Investigating the drillability of laminated sandstone based on the brittleness index, considering the effect of orientation and spacing of lamination

Brittleness index is one of the important parameters in rock engineering, which affects the drillability of the rocks in various geotechnical projects such as tunnels, caves, dams, oil and gas wells, road trenches, and building stone quarries. Investigating the drillability of the rocks before drilling operations can significantly help planning and managing the implementation of geotechnical projects, which will save time and cost of exploration operations. In this paper, the drillability of two laminated sandstone samples (with various lamination spacing) has been investigated based on the brittleness index, considering the orientation and spacing of lamination. For this purpose, after preparing cylindrical cores, uniaxial compressive strength and Brazilian tensile strength of sandstone samples at lamination angles (β) of 0°, 30°, 45°, 60°, and 90° were determined. Next, based on the results of these strengths, the brittleness index values were calculated in the various βs. Based on the data analysis, lamination orientation plays a significant role in the drillability, so that the easiest and hardest drilling conditions are obtained at β of 30° and 90°, respectively. Also, the results indicate that the sandstone sample with lesser lamination spacing had more suitable conditions in terms of drillability compared to other sandstone samples. In the end, the findings of the present research can be useful and efficient in practice for geotechnical projects that require drilling in laminated rocks.