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Research Paper (postgraduate) from the year 2022 in the subject Engineering - Mining Engineering, , language: English, abstract: This study used non-experimental approaches to evaluate the shear strength of unsaturated soil. Numerous reasons exist for considering non-experimental approaches acceptable for determining the shear strength of unsaturated soils. One of the primary reasons why non-experimental techniques might be regarded a viable option is because performing tests to determine the shear soils is a complicated and time-consuming operation. Typically, the technique entails a number of operations that need specialized equipment and the execution of methodical stages. If the findings are required quickly, the time necessary to obtain them might be harmful to the entire operation. Due to the fact that engineering processes frequently need fast results, experimental approaches may not be effective in certain circumstances.
Unsaturated Soils: Advances in Geo-Engineering comprises 136 contributions from leading international researchers and practitioners, presented at the First European Conference on Unsaturated Soils (Durham, UK, 2-4 July 2008). The papers report on the latest advances in geo-engineering aspects of unsaturated soils. It is the first collection to focu
The triaxial test has been extensively used to evaluate both saturated and unsaturated soil behaviors. The conventional triaxial test apparatus for saturated soils cannot be used to test unsaturated soils due to difficulties in soil volume and suction measurement. In 1961, a suction-controlled triaxial test apparatus was developed to investigate behavior of unsaturated soils. Since this development, the suction-controlled test has been widely used for unsaturated soil characterization. Most important concepts concerning unsaturated soil mechanics were developed based upon results from suction-controlled tests. However, the suction-controlled triaxial test on unsaturated soils, which is a drained test, is usually laborious, time-consuming, and costly, and may not be justifiable for routine engineering projects. The constant water content (undrained) test has been widely used to investigate saturated soil behaviors. However, for unsaturated soils, due to difficulties in direct, rapid, and reliable suction measurement, the constant water content test was rarely used for unsaturated soil behavior evaluation. In addition, accurate volume change measurement of unsaturated soils was a great challenge for researchers. Recently, the Modified State Surface Approach (MSSA) has been developed to calibrate unsaturated soil behaviors. According to MSSA, both results from suction-controlled and constant water content triaxial tests can be used for constitutive behavior calibration on unsaturated soils. In this study, a new triaxial test system was developed to investigate unsaturated soil behaviors through constant water content triaxial tests. To measure soil suction variation during testing, a new type of high-suction tensiometer was developed based on a commercial miniature pressure transducer. A 15 bar air-entry ceramic disc was used as the filter of the high-suction tensiometer. After saturation and calibration, this new type of high-suction tensiometer could be utilized for matric suction measurement on unsaturated soils with a maximum measurable suction up to 1100 kPa determined via a free evaporation test. To measure the volume change of unsaturated soils during triaxial testing, a photogrammetry-based method was developed by integrating photogrammetry, optical-ray tracing, and least-square estimation techniques. Through two validation tests on a stainless steel cylinder and a saturated sand specimen, the average point and total volume change measurement accuracy were determined to be approximately 0.065 mm and 0.05%, respectively. With this method, the conventional triaxial test apparatus for saturated soils can be used for triaxial testing on unsaturated soils without any modification. In addition to total volume change measurement, the newly developed photogrammetry-based method can also be used to investigate the deformation characteristics of soils during triaxial testing such as full-field deformation, volumetric strain non-uniformity, full-field strain distribution, and shear band evolution process. To evaluate the performance of the new triaxial testing system, a series of constant water content triaxial tests were carried out on unsaturated soils. New methods were proposed to characterize shear strength of the tested unsaturated soils. Also, an example was given to calibrate the constitutive behavior of an unsaturated soil based on results from the constant water content triaxial tests. Analysis results indicated that the proposed triaxial testing system is a cost effective and time efficient alternative to the suction-controlled triaxial testing system. In geotechnical and highway engineering, many projects involve unsaturated soils at shallow depths with low confining stresses (less than 100 kPa). To investigate the behavior of unsaturated soils at low confining stresses, the new triaxial testing system was simplified to a modified unconfined compression testing system. In this simplified system, negative air pressure (i.e., vacuum pressure) was used to provide the low confining stress for the triaxial tests. The high-suction tensiometers were used to monitor soil matrix suction variation during testing. A photogrammetric method was utilized for deformation measurements of unsaturated soils during triaxial testing. A series of undrained triaxial tests was also carried out to demonstrate the use of the modified unconfined compression testing system for unsaturated soil behavior evaluation under different confining stresses.
This book comprises selected proceedings of the International Conference on Recent Advancements in Civil Engineering and Infrastructural Developments (ICRACEID 2019). The contents are broadly divided into five areas (i) smart transportation with urban planning, (ii) clean energy and environment, (iii) water distribution and waste management, (iv) smart materials and structures, and (v) disaster management. The book aims to provide solutions to global challenges using innovative and emerging technologies covering various fields of civil engineering. The major topics covered include urban planning, transportation, water distribution, waste management, disaster management, environmental pollution and control, environmental impact assessment, application of GIS and remote sensing, and structural analysis and design. Given the range of topics discussed, the book will be beneficial for students, researchers as well industry professionals.
The shear strength behavior of unsaturated soils is a complex phenomenon. The major factors that lead to the complex behavior are grain size, natural alteration in status of moisture and associated capillary potential. The need for research is felt to understand the various aspects associated with development of shear strength of unsaturated soils. The research is conducted to obtain the most economical and reliable design solutions. The magnitude of positive pore water pressure developed in saturated soil reduces the shear strength to a great extent. The tensile pore water pressure in the capillary meniscus developed around the soil grain contacts, on the contrary, enhances the factor of safety in the case of unsaturated soil mass. In this research, the shear strength of unsaturated soil is studied for a range of saturation based on the parametric study. The principle of effective stress has proven to be the basis for understanding the shear strength of saturated soil mass and it has provided an explanation for the geotechnical engineering problems. The thesis presents a study on the shear strength of the soil specimen using the direct shear apparatus. The previous research was mainly directed towards evaluation of shear strength under controlled soil suction, by modifying the apparatus. A simple technique is put forward in this research by making use of the conventional direct shear apparatus for testing the unsaturated soil. The suction stress was induced in the soil specimen and the shear strength was evaluated. The soil water characteristic curve has been used in the research to determine the tensile pore water pressure. Hypothesis based on parametric study has been put forward to present a technique to determine the unsaturated soil shear strength parameter in the thesis.
This volume presents the work of postgraduate and postdoctoral researchers on unsaturated soil mechanincs. Topics covered include: innovative experimental techniques; new experimental data on compacted, collapsible and swelling soils; and advances in constitutive modelling.
The testing of unsaturated soils requires greater care and effort than that of saturated soils. Although unsaturated soil mechanics has been embraced by geotechnical engineering, engineering practice has not yet caught up as the characterization of unsaturated soils is difficult and time-consuming, and made harder still by a lack of standards. Laboratory Tests for Unsaturated Soils collates test procedures to cover all laboratory tests for characterising unsaturated soils. It covers the background, theory, test procedures, and interpretation of test results. Each test procedure is broken down into simple stages and described in detail. The pitfalls of each test and the interpretation of the test results are explained. Test data and calculation methods are given, along with many numerical examples to illustrate the methods of interpretation and to offer the presentation of typical results. The book is especially useful for students and researchers who are new to the field and provides a practical handbook for engineering applications.
These volumes contain the contributions to the Second European Conference on Unsaturated Soils, E-UNSAT 2012, held in Napoli, Italy, in June 2012. The event is the second of a series of European conferences, and follows the first successful one, organised in Durham, UK, in 2008. The conference series is supported by Technical Committee 106 of the International Society of Soil Mechanics and Geotechnical Engineering on Unsaturated Soils. The published contributions were selected after a careful peer-review process. A collection of more than one hundred papers is included, addressing the three thematic areas experimental, including advances in testing techniques and soil behaviour, modelling, covering theoretical and constitutive issues together with numerical and physical modelling, and engineering, focusing on approaches, case histories and geo-environmental themes. The areas of application of the papers embrace most of the geotechnical problems related to unsaturated soils. Increasing interest in geo-environmental problems, including chemical coupling, marks new perspectives in unsaturated soil mechanics. This book will provide a valuable up-to-date reference across the subject for both researchers and practitioners.