The Effect of Weathering and Age on Shear Strength of Questa Mine Rock Piles, New Mexico, USA

摘要

Weathering of mine rock piles is an important process that can change the shear strength of these materials. Laboratory and in-situ shear tests were conducted on Questa rock-pile materials to evaluate the effect of weathering and age on their cohesion and friction angle. The laboratory shear box used was 5 cm wide and the in-situ shear boxes were 30 and 60 cm wide. The normal stress for the in-situ tests ranged from 15 to 70 kPa, whereas the normal stress for the laboratory shear testing included a wider range of 20 to 650 kPa. The results indicated that the average cohesion of rock pile material at the near surface has increased with age of the material where the in-situ tests were conducted. Higher cohesion values are found in the more weathered samples, but not all weathered samples have high cohesion values. This increase in cohesion is due to the presence of the cementing minerals resulting from weathering, the matric suction, and the compaction of the material with time. The average friction angle of Questa material is high and show similar values for the different rock piles. The angularity of particles, interlocking of grains, low percentage of fine-grained material and high to extremely high durability index of rock fragments in the rock piles are the major reasons for the observed high friction angles.