Neutrally Buoyant Bulkhead for Rectangular Tunnel Install

The Challenge

A municipal waterworks contractor came to MRD, Inc. with the request for a bulkhead to seal off two rectangular tunnels connecting a lake to a large metropolitan city. Their sealing requirements included sealing a poured concrete rectangular tunnel with sharp internal corners while workers were present working behind the bulkhead. Bulkhead working pressure was 30′ water head and bulkhead was to be neutrally buoyant to be installed by divers. Sealing and restraint was to be redundant in design due to critical working conditions.

The design required both a highly reliable Sealfast® inflatable seal and a mechanically actuated seal for maximum safety.

Total bulkhead weight out of water.

The final bulkhead design met all criteria. Due the requirement that the bulkhead had to be tipped up into position, MRD, Inc. had to implement a design with sufficient clearance around the bulkhead while still sealing to rough concrete and into sharp, inconsistent internal corners. MRD, Inc. constructed a template for the diving contractors to carry into position to take specific dimensions for guaranteed fit.

Weight in water (water added to produce small positive weight)

MRD, Inc. provided rigorous PE stamped design drawings and feasibility studies to ensure bulkhead performance. MRD, Inc. also provided custom-designed anchor restraint channels to hold the bulkhead in place. Adjustable buoyancy tubes and internal air chambers allowed the customer to easily move the bulkhead into position.

MRD, Inc. provided specialized internal plumbing circuits so that customer could undertake the additional step of proving a seal boundary existed between the mechanical and inflatable seals. A load centering plate was provided between the anchor channels and the bulkhead to distribute the load in the event of single restraint channel failures.

Fully assembled bulkhead with buoyancy chambers installed.

Bulkhead shown from rear view with center rewatering port and centering anchor restraint channel bearing plate.

Side view of bulkhead showing blue front mechanically -actuated seal and black inflatable seal.

Special anchor molded sections were utilized on the inflatable seal to seal into the sharp interior tunnel corners. Retaining clips shown on blue mechanical seal to hold seal in position during buoyant installation. All penetrations were leak-free, including inflatable seal inflation ports.

MRD, Inc. fabricated adjustable positioning brackets that allowed divers to hold bulkhead against the anchor restraint pads during underwater installation.

Anchor restraint channel with bearing pad shown above.

NR-7

The bulkhead was successfully utilized in two separate tunnel installations and the project was successfully completed earlier this year. The bulkhead final dimensions were 8′ wide by 6′ tall. The bulkhead provided proved to be leak-tight underwater, which was expected due to MRD, Inc.’s experienced welding team and rigorous leak-testing protocol prior to shipping. Fully buoyant bulkhead design was achieved as bulkhead weight had to be adjusted to a positive weight underwater using re-watering chambers present in the bulkhead buoyancy tubes.