Currently, many formulas are used to calculate the ultimate bearing capacity. However, these formulas have disadvantages when being applied in practice since they can only be applied for calculating simple footing shapes and uniform grounds. Most formulas do not take into account the size effect of the footing on the ultimate bearing capacity, except for the formula by the Architectural Institute of Japan. The advantage of using the finite element method (FEM) is its applicability to non-uniform grounds, for example, multi-layered and improved grounds, and to complicated footing shapes under three-dimensional conditions. FEM greatly improves the accuracy in estimating the ultimate bearing capacity. The objective of this study is to propose a rigid plastic constitutive equation using the non-linear shear strength property against the confining pressure. The constitutive equation was built based on experiments for the non-linear shear strength property against the confining pressure reported by Tatsuoka and other researchers. The results from tests on Toyoura sand and various other kinds of sand indicated that, although the internal friction angle differs among sandy soils, the normalized internal friction angle decreases with an increase in the normalized first stress invariant for various sands despite dispersion in the data. This property always holds irrespective of the reference value of the confining pressure in the normalization of the internal friction angle. The applicability of the proposed rigid plastic equation was proved by comparing it to the ultimate bearing capacity formula by the Architectural Institute of Japan, which is an experimental formula that takes into account the size effect of the footing. The results of rigid plastic finite element method (RPFEM) with the proposed constitutive equation were found to be similar to those obtained with the Architectural Institute of Japan's formula. It is clear that RPFEM, with the use of the non-linear shear strength against the confining pressure, provides good estimations of the ultimate bearing capacity of the footing by taking account of the size effect of the footing.
Most of the contemporary ultimate bearing capacity (UBC) formulas assume a linear yield function in shear stress-normal stress space. However, experimental investigations have corroborated the non-linearity in the failure envelopes of sandy soils. This study focused on the assessment of the stress level effect on the UBC of surface strip footings ascribed to the soil unit weight (γ), footing size (B), and uniform surcharge load (q). The rigid plastic finite element method (RPFEM) was employed for the analysis. The analysis method was validated against the centrifuge test results from the published references in the case of various sandy soils with different relative densities. The RPFEM, using the mean confining stress dependence property of Toyoura sand, is utilized in non-linear finite element analysis of model sandy soil. The normalized ground failure domains in the case of the non-linear shear strength model are gleaned smaller than those in the case of the linear shear strength one. The numerical results are compared with the guidelines of the Architectural Institute of Japan (AIJ) and the Japan Road Association (JRA). The modification coefficients are ascertained for the frictional bearing capacity factor (Nγ) and surcharge bearing capacity factor (Nq), and a modified UBC formula is proposed. The performance of the proposed UBC formula is examined against the analysis results and various prevailing UBC guidelines.
Steel pipe sheet pile (SPSP) reinforcing method for existing caisson foundation in water, which involves driving SPSP around the caisson foundation and then connecting the SPSP to the caisson at the top, is proposed. The practicability of applying this method and the reinforcement mechanism of SPSP reinforced caisson foundation system is investigated by conducting three-dimensional elasto-plastic finite element analysis. In the simulation, to propose more effective and reasonable design / construction method, the following factors that affect the effectiveness of SPSP reinforcement are considered: 1) connection condition of the caisson to SPSP reinforcement; 2) pile length. Based on the results of analysis, the authors try to estimate the SPSP reinforcement effect and reveal the mechanism which the lateral bearing capacity of reinforced foundation system is increasing.
An Incompletely End Supported Pile (IESP) is a pile in a soft soil layer underlain by a hard soil layer that does not reach the bottom hard layer in practice. This study estimates the end bearing capacity of IESP by using an inhouse Rigid Plastic FEM code (RPFEM), considering shear strength non-linearity of soil against confining pressure, and soil-foundation interaction. The effect of the distance between the pile tip and the bottom hard soil layer (d/B) on the end-bearing capacity of IESP was mainly investigated for three types of soil: cohesive soils, cohesionless soils and intermediate soils. Also, theratio (r) of the end bearing capacity of the pile when it reaches the bottom hard layer to that of the pile when the bottom layer has no influence was was considered. By considering the shear strength non-linearity, the end bearing capacity was accurately estimated. The estimations were consistent with previous analytical, experimental and numerical solutions. It is found that the end bearing capacity inversely decreases with the distance d/B and becomes constant around d/B = 3. Based on the results, a formula for estimating the end bearing capacity of IESP is proposed. Comparisons with methods in existing literature confirmed the reliability of the proposed equation.
This study addresses the assessment of bridge damage risks associated with heavy rainfall, focusing on landslide susceptibility and driftwood generation potential. By integrating convolutional neural networks (CNNs) with traditional machine learning methods, the research develops an advanced predictive framework for estimating driftwood accumulation at river bridges—a recognized challenge in disaster management. Concentrating on the Tokachi River basin in Hokkaido, Japan, the research utilizes diverse environmental and geographical data from authoritative sources. The findings demonstrate that the innovative approach not only enhances the accuracy of driftwood volume predictions but also distinguishes the effectiveness of CNNs compared to conventional methods. Crucially, areas prone to landslides are identified as significant contributors to driftwood generation, impacting bridge safety. The study underscores the potential of machine learning models in improving disaster risk assessment, while suggesting further exploration into real-time data integration and model refinement to adapt to changing climate conditions and ensure long-term infrastructure safety.
The 2018 Hokkaido Eastern Iburi earthquake with the JMA seismic intensity of 7 occurred at a central south part of Hokkaido, Japan at 3:08 a.m. on September 6, 2018. Considering the social importance of this historical earthquake-induced geo-disaster, the Japanese Geotechnical Society (JGS) organized a "JGS Survey Team for Geotechnical Disasters in Hokkaido, Japan Induced by the 2018 Hokkaido Eastern Iburi earthquake," mainly comprised of experts from the industry and academia of the Hokkaido branch of JGS. The aim of the survey team was to investigate the phenomena and factors which contributed to disaster recovery and disaster prevention/mitigation from both short- and mid- to long-term perspectives, and to provide academic advice to related government organizations. Based on the results of the site investigations conducted by the JGS survey team (JGS, 2019), this report provides a summary of the geotechnical damage caused by 2018 Hokkaido Eastern Iburi earthquake by presenting the detail of strong seismic motion and a various types of geo-disasters which occurred due to the earthquake. Furthermore, this report highlights future research issues on disaster prevention/mitigation in Hokkaido considering the features of the geo-disasters attributed to the earthquake.
