Argillaceous Swelling Rocks - Methods for Laboratory Testing
1996 Edition

Sampling involves using core borings with double or triple tube barrels approximately 100 mm in diameter or selecting intact blocks suitable for making at least three undisturbed specimens plus additional material for identification. Samples must be cleaned, logged, and wrapped in waterproof liners followed by aluminum foil sealed with paraffin wax to preserve natural moisture and density. For transport, cushioned containers are used to prevent damage and exposure to extreme temperatures. Storage should be minimized and maintained at a stable temperature of 27°C, avoiding direct sunlight and humidity changes. Specimens are machined into right circular discs with diameters between 50 and 100 mm and thicknesses of 20 to 30 mm, using air-cooling or anti-swelling agents. Fragile argillaceous rocks require special trimming using a stainless steel confining ring and manual presses as described in Annex A to maintain sample integrity.

The process starts with precise measurement of specimen thickness and diameter at multiple points with ±0.1 mm accuracy, and recording the specimen and ring masses. The specimen is placed snugly within a stainless steel ring and assembled with porous plates and a rigid loading plate. An initial axial seating load of 25 kPa is applied, and the specimen is submerged in distilled water covering the porous plates. Axial force and displacement are recorded over time while incrementally increasing axial load to compensate for swelling strain, with small load increments especially near the test conclusion. Testing continues until axial displacement ceases or maximum axial load is reached. Final calculations involve determining the cross-sectional area and dividing the peak axial force by this area to obtain maximum axial swelling stress. Post-test, specimens are oven dried at 105 ± 2°C to constant mass for moisture content analysis.

Measuring axial swelling strain requires two micrometer dial gauges with a sensitivity of 2.5 microns, set up to detect changes in specimen thickness. The loading assembly includes a stainless steel loading plate and a polished steel sphere piston mounted on a rigid frame capable of applying controlled loads up to 10 kN. Radial swelling strain measurement is facilitated by a polished stainless steel ring of 5 to 10 mm thickness which provides a rigid radial restraint, limiting radial strain to below 10⁻⁴. Porous metal plates are installed above and below the specimen to allow water flow. An electromechanical load cell with ±0.5% accuracy records axial forces. A thin flexible stainless steel band may also be used to monitor changes in specimen circumference.

To ensure consistent and reliable results, the laboratory environment must maintain the temperature at 27 ± 2°C throughout the duration of the test. Distilled water is typically used for specimen immersion; however, site-specific or chemically characterized water can be substituted if necessary. Specimen dimensions must be measured with precision (±0.1 mm), and mass recorded with 0.1 g accuracy. A seating axial load of 25 kPa is applied before swelling begins, and axial force is increased stepwise to compensate swelling strains, particularly near the test end with increments around 0.05%. The test continues until axial displacement stabilizes or the maximum force is attained. After testing, specimens are oven dried at 105 ± 2°C to constant mass and cooled in a desiccator before final mass recording.

The testing framework provides a progressive evaluation starting with sampling and specimen preparation (Part 1), followed by quick estimation of maximum swelling stresses and strains (Parts 2 and 3) for preliminary design and field assessments. For comprehensive analysis, Part 4 delivers detailed stress-strain behavior over extended periods (up to four months), enabling accurate modeling of swelling effects under various load conditions. Engineers use maximum swelling stress values to predict uplift or heaving forces impacting foundations and structures, while swelling strains help estimate potential deformations and displacements. The full stress-strain profiles support time-dependent behavior analysis, improving stability and serviceability evaluations and guiding effective mitigation strategies against swelling rock hazards.