Method of test for laboratory determination of water content, porosity, density and related properties of rock material
1991 Edition

According to IS 13030, testing should be conducted on a minimum of three specimens derived from a representative sample. Specimens are preferred to be shaped as right cylinders or prisms. Each specimen should weigh at least 50 grams or have a minimum dimension that is ten times the largest grain size, whichever is greater. For example, a cube with 27 mm sides generally satisfies the 50 g mass requirement for typical rock densities. Additionally, samples should originate from at least ten lumps meeting the size criteria. This recommendation applies to non-friable, coherent rocks that can be machined without swelling or crumbling. Proper sampling and handling practices must be observed to maintain the water content within ±1% of the natural in situ condition.

For rocks that exhibit swelling or disintegration upon immersion in water, IS 13030 advises employing the mercury displacement combined with grain specific gravity technique. This method is suitable for irregularly shaped rocks that are water-sensitive, as it avoids direct contact with water. In contrast, saturation and buoyancy methods are reserved for rocks that remain stable without swelling or disintegrating. Mercury displacement allows volume measurement without water exposure, ensuring accurate porosity and density determination without damaging the specimen.

Porosity determination using saturation and buoyancy involves several measured masses: M1 (mass of container and water), M2 (mass of container, water, and submerged sample), M3 (mass of container and saturated sample, surface dry), and M4 (mass of container and dry sample). The dry mass of the sample (Ms) is obtained as M4 minus M3. Bulk volume (V) is calculated by dividing the difference between saturated surface dry mass and saturated submerged mass by the density of water. Pore volume (Vv) is found by dividing the difference between saturated surface dry mass and dry mass by water density. Porosity (n) is expressed as the ratio of pore volume to bulk volume multiplied by 100, or alternatively by the ratio of mass differences. This method suits irregular specimens that don't swell in water.

Mercury displacement testing requires rigorous safety protocols due to mercury's toxicity and vapor hazards. Tests must be performed inside a fume cupboard or a well-ventilated area with exhaust ventilation to prevent vapor inhalation. Mercury spills should be cleaned immediately, using powdered sulfur to convert mercury into less volatile mercury sulfide. Self-indicating silica gel should be used as a desiccant to maintain sample dryness. Consistency in the liquid used for volume measurements is critical, and adjustments should be made for temperature-induced density variations. Direct skin contact and inhalation of mercury vapors must be strictly avoided.

To maintain accurate water content representative of in situ conditions, IS 13030 recommends sampling at least ten lumps, each weighing 50 grams or larger or measuring at least ten times the maximum grain size. Samples should be stored in airtight, corrosion-resistant containers with secure lids to prevent moisture loss. Cooling should be performed in desiccators containing self-indicating silica gel to avoid moisture exchange during temperature changes. These precautions help keep the water content within ±1% of the original state. Water content should be reported to the nearest 0.1%, with explicit notes on preservation measures taken.