The Motorway M3 side roads were originally constructed using
low shear strength soils. In recent years some slip failures
have begun to occur at various locations in the side slopes.
Surrey County Council therefore decided to repair the slopes,
and of the options considered, the use of a reinforced soil
technique was selected.
The existing side slopes were constructed at 24° to the horizontal,
which had led to slip failure in several locations.
were considered to reinstate the slopes, such as structural concrete
retaining walls or rebuilding the slopes at shallower slopes.
Due to restricted land and also for economical reasons, the client
decided to opt for the reinforced soil option.
team carried out the design which included reinstating the slopes
by 1.8 m of reinforced soil built at 45° with the remainder
of the slopes being constructed at 18°. The design included
the use of granular fill reinforced with TENAX TT 201 SAMP geogrids.
Three layers of the geogrids were used at 600 mm spacing. The
reinforced fill used was of the Department of Transport Specification
granular fill Class 6F2.
The facing of the slopes were then protected
with TENAX MULTIMAT 100 erosion control matting which were tied
to the geogrids and then filled with topsoil and sown with selected
grass seed. The foundation soils consisted of superficial deposits
with low shear strengths, therefore it was decided to replace
these with Class 6F2 granular fill compacted to 95% maximum density.
The use of TENAX geogrids in reinforcing the M3 motorway slopes,
- the reinstatement of the slopes with 45° slopes thus minimising
- fast construction, using standard plant;
- creating an "environmentally friendly" vegetated
- the most economical solution.