Numerical analysis of landslide-generated debris flow on July 3, 2021 in Izu Mountain area, Shizuoka County, Japan

With the increasing of extreme rainfall frequency, landslides accompanied by mudslides often lead to serious casualties and property damage. On 3rd July 2021, a debris flow occurred in Izu Mountain area, Shizuoka County, Japan, and then resulted in 26 deaths and 131 houses destroyed, where houses were mainly built along the banks of the creek. In order to analyse the landslide state and distribution, a two-dimensional debris flow dynamic model(Massflow) was selected to simulate the process of the landslide-generated debris flow. When the model results are considered together with remote sensing images, the volume distribution of the unstable landslide is also able to be determined. The results show that(1) the affected areas are mainly concentrated at the outfall of the gully and on both sides of the streets.(2) The pore pressure ratio is an important factor affecting the damage range of this debris flow.(3) The increase of the pore pressure ratio in the landslide make the movement distance of debris flow increase significantly.

Suppression of Methane Gas Emissions and Analysis of the Electrode Microbial Community in a Sediment-Based Bio-Electrochemical System

The effects of bioelectrochemical systems (BESs) for the suppression of methane gas emissions from sediment were examined using a laboratory-scale reactor system. Methane gas emissions from acetate were suppressed by approximately 36% from control based on the installation of a BES in which carbon-graphite electrodes were buried in sediment and arbitrarily set at certain oxidative potentials (+300 mV vs Ag/AgCl) using a potentiostat. Meanwhile, methane gas emissions increased in the BES reactor where the electrode potential was set at -200 mV. Results obtained from pyrotag sequencing analysis of the microbial community on the surface of the buried electrodes targeting 16S rRNA genes demonstrated that the genusGeobacterhad drastically propagated in a sample from the reactor where the electrodes were buried. Quantitative analysis of 16S rRNA genes of archaea also revealed that the archaeal population had decreased to approximately 1/6 of its original level on the electrode of the BES set at +300 mV. This implied that the oxidation-reduction potential (ORP) in the sediment was raised to the inhibition level for methanogenesis in the vicinity of the buried electrode. Analysis of electron flux in the experiment revealed that electrons intrinsically used for methanogenesis were recovered via current generation in the sediment where a potential of +300 mV was set for the electrode, although most electrons donated from acetate were captured by oxygen respiration and other electron-accepting reactions. These results imply that BES technology is suitable for use as a tool for controlling re-dox-dependent reactions in natural environments, and that it also brought about changes in the microbial population structure and methanogenic activity in sediment.

Sendai Water Pipeline Response to the 2011 Tohoku Earthquake

Damage caused by the 2011 Tohoku Earthquake （Mw 9.0） to transmission and distribution pipelines in Sendai City is summarized. The locations of the pipeline repairs are discussed relative to earthquake intensity, geomorphologic conditions and landform change in the developed areas of hilly land. Repair rate （repairs/km） is summarized according to pipe material and presence or absence of artificial landform change. The following findings were obtained： （1） More than 80% of the repairs took place in pipelines installed in higher lands such as hill and terrace areas consisting of hard soils; （2） Nearly all the pipe repairlocations in hill areas are where landform change was made through land development tor residential purposes over me past several decades; （3） The aforementioned repair rate was more than 3.6 times than that of other lowland areas where no landform change occurred. The heaviest concentrations of pipe repairs of vinyl chloride pipes and ductile iron pipes were observed within the boundary area between cutting and filling, having a thickness between -2.5 m and 2.5 m. Approximately 78% of the all pipe repairs occurred outside of areas where severe ground failures took place. A mechanism of pipe damage in the areas free of severe ground failure was discussed.

Experimental Studies on Penetration of Pulverized Clay-Based Grout

For the geological disposal of high level radioactive wastes, an excavation damaged zone （EDZ） having high hydraulic conductivity resulting from the development of fractures in the rock adjacent to the tunnels will be one of the potential pathways for radioactive contaminant transport. The potential pathways will be sealed by closure components, that is, a combination of tunnel plug, backfill and grout, the latter material being a clay-based mixture in consideration of the need for long-term stability of the seals. Clay-based grout is one of the effective candidate materials that can be used to interrupt the migration of radionuclides through an EDZ. Laboratory testing of clay-based grout using pulverized bentonite, with the objective of improvement in grout penetration into a rockmass, was conducted. The results showed that the pulverization of clay-based grout had a positive effect on filtration.

Application of Brillouin Optical Correlation Domain Analysis for Crack Identification in Concrete Structure

This paper investigates the application of distributed optical fiber strain sensors to civil engineering structures, because no other tool can satisfactorily detect the location of the unpredictable phenomenon. In fact, the locations of cracks in the concrete structure are unknown a priori; therefore, a fully distributed sensor is necessary to detect them. The Brillouin optical correlation domain analysis （BOCDA）, which offers high spatial resolution by using stimulated Brillouin scattering along the whole length of the optical fiber, is used in a wide range of civil engineering applications, and the same has undergone significant development over the last decade. In this paper, it is demonstrated how a BOCDA-based strain sensor can be employed to monitor cracks in concrete. Crack monitoring on the surface of the concrete member provides useful information for evaluating stiffness and durability of the structure, particularly for early detection of tiny cracks, which is essential for preventing crack growth and dispersion. The crack-induced strain distribution was analytically investigated, and it was proved that BOCDA can identify even a small crack before its visual recognition by a beam test. Moreover, periodical crack monitoring was successfully executed on a pedestrian deck for five years.