LARGE DIAMETER HDPE SLIPLINING WHERE EXPERIENCE MATTERS

Transcription

1 LARGE DIAMETER HDPE SLIPLINING WHERE EXPERIENCE MATTERS Luis Aguiar Assistant Director Water Operations, Miami-Dade Water and Sewer Department Rafael Ortega President, Aurora Technical Services, LLC Robert J, Card Chief Pipe Engineer, Lockwood, Andrews & Newnam, Inc. ABSTRACT With the infrastructure aging and having to be extended beyond its useful life, the need for municipalities and governmental agencies to do more with less funding is even greater! As such, over the last several years, the use of HDPE for sliplining has increased in its use. Most recently, the use of HDPE for sliplining applications has become a viable alternative for large diameter and pressure pipe rehabilitation. This presentation will discuss Miami-Dade s ongoing experience in dealing with their aging infrastructure by using HDPE to slipline both large diameter lines and pressure pipes. The presentation will discuss the HDPE sliplining lessons learned in Miami-Dade and will also discuss some experiences in other regions of the USA. The experience discussed will include case studies involving 72-inch, 42-inch and 36-inch sliplining in both water and wastewater applications. The lessons learned will be highlighted. A common element in each of the applications in Miami-Dade and in the other installations across the USA that will be discussed is that Experience Matters. The experience applies to all aspects of the installation engineering, material and contractor s installation. BACKGROUND HDPE is now used in specialized applications across the United States. Examples of this include horizontal directional drilling (HDD) and sliplining existing water and wastewater pipes. Miami-Dade Water and Sewer Department (WADS) has utilized HDPE in these applications. Following is a discussion on one such recent use of large diameter HDPE pipe.

2 Miami, Florida 72-inch Force Main Pipe On June 18th, 2010, a portion of a 72-inch Prestressed Concrete Cylinder Pipe (PCCP) force main experienced a catastrophic failure. The corresponding failed pipe, along with an adjacent pipe segment, were removed and replaced at that time. Photo 1, failed 72 PCCP A forensic analysis of the failed and adjacent pipes suggested the primary mode of failure to be loss of structural integrity resulting from corrosion-induced hydrogen embrittlement of the Class IV prestressing steel wires. It was further believed the pipe section may have had pre-existing wire break damage and that a pressure transient, or surge event, could have increased the pressure inside the 72-inch force main, causing the failure. Due to concerns over the condition of the pipeline, and the risk associated with an additional failure, in November, 2010 WASD contracted a company to perform an internal inspection and a condition assessment of the 72-inch force main's prestressing wires. Pipeline inspection, engineering analysis, and condition assessment of the 72- inch force main were conducted between January and February Based on the results of these inspections, approximately 1.5 miles of the force main was rehabilitated by slip lining the existing 72-inch force main with HDPE under an emergency contract. WASD Commissioned Lockwood, Andrews and Newnam, Inc. (LAN) in May, 2013 to investigate the conditions along the existing force main s corridor for the purpose of establishing a conceptual design for the rehabilitation of the remaining 3.5 miles of the 72-inch PCCP force main. This conceptual design included utilizing either slip lining the existing 72-inch force main with 63-inch outside diameter HDPE or installing cured in

3 place pipe (CIPP). However, due to the size of the force main, and the internal pressure that was required, CIPP was found not to be a viable alternate. WASD decided this project would be constructed as a Design-Build contract, meaning that the constructor (contractor) would team with an engineering firm to take the LAN supplied conceptual design to 100% fruition. Bids for doing this work were received in December, 2014 and construction commenced in October, 2015 during the dry season in Miami, Florida. The new DR inch HDPE that was to be inserted into the existing 72-inch PCCP was butt fused together on site and the pipe was strung out along the right of way, including using the canal that was immediately adjacent to the site. Photo 2, HDPE strung out along the right-of-way The flow into the 72-inch force main was halted on November 1, 2015 and the construction of the rehabilitation commenced. Because this work was scheduled for the dry season in Miami, the flow bypass designs required much smaller pipe than wet weather construction would have yielded. Then, on November 7 th, a 100 year storm hit Miami, causing severe backups in the bypass system and a major overflow at a pumping station. Subsequently another major rain event hit Miami in December, causing yet more problems with the bypass system. The project was completed in early April, 2016 and the force main is back in full operation. Even with the storm delays, the project came in on time and on budget with minor additional changes. All told, approximately 3.5 miles of HDPE was installed by sliplining in 10 separate pulls. Based on available information, this is the largest HDPE sliplining project completed in the United States too date. Houston, Texas 42-Inch Water Main Pipe

4 During the early morning hours of June 8, 2004, an existing 42-inch water main in Houston suffered a catastrophic failure. This failure occurred in a pipe section of PCCP installed in 1991 through 1992 that supplies water to an area of approximately 75 square miles in Houston, TX. The City of Houston (City) authorized LAN to assist in the failure assessment and to design the repair for the water line. Photo 3, Houston, Texas 42-inch failure Immediately following the rupture, LAN performed a visual inspection of the failed water line and testing of mortar and wire samples. Internal observations of the pipe revealed longitudinal cracks along the crown and spring line on both sides of the pipe. Further inspection revealed the internal cracking appeared consistently at invert, crown, and spring lines for a distance of approximately 25,000 linear feet. The visual inspection was accompanied by sounding to determine if the mortar lining was delaminating from the steel cylinder; however, the lining did not exhibit any noticeable delamination. The pipe was deemed to be unfit to be placed back in service without major rehabilitation for a distance of the 25,000 feet with substantial damage. Based on the analysis performed of the City s operations, it was determined the repeated rapid closure of an emergency shut-off valve within the plant probably created pressure transients which could have exceeded the pipe design and caused the pipe to fail. Hydraulic modeling of this closure scenario performed after the failure indicated that pressures in the pipe could have surged above the maximum design of the pipe of 150 psi for a total surge pressure of approximately 300 psi. The excessive pressure

5 zone was shown to extend approximately 25,000 linear feet from the pump station, which corresponds well with the visual inspection observations. Photo 4, failed pipe section after removal Due to the extent of damage observed and risk of collateral damage in the event of a second failure, it was determined the 42-inch water line could not be placed back in service at full pressure without extensive rehabilitation. The potential for further catastrophic failures is likely if the operational pressures exceed the steel cylinder s pressure sustaining capability (determined to be on the order of psi). Hydraulic modeling of the area suggested that groundwater wells alone were not sufficient to meet the upcoming summer peak water demands in the area. Therefore, the City was faced with the task of rehabilitating 25,000 linear feet of 42-inch water line and safely returning it to service before upcoming summer peak water demands. This schedule left only ten months to complete both design and construction. Four potential options were evaluated: 1) Remove and Replace, 2) Installation and Abandonment, 3) Sliplining, and 4) Rehabilitation with Internal Reinforcing When comparing the four options, sliplining was found to be the lowest cost and the line could be placed back in service for the summer demands. Additionally, sliplining could be accomplished with minimal excavations, reducing the impact on the surround area that had become more developed since the time of the original 42-inch water main installation. Therefore, the project moved forward with DR 17, inch diameter HDPE as the chosen option.

6 The HDPE pipe installation required the preparation of approximately 40 pits as insertion and receiving pit for each segment installed. The fused sections ranged from approximately 1,700 linear feet to approximately 300 linear feet. The contractor was able to install approximately 6,000 linear feet of pipe per month, and completed installation of the HDPE sections within four months of notice to proceed. Another two months was spent installing valves, fittings, disinfecting the new pipe and restoring pavement. Photo 5, HDPE butt fusing By sliplining the existing distressed water main instead of traditional open-cut installation of a new main, the City was able to restore the surface water supply to prior to the onset of the summer peak demand.

7 Photo 6, pits San Francisco, California 36-inch Force Main Pipe Due to repeated failures of an existing 36-inch steel force main, the City of San Francisco Public Utility Commission (SFPUC) elected to rehabilitate the sewer force main under an emergency procured design-build contract. The existing steel force main was installed along The Embarcadero. This shoreline drive along San Francisco bay is adjacent to the Ferry Building. The 36-inch pipeline force main was originally installed in the mid 1970 s. The line had previously been repaired multiple times throughout the years using various methods including internal joint seals. Furthermore, due to the congested corridor, several utilities, including a duct bank, containing 8 each of 2-inch conduits, was subsequently installed directly above the majority of the force main. An existing BART platform was installed around the 36-inch force main. Due to the obstructions in place during the construction of the original 36-inch force main, there are multiple double offsets throughout the line (ranging from 5 degrees to 14 degrees). In a few locations the bends were located within a few feet of each other presenting complications to the sliplining process. Due to the proximity to the Bay, dewatering of the excavations was not feasible (due to the influx of bay water and the influence of bay tides) and the shoring had to include a watertight interlocking capability and a seal slab. The fill material encountered was comprised of building and ship debris used to expand the bay front over 100 years ago after a major earthquake. Since the force main serves as an integral part of San Francisco s wastewater system, the follow constraints existed: No more than 24 hour shut down If a shutdown took place for more than 15 hours, the ensuing shut down could not take place for 4 days Once breached, the force main had to be returned to full service.

8 The HDPE line was determined to be 28 OD DR 26 for an internal pressure rating of 80 psi. Due to the annular clearance, the OD of the fused seam was not removed. The challenges during construction were significantly increased due to the traffic control requirements. The Embarcadero is located along the San Francisco Bay. Traffic counts exceed 40,000 vehicles per day every day of the week. Additionally, due to the road s proximity to the bay, and the number of shops and businesses facing the bay, pedestrian traffic is non-stop throughout the day and only lessens during the early dark hours of the morning. Photo 7, the Embarcadero Due to the tight site constraints, the laydown area for stringing the fused HDPE sections and pulling the pipe in place limited the construction approach to sliplining the force main. Rollers were used for deflecting the HDPE while inserting the pipe from on above the ground into the host pipe. This allowed the use a smaller size of pits; see Figure 8. These rollers were aligned to comply with the material s bending radii and limiting the pull forces required to insert the HDPE. Figure 8, rollers and HDPE pipe strung along the Embarcadero As a precaution, the original force main was CCTV inspected to identify potential problems with inserting the HDPE liner. Although there were a higher number of previously performed joint repairs than originally expected, the interior of the line was in

9 relatively good condition but did require the removal of the previously installed joint seals. Photo 9, HDPE insertion The liner was lubricated with bentonite slurry to reduce the friction and decrease the potential for gouging the liner while pulling. To confirm the maximum allowable stresses in the liner were not exceeded, the tension during pulling was constantly monitored. LESSIONS LEARNED Several lessons have been learned from inserting HDPE into an existing host pipe. The follow are some of the key lessons reinforcing the premise that Experience Matters; HDPE provided several advantages for the projects. It provides material flexibility to maneuver through tight bends and its lightweight nature permitted the work to proceed with less equipment and associated noise to the congested sites. But, to achieve success requires understanding the limitations and strengths of HDPE pipe material. A project involving significant challenges cannot be successfully completed without detailed planning at every stage of the project. Every detail, including the small ones, need to be considered. Based on the past experience nothing can be left to chance. It is important to identify early in the design process the work areas for fusing HDPE pipe and stringing the pipe for insertion. This enables the permitting

10 process to start early and to incorporate any restrictions into the contractor s scope at the time of bidding. Although, a lot of this is up to the contractor s methods and means, based on experience, the owner and design team are in the best position to identify the constraints and thus reduce the potential for field changes. CCTV or other internal inspection of the host pipe prior to inserting the HDPE pipe is recommended. This intermediate step will confirm the host pipe conditions and avoid delays during insertion. They key to this is having an experienced engineer review the CCTV to address the risks prior to starting the inserting process. Dewatering or installing watertight shafts for insertion will aid in the longer pulls. The presence of groundwater can dilute the lubricant and significantly increase the pulling forces in the longer sections while inserting the pipe. Some amount of groundwater is normally not an issue. The experienced field team can differentiate what volume of water is acceptable. The bypass system for sewer and force mains should normally be designed to handle wet weather flows no matter which season of the year the construction is performed. The critical step is determining what are the wet weather flows not just what normally pumped. Creative Solutions. A key consideration during the installation process is to remain flexible and to respond quickly to different situations encountered. The approach should be a collaborative effort between the design team and the contractor. This collaborative effort creates a balance between the technical needs of the project while adhering to the project schedule constraints. But, the collaborative effort requires both parties to be experienced to avoid costly delays. Based on the success use of HDPE to rehabilitate water and wastewater lines, sliplining the existing pipe with HDPE pipe material will typically save the owner significant time and dollars, lower the impact on the area, and overall reduce the duration of the project. But, to maximize these benefits requires experience.