caa a22 4500 605454442 CHVBK 20210128100207.0 cr unu---uuuuu 210128e20151101xx s 000 0 eng 10.1007/s10064-014-0710-9 doi (NATIONALLICENCE)springer-10.1007/s10064-014-0710-9 On the difficulties of geotechnical sampling and practical estimates of the strength of a weakly bonded volcanic soil [Elektronische Daten] [Elif Avşar, Resat Ulusay, Ömer Aydan, Mahmut Mutlutürk] Volcanic soils, which cover significant parts of the world's surface, including urban areas, structures and infrastructures, may create geo-engineering problems. These soils exhibit distinctive geomechanical behaviours that are a consequence of their formation history, mineralogy and structure. This paper presents the results of an experimental investigation into geo-engineering properties of a volcanic soil observed in the city of Isparta, Turkey. The study focuses on the difficulties experienced in geotechnical sampling of the soil, its microstructural, mineralogical and physical properties, and particularly the estimation of its uniaxial compressive strength (UCS) using practical approaches. For this purpose, laboratory experiments covering the determination of mineralogical-petrographical and geomechanical properties, such as physical properties, UCS, and needle penetration index (NPI) using a specially manufactured needle, were conducted. The volcanic soil is weakly bonded, highly porous, well-graded silty sand and has a hypocrystalline texture. The weak bonding of the soil is volcanic ash formed by disintegration of volcanic glass, and the soil has some voids and a considerable amount of intact bonding between grains. The most important difficulty associated with this volcanic soil is field sampling and sample preparation for laboratory testing due to the weak bonding that governs internal stability. The UCS of the soil ranges between 29 and 132kPa, and except for in a few samples, the UCS is lower than 100kPa. The soil generally shows strain softening behaviour during the UCS tests; however, a few samples failed in a brittle fashion. As the natural water content and degree of saturation increases above approximately 11 and 42%, respectively, there is a decline in the UCS of the soil. This is due to the increased exposure to water, which apparently softens the bonding, causing some loss of interlocking among the grains. Statistical evaluations suggest that the UCS of the volcanic soil can be estimated from the NPI using a needle with a diameter of 1.7mm. In practical terms, the study provides some approaches and recommendations for the estimation of strength of weakly bonded volcanic soils for which geotechnical sampling is extremely difficult and/or impossible. Springer-Verlag Berlin Heidelberg, 2014 Volcanic soil nationallicence Uniaxial compressive strength nationallicence Needle penetration index nationallicence Laboratory sampling nationallicence Prediction equation nationallicence Microstructure nationallicence Avşar Elif Department of Geological Engineering, Selçuk University, Konya, Turkey aut Ulusay Resat Department of Geological Engineering, Hacettepe University, Beytepe, 06800, Ankara, Turkey aut Aydan Ömer Department of Civil Engineering and Architecture, University of the Ryukyus, Okinawa, Japan aut Mutlutürk Mahmut Department of Geological Engineering, Süleyman Demirel University, Isparta, Turkey aut Bulletin of Engineering Geology and the Environment Springer Berlin Heidelberg 74/4(2015-11-01), 1375-1394 1435-9529 74:4<1375 2015 74 10064 https://doi.org/10.1007/s10064-014-0710-9 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s10064-014-0710-9 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Avşar Elif Department of Geological Engineering, Selçuk University, Konya, Turkey aut NATIONALLICENCE 700 1- Ulusay Resat Department of Geological Engineering, Hacettepe University, Beytepe, 06800, Ankara, Turkey aut NATIONALLICENCE 700 1- Aydan Ömer Department of Civil Engineering and Architecture, University of the Ryukyus, Okinawa, Japan aut NATIONALLICENCE 700 1- Mutlutürk Mahmut Department of Geological Engineering, Süleyman Demirel University, Isparta, Turkey aut NATIONALLICENCE 773 0- Bulletin of Engineering Geology and the Environment Springer Berlin Heidelberg 74/4(2015-11-01), 1375-1394 1435-9529 74:4<1375 2015 74 10064