Tunnel Business Magazine

AUG 2018

TBM: Tunnel Business Magazine is the market leader for North America. TBM is written for leading professionals in all aspects of tunneling and covers project stories, design elements, contracting strategies, legal issues, new technology and more.

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under a polymer slurry. These losses were unexpected because the onsite debris was reported to be predominately contained within a silt and clay matrix. Independent testing revealed some areas of little to no clay and a high presence of cinder in the fill soils. The classification of soil was determined to be different than that presented in the geotechnical information provided. Chemical additives to the polymer slurry to increase viscos- ity and prevent loss were unsuccessful in controlling the vol- ume and speed of the slurry loss. Fortunately, the slurry loss issue was solved by switching to a less viscous bentonite slurry for the remainder of the project. The bentonite slurry was suc- cessful presumably by sealing continuous voids through filter cake development. The diaphragm wall was excavated using a hydraulic clam- shell on a Liebherr 855 duty cycle crane. The 32 panels were ex- cavated under four primary headers and completed in a follow- up to closure pattern. The panels were excavated to the top of competent shale, averaging 46 ft deep. Despite the three-week delay reconfiguring the slurry plant equipment for bentonite production, the diaphragm wall was completed on the original milestone sche ember 2017, taking just five weeks to complete construction thanks to orga- nization, logistics and planning. The project delivered a techni- cally successful outcome and met schedule and cost goals for the owner and contractor. Following the excava on returned in ch 2018 and installed 232 tension micropiles through the bottom slab. The tension piles precluded the need to excavate ap- proximately 12,500 cubic yards of bedrock that was going to be replaced by concrete, thereby saving schedule and money. The overall project is scheduled for completion in 2024. Jewels Stover is Project Manager, Major Projects, for Nicholson Construction Co. TUNNELINGONLINE.COM F E A T U R E S T O RY 2 5 TBM: TUNNEL BUSINESS MAGAZINE // AUGUST 2018 BY JEWELS STOVER

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