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  1. In-Situ Ground Surveying by the NSWS Testing Machine Download Article

    Shinya Inazumi, Kozo Okita, Takumi Kondo and Kenji Kazarashi
    • Article Type: Research Article
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    • Pages (1-9)
    • No of Download = 942

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    This paper outlines the development of the NSWS (Nippon Screw Weight System) testing machine. In compliance with the Swedish sounding (SWS) test that determines loading and rotational penetration resistance. The NSWS was developed as an in-situ ground surveying device to detect super soft zones in the ground, including hollows and loosening, in detail, by allowing operation in the 0 to 2500N load range, with very close measurements intervals and penetration speed control, the features of which cannot be achieved by the SWS testing machine. Additionally, findings from an in-situ surveying of in-ground hollows identified using the NSWS testing machine are reported in this paper. The machine achieved a conversion N-value measuring intervals of 2.5cm (or 3.8cm), determination of ranges of hollow and loosening zones through pre-setting of penetration speed, and detection of super soft zones of conversion N-values 1 and below with a load range of 0 to 1000N.

  2. Effect of Mixing Fine Sand on the Drained Shear Strength of Completely Decomposed Granite Soil Download Article

    Haider, M. Mekkiyah, Huat B. B. K, M.A. Malek and Mohd Noor Dis
    • Article Type: Research Article
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    • Pages (10-18)
    • No of Download = 1980

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    Experimental test results presented in this paper were from a series of triaxial compression tests studied under drained conditions for Completely Decomposed Granite (CDG) soil mixed with fine sand content of (0, 10, 20, 30, and 40%). The CDG soil showed high compressibility during isotropic consolidation, probably due to the use of the moist tamping method and the effect of weathering degree on the soil structure. The tests results produced a unique Critical State Line (CSL) in the e-lnp plane, and these lines were parallel for each mixture and moved downward with increasing fine sand content. The fine sand content, at which the intergranular void ratio of the CDG-fine sand mixture became equal to emax for plain CDG soil, was named as Transition Fine Sand Content (TFSC), which occurred at 20-30% fine sand content. Normalization of the critical state stresses showed that for the samples with low P/P'c between 0.58 and 0.65 (i.e. the CDG soil mixed with fine sand), the stress paths moved directly towards the critical state without passing through the boundary surface of the soil mixture, which revealed the impact of the fine sand addition to the CDG soil structure, reflecting an improvement in the soil strength behavior by developing a strong interlocking among the particles of the mixture. It was also observed that a small portion of stress paths could pass through the boundary of Hvorslev surface in the case of low fine sand content (≤ 10 %) and the boundary of Hvorslev surface observed clearly in the case of plain CDG soil. The friction angle increased at steady state from 28- 32.6, and the cohesion decreased from 15 to 8.3 kN/m2 with increasing fine sand content. A comparison of critical state parameters and strength properties between weathered granite CDG soil from Malaysia and Hong Kong were also made and summarized in this study.

  3. Experiments on Rockfall Protection Embankments with Geogrids and Cushions Download Article

    Koji Maegawa, Tetsuya Yokota and Phuc Tran Van
    • Article Type: Research Article
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    • Pages (19-24)
    • No of Download = 1091

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    There are various protection measures against rockfalls. An embankment is effective in rockfall hazard mitigation at a dangerous slope end. The slope rockfall tests on full-scale embankments have been carried out. These embankments are made of sandy soil reinforced with geogrids. The cushioning layers which are made of geocells filled with crushed stones of 5-13 mm in diameter are also placed on the mountain side of the embankment. A boulder, i.e., RC block rolls down the test-site slope, and hits against the embankment. A new system of measuring instruments is employed in order to evaluate the impact force and the impact energy. One of important observations is a possibility that a rolling boulder carries it toward the top of an embankment because of its rolling momentum. The experimental results, especially the relationship between impact force and impact energy is discussed in this paper.

  4. Effect of Climatic Change on Groundwater Quality Around the Subsurface Dam Download Article

    A.K.M. Adham, Akira Kobayashi and Akira Murakami
    • Article Type: Research Article
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    • Pages (25-31)
    • No of Download = 770

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    The effect of climatic change on groundwater quality around subsurface dam area has been observed using numerical simulation. The study is related to sustainable groundwater development from subsurface dams constructed in the south islands of Japan where limestone is the underground geology. The model includes dispersion/diffusion, advection, ion exchange, formation of complexes in the aqueous phase, and the dissociation of water. The mass action, transport, and site action equations are expressed in a differential/algebraic form and solved by FEM. Results reveal that dissolution of limestone is proportional to the acidification of rainwater i.e. inversely proportional to the pH of rainwater. The resulting increase in calcium ion concentration is expected to block the filter of the pumping well and deteriorate the quality of groundwater as well. Again, dissolution of limestone is proportional to the increase of intensity of rain that leads to the increase of velocity of water. Dissolution of limestone was inversely proportional to the temperature.

  5. Simulation of Root-Reinforcement Effect in Natural Slopes Based on Progressive Failure in Soil-Root Interaction Download Article

    Ram Chandra Tiwari, Netra Prakash Bhandary, Ryuichi Yatabe, Deepak Raj Bhat
    • Article Type: Research Article
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    • Pages (32-38 )
    • No of Download = 913

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    A new numerical scheme in Finite Element Method (FEM) along with Mesh Free Method (MFM) and suitable convergence criterion is used to simulate the progressive nature of failure in soil-root matrix continuum. With the consideration of homogenizing approach, the complex behavior of soil-root interaction can reliably be captured of any natural slopes. Root-reinforcement effect has significant role in modifying stress anisotropy and displacement behavior of the slope. Result shows that stability factor first increases with RAR, after attaining certain stability factor further increment of RAR within certain limit does not impart on stability factor of slopes. After certain RAR say more than 0.5%, there is no any change on stability factor. Results show that vegetation has significant influences on safety factor in certain effective RAR-range, which further illustrates the necessities of vegetation cover in slopes; however, it requires more realistic model parameters and boundary conditions to perform more relevant simulations.

  6. Residual-State Creep Test in Modified Torsional Ring Shear Machine: Methods and Implications Download Article

    Deepak Raj Bhat, Netra Prakash Bhandary, Ryuichi Yatabe and Ram Chandra Tiwari
    • Article Type: Research Article
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    • Pages (39-43)
    • No of Download = 755

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    Landslide mass are supposed to reach residual state which naturally demands residual-state creep study. To study the creep behavior of landslide soils, a method for residual-state creep test with a modified torsional ring shear machine was developed in laboratory, which can simulate the creeping landslide phenomena. To understand the creeping behavior of landslide soils, three representative landslide soil samples, which have higher percentage of Smectite, Chlorite, and Mica are taken in this study. A series of residual-state creep test (i.e. seven tests) with varying applied constant shear stress for each sample were conducted, the results thus obtained are interpreted in terms of Residual-State Creep Stress Ratio (RCSR), at which the soil samples fail at their residual state. The term RCSR is the ratio of applied constant shear stress with residual strength. The test results show that when RCSR ≤1, the soil does not show creeping behavior where as the soil undergo creeping behavior when RCSR>1.This paper mainly focus on the methods of residual-state creep test, its implications for the study of creeping displacement behavior, and further possibilities of landslide displacement prediction based on experimental findings.

  7. Physical and Chemical Properties of Tsunami Deposits in the Northeast Area of Fukushima Prefecture after the Tohoku-Kanto Earthquake Download Article

    Fujikawa, T., Okazawa, H., Nakamura, T., Takeuchi, Y. and Komamura, M.
    • Article Type: Research Article
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    • Pages (44-49)
    • No of Download = 985

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    The damage done by deposits left by the tsunami triggered when the 11 March 2011 earthquake struck extended over a wide area in the coastal parts of the Tohoku district of Japan. The objectives of this study are to clarify physical and chemical properties of the tsunami deposits in Minamisoma City in northeast Fukushima Prefecture. From field research and measurements, two kinds of tsunami deposits, a sandy material and a muddy one, were observed. Muddy deposits, composed of small particles, were distributed in areas relatively far from shore. The particles in these deposits were light, and they contained high proportions of organic matter. Sandy deposits, on the other hand, had larger, much denser particles and were observed near the shoreline. The electrical conductivity of the muddy deposits at Kashima was very large. The Cl- and SO42- contents of the deposits were higher than those of paddy soils beneath. From an approximation of the shape of the area inundated by the tsunami and the bulk density and thickness of the deposits, we estimate that a dry mass of 193,000 Mg was deposited.

  8. Alternative Employment of Crushed Shell Particles in Capillary Barrier of Soil Download Article

    Nakafusa S., Kobayashi K., Morii T. and Nishimura T.
    • Article Type: Research Article
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    • Pages (50-55)
    • No of Download = 636

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    Capillary barrier is a tilting soil layer system which is composed of a finer soil layer underlain by a coarser soil layer. Water which infiltrates into the soil is suspended just above an interface between the soil layers and diverted downward along the interface, with the result that a vertical movement of water into deeper soil layers below the interface stops within some length along the interface. As the water diversion in the capillary barrier is caused by a sharp contrast in water retention capacity between the finer and coarser soils, any material which can provide the sharp contrast in water retention capacity can be alternatively employed in the capillary barrier system. In the study a coarse-grained material of crushed shell particles is selected as an alternative candidate for the lower layer soil of the capillary barrier, and its water retention capacity is measured to examine a practical effectiveness of the crushed shell particles in the capillary barrier system.

  9. Characteristics of Flood Disasters in Low Floodplain Along a Big River Due to Overflow Levee Breach Download Article

    Md. Serazul Islam and Tetsuro Tsujimoto
    • Article Type: Research Article
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    • Pages (56-63)
    • No of Download = 779

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    During flooding season, large amount of water flows through Bangladeshi river and it causes earthen levee failure and huge damage occurs in the inhabitants inside the levees. Thus it is important to recognize the process of inundation and we have attempted to do through numerical simulation. As for simulation scheme, schematic model area is considered with main channel, levee and floodplain, and they are roughly composed of the same sediment characteristics because the flood plain have been formed by flooding sediment, the levees have been made by piling up the sediment dredged from the river bed. Therefore, we treat these three components simultaneously in the simulation model. The main channel, levee, floodplain and flow parameters are selected in conformity with the study field of Sirajganj district and Jamuna River in Bangladesh. And RIC-Nays a two-dimensional numerical model for flood flow and morphology is utilized in this study upon confirmation through the experimental and other numerical study. Based on the calculated results, inundation of water and sediment in the floodplain and evolution process of levee breach are investigated. Levee breach is considered to initiate in the middle of the levee with crest opening. We change the opening size in vertical and longitudinal scales, and the inflow discharge. For the floodplain slope is also taken into account.

  10. Shear Deformation development and the Increase of Pore Pressure due to Rainfall Infiltration in Sandy Model Slope with Different Inclination Download Article

    Sasahara K. and Sakai N.
    • Article Type: Research Article
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    • Pages (64-70)
    • No of Download = 832

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    Monitoring of surface displacement of slope has been widely adopted as time prediction method of shallow landslide due to rainfall. Modeling of shear deformation according to rainfall infiltration is necessary for establishment of the method. In order to examine the constitutive relation for the model, surface displacement, pore pressure at the base, volumetric water content (hereafter, V.W.C.) and suction, shear strain in the sandy model slope are monitored during artificial rainfall. Analysis of the monitored data shows that surface displacement and shear strain in the slope proceed at small rate under unsaturated condition first, then increase remarkably with the rise of pore pressure. Unsaturated component of surface displacement of steeper slope is larger than that of gentler slope. It is likely to be due to that shear strain with the increase of suction is larger in steeper slope while shear strain according to the increase of pore pressure is larger in gentler slope.

  11. Estimation of Earthquake Ground Motion in Padang, Indonesia Download Article

    Rusnardi R., Kiyono J. and Ono Y.
    • Article Type: Research Article
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    • Pages (71-77)
    • No of Download = 1241

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    Several powerful earthquakes have struck Padang during recent years, one of the largest of which was an M 7.6 event that occurred on September 30, 2009 and caused more than 1000 casualties. Following the event, we conducted a questionnaire survey to estimate the shaking intensity distribution during the earthquake. About 500 residents of Padang were interviewed. The residents received explanations for each item on the questionnaire from the interviewers, and answers were filled in directly on the answer sheets. From this survey we produced a map of the shaking intensity distribution in Padang. In addition to the questionnaire survey, we performed single observations of microtremors at 110 sites in Padang. The results enabled us to estimate the site-dependent amplification characteristics of earthquake ground-motion. We also conducted a 12-site microtremor array investigation to gain a representative determination of the soil condition of subsurface structures in Padang. From the dispersion curve of array observations, the central business district of Padang corresponds to relatively soft soil condition with Vs30 less than 400 m/s, the predominant periods due to horizontal vertical ratios (HVSRs) are in the range of 2.0 to 4.0 s, and the seismic intensity obtained is upper 5 (5+) in the JMAi scale. By making these observations, we can obtain a relationship between soil types, predominant periods and seismic intensities.

  12. Finite Element Modeling of Innovative Shallow Foundation System for Reactive Soils Download Article

    Mostafa A. Ismail and Mohamed A. Shahin
    • Article Type: Research Article
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    • Pages (78-82)
    • No of Download = 16065

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    Granular pile anchor foundations (GPAF) are a promising foundation system that can be used to mitigate the serious consequences of volumetric changes of reactive soils, both during expansion and shrinkage. This paper presents results from 3D finite element analyses, using PLAXIS software, undertaken on a typical double-story building constructed over a system of GPAF in a reactive soil. The study investigates the ability of the GPAF system to resist the forces induced by soil movement due to moisture variation, and the impact of this resistance on the straining actions affecting the superstructure. The results confirm the efficiency of the GPAF system in arresting the movement of the reactive soil, which in turn improves the structural responses of the building in terms of induced deformations, angular distortions and internal forces.