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Dam monitoring flaws and performance issues: Some thoughts and recommendations
Published in Jean-Pierre Tournier, Tony Bennett, Johanne Bibeau, Sustainable and Safe Dams Around the World, 2019
M.G. de Membrillera, R. Gómez, M. De la Fuente
For many years, observation wells, also known as “open standpipes” were very common in Spain, and most core drilling activities eventually ended up with the supply of observation wells. They consist of a slotted plastic, reinforced fiberglass or steel pipe attached to a standpipe, installed in a borehole and surrounded with sand. The slotted pipe is often wrapped in filter fabric to prevent clogging, and the hole is always sealed at the top with mortar, giving room for the water level dip meter used for measurements. Observation wells measure the maximum water pressure intersected by the borehole, but they neither measure pressure at a point nor account for flownet effects. Observation wells can be useful to estimate the phreatic surface and generate qualitative information but, in most situations, they are not adequate and piezometers should be installed instead (mainly vibrating wire or Casagrande ones).
Water in the soil
Published in Willem F. Vlotman, Lambert K. Smedema, David W. Rycroft, Modern Land Drainage, 2020
Willem F. Vlotman, Lambert K. Smedema, David W. Rycroft
Groundwater fills the pores of the permeable strata in the earth’s upper crust (aquifers). The groundwater in these strata may be under normal static or dynamic pressure or it may be subjected to an over-pressure. The latter may occur when an aquifer is overlain by a poorly permeable layer. Such aquifers are termed confined aquifers. Aquifers of different types may occur at varying depths, over or underlying each other. The free groundwater found in or directly below the soil layers is called phreatic groundwater and its surface is termed phreatic level or watertable.
Natural Water Content of a Soil Sample
Published in Bashir Ahmed Mir, Manual of Geotechnical Laboratory Soil Testing, 2021
Water on, above, and below the ground surface may exist in different forms such as liquid, gaseous, (e.g. vapors) or solid (e.g. frozen ice) states. Water below or underneath ground surface is termed as subsurface water. At varying depths under the ground surface, there is a zone of saturation in which water fills all the pores in the soils and the openings in the underlying rock. The water in the zone of saturation is commonly termed as “ground water,” its upper surface being the “ground water table or water table” of phreatic surface, which has the atmospheric pressure.
Effect of explosive cratering on embankment dams
Published in International Journal of Geotechnical Engineering, 2018
George Afriyie, Abass Braimah, Mohammad T. Rayhani
The steady seepage condition in the embankment dam was modelled by defining the water table (phreatic surface) and partitioning the soil mass into two parts. The part under water was modelled with saturated soil properties while the part above the phreatic surface was modelled with unsaturated soil properties. To incorporate the effects of steady seepage conditions within the embankment in LS-DYNA, the water within the embankment was applied as a boundary condition. The embankment dam was modelled with SEEP/W, a component of GeoStudio (2007), to determine the position of the phreatic surface on the 2-m-high dam at full reservoir level. Figure 6 shows a typical GeoStudio simulation showing the phreatic surface. The pore water pressure distribution within the embankment was defined by selecting nodes of the embankment dam below the phreatic surface and applying undrained soil properties. The reservoir upstream as well as water at the toe of the dam were not modelled to reduce the simulation time, however, the pressure by height of water was applied to the surfaces of the embankment in the upstream and downstream. The output data that can be retrieved from pore water analysis in LS-DYNA include total pore water pressure head, excess pore water pressure head, hydraulic pore water pressure head and volume change. The pore water pressure analysis in LS-DYNA is independent of the material model. The output that was required for the pore water pressure was specified as excess pore water pressure for the output of the simulation with pore water. In calculating the excess pore water pressure, LS-DYNA estimates the excess pore water pressure by considering the volume change that takes place at each node. The parametric study conducted considered the effect of charge mass, reservoir height and density of embankment material.