Seismic retrofit of Tuttle Creek Dam

This paper discusses the seismic retrofit of Tuttle Creek Dam near Manhattan, Kansas, including investigations, seismic analyses, design, construction, and stabilization techniques used. Original plans called for stabilization of the upstream and downstream slopes and installation of an upstream cutoff wall to reduce underseepage. However, constructability and dam safety issues, along with the results of refined seismic deformation analyses, led to cancellation of the jet grouted upstream slope stabilization and cutoff wall. Downstream slope stabilization was to be accomplished by jet grouting or soil mixing, but ultimately was accomplished using a self-hardening cement-bentonite (C-B) slurry to construct transverse shear walls. A total of 351 transverse shear walls were constructed along the downstream toe by primarily clamshell equipment. Typical shear walls are 13.7 m long, 1.2 m wide, and extend 18.9 mdeep or about 6.1 m into the coarse foundation sands. The walls are spaced at 4.3mon center along the downstream toe for a replacement ratio of about 29%. In addition to the transverse shear walls, the relief well collection ditch along the downstream toe was replaced with a buried collector system to further improve downstream stability and underseepage control.