ISO 11461 pdf download.Soil quality — Determination of soil water content as a volume fraction using coring sleeves — Gravimetric method
1 Scope
This International Standard specifies a method for the gravimetric determination of soil water content as a volume fraction. The method is applicable to all types of non-swelling or non-shrinking soils where coring sleeves can be used for sampling. It is not applicable to soils where stones, tough roots or other factors prevent collection of soil cores. It is used as a reference method (e.g. the calibration of indirect methods for determination of water content). NOTE The determination of water content as a mass fraction is described in ISO 1 1465.
2 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply. 2.1 water content volume fraction volume of water evaporating from the soil when dried to constant mass at , divided by the original bulk volume of the soil NOTE The water content volume fraction is sometimes also referred to as “volumetric water content”. 2.2 constant mass mass reached when during the drying process the difference between two successive weighings of the sample, after a drying interval of , does not exceed (mass fraction) of the last determined mass NOTE Usually to is sufficient for drying most soils to constant mass, but certain soil types and large or very wet samples will require longer.
4 Principle
Soil samples of known volume are dried to constant mass at . The difference in the mass of the soil sample, before and after the drying procedure, is taken as a measure of the water content. The water content is calculated as a volume fraction. NOTE Organic matter can oxidize during drying. This has no significant effect on the water content determined. However, drying at lower temperatures, e.g. , can lead to significantly lower values of the water content. Hence, drying at a temperature lower than is not recommended.
5 Apparatus
5.1 Drying oven, thermostatically controlled with forced air ventilation and capable of maintaining a temperature of . Differences in temperature between various positions in the oven shall be less than . NOTE By measuring the temperature at the centre of a sample during or directly after the drying procedure using a thin thermocouple with low thermal capacity, it is possible to determine whether the oven is working efficiently. These measurements should be carried out on dry samples, to prevent temperature differences due to evaporation. 5.2 Desiccator with an active drying agent. 5.3 Balance, capable of weighing accurately to within of the mass of the dried sample. 5.4 Coring sleeves, of known volume, fitted with water- and vapour-tight caps of known mass to prevent evaporation of water from the samples. Each sleeve shall have a sharp cutting edge or shall be used with a holder with a sharp cutting edge. The volume of each coring sleeve shall be greater than . The precise dimensions of the coring sleeves will depend on the goal of the investigation. 5.5 Pushing rod, for the coring sleeves. 5.6 Dishes of known mass, to support the soil in the coring sleeves while handling them in the laboratory.
6 Field sampling
6.1 General For the direct determination of water content volume fraction, a sample of known volume is required and coring sleeves are therefore used for sample collection. The size of the coring sleeves and the number of samples required will be governed by the objectives of the investigation and usually the need to represent the soil more generally; one should take into account the size of the structural elements of the soil and its variability. Samples shall be collected, transported and stored so that their water content does not change from that at the time of sampling.