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Jet grouting tested at Wickiup dam

The US Bureau of Reclamation (USBR) has completed jet grouting tests at Wickiup dam on the upper Deschutes river in Oregon, US. Jet grouting was used to stabilise the foundation layers beneath the dam.

Wickiup dam is a zoned earthfill structure with a maximum structural height of 30m and a crest length of 4.3km. The dam impounds a reservoir that was built over foundation material consisting of layers of volcanic ash and fine-grained sand, silt and clay. Recent dam safety studies have shown that these volcanic ash and silt layers could liquefy following a moderate earthquake and cause the dam to fail. USBR began exploring options to strengthen the foundation layers by treating the layers that could liquefy during an earthquake. These are relatively deep (about 20m below ground), so a jet grouting method was recommended and tested.

The jet grouting process involved drilling a 15cm diameter hole to a depth of about 20m using conventional rotary drilling techniques. The contractor, Hayward-Baker of California, began testing at the end of November 1999 and completed the work by the end of the year. A USBR drill crew completed verification core drilling in January 2000, giving the opportunity to analyse the extent of the soil replacement and determine the strength of the resulting soil and grout mix. The verification indicated adequate strengths of the grout material.