Satoshi Nishimura

Nature-based slope stabilization offers a sustainable solution to enhance the climate resilience of long linear infrastructures in Thailand's changing climate. This approach integrates local species such as vetiver grass with biochar-amended soil, erosion control blankets, capillary barrier systems, and flexible bioengineering structures—including vegetated flapped soil bags and micro screw piles. This combination effectively improves erosion control, slope stability, and movement tolerance while fostering vegetation growth and promoting biodiversity. However, the adaptive and continuously growing nature of these living systems necessitates in-depth investigation of their mechanical and hydraulic behaviours. This study emphasizes the critical role of IoT-based monitoring systems in delivering early landslide warnings and assessing the performance of nature-based slope stabilization. Key parameters include pore-water pressure, suction, slope deformation which are then used to estimate the performance metrics for geotechnical stability and water demand. Field data from various bio-stabilized slopes across Thailand—collected through tensiometers, tiltmeters, inclinometers—demonstrate the system's efficacy. The integration of advanced technologies, such as remote sensing and NASA's Soil Moisture Active Passive (SMAP) mission, is also discussed, highlighting future research directions in enhancing slope stability and resilience. Potential carbon credit gains are also discussed by means of root mass measurement and evapotranspiration flux.

In this study, the one-dimensional thermo-mechanical behaviour of three types of peat with different natural water contents was investigated, under a variety of thermo-mechanical loading paths, to establish a rational phenomenological interpretation of their responses. The results from temperature-controlled incremental loading and constant-rate-of-strain and consolidation tests suggest that a unique effective stress–volumetric strain relationship exists at a given set of viscoplastic strain rate and temperature, or ‘isothermal isotaches’ exist. The coefficient of thermo-plastic compression and the coefficient of secondary consolidation were jointly adopted to describe the simultaneous temperature and strain-rate dependency of peats. Their ratios to the compression index are largely unique regardless of the type of peats. The test results indicate that testing peats in a laboratory (20–25°C) can lead to an underestimation of the in situ (∼10°C) yield stress by about 30%. The potential temperature dependency of the coefficient of secondary consolidation, λα*, was reappraised by redefining the coefficient within the framework of the isotache concept. The test results show that λα* is only slightly dependent on temperature.

A deformation measurement system for laboratory soil testing based on stereophotogrammetric image analysis was developed with a purpose of characterising soil behaviour continuously from small to large strains. The system is applicable to triaxial tests with pressure chamber and confining fluid by correcting the refraction-induced distortion of images by ray tracing. In comparison to similar existing studies, the present study put priority in precision and accuracy in relative displacement tracking, which is the key feature in resolving small strain in soil specimen and characterising its stiffness. The displacement tracking is performed with a hybrid algorithm combining Particle Tracking Velocimetry (PTV) for primary target matching and subpixel Digital Image Correlation (DIC) for more precise image matching. The deformation of clay samples with and without end lubrication was compared by visualising the deformation at different levels of strain. This paper is basically a summary of Nishimura (2022). Another example of application in laboratory testing involving fine particle suffusion is also shown. Some notes on implementation of the technique for good practice and on future development are additionally described.

The volume change behaviour of fine-grained soils under repeated freeze–thaw cycles was investigated in context of artificial ground freezing, in which relatively quick freezing is achieved under confinement. Laboratory cyclic freeze–thaw tests with large freezing rates were performed on two clays in two different laboratory set-ups, either with isotropic pressure or with one-dimensional configuration. After freeze–thaw cycles, soils appear to reach residual states unique to each stress level, and the freeze–thaw residual line (FTRL) is defined to represent them. The current soil state's distance to the FTRL, defined as the freeze–thaw state parameter, is well correlated to subsequent volume changes. The one-dimensional freezing set-up provides a correlation more representative of the net effect of freeze–thaw, as all-around freezing under isotropic pressure subjects the specimen to unnatural shear straining. The different nature of freeze–thaw-induced volume changes was observed for high-plasticity Kasaoka clay and low-plasticity kaolin, as characterised by different configurations of the FTRL to the normal compression line. X-ray computed tomography confirmed largely uniform deformation in most of the adopted test conditions, while lower stress and slower freezing led to partial vertical cracking. This type of non-uniformity is shown not to be a main cause of the observed overall freeze–thaw-induced volume changes.

Dredged soils have been used as construction materials by alkaline activation with steel slag (steel slag-dredged soil mixtures) at harbors. Such mixtures develop strength chiefly by calcium silicate hydrate (C-S-H) formation by the pozzolanic reaction. However, the strength of such mixtures is unpredictable, and in some cases, mixtures have been too soft for the intended engineering application. An identification of strength development indicators would accelerate evaluation processes for strength development to facilitate and promote the utilization of such materials. This paper focuses on the relationship between the characteristics of soil organic matters in dredged soils and the strength development of the mixtures by a comparison of eight dredged soils collected from eight different Japanese harbors. The characteristics of the soil organic matters were identified to determine as indicators of mixtures with weak strength development, i.e., enriched sulfur content in extracted soil organic matter (humic acid) fraction, and the N/C ratio of humic acid similar to land humic acid standards. Increases in the validated fraction of dredged soils and steel slag by replacing fractions disadvantageous to construction resources would contribute to reduce waste production, which would lower the environmental impact of the use, aiming to achieve sustainable utilization of such materials.