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| Question | Answer |
| Head | Flow of water through interconnected voids from the points of high energy to low energy. |
| pore water pressure. | The pressure in the water within the soil voids |
| pressure head | if pore water pressure is known then the pressure can also be expressed in terms of equivalent height of water which will exert this pressure. |
| Elevation head (z) | vertical elevation from the datum |
| Piezometer | A open standpipe for measuring pressure head. |
| Total head | Piezometric head |
| i= | hydraulic gradient |
| k= | hydraulic conductivity or coefficient of permeability. |
| v= | discharge velocity |
| Darcy's Law | v=ki |
| the quantity of water flowing through the soil in unit time | q = vA= kiA where: A=c/s area |
| gamma(w) = | 9.81 kN/m^3 |
| Factors affect permeability of soil | 1) Soil type 2) The properties of pore fluid (viscosity) 3) The void ratio of the soil (will be discussed later) 4) The shape and arrangement of pore ‐ very difficult to describe mathematically 5) Degree of saturation‐ increase in degree of saturation increases the permeability |
| Constant head permeability test is | used for coarse‐grained soils |
| Falling head permeability test is | used for fine‐grained soils |
| Phreatic zone: | Portion below groundwater table. |
| Aquifer: | Some soils, such as sands and gravel, can transmit large quantity of groundwater. |
| Aquicludes: | Other soils such as clay transmit water very slowly, |
| Aquitards: | Intermediate soils, such as silty sand, can pass water slow‐to‐moderate rate |
| Unconfined aquifer: | Upper aquifer. Bottom flow boundary is defined by an aquiclude while the upper flow boundary (groundwater table) is free to reach its natural state. |
| Confined aquifer: | Lower aquifer(s). Both upper and lower flow boundaries are defined by aquiclude. Most confined aquifers are artesian, which means water at the top of the aquifer is under pressure. |
| Field Instrumentations | 1. Open standpipe piezometer 2.Observation Well |
| Essential Points | - Flow of water through soils is governed by Darcy’s law, which states that the velocity is proportional to the hydraulic gradient (v=ki). - The proportionality constant is the hydraulic conductivity. - The hydraulic conductivity depends on soil type, particle size, pore fluid properties, void ratio, pore size, homogeneity, layering and fissuring, and entrapped gases. - In coarse-grained soils, the hydraulic conductivity is determined using a constant-head test while for fine-grained soils a falling-head test is used. - In the field, a pumping test is used to determine the hydraulic conductivity. - Wellpoints are used at a construction site to lower the groundwater level. |
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