Potential use of crushed pyroclastic rocks from mount Kelud as alternative backfill materials

Abstract Pumice and scoria are pyroclastic rocks that can be found where volcanic mountains appear. In Indonesia, pumice and scoria are found in large deposits in the area of Mount Kelud at Kali Putih River in Blitar Regency, Province of East Java. Thus, it is important to evaluate their potential uses as alternative backfill materials. Standard Proctor compaction tests were conducted to determine the maximum dry density (MDD) and optimum moisture content (OMC) to evaluate their compaction properties. Constant head permeability tests were also conducted to determine the coefficients of permeability. Direct shear tests were also applied to investigate the shear strength characteristics of these materials. The results showed that the MDD values of scoria are slightly higher than pumice. The OMC values of pumice and scoria are 23% and 15.5%, respectively. The internal friction angle of pumice and scoria are higher than natural sand, which are approximately 55-64º and 46-59º respectively. Pumice and scoria with different relative densities had coefficients of permeability that ranged from 0.0003 to 0.002 cm/s and 0.001 to 0.002 cm/s respectively. Due to their mechanical properties, it can be concluded that these materials have potential as alternative backfill materials.