The Ring of Fire traverses Japan, and many earthquakes occur there. Pumice sand is one of the materials often found in volcanic areas. Due to the swift cooling process, it is very porous, making it susceptible to crushing. When an earthquake occurs, pumice sand also has liquefaction potential and often triggers landslides in several areas. This research aims to determine pumice sand's liquefaction potential to provide a design reference. This study used unnatural pumice sand from Kyushu Island's Kirishima mountain area, sold by agriculture companies. Initial attributes were studied, including relative density (D_r) and specific gravity (G_s). Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) testing were used to establish pumice sand's pore character and chemical composition. Pumice sand was remolded, and various undrained triaxial cycle tests were performed with cyclic stress ratios (CSR) of 0.15, 0.20, 0.25, 0.30, and 0.35 and D_r fluctuations between 40% and 70% and also a variation of confining pressure 50 kPa and 100 kPa. The outcomes of this study demonstrate that a higher density of pumice sand leads to a more significant number of cycles required to attain liquefaction conditions. At the same time, confining pressure significantly affects liquefaction resistance, which can be seen as a reduction in confining pressure also increases liquefaction resistance.

High energy demand forced many countries to reopen or expand production of electricity from coal power plants. Apart from being one of the most polluting technological processes emitting millions of metric tons of carbon dioxide in the atmosphere. This process also produces an enormous quantity of coal fly ash which has been successfully used as a mineral admixture in concrete industry and also as a feed material for producing Portland cement for many decades. A lot of efforts have been made to find a way to use fly ash in geotechnical engineering. Numerous studies show the benefits of using fly ash as a mixture for soil replacement and for limited use as soil improvement. Using fly ash for geotechnical purposes in seismic prone regions requires behavior of soil - fly ash mixture in static and dynamic conditions. This paper presents the results from laboratory testing performed on mixtures of natural sand material (Skopje Sand) and 5, 10 and 20% fly ash. Before using fly ash in element tests, extensive investigation was done on chemical and mineralogical composition as well as on classification of used fly ash. Cyclic and monotonic triaxial tests and direct simple shear tests were performed on sandy-fly ash mixtures specimen. The results of the mixtures are compared with existing results for clean Skopje Sand. The results from this study show that as the fly ash amount increases in the mixture, the relative density has more influence on the peak and residual strength of the material. The strength properties of natural Skopje Sand can be improved with low quantities of fly ash, around 5%, and there is no regular trend of the liquefaction resistance in function of the amount of fly ash, for high percentage of fly ash.

Focusing on the effects of pre-shear histories on liquefaction behavior of granular media in this study, a series of cyclic bi-axial tests were conducted on assembly of metal rods, while maintaining a constant-volume condition that is equivalent to an undrained loading condition on saturated specimens. In the test cases with pre-shear histories, the cyclic loading was terminated when the double amplitude vertical strain reached a target value that was set in a range of 0.2 to 2.0%, and the specimen was re-consolidated isotropically, followed by the second cyclic bi-axial loading with the same amplitude of the cyclic deviator stress as in the first loading stage. During the tests, two digital cameras were used to record the side views of the specimen, and possible changes in the local void conditions were analyzed by conducting image analyses of the specimen photos. As a result, with the increase in the double amplitude of the vertical strain during the pre-shearing stage, densification of locally loose zones during pre-shearing became more significant, which may have induced the observed increase in the liquefaction resistance with the degrees of the pre-shearing.

Microbial induced calcite precipitation (MICP) is an environmentally friendly technique that involves the use of microorganisms to reinforce soil. The combination of MICP and fiber reinforced soil can better withstand seismic action. Especially, carbon fiber (CF) has a higher strength and modulus. In this study, 0.3% (relative to the sand weight) of CF was added to the calcareous sand, and the calcareous sand was reinforced with MICP-CF combined treatment. The liquefaction resistance of MICP-CF solidified calcareous sand was studied by cyclic triaxial (CTX) test and SEM scanning. The results showed that MICP treatment could improve the liquefaction resistance of calcareous sand. After adding CF, the accumulated cycles of axial strain ε_a were longer and developed slowly in the direction of extension until failure. The initial liquefaction did not occur when the ε_a reached 5%, and the pore water pressure directly entered the stabilization stage. SEM scanning showed that the great mechanical system of CF, calcite, and sand particles was strengthened after MICP solidified, which effectively enhanced the connection effect between sand particles and the cyclic resistance of calcareous sand.

This study conducts out unsaturated, compacted soil that aims to appear the axial strain properties under cyclic loading.The cyclic triaxial apparatus and relative humidity air circulation system in order to control high suction are employed.Test programs consist of two series, and Series 1 investigatesthe influence of compaction water content on deformation properties. Other hands, establishing suction and lateral confining pressure are key features in Series 2. The obtained summary is appeared as follows. Unsaturated, compacted soil have verification that smoothly axial deformations are interpreted, and compression deformations are occupied through the cyclic loading. Comparing axial strain properties with/without applying high suction, the specimens with high suction seem to be easy occurrence compression large deformations.

Saturated coarse-grained soils (mostly sands) are prone to developing pore water pressure (PWP) when sheared in undrained conditions. If different sands are prepared with the same preparation method and tested under the same conditions (consolidation stress, load amplitude, etc.), they will show different tendencies in the PWP build-up. Obviously, this tendency depends on the granulometric properties of the tested sand and can thus be considered an index property (analogous to the loosest or densest soil state). A simplified cyclic shear test for the investigation of the PWP build-up in sands is presented in this research. The principle of this experimental procedure is based on the evolution of the PWP during cyclic shearing of a water-saturated sand specimen. The procedure can be divided into three phases. At the beginning of the test, a de-aired sand-water mixture is installed in the membrane using a funnel. As a result, high saturation of the soil specimens after installation is obtained in case of any sand. The effective stresses are increased by applying negative pressure (suction) to the soil specimen. Cyclic loading is applied to the top cap of the specimen in the horizontal direction, which creates a kind of simple shear deformation of the soil specimen. Undrained conditions during the experiment allow for the PWP build-up. The duration of a single shear test, including specimen preparation, is approximately 30 minutes. By evaluating the rate of the measured PWP at different initial relative densities, the dependency of the PWP build-up of the tested soil on the variation of the relative density can be determined. This enables a comparison of the sensitivity of different soils to the development of the PWP. The experimental procedure was validated on several sands using the results of the undrained cyclic triaxial tests. Furthermore, the dependence of the pore water pressure development on various influencing factors (relative density, degree of saturation, load amplitude, consolidation stress, etc.) was investigated. This method aims to assign an index value to every tested sand and thus quantify its sensitivity to density changes with respect to liquefaction.

Earthquake-induced excess pore water pressure in saturated granular soils has been studied for many years, but it is still an important area of research, as demonstrated by the most recent seismic events that caused devasting liquefaction-induced damage, e.g., in Türkiye 2023, Italy 2012, and New Zealand 2010-2011. The mechanism of undrained pore pressure build-up in pyroclastic soil under cyclic loading is analyzed within the framework of the steady state theory through cyclic triaxial tests performed on different pyroclastic soils (i.e., Cervinara (Italy) and Rangiriri (New Zealand)). The analyses of the experimental results show the dependency of the mechanism of excess pore water pressures on the history and stress state of the investigated soil by using two key parameters of the steady state theory. A new pore water pressure model based on these two key state parameters is proposed to reproduce the response of granular soils, which can be of a different nature from the pyroclastic ones.