Reinforcement of a Highway Embankment over peat layers

PRODUCTS:

TENAX LBO SAMP geogrids

Location - Date: Highway M7, Balaton Lake, Hungary, 2004

Designer: Technical University of Budapest, Department of Geotechnics

Contractor Vegyépszer Rt.

Problem
The highway M7 from Budapest to Croatia, in the western region of Lake Balaton had to be constructed over thick peat layers with very low CBR values.

Due to the short construction program and the thickness of the peat layers, soil substitution was not an option. 14.5 km of the highway was to be constructed in this area, the peat layers were typically 3 m – 4 m deep. Due to the very low bearing capacity it was difficult to walk on the proposed route and impossible to access the area with trucks.

The most critical part was between km 165+800 to km 167+150, in this section the peat layers were 6 m - 8 m deep.
To carry the new highway a 9 m – 11 m embankment was to be constructed. At the base of the foundation layer a minimum bearing capacity of 25 MPa was required.

Solution
Following laboratory tests of the subsoil a design was carried out by the Technical University of Budapest. The most economical solution was to incorporate a 30 x 30 kN/m TENAX LBO 330 SAMP rigid integral geogrid within the permanent works. A nonwoven geotextile was also specified to act as a filter fabric. Construction and results at the most critical sections:

The TENAX geogrids were installed using the wraparound technique during the placement and compaction of the Dolomit layers. In both of the sections the measured improvements in the bearing capacity have exceeded the design requirements.

Conclusions
The goals of a reinforced granular layer below an embankment that has to be built on soils with a very low bearing capacity are these:

• To reduce settlements
• To improve the load distribution
• To prevent rotational failure at the toe of the slope.

The use of TENAX LBO 330 SAMP integral geogrids substantially increased the bearing capacity and settlement was reduced.
It was possible to access the area with heavy trucks during the construction phase and the embankment could be built with extremely poor underlying subsoil conditions.