Geoplatform-assisted embankment reinforcement

Contents

Geoplatform application

Conclusions

Geoplatform application

High costs and tight schedules encourage designers to develop new technologies and cost-effective solutions that allow to:

• accelerate construction rate;
• avoid soil replacement operations;
• provide easy and safe site access for personnel and equipment;
• minimize the volume of filler soil by preventing its penetration into weak layers.

Gexa’s engineering center is often urged to calculate embankment foundation reinforcement with geosynthetic materials, including applications with geoplatforms.

As an example of a single project design, let’s consider the engineering solution for building an embankment in a problem area of Tatarstan’s Alekseevskoye – Almetjevsk toll highway construction (a creek crossing).

The problem area of Tatarstan’s Alekseevskoye – Almetjevsk highway construction was characterized by the base soaked clayey soil combined with the embankment inundation by surface and ground water.

The embankment construction and the section further operation are exposed to complicated hydraulic conditions i.e. the base clayey, swamp material (from soft-plastic to fluid consistency, schistose structure), the embankment inundation either by surface water (up to 2.5 m) or ground water. As specified by the project design, the embankment height amounted to 5 m, with the slope ratio of 1:2 and the subgrade top width of 28.5 m. The embankment was filled with fine sand, with average dust and clay content of up to 5%, density of 1.88 t/m3 and the following strength parameters: the internal friction angle &nbsp ϕ = 38°, cohesion with the structure С = 0.005 MPa.

The calculation analysis showed the following:

• the natural ground stability in terms of minimal stability with no plastic deformation area at safety factor of ≥ 1 is not secured, with stability factor calculated per uniformly distributed load method equal to 0.39;
• in case of calculations allowing development of permissible failure zones (per SoyudorNII method), the foundation stability is also unsecured, with stability factor of 0.32, when the required value is 0.88;
• the overall final settlement value is 67 cm;
• the settlement stabilization to reach the required value takes from 6 months to 4 years.

The following engineering solution was implemented in order to secure the foundation strength and make its stabilization period acceptable (1 to 1.5 year):

• installation of a 0.5 m to 0.8 m thick half-casing of Geospan GT PP 80 reinforcing geotextile (≥ 80 kN/m strong), laid by separate fabrics across the embankment axis, with the casing upper layer 4 m to 5 m embedded in the embankment body;
• installation of a volumetric geogrid layer (rib height of 20 cm, high strength of weld joints) directly on the casing lower layer, with the geogrid cells filled by M800 macadam.

The geoplatform enabled a substantial increase in the embankment lower part stiffness and allowed to:

• Distribute the load evenly, resulting in relative increase of stability factor by 25%;
• reduce the settlement difference at the embankment cross section axis and edge, which means lower requirements to the foundation consolidation design value as per RIM 218.5.003-2010;
• lower deformation variations caused by the geotechnical profile nonuniformity.

Conclusions

Embankment soil reinforcement using geoplatforms can be an efficient way of constructing proper road structures with a certain stress-strain behavior. Such construction shall be based on research and calculations.

Embankment reinforcement with geotextile is carried out to absorb static and dynamic tensile loads, prevent local damage, increase elastic modulus and shear resistance of the application layers.