2014 Issue

28 and “Qms” (see Figure 13) reactivated the slide resulting in the condemnation of some homes. The EIS alignment also crossed other landslides which had been active in the last 50 years. It also crossed a dozen active faults in residential neighborhoods. Because of these risks, the University Avenue alignment, which avoided these geohazards, was adopted after CUWCD’s EA revision process. 6. 60” NSA Pioneer Crossing: 4 Mile Pipe in Compressible Soils & Highway Fills TheNorth ShoreAqueduct (NSA) is a 17mile 60- to 48- inch pipeline and part of the CUWCDWater Development Project (CWP) which will deliver 150 cfs of potable water to six agencies in northern Utah County and southern Salt Lake County (see Figure 14). The NSA gets its name from the north shore of Utah Lake - which it parallels – and is located about 0.5 to 1.5 miles inland of the soft, marshy shoreline. The geology con- sists of compress- ible lake-bed and river delta clay and silt sedi- ments on top of artesian aquifers. Pipe design pressures are over 260 psi for the 11 miles of 60-inch pipe in soft soils. High pressures and soft saturated ground make thrust blocks impractical, so all joints are welded. CUWCDcoordinatedwithUDOT tobuild the Pioneer Crossingpipe beneath and just before UDOT placed Pioneer Crossing Highway fills. Highway fills were typically shallow and uniform so they did not cause the pipe to differentially settle. The highway now pro- tects the pipe from future bending by preventing fill placements over the pipe. At two deeper fills, the 60-inch pipe was tapered gradually (over 1000 feet) in and out of fills to keep differential settlements small. At the Pioneer Cross- ing Jordan River bridge, abutment fills induced 23-inches of differential settlement. However, this large settlement did not adversely affect the pipe because the pipe was built: • 60 feet away from the bridge abutments, and • six months after completion of the bridge abutment fills (see Figure 15). 7. 60” NSA Vineyard Connector: 7 Mile Pipe in Developing Area with Compressible Ground The Vineyard Connector Pipe has the same differential settlement risks as the Pioneer Crossing Pipe, but the settlement locations are undefined. For example, the Vineyard Highway concept plan showed fill depths at pipe crossings of 10 to 20 feet. Geotechnical engineers forecasted such fills would settle ground 3 to 14 inches which unless mitigated, would break or yield welds at double lap joints (refer to item 3 where the Alpine-1 90” pipe broke 4 times in 280 feet due to 6.5 inches of differential settlement). Because UDOT has indefinitely delayed construction of the highway, it could not commit to future fill locations. It was impractical for CUWCD to pay expensive pre-settling costs for undefined fill locations. Figure 14. The 23mileCWP System (shown in heavy lines) includes theNorth ShoreAqueduct (NSA) which has 11 miles of 60-inch pipe in compressible soils on top of artesian aquifers. - The 4 mile Pioneer Crossing Pipe (dashed line) was built concurrently with the Pioneer Crossing Highway, so design and construction had to address pipe bending and joint weld stresses due to fills settlement. - The 7 mile Vineyard Connector (solid black line) was to be built concurrently with the Vineyard Connector Highway but highway funding was delayed. The Vineyard Connector Pipeline is adjacent to and occasionally crosses the highway ROW. Due to soft ground settlement risks, the pipe was butt welded so it can better tolerate bending from 1) the future highway fills and 2) filling by future developments. Figure 15. Hardwood mats were needed to keep equipment from sinking in the soft ground. Figure 15. At Jordan River crossing, highway fills settled for six months before the pipe was built 60 ft away. Figure 16. Pre-settling ground where future development was likely to result in non- uniform settlement. CUWCD AQUEDUCT | continued from page 27