Repeated Lift-off Testing of Single Bore Multiple Anchors for Dam Retaining Wall over a 5-Year Period

lateral displacement due to global instability of the in situ soils. After a failed remediation attempt with traditional tiebacks in 1996, a remediation effort was implemented in 2002 to limit the rate of movement of the wall while additional studies were conducted. The remediation design called for installation of additional anchors bonded within a high plasticity, stiff clay layer. The length of the bond zone of the anchors was limited by the presence of an artesian aquifer underlying the clay layer; therefore, the design unit bond stress was relatively large. To reduce the potential for creep and increase the unit bond strength, the contractor selected the Single Bore Multiple Anchor (SBMA) system with comprehensive, selective post grouting.

The anchors were effective in reducing significantly the rate of movement of the wall. Presently, the wall is being monitored for displacement and periodic lift off tests of the 2002 SBMA tiebacks are being performed while possible additional remediation efforts are devised for future implementation as needed. The monitoring and lift off test data provided a unique opportunity to correlate the response of the anchors with the wall movement. This paper describes the design and construction of the SBMA anchors, testing of a sacrificial anchor, lift-off testing procedures and results, and conclusions.

• Background

• Bond Zone Materials

• Single Bore Multiple Anchor System

• Sacrificial Anchor Installation and Testing

• Details of Anchor Construction

• Lift-Off Testing Procedures

• Lift-Off Testing Results

• Conclusions

• Acknowledgements

• References