Economic Link Road, Cross Hands (Coal Mine Treatment and Geotechnics)

Outcome:

In a complex geological setting, we have helped enable the cost-effective design of a new link road, by systematically investigating the chosen route and delineating/assessing the variable hazards along its 2km length which included, for example:
- Historical mine workings, quarrying and landfill;
- Low strength soils;
- Shallow groundwater, and;
- Structurally complex bedrock.

Geotechnical design checks and construction advice has been provided relative to each hazard and where required, remedial works have been undertaken to mitigate potential unacceptable subsidence risks posed by historic coal mining. In keeping with the client requirements, we have provided flexible design support as and when needed and have ensured that a tight schedule has been maintained despite design changes and variable conditions being encountered during the construction phase.

Project Details:

We have been providing geotechnical design checks for the Phase 2 portion of a new link road which is intended to ease congestion and to provide opportunities for development and economic growth in the Cross Hands area. The proposed 2km route traverses agricultural land underlain by Quaternary Deposits and Lower/Middle Coal Measures bedrock which has experienced significant localised deformation.

Historic mining and quarrying has occurred across the route with areas of landfill also present.

 

 

Following a detailed desk-based review, extensive focused investigation across the route allowed us to develop a Geoenvironmental and Geotechnical chainage hazard assessment for the client based on the ground model proven and the proposed design. This allowed the team to focus on critical areas and provided a useful hazard guide for the contractor during construction. This included a detailed Coal Mining Risk Assessment which allowed a Coal Authority approved remedial strategy to be developed, consisting of the recommendation of basal reinforcement in areas of moderate mining risks and the delineation of higher risk areas requiring remedial stabilisation. Remedial action consisting of drilling and grouting in an area where shallow mine workings were proven in the Pumpquart and Trichwart coal seams (Lower Coal Measures) was designed, supervised and checked by ESP through 2018.

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We prepared geotechnical design reviews, which included a deep cutting in structurally complex bedrock and a large embankment over localised low strength peat, clays and thick Made Ground associated with surface mining. Slope modelling allowed a cost-effective design to be developed with minimal reinforcement. The design also enabled the re-use of site won materials, which has lowered disposal costs and improved the sustainability of the project.

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