Method of tests for timber props for mines
1971 Edition

The standard defines eccentricity as the greatest deviation from a taut string stretched along the prop's length within the plane containing its natural and longitudinal axes. It is calculated using the formula: e = (8 × 100) / A, where '8' is the maximum deviation in millimeters and 'A' is the prop length in millimeters. While specific dimensional limits are not detailed, the pro forma mandates recording the average diameter and length-to-diameter ratio, which typically should not exceed 20 to prevent buckling. Props are generally circular or polygonal with diameters between 75 and 150 mm, and eccentricity should be minimized, ideally under 5%, to ensure effective axial load transfer and reduce bending stresses.

Compressive strength assessment involves loading the timber prop parallel to its grain at a controlled rate until failure occurs. Tests are performed on full-size props or small clear specimens as per referenced standards. Key recorded parameters include species, supplier, condition (air-dried or green), average diameter, weight, length-to-diameter ratio, eccentricity, loading rate, maximum load sustained, compressive stress at failure, and failure mode. Compressive stress is calculated by dividing the maximum load (converted to Newtons) by the cross-sectional area in square meters. This method ensures the props' adequacy for mining support applications.

Moisture content determination involves extracting a disc approximately 2.5 cm in length from near the prop's failure point or central section, avoiding the ends. Moisture is measured in three zones: peripheral, intermediate, and core, with results recorded and averaged. The oven-dry method is used, where the specimen is weighed before drying (W1), then dried at 103 ± 2°C until weight stabilization, followed by re-weighing (W2). Moisture content percentage is calculated as ((W1 - W2) / W2) × 100. Multiple specimens per prop are tested to ensure accuracy, and results are documented in the standardized report.

The conditioning regimen divides props into three groups: 25% are tested as received (typically green if moisture exceeds fibre saturation point), 50% are air-dried in shaded, ventilated conditions for one month to simulate dry environments, and the remaining 25% are submerged in water for one month to represent saturated conditions. This approach ensures testing reflects realistic service conditions, with moisture content subsequently measured from a sample disc taken near the failure area.

Test reports must follow the prescribed pro forma and include timber species, supplier information, condition at testing (air-dried, green, or as received), average diameter, weight, length-to-diameter ratio, and eccentricity. For major compression tests, data on loading rate, maximum load, compressive stress, failure mode, and remarks are required. Minor tests report dimensions, weight, moisture percentage, specific gravity at test and oven-dry states, fibre stress at elastic limit, modulus of rupture, failure descriptions, and any observations. Moisture content for peripheral, intermediate, and core zones along with average values must be recorded. All values should be rounded according to relevant rounding standards, and testing personnel signatures should be included to verify authenticity.