Evaluation of single particle loading test to estimate the uniaxial compressive strength of sandstone

Researchers have introduced a variety of innovative methods for indirect determination of uniaxial compressive strength (UCS) for use when preparation of standard cores is impossible or uneconomical, such as for oil wells or underground drilling. One indirect method is the single-particle strength test. The present study evaluated the use of this method to determine the UCS of 13 sandstone blocks (10 for testing; 3 for validation) collected from different geological formations in Iran. Standard (NX) cores 109.4 mm in length and 54.7 mm in diameter were prepared from the blocks and used to measure the UCS. The blocks were then crushed into small particles; to eliminate the differences in their shapes, the particles were reshaped into spherical form. Next, single particle loading was performed on 300 sandstone particles and the single-particle compressive strength index (SCSI) was determined for each. An average of R=0.96 was obtained between UCS and SCSI. The results of verification of the proposed equations showed that they predicted UCS with 85% accuracy. A comparison of the results of this study and those of previous studies on microcrystalline limestone showed that, although the equations for sandstone and microcrystalline limestone follow a similar pattern, the lithology of the rock affected the results of the single-particle loading test. A better alternative is to use a distinct equation for each lithology. Future study should examine the possibility of establishing a lithology-independent equation with an acceptable correlation coefficient for both sandstone and microcrystalline limestone particles.