lecture 6

# lecture 6 - Groundwater Movement Lecture 6(Max Qinhong Hu...

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Groundwater Movement Lecture 6 (Max) Qinhong Hu d l Hydrogeology (GEOL 4320 and 5328) Fall 2009

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Potential Field Trip (Geology, Hydro, Geochem) With students in “Environ Geochem” class Nov. 5 - 12 Leave on Thur. night, back in a week ay 1: 15 r drive to east Tennessee Day 1: 15-hr drive to east Tennessee Day 2: arrive in the morning, explore a cave Day 3: more caves Day 4: got to West Virginia Days 5-6: more caves in West Virginia; drive back What you need: food, camping gear, hard hat, cave light 2
Outline Specific yield and retention Compressibility and effective stress Groundwater flow equation l N t Flow Net low across a boundary Flow across a boundary LOWNETz ercises 3 FLOWNETz exercises

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Specific Yield and Retention Specific yield S y : the ratio of the volume of water yielded, from soil or rock by gravity drainage after being saturated, to the total volume of the soil or rock (Meinzer, 1923) Specific retention S r : the ratio of the volume f water a soil or rock will retain after of water a soil or rock will retain after saturation against the force of gravity to the tal volume total volume Water can be retained as a film on the surface f grains or held in small openings by of grains or held in small openings by molecular attraction 4
Specific Yield and Retention r r V S y y V S T V T V y r T V V V y r S S n 5

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Calculation Example: Question Question : After a soil sample is drained by gravity with a water mass of 20 g , the weight of the soil sample is 85 g . Then the sample is oven-dried, and the sample weighs 80 g . The ulk density of the wet soil is 65 g/cm 3 and bulk density of the wet soil is 1.65 g/cm , and the density of water is 1 g/cm 3 . Calculate the specific yield, specific retention, and porosity of the sample. 7

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Calculation Example: Answer h t t l l f th l The total volume of the sample is: 3 3 ) 20 85 ( g g hevolumeofwaterretainedinthesampleafter 3 6 . 63 / 65 . 1 cm cm g V T The volume of water retained in the sample after draining is: 0 5 3 3 5 / 1 ) 80 85 ( cm cm g g g V r The volume of water that was drained by gravity is: 0 8 3 3 20 / 1 20 cm cm g g V y
Calculation Example: Answer The specific retention is: 5 3 cm V % 9 . 7 6 . 63 3 cm V S T r r The specific yield is: 0 3 V % 4 . 31 6 . 63 20 3 cm cm V S T y y The porosity of the sample is: 9 % 3 . 39 % 4 . 31 % 9 . 7 r y S S n

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combination of A combination of porosity and tractive forces attractive forces 12
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Depends on grain size, shape and distribution of pores, compaction of the stratum, time of drainage In general, specific ields for thick yields for thick unconsolidated rmations tend be 15 formations tend be 7–15%

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Outline Specific yield and retention Compressibility and effective stress Groundwater flow equation l N t Flow Net low across a boundary Flow across a boundary LOWNETz ercises 16 FLOWNETz exercises
Compressibility l id ibilit fl id li htl Fluid compressibility: fluids are slightly

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lecture 6 - Groundwater Movement Lecture 6(Max Qinhong Hu...

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