Driven Pile is Creating a Better Tomorrow - METRO Green Line Extension, SWLRT (Southwest Light Rail Project)February 23, 2023
Driven Pile is Creating a Better Tomorrow
METRO Green Line Extension, SWLRT (Southwest Light Rail Project)
METRO Green Line Extension, known to some as SWLRT (Southwest Light Rail Project), is an investment into the future of Minnesota's growing economy. This Extension not only supplies a connection between cities, but it enables the sprawling workforce further access to jobs from across Minnesota, building local economies, and enabling reliable transportation for thousands of residents. Since 2019, International Construction Equipment, Inc. has been supplying various pile driving equipment for the monumental Southwest Light Rail Project (SWLRT) in downtown Minneapolis.
Every segment of the SWLRT project has involved pile driving activities of one kind or another. These piles are used to support the foundations of bridges, tracks, and other structures. The massive amounts of sheet piling used to support excavation work, build cofferdams, abutments, walls, and other construction elements have been scrupulously installed for safety. If you laid all the piles being used on this project end to end, they would stretch from the Twin Cities to Duluth, MN which is a little over 154 miles of sheeting. ("Construction Update: February 7, 2020, Web: swlrt.org Twitter ...")
As the largest public infrastructure project in Minnesota's history, Metro Green Line Extension includes the construction of 16 new transit stations, two light rail tunnels, and a 14.5-mile double track that will serve the south-western suburban cities, including St Louis Park, Hopkins, Minnetonka, and Eden Prairie. The new corridor will also share 7.8 miles with freight railroad tracks, requiring close coordination with Twin Cities & Western Railroad and BNSF Railway during construction and later during light-rail transit (LRT) operation. According to the Metro Council website, the structures include 29 new bridges (LRT, pedestrian, freight, and roadway); seven bridge modifications, pedestrian tunnels, two "cut-and-cover" LRT tunnels (which means opening the street from the top-down, building the system, and roofing it to restore surface traffic), and more than 100 retaining walls. The projected completion date for the whole $2.7-billion project is 2027. Although there have been delays in the timeline due to the complexity and changing of construction plans and contract modifications, Lunda/McCrossan Partnership has the pile driving work for the project nearly completed.
Lunda/McCrossan Joint Venture, based in Maple Grove, Minnesota, was awarded this contract in November of 2018 and got straight to work on the first phases of construction. By March of 2021, Lunda/McCrossan had driven H-Beams for retaining-wall supports in areas with buildings that were sensitive to specific frequencies and vibrations. By using an ICE® 18VM (aka 18ZR) Vibratory Pile Driver/ Extractor (1600 in-lbs) the venture was able to avoid perceived disruptions and unknown issues with rogue startup or shutdown signals that can occur in certain soil conditions. The ICE® variable moment pile hammer, also known as "zero resonance" technology, is specialized to enable shifting into driving modes thus ending undo shake. For this project, it was important to cut unnecessary disturbances to the nearby structures due to ground sensitive soil and back into the crane.
Knowledgeable in soil mechanics, the engineering experts at Lunda/McCrossan additionally employed both the ICE® 50B (5000 in-lbs) and ICE® 28D (2,800 in-lbs) Vibratory Pile Driver and Extractors, as well as two Hydraulic Impact Hammers, the ICE® IP-3 (max 26400 ft-lbs) and IP-5 (max 44000 ft-lbs), limiting disruptions to the area by properly sizing hammers to ensure public safety while driving in varied soil conditions. The early successes that their expert operators achieved utilizing ICE® equipment quickly aided in surpassing timelines. In early 2022, this extraordinary team of contractors installed 95-miles of piles, poured more than 200,000 cubic yards of concrete to complete 11 of 16 stations, 25 of 29 bridges and 7 of 8 tunnels, as well as completing a total of 114 of 131 retaining walls. Additionally, 95% of 946 private utilities and 75% of 1,300 public utilities have been re-routed or upgraded and tracks have already been laid.
Currently, the Lunda/McCrossan team is working on a 2,236' (ft) tunnel in the Kenilworth corridor of Minneapolis. Tunnel excavation began in 2020 and, once completed, will run under Cedar Lake Parkway and the Kenilworth Trail. As sheet pile is installed, the excavation work and tunnel structure construction activities then take place. The tunnel is being built using a "cut-and-cover" method, where a trench is first excavated to create the tunnel and after the tunnel is constructed, it is then covered up. The tunnel is divided up into 30 segments or cells that average 100' (ft) in length, approximately 1,300 pairs of sheet piles are used to create each cell.
There are different construction activities going on at any one time in seven consecutive cells, creating a work area over 700' (ft) long. During the excavation phase, soil is removed from three different cells simultaneously, and the contractor installs a series of supports called "struts and walers" to supply added support to build the tunnel. Strut placement slows excavation because materials and equipment must move around them. Due to tight site access, excavation progresses in a specific linear way to remove and transport soil to other parts of the corridor. The excavation extends about 15' to 20' (ft) below the water table, further slowing the process, as it is more difficult to scoop and place saturated soils.
Additionally, underwater specialists, divers, must check the sheet piles for gaps and make repairs, as necessary. This all occurs in a work site that is only about 50' (ft) wide. Construction of the tunnel involves pouring concrete in six distinct phases each needing time to cure before the next phase of work can start. Once excavation is completed in a cell, a concrete tremie seal ranging from 4' - 10' (ft) in thickness is poured underwater to create an anchor for the tunnel structure and seals off the excavation from groundwater so the tunnel can be constructed in dry conditions. After the water is removed from the cell, the sheet piles are sprayed with concrete to create a uniform surface. A layer of concrete is poured on top of the rough tremie surface to create a level surface for tunnel construction. The struts and walers are removed and a concrete slab is then poured to create the tunnel floor, which will serve as the final surface for the track bed and rails. The tunnel walls and ceiling are poured in one concrete pour, in approximately 30-foot-long segments. A final topping layer of concrete is then poured.
The finished tunnel includes a waterproof membrane to prevent water from entering the finished tunnel and steel rebar to make it structurally sound. The access constraints limit the opportunity to work simultaneously in multiple cells. In most cases only one concrete pour can take place in a day. This makes the job challenging because of the inability to access the tunnel site from the west end of the corridor due to the construction of the Cedar Isles Condos secant wall foundation being installed. Even with limited access, this joint venture team is still completing about one cell per month which is a marvelous feat.
During the most current phase of the project, the use of the ICE® IP-3 and ICE ® IP-5 Hydraulic Impact Hammers (HIH) have been beneficial to the surrounding communities as they generate lower impact noise than diesel impact hammers with the controlled stroke. The ICE® HIH's variable stroke, when effectively setup, will stop damaging impact velocities to concrete piles. In this case, the settings we dialed in to use the heavy weight of this ram accompanied by shortening the stroke producing effective and safe piling within the corridor's tight space restraints. Pleased with the performance of the various ICE® equipment they currently own, including 2 of the 18VM/ 18ZR units, as well as those they have rented in the past, Lunda/McCrossan has expanded their fleet with an additional two more ICE® IP-3's starting on this project this winter.
Once completed, the railway vehicles on the new METRO Green Line Extension, SWLRT track, will be in service 21 hours a day, allowing commuters and visitors more flexibility when using local public transportation. According to The Metropolitan Council, the regional policy-making body, planning agency, and provider of essential services for the Twin Cities metropolitan region, "Nearly 56,000 people live within a 10-minute walk of the corridor." This means that people traveling to and within the corridor will have access to "81,000 jobs along the extension, in addition to the current 145,000 jobs in downtown Minneapolis and close to 36,000 residents (about twice the seating capacity of Madison Square Garden) already living downtown will have easier access to job opportunities in the southwest metro and other communities connected by this transit system." In fact, even during construction, the METRO Green Line Extension has already seen more than $2 billion of investment within a 10-minute walk of the line, further strengthening the local economy and the importance of this project. Ridership on the new Southwest Light Rail Transit is expected to see 30,000 passengers daily and annually over 10 million patrons (about half the population of New York) by 2030. Lunda/McCrossan Partnership has worked diligently to install a solid driven foundation that is the support for the new transportation routes supplying easier access to employment, educational and entertainment opportunities. It is 100% fair to say that the driven pile is building a better world for the residents of Minnesota.
Pollyanna Cunningham, MA, MBA
Vice President Marketing, Brand and Media Relations
Vice President IT and IT Comm
ICE® - International Construction Equipment, Inc
Office - 704-821-8200
Email - email@example.com
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