Effects of material texture and packing density on the interfacial polarization of granular soils

Many electrical and electromagnetic (EM) methods operate at MHz frequencies, at which the interfacial polarization occurring at the solid-liquid interface in geologic materials may dominate the electrical signals. To correctly interpret electrical/EM measurements, it is therefore critical to understand how the interfacial polarization influences the effective electrical conductivity and permittivity spectra of geologic materials. We have used pore-scale simulation to study the role of material texture and packing in interfacial polarization in water-saturated granular soils. Synthetic samples with varying material textures and packing densities are prepared with the discrete element method. The effective electrical conductivity and permittivity spectra of these samples are determined by numerically solving the Laplace equation in a representative elementary volume of the samples. The numerical results indicate that the effective permittivity of granular soils increases as the frequency decreases due to the polarizability enhancement from the interfacial polarization. The induced permittivity increment is mainly influenced by the packing state of the samples, increasing with the packing density. Material textures such as the grain shape and size distribution may also affect the permittivity increment, but their effects are less significant. The frequency characterizing the interfacial polarization (i.e., the characteristic frequency) is mainly related to the electrical contrast of the solid and water phases. The model based on the traditional differential effective medium (DEM) theory significantly underestimates the permittivity increment by a factor of more than two and overestimates the characteristic frequency by approximately 1 MHz. These inaccurate predictions are due to the fact that the electrical interactions between neighboring grains are not considered in the DEM theory. A simple empirical equation is suggested to scale up the theoretical depolarization factor of grains entering the DEM theory to account for the interaction of neighboring grains in granular soils.

High-temperature effect on the material constants and elastic moduli for solid rocks

Thermally coupled constitutive relations are generally used to determine material constants and elastic moduli (Young's modulus and shear modulus) of solid media. Conventional studies on this issue are mainly based on the linear temperature dependence of elastic moduli, whereas analytical difficulties are often encountered in theoretical studies on nonlinear temperature dependence, particularly at high temperatures. This study investigates the thermally coupled constitutive relations for elastic moduli and material constants using the assumption of axisymmetric fields, with applications to geologic materials (marble, limestone and granite). The Taylor power series of the Helmholtz free energy function within dimensionless temperatures could be used to develop the thermally coupled constitutive relations. The thermoelastic equivalent constitutive equations were formulated under the generalized Hooke's law. The material constants of solid rocks were determined by fitting experimental data using axisymmetric stress and strain fields at different temperatures, based on their thermomechanical properties. For these geologic materials, the resultant equivalent elastic moduli and deformations were in good agreement with those from the experimental measurements. Thermal stresses, internal moisture evaporation and internal rock compositions significantly affected the experimental results. This study provides a profound understanding of the thermally coupled constitutive relations that are associated with the thermomechanical properties of solid rocks exposed to high temperatures.

Weathering conditions of Buddhist caves dug in soft rocks and conservation attempting from the deterioration

<p>The Taya Cave, a sacred Buddhist cave, locates in the precincts of Josenji Temple in Yokohama City, central Japan. The geologic materials of the hills surrounding the cave are soft rocks composed of early Quaternary sedimentary rocks. The cave has a complex three-layer structure with a total length of 570 m. The excavation of the cave is estimated to start in the Kamakura era around A.D. 1200. Since then, the cave became a training place for Buddhists until around 19 C. There are many Buddhist reliefs on the walls and ceiling inside the cave. Because the bedrock is extremely weak, the rocks easily break when they get wet again after drying, namely prone to slaking. Thus, weathering and deterioration have progressed in various parts of the cave. Many valuable Buddhist reliefs have damaged by exfoliation. The walls at several points in the cave have also collapsed on a small scale. Therefore, it is necessary to investigate such deteriorated parts in the cave by simple non-destructive tests of physical and mechanical properties by using Silver Schmidt hammer and ultrasonic velocity test. These measurements clarified the vulnerable points even in the main worship route of the cave. In October 2018, a stainless-steel door installed at the cave entrance to save from deterioration due to slaking. The effect of the door was verified as well by monitoring the environmental conditions inside the cave. Environmental monitoring results revealed that the temperature and humidity near the entrance changed most drastically in this cave. Although the door was closed only at night, the range of maximum and minimum values ​​of temperature and humidity near the entrance became smaller after installation than before. Non-destructive measurements and in situ environmental monitoring are a useful way to assess weathering without damaging geoarchaeological sites. </p>

Low-level ionizing radiation and associated risk in an urban environment: the importance of both paving and building materials

<p>Natural radioactivity depends on primordial radionuclides which decay across a chain of transformations to achieve a stable nuclear state. Transformations involve the emission of particles and photons whose energy can be harmful to organisms even at low-dose. K-40, Th-232 and U-238 are responsible for most of the natural emission of gamma rays from the earth’s crust and volcanic rocks are, in general, the most emissive materials.</p><p>Volcanic rocks and related volcano-sedimentary lithified deposits have been quarried for construction purposes and for road paving, since the Greek times, in the area where the city Naples is located, halfway between the volcanic districts of Phlegrean Field and Mt. Somma-Vesuvius, respectively. For centuries, lithified pyroclastic products, such as grey or yellow tuffs, have been used mainly for buildings and vertical structures; lava blocks from Phlegrean Fields and, since 18<sup>th</sup> century, from Vesuvian effusive materials have been historically used to pave the roads of the old town.</p><p>However, in the last few decades, <span>deteriorated </span><span>historical paving materials of some roads serving areas undergoing renovation have been partially replaced by volcanic materials of Etnean origin (proceeding from Sicily, indeed) or covered/replaced by non-geologic materials (NGMs) (e.g., asphalt).</span></p><p>Considering that 120,000 people live in the old town (over an area of 4 sqkm) being potentially exposed to low-dose ionizing gamma radiations, a survey to estimate the contribution of geological materials to the ambient dose equivalent rate (ADER) was completed. A radiological risk assessment was also completed.</p><p>Specifically, 2548 measurements of ADER (µSv/h) were made in the open air at 0.2 (ADER0.2) and at 1 m (ADER1) above the ground, respectively, using a handheld gamma-ray spectrometer. Besides, a total of 13 samples of paving materials were collected and analyzed by means of a high purity germanium detector at the Center for Ecological-Noosphere in Armenia.</p><p>Results revealed a significant activity of all materials, except for NGMs. ADER1 and ADER0.2 values ​​showed a strong dependence on the distance from the ground in the streets paved with geologic materials, while the distance from the ground resulted to be not relevant for ADER in areas paved by NGMs .</p><p>Based on the ADER1 data, a Monte Carlo simulation was conducted to calculate the outdoor excess lifetime cancer risk (ELCRout) for the population of the study area and for each district belonging to the old town.</p><p>In one of the districts showing the highest average ELCRout, 51 additional ADER1 measurements were also conducted inside private dwellings to assess the indoor ELCR (ELCRin). Finally, the total excess lifetime cancer risk (ELCRtot) was estimated by summing values of ELCRout to ELCRin.</p><p>The average ELCRout obtained for the entire study area (1.33E-03) and for individual districts (from 5.20E-04 to 1.44E-03) exceeds the world average reference value (2.9E-04).</p><p>ELCRin (4.35E-03) and ELCRtot (5.79E-03) are also higher than the average reference values proposed in the literature.</p><p>This study revealed that low-dose gamma radiations, emitted by paving or building materials of volcanic origin can pose a radiological risk to human health.</p>

The horizontal displacements in active fault zones in Central Asia based on data on the mechanisms of earthquake foci

The directions of horizontal displacement along active geological faults in Central Asia are determined based on data on the mechanisms of earthquake foci that occurred near these faults. The results were compared with geologic materials. In eight cases out of ten, the analysis of calculating the direction of displacement obtained from seismological materials is consistent with the kinematics of faults.