Road Embankment Slope Stabilisation Design

Catagory: Geotechnical Design

Location: County Durham, UK

Client: Durham County Council

Sector: Transport

A road in County Durham, was experiencing slip failure in a northern direction with a surface crack within the asphalt measured on 20th May 2014 at approximately 55mm wide.

OGI was engaged to assess the reasons for the failure of the ground beneath the road, and to advise on engineering techniques to stabilise the ground embankment, which would enable the repair of the road to be carried out.

Causes of Slope Failure

Tension Cracks

Tension cracks caused by the steep embankment batter angle, resulted in low horizontal total stress due to reduced support.

Reduction in Shear Strength

Reduced shear strength of the cohesionless soil, caused by high pore water pressure lowering the effective stress in the granular fill.

Slope Face Degradation

Slope face degradation from saturated soil exposed on the batter face, caused a shallow slip where the granular fill dried out.

Existing Drainage Issues

The existing drainage trench channelled surface water and acted as a land drain, increasing flow rates and water pressure beneath the road.

Solution

Pore Water Pressure

Permanent reduction of excess pore water pressure in the fill beneath the road, using a combination of a drainage and a pore pressure relief system.

Fill Material

Improvement of fill material to have sufficient strength for the geometry of the steep road embankment.

Slope Stability

Improvement of the embankment face through slope stabilisation techniques to prevent progressive failure of the granular face.

Existing Drainage

Improvement of the existing drainage trench to effectively catch run off water from the road surface and adjacent field, to prevent surface water entering the drainage system beneath the road.

Additional Drainage

Additional local drainage added to the existing system between the toe of the embankment and the burn to alleviate progressive failure of the slope.

Full Remediation

Remediation of not just the effected slope but also surrounding area to prevent wider slip failure occurrences and mitigate future ground movement.