This project involved creating a petrol filling station site on an old steelworks slag/clinker heap. Over 19000 m3 of material was excavated to form the level site into the side of the slag heap. The vertical height between top and new forecourt level was 23 metres requiring significant retaining structures.

Design also focused on the visual impact and how the structures could be softened and avoid dwarfing the 6 metre high forecourt canopy. A retained earth profile which created upper and lower retaining walls with a steep graded section between them was selected.

Solution:
The construction method involved the Main Contractor reducing levels in phases with Phi Group soil nailing and stabilising each cut face before moving on to the lower stage. In order to maintain stability of the variable materials while soil nailing Phi Group predrilled the full depth of the retaining wall faces using 100mm diameter mini piles at 1.0 metre centres reinforced to span between undisturbed levels and the stabilised areas. The ground itself arching horizontally between the mini piles.