Miami-Dade s Force Main Government Cut Replacement Project

Transcription

1 North American Society for Trenchless Technology (NASTT) NASTT s 2014 No-Dig Show Orlando, Florida April 13-17, 2014 Paper MA-T5-03 Miami-Dade s Force Main Government Cut Replacement Project Norman Joyal, PE 1, Steve Mancini 2, Orlando Castro, PE 3, Ray Post 4, Jeffrey Weakly 5, Glenn Boyce, PhD, PE 1, Eduardo Vega, PE 6 1 Jacobs Associates, Walnut Creek, CA, USA 2 Ric-Man Construction, Inc., Detroit, MI, USA 3 Hazen & Sawyer, PC, Coral Gables, FL, USA 4 Michels Corporation, Brownsville, WI, USA 5 Super Excavators, Inc., Menomonee Falls, WI 6 Miami-Dade County Water & Sewer Department, Miami, FL, USA ABSTRACT: Miami-Dade Water and Sewer Department (MDWASD) owns and operates a 54-inch (1,370 mm) force main that transmits sewage from Miami Beach to Fisher Island and then onto the Central District Wastewater Treatment Plant on Virginia Key. The force main crosses Government Cut with a top-of-pipe elevation that conflicts with the Federal Navigational Dredging Project, which proposes to widen and deepen the channel to increase the Port of Miami s capacity. To accommodate the US Army Corps of Engineers dredging project schedule, the replacement force main must be designed, constructed, and commissioned prior to the start of channel deepening. Ric-Man Construction s design-build team designed the replacement force main as a two-pass microtunnel containing a 72-inch-diameter (1,830 mm) steel casing with a 60-inch-diameter (1,525 mm) fiberglass carrier pipe. The 1,178-foot-long (359 m) force main was constructed from a secant pile shaft on Fisher Island to the secant pile receiving shaft constructed in the water. During an inspection of the then-existing prestressed concrete cylinder pipe force main after construction started, the segment of force main that passes beneath the Miami Beach Marina was deemed vulnerable to imminent failure. Therefore, a second 689-foot-long (210 m) drive from Miami Beach to the Water Shaft was added to the project. The first drive across the shipping channel was completed in February 2013, and the second drive from Miami Beach to the Water Shaft was completed in May This paper discusses design and construction of the pipeline crossing, and presents information collected during construction. 1 INTRODUCTION The Miami-Dade Water and Sewer Department (MDWASD) recently completed a project to replace the existing sewer force main under the Port of Miami navigation channel in Biscayne Bay. The existing 54-inch (1,370 mm) force main was a prestressed concrete cylinder pipe (PCCP) that conflicted with the Port of Miami s Federal Navigational Dredging Project, which will deepen and widen the harbor and channels, beginning in The Port of Miami s dredging project will expand the Port by dredging the bay to allow new, larger cargo ships to enter the port. This project is related to the New Panamax project, which involves a major expansion of the Panama Canal. The Port, which is currently 42 feet (13 m) deep, will have to be dredged to 50 feet (15 m) in depth to allow the new Super Post Panamax megaships to enter the Port. The dredging project along with port facility improvements will make the Port of Miami capable of berthing even the second largest container vessels in the Paper MA-T

2 world, the new Maersk Triple E Class vessels, which will have a draught of 48 feet (14.6 m) and will be nearly 200 feet wide (61 m). MDWASD owns, operates, and maintains a 54-inch-diameter (1,370 mm) prestressed concrete cylinder pipe (PCCP) force main that transmits wastewater from the City of Miami Beach and from communities further north including Surfside, Bal Harbour, Bay Harbor Islands, and North Bay Village, under Government Cut, across Fisher Island and under Norris Cut to the 143-mgd Central District Wastewater Treatment Plant (CDWWTP) at Virginia Key. The pipe does not have redundancy and could not be taken out of service. The tie-in to the existing force main was originally going to be made from the Water Shaft constructed adjacent to the existing force main just outside the Miami Beach Marina (see Figure 1). During construction, an inspection of the condition of the existing 54-inch force main found several defective segments between the in-water retrieval shaft and the City of Miami Beach force main, which discharges into the MDWASD pipeline. The inspection was made by Pure Technologies (2011) via an electromagnetic survey launched from Miami Beach. As a result of the inspection, the design-build team installed a second 689-foot-long (210 m), 72-inch-diameter (1,830 mm) microtunnel from a new launch shaft at the very southern tip of Miami Beach to the Water Shaft to replace the defective pipe segment (see Figure 2). Figure 1. Microtunnel sewer main alignment between Fisher Island (left) and the Water Shaft (right). Figure 2. The various alternative alignments considered between the Water Shaft and Miami Beach and new surface alignment to tie-in point. Paper MA-T

3 The first microtunnel drive from Fisher Island to the Water Shaft was completed by Michels Corporation in the latter part of February The second microtunnel drive between Miami Beach and the Water Shaft was completed in the early part of May The intervening period between the two drives was used by Ric-Man Construction to construct the secant pile launch shaft in South Pointe Park. In the fall of 2010, MDWASD solicited proposals from design-build teams to replace the water and sewer mains. MDWASD received five proposals and conducted interviews. The design-build team of Ric-Man Construction with Hazen & Sawyer as the civil designers was selected. The design-build teams were required to provide base bids for the replacement mains using microtunneling technology. However, the teams were allowed to include bid alternates to the base bid at no cost to MDWASD. The water main replacement was completed using horizontal directional drilling in 2011 and a 1,583-foot-long (482 m), 24-inch (610 mm) ID HDPE pipeline was installed (Boyce et al., 2013). 2 SELECTION OF ALIGNMENT In the predesign stages, MDWASD s design engineer AECOM looked at alignment alternatives. The more straightforward approach was an alignment that went directly from Fisher Island to South Pointe Park. From there, the new alignment would follow city streets to an on-land tie-in point near the Miami Beach Marina. Because South Pointe Park is surrounded by several high rise condominiums that look out across Government Cut at their richer counterparts on Fisher Island, this alignment was met with a lot of resistance. There was so much resistance that MDWASD located the tie-in point outside the city limits of Miami Beach out in the water near the existing force main. That is the concept design the design-build team had to carry forward to final design (see Figure 2). To get a better understanding of the political climate that MDWASD had to navigate through for the Fisher Island work, a brief history of Fisher Island s origination is warranted. Named for automotive parts pioneer and beach real estate developer Carl G. Fisher, who once owned it, Fisher Island is 3 miles (4.8 km) offshore. No road or causeway connects to the island, which is only accessible by private boat or ferry. Once a one-family island home of the Vanderbilts, and later several other dignitaries, the island was sold for development in the 1960s. After years of legal battles and changes in ownership, commercial development of the island was finally started in the 1980s, with architecture matching the original 1920s Spanish-style mansions that occupied the island. Although no longer a onefamily island, Fisher Island still remains inaccessible to the public and uninvited guests, and is as exclusive by modern standards as it was in the days of the Vanderbilts, providing similar refuge and retreat for its residents. The tie-in point on Fisher Island was more straightforward as the microtunnel had to originate somewhere near the landfall of the existing 54-inch (1,370 mm) force main that cuts across Fisher Island. As it turns out, the tie-in was conveniently located in the parking lot for the golf course carts. Even so, the island residents and Fisher Island s Home Owners Association imposed difficult restrictions on Ric-Man Construction. This included severe limitations on use of the island ferries, which required the Ric-Man Construction to barge its equipment and materials to a separate landing with its own set of restrictions. Manpower was brought to the site by a boat dedicated to shuttling the contractor s resources between sites and a staging area on the Port of Miami property. As part of the MDWASD design-build contract, Ric-Man Construction was required to inspect the existing force main at the tie-in location after the Water Shaft was under construction. Those efforts revealed that concrete pipe was severely distressed, and it was determined that the existing force main was facing imminent failure. Failure of the existing force main, especially in the segment that extends beneath the Miami Beach Marina, would have been an environmental disaster not only for the aquatic life and local beaches, but for the economic life of Miami Beach. Failure of the existing force main would have necessitated a severe curtailing of sewer service for all of Miami Beach. To circumvent such a disaster, MDWASD was left with one option to bypass the force main segment that was aligned beneath the marina. This necessitated a second microtunnel alignment to bypass the water shaft tie-in and reroute the existing force main to mainland Miami Beach. Few options were available to locate a shaft on the Miami Beach mainland (in South Pointe Park). Figures 3 and 4 show the shaft location selected to minimize the amount of disruption to the park, and the new alignment through city streets to the new tie-in location. Paper MA-T

4 Figure 3. Final alignment to tie back into the existing force main. Figure 4. Construction work site for the jacking shaft at South Pointe Park, Miami Beach. Paper MA-T

5 3 GEOTECHNICAL CONDITIONS MDWASD hired AECOM as its designer to assemble the design-build criteria documents. The AECOM team undertook a site-specific subsurface exploration and testing program. The program was divided into four phases: Phase I: Desk Study conducted during preliminary design to research and compile existing subsurface data in the project vicinity. Phase II: Subsurface explorations consisting of seven borings and associated laboratory testing, completed by Geosol in Phase III: Geophysical survey consisting of bathymetry, seismic reflection, and seismic refraction, completed by Technos in 2009 and Robayna & Associates in Phase IV: Exploration program (supplemental program) consisting of 12 borings and laboratory testing, completed by Geosol in Ten borings were drilled for the original sewer force main crossing three land borings and seven water borings. For the second microtunnel, six soil borings were drilled, two of which were drilled over water, and two rock core borings were drilled one of which was drilled over water. The geological setting for the sewer force main crossing basically consists of four units: Artificial Fill (Af), Miami Formation (Qm), Fort Thompson (FT), and Tamiami Formation (TT). The units are subdivided by layers of sand and limestone. Table 1 provides a summary of the geological units and their subunits. Of note is the presence of sand layers sandwiched by limestone rock above and below. The limestone is also porous, with numerous voids and cavities, most of which are filled with sands and silts. The geotechnical profile for the proposed sewer force main alignment and the interpreted geologic conditions between borings are presented in Figure 5, with unit symbols provided in Table 1. Based on the heterogeneous nature of all the ground anticipated to be encountered along the alignment, the face conditions were considered to be mixed face (soil/bedrock). Engineering characteristics and properties will differ markedly between some strata groups such that ground behavior will vary as each strata group is excavated. The main construction risks associated with the formations along the alignment consisted of: Mixed-face conditions with competent zones embedded in softer materials Sudden and large-scale water inflow from karst features and zones Flowing sands Rock mass with frequently changing deformation and hydraulic characteristics FT-1/FT-6 TT-1/TT-2 Figure 5. Vertical profile for the microtunnel crossing between Fisher Island (left) and the Water Shaft (modified from AECOM, 2010). Similar ground conditions were encountered in the soil and rock core borings completed for the second microtunnel alignment from Miami Beach to the Water Shaft. Because this alignment did not encroach upon the future dredge area, the vertical alignment could be set much higher in the Fort Thompson formation. However, the borings revealed that the preferred vertical alignment would transition from limestone materials into loose sand and back Paper MA-T

6 into limestone materials as the alignment transitioned from land to water. To minimize the potentially adverse impacts of microtunneling through these varied ground conditions, the alignment was lowered to set the tunnel zone entirely within the limestone of the Fort Thompson formation. This required a South Pointe Park Shaft about 68 feet deep (22.3 m) from the ground surface to the working slab. Table 1. Geological units in the Miami/Government Cut Area. Geological Unit Description Symbol Artificial Fill SILTS to fine SAND with LIMESTONE rock fragments Af Miami Formation Soft to medium marine LIMESTONE Qm Fort Thompson Tamiami Formation Loose to medium dense fine SAND Medium to hard sandy LIMESTONE Hard to very hard freshwater LIMESTONE Medium to hard shelly LIMESTONE Loose to medium SAND Medium hard porous shelly LIMESTONE Medium dense to very dense SAND Soft to hard porous to vuggy LIMESTONE FT-1 FT-2 FT-3 FT-4 FT-5 FT-6 TT-1 TT-2 4 SHAFT CONSTRUCTION The tunnel horizon for the channel crossing was set at about 92 feet (28 m) below Fisher Island ground elevation. This necessitated a shaft that was about 97 feet (29.5 m) deep to the working slab. Ric-Man Construction elected to use 10-foot-long (3 m) sections of 72-inch-diameter (1,830 mm) Permalok steel casing. The jacking shaft was constructed with an interior clear diameter of 22 feet (6.7 m). A wet extraction of the microtunnel machine was planned and this required a receiving shaft with an interior clear diameter of 13 feet (4 m). The jacking shaft on Fisher Island consisted of 42-inch-diameter (1,067 mm) by 122-foot-long (37 m) secant piles drilled in a circular arrangement along a 28 foot (8.5 m) layout diameter. Pregrouting along the layout diameter was completed at 6-foot (1.8 m) intervals prior to excavating and concreting the secants to minimize erosion and loss of secant concrete into the porous formational materials. After the circular secant pile wall was constructed, the shaft interior was excavated in the wet. Upon completion of the excavation, reinforcing steel for the structural bottom slab was set. This was followed by lowering of an open-ended bolted steel corrugated metal pipe (CMP) liner sleeved inside the excavated shaft (see Figure 6). Once this was in place, concrete for the structural slab was placed with a short protrusion of the CMP liner into the slab concrete. To complete the shaft, the annular space between the secant piles and the CMP liner was grouted. The shaft interior was dewatered when the structural concrete attained its design strength. The receiving shaft was constructed using the same construction technique except that all of the work had to take place from a work platform built out over the water (see Figure 7). The receiving shaft was 97-feet-deep (29.5 m) from the platform down to the shaft working slab. Like the other two shafts, the South Pointe Park jacking shaft required for the second microtunnel drive was constructed using the same technique. The primary difference was that the alignment could be set higher as this new alignment did not encroach upon the planned dredging work. Consequently, a jacking shaft only 68 feet deep (22.3 m) was required. However, that also meant that a temporary work platform had to be constructed inside the 97-foot-deep (29.5 m) Water Shaft to receive the microtunnel boring machine from Miami Beach. Paper MA-T

7 Figure 6. CMP liner being readied for lowering into shaft. Note the assembled structural steel for the slab bottom (middle foreground). (Photo courtesy Ric-Man Construction) Figure 7. Receiving shaft construction from the over-water platform. Note drill used to core and excavate the secant piles. (Photo courtesy Ric-Man Construction) 5 MICROTUNNELING The Ric-Man Construction hired Michels Corporation to construct the microtunnel beneath the navigation channel. Michels elected to use an SL-74 Akkerman machine to tunnel the 72-inch (1,830 mm) steel casing. A lubrication plan was submitted as part of the Michels work plan. In general, it consisted of grout/lubrication ports in every pipe and a primary lubrication line from which whip lines emanated for manual servicing of the lubrication ports. However, within the first 250 feet (76 m) of tunneling, the jacking forces were increasing rapidly. Projecting out the increase in the first 250 feet over the length of the tunnel, it was apparent that the capacity of the jacking system (800 tons, 725 Mg) would be reached a little over halfway through the drive. This far exceeded the jacking forces predicted (see Figure 8). The belief was that the lubrication, which was being injected in the first 250 feet was not staying within the annular space and was probably bleeding out in the porous formational materials or being washed Paper MA-T

8 out by tidal flows through the interstitial spaces of the limestone (see Figure 9). If indeed that was the case, this could also have allowed sand to pack into the annular space, thereby contributing to a rapid increase in jacking forces. Trend line for jacking forces based on increase in first 250 feet (76 m) Figure 8. Jacking force records for the Fisher Island to Water Shaft microtunnel drive. Figure 9. Porous limestone rock (coral) from the core drilling for the secant piles. The microtunneling plan made provisions for an intermediate jacking station (IJS) that was going to be installed if and when about 70 to 80 percent of the system capacity was reached. In lieu of installing the IJS prematurely, the contractor elected to embark on an aggressive lubrication regime in their endeavor to bring the jacking forces back Paper MA-T

9 in line with what they had predicted. The first aggressive lubrication injection occurred around 250 feet (76 m) (see Figure 8). The lubrication quantities were increased from an average of less than 100 gallons/foot/day (g/f/d) (~375 liters/foot/day) to about 400 g/f/d (~1,515 l/ft/d) over a three-day period. During this three-day period, an average of one casing segment per day was advanced. As shown on the jacking force plot in Figure 8, there was an immediate reversal in jacking forces following this aggressive lubrication regime. After this initial reduction in jacking forces, the lubrication quantity was increased to about 100 g/f/d (378 l/f/d) for the next five pipe segments. However, the jacking forces gradually increased over those five pipe segments such that the jacking forces were again approaching the previous trend line. This prompted the contractor to again embark on another aggressive lubrication regime in which 350 g/f/d (1,325 l/f/d) of lubrication were injected for the subsequent four pipe segments. The jacking force plot in Figure 8 shows a marked reduction in jacking forces such that the jacking forces were now in line with the contractor s projected jacking force plot. The contractor continued to inject copious amounts of lubrication at an average rate of about 200 g/f/d (~760 l/f/d) over the remainder of the microtunnel drive. By doing so, Michels was able to maintain the jacking forces at or below the predicted jacking force plot. Microtunneling through the porous limestone also took its toll on the microtunnel equipment. As would be expected, mining through the limestone coral rock proved to be quite abrasive. The limestone coral is naturally sharp, and it maintains that attribute when mined. The mining process produced an abundance of rock chips that were typically in the size range of 0.5 to 1 inch (13 to 25 mm). Over time, the abrasive rock took its toll on the components of the slurry transport system. Some hoses were eaten through, but the booster pumps appeared to take the brunt of the abrasion. Impellers were worn down, and in a couple of instances the impeller housing was worn through (see Figure 10). Figure 10. Abrasion of the impeller housing (left) and impeller (right). Ric-Man Construction hired Super Excavators Inc. as the microtunneling contractor for the second drive from South Pointe Park to the Water Shaft. Super Excavators benefited from the experience gained in mining the first microtunnel. The microtunnel boring machine was required to be outfitted with new flexible hoses to ensure used worn hoses would not be exposed to the abrasive limestone. Before arriving on-site, Super Excavators voluntarily went through and refurbished the slurry pumps earmarked for the project including spare pumps. In addition, Ric- Man Construction required Super Excavator to install an automatic lubrication system that was controlled from the surface to provide a more effective means of delivering lubrication to the annular space. The effectiveness of the automatic system bears out in the jacking force plot (shown in Figure 11), which closely follows the predicted jacking forces. 6 STAKEHOLDER ISSUES Both the Fisher Island and Miami Beach launch shafts were located in an exclusive area of South Florida. As mentioned earlier, Fisher Island is an island with multimillion dollar residences and is only accessible by ferry or boat. The island is mainly occupied during the winter months when residents, who predominantly live in the Paper MA-T

10 northern states, spend their days golfing and boating to get away from the cold weather. These stakeholders did not want to be bothered by the noise and vibration of heavy equipment involved with construction. Figure 11. Jacking force records for the South Pointe Park to Water Shaft microtunnel drive. The stakeholders in the area of Miami Beach launch shaft are a part of the South of Fifth Neighborhood Association (SOFNA). Association members include ultra-luxury condos, restaurants such as the famous Joe s Stone Crab and Smith & Wollensky, as well as other high-profile commercial interests. These stakeholders were very concerned with the noise, vibration, work hours, and traffic interruptions that could result from the project. The Apogee Condominium is a recently constructed, 22-story, ultra-luxury condo with many famous residents including Hollywood stars and professional sports icons. The condominium was located less than 200 feet from the launch shaft. Noise and vibration monitoring as well as working hours and maintenance of traffic were the primary concerns of the residents of the building. The concerns of the stakeholders for Miami Beach were addressed by accommodating the residents requests for limited working hours and work days during the November and December/January Holiday periods. In addition, noise and vibration monitoring equipment was installed near both the Fisher Island and Miami Beach work areas. This equipment reports longitudinal, transverse, and vertical vibration levels in inches per second (in./s), as well as sound in decibels (db), as depicted in Figure 12. Noise and vibration readings were transmitted via text message to select construction and management personnel, and weekly continuous monitoring reports were transmitted to MDWASD. Action plans to mediate a spike in vibration or sound were developed should any readings exceed background levels. 7 SUMMARY This project had to prevail over difficulties and challenges from the outset, starting with the alignment selection all the way through construction. The design had to overcome an alignment that presented numerous challenges, especially the selection of the Water Shaft to retrieve the microtunnel boring machine and to make the tie-in connection. The design also had to overcome the challenge of adding a second drive back to the Miami Beach Paper MA-T

11 mainland to bypass the existing PCCP force main that was deemed to be at the point of imminent failure. Likewise, construction proceeded under extremely challenging circumstances and in difficult and unforgiving ground conditions. The horizontal and vertical alignments were restricted by easements, severe limits were imposed on access to Fisher Island, an unprecedented Water Shaft was required for the force main tie-in and two microtunnel boring machine retrievals, and land-based shafts had to be shoe horned into confined and restricted working space on Fisher Island and at South Pointe Park. And in the end, the porous limestone ground conditions presented their own set of challenges for construction of the shaft and the cased microtunnel. Figure 12. Noise and vibration monitoring data and equipment Several microtunneling challenges that were overcome stand out. First, an aggressive and vigilant lubrication program was necessary for mining through the Fort Thompson Formation to minimize rapid increases in jacking forces. Absent such a program, the contractor would have been at the mercy of ground conditions that are very unforgiving. Second, the abrasiveness of the mined ground brings to light the importance of having new flexible hosing and new or refurbished fixed components on the return side of the slurry transport system. This included refurbishing slurry pumps, especially those housed behind the microtunnel machine or in-line booster pumps. Despite all of the challenges and difficult ground conditions that presented themselves, the steel casing for the two microtunnel drives was successfully completed. The fiberglass carrier pipe was installed and backfilled. And the new deeper force main between Miami Beach and Fisher Island is in service as the Port s dredging project begins. 8 REFERENCES AECOM Contract No. W-924 Volume 2, Book 1, Water Main Microtunnel Geotechnical Baseline Report, October, 64pp. Boyce, G., S. Mancini, C. Camp, R. Zavitz, O. Castro, and E. Vega Miami-Dade s Water Main Government Cut Replacement Project. In Proceedings of North American No-Dig 2013, NASTT, March, Paper MA Jacobs Associates Daily Inspection Reports for Microtunneling Beneath Government Cut Channel. Miami- Dade 54-inch Force Main Replacement Government Cut. Jacobs Associates Daily Inspection Reports for Microtunneling Between South Pointe Park and Over-Water Shaft. Miami-Dade 54-inch Force Main Replacement Government Cut. Pure Technologies Letter Report to MDWASD titled Miami Beach to Virginia Key PipeDiver Government Cut Results Preliminary Condition Assessment of PCCP. December 19. Paper MA-T