Geosynthetics August/September 2019 - 27
Case Study
Stabilization of subgrade
soils during Interstate
95 lane widening
By Bryan C. Gee, Eric Klein and William T. Maier
T
he Maryland Transportation Authority (MDTA) is implementing a multiyear, multiphase project to add express toll lanes (ETLs) to Interstate 95.
The ETLs are providing significant congestion relief in one of the most heavily trafficked corridors in the United States. The major modification to I-95
consists of adding two ETLs in each direction. The eight general purpose lanes
(GPLs) will be maintained. The ETLs are located between the northbound and
southbound GPLs and separated from the GPLs by a concrete barrier. The ETLs
were designed for a 25-year life and 9.5 million 18-kip (80-kN) equivalent single
axle loads (ESALs). The areas where the very soft soils were encountered were
northbound ETLs just north of the I-95 bridge over White Marsh Run and south
of the Maryland 43 bridge over I-95.
Some areas with very low California Bearing Ratio (CBR) values were
encountered during the design phase. The contractor was given the choice of
using a lime/fly-ash mixture or to undercut and replace with a separation fabric
and stone (Figure 1). Where soft soils had been encountered previously, they
were thin enough that the contractor simply removed the soft soils and replaced
them with a separation fabric and stone.
PROJECT HIGHLIGHTS
I-95 LANE WIDENING
OWNER
Maryland Transportation
Authority (MDTA)
LOCATION
Baltimore, Md.
GENERAL CONTRACTOR
Tutor Perini Corp.
DESIGN ENGINEER
RK&K/URS
GEOSYNTHETIC PRODUCT
Geogrid
GEOSYNTHETIC MANUFACTURER
Site conditions
The soils in these areas were weak, saturated clays and silts with very low shear
strength. CBR values were well below 1%, and the poor soils extended to depths
of at least 6 feet (1.8 m). Using a calibrated drop hammer penetrometer, the
CBR values were found to range from 0.1% to 0.5%. These poor soils were first
encountered in March 2014, but they were thin enough that they were simply
undercut. As the project advanced the poor soils got deeper, and test pits determined that the undercut would be significant. The roadway was to open in fall
2014. To undercut and replace or to mobilize the lime/fly-ash mixing equipment
would have delayed the opening of the toll road.
Tensar
Bryan C. Gee, P.E., is director of
education and training at Tensar
International Corporation.
Eric Klein, P.E., D.GE, F.ASCE, is senior
manager, geotechnical at RK&K/URS.
William T. Maier is northeast regional
manager at Tensar Roadway Systems.
All photographs and illustrations courtesy of the authors.
www.GeosyntheticsMagazine.com
27
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Geosynthetics August/September 2019
Table of Contents for the Digital Edition of Geosynthetics August/September 2019
Geosynthetics August/September 2019 - Cover1
Geosynthetics August/September 2019 - Cover2
Geosynthetics August/September 2019 - 1
Geosynthetics August/September 2019 - 2
Geosynthetics August/September 2019 - 3
Geosynthetics August/September 2019 - 4
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