Engineering properties of a low-grade metamorphic limestone

A particular type of limestone in Singapore is studied in this paper. Seventeen uniaxial compressive strength (UCS) tests and seventeen Brazilian tensile strength (BTS) tests are conducted. From a comprehensive petrographical study, the generally high UCS and BTS values are found to be attributed to the respective mineralogy and texture, as a result of the prevalence of low-grade metamorphism. Altered grain boundaries resulted from pressure solution are observed. Wavy suture contacts between interlocking and interpenetrating grains are common. Signs of subsequent precipitation (cementation) processes are recognized, which reduce the primary porosity and enhance the packing of the rock. On the other hand, with the aid of a high speed video capturing technology during the loading tests, exceptional low strengths obtained in certain specimens can be accounted for. An analysis of the high speed videos reveals that the early crack initiation is often favored along calcite veins, mudstone stringers, fossil fragments and hair-line cracks etc., which appear to be local zones of weakness. We also attempt to correlate the presence of heterogeneities in the rocks with the specimen failure mode under uniaxial compression. In summary, the results presented in this technical note fill in an existing gap of the engineering geology literature of Singapore with respect to limestone. The novelty of our research approach, which integrates the microscopic study and the high speed video imaging technique, is demonstrated to account for the large strength variation of the study limestone.