Ryosuke Uzuoka

This paper presents a comparison of the seismic response of single-span bridge rocking foundation (SSBRF) and two-span bridge rocking foundation (TSBRF) bridge models incorporating rocking shallow foundations supported on dry soil. Physical models representing one- and two-span sections of a prototype bridge were tested in a geotechnical centrifuge and subjected to scaled historic earthquake motions. Foundation settlements, rotations, and deck drifts were measured to evaluate differences between the two configurations under dry conditions. Results indicate that both systems exhibited settlement-dominated rocking behaviour, with residual settlements and rotations remaining small. On average, the TSBRF developed ≈38% larger maximum foundation rotations and 189% larger residual rotations at the leading foundation than the SSBRF. Deck drifts were minor and well below allowable limits, and no toppling occurred. Relatively slight differences were observed between the single- and two-span systems, suggesting that bent location, number of bents, and span configuration had limited influence on responses in dry soil conditions. Slightly larger settlements in the single-span system during higher-intensity motions may reflect the stabilising effect of additional bents in the two-span configuration. These observations provide insight into the soil behaviour of bridge systems with rocking shallow foundations in dry conditions.

One of the most significant incidents of rain-induced rapid, long-traveling landslides (RRLL) in Sri Lanka occurred in 2016 in Aranayake, located 70 km east of Colombo. The fluidized landslide mass traveled approximately 2 km, resulting in the loss of 125 lives. This heartbreaking occurrence underscored the necessity for adequate early warning and disaster management systems more than ever, as the existence of these concealed unstable soil masses and their potential runout distances are challenging to forecast. In 2020, the National Building Research Organization in Sri Lanka (NBRO) and the Secretariat of the International Consortium on Landslides (ICL) launched a collaborative 5-year research initiative called “Development of Early Warning Technology of Rain-induced Rapid and Long-travelling Landslides (Project RRLL)” under the SATREPS framework. SATREPS, “Science and Technology Research Partnership for Sustainable Development,” is a Japanese government program promoting international collaborative research. This project was also approved as one of the International Programmes on Landslides (IPL-249) in 2019 because of its importance. The project has significantly progressed in forecasting mountain rains and RRLL occurrences in its pilot study sites in the nation’s central highlands. Also, the developed technologies included an Augmented Reality (AR) Viewing System to disseminate information on mountain rains and RRLL hazards predicted 1 day in advance to the last mile as an augmented reality, with an actual diorama displayed as its background on a smartphone, iPad, or PC screen. The Project was completed by March 2025, and this article summarizes its activities and achievements, including those for social implementation.

Fluid flow in porous media is conventionally modeled with Darcy's law, which neglects internal viscous shear and cannot resolve velocity gradients at sharp permeability contrasts, conditions found at filter interfaces within earth dams, levees, and embankments. Although the Darcy-Brinkman (DB) equation overcomes this limitation through a viscous diffusion term, existing DB formulations are generally restricted to saturated or rigid porous media. Consequently, unsaturated soils, where pore water and pore air coexist and flow conditions vary across the phreatic surface, lack a unified DB-based framework. This study extends the Theory of Porous Media-based three-phase framework of Uzuoka and Borja (2012) for unsaturated poroelastic solids by incorporating the DB formulation. The Brinkman viscous term is introduced into the momentum balances of both pore water and pore air, with each fluid phase retaining its own momentum equation. The resulting formulation provides a unified description of flow in saturated and unsaturated porous media within a single set of governing equations. Verification against four benchmark problems, including one-dimensional flow in a porous channel, plane Poiseuille flow, coupled free-fluid and porous flow, and a newly derived analytical solution for the DB flow through a saturated layered system, confirms the correct implementation of the Brinkman extension and the quantification of interfacial viscous shear. Application to a partially saturated layered system reveals a systematic spatial variation of interfacial shear stress, with the maximum shear at the outlet exceeding the inlet value by 66-76%, demonstrating a localization mechanism that cannot be captured by conventional Darcy-based formulations.

The influence of initial stress anisotropy on liquefaction resistance was investigated using three-dimensional discrete element method (DEM) simulations of undrained cyclic torsional shear in hollow cylindrical specimens. A coupled analytical servo mechanism was developed in which the servo coefficients are derived from a volume-constrained stiffness matrix that accounts for the cross-coupling between radial and axial wall movements, enabling direct reproduction of laboratory hollow cylinder apparatus (HCA) boundary conditions. Specimens at two relative densities were consolidated to a mean effective stress of 100 kPa at five lateral-to-vertical effective stress ratios (K_0 = 0.5-2.0) and subjected to cyclic loading across multiple cyclic stress ratios to systematically separate the respective roles of relative density and stress anisotropy. The results show that liquefaction resistance decreases monotonically from compression-state (K_0 < 1) to extension-state (K_0 > 1) anisotropy, consistent across all CSR levels and both densities. Macroscopic analysis reveals that the K_0 states exhibit distinct shear-wave velocity degradation trajectories, with the compression-state specimen maintaining higher stiffness for longer, which explains the observed resistance ordering. Microscopic analysis demonstrates that, while the mechanical coordination number primarily reflects packing compactness, the signed fabric anisotropy indicator correlates more directly with the variation in liquefaction resistance among different K_0 states. Decomposition of the fabric tensor in the cylindrical coordinate system shows that contacts whose normals lie on the z-theta plane (the plane on which the torsional shear stress acts) directly resist torsional shear, and compression-state consolidation concentrates a larger fraction of contacts onto this plane. Contact-density distributions and force-chain visualizations further show that initially distinct fabric morphologies progressively converge toward a common dynamic equilibrium in the post-liquefaction stage, regardless of the initial stress anisotropy.

大地震後の降雨時には斜面や盛土の浸透挙動が振動の影響を受ける可能性が指摘されている。ここでは振動で変形した斜面や堤防の浸透現象を観察した遠心模型実験結果に基づいて，浸透現象に対する振動の影響を考察し，地震後の降雨による地盤災害を軽減するための今後の課題を整理する。