PVD カイリョウ ジバン ニオケル モリド カジュウ ニヨル ソクホウ ヘンケイ ヨソクホウ

博士（工学）佐賀大

Preloading of harbor's quay walls to improve marine subsoil capacity

Preloading is an improvement technique for compressible soils, and has been applied at DjenDjen port in Jijel province, Algeria, as part of its development and expansion. In addition, this treatment to eliminate the risk of wharf caissons instability. Decent number of research and development works of the preloading process in different countries by several authors have been cited, with the aim of justifying our research and results. The objectives are to understand and apprehend the coastal soil preloading method and its application in terms of the sensitivity of the intervening factors on its achievements, and their effect on the behavior of the soil and the marine structure during and after its implementation. Furthermore, a numerical simulation of the real test of the method of treatment is carried out, by the plaxis 2D code in finite elements, also respecting the actual construction phasing of this structure, in order to compare the calculation results with in-situ measurements to validate the numerical models and to check the stability of the harbor structure. A matrix of  consolidation process during pre compression is proposed

Analyzing consolidation data to predict smear zone characteristics induced by vertical drain installation for soft soil improvement

In this paper, the effects of variability of smear zone characteristics induced by installation of prefabricated vertical drains on the preloading design are investigated employing analytical and numerical approaches. Conventional radial consolidation theory has been adopted to conduct analytical parametric studies considering variations of smear zone permeability and extent. FLAC 2D finite difference software has been employed to conduct the numerical simulations. The finite difference analyses have been verified using three case studies including two embankments and a large-scale laboratory consolidometer with a central geosynthetic vertical drain. A comprehensive numerical parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Furthermore, the construction of the trial embankment is recommended as a reliable solution to estimate accurate smear zone properties and minimise the post construction settlement. A back-calculation procedure is employed to determine the minimum required waiting time after construction of the trial embankment to predict the smear zone characteristics precisely. Results of this study indicate that the accurate smear zone permeability and extent can be back-calculated when 30% degree of consolidation is obtained after construction of the trial embankment. © 2014 Techno-Press, Ltd

Analysing ground deformation data to predict characteristics of smear zone induced by vertical drain installation for soft soil improvement

University of Technology, Sydney. Faculty of Engineering and Information Technology.The use of prefabricated vertical drain (PVD) assisted preloading has been recognised over the last two decades as a very efficient method of ground improvement for sites with deposits of deep soft soil. One of the major parameters influencing the PVD assisted consolidation process, and consequently the required preloading time, is the formation of a smear zone around the vertical drains, and the corresponding soil properties. In this research a systematic procedure integrated with a developed numerical code is proposed to accurately back calculate the properties of the smear zone based on the consolidation data collected in the laboratory and in the field. Furthermore, an expanded back calculation method is developed to determine the minimum required degree of consolidation and corresponding time after the construction of the trial embankment that would result in accurately predicted smear zone characteristics. The explicit finite difference program FLAC 2D was used to develop the numerical code, simulate the laboratory testing and PVD assisted preloading case histories. Furthermore a comprehensive parametric study was conducted to investigate the effect of smear zone properties variations on the preloading process, and back calculated characteristics of the smear zone. A large and fully instrumented Rowe cell apparatus was used to investigate the effect of the smear zone on the consolidation process and verify the developed numerical code. The Rowe cell was filled with the intact zone, smear zone, and vertical drain materials to evaluate the permeability and extent ratios of kh/ks=4 and rs/rm=3, respectively. The back calculation procedure was used to conduct the parametric study and predict the properties of the smear zone. According to the results, the predicted properties of the smear zone were similar to the properties of the applied soil, proving that the proposed back calculation procedure integrated with the developed numerical simulation can successfully predict these properties. The developed numerical code was used to simulate five PVD assisted preloading case studies, including four trial embankments and a large scale consolidometer, while the back calculation procedure was used to conduct a parametric study to determine the extent and permeability of the smear zone. According to the results, integration of the back calculation procedure in the numerical code can be used as a reliable tool to make an accurate prediction of the smear zone characteristics in PVD and vacuum assisted preloading projects. The developed method in this research can be considered as a practical, accurate and cost effective tool, due to its capability in precise estimation of the extent and permeability of the smear zone in the early stages of constructing the trial embankment. In this study, the proposed systematic back calculation procedure was extended to determine the minimum degree of consolidation (i.e. the minimum waiting time after constructing the trial embankment), and accurately predict the properties of the smear zone. The numerical results of the simulated case studies were used to conduct the analyses. Accordingly, it is found that the extent and permeability of the smear zone can be predicted very well with the proposed calculation procedure when at least 33% of predicted final settlement has been reached (i.e. 33% of the degree of consolidation)

Behaviour of soft soil improved with vertical drain accelerated preloading incorporating visco-plastic deformation

University of Technology, Sydney. Faculty of Engineering and Information Technology.Creep also known as time dependant viscous behaviour of soil is a significant part of the soft soil settlement, which may cause substantial deformation in the long-term. Post-construction settlement of soft soils can be significant throughout the life time of the structure. Consequently, to minimise the post-construction deformation and improve the bearing capacity and the shear strength of the soft soil deposits, preloading combined with vertical drains is frequently used as a ground improvement technique. Soil disturbance induced by the installation of vertical drains results in reducing the horizontal soil permeability and the shear strength in the disturbed zone. Thus, the soil disturbance contributes to the reduced hydraulic conductivity and overconsolidation ratio (OCR) of the soil in the vicinity of drains, influencing soil deformation. Based on the available literature, there is a lack of understanding with respect to the combined effects of the overconsolidation ratio and the hydraulic conductivity profiles in disturbed zone and the nonlinear visco-plastic behaviour of soft soils. These combined effects influence the creep parameters and the settlement rate and accordingly deformation of soft soils improved using vertical drains assisted preloading. In this research, the elastic visco-plastic model has been incorporated in the consolidation equation to investigate the effects of soil disturbance induced by the installation of vertical drains on the long term performance of soft soil deposits. The elastic visco-plastic model consists of a nonlinear creep function with a creep strain limit. The applied elastic visco-plastic model is based on the framework of the modified Cam-Clay model, capturing the soil creep during the excess pore water pressure dissipation. Finite difference formulations for fully coupled one dimensional axisymmetric consolidation have been adopted to model the time dependent behaviour of the soft soil, combining both vertical and radial drainage. Crank-Nicholson scheme is applied in formulating the finite difference procedure, since this scheme uses two steps in partial differentials of pore water pressure over distance, stabilising the process quicker. An array of laboratory tests were carried out using Oedometer and small and large Rowe cells apparatus to verify the developed numerical code for the axisymmetric solution. The Oedometer tests were conducted to choose the soil mixtures for disturbed and intact zones. Two sets of small Rowe cell tests were carried out on selected soil mixes to obtain the elastic visco-plastic model parameters. A large Rowe cell was used to carry out the vertical drain assisted consolidation tests by installing a vertical drain in the centre of the cell. To simulate the disturbed zone for the area surrounding the vertical drain, a different mix with reduced permeability was used. A compacted sand column covered with flexible porous geotextile was installed in the centre to simulate the vertical drain. The cell is fully instrumented and consists of a vertical displacement gauge at the surface level and nine pore water pressure transducers on the sides and at the base of the cell. Comparison of laboratory measurements and numerical predictions shows that the proposed finite difference procedure incorporating the elastic visco-plastic soil behaviour is appropriate for the consolidation analysis of preloading with vertical drains. Two case studies of vertical drains assisted preloading were numerically simulated to investigate the effects of soil disturbance caused by the installation of vertical drains. Different variations of the overconsolidation ratio and hydraulic conductivity in the disturbed zone in combination with time dependant behaviour of soft soils were considered. Different OCR and initial hydraulic conductivity profiles in the disturbed and transition zones result in various visco-plastic strain rates and creep strain limits. Consequently, the induced changes in visco-plastic strain rate and creep strain limit influence the settlement rate at any given time. Therefore, the selection of OCR and initial hydraulic conductivity profile in the disturbed zone has a significant effect on selecting unloading time and therefore the post construction settlement. It was observed that the creep coefficient and the creep strain limit vary during loading and unloading and also during excess pore water pressure dissipation. The creep coefficient and the creep strain limit are functions of the vertical effective stress and time. The proposed solution can readily be used by practicing engineers considering layered soil deposits, time dependent loading and unloading, while incorporating combined effects of soil disturbance and visco-plastic behaviour

English Language Learning Beyond the Borders: Constructing E-Collaborative Learning between Students of Different Regions

The continuous claim about the unsatisfactory performance of Malaysian graduates during interviews and at workplace in relation to their communication skills in English is alarming. This raises questions about the extent to which future workforce is prepared for this globalised world which requires them to interact and collaborate with individuals not only from their own country but also from other countries. At higher learning institutions, many English language educators face challenges in creating language learning environment that supports intercultural communication. In preparing future workforce for international communication, English language teaching and learning needs to go beyond the four walls of a classroom, over to other regions. An alternative to provide such language learning environment is by designing e-collaborative learning that provides opportunities for language learners to learn the language with students from other countries in a meaningful way. This paper showcases the impacts of e-collaborative English language learning conducted between engineering students of one technical university in Malaysia and one higher learning institution in Bordeaux, France for about one semester. At the end of the semester, the students from both countries wrote a reflection of their experience. The data from the reflective writing were analysed using thematic analysis to highlight the impacts of the e-collaborative learning on students' intercultural communicative competence. This study highlights key considerations to structure e-collaborative language teaching and learning among students of different regions

Numerical analysis to quantify the influence of smear zone characteristics on preloading design in soft clay

In this paper, the effects of uncertainties of smear zone characteristics induced by installation of prefabricated vertical drains on the preloading design are numerically investigated. FLAC 2D finite difference software with additional developed subroutines has been employed to conduct the numerical simulations. The finite difference analyses have been verified using a case study. Furthermore, a comprehensive parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Results of this study indicate that the assumptive properties for smear zone characteristics may result in inaccurate predictions of ground deformations and pore water pressures. This may lead to early removal of the surcharge in the construction process causing excessive post construction settlement. It is recommended to practising engineers to use results of trial preloading to back calculate the required smear zone characteristics in the early stages of embankment construction to optimize the design

アツミツカテイ ニ ショウジル ジバン ノ フキンイツセイ ノ エイキョウ オ コウリョ シタ アツミツ ケイサンホウ

博士（工学）佐賀大

Predictions and observations of soft clay foundations stabilized with geosynthetic drains and vacuum surcharge

This chapter starts with an introduction of a revised analytical model of radial drainage with vacuum preloading in both axisymmetric and plane strain conditions. Observed from large-scale radial drainage consolidation tests, the influence of vacuum pressure distribution along the drain length is examined through the dissipation of average excess pore pressure and associated settlement. The details of an appropriate conversion procedure by transforming permeability and vacuum pressure between axisymmetric and equivalent plane strain conditions are described through analytical and numerical schemes. The effects of the magnitude and distribution of vacuum pressure on soft clay consolidation are investigated on the basis of average excess pore pressure, consolidation settlement, and time analyses. The writers describe a multi-drain plane strain finite element method analysis based on permeability conversion, which is employed to study the behavior of embankments stabilized at the site of the Second Bangkok International Airport with vacuum-assisted prefabricated vertical drains. In the field, a constant suction head is not always stable because of the occurrence of air leaks; therefore the magnitude of applied vacuum pressure was adjusted accordingly. The theoretical (numerical) predictions are compared with measured field data such as settlements, excess pore pressures, and lateral movements. The case history analysis employing the writers’ model indicates improved accuracy of the predictions in relation to the field observations. The data indicate that the efficiency of the prefabricated vertical drains depends on the magnitude and distribution of vacuum pressure as well as on the extent of air leak protection provided in practice