We were contracted by Roundout Constructors to perform detailed inspection and measurements of an existing horizontal drift and submarine door,removal of existing plumbing components,remove and replace a 24-inch gate valve encased in concrete. The work was performed in an access shaft of the Delaware Aqueduct system,owned and operated by New York City’s Department of Environmental Protection. The drift and valve are located in approximately 685 feet of water,at the bottom of an 13-foot diameter shaft,north of New York City.
The purpose of the project was to inspect and verify the condition of the drift and submarine door,remove several pieces of plumbing and replace a valve to allow de-watering of the system.
Prior to start of the project on-site,all aspects of the project had to be performed in a full-scale mock-up,to demonstrate the methodology and constructibility of the tasks. Full-size mock-ups were designed and built addressing the salient points of the project. Highly specialized tooling had to be designed and work plans drawn up simply to get to the work location. All the tools,equipment and personnel had to come and go via an 13-foot diameter shaft. To complicate matters,the top of the shaft was enclosed by a concrete structure with doors on opposing sides,10-feet wide by 15-feet high,that limited access. We designed and built all of the mock-ups,specialized tooling and equipment in our Seattle office. The mock-up demonstrations were carried out at a local shipyard in shallow water. Access to the shaft and drift required the specialized design of components and rigging to move tooling into place. A track system was designed to allow for adjustment in both the X and Y axis,allowing for a consistent,repeatable point to be moved in and out of the drift. A fast-scanning sonar head was mounted to a purpose built cart,combined with some tactile measurements,we were able to achieve measurement of the 70 feet long drift to within +/- 1/8”. The track system and cart were also designed to accommodate the core drill base which allowed for sample cores to be taken at any radial location along the drift.
Sections of the existing 24-inch manganese bronze piping: elbow,tee and needle valve were removed. Piping was cut using a remotely operated rotary mill. Approximately 25,000 pounds of piping was removed. A 24-inch gate valve,encased in concrete to above the valve bonnet was completely exposed using a combination of hydraulic splitting and ultra high pressure water blasting to remove approximately 7 cubic yards of concrete. 1 ¾” holes were cored over 6-feet deep to accept the hydraulic splitters. A detailed plan of the hole spacing and splitting sequence was planned and performed on a mock-up of the valve and concrete encasement in our yard in Seattle to ensure that there would be no stress on the active valve during the concrete removal. This was critical,because the allowable work periods would not have let us return to the project until late fall of 2009. The valve was exposed and removed,and we then completed installation of the new hydraulically operated valve.
Working at 685 feet of water required the use of saturation diving. The complete system was moved into the building that housed the shaft. Every component had to be moved through a 10-foot wide door. This system was set up to accommodate 6 divers. The system is equipped with re-breathers,enabling the reuse of the helium component of the breathing gas mixtures.
In preparation for the upcoming bypass tunnel installation Global Diving & Salvage,Inc. was further contracted to install a mechanical plug to isolate the dewatering shaft from the Delaware Aqueduct in upstate New York. At the bottom of the shaft is a horizontal drift that was used for access during the original construction. The drift has a bronze hemispherical submarine door to isolate the aqueduct from the shaft. Depending on the demand,this door can see up to 1,100 feet of head pressure.
To install the pumps and plumbing required to support the bypass operation the shaft will need to be dewatered. To provide an added safety measure,saturation divers installed a mechanical plug approximately 50 feet into the drift.
The plug weights over 23,000 pounds,is five feet wide by seven feet tall and approximately four feet thick. It has a mechanical seal as well as two grout actuated seals to seal the perimeter. To withstand the over two million pounds of force the plug may see a series of struts were mechanically anchored into the drift walls around the perimeter of the bulkhead.
Highly specialized tooling and fixtures were developed for this project in order to assist the diver in the installation of the plug and its components. Divers were transported to and from the work site by an eight foot diameter diving bell. Given a shaft diameter of only thirteen feet,all materials and tools had to be lowered prior to the bell being launched and had to be retrieved after the bell was recovered.
A detailed rigging plan was developed to allow for the loads to be lowered in the center of the shaft then pulled over to the side wall to allow room for the bell. A track system was installed along the floor of the drift to allow the divers to move the equipment and materials to the plug location.
A remote operated hydraulic crane was also designed and fabricated by Global specifically for this project. The crane,operated from the surface,assisted the diver in handling and installing the various pieces of the plug,some of which weighted up to 500 pounds.