Annex L (p. II)

(informative)

L.2 Sample guidelines for presentation of groundwater measurements

(1) The presentation of the groundwater measurements can be made in different ways depending on the purpose of the measurements and the presentation of other ground investigations. As the groundwater conditions normally influence the interpretation of the total ground situation the results should be presented in both plans and profiles. In addition it can be necessary to present long term measurements and pore pressure profiles in special diagrams.

(2) In a plan the elevation of the groundwater table can be indicated at its actual position as follows:

• o         No. 16
• GW +8,30 82-03-15
• GL +9,20

where:

(3) The results of groundwater observations in boreholes, pipes or piezometers can be presented in a simplified way in sections according to figure L.2.

Figure L.2 indicates a measurement made in a piezometer where the ground surface elevation was +9,33 m and the centre of the filter was located at elevation +4,73. During the measuring period 1982-04-21 to 1982-05-27 the highest observed level was +7,33 m and the lowest +6,23 m. The borehole No. 5 is indicated above.

(4) The results from a number of piezometers at different depths in one measuring station can be compiled like the examples in figure L.3, where also a reference hydrostatic line is indicated. Figure a) indicates the pore pressure measured at each level at three occasions. Figure b) indicates the maximum and minimum pressures measured during the measuring period 1989-04-10 to 1989-10-12 and the mean values from each elevation.

(5) In case of presentation of long term measurements the example in figure L.4 can be followed. Alternatively the groundwater level can be expressed in depth below ground surface in m or as a pore pressure in kPa.

L.3 Sample guidelines for derivation of groundwater pressure

(1) The natural groundwater pressure is part of the hydrological cycle being influenced by the precipitation, evapotranspiration, snow melting, surface run off etc.

(2) In order to establish a model of the groundwater situation for a building or a civil engineering project site and the surrounding area, available hydrogeological information should be compiled and compared to the actual groundwater measurements. Such information could be:

• water level fluctuations;
• geohydrological maps;
• previous measurements in the surroundings;
• typical water levels of surface water or in wells;
• long term measurements in similar aquifers.

(3) The groundwater measurements for a project normally only contain a short series of measurements. In these cases it is important to make a prediction of the expected groundwater pressure for the actual design situation. Such a prediction can be based on the model mentioned above and on long term measurements of the groundwater in a similar aquifer in the same region as the project in combination with a short term measurement on the site.

(4) Using statistical methods it has been possible to predict the groundwater pressure within a few decimeters based on 15 to 20 years measurements in a reference system and a 3 month measuring period on the actual site, see figure L.5.

(5) A conceptual model can also simulate the groundwater fluctuations by a conceptual model. Precipitation and air temperature can be used as input in the model. The groundwater response is calibrated against long term measured groundwater fluctuations in the region.

For additional information and examples, see Annex M.