Crane Valley Dam Seismic Retrofit

Project Description:

Crane Valley Dam is located about 40 miles Northeast of Fresno in Madera County, California on the North Fork of Willow Creek, a tributary of the San Joaquin River. The dam was built between 1902 and 1911 when very little was known about seismic activity. The dam is a 145-foot high, hydraulic earth and rock fill embankment, with a thin central concrete core wall. The dam is 1,880 feet long, and the crest of the dam is at 3,380 feet elevation.

After completing studies on the dam stability at the request of the Division of Safety of Dams (DSOD), the results indicated that modifications to the dam were necessary to meet current standards for seismic stability. Further analysis showed that in the event of an earthquake, the dam could slump and allow water to flow over the top, causing flooding downstream.

A retrofit design was developed to modify the Crane Valley Dam to increase the stability of the dam structures to meet state and federal safety guidelines. The dam modification would consist of the addition of approximately 253,000 cubic yards of rock fill to selected areas on the upstream and downstream faces of the dam.

BSK’s Roles & Responsibilities

BSK was a subcontractor to Parsons, the designated quality assurance/quality control contractor responsible for verifying to DSOD and FERC that the dam was built in accordance with the engineer of record’s design. Specifically BSK’s work included:

  • QA testing and inspection for the owner, PG&E.
  • Compaction testing during construction of the upstream and downstream rock fills buttresses. Tests included Nuclear Density, Sand Cone, and Water Replacement.
  • Concrete and CLSM sampling and testing.
  • Performed 30 ton proof load testing on the rock fall protection netting anchors.
  • Performed compaction testing and observations during restoration of the MSHA-regulated Wishon Quarry, including Nuclear Density, Sand Cone, and Bulk Density testing.
  • Material acceptance testing at the Wishon Quarry and Raymond Quarry including gradation, durability, sand equivalent, Sulfate Soundness, Specific Gravity and Absorption, and testing of rip rap materials.
  • Groundwater monitoring beneath and downstream dam during foundation excavation (included flow rate and turbidity monitoring of water in the ejector well system). Performed well abandonment inspections during removal of the Downstream Dewatering System.
  • Installed temporary piezometers and inclinometers wells, and logged borings for each well.
  • Acquired inclinometer data weekly on the dam during construction.

Problems/Issues Encountered

The project faced many restrictions and strict deadlines placed by various regulatory agencies. One such deadline was issued by the DSOD, with a strict deadline for completion of test fills to begin construction. If these deadlines were missed, the work would be delayed for six months.

In another example the contractors testing lab was not going to meet the deadline for proof testing on the rock fall protection netting anchors.

BSK Solutions

To meet the deadlines for the completion of test fills to begin construction, BSK had technicians on site for 12-14 hours per day for two months straight. We came through many times to meet deadlines even, often working seven days a week on site and seven days a week in the lab and office.

BSK was called on to perform the 30-ton proof load testing on the anchors. Within 24 hours, we were able to manufacture a testing device to safely and accurately test the anchors to 120,000lbs. Although this was not in our original scope of work, we rose to the challenge and delivered this extra service, to meet deadline and prevent delay to the project.

Parsons was also the engineer of record for a structure to protect the powerhouse penstock pipe during construction. This structure became a permanent part of the dam. BSK observed and inspected pressure grouting operations to stabilize loose subgrade surrounding eight drilled piers for the bridge deck. This was an addition to BSK’s original scope, requested by Parsons after they had seen our commitment to quality and ability to help them in meeting deadlines.