Kazuhiro Oda

Stress Sharing Behavior and Its Mechanism during Consolidation Process in Composite Ground Improved by Sand Compaction Piles with Low Replacement Area Ratio

In order to accurately design a sand compaction pile (SCP) with low replacement area ratio, it is important to understand the mechanical interaction between the sand pile and clay ground and its mechanism during consolidation process in composite ground. In this article, therefore, a series of numerical analyses on composite ground improved by SCP with low replacement area ratio were carried out. The applicability of numerical analyses, in which an elasto-viscoplastic consolidation finite element method was applied, were confirmed by comparing the results obtained from a series of laboratory model tests with the composite ground improved by SCP. Through the results of the numerical analyses, mechanical behavior of the sand pile and clay in composite ground during consolidation is elucidated, together with a stress sharing mechanism between sand pile and clay.

Slope Disaster Monitoring System Using Battery-Operated Wireless Sensor Network

This paper develops a slope disaster monitoring system using distributed sensors. The sensor node has wireless communication and tilt detection capabilities. Each sensor node communicates to each other and sends the corrected data to a base station, which can send an alert message to administrators in case of emergency. The developed slope disaster monitoring system is installed on a slope along the Chugoku Expressway. This first experimental study showed a significant potential of the developed distributed sensor network for detecting slope failures, but it also clarify that the wireless communication capability is sensibly influenced by relative geometric alignments of each sensor nodes. The second experimental study has begun along the Maiduru-Wakasa expressway. Since the geometric alignments are modified, we are having an improved wireless communication correspondence.

Spatial Interpolation of consolidation properties of Holocene clays at Kobe Airport using an artificial neural network

The spatial distribution of the consolidation properties for a seabed must be appropriately estimated to accurately predict the consolidation settlement due to large-scale reclamation. The soil properties must be estimated at arbitrary positions in the ground from data collected during soil investigation. In this study, an artificial neural network was applied to spatially interpolate consolidation properties such as the natural water content, void ratio, plastic index, compression index, and pre-consolidation pressure. The estimation accuracy of consolidation properties was judged based on four indexes: R2, G, MARE, and SR. The artificial neural network estimated the appropriate consolidation properties with high accuracy; this confirmed the availability of spatial interpolation of consolidation properties by using an artificial neural network.

IDENTIFICATION OF SLOPES WITH HIGHER RISK TO SLOPE FAILURES BASED ON INFORMATION PROCESSING TECHNIQUES

In recent times, the sediment disasters, such as slope failures, debris flows, and landslides, caused by typhoons or cloudbursts have occurred in Japan. The progression of global warming will increase the scale of typhoons and cloudbursts striking the Japanese Islands, and there is a concern that the frequency of sediment disasters may increase. Therefore, it is important to identify slopes with a higher risk to sediment disasters to prevent future disasters. In this study, a method based on artificial neural networks and mathematical statistics was used to identify such slopes. In the proposed method, the self-organizing map (SOM), cluster analysis, and Hayashi’s second method of quantification are combined. The proposed method was applied to the data gathered from periodical inspections of road slopes. In the results, slopes with a higher risk to slope failure were identified and ranked according to their risk.

Sedimentation properties and modeling of dredged soil

ABSTRACT When dredged soil containing coarse soil is used for the construction of reclaimed ground that is in contact with the surface of seawater, there is a high possibility of the generation of nonuniformly reclaimed ground due to the segregation of fine-grained soil from coarse-grained soil. It is difficult to assume uniform properties of reclaimed ground because the properties are defined and formed by the spontaneously segregating sedimentation. Estimation of the soil’s volume change lacks accuracy if the properties of the reclaimed ground are assumed to be always uniform. Therefore, for pump-dredged reclamation, a predictive study and various experiments are required to estimate the physics and properties of the dredged soil sedimentation. Accordingly, this study demonstrates a modeling test to understand the characteristics of the sedimentary ground using the changing ratio of fraction of the sample passing through a 75-µm sieve. The effect of particle arrangement on hindered settling properties, sedimentation properties, the distribution of water content of sedimentary ground, and physical properties can be determined by the modeling test. The study also suggests the calculation method for the travel distance of the outlet and the volume of input soil based on the experimental results.

Numerical Simulation and Parametric Study of a Single Pile in Clay Layer to Examine the Effect of Loading on Settlements and Skin Friction Distribution

Skin friction is a shear stress distributes along pile’s shaft as a reason of the movement between pile and adjacent soil. Applying loads on the pile head lead the pile to move downward and the adjacent soil to move upward resisting this movement, and a positive skin friction distribution will occur. On the other hand, applying a surcharge load on the surface next to the pile will cause extra settlements in the soil layers which may be larger than the pile settlements, and a negative skin friction (NSF) will be distributed along the pile’s shaft. Load combination on both; pile and the adjacent soil, is a common reason of NSF phenomenon. To study the loading effect widely, a parametric study was carried out in this paper for different cases including pile and surcharge loading. This parametric study was held by a numerical simulation using elastic-plastic soil model defined by Matsui-Abe and the elastic-viscoplastic soil model defined by Sekiguchi-Ohta model to study the case of a single pile driven in a loaded soft clay layer. The model was first validated by comparing the results obtained from the primary consolidation with field test measurements. The comparison between two soil constitutive models was important to examine the effect of loading in different cases of soil behavior. Viscosity effect on NSF distribution was studied and shown in the graphs. As NSF may lead to pile’s material fracture and structural failure, the aim of this paper is to examine the effect of loading on NSF, and clarify the viscosity behavior during primary consolidation stage. Viscous effect, surcharging and pile load combination have played a major rule in changing the skin friction distribution.

Open image in new windowUnderstanding of Landslide Movement at Bumi Waluya Railway Station, Garut, Indonesia

Mitigation of a slow-moving landslide hazard requires a good knowledge of the landslide movements. This paper presents results of geophysical investigation and slope movement monitoring to understand the characteristics of an active landslide above a railway station in Garut, Indonesia. For this purpose, a series of resistivity surveys was then conducted using a dipole-dipole method to map the hydrological condition of the landslide area, and geotechnical monitoring was conducted to characterize the movement. Based on the N–S resistivity profiles, highly saturated zones, indicated by low resistivity values, exist in soil layers at a depth greater than 7.5 m. The saturated zone also develops in the near-surface soil layer in the landslide body. The slope movement monitoring records suggest that the landslide consists of several landslide segments with different rates of movement and deep sliding zone. Based on this current study, the characteristics of landslide movement is very site specific and is mainly associated with localized hydrological conditions. Because the surface water infiltration from the irrigation ditches and rice fields controls the landslide reactivation, a better surface water and sub-surface water management is, therefore, necessary to reduce the landslide risks to the railway infrastructures.

EFFECT OF STIFFNESS OF THIN BEARING LAYER ON TOE BEARING MECHANISM OF STEEL PIPE PILE WITH A CONCRETE BULB

It has been known that the sufficiently stiff layer can be considered as a load-bearing layer of piles, even if its thickness is thin. The authors have studied the toe bearing resistance of pile on a thin load- bearing layer, in order to establish the design method about pile on a thin load-bearing layer. In this paper, the effect of stiffness of load-bearing layer on characteristics of toe resistance of steel pipe pile on a thin load-bearing layer is discussed through a series of numerical analyses. First, a field loading test of steel pipe piles with a concrete bulb on a thin load-bearing layer is reproduced through the numerical analysis, in which a soil-water coupled with an elast-plastic finite element method is applied, to confirm the availability of the numerical analysis proposed. Second, a series of numerical analyses are carried out in which the deformation modulus of the load-bearing layer and the thickness of load-bearing layer are chosen as a variable parameter. The results of the numerical analyses show that the stiffness of load-bearing layer affects the resistance when the yielding of load-bearing layer occurs.

Decision Criteria of Slope Hazards by Multi-step Monitoring using a WSN

Expressways link every city in Japan and serve as a main lifeline in emergencies response. However, slope disasters in recent years of expressways may occur without warning due to unexpected heavy rain. This paper proposes decision criteria for slope hazards using a multi-point and multi-step monitoring system. A sensor module with a mesh networking protocol is developed. A compact battery pack gives the module an operating life of more than three years. The installation position of sensors is decided by the safety factor for the stability of a half-infinite slope. Decision criteria for slope hazards caused by heavy rain are proposed based on laboratory test results. The laboratory results agree well with field experiment results.