in the area, leaving developers, contractors,
and engineers grappling with soil stabilization issues.
One such developer is KB Home. The innovative, California-based builder of entry-level
and trade-up homes has developed several communities around Austin, including Berdoll
Farms, a 680-home subdivision east of the airport. Roadwork in the first four sections of
the development included subgrade stabilization with lime. However, thanks to a new
understanding of the benefits of mechanical stabilization, the consultant now specifies Tensar
BX Geogrids instead of lime.
“It all started with a presentation we made to civil engineering firm Carlson, Brigance &
Doering on the benefits of using BX Geogrids versus lime when building on expansive
clay soils,” commented Carey Witt, P.E., of Tensar Earth Technologies’ (TET) distributor
Geo-Solutions, Inc. “Carlson (which prepared the Berdoll Farms land plan) asked us to contact
Austin Engineering, which was building the infrastructure for several KB Home communities.”
“We were looking for a way to speed up the construction process with a better product.
So we asked for evidence of previous geogrid applications in the area,” added Vice President
of Austin Engineering Kerry Keller. Witt provided the data, and the two firms agreed to
collaborate on a proposal for KB Home.
SpectraPave2™ Software Provides Reliable Design Data
Witt developed the proposal using TET’s SpectraPave2 Software. Created to support the
analysis and design of flexible pavements and unpaved roads, SpectraPave2 enables users
to compare BX Geogrids with conventional approaches.
The rigidity of Tensar BX Geogrids allowed Austin Engineering ❿
to traffic the geogrid directly with rubber-tired equipment.
Using Tensar Geogrid in lieu of lime stabilization at Berdoll
Farms allowed for a faster installation of the pavement section.
❷
The software application features three analysis modules including:
Subgrade Improvement, which indicates required thicknesses for
unreinforced and BX Geogrid-reinforced subbases; Subgrade Improvement
Cost Analysis, which provides cost comparisons between those subbase
options; and Base Course Reinforcement, which addresses serviceability
analysis and long-term design issues for unreinforced and reinforced
pavement sections. The program also includes a reference data section
which supports the development of paving solutions.
“I used the Base Course Reinforcement module, which includes
AASHTO guidelines to compare different alternatives including BX Geogrids.
The data indicated that geogrids would confine and stabilize the subgrade
soils and reinforce the base course,” Witt said. The engineer, who routinely
provides SpectraPave2-based proposals to geotechnical and civil engineers in
Austin and San Antonio, added that the software is easy to use and understand.
The BX Geogrid proposal, which required approval by the City of Austin, was
referred back to San Antonio’s Integrated Testing and Engineering Co. (InTEC).
InTEC had made the initial paving recommendations using lime stabilization in
accordance with the cities’ criteria.
“
This was our first experience with
BX Geogrid and it’s superior to lime.
It installed quickly...saving us two
weeks to a month in the first Berdoll
Farms section where it was used.
Kerry Keller
Vice President
Austin Engineering
”
InTEC’s Paul Palaniappan, Ph.D., P.E., explained some of the common concerns of using lime stabilization in
this type of application. “Lime is weather-dependent, and quality control is often difficult to maintain. Stiff BX
Geogrids, on the other hand, are effective regardless of the weather conditions,” he said. The geotechnical engineer
revised the pavement design and included a total of 36,000 square yards of BX Geogrid.
“That got us over the hump,” Witt added, noting that the City of Austin has since used Tensar BX Geogrid on
several other public works projects.
BX Geogrid Gets Thumbs-up and Rolls into
Other Developments
“We had used lime on other projects and experienced
surface cracking,” commented Austin Engineering’s
Keller. “This was our first experience with BX Geogrid,
and it’s superior to lime. It installed quickly and more
easily than lime, saving us two weeks to a month in
the first Berdoll Farms section where it was used. Its
stability has exceeded our expectations.” Keller added
that compared to lime-treated roadwork, incidental
cracking is greatly reduced when using BX Geogrids.
Brett Pasquarella, P.E., project manager at Carlson,
Brigance & Doering, agreed. “Installation is much
faster than lime stabilization, and at the present time,
appears to be holding up well,” he said.
Apparently, KB Home is pleased as well; Tensar
BX Geogrid has replaced lime in three more of its
Austin communities.
➛ The aggregate and BX
Geogrid composite
yielded a bridge over
challenging soft soil
conditions.
❷ The BX Geogridreinforced base course
formed a construction
platform, so that the
pavement installation
could commence
without delay.