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Stabilisation of a road embankment on very soft clay soil, for the construction of a new Expressway in Bangkok, Thailand



Road section on marshy soil

Road section on marshy soil (unconsolidated soft clay)



TENAX LBO bi-oriented geogrids



Bangkok, Thailand


Expressway and Rapid transit Authority of Thailand
Bangkok Expressway Co. Ltd


Freeman Fox Intercon Consultant Ltd. Bangkok


Kumagai Gumi Co. Ltd, Japan
BBCE Joint Venture: (Bilfinger +
Berger Bauaktiengesellschaft, Germany
Ch. Karnchang Co. Ltd, Thailand
Expert transport Co. Ltd, Thailand




The new Bangkok Expressway was crossing a marshy area with a very soft soil consisting of normal consolidated Bangkok clays, 20 m deep. The site investigations showed that the bearing capacity of the foundation soil was too low to support a "traditional" highway embankment.

The first idea was therefore to widen the embankment base with large berms, in order to distribute the load on a wider area, thus involving deeper soil layers and therefore increasing the global bearing capacity. It appeared fundamental to provide the enlarged base with a sufficient stiffness, in order to decrease both the vertical stresses and the differential settlements.

In addition to the above considerations, a high stiffness was required for the initial construction phase to allow the heavy plant to operate on site without sinking into the extremely soft soil that was often waterlogged.


The design required four horizontal layers of biaxially oriented geogrids for stabilizing this embankment. The geogrids were installed at 300 mm vertical spacing.

The design engineers, considering the fundamental structural function performed by the geogrids, issued very stringent specifications for the reinforcement.

The geogrid manufacturer was required to provide evidence that a professional quality control procedure would be implemented during the production process and that a certificate of conformity for the specific product would be issued for this project, including:

  • Testing certificates by independent laboratories;
  • Tensile creep test results, adequate to determine the design tensile strength of the geogrids for a design of 1 year under constant load (1 year was the anticipated time for the consolidation of the clay soil under the embankment);
  • Tensile secant modulus at 2% and 5% elongation;
  • Proof of UV stabilisation.

The geogrids chosen by the Contractor, with the full approval of the design engineers, were TENAX LBO 302 SAMP bi-oriented geogrids.

The TENAX engineers were able to produce a proper answer to all the project requirements. In addition, the whole production lot for the Bangkok Expressway (about 150.000 m² of geogrids) were tested and certified by SGS (Societé Générale de Surveillance), a specialised international QC/QA firm.


estabilizacion de un camino



Tab. 1

Design specs for the geogrid
Direction (MD)
Direction (TD)
Tensile strength
(95% lower confidence limit)
17.5 kN/m 31.5 kN/m






Tab. 2

Long term strength of TENAX LBO 302 SAMP geogrid for 1 year of continuous constant load at 20°C.

Direction (MD)
Direction (TD)

Tensile strength

4.70 kN/m

7.80 kN/m



Tab. 3

Characteristics measured by the Quality Control on the entire production lot of TENAX LBO 302 SAMP geogrid

95% Lower
conf. limit
Tensile strength 34.66 kN/m 1.19 kN/m 32.71 kN/m
Yield point elongation 9.92% 2.57% ---
Tensile mod. at 2% el.
608 kN/m 50.3 kN/m 525 kN/m
Tensile mod. at 5% el. 476 kN/m 29.2 kN/m 429 kN/m



Tensile strength 19.8 kN/m 0.59 kN/m 18.85 kN/m
Yield point elongation 19.15% 0.66% ---
Tensile mod. at 2% el.
325 kN/m 18.3 kN/m 295 kN/m
Tensile mod. at 5% el.
234 kN/m 9.4 kN/m 180 kN/m




TENAX geogrids in this project, as well as in many others, have proven to be a product with the highest technical characteristics and with guaranteed properties. TENAX LBO 302 SAMP passed severe controls before being utilized as a structural element for the stabilisation of an embankment on very soft soil.

The ease of installation of TENAX geogrids allowed the Contractor to maintain high installation rates and allowed to use an innovative technology for stabilizing the embankment, thus obtaining consistent savings over traditional solutions.







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