Articles
<![CDATA[EARTH SEWING TECHNIQUE FOR THE PRESERVATION OF FANASAKO HISTORICAL KILN SITES ]]>
<![CDATA[X. J. Chai]]>;
<![CDATA[S. Hayashi]]>;
<![CDATA[Y. J. Du]]>
<![CDATA[ Lowland Technology International Vol 6 No 1, June (2004) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[The Funasako historical klin sites, which are located in the northern part Kyushu Island in Japan, have been considered as public exhibition areas. This requires preservation of the kiln remains by reinforcement of the soil. Considering the complicated local topography, the reinforcement method that was proposed is a combination of chemical grouting and soil nailing, and is termed the Earth Sewing Technique (EST) in this paper. In order to prevent disturbance of the soil in the kiln remains, a drilling hole diameter for soil nailing of 7 mm with a tendon (bolt) that has a diameter of 3 mm was selected. Field full-scale pullout test at a model kiln site were carried out before applying the reinforcement technique to the real historical kiln sites. This paper presents the field pullout results and the results of a series of laboratory pullout test that were conducted to investigate the critical factors affecting the perfomance of the EST. Design parameters have been recommended based on rational interpretation of the field and laboratory pullout test results. The pullout strength-water content relationships were found to be very useful for understanding and evaluating the shear strength capacity of soil nailing in partially saturated cohesive soils.]]>
<![CDATA[INVESTIGATION ON SOME FACTORS CONTROLLING THE SORPTION OF HEAVY METALS ON ARIAKE CLAY ]]>
<![CDATA[Y. J. Du]]>;
<![CDATA[S. Hayashi]]>
<![CDATA[ Lowland Technology International Vol 7 No 1, June (2005) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[Sorption of contaminant is one of the key mechanisms in controlling transport of contaminant in clay barrier. In this study, the potential sorption of heavy metals on Ariake clay, which is a typical Japanese marine clay, is examined. Two types of heavy metals, Cd2+ and Pb2+, were selected as key contaminants and series of batch tests were performed for investigating factors controlling the sorption of Cd2+ and Pb2+ on Ariake clay. The batch test results show that the sorption of Cd2+ and Pb2+ on the Ariake clay arrived at an equilibrium condition less than the contact time prescribed by the ASTM and US EPA standards. It is found that the sorption was significantly controlled by the solid: solution ratio. With the increase in the solid: solution ratio, the sorption of Cd2+ decreased. The batch test results show that the sorption of Cd2+ increased with the increase in the pH of solution. The influence of pH on the sorption was found to be solid: solution-dependent. At relatively lower solid: solution ratio, the sorption of Cd2+ increased with increasing pH, whereas it marginally increased at relatively higher solid: solution ratio. It is concluded that the solid: solution ratio could be the crucial factor for controlling the sorption of heavy metals on the Ariake clay.]]>
<![CDATA[LOWLAND TECHNOLOGY INTERNATIONAL SPECIAL ISSUE – FOREWORD – ]]>
<![CDATA[H. Araki]]>;
<![CDATA[S. Hayashi]]>
<![CDATA[ Lowland Technology International Vol 9 No 2, Dec (2007) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[Lowlands imply regions having low elevation, which are particularly susceptible to climatic, sea water level and environmental changes. For example, global warming, which appears to be causing a rise in sea level, must ultimately affect the safety of coastal dikes and other coastal infrastructures, as well as threaten the water and ecological systems in lowland areas. Lowland regions are also particularly vulnerable to natural disasters. In 2004, several large earthquakes and Tsunami in the Asian region caused major damage in lowland areas. The importance of exploration of problems in lowlands has been recognized by researchers, planners, engineers and administrators all over the world.]]>
<![CDATA[ANALYSIS ON GROUNDWATER WITHDRAWAL AND LAND SUBSIDENCE IN SHANGHAI ]]>
<![CDATA[Y.-S. Xu]]>;
<![CDATA[S.-L. Shen]]>;
<![CDATA[S. Hayashi]]>;
<![CDATA[Z.-Y. Cai]]>
<![CDATA[ Lowland Technology International Vol 9 No 2, Dec (2007) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[Large-scaled land subsidence due to withdrawal of groundwater in Shanghai was observed. A method based on 3D-groundwater flow model is presented at first to calculate land subsidence in this paper. The model considers the aquitard-aquifer condition of Shanghai soft ground. Based on the proposed groundwater flow model combined with the compressibility of soil layer, subsidence is calculated through unifying in a one model condition. The anisotropic characteristics of soil layer are also considered in the model. The land subsidence, groundwater flow vector, and groundwater drawdown were analyzed using the proposed method. Through comparing between the measured value and calculated value, it indicates that the model simulated the measurement value well. Groundwater flow from west to east at the beginning stage and it flows from east to west after the long-term groundwater withdrawal. Groundwater level is depressed along with groundwater withdrawal.]]>
<![CDATA[MODELLING STRAIN-SOFTENING BEHAVIOUR OF CLAYEY SOILS ]]>
<![CDATA[J.-C. Chai]]>;
<![CDATA[J. P. Carter]]>;
<![CDATA[S. Hayashi]]>
<![CDATA[ Lowland Technology International Vol 9 No 2, Dec (2007) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[A method for modelling the strain-softening behaviour of clayey soils under undrained and/or partially drained conditions is proposed and applied to simulate the mechanical behaviour of undisturbed Ariake clay and limestabilized Ariake clay samples under undrained conditions. The proposed method is based on the Modified Cam clay (MCC) model. It is assumed that during the softening process, the strain increments can still be calculated by the MCC model, but the effective stress path is enforced to follow the projection of the critical state line (CSL) in a p’– q plot (i.e., q = M p’ where p’ is mean effective stress, q is deviator stress and M is the slope of the CSL in the p’– q plot). Therefore the method is not completely rigorous in the applied mechanics sense, rather it is a pragmatic approach. The proposed method has been incorporated into a finite element code and its performance was verified by simulating undrained triaxial compression tests. Subsequently, the method has been applied to simulate the mechanical behaviour of both natural and lime-stabilized Ariake clays. Comparing the simulated results with the test data indicates that the method simulated both the shear strain versus deviator stress curve and the effective stress path reasonably well. However, the results also showed that in the case of the lime-stabilized Ariake clay, the adoption of a high initial stiffness under lower confining stress should be considered. It is suggested that the proposed method can be used to analyze geotechnical problems involving strain-softening behaviour with reasonable accuracy.]]>
<![CDATA[NOVEL THERMO-PVD CONSOLIDATION TECHNIQUE FOR SOFT SOILS ]]>
<![CDATA[C. Pothiraksanon]]>;
<![CDATA[D. T. Bergado]]>;
<![CDATA[H. M. Abuel-Naga]]>;
<![CDATA[S. Hayashi]]>;
<![CDATA[Y. J. Du]]>
<![CDATA[ Lowland Technology International Vol 9 No 2, Dec (2007) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[Previous research efforts on investigating the thermo-hydro-mechanical behaviour of fine grained soils as well as recent extensive experiments conducted on soft Bangkok clay have demonstrated that saturated fine-grained soils subjected to temperature less than boiling point of water (100OC) undergo volumetric and shear strength changes depending on the stress history. These features encouraged employing the thermal load only, up to 90OC, or in combination with mechanical loading as ground improvement technique. This paper addressed the applicability of this technique through a series of large oedometer tests conducted on soft Bangkok clay. Heating was achieved using flexible wire heater attached to the PVD point or using separate line heat source. The clay has been subjected to either thermal load or thermo-mechanical load. The test results show that a combination of the thermal and mechanical load gives promising results and is a viable technique since it accelerates the rate of consolidation and increases the amount of total settlement. This behavior can be attributed to the increase in the soil hydraulic conductivity as the soil temperature increases. Therefore, raising the soil temperature during the preloading period can enhance the performance of the PVD, particularly, by reducing the drainage retardation effects due to the smear zone around PVD.]]>
<![CDATA[CETEAU PVD VACUUM SYSTEM IN SOFT BANGKOK CLAY: A CASE STUDY OF THE SUVARNABHUMI AIRPORT PROJECT ]]>
<![CDATA[J. Saowapakpiboon]]>;
<![CDATA[D. T. Bergado]]>;
<![CDATA[S. Hayashi]]>;
<![CDATA[J. C. Chai]]>;
<![CDATA[N. Kovittayanon]]>;
<![CDATA[T. P. de Zwart]]>
<![CDATA[ Lowland Technology International Vol 10 No 1, June (2008) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[A new improvement technique is currently applied for soft Bangkok clay combining capped PVD with vacuum pressure and embankment loading whereby the prefabricated vertical drains (PVD) are connected by PE tubes to a vacuum pump called “CeTeau PVD Vacuum System”. The method uses a surface soil layer as a sealing layer for leakage protection and there is no need to place air-tightening geomembrane sheets on the ground surface. This method has two advantages for situations of a) high air/water permeability layer exist near the ground surface, and b) combining vacuum pressure with embankment load. An actual field project combining PVD vacuum and embankment loading has just been completed. The performance data of the system during the improvement of the section EW-4, a part of the third runway of Suvarnabhumi International Airport, Thailand are presented and interpreted. The monitored data indicated that the system mobilized -60 kPa atmospheric pressure. This allowed for unprecedented loading and settlement rates during the construction of an embankment and achieved the required degree of consolidation within the specified time period. The prediction by PVDCON FEM Software generally agreed with the observed values. As expected, increasing the Kh/Ks and OCR values resulted in lower settlement values.]]>
<![CDATA[EVALUATION OF PERFORMANCE OF CHINESE STANDARD MUNICIPAL SOLID WASTE LANDFILL BOTTOM LINER SYSTEMS ]]>
<![CDATA[Y. J. Du]]>;
<![CDATA[S. Y. Liu]]>;
<![CDATA[S. Hayashi]]>
<![CDATA[ Lowland Technology International Vol 10 No 1, June (2008) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[It is reported that nearly 80 % of the Chinese municipal solid waste (MSW) landfills were open-dump without strict landfill bottom liners. A serious environmental pollution has been exposed to landfill impacts. To solve this problem, Chinese Government prescribed standard MSW landfill bottom liners. However, very limited research has been conducted to evaluate the performance of the standard MSW landfill bottom liners prescribed Chinese Government. In this paper, it was assumed that the two standard Chinese landfill liners were applied in assumed field scenario, in which an aquifer was below the landfill. With the one-dimensional advection-diffusion-dispersion theory of contaminant transport, the impacts of the landfills on the aquifer were assessed. The performance of the two types of Chinese MSW landfill bottom liner systems was evaluated based on: 1) the leakage rate through the liners which were applied in assumed landfills; 2) the peak concentration of the target contaminant in an aquifer overlain by the assumed landfills, and 3) the maximum total mass per unit area of the target contaminant discharged into the aquifer. The performance of the German standard MSW landfill bottom liner system was evaluated and compared with that of Chinese ones. The calculated leakage rate, peak concentration and the maximum total mass per unit area in the aquifer of the target contaminant show that the performance of the Chinese standard landfill liner Type 2 is practically the same as that of the German standard landfill liner, while the Chinese standard liner Type 1 is less effective, with regarding the mitigation of the impact of landfills.]]>
<![CDATA[PERFORMANCE OF FULL SCALE TEST EMBANKMENT WITH REINFORCED LIGHTWEIGHT GEOMATERIALS ON SOFT GROUND ]]>
<![CDATA[T. Tanchaisawat]]>;
<![CDATA[P. Voottipruex]]>;
<![CDATA[D. T. Bergado]]>;
<![CDATA[S. Hayashi]]>
<![CDATA[ Lowland Technology International Vol 10 No 1, June (2008) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[Embankment construction using reinforced lightweight geomaterials over soft ground will alleviate problems of instability and large settlements. Backfills of retaining structures can also be constructed using lightweight materials resulting in lower vertical loads and, consequently, reduced settlements. The aim of this study is to investigate the behavior of lightweight geomaterials consisting of tire chip-sand mixture reinforced with geogrids for use as embankment construction on soft ground. The experimental results indicated that the mixing ratio of 30:70 % was the most suitable fill material. The full scale field test embankment was constructed at the campus of Asian Institute of Technology (AIT) in Bangkok, Thailand. The geogrid reinforced embankment system was extensively instrumented in the subsoil and within the embankment itself in order to observe its behavior during construction and post construction phases, and thereby evaluate its performance. The unit weight of rubber tire chip-sand mixtures is about 75% lighter than conventional sand. The total settlement at ground surface is 67.5% less when compared to the conventional backfill without foundation treatments. The maximum lateral wall movement observed at 13 months after construction at top of wall is 45% smaller when compared to conventional sand backfill on untreated ground. Finally, the geogrid reinforcements correspond well with the bilinear type of maximum tension line.]]>
<![CDATA[CUMULATIVE PLASTIC STRAIN AND THRESHOLD STRESS OF A QUASISATURATED COMPACTED SILTY CLAY ]]>
<![CDATA[J. T. Shahu]]>;
<![CDATA[Yudhbir .]]>;
<![CDATA[S. Hayashi]]>
<![CDATA[ Lowland Technology International Vol 10 No 2, Dec (2008) ]]>
Publisher : <![CDATA[International Association of Lowland Technology ]]>
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<![CDATA[The knowledge of cumulative plastic strain and stability threshold of subgrade soil under cyclic loading is of prime importance in a proper design and maintenance planning of highway pavement structures and railway tracks. The soil beneath a pavement or a track usually exists under quasi-saturated conditions wherein the water voids in the soil remain continuous. Quasi-saturated specimens are essentially partially saturated at low confining pressures. However, with the increase in confining stresses, the air voids in the quasi-saturated specimens are dissolved into solution and the soil behaves like saturated material. Both monotonic and cyclic undrained triaxial tests have been carried out on quasi-saturated compacted specimens of a silty clay. The monotonic tests have been used to develop critical state soil mechanics framework for quasi-saturated behavior. The cyclic undrained behavior of quasi-saturated specimens has been then interpreted using this critical state framework. A generalized bilinear log-log model is proposed for the prediction of cumulative plastic strain with number of load cycles for fine-grained soils. Threshold stress is evaluated using both plastic strain development and pore pressure generation criteria. A generalized relationship between threshold stress ratio and plasticity index is proposed for a variety of soils at low and relatively high confining stresses.]]>
