CLEARWATER DAMFOUNDATION DRILLING AND GROUTING FOR REPAIR OF SINKHOLE ONUPSTREAM EMBANKMENT

摘要

Clearwater Dam, located in Southeast Missouri, experienced a sinkhole on the face of thernupstream embankment on 14 January 2003. The sinkhole appeared approximately 8 monthsrnafter the dam experienced a pool of record in May 2002.rnThe presentation will begin with a brief discussion of the dolomite karstic geology, the tworntypical zoned embankment sections, which comprise 2000 feet of the dam on the left abutmentrnridge (average height of 35 feet), and the 2300 feet of dam in the river valley (average heightrnof 170 feet) and the seepage history at Clearwater Dam, which was initially impounded inrn1948. Throughout the history of the dam, the left abutment ridge and the leftrnabutment/embankment contact was the focal point of seepage and the major cause ofrnconcern. On 14 January 2003, a sinkhole formed in the valley section of the embankment, onrnthe upstream face of the pervious shell, causing concern that the entire dam may bernexperiencing unacceptable seepage distress.rnThe presentation covers the emergency response to the sinkhole discovery and initialrnassessment of risk and consequences of dam failure. Geophysical investigations performedrn(Feb 2003) on the upstream face of the dam are discussed to infer embankment andrnfoundation material damage relative to depth and position from the sinkhole surface. The usernof the Sonic drilling method to investigate the foundation of the dam (March 2003) and therndownhole geophysical tests performed utilizing these boreholes (May 2003) will be discussed.rnOriginal construction photographs are presented of geological features, which may haverncontributed to sinkhole development.rnIn December 2003, a drilling investigation and grouting program was begun to provide arnlocalized repair of the foundation rock in the vicinity of the sinkhole (200 feet either side of thernsinkhole). The Sonic drilling method is being used to advance the boreholes through thernpervious shell and the clay core of the embankment. During the investigation process, in-siturnfalling head tests and low pressure hydraulic testing will be performed to determine thernintegrity of the embankment/foundation rock contact. A detailed discussion will present thernfindings of the computerized grouting program performed in the top 50 feet of the foundationrnrock. The presentation will conclude with a brief discussion of the long-term solutionsrnconsidered for the seepage problem.