- 2Pore water pressure below the water table
- 3Pore water pressure above the water table
- 3.2Measurement methods and standards
General principles[edit]
- Water elevation difference, water flowing from higher elevation to lower elevation and causing a velocity head, or with water flow, as exemplified in the Bernoulli's energy equations.
- Hydrostatic water pressure, resulting from the weight of material above the point measured.
- Osmotic pressure, inhomogeneous aggregation of ion concentrations, which causes a force in water particles as they attract by the molecular laws of attraction.
- Absorption pressure, attraction of surrounding soil particles to one another by adsorbed water films.[1]
- Matric suction. The defining trait of unsaturated soil, this term corresponds to the pressure dry soil exerts on the surrounding material to equalise the moisture content in the overall block of soil the and is defined as difference between pore air pressure,, and pore water pressure, .
Pore water pressure below the water table[edit]
Equation for calculation[edit]
- ,
- ps is the saturated pore water pressure (kPa),
- gw is the unit weight of water (kN/m3),
- (English Units 62.43 lb/ft^3)[4]
- hw is the depth below the water table (m),
Measurement methods and standards[edit]
Pore water pressure above the water table[edit]
Equation for calculation[edit]
- ,
- pg is the unsaturated pore water pressure (Pa) at ground level,
- gw is the unit weight of water (kN/m3),
- dw is the depth of the water table (m),
- ,
- pu is the unsaturated pore water pressure (Pa) at point, z, below ground level,
- zu is depth below ground level.
Measurement methods and standards[edit]
Matric pressure[edit]
Pneumatic pressure[edit]
See also[edit]
References[edit]
- ^Mitchell, J.K. 'Components of Pore Water Pressure and their Engineering Significance'(PDF). Retrieved 2013-02-17.
- ^Das, Braja (2011). Principles of Foundation Engineering. Stamford, CT: Cengage Learning. ISBN9780495668107.
- ^ abWood, David Muir. 'Pore water pressure'. GeotechniCAL reference package. Bristol University. Retrieved 2014-03-12.
- ^ National Council of Examiners for Engineering and Surveying (2005). Fundamentals of Engineering Supplied-Reference Handbook (7th ed.). Clemson: National Council of Examiners for Engineering and Surveying. ISBN1-932613-00-5
- ^Dunnicliff, John (1993) [1988]. Geotechnical Instrumentation for Monitoring Field Performance. Wiley-Interscience. p. 117. ISBN0-471-00546-0.
- ^Materials Engineering and Research Laboratory. 'Procedure For Using Piezometers to Monitor Water Pressure in a Rock Mass'(PDF). USBR 6515. U.S. Bureau of Reclamation. Retrieved 2014-03-13.
- ^ abCoduto, Donald; et al. (2011). Geotechnical Engineering Principles and Practices. NJ: Pearson Higher Education, Inc. ISBN9780132368681.
- ^Zhang, Y; et al. (2015). 'Rate effects in inter-granular capillary bridges.'. Unsaturated Soil Mechanics-from Theory to Practice: Proceedings of the 6th Asia Pacific Conference on Unsaturated Soils. CRC Press. pp. 463–466.
- ^Rawls, W.J., Ahuja, L.R., Brakensiek, D.L., and Shirmohammadi, A. 1993. Infiltration and soil water movement, in Maidment, D.R., Ed., Handbook of hydrology, New York, NY, USA, McGraw-Hill, p. 5.1–5.51.
- ^ISO (1995). 'Soil quality -- Determination of pore water pressure -- Tensiometer method'. ISO 11276:1995. International Standards Organization. Retrieved 2014-03-13.
- ^ abBS 7755 1996; Part 5.1
The variation in percentage consolidation with time within a clay layer subjected to a non-uniform initial excess pore water pressure distribution can be difficult to evaluate, and as a result, often a uniform initial distribution is assumed in most analyses. However, by utilizing some of the key features of consolidation in terms of excess pore water pressure dissipation, it is possible to simply adjust the uniform case to account for any number of non-uniform initial excess pore pressure distributions. By observing the decay of excess pore water pressure with time resulting from various non-uniform initial distributions, it is clear that any initial asymmetry or skewness is quickly dispersed, and the distribution of excess pore pressure with depth becomes sinusoidal (or half-sinusoidal if singly drained) shortly after consolidation has commenced. In other words, once the pore pressure decay due to a non-uniform initial distribution has become sinusoidal, it will actually decay at the same rate as the uniform case – however, it will be “ahead” or “behind” the uniform case by some constant factor. Once this factor has been determined, it is possible to simply adjust the rate of consolidation resulting from a uniform initial pore pressure distribution (the values of which are widely available in literature) to account for any number of realistic non-uniform initial excess pore pressure distributions.