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HORIZONTAL FEET VERTICAL FEET After the land leg tunnel construction is complete, the contractor will continue with other work necessary for installation of the valve chamber structure, connection with the tunnel, and finishing for LLO mechanical work within the gate shaft to control the water release into Schoharie Creek. MICROTUNNELING CONSTRUCTION FOR LOW LEVEL OUTLET TUNNELS Air lock hyperbaric chamber allows safe personnel access to the tunnel face plished predominantly from the reservoir surface with a working barge platform. The finished grades will be verified by sonar. The Crest of the Gilboa Dam (full pool) is 1130.00 feet while the bottom reservoir sediment layer at the intake and MTBM receiving site is recorded at El. 996 feet. As part of the receiving site and intake structure foundation preparation, it is required that the limits of the intake structure foundation be dredged with hydraulic and mechanical techniques to remove the sediment and glacial till respectively. The dredged limits of the receiving site are to be replaced with tremie concrete for 75-feet along the tunnel alignment and around the 30-foot diameter, 26-foot tall cofferdam built at the center line of the water leg tunnel to the Jacking Shaft. The cofferdam will be fitted with a prefabricated breakout eye for the MTBM reception and filled with sand pending the arrival of the MTBM at the completion of the water leg tunnel mining. After tunnel construction is complete, a specialty underwater diving team will install the intake elbow within the cofferdam and secure it in place with tremie concrete, the bulkhead atop the elbow and the intake structure atop the cofferdam. The bulkhead atop the elbow will remain in the closed position until the tunnel is ready to be flooded. RECEIVING SITE AT PORTAL/VALVE CHAMBER The receiving site for the land leg microtunneling is downstream of the dam at the portal, along the bank of Schoharie Creek. This portal will remain as the eastern wall for the opencut excavation portal housing the bifurcation piping connection between the tunnel and the valve chamber, which controls drawdown of the reservoir. Preparation required to receive the MTBM includes a 10-foot cube grout plug installed to stabilize the hole-through area at the portal face for MTBM break-out upon completion of the land leg tunnel. The two tunnel segments are to be constructed utilizing a 108-inch-diameter MTBM with slurry pressurized face (AVN2200AB) manufactured by Herrenknecht. Per contract requirements, the new MTBM is specifically designed and fabricated for use on the LLO project. The MTBM design requirements include the ability to mine through mixed ground conditions containing cobbles and boulders sized up to 30% of the outside diameter of the MTBM. It is also designed to operate under external hydrostatic pressure equivalent to 153 feet of water head, allowing for underwater retrieval. The MTBM is required to be equipped with an air lock hyperbaric chamber which allows safe personnel access to the tunnel face for obstruction intervention or disc cutter maintenance under pressures up to 5 bar. An extensive list of additional functionalities for the MTBM is included in the design requirement. The jacking pipe scheduled for use as the initial and final ground support, for both land and water leg tunnels, is 108-inch, 1.375-inch thick Permalok steel pipe with T-7 gasketed joints. Two intermediate jacking stations are required for each of the tunnel legs. Utilization of butt welded steel jacking pipe joints are not allowed for this project. 1250 1250 1200 1150 Roadway & Drive Gate Shaft (Jacking Shaft) Roadway & Drive Normal Pool Water Level El. 1130.00. Water level varies 1200 1150 1100 1050 Valve Chamber Tunnel Portal (MTBM Receiving Site) Approximate Ground Surface Top of Bedrock Intake Structure (MTBM Receiving Site) 1100 1050 1000 NE FLOW SE FLOW ~ 1000 950 Inv. El 977.00 950 900 LEGEND: 900 850 MAN-MADE FILL GLACIOFLUVIAL DEPOSIT GLACIAL TILL DEPOSITS 850 RESERVOIR SEDIMENT GLACIAL LAKE DEPOSITS BEDROCK 800 800 24+00 23+00 22+00 21+00 20+00 19+00 18+00 17+00 16+00 15+00 14+00 13+00 12+00 11+00 10+00 9+00 8+00 7+00 6+00 5+00 4+00 3+00 2+00 1+00 0+00 -1+00 -2+00 Land Leg & Water Leg Profiles. LLO tunnel is mined in bedrock for about 80% of the alignment 24 NASTT-NE NORTHEAST JOURNAL OF TRENCHLESS TECHNOLOGY <strong>PRACTICES</strong> 2016 | WWW.NASTT-NE.ORG
FISH AND WILD LIFE PERMIT REQUIREMENT With the presence of bald eagles (endangered species) nesting at the site, blasting to excavate the Gate Shaft and any other construction activities within 660 feet of the eagle nests are prohibited between January 1 and July 31. This leaves a limited window to commence and complete shaft construction. TUNNEL CONSTRUCTION REQUIREMENTS It is stipulated that the land leg tunnel will be constructed first so that lessons learned with MTBM performance and ground behavior can be carried over into the water leg operation. As a requirement for the water leg construction, three bulkheads will be installed: Geotechnical boring at cofferdam site for Intake Structure SUBSURFACE CONDITIONS The geologic profile at the Gate Shaft includes a 29.3-foot overburden, predominantly glaciofluvial deposits consisting of stiff to hard silty/clay with traces of sand and gravel. These soil materials have low permeability, with the groundwater level varying between 6 and 10 feet below ground level, generally following the land topography. The bedrock consists of fine grained sandstone with occasional layers of siltstone and clay seams. It is expected to be strong and abrasive - the rock is generally moderately fractured to massive with Rock Quality Designation (RQD) 88 - 100 percent and an average recovery of 99 percent. The LLO Tunnel will be mined in bedrock on either side of the Gate Shaft for approximately 1,725 LF, about 80% of the entire alignment, except for the short reach of mixed ground conditions at the terminal ends of the tunnels. This consists of very compact granular glacial till soil materials, predominantly coarse to fine sands with moderate amounts of silt and varying amounts of gravel. Occasional cobbles and boulders are anticipated from the rock interface to the receiving sites. The bottom of the reservoir is comprised of silt and miscellaneous debris deposited over the years. SPECIFIC FEATURES & REQUIREMENTS GROUNDWATER CONTROL Because of relatively high rock permeability and close proximity of the Schoharie Reservoir, with a water elevation at 1,130 feet, a pre-excavation grouting program is required around the Gate Shaft perimeter. The pregrouting will extend the full 187-foot depth of the shaft to seal off potential pathways of groundwater inflows during shaft construction and launch of the MTBM. INTAKE STRUCTURE AND MTBM RECEIVING SITE Due to the soft silt/clay deposits at the bottom of the reservoir, dredging will be done to remove the soft sediments to competent depth for the intake structure foundation. Ground modification will then be performed to replace the dredged area with tremie concrete in order to stabilize the cofferdam. This will also improve the soils for microtunneling operations. When the MTBM breaks through into the cofferdam, it will be rigged and hoisted to the surface via the wet retrieval method, with assistance from the specialty diving operation. • Bulkhead No. 1: On the inside face of the land leg in the Gate Shaft. • Bulkhead No. 2: Directly behind the MTBM to provide a seal at the front of the lead pipe. • Bulkhead No. 3: At the rear of the lead pipe. The two lead bulkheads are to be fabricated watertight with power cables, slurry lines, and access hatch to the face of the MTBM for obstruction intervention and disk cutter maintenance. In addition, the contract stipulates an air lock compatible with the MTBM. PROJECT CONSTRUCTION STATUS The construction contract was awarded to Southland Renda Joint Venture, with a Notice to Proceed (NTP) date of June 29, 2015. The contractor has mobilized to the site, working with the Construction Manager in providing critical submittals for long lead equipment, materials, and permits. Preparatory work has begun, and includes site clearing, temporary access road construction, and geotechnical borings in the valve chamber area for wing wall foundations. Excavation at the gate shaft has advanced into bedrock with blasting and ground support activities in full throttle. Excavation at the valve chamber east wall for the land leg MTBM retrieval site has progressed to the tunnel horizon with soil nail ground support method. NASTT-NE NORTHEAST JOURNAL OF TRENCHLESS TECHNOLOGY <strong>PRACTICES</strong> 2016 | WWW.NASTT-NE.ORG 25
Page 1 and 2: NORTHEAST JOURNAL OF TRENCHLESS TEC
Page 3: Underground Pipeline Mapping Techno
Page 6 and 7: SPR PE Yes, we can manufacture a ne
Page 8 and 9: TRENCHLESS GROWTH IN THE NORTHEAST
Page 10 and 11: NASTT NORTHEAST REGIONAL CHAPTER DE
Page 12 and 13: NASTT NORTHEAST REGIONAL CHAPTER BO
Page 14 and 15: ANNOUNCEMENT 2016 NORTHEAST TRENCHL
Page 16 and 17: What are Trenchless Technologies? T
Page 18 and 19: NORTHEAST TRENCHLESS ASSOCIATION: N
Page 20 and 21: “EMPOWERING THE FUTURE OF THE TRE
Page 22 and 23: 108-INCH LOW LEVEL OUTLET CONSTRUCT
Page 26 and 27: UNDERGROUND ENGINEERING McMillen Ja
Page 28 and 29: WHAT’S HOLDING BACK CURED-IN- PLA
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