Phreatic surface

The pores within the zone of saturation are filled with water, generally referred to as phreatic water. The upper surface of this zone is therefore known as the phreatic surface but is more commonly termed the water table. Above the zone of saturation is the zone of aeration... 

When the downstream dam site is considered, the retained reservoir level will be 2475 a.s.l. The specified phreatic surface in this model was selected to be the same level of water damming. The colluvium and heavily weathered bedrock were considered to be permeable while the bedrock was assumed to be impermeable. The shear strength parameters of the saturated deposit are selected as 0.7 times of the dry condition referring to the research of Liu (2009). The hydrostatic pressure on the slope was also considered. Figure 9 shows the pore pressure of the colluvium and the phreatic line can be obtained from the result. Figure 10 illustrates the displacement contour and vectors after 1000 iteration steps. Figure 11 shows the cross sectional map of the displacement in Y direction after partial saturation. It can be concluded that, unlike the seismic condition, the... 

The water table (or phreatic surface) is not a boundary separating zones where seepage and pore pressures exist from those where they don t exist it is simply a line of zero pore pressure. 

Shallow wells are those that are less than 100 ft deep. Such wells are not particularly desirable for municipal supplies because the aquifers they tap are likely to fluctuate considerably in depth, making the yield somewhat uncertain. Municipal wells in such aquifers cause a reduction in the water table (or phreatic surface) that affects nearby private wells, which are more likely to utilize shallow strata. Such interference with private wells may result in damage suits against the community. Shallow wells may be dug, bored, or driven ... 

The relative density of the hydraulic fill can also be determined by indirect testing. Especially for sand layers deeper than 2 m below the surface or below the phreatic surface, it may be virtually impossible to determine the in situ density using the direct measurement methods. In granular material, the only option for taking undisturbed samples is by freezing the soil prior to the sampling. Often the Cone Penetration Test (CPT) is used to determine the relative density of those submerged or deep sand layers. Over the years several correlations have been established between cone resistance and relative density. 

One approach used to date (Plummer et al., 1976 Halley and Harris, 1979 Budd, 1984, 1988) is to assume that the rate of conversion of aragonite to calcite (dA/dt) in the phreatic freshwater zone is directly proportional to the mass of aragonite present at a given time, and that the surface area of aragonite per unit mass of aragonite present in the phreatic zone does not change with time ... 

In a warm and semi-arid climate thick calcretes can develop. Alteration in the vadose zone is relatively rapid but not as rapid as in the phreatic zone. Surface karst is present locally, and caves are small and rare. The mineralogical changes follow the pattern of Figure 7.25, but at a rate slower than that for a warm, subtropical climate like Bermuda. Under the extreme of a warm, wet tropical climate, extensive terra-rossa soils can develop, and dissolution features, such as caves, solution pipes and fractures, should be prevalent. Mineralogical stabilization should occur rapidly. 

Figure 7.42. Comparison between (A) an idealized plot of variation in 8180 and 813C for carbonates subjected to vadose and phreatic meteoric diagenesis (after Lohmann, 1988) with (B) the meteoric alteration trend observed for the Key Largo Limestone, Florida, U.S.A. (after Martin et al., 1986). The critical trend in isotopic composition is termed the meteoric calcite line. This trend may be modified at the water recharge surface where evaporation is an important process, caliche is formed and the diagenetic phases are depleted in 13C derived from soil-gas CO2. Another modification can occur distally to the recharge area where precipitating carbonate cements may have isotopic ratios nearly equivalent to dissolving phases.

Through-Flow Systems Unconfined and Confined 2.8.1 Phreatic (Unconfined, Free Surface) Aquifers... 

Phreatic aquifers have free communication with the aerated zone. The synonym free surface aquifer relates to the free communication between the aquifer and the vadose zone. An example is shown in Fig. 2.5. The term phreatic originates from the Greek word for a well. 

Confined aquifers are water-bearing strata that are sealed at the top and the bottom by aquiclude rocks of low permeability (Fig. 2.6). Confined aquifers are commonly formed in folded terrains (section 3.4) and have a phreatic section, where the aquifer rock beds are exposed to recharge infiltration, and a confined section, where the aquifer rock beds are isolated from the landscape surface by an aquiclude (Fig. 2.6). 

The water in the saturated zone of the phreatic section of a confined system exerts a hydrostatic pressure that causes water to ascend in wells. In fact, a confined aquifer can often be identified by the observation that water ascends in a borehole to a level higher than the level at which the water was first struck. In extreme cases the water ascends to the surface, constituting an artesian well. This phenomenon of water ascending in a well and flowing by itself was first described in 1750 in the area of Artois, a province in... 

Fig. 2.6 Components of a confined aquifer with through-flow tilted, or folded, water-bearing rock strata, sealed at the top and the base by aquicludes. Each active confined system also has a phreatic section at outcrops of the aquifer rocks. The level of the water table in the phreatic section defines the piezometric head in the confined section. Water ascends in boreholes drilled into confined aquifers. Water reaches the surface in artesian flow in boreholes that are drilled at altitudes lower than the piezometric head.

The level water reaches in an artesian well reflects its pressure, called the piezometric, or confined, water head (Fig 2.6). In boreholes drilled at altitudes that are lower than the piezometric head, water will reach the surface in a jet (or wellhead pressure) with a pressure that is proportional to the difference between the altitude of the wellhead and the piezometric head. The piezometric head is slightly lower than the water level in the relevant phreatic section of the system due to the flow resistance of the aquifer. Confined aquifers often underlay a phreatic aquifer, as shown in Fig. 2.7. The nature of such groundwater systems may be revealed by data measured in boreholes and wells. The water levels in wells 1 and 2 of Fig. 2.7 did not rise after the water was encountered, and both wells reached a phreatic aquifer. Well 3 is artesian, and the drillers account should include the depth in which the water was struck and the depth and nature of the aquiclude. The hydraulic interconnection between well 1 and well 3 may be established by... 

The area studied by Mihevc and his colleagues, included large, horizontal, epiphreatic caves. In contrast, all of the features currently accessible on the surface of Laski Ravnik were originally deep phreatic, oblique (reflecting the dip of the enclosing strata), and relatively small. All of the denuded channels in the area are filled with a variety of clastic sediments, and localized flowstone deposits also occur. Where visible and washed clean, the channel walls are seen to be modified to some extent by small-scale spalling. 

A Original phreatic channel, not yet influenced by the zone of surface-weathering. 

Most soils have some amount of water in the soil voids. The water may be gravitational, capillary, or hygroscopic. The basis for distinction is the force that influences the water behavior. Stabilization methods are concerned mainly with gravitational water, generally present beneath the soil surface in areas requiring stabilization. The topography of the surface below which water is continuous is called the water table or the phreatic line. 

Water removal is much simpler when the bottom of the excavation is above the surface of the ground water (the phreatic line). Surface runoff water which accumulates in a pool within the excavation can be removed by pumping from a sump. Sumps are made at a low area in the excavation by burying a container (such as a 55 gallon drum) with its upper rim level with or just below ground surface. As water accumulates in the drum, it is pumped away from the site. 

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