hydrogeology21
Geotechnical
For your consideration and input. I am performing an evaluation for a dam which utilizes a concrete gravity spillway structure with monoliths placed on firm bedrock, an installed double line grout curtain to control seepage and relief drains to collect the seepage that passes through the grout curtain. The right embankment has an impervious core with adequate transition zones with filter drains adjacent to the impervious core to collect seepage and prevent piping. The entire left embankment is constructed of impervious material with chimney and blanket drains to collect seepage. The left embankment also uses a cutoff trench excavated to firm rock and a grout curtain along the trench. Several piezometers monitor the hydrostatic pressures in the foundation and embankment (right and left). The data goes back to the early 80's approx. 5 years after an extensive grouting program was undertaken for the right embankment due to high heads before first impoundment. The program was successful and the %pool reflected reduced greatly from before to after grouting. The piezometers on the right embankment( which is entirely impervious material) generally appear to be functioning as expected except one (sensing the impervious core) which has historically read dry up until the last 5 years in which it has slowly risen 14 ft. just above winter pool. However, there is no response to summer, winter or high pool so this could be malfunctioning piezometer. The left embankment has 10 piezometers installed. 5 sensing rock or top of rock and 5 sensing the impervious core. All pz's sensing the core have slowly increased with time (see attached). Each pz is responsive to normal pool fluctuations as expected however as in the case attached each pz has risen over the last 28 years (4-8 ft) approacing summer pool. Any thoughts please? Thanks in advance.
