2014 Issue

27 Figure 14. Isolation valve piping by slide. Figure 12. The 2004 EIS alignment (large black dots) crossed inactive and active landslides (shaded areas) mapped by Provo City. The Sherwood Hills Slide was of special concern. It moved 2 to 14 inches in 2006-07 causing several homes to be condemned. The EIS align- ment also crossed several active faults (thin gray lines). The value engineering team suggested two alternative alignments, each 5 miles long, which avoided all landslide hazards and all but one faults. The University Ave. (the heavy black line) alignment was approved in an EA revision, designed and is nearing completion. Figure 13. Sherwood Hills Slide, which abuts the EIS alignment (white dot line), moved in 2006-2007. Trenching at toe of this slide was deemed very risky. In 1986 the massive Thistle Landslide dammed-up Spanish Fork Canyon 100 feet deep and forced the emergency realignment of the railroad and highway in the canyon. The realigned highway road cuts and fills triggered shallow surface slides on an ancient slide matrix. Three 700-foot wide areas moved because road con- struction occurred during a record (500 yr) wet hydrologic period. Inclinometers installed to monitor the slide found: 1) the ancient slide slip plane was over 100 feet deep and was not moving; 2) the main 1986 shallow slide , called “Blacks Slide,” was 10 feet deep at the toe of road cut and 25 feet deep at the center of slide moved for about 1 year after highway construction. A shallow “block slide” stopped moving during highway construc- tion. No shallow slide movement occurred in the 100-foot wide highway surface. Initial the design team looked at routing the Utah Lake System’s (ULS) 96” Spanish Fork Canyon Pipeline around the slide, tunneling under it, or cross it above ground (Fig. 12). But, these all proved to be high cost, high risk, and high maintenance. Though test holes found little hard rock, rock exposures were seen uphill of Blacks Slide - implying there was a large rockmass under the shallow slide. CUWCD was pleased in construction to find 100-foot length of trench bottom with hard bedrock (see Fig. 13) below the outcrop. Also, reliability on this pipe was less critical than other CUWCD aqueducts as water deliveries could be re-routed through the Span- ish Fork River (see Figure 13). For these reasons, the lowest risk, cost and maintenance option was to bury the pipe in the highway (away from the toe of the shal- low slides) and accept the lesser risk of potential damage f rom a shallow slide rather than the k n ow n h i g h - ma i n t enance , high-cost and risk of either a tun- nel, a circumvent- ing pipe (in one of several poor geologic align- ments), or a 96-inch high pressure (240 psi) above ground pipe between the highway and a railroad below. An isolation valve vault (Figure 14) was built which allowed a 560 cfs turnout just upstream of Blacks Slide to divert pipe flows around the slide by routing waterflows through the Spanish Fork River. To monitor for slidemovement at the pipe, strain gages were installed on the double lap welded joints. An underground drain panel was added north of the pipe to drain water away from the toe of the slide (which ironically became useless because it was found to be located in impervious clay). 5. 60” Provo Pipe: 5 mile realignment to avoid Provo Landslides and Faults In the 2004 Utah Lake System (ULS) EIS planning, CUWCD aligned a 9 mile pipe through Provo City – on the east bench which had wider streets, less traffic and fewer utilities – primarily at the request of Provo City. In 2010, CUWCD began predesign with a value engineering review of the planning work. Geohazard mapping gathered for this review showed the EIS alignment as high risk. The EIS alignment also had new hydraulic capacity constraints that made an alignment revision valuable. When the EIS alignment was placed over the geohazards mapping, it crossed several landslides and active faults which would put the pipe unnecessarily at risk (see Figure 12). Alternative alignments to the west each avoided these geohazards and also solved the capacity constraints. The Sherwood Hills Slide was of special concern as pipe trenches on the EIS alignment would cut the toe of this very unstable slide. Figure 13 shows slide areas that moved 2- to 14-inches in 2006 and 2007. Irrigation from the homes built in slide areas “Qmsy” CUWCD AQUEDUCT | continued on page 28