Damp problems that might occur in a below-ground level bakery at an Asda store in Walsall have been overcome by using Delta-NP Drain from Delta Membrane Systems.
The store at Shannon Mill is a mixed development scheme with apartments above. The bakery and car park for the store have been placed below ground level on a very wet site where severe water ingress and soil erosion were inevitable.
To overcome these problems, Delta-NP Drain membrane is fixed to the piled foundations of the store and apartment structure. The soil and between the piles is bound and held back by the Delta-NP Drain. Water is allowed to pass through, and this is drained down in the void in the middle of the membrane, into a channel cast into the ground slab for disposal.
Delta-NP Drain features a two-layer design. The first is a polyethylene drainage sheet with a dimple profile pattern – giving it high strength, durability, and increased drainage capacity. The dimple sheet keeps incoming water away from the structural sealing layer.
Layer two is a polypropylene geotextile mat securely bonded to the dimple crowns by thermal welding. The rot-resistant geotextile removes suspended soil particles and prevents clogging of the flow passages in the dimple texturing.
In total, some 1,500m2 of Delta-NP was used on this project which is a mixture of Grade 1 and Grade 3 basement constructions. As Delta Project Manager, Paul Durham explains: "BS 8102 dictates how to keep water out of basement structures. Grade 1 is a car park where there is an acceptable amount of water ingress allowed. With Grade 3, for health reasons, no penetrating water or damp formation is permissible – and this is the grade demanded for the bakery."
Apart from controlling the damp ingress, Delta-NP Drain is also being used to give stability to a 100mm dense concrete block wall.
The fixing heads of the plugs (which fix the Delta-NP Drain to the concrete piles) are also being used to tie into the finishing block wall. This then ensures the block wall is structurally tied to the piles themselves.
Fixing plugs in the Delta-NP Drain have a small hole in their heads. These allow the screwing-in of ties, which then sit in the wall’s mortar joints.
Overall, Delta-NP Drain has solved a number of significant issues in the construction of the bakery and car park at this branch of Asda.
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