Geotextile Reinforcement of Low-Bearing-Capacity Soils
Comparison of Two Design Methods Applicable to Thawing Soils
KAREN S. HENRY
INTRODUCTION
METHOD CURRENTLY USED BY THE ARMY
(TM 5-818-8)
Thawing fine-grained soils are often saturated
or even supersaturated and thus have extremely
The design method currently used by the U.S.
low bearing capacity. Geotextiles have been used
Army for the stabilization of low-bearing-capac-
in the construction of low-volume, unsurfaced
ity soils for low-volume roads and trails with
roads on weak and saturated soils to reinforce the
geotextile and aggregate was developed by the
base coursesubgrade interface and therefore are
U.S. Forest Service (Steward et al. 1977) based on
good candidates for use in stabilization of thaw-
theory presented by Barenberg et al. (1975).* The
ing soils. To stabilize weak soil with a geotextile
design method is presented in TM5-818-8 (1995)
for trafficking, the geotextile is placed directly on
as a series of soil strength vs. aggregate thickness
the soil and then covered with aggregate. The de-
design curves for various wheel loads (defined
sign involves selecting aggregate thickness and the
below), with a tire pressure of 552 kPa (80 psi) (Fig.
geotextile. There are two commonly used tech-
1 through 3). The design procedure includes
niques for designing for soil reinforcement using
geotextiles, one of which is prescribed in U.S.
1) Converting soil strength to an equivalent cohe-
Army guidance.
sion, c.
The current Army design technique for static
2) Selecting a maximum wheel load.
loading of low-volume roads on low-bearing-ca-
3) Selecting a value for a bearing capacity factor,
pacity soils was examined for ease of use and ap-
Nc. Nc values used with design curves for static
plicability to the reinforcement of thawing soil,
loading are 6.0 with geotextile and 3.3 without
specifically for Army vehicles. Static loading is
geotextile.
defined as up to 100 passes of a vehicle at the maxi-
4) Using the product cNc in the appropriate de-
mum wheel load and a minimum rut depth of 0.10
sign chart (e.g., Fig. 1), and determining the
m (4 in.). Information about Army vehicle load-
depth of aggregate required with and without
ing and design curves for specific Army vehicles
a geotextile.
is provided in this report to help make the design
5) Determining which section is less costly to build.
technique easier to use.
6) If use of a geotextile is advantageous, specify-
Another design method that offers the poten-
ing one according to geotextile construction sur-
vivability requirements.
tial to reduce required aggregate thickness over
the geotextile (and thus cost) was compared with
Although TM5-818-8 does not specify the ag-
the Army method. Theory and results from both
gregate properties required for low-volume roads,
design methods are presented in this report. Al-
though both design methods include traffic load-
ing for up to 1000 vehicle passes, here we deal only
with design for static loading, which involves a
*The low-bearing-capacity soils were assumed to be soft,
maximum of 100 vehicle passes.
cohesive soils by Barenberg et al. (1975).
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