Rock Slope Stability Assessment, Stembridge, Llanrhidian
Introduction:
During a period of heavy rainfall, failures occurred within a rock slope above the main North Gower access road, causing a significant traffic hazard, particularly given the limited sight distance available to motorists.
ESP undertook a geotechnical inspection of the exposed rock slope and evaluated the ongoing risks to motorists via a number of potential failure mechanisms, including those caused by vegetation. We also provided recommendations for cost effective remedial measures, including defining those required urgently, and those which were less urgent, albeit necessary.
The remedial works assessment required careful consideration due to the particular site constraints. ESP subsequently supervised the urgent remedial works to ensure that the immediate risks were mitigated.
Details:
We undertook a desk study review of historical and geological information for the local area to establish the geological setting of the road cutting. This was then followed by a careful rock slope stability assessment of the exposed slope to determine the nature of the material and discontinuities within the face. Slit trenches were excavated to allow precise identification of the rock mass properties.
The kinematic potential for a number of rock slope failure mechanisms was assessed, and the risk of further rock failures impacting on the highway evaluated including appraisal of geotechnical, geometric, and traffic factors. A Rock Hazard Rating system was then implemented, including assessment of motoring/traffic factors in addition to rock slope factors, to provide an overall rating score, which is used to define the level of risk.
A number of remedial measure options were recommended based on risk and benefit; some measure were urgently required.
We subsequently supervised de-vegetation, re-profiling and scaling works on the basis of our recommendations to mitigate the immediate risks. Concrete barriers were placed along the slope toe, and the carriageway was widened on the opposite side of the road. Regular inspections of the rock slope are being implemented to review ongoing stability and ensure the safety of motorists maintained.