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Salt River Project:
Horse Mesa Dam
Location
Maricopa County, AZ USA

Binding Soils For Strength & Stability

THE CUSTOMER

The Horse Mesa Dam is a concrete thin arch dam located in the Superstition Mountains, northeast of Phoenix in Maricopa County, AZ. The dam is 660 feet (200m) long, 300 feet (91m) high and was built between 1924 and 1927. The dam includes three conventional hydroelectric generating units delivering a total of 32 megawatts (MW) and a pumped-storage unit with a capacity of 97MW. The dam and associated infrastructure were listed on the National Register of Historic places in 2017.

THE PROBLEM

The soil cement roadway was constructed atop a relatively thin layer of decomposed granite that overlies a section (of unknown depth) of open graded cobbles and boulders. Surface water run-off directed to the relatively small ditch on the south side of Forest Road 80 appeared to be infiltrating through soil materials adjacent to the canyon wall bedrock, and was suspected of migrating or piping through the subsurface underneath the roadway and into Canyon Lake at the north side of Forest Road 80.

THE RESULTS

URETEK’s technicians effectively utilized the URETEK Deep Injection® Process across affected Horse Mesa Dam access road. The process effectively and quickly filled existing voids, consolidated weak soil with existing aggregates, stemmed potential water flow that would lead to further erosion and increased the soil load-bearing capacity in the area of concern. Great care and material control were required as the project materials could not migrate to adjacent rivers nor be harmful to marine life. URETEK polymer products were carefully chosen and applied resulting in no migration or possibility of marine life problems. Forest Road 80 stability was increased, future water erosion due to infiltration was reduced and sub-surface voids were filled along with aggregate and soil binding for additional strength.

Project statistics are:

• All identified subterranean voids, at various depths and sizes were filled.
• Successful injection, void fill, and soil binding occurred from depths of 6” to 6’
• Successful drilling through bedrock to get void access
• All voids were filled and the job completed in five working days

THE SOLUTION

It was determined that a fast, environmentally friendly approach was needed to achieve the project goals of void fill, soil bonding and adding strength to the area. The URETEK Deep Injection® Process was utilized to effectively fill subsurface voids, compact/ densify existing underlying supporting soils to the point of refusal and to bind together aggregates. URETEK’s structural grade exothermic polymer was injected through 5/8” (penny size) holes drilled through sub-surface bedrock in a grid pattern, into existing voids, effectively stabilizing and strengthening soils to reduce future erosion and settlement. Due to the project’s proximity to the river, it was critically important that the void filling material not be hazardous to marine life.

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