Geosynthetics February/March 2022 - 18

Reinforcement over soft soils with high-strength geogrids
The Administración Portuaria
4a
Integral de Guaymas S.A. de C.V. (API
Guaymas) decided on a major renovation
of the area to build new concrete
pavement over the storage area using an
RGM with high-strength geogrids as a
basal reinforcement solution (Figures
4a and 4b). It was chosen because of
its advantages compared to traditional
solutions: easy and fast installation,
more cost-effective application and
excellent performance.
The development of the port took
4b
FIGURES 4a and 4b Basic layout of (a) the rigid
beam design approach and (b) the catenary
design approach
place through subsequent stages of land
reclamation from the sea, causing the
foundation soil to be saturated and very
soft. In fact, the geotechnical investigation
carried out over the project area of
7,654 square yards (6,400 m2) showed a
45.9 foot (14 m) deep layer of soft soil
characterized by gray-green silty sands
and dark brown sandy clays with high
plasticity. The total tensile strength of
geogrids required to support the load of
the RGM and the overload of the minerals
dumped in the area for a total uniform
load of 9,398 psf (450 kPa) was calculated
using the design method for embankments
on soft soils included in the British
Standard BS8006-1:2010. This method
considers both short- and long-term tensile
strength of the geogrid; hence, the
resulting ultimate tensile strength already
considers all the reduction factors for
tensile creep, installation damage and
environmental degradation.
The detailed design of geogrid
FIGURE 5 Port of Guaymas high-strength
geogrid detail
18
Geosynthetics | February March 2022
reinforcement was carried out using
the geogrid design method (Rimoldi
and Scotto 2012; Rimoldi and Simons
2013). This method, based on elastic
multilayer analysis, allows for the introduction
of different geogrid layers at
various elevations and for the design
strain to be set for each geogrid. Given
the RGM thickness and considering
separately the effect of the static loads
and the instant effect of dynamic loads,
it is possible to calculate the distribution
of the horizontal tensile forces in the
RGM structure and select the appropriate
geogrid for each layer based on a
limit state criterion. In this case, restriction
of the deformation was chosen as
limit state criterion, so the geogrid strain
was limited to a maximum of 5%, as suggested
by practical experience and by the
BS8006-1:2010.
The geogrids used in the RGM were
high-strength uniaxial geogrids characterized
by a high-tenacity polyester
core covered in polyethylene resistant to
physical, chemical and biological conditions
found in reinforced soil structures
(Figure 5). The RGM layout consisted
of a 3.28 foot (1 m) thick aggregate layer
with two sets of transversally installed
high-strength uniaxial geogrids.
The construction of the RGM
included the following steps:
1. Preparation of the site by excavating
to a 3.9-foot (1.2-m) depth the
entire area and clearing it from sharp
objects that could possibly damage
the geogrids.
2. Placement of an 8 inch (0.2 m) thick
layer of good-quality soil (wellgraded
sand and gravel mixture,
with friction angle [φ]=36°) to get a
perfectly flat surface.
3. Installation of the first layer of
high-strength geogrid (Figure 6).
The rolls were placed on the western
side of the storage area with the
use of a lifting beam and unrolled
carefully toward the eastern side,
ensuring that no slack or undulations
occurred. At both the edges,
6.56-foot (2-m) anchorage lengths
were left out.
4. Installation of the second layer of
high-strength geogrids by placing
the rolls on the southern side of the
area and unrolling them carefully
toward the northern side, perpendicular
to the first geogrid. Also, for
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