Embankment on mining area with cavities

Embankment on mining area with cavities

European route E20, Estonia | MDB Texinov

Project:
The E20 motorway goes across Estonia from West to East and is a major line for European transport. On the section between Kukruse and Jöhvi, the motorway goes through an ancient oil shale mining area, where the galleries are not precisely located, with risks of collapse.

Specifications:

  • Embankment characteristics: Base width 25 m – typical height 2 m
  • Motorway overloads (20 kPa)
  • Ground formation: low bearing capacity soil

For the 7 km section, in case of sinkholes forming of up to 4 m diameter, the allowed subsidence on the road surface is maximum 16 cm in 99 years, without maintenance.
All calculations according to British Standard BS 8006:1995.

Engineering solution:
To ensure security of the construction and the operating of the motorway, it was decided to use a reinforcement geogrid. The geogrid will keep the road safe when a sinkhole appears by bridging the gap created.

Solution: special high tenacity polyester geogrid with tensile strength 1350 kN/m in M.D.
GEOTER® FPET 1350/135
Quantity : 440 000 sq.m

  • Design of the geogrid according to the specifications approved by EGIS Geotechnique, one of France’s leaders in geotechnical and materials engineering.
  • Mechanical properties tested and certified by tBU (Institut für textile Bau-und Umwelttechnik, Greven)
  • Global geogrid safety factor Fgtx including creep partial factor reduction for a 99 years time period

The use of a very high strength polyester geogrid allowed construction of the Kukruse-Jöhvi section in 2009 with important costs savings for the contractor and a reduced  operating time.