A photo shows an empty “room” with gleaming white walls and ceiling, perhaps part of a new laboratory facility? Perhaps a dust-free space in a manufacturing plant? Or will it be an environmentally-controlled storage area?
None of the above.
The photo is of a recently rehabilitated, badly deteriorated sluice gate operating chamber above a wet well at an influent pump station in the city of Houston’s Almeda Sims Wastewater Treatment Plant, and it is 34 feet below ground. The treatment plant is 39-years- old, normally treats 20 million gallons per day (MGD) and can flow as high as 80 MGD in extreme wet weather.
“The plant is old and had a major piping failure which flooded a dry well and shut down more than half the plant,” said Mark Boyer, president, Boyer, Inc., the prime contractor for the project.
Boyer was called in to make repairs under an emergency contract to get the station back in operation. A temporary flow bypass was set up so that initial repairs could be made to the pumps and controls to get at least part of the pump station back in operation. While making the initial repairs, it was discovered extensive work was necessary that would require long-term bypassing of the influent pump station. Without it, there was no way to clean the wet well and repair or replace piping, valves and refurbish the pumps.
Boyer developed a design/build plan to create a permanent means to bypass the pump station for current and future repairs, and scheduled maintenance. The proposal called for constructing a diversion structure over the existing 84-inch influent tunnel and lining it entirely with Danby PVC grout-in-place pipe liner, to make it corrosion resistant. Normally used for man-entry installation in pipes of diameters of 36 inches and greater, Danby LLC President Mike Spero said the combination of the ribbed profile of the rigid PVC liner and the highly fluid nature of the grout combined to produce a highly integrated structure with the PVC liner “tied” to the original pipe through the grout which, in addition, provides some direct repair of the old pipe.
“The result,” he said, “is a structural rehabilitation of the pipe and a lining that will prevent corrosion.”
Spero said the 20-foot diameter by 50-foot deep diversion structure was constructed by installing 60-foot deep auger cast secant piles, constructing concrete ring beams as the interior was excavated, pouring a bottom slab, then placing rebar and installing the Danby PVC vertical panels.
“The interior forms were set and the 10-foot lift of concrete was poured pushing the Danby panels tight against the forms and integrating them into the wall,” he continued. “This was repeated in 10-foot lifts until the entire structure was complete. Danby panels were installed for the floor and locked in with high-strength flowable grout.”
Rehab needs grow
During the temporary bypassing, it was discovered that there was extreme deterioration of two junction boxes, a sluice gate operating room over the wet well, and two 84-inch diameter concrete connecting pipes.
The project was expanded to repair and line all of these structures with Danby PVC lining.
After the full flow bypass system was installed and operational in November 2011, Boyer crews were able to enter the wet well, clean it and make the repairs to the piping, valves and pumps to get the pump station totally operational. Once these critical functions were restored the rehabilitation of the deteriorated structures and pipes could begin.
“Before the liner could be installed, surfaces were cleaned and a 10,000 psi water blaster was used to remove any loose or deleterious material,” said Boyer. “Personnel entered the 45-foot-deep structure through the influent line. Hydraulic cement and Avanti chemical grout injection were used at joints to control ground water infiltration.”
A removable cofferdam was placed in the diversion chamber to raise the flow level so that three 75-horsepower submersible bypass pumps could operate. The Boyer-designed, proprietary arched coffer dam required no cast-in-place hardware to function in the diversion chamber. A unique feature, added Boyer, is its ability to by-pass the flow over the top without any human action preventing costly sewer over flows.
“Workers were now able to access the connecting sewers, junction boxes and wet well through the dry side of the cofferdam,” Boyer continued. “The bypass pumps could handle the peak dry weather flow and small rain events. When a major storm occurred, crews were evacuated and the flow allowed to top over the cofferdam and flow into the wet well where the now-refurbished main pumps could be activated. Whenever this occurred, major re-cleaning was required.”
Because of the level of deterioration, Boyer said rebar was installed to replace the steel loss from the original host structures and pipe.
First in U.S.
“The Danby system,” Spero explained, “normally is spiral wound from coils for lining circular, elliptical, or arch pipes. Panels are used for more unusual non-circular shapes. The system can be adapted to line just about any shape. Although it has been used overseas to line chambers and manholes, this is the first major use of the panels installed vertically in the U.S. Because the Danby material is rigid PVC, it is ideally suited to resist the high groundwater pressures encountered on this project.”
One junction box was circular, 20-feet in diameter, 20-feet high of cast-in-place concrete with a concrete slab on top with a 9-by-9-foot square opening. On top of that, was a 9-by-9-foot precast concrete box 25-feet high with a concrete slab top at grade. Its walls were described as almost completely corroded.
“The ground level top slab was removed for access,” Boyer said. “It was decided to make the rehabbed structure an 8-by-8-foot box for its entire 45-foot depth. Eight-foot wide by 10-foot high Danby panels were assembled above ground by connecting eight 12-inch wide by 10-feet long vertical panels, lowering those into position, and connecting them with 90-degree PVC corner strips. Ten-foot high modular concrete forms were set against the Danby panels and concrete poured from above. This process was repeated for the entire 45-foot-deep structure. The half pipe invert of the chamber and the spring line shelves were also lined with PVC.”
The other junction chamber was a below ground structure and not directly connected to the surface, Spero said. The 13-by-15-foot chamber had only the upper 12-feet lined with Danby panels since that was the only part that was ever above the water level and the only portion that had corrosion.
“The support beams and ceiling of the chamber were also Danby lined,” he added. “PVC panels were individually installed, fitted and field trimmed where required. High-strength, 6,000 psi grout was pumped to this location to lock the panels in place and rehabilitate the structure. Grout was introduced from the top of the forms which were supported by scaffolds and shoring and internally braced.”
A 15-by-27-foot, 12-foot-high sluice gate operating room was above the wet well and connected by two square openings.
The room was only accessible through a stainless steel marine watertight door.
“Apparently this door had been leaking water and fumes from the wet well so it had been previously welded shut,” said Boyer. “Crew members refurbished the door making it operational and water and gas tight. In addition to being subject to fumes and humidity from the wet well, most major storms flood this room. The walls and ceiling had lost more than six-inches of concrete in some locations and most of the inner layer of rebar was missing. The Danby panels in this room were individually installed and the grout pumped into the top of the wall. The ceiling was then installed and the grout pumped into grout holes at the peak.”
Two 84-inch connecting pipes are between the two junction chambers and connect one to the diversion chamber.
Parts of these pipes were extremely deteriorated and there was significant groundwater infiltration, Boyer said. Additional steel reinforcement was added and water leaks were plugged. Steel bolsters are attached to the pipe wall to properly space the liner. Using 300-foot long coils of 12-inch wide Danby material, the liner was spiral wound into the pipe and the panels connected with a mechanically locking, gasket joiner strip.
“They were installed using a handheld, palm-size pneumatic hammer,” Spero explained. “The same joiner strip is used to connect the individual panels in the other parts of this project. One pipe is 30-feet long; the other is 80-feet long with a 30-degree bend. Once the liner is installed, grout ports were drilled at predetermined levels along the length of the rehabilitated pipe. The pipes were grouted in lifts of 12 inches.”
In summary, Boyer observed the project was extremely complex where every aspect of construction had to be planned around an operating wastewater treatment plant.
“This was an older facility that had been expanded and upgraded numerous times and not all the plans were available or accurate,” he said. “Many times unknown and unexpected pipes, conduits and conditions were discovered. This facility now has a new lease on life with many parts restored to better than original condition and protected against future deterioration. The city now has the ability to bypass flow around the influent pump station and can schedule maintenance and make repairs when required. This project demonstrated that severely-deteriorated concrete structures can be effectively renewed and protected from future corrosion regardless of the existing condition, location, size or shape.”
FOR MORE INFO:
Boyer Inc., (713) 466-5395, www.boyerinc.com
Danby LLC, (281) 598-1126, www.danbyrehab.com
Avanti International, (281) 486 5600 or (800) 877 2570, www.avantigrout.com