Pumice soil grains are characterized by their vesicular nature, which leads to lightweight, crushable grains with an extremely rough and angular surface texture. These characteristics give pumiceous soils particular engineering properties that are distinct from more commonly encountered hard-grained materials, making them problematic for engineers interested in assessing the risk and potential consequences of liquefaction. Natural pumice-rich soils are found with varying amounts of pumice; however, it remains unclear how the quantity of pumice present in a soil mixture alters the behaviour. This paper investigates the effect of pumice content on cyclic resistance using blends of a hard-grained sand and a pumice sand through a series of triaxial tests. Overall, the cyclic resistance was found to reduce with increasing pumice content. Furthermore, the cyclic resistances appeared to fall into three bands: (a) little apparent reduction in cyclic resistance for pumice contents up to 40%, (b) a reduction in cyclic resistance of approximately 20% at pumice contents of 80% and higher, and (c) a transitional zone. However, despite the lower cyclic resistance, the patterns of pore pressure generation and strain development did not appear to be affected by the amount of pumice in the soil mixture. (c) 2025 Japanese Geotechnical Society. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons. org/licenses/by/4.0/).

Crushable porous soils, such as volcanic pumice, are distributed worldwide and cause a variety of engineering problems, such as slope hazards. The mechanical properties of these soils are complicated by their high compressibility due to voids in the particles themselves and changes in the soil gradation due to particle crushing. They are usually classified as problematic soils and discussed separately from ordinary granular soils, and their behaviour is not systematically understood. In this study, isotropic and triaxial compression tests were conducted on artificial pumice in order to determine the relationship between the mechanical properties and the particle crushing of crushable porous granular materials. The results showed that the mechanical behaviour of artificial pumice, representative of such materials, can be explained using a particle crushing index, which is related to the degree of efficient packing. Furthermore, a new critical state surface equation was proposed. It is applicable to crushable porous granular materials and shows the potential for expressing the critical state or isotropic consolidation state of such materials as a single surface in a three-dimensional space consisting of three axes: the stress - void ratio - crushing index. The validity of this new equation was confirmed by applying it to natural pumice from previous research. (c) 2025 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Volcanic pumice, with special characteristics such as crushable particles and high water retention, is distributed throughout Japan and serves as the source layer for slope hazards characterised by post-failure gentle slope flows and long-distance flows. The aim of this study is to determine the relationship between the crushing characteristics and the mechanical properties of porous pumice, which often contributes to such disasters. As the porous pumice material, Ta -d pumice, which caused numerous slope disasters during the 2018 Hokkaido Eastern Iburi Earthquake in Japan, was collected and subjected to a series of triaxial compression tests. The grain size distribution of the pumice before all the tests was adjusted to be uniform, and the amount of crushing was quantified by measuring the grain size distribution after the tests. The results suggest that the critical state and isotropic consolidation of porous pumice can be systematically expressed in a three-dimensional space with the axes of the void ratio, mean effective stress, and degree of particle crushing. Furthermore, a gentle slope disaster with an inclination of less than 21 degrees, that had occurred at the site from which the Ta -d pumice was collected, was discussed in terms of its flow potential, showing that the flow distance can be adequately explained. (c) 2023 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

The September 6, 2018, earthquake in the eastern part of Hokkaido, Japan, caused extensive slope failures in Atsuma-town, Hokkaido, Japan. In this study, the authors performed in situ investigations, including trenching and portable dynamic cone penetration tests, on weathered fallen pumice sediments, which are one of the causes of the slope failures. In addition, we performed direct box shear tests on undisturbed samples collected from an undisturbed area under various shear conditions to characterize mechanical properties of the soil. The parameters obtained from the mechanical tests were used to evaluate slope stability under normal and seismic conditions with an infinite-length slope model. The results showed that the slopes where seismic failures occurred had a fragile layer from the surface to a depth of approximately 1.5 m, which generally corresponded to the depth of failure. Weathered pumice deposits with extremely high-water content existed at the boundary between the weak layer and the basement layer, and their shear strength was velocity dependent. It has been shown that an infinite-length slope stability analysis can be performed by using mechanical parameters for which velocity dependence of horizontal acceleration and shear strength due to seismic motion are accounted for.

Pumice sand is a volcanic material widely distributed in volcanic areas such as Japan, Indonesia, and countries traversed by volcanic mountains. Geotechnical problems regarding pumice sand often occur in these areas, such as landslides because of the pumice crushable structure. Based on previous research, some failure phenomena are caused by the existing pumice layer, and not so many studies describe the behavior of pumice single particle located at Kyushu Island, Japan. This study conducted a series of tests to clarify pumice material's microscopic and mechanical properties. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) tests were carried out on pumice materials to determine the microscopic and chemical compounds in the pumice material. Then, single -particle crushability tests were carried out as representative of the mechanical behavior of pumice sand particles. The approach using linear regression fitting is carried out using conventional frequentist and Bayesian hierarchical approaches to obtain the strength behavior of the pumice sand. An overview of pumice microscopy conditions and minerals can be helpful when ground improvement and soil stabilization are discussed for this pumice material and the effect of particle shape on pumice strength is observed. According to this study, oxygen, silica, and alumina dominate pumice sand chemical components. The aspect ratio and the roundness coefficient of pumice sand do not significantly impact particle stress. Particle size reduces and increases particle stress in single -particle crushability tests. Single -particle crushability reduces pumice particle pore area and increases the number of pores.

Pumices with high pore voids of volcanic origin are distributed throughout Japan and are the causal layer of slope failures. In many cases of surface failures, it is difficult to assume that the resulting layers are fully saturated. The high water-holding capacity of the pumice suggests that they were deposited in an unsaturated state with a high degree of saturation. In this study, saturated triaxial compression tests and fully undrained unsaturated triaxial compression tests were conducted on artificially produced pumice and natural pumice while measuring the amount of crushing. This is to clarify the relationship between the crushing and mechanical properties of pumice with porous particles, which are often the cause of such disasters, and their behaviour under unsaturated conditions. The results showed that the pumice stones have an ultra-high pore structure. Moreover, pumice with porous particles reached a steady state under both saturated and highly saturated unsaturated conditions, and the amount of crushing increased under highly saturated unsaturated conditions.