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Kingston Tunnel
Kingston Tunnel
Kingston Tunnel
Kingston Tunnel
Kingston Tunnel
Kingston Tunnel
08-09-2014

In Kingston, New York, the tunnel on Washington Avenue was built around 1900 for conveying lake water to the city. At that time it was customary to design brick tunnels with elliptical, or horseshoe cross-section. By 1920s, the tunnel was converted into a combined sewer. Eventually the need arose for a separated system and a sanitary pipe was added. The 24" crown arch was added to create a new sanitary drain which later was covered with concrete. This created a new invert, reducing the height of the remaining tunnel to 43".

In 2011, about 100 years later, Washington Avenue roadway developed a pothole that rapidly formed a large sinkhole endangering houses on both sides of the street. Subsequent inspection revealed brick liner deterioration and ground-water infiltration. It was determined that the sink-hole had been created by the infiltration caused loss of overburden into the tunnel. 

Sink-holes had been encountered already earlier in 1985 in Kingston. Similar sinkholes had developed due to several collapses of an elliptical sewer.

Trenchless Technology in 1985 was still a very new idea. At the time Link-Pipe had been the only company offering short repair instead of complete relining. Up to this time, Link-Pipe had developed No-Dig repair technology only for round pipes. Appreciating the opportunity, Link-Pipe decided to create a Research & Development program to develop an elliptical and tear-drop PVC repair sleeve.

When Washington Ave sinkhole developed in 2011, Kingston Department of Public Works inspected 25-year old repair of the elliptical sewer and found it in excellent condition. This gave Kingston Deparment of Public Works the idea to contact Link-Pipe again.

TUNNEL CONDITION AND DESIGN DEVELOPMENT

The brick tunnel is situated 87' below the street surface. Sandy water-bearing soil reaches down to the tunnel exerting high hydraulic pressure on the tunnel structure. Inspection revealed large amounts of fine sand filling in places the conduit almost to the crown.

At some time a diversion drain for sanitary sewage was installed on the invert of the tunnel's. The drain had then been embedded in concrete forming a new tunnel invert 43 inches below the crest of the crown.

Brick horseshoe tunnel presented a new design challenge. Link-Pipe decided to offer a solution to rehabilite of what had become a dangerously unstable brick arch structure with concrete invert. A research & development project was set up. The design addressed the problems and tests on the prototype liner showed it to have the strength and suitability of the design assumptions.

One of the limiting design parameters was the need to pass the repair sleeve through the 30-inch diameter and 80-feet deep access shaft. Then it was to be assembled at the bottom of the shaft before passing it into the tunnel.

Once the design was completed, a prototype was built and tested in a mockup tunnel. Factory is an ideal work environment compared to field conditions. Several practical steps had to be developed in the factory before the sleeve was ready for field testing. For this purpose a full-scale testing mandrel was built.

After in-house testing was completed, the prototype was shipped to the contractor for tests associated with work conditions. In this process the crew had been assigned by the contractor to work in the tunnel.

In the design stage it was anticipated that hydraulic jacks are needed to install the liner. However, it turned out that the tunnel dimensions were loftier than shown in design drawings and it became possible to eliminate jacks altogether. This simplified the installation process for the crew who expected to encounter very cramped workspace in the tunnel.

One of the main issues that came up was how to secure safety of workers in the tunnel. Structural integrity of the 100-year old brickwork was compromised in several locations and loose material from the arches could randomly fall while people were working in the tunnel. The liner was not designed to be independently stable. It needed lateral support from the brickwork, or in case this was lacking, confinement had to be created. The problem was solved with the cooperative effort of Link-Pipe and the Work Crew. Liner segments were made structurally adequate against falling debris by wedging the liner tight against the old brickwork.

The repair sleeve is made of rigid PVC plate. For safety, the liner is secured by wedges to provide the necessary lateral support because of unpredictably falling debris. The resulting loads that may affect the liner are also unpredictable. This requires that a high safety factor is applied in strength design of the liner. Factor of Safety 25 was chosen.

INSTALLATION OF LINK-PIPE PVC SLEEVES

Proceeding with the installation soon further concrete protrusions were discovered left when the tunnel was altered when the new sanitary sewer under the invert was installed. Since it was considered too expensive to chip off the excess concrete, it was considered easier to adjust the sleeves. Link-Pipe set up a process to do the changes on location as more adjustments were anticipated as the work progressed.

After all adjustments had been made, the Sleeve installation proceeded and soon it came the time to grout the sleeves in place.

CONCLUSIONS

The100 years old tunneling technology with its dimensional inaccuracy was overcome by application of Link-Pipe technology. All needed adjustments were accomplished.

The 80-foot deep shaft with 30" diameter was a challenge, but it was overcome by Link-Pipe technique of making liner components small enough to pass and then assemble them on the bottom of the shaft.

Once the sleeves were wedged into position in the tunnel, high design factor of safety was assured. This also secured the Worker Safety.

Finally: Pumping the annular space full of cement grout completed the job.

The project was completed on schedule.