Toshihiro Noda

Super Loading Yield Surface Concept for the Saturated Structured Soils

“Superloading surface concept” is newly developed for the description of elasto-plastic behavior of highly structured soils. The superloading surface, which is similar in shape to the original Cam-clay yield surface, is located above the Cam-clay and the size ratio between two yield surfaces gives the degree of the structure of soil skeleton. The evolution law of the size ratio describes the decay of the structure as plastic deformation proceeds, and the superloading surface falls exactly on the Cam-clay yield surface at the end of the completely remolded state. When the soil is reloaded after elastic unloading, the elasto-plastic behavior of the soil is described by the Hashiguchi’s subloading surface, which is also similar in shape to the superloading surface. The size ratio between super and subloading surfaces gives the OCR.

Undrained Creep Rupture of Normally Consolidated Clay Due to Bifurcation Mode Switching During Pore Water Migration

In the present study, we newly interpret the undrained creep rupture of normally consolidated soil as a result of the change in the initial higher bifurcation mode to lower one during pore water migration within the clay; i.e., “mode switching”. The computation is performed not as a single soil element as in the classical soil mechanics, but as a soil-water coupled initial-boundary value problem of a soil specimen, in which only the “inviscid” original Cam-clay model with the subloading surface concept and the Darcy’s law are used. As a result, just after the constant applied load, the axial strain is progressing at a very slow rate, however, the strain rate increases immediately when the strain reaches 5.7%. During the time, it is observed that the excess pore pressure tends to be homogeneous and then rises again due to the occurrence of softening in some element.

Creep-Like Delayed Failure of Clayey Ground after the End of Embankment Construction

Even in normally or lightly overconsolidated clay foundations, failures have been observed some days/weeks after the end of the embankment construction. The clay foundation stays apparently stable just after the completion of construction, but with the passage of time instability develops gradually instead of expected consolidation and it may undergo catastrophic failure in an unexpected moment. In this paper such a creep-like delayed failure of a homogeneous normally consolidated clay foundation is investigated through the soil-water coupled finite deformation computation with the use of the invicid subloading surface Cam-clay model.

620 Maybe the World's First Attempt on Vibration Engineering Lecture : Report of Experience-Based Program : Building to Perform a Lecture Vibrated Freely

Susumu HARA, Nobuo FUKUWA, Toshihiro NODA, Takashi TASHIRO, Jun TOBITA, Takuya NAGAE, Kazumi KURATA and Tsuyoshi INOUE Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan

Determination of Parameter in SYS Cam-Clay Model of Ultra-Soft Clay

Parameter analyses in the constitutive model determine the precision of numerical results. Cam-clay model is the first elasto-plastic model in the world and widely used in the practical engineering. SYS Cam-clay model is proposed based on Cam-clay model by incorporating the concept of overconsolidation, soil structure and anisotropy. There are two groups of parameters in this model, elasto-plastic parameters that are exactly same as those in Cam-clay model and evolutional parameters that decide the variation of overconsolidation, soil structure and anisotropy. The detailed process to determine the parameters is introduced step by step.

Influence of Bending of Plastic Vertical Drain on Consolidation via Vacuum Preloading

The soft ground improvement employing vacuum preloading is widely used in Tianjin. In the application of vacuum preloading, the bending of plastic vertical drains (PVDs) often occurs accompanying the large settlement of the soft ground or the significant shear strain at the ground surface. In order to investigate the influence of bending of PVDs on the ground consolidation, three different bending shapes of PVDs are assumed and a series soil-water coupled finite element analyses are carried out. It is found that: 1) the macro-element method is available to take the bending effect of PVDs into consideration; 2) the bending at the bottom of PVDs has much impact on the consolidation of ground even though the hydraulic gradient at the bottom is much smaller than that at the top; 3) Due to the bending of PVDs at the bottom the drainage capacity is much influenced and the volumetric compression only occurs at the first few layers of the ground.

Realization of Uniform Deformation under Three-Dimensional Condition Based on Soil-Water Coupled Analysis Considering Inertia Forces

In the paper, based on soil-water coupled finite deformation analysis, theoretical considerations and numerical calculations were carried out under undrained three-dimensional condition in order to reproduce a uniform deformation field. At first, a theoretical consideration was assumed to realize a uniform deformation for a saturated soil, according to which the initial velocity and acceleration in both vertical and circumferential directions should be applied to each node to remove the influence of inertia effect. This first theoretical analysis is useful and can guide the numerical calculation. Next, the paper realized a uniform deformation of a three-dimensional cylinder specimen under undrained boundary conditions using the soil-water coupled analysis in which the SYS Cam-clay model is employed as the constitutive model for soil skeleton. The numerical results show that without the inertia forces there is no localized deformation in the specimen.

Seismic Stability Analysis of Light-Weight Column Considering Depth of Liquefiable Layer

A series of light-weight column for receiving the wireless signals to control the stoppage of gas supply are built on the liquefiable ground and their seismic stability should be precisely investigated to prevent the second accident. For the conventional judgment of liquefiable ground, if the soil type of the ground surface is the same, the potential liquefaction of the ground is also the same. In this paper, based on the soil-water coupled finite element method the influence of the depth of the liquefiable layer is taken into consideration and it is found that the seismic stability of the column varies significantly depending on the depth of liquefiable layer even though the embedment depth of the column is the same. Therefore, it is necessary to con-sider the depth of liquefiable layer for the high accuracy analysis.

Seismic response analysis of a coastal artificial reclaimed ground containing a soft layer

The seismic resistance of a coastal artificial ground situated within the Port of Nagoya against the Tokai-Tonankai-Nankai triple-segment earthquake was assessed. The analysis was carried out using the elasto-plastic constitutive equation for soils (SYS-Cam clay model) mounted on the soil-water coupled finite element deformation analysis program The model focuses attention on the action of the soil skeleton structure, and the analysis allows description of the mechanical behavior of a wide range of soils without distinguishing between static and dynamic behavior. When considering earthquake damage, attention usually tends to focus only on the phenomenon of liquefaction in sandy grounds. In this paper, finite element analysis was employed to simulate the phenomenon of liquefaction of soft sand and, in addition, to show that because of disturbance of the soil during the earthquake, there is a danger of large settlement occurring over a long period after the earthquake in the soft clay layer directly beneath the area that is under the action of vertical loads.

Numerical Analysis on Co- and Postseismic Behavior of Sandy/Clayey Soil Ground Improved by Sand Compaction Pile Method

The co- and post-seismic behaviors of typical loose sandy ground and soft clayey ground improved by the sand compaction pile (SCP) method were investigated using a soil-water coupled finite element deformation analysis program incorporating the SYS-Cam clay model. The results indicated that the deformation caused by earthquakes was suppressed in the SCP improved grounds, irrespective of whether they were sandy or clayey. Although the surrounding ground was liquefied in the case of SCP-improved sandy ground, the confining pressure was maintained in the SCP interpile zone because of the compaction effect produced by the cavity expansion of the sand piles. In the case of the SCP-improved clayey ground, negative excess pore pressures appeared in the SCP sand piles because of the hardening that results from plastic expansion and stress was concentrated on them.