The M-Street project widens northbound and southbound of I-5 through Tacoma by adding a new northbound I-5 bridge over the I-705 interchange. Malcolm was awarded both the large diameter drilled shafts for the bridge pier foundation, as well as the required soil nail and shotcrete shoring walls. The three bridges required 53 fully cased drilled shafts between 7 and 11 feet in diameter. Depending on the location, the permanent casing consisted of either slip in casing, oversized permanent driven casing, or oscillated permanent casing. Shaft integrity testing consisted of both CSL and Thermal Integrity testing. The shoring walls consisted of 3,500 permanent soil nails, and 58,000 square feet of 6 inch thick shotcrete. Geological conditions were difficult requiring much of the walls to be constructed in gravels with fine contents at or below 8 %. Vertical elements were installed for the full height of the wall on 4 foot centers to help ensure face stability. An unexpectedly high water table was encountered around 15 feet above bottom of wall which required that 12 deep wells be installed in order to lower the water table below the bottom of the wall.
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