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Case Study Retrospective Installation – St John’s Retail Park, Somerset

At St John’s Retail Park in Devon concern was raised over the measures installed to protect the building from methane and carbon dioxide gas present in the ground. Although a gas resistant membrane had been installed below the floor and below the membrane a manifold of perforated pipes to passively vent the gas safely to atmosphere both gases had been detected inside the retail areas.

Investigations at the site revealed extensive settlement of the ground which it was thought may have disrupted the vent pipes and also compromised the membrane by being partially adhered to the cast concrete and in areas of non adhesion becoming distorted by the settlement and causing failure of the membrane. To rectify the situation and restore the protection 3no. Positive Pressurisation Units were installed. Connected directly to the ground below the building they now introduce fresh air to the oversite and dilute and dispersed the gas to create and maintain a Clean Air Blanket system of gas protection.