Neutrally Buoyant Bulkhead for Rectangular Tunnel Install


Neutrally Buoyant Bulkhead for Rectangular Tunnel Install


A municipal waterworks contractor came to MRD 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′ of 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.

3,100 POUNDS

Total bulkhead weight out of water.


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


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


MRD 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 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.

Neutrally Buoyant Bulkhead CAD Render | Showcase Projects | Mechanical Research & Design, Inc., Manitowoc Wisconsin
CAD render showing the bulkhead support components, seals and placement when installed in tunnel.
Mechanical Research & Design, Inc. | Innovation Redefined | Manitowoc Wi

The bulkhead was successfully utilized in two separate tunnel installations. The bulkhead final dimensions were 8′ wide by 6′ tall. The isolation barrier provided proved to be leak-tight underwater, which was expected due to MRD’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.

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