14 GROUNDWATER MEASUREMENTS IN SOILS AND ROCK
14.1 General
(1)P Groundwater measurements consist of determining the groundwater table or the pore pressure in soils and rock with different types of equipment for observation or monitoring purposes. The measurements are made by installing open pipes or pipes provided with filters and possibly transducers and loggers to record the pressure at the level of the tip.
(2)P Groundwater measurements shall be used to determine the water pressure or pore pressure and their variations at pertinent levels for design purposes.
(3)P Groundwater measurements shall also be used for monitoring purposes to control the pressure during certain activities or for risk evaluations.
(4)P This section handles the measurement of positive pore pressures related to the atmospheric pressure for building and civil engineering purposes. Thus measurements of negative pore pressures are not considered. Groundwater sampling and determination of groundwater quality are also outside the scope of this section.
(5)P Groundwater measuring for geotechnical purposes shall be carried out in accordance with the requirements given in this section.
(6)P Any deviations from the requirements given below shall be thoroughly reported.
(7) Additional guidelines for groundwater measurements, presentation of measurement and derivation of groundwater pressure can be found in annex L.
14.2 Definitions
(1)P closed systems: system where the groundwater in the equipment is prevented from contact with the atmosphere and the pressure is recorded by a transducer.
(2) The advantage of closed systems is that only a small amount of water has to flow into or out of the piezometer at fluctuations in the pressure. There are hydraulic, pneumatic and electric closed piezometer systems.
(3)P filter tip: tip for groundwater pipes or piezometers provided with a filter to prevent particles from entering the equipment.
(4)P galvanic cell: coupling of different metals or alloys in the ground resulting in a corrosion cell and an electric current and possibly pore pressure changes.
(5)P groundwater fluctuations: variations in the groundwater table or pore pressure distribution with time.
(6)P groundwater table: water level where the pore pressure is equal to the atmospheric pressure at that point and time.
(7)P high air entry value filter: filters with small pores so that, when saturated, they give a high resistance to air entry.
(8)P groundwater measuring station: place where one or more equipment for groundwater measurements are located.
(9)P open systems: systems where the groundwater in the equipment has a direct contact with the atmosphere and the measurements are made as water levels in the borehole, pipe or plastic hose.
(10) The open system in practice consists of three different types: an observation borehole with or without a casing, an open perforated pipe with a possible filter of coarse sand or geotextile and finally a pipe provided with a filter tip and possibly an inner plastic hose.
(11)P piezometers: equipment for groundwater measurements including both closed and open systems.
(12)P pore pressure: pressure of water (or gas) in voids and fissures in the ground at a certain point and time.
(13)P time lag: time elapsed between a change in atmospheric pressure and corresponding change in the pore pressure.
