Dear researchers/engineers
I was reviewing a report of a dam monitoring during construction. considering a specific piezometer, it is installed at time t1 and elevation z1. but the casing datum is z2 (near 15 meters above z1). the overburden pressure is zero until t3 days after installation. after t3 the B-value is calculated 1.350. B-value is calculated by this formula : [the piezometric pressure (read at time t4 - initial read)]/[overburden pressure (gamma * elevation at t4 - z2)]
the first thing comes to mind as an issue is without overburden pressure there's an increase in piezometric pressure.
can anyone suggest anything?
Thanks
Hamed, this question is difficult to answer without some geologic/hydrogeologic context to the location of the dam/fill. Long-term excess piezometer levels were recorded in the shale foundation underlying Gardner Dam in Saskatchewan, Canada where it was originally presumed to be related to pore water pressure due to dam construction. Over time these piezometer readings did not abate but did the opposite, increasing to above the dam crest, causing much concern among the geotechncial engineers involved. Subsequent work demonstrated that the piezometer readings were due to adjustment of the regional groundwater levels to the change in the discharge pattern along the valley. A primary reference was a report by Van Everdingen, R. O. Influence of the South Saskatchewan reservoir (Canada) on piezometric levels in underlying bedrock aquifers
Thanks Dear John for sharing this. that was useful. the important thing about this dam (the one in my question) is there's no water behind the dam and not situated in impounding phase.
Hamed, I did expect that this dam is under construction and while the example I provided was a regional groundwater response due to impoundment there is evidence that the piezometer levels in the shale beneath the embankment itself responded to the earth fill blocking the historical groundwater discharge path resulting in locally elevated levels. This was not understood at the time and was only better understood after the problem of the higher than dam pressures persisted for years and alternative explanation to loading induced pore pressures was allowed to be explored.
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