Geosynthetic Encased Columns For Soft Soil Improvement

The geosynthetic encased column (GEC) is a relatively recent method developed for soft soil improvement. The method was firstly introduced as a concept in the 1980s and first practical applications started in the 1990s. GECs have been widely used in some parts of the world for the last three decades. However, there is no book in the literature summarizing the knowledge accumulated during this period in relation to this soft ground improvement technique. The purpose of this book is to provide readers with the GEC fundamentals and practical applications. Chapter 1 presents the general principles of this ground improvement technique including the methods used for GEC installation and how the material properties may be selected. Chapter 2 presents the design methods, thus settlement calculations by means of analytical methods and stability calculations by limit equilibrium methods are explained in detail. Chapter 3 presents calculation examples illustrating the usual steps to be done for both service limit state and ultimate limit state designs. Then field performances exemplifying practical applications of the GEC technique are presented in Chapter 4 for some case histories. Following numerical analyses, often used in design to complement analytical methods, are presented in Chapter 5. Annexes I and II at the end contain the charts developed to perform settlement calculations. The book combines the experiences of four authors with different academic and industry backgrounds to describe GEC design and performance. It is aimed at civil engineers in general, particularly geotechnical engineers, either working in design or in practice, at graduate students, and at senior undergraduate students.

The geosynthetic encased column (GEC) is a relatively recent method developed for soft soil improvement. The method was firstly introduced as a concept in the 1980s and first practical applications started in the 1990s. GECs have been widely used in some parts of the world for the last three decades. However, there is no book in the literature summarizing the knowledge accumulated during this period in relation to this soft ground improvement technique. The purpose of this book is to provide readers with the GEC fundamentals and practical applications. Chapter 1 presents the general principles of this ground improvement technique including the methods used for GEC installation and how the material properties may be selected. Chapter 2 presents the design methods, thus settlement calculations by means of analytical methods and stability calculations by limit equilibrium methods are explained in detail. Chapter 3 presents calculation examples illustrating the usual steps to be done for both service limit state and ultimate limit state designs. Then field performances exemplifying practical applications of the GEC technique are presented in Chapter 4 for some case histories. Following numerical analyses, often used in design to complement analytical methods, are presented in Chapter 5. Annexes I and II at the end contain the charts developed to perform settlement calculations. The book combines the experiences of four authors with different academic and industry backgrounds to describe GEC design and performance. It is aimed at civil engineers in general, particularly geotechnical engineers, either working in design or in practice, at graduate students, and at senior undergraduate students.

Some normally consolidated soft soils manifest strength sensitivity, ie these soil manifest strain softening when shear in an undrained mode. These soils, referred to as sensitive soft soils, have the typical features of strain hardening in drained shearing and strain softening in undrained shearing. The consolidation lines of these soils are also curved (concave upwards) in the semi-log space. However, under high consolidation stress or upon large shearing, these soils re-gain the features of re-constituted soil. Ground improvement methods like stone columns were reported as not effective when installed in the sensitive soft clays. But mechanism of the un-effectiveness of the stone columns remains unknown because of lack of a suitable and simple model for simulating the stress-strain behaviours of sensitive soft soils. Although these soils have a meta-stable micro-structure, models that developed for simulating structured firm soils are not suitable for simulating sensitive soft soil features. Thus, a new model was formulated. The new model can degenerate back to a Modified Cam Clay model. The ability of new model in simulating a range of behaviour was verified by using the finite difference (FD) method in solving the partial differential equations of the soil model for a range of tri-axial test conditions. The model was further implemented in coupled analysis formulation and coded into FEM program AFENA. Various cases with different soil parameters were then simulated and compared with the FD solutions for various triaxial tests so as to check the stability of the FEM code. The coupled FEA was then used to simulate the performance of geosynthetic-encased stone columns. A new stone column element and a geo-encasement element were developed and coded into AFENA. The stone column simulations were then done for both non-sensitive soils (represented by Modified Cam Clay model) and sensitive soft soil (represented by the new model). Parametric study was conducted to examine the performance of the geo-encased stone columns in both types of soils. Furthermore, two different installation methods: wished-in installation and full displacement installation were studied numerically. Cross comparison was done to investigate how the sensitive soft soil features interact with the installation method in affecting the performance of the geo-encased stone columns. A range of factors that influence the geosynthetic-encased stone columns performance installed in soft soils were also made clear.

Embankment construction projects on very soft soil often give rise to serious problems. This volume on geotechnics and soft soil engineering therefore treats all phases of the design and construction process exhaustively, from the first investigation step to the monitoring of constructed work. The book presents the development concepts necessary fo

Geosynthetics in Civil and Environmental Engineering presents contributions from the 4th Asian Regional Conference on Geosynthetics held in Shanghai, China. The book covers a broad range of topics, such as: fundamental principles and properties of geosynthetics, testing and standards, reinforcement, soil improvement and ground improvement, filter and drainage, landfill engineering, geosystem, transport, geosynthetics-pile support system and geocell, hydraulic application, and ecological techniques. Special case studies as well as selected government-sponsored projects such as the Three Gorges Dam, Qinghai-Tibet Railway, and Changi Land reclamation project are also discussed. The book will be an invaluable reference in this field.

Gain a stronger foundation with optimal ground improvement Before you break ground on a new structure, you need to analyze the structure of the ground. Expert analysis and optimization of the geo-materials on your site can mean the difference between a lasting structure and a school in a sinkhole. Sometimes problematic geology is expected because of the location, but other times it's only unearthed once construction has begun. You need to be able to quickly adapt your project plan to include an improvement to unfavorable ground before the project can safely continue. Principles and Practice of Ground Improvement is the only comprehensive, up-to-date compendium of solutions to this critical aspect of civil engineering. Dr. Jie Han, registered Professional Engineer and preeminent voice in geotechnical engineering, is the ultimate guide to the methods and best practices of ground improvement. Han walks you through various ground improvement solutions and provides theoretical and practical advice for determining which technique fits each situation. Follow examples to find solutions to complex problems Complete homework problems to tackle issues that present themselves in the field Study design procedures for each technique to simplify field implementation Brush up on modern ground improvement technologies to keep abreast of all available options Principles and Practice of Ground Improvement can be used as a textbook, and includes Powerpoint slides for instructors. It's also a handy field reference for contractors and installers who actually implement plans. There are many ground improvement solutions out there, but there is no single right answer to every situation. Principles and Practice of Ground Improvement will give you the information you need to analyze the problem, then design and implement the best possible solution.

Conventional stone columns are commonly used as a form of ground improvement in soft soils, for the support of lightly and moderately loaded structures such as embankments. However, their use in very soft and extremely soft soils is limited by the low stiffness and minimal confinement provided by the soft soil. To extend their use to such soft soils, a method of geotextile encasement has recently been developed, providing additional circumferential confinement. The technique has been used on numerous projects throughout Europe and more recently in South America. Although geotextile encasement provides a practical form of ground improvement, its use can be limited in some cases by excessive settlements, resulting from the adopted materials and installation practices. To investigate the potential benefits of using a stiffer encasement than geotextile (and to broaden the appeal of geosynthetics in ground improvement), the use of geogrid encasement is investigated.The research presented in this thesis was used to investigate practical aspects of geogrid encasement including developing effective and efficient methods of encasement construction and assessment of encased column performance. The research was undertaken using a four-stage approach comprising small-scale laboratory testing, numerical simulation of small-scale tests, medium-scale laboratory testing and scaled-up numerical modelling of full-scale columns. Small-scale testing was undertaken on isolated and simulated group columns to investigate whether the full-length of the column needed to be encased, the impact of geogrid stiffness and methods of constructing the encasement. Numerical modelling was undertaken using the PLAXIS software package and was initially used to reproduce the small-scale test results. Following this, the models were scaled up to investigate the impact of different parameters on full-scale encased column behaviour. Medium-scale testing of unconfined columns was used to investigate methods of encasement construction including the suitability of different geogrids and stone column aggregates.The research indicates that geogrid encasement can be constructed at relatively low cost and most effectively by constructing sleeves with a full circumference of overlap, fixed in position using cable ties. The technique relies on interlock between the overlapped section of geogrid and protruding aggregate to provide a level of fixity similar to welding. Biaxial geogrids provide the stiffest and most reliable encasement material, particularly when used with typical stone column aggregates.Based on the results of modelling and testing, geogrid encased columns are expected to reduce untreated settlements by between 50% and 95%, depending on properties such as geogrid stiffness, column density, soil stiffness and encased length. By progressively increasing the replacement ratio, geogrid stiffness and the encased length of a column, the stiffness of the treated soil mass may be steadily increased. Although the research indicates that geogrid encasement is likely to provide a stiffer alternative to geotextile, site testing is recommended to confirm some aspects of performance, including installation techniques.

The book reviews recent developments and research results on excavations and foundations found in and on soft soil deposits. It gives an overview of the material properties of soft soils and offers new foundation improvement techniques in road and railways. It also examines different types of foundations and stabilization methods. The book will serve both practicing and research engineers in the field of geotechnical engineering.

Conventional stone columns are commonly used as a form of ground improvement in soft soils, for the support of lightly and moderately loaded structures such as embankments. However, their use in very soft and extremely soft soils is limited by the low stiffness and minimal confinement provided by the soft soil. To extend their use to such soft soils, a method of geotextile encasement has recently been developed, providing additional circumferential confinement. The technique has been used on numerous projects throughout Europe and more recently in South America. Although geotextile encasement provides a practical form of ground improvement, its use can be limited in some cases by excessive settlements, resulting from the adopted materials and installation practices. To investigate the potential benefits of using a stiffer encasement than geotextile (and to broaden the appeal of geosynthetics in ground improvement), the use of geogrid encasement is investigated. The research presented in this thesis was used to investigate practical aspects of geogrid encasement including developing effective and efficient methods of encasement construction and assessment of encased column performance. The research was undertaken using a four-stage approach comprising small-scale laboratory testing, numerical simulation of small-scale tests, medium-scale laboratory testing and scaled-up numerical modelling of full-scale columns. Small-scale testing was undertaken on isolated and simulated group columns to investigate whether the full-length of the column needed to be encased, the impact of geogrid stiffness and methods of constructing the encasement. Numerical modelling was undertaken using the PLAXIS software package and was initially used to reproduce the small-scale test results. Following this, the models were scaled up to investigate the impact of different parameters on full-scale encased column behaviour. Medium-scale testing of unconfined columns was used to investigate metho.

The book comprises select proceedings of the 2016 annual conference of the Indian Geotechnical Society (IGC 2016), with technical papers on the theme “Ground Improvement and Geosynthetics”. The papers cover a wide range of topics, including chemical modification using admixtures, microbial-induced carbonate precipitation, geopolymers, fly ash and other industrial wastes, modification using geosynthetic materials such as natural and synthetic fibers, expanded polystyrene (EPS) geofoam, prefabricated vertical drains, geosynthetic encased-granular columns and mechanical densification through sand columns. This book is a valuable reference for researchers and practicing engineers alike.