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In this study experimental and numerical investigations have been carried out with the emphasis on studying the behaviour and liquefaction state of typical silty sand sampled from the Mekelle area in Ethiopia under monotonic and cyclic undrained loadings. Experiments have been carried out to measure the pore pressure accumulation, deformation characteristics and related effective stress paths. A numerical model was then used to simulate the behaviour and liquefaction state associated with the changes in the stress-strain-pore pressure levels by means of the finite element method (FEM) using the FE code Tochnog (Tochnog Professional Company 2021).
This book presents 09 keynote and invited lectures and 177 technical papers from the 4th International Conference on Geotechnics for Sustainable Infrastructure Development, held on 28-29 Nov 2019 in Hanoi, Vietnam. The papers come from 35 countries of the five different continents, and are grouped in six conference themes: 1) Deep Foundations; 2) Tunnelling and Underground Spaces; 3) Ground Improvement; 4) Landslide and Erosion; 5) Geotechnical Modelling and Monitoring; and 6) Coastal Foundation Engineering. The keynote lectures are devoted by Prof. Harry Poulos (Australia), Prof. Adam Bezuijen (Belgium), Prof. Delwyn Fredlund (Canada), Prof. Lidija Zdravkovic (UK), Prof. Masaki Kitazume (Japan), and Prof. Mark Randolph (Australia). Four invited lectures are given by Prof. Charles Ng, ISSMGE President, Prof.Eun Chul Shin, ISSMGE Vice-President for Asia, Prof. Norikazu Shimizu (Japan), and Dr.Kenji Mori (Japan).
This conference brought together specialists in cyclic soil behaviour in order to discuss important results and new ideas in the field, and to share expertise in design of various problems involving cyclic or dynamic behaviour of soils. This book covers a variety of topics: * Theory and analysis, including constitutive relations of soil under cyclic loading, post-seismic stability analysis of soil/structure, dynamic stability of structures, liquefaction analysis of marine structures due to cyclic loading, and more * Cyclic and dynamic laboratory and model testing, centrifuge testing and in-situ testing. * Numerical analysis, including computer methods * Design of industrial applications and marine structures, installation methods of piles, vibrocompaction, densification of ballast in railway structures, case studies of earthquakes and post-liquefaction observations.
In the last few years, many studies have focused on the behavior of unsaturated sands subjected to dynamic loading. Despite some achievements, much remains unclear about the behavior of unsaturated soil such as: (i) the behavior before and after the main shock and the effect of foreshocks on the liquefaction potential; (ii) the effect of the saturation degree on the CSR (cyclic stress ratio); (iii) in the case of dense soils, what is the effect of unsaturation on the CSR-number of cycles relationship to reach liquefaction? This research work tries to provide some answers to these questions.Two groups of tests were carried out by triaxial dynamic apparatus to survey the sand mechanical behavior when subjected to cyclic loading as well as the residual strength after liquefaction under monotonic loading. All the samples were prepared by the wet tamping method. The vacuum method was used to control the saturation degree of the samples. Then, the Skempton parameter B was used to evaluate the saturation degree of the samples. After that, sample consolidation and cyclic loading were conducted step by step. After that the samples was subjected to the cyclic loading to study the liquefaction and then the monotonic loading to study the residual strength.The results of cyclic loading process show that the liquefaction susceptibility is directly proportional to the sample saturation degree. The results of the monotonic loading show that the strength of sand recuperates when the pore water pressure dissipates after liquefaction.Besides, the experimental protocol established in this study has handled well the main challenges of the unsaturated soil liquefaction tests.
These proceedings are a continuation of the series of International Conferences in Germany entitled "Mechanics of Unsaturated Soils." The objective is to discuss and understand unsaturated soil behaviour, so that engineered activities are improved in terms of judgement and quality. In addition to knowledge of classical concepts, it is a challenge to adapt convincing new concepts and present them in such a way that they can be used in engineering practices.
The objectives of this dissertation are to measure and calculate surface free energies of soil particles, to understand the mechanical behavior of unsaturated silty sand through first studying the stress-strain relationship, the effects of matric suction and pore water chemistry and second to interpret the behavior by the critical state frame work, to develop a method to predict cone tip resistance in unsaturated soils, and to present the concept of pseudo strain and dissipated pseudo strain energy. Universal Sorption Device (USD) is developed to measure surface free energies of soil particles. The test results on a soil sample shows that specific surface area increased with decreasing particle size. The components of surface free energies and the work of adhesion increased with decreasing particle size. A servo controlled triaxial testing device is developed to test 15.24 cm in height and 7.62 cm in diameter, recompacted specimens of unsaturated soil under varying matric suction and different pore chemistry. During the test, the matric suction is maintained constant. Results from the triaxial drained tests are used for validation of the constitutive models proposed by Alonso et al. (1990). Predictions from the model are in good agreement with experimental results. The critical state model for unsaturated soil is used to calculate cone tip resistance in unsaturated silty sand. The calculated cone tip resistance is used to evaluate the liquefaction potential of unsaturated soils. The results from the stress based liquefaction potential analysis reveal that even in an unsaturated condition soil is susceptible to liquefaction. By applying the pseudo strain concept, it is possible to account for the viscous resistance of water during cyclic loading. The results of undrained cyclic triaxial tests are used to calculate pseudo-strain and dissipated pseudo strain energy. The results of calculated dissipated pseudo strain energy suggest that the effect of initial matric suction is evident. On the other hand, the effect of surface tension increase or decrease due to existence of chemical on the pore water is negligible.