G1-Text-Lecture20-Permeability

G1-Text-Lecture20-Permeability - !"" #$ % ! &...

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Unformatted text preview: !"" #$ % ! & ' ! () * # ,-! + + ( -! !( .* / !0 + -! 0 +0 ) , ! ) * + 1 ( "" " + 1) 2 # +( ! ! 1* ,-! 2 " $% & '( ( ,-! !( ' ! # ! # !"" #$ % ! & ' ! () * + THE HYDROLOGIC CYCLE A part of the precipitation falling on the surface runs off toward the farm pond or the river, where some is evaporated and returned to the atmosphere. Of that part filtering into the ground, some is removed by the vegetation as evapotranspiration. Some part seeps down through the zone of aeration to the water table. Below the water table the water moves slowly toward the stream, where it reappears as surface water via springs in the streambed. Water in a confined aquifer can exist pressures as high as its source, hence the flowing well. Water trapped above the upper clay layer can become perched and reappear as a small seep along the river bank. $ !"" #$ % ! & ' ! () * + ) " & !"" #$ % ! & ' ! () * + , + 3 +( ! # * ( 4 / !5 - ./ + , - 5 6 72 6 7 8% * ," , 0 3 4 ' 12 % !"" #$ % ! & ' ! () * + 0 +0 % ) , * ," 98: - 4 # " ) ! ) -∝, -∝7 -∝ % # -6: 7 % -6: ; - 5' / "* 7 + !7 " - < 4 4 96: 4 8 < 7 , 7 , !"" #$ % ! & ' ! () * + : !"" #$ % ! & ' ! () * + ,-! " = !"" #$ % ! & ' ! () * 1 (; + !* * dh dr 2kπ q = kiA = k ( 2π rh ) ∴ = r r q r2 r1 q r 2 ln 1 = h12 − h2 ∴ kπ r2 3 (; ( k= % h1 hdh h2 q ln r1 / r2 π ( h12 − h22 ) + 9 +: ! ) !"" #$ % ! & ' ! () * + Pumping from auger holes (FDOT type slug test) Water is either pumped out or, charged in. Using the Ernst equation, the permeability k is found from k= 40 r ∆y l y y ∆t 20 + 2− r r where r(m) is the radius of auger hole, and y(m) is the average drop of the WT in time t(minutes) FLOW THROUGH UNSATURATED SOILS. When clay becomes unsaturated its k greatly diminishes, because the entry of air traps it into a portion of the pores, and flow is confined to the smaller diameter pores. There can be on order of change in the permeability for small changes in water content. FLOW THROUGH ROCK. Water flow through intact rock follows Darcy’s law. When the rock has open joints the flow could become turbulent. In laminar flow, the permeability kE is a2g 2a * 3γ b where a = half-width of the joint (m) b = joint spacing (m) g = gravitational constant (9.81 m/sec2) γ = viscosity of water kE = EXAMPLE: For a fissured schist, with 1mm wide joints spaced at 1m, kE = 2 ( 0 . 0 0 5 m ) 3 ( 9 .8 1 m / s e c 2 ) 2a a 2 g * = = 8.3x10-4 b 3ν 3 (1m ) (1 X 1 0 − 6 m m 3 / m − s e c ) A Guide to the Coefficient of Permeability of Intact Rocks (SOURCE: Based on Louis 1968; Serafim and Del Campo, and Vutukuri, 1978) m/sec 1965; Serafim, 1968; Winterkorn and Fang, 1975; Lama and Rock Type Test Calcite Slate Granite (fresh) Granite (weathered) Granite Schists (fissured) Lab Lab Lab Lab Coefficient of Permeability (m/sec) (0.01 to 1) * 10-7 (0.1 to 1) * 10-9 (0.1 to 1) * 10-10 (0.1 to 1) * 10-5 Field Lab (0.1 to 1) * 10-4 (1 to 3) * 10-4 > !"" #$ % ! & ' ! () * + A Guide to the Coefficient of Permeability of Intact Rocks (SOURCE: (SOURCE: Based on Louis 1968; Serafim and Del Campo, 1965; Serafim, 1968; Winterkorn and Fang, 1975; Lama and Vutukuri, 1978) Coefficient of Rock Type Test Permeability (m/sec) Calcite Lab (0.01 to 1) * 10-7 Slate Lab (0.1 to 1) * 10-9 Granite (fresh) Lab 10 (0.1 to 1) * 10-10 Granite Granite (Weathered) Lab (0.1 to 1) * 10-5 Field (0.1 to 1) * 10-4 Lab (1 to 3) * 10-4 Granite Schists (fissured) 1 ( ,"" / !"" #$ % ! & ' ! () * + 85 ? , . 8/@ !B (A C !"" #$ % ! & ' ! () * + (A B C & ! # ( D " + E F G $ !"" #$ % ! & ' ! () * + ; - - ! ! & !"" #$ % ! & ' ! () * + ! ! # ( " + " E F! G ! E F - !" G E F ' ! ! # $% / !"" #$ % ! & ' ! () * + ΣFy = 0 & ' Ground Surface Discontinuous Moisture Zone vapor flow Capillary Capillary Fringe Zone hc B capillary flow Capillary Capillary Saturation Zone Water Table z 100% Saturation Zone &/// ()* + ,( & - 8 . /' ...
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This note was uploaded on 09/11/2011 for the course CEG 4011 taught by Professor Staff during the Summer '10 term at FIU.

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