Tuff as rock and soil: Review of the literature on tuff geotechnical, chemical and mineralogical properties around the world and in Indonesia

Volcanic tuffs are defined as relatively soft and porous pyroclastic rocks which are usually formed by lithification and cementation of volcanic dust or ash. Previous studies on geotechnical properties of tuffs have been carried out with the aim of engineering and alternative materials for cement aggregate materials, dam construction materials, and pavement materials. This paper aims to review several studies of tuff material that have been carried out from several locations around the world and in Indonesia. Tuff rock has geotechnical properties such as 18-25 kN/m3 of unit weight, 1.5 - 2.4 gr/cm3 of bulk density, 2.29 - 2.64 gr/cm3 of particle density, highly varied compressive strength depending on the degree of weathering, 0 - 1.45 MPa of cohesion, friction angle = 24° - 45° of friction angle, and 4% - 42% of porosity. The properties of tuff soil depend on the environment at the deposit location and particle size. Tuff soil (residue) is a product of in situ weathering of pyroclastic materials with high silt content in sandy soils and contains a few silty clay soil. Tuff unit weight varies from 0 to 0.1 MPa, and friction angle from 10° - 40°. Based on the plasticity index data, tuff soil is included in the category of silt soil with low plasticity (CL) and silty soil with high plasticity (CH). Mineralogy studies generally show that there are two groups of minerals: major rock-forming minerals such as olivine and pyroxene, and secondary rock-forming minerals such as zeolites (phillipsite and chabazite), smectite and calcite. There are montmorillonite clay minerals in some tuff samples, but the percentage is small, fewer than normal limits.