Ultrafine Cement Pressure Grouting to Control Ground Water in Fractured Granite Rock


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Title: Ultrafine Cement Pressure Grouting to Control Ground Water in Fractured Granite Rock

Author(s): David W. Moller, Henry L. Minch, and Joseph P. Welsh

Publication: Special Publication

Volume: 83


Appears on pages(s): 129-152

Keywords: cements; fineness; grout; pressure grouting; pumped storage; seepage;tunnels.

Date: 10/1/1994

The Helms Pumped Storage Project is a new hydroelectric facility located in the Sierra Nevada mountains O f California. During excavation of the underground powerhouse complex, a previously unidentified shear zone was encountered in the granitic rock. The shear zone was a near vertical plane, up to 35 ft. in stratigraphic thickness, and was intersected by several tunnels near the powerhouse. During initial water filling of the power tunnel, the shear zone became a conduit for high pressure tunnel water (818 psi), allowing it to leave the power tunnel and seep into adjoining dry access tunnels. An innovative grouting program utilizing ultrafine cement (Blaine fineness of 8,880 cm /g) and pump pressures which were increased progressively with depth (up to 700 psi) was used to create a barrier between the pressure tunnel and the shear zone. The grouting program successfully reduced ground water pressures and seepage downstream of the barrier to acceptable levels. The program demonstrated the superior penetrating capability of grout made with ultrafine cement compared to type II and type III portland cement, and indicates that ultrafine cement grout can be an effective substitute for chemical grout when the properties of a cement grout are required.