With growing infrastructure developments in hilly areas and due to
economical constraints of using locally available rockfill materials for construction of embankments, practicing engineers must be acquainted with geotechnical response of non-conventional granular soils. These materials are most likely to disintegrate with time due to physical and chemical weathering. In general, the laboratory investigations on durability characteristics of such materials are only made through simple slaking tests. However, studies examining the effects of slaking-induced disintegration of soil grains on the
geotechnical engineering analysis and design parameters are rather limited. This is essentially due to the reason that the grains of standard laboratory sands are mostly durable and hence, the stress-strain response is considered to be unaffected by the presence of water.
In order to explore the possible effects of deterioration of soil grains on static and dynamic properties of granular soils, a series of consolidated drained torsional shear tests on various crushed soft rocks were performed under saturated and dry conditions and compared with a well reported Toyoura silica sand consisting of durable grains. Due to the sensitivity of crushed rockfill to
deteriorate upon water-submergence, test under dry conditions represented the response of a soil with intact grains, whereas a similar test under saturated condition simulated the potential reduction in strength and stiffness of the soil with time. From the grain size distributions determined after each test, a degradation index was defined to quantify the degree of disintegration of grains.
Strength and deformation properties determined from monotonic as well as cyclic shear tests were then compared with this index. Possible correlations of water-induced deterioration of soil grains with consolidation behaviour, peak shear strengths, friction angles, dynamic shear stiffness, and volume-change characteristics during shearing were explored. In addition, the effects of confining stress and shear strain level on particle breakage were also investigated.
It was concluded that time-dependent characterization of rockfill materials by monitoring the degree of deterioration can be helpful to avoid catastrophic geotechnical failures. Nonetheless, this study is a caution to conventional soil mechanics in which decay of grains and loss of soil strength with time are often uncared.
Table of Contents
CHAPTER 1 Research Curriculum
1.1 General
1.2 Problem Statement and its Significance
1.3 Objectives and Specific Aims
1.4 Scope of the Work and Limitations
1.5 Duration and Place of this Research
1.6 Thesis Organization
CHAPTER 2 Literature Review
2.1 Introduction
2.2 Response Analysis of Granular Soils
2.2.1 Time-dependent behavior
2.2.2 Laboratory studies on particle breakage and constitutive modeling of grain crushing
2.2.3 Effects of water on mechanical response of granular soils
2.3 Geotechnical Engineering and Geology
2.3.1 The geotechnics of crushed soft rocks
2.3.2 Modeling of weathering-induced degradation of soft rocks
2.4 Other Concerns in Geotechnical Engineering
2.5 Concluding Remarks
CHAPTER 3 Experimental Setup
3.1 Introduction
3.2 Background of Hollow Cylinder Devices
3.3 Advantages of Torsional Shear
3.4 General Description of the Apparatus
3.4.1 The hollow torsional cell
3.4.2 Loading system
3.4.3 Measuring system
3.5 Stress and Strain Components in Hollow Cylindrical Specimens
3.5.1 Stress components
3.5.2 Correction of stress components for membrane forces
3.5.3 Calculation of principal stresses
3.5.4 Strain components
3.5.5 Summary of stress-strain formulation in hollow cylinders
3.6 Calibration of Loading and Measuring Systems
3.7 Torsional Shear Test Procedure
3.7.1 Materials
3.7.2 Sample preparation method
3.7.3 HCTS test steps
3.8 Summary
CHAPTER 4 Materials and Methodology
4.1 General
4.2 Materials
4.2.1 Sampling sites
4.2.2 Material preparation
4.2.3 Physical properties of test materials
4.2.4 Quantification of particle disintegration
4.3 Choice of the Apparatus
4.4 Research Methodology
4.4.1 Experimental program
4.4.2 General experimental procedure and stress paths
4.5 Definition of Various Terms
4.6 Summary
CHAPTER 5 Experimental Phase - I: Monotonic Torsional Shear
5.1 Introduction
5.2 Parameters for Comparison of Test Results
5.3 Illustration of Test Conditions
5.4 Experimental Results on Toyoura Sand
5.4.1 Consolidation behavior of TS specimens
5.4.2 Monotonic torsional shear response of TS specimens
5.4.3 Failure envelopes of TS specimens
5.4.4 Shear banding and failure mode of TS specimens
5.5 Test Results on Crushed Sandy Mudstone – HB
5.5.1 Saturation response of HB specimens
5.5.2 Consolidation behavior of HB specimens
5.5.3 Stress-strain and volume-change response of HB specimens
5.5.4 Failure envelopes of HB specimens
5.5.5 Deterioration of soil grains of HB specimens
5.5.6 Shear banding and failure mode of HB specimens
5.6 Test Results on Crushed Massive Mudstone – DS
5.6.1 Saturation response of DS specimens
5.6.2 Consolidation behavior of DS specimens
5.6.3 Stress-strain and volume-change response of DS specimens
5.6.4 Failure envelopes of DS specimens
5.6.5 Deterioration of soil grains of DS specimens
5.6.6 Shear banding and failure mode of DS specimens
5.7 Test Results on Crushed Dolomitic Limestone – GN
5.7.1 Saturation response of GN specimens
5.7.2 Consolidation behavior of GN specimens
5.7.3 Stress-strain and volume-change response of GN specimens
5.7.4 Failure envelopes of GN specimens
5.7.5 Deterioration of soil grains of GN specimens
5.7.6 Shear banding and failure mode of GN specimens
5.8 Test Results on Crushed Sandy Mudstone - YK01
5.8.1 Saturation response of YK01 specimens
5.8.2 Consolidation behavior of YK01 specimens
5.8.3 Stress-strain and volume-change response of YK01 specimens
5.8.4 Failure envelopes of YK01 specimens
5.8.5 Deterioration of soil grains of YK01 specimens
5.8.6 Shear banding and failure mode of YK01 specimens
5.9 Test Results on Crushed Massive Mudstone – YK02
5.9.1 Saturation response of YK02 specimens
5.9.2 Consolidation behavior of YK02 specimens
5.9.3 Stress-strain and volume-change response of YK02 specimens
5.9.4 Failure envelopes of YK02 specimens
5.9.5 Deterioration of soil grains of YK02 specimens
5.9.6 Shear banding and failure mode of YK02 specimens
5.10 Summary of the Test Results
5.11 Concluding Remarks
CHAPTER 6 Experimental Phase – II: Cyclic Torsional Shear
6.1 Introduction
6.2 Experimental Program and Test Conditions
6.3 Cyclic Torsional Shear Tests on Toyoura Sand
6.3.1 Loading history
6.3.2 Consolidation history of TS specimens
6.3.3 Cyclic shear response of TS specimens under Ko=1.0
6.3.4 Cyclic shear response of TS specimens under Ko=0.5
6.4 Cyclic Torsional Shear Tests on Crushed Mudstone
6.4.1 Loading history
6.4.2 Consolidation history of DS specimens
6.4.3 Cyclic shear response of DS specimens under Ko=1.0
6.4.4 Cyclic shear response of DS specimens under Ko=0.5
6.4.5 Effects of cyclic loading on deterioration of soil grains
6.5 Summary
CHAPTER 7 Data Analysis and Interpretation
7.1 General
7.2 Analysis of the Results from Experimental Phase – I
7.2.1 Mechanism of water-induced deterioration
7.2.2 Effects of mineral type on saturation response
7.2.3 Effects of disintegration on particle shape
7.2.4 Quantification of deterioration of soil grains
7.2.5 Degradation index and conventional slake durability test
7.2.6 Correlations of degradation index with consolidation response
7.2.7 Correlations of degradation index with mechanical properties
7.3 Analysis of Results from Experimental Phase – II
7.3.1 Deterioration of soil grains under cyclic loading
7.3.2 Dynamic properties of soils undergoing deterioraion of grains
7.3.3 Volume-change response of crushed rocks to cyclic loading
7.4 Summary
CHAPTER 8 Conclusions and Recommendations
8.1 General
8.2 Conclusions
8.3 Recommendations for Future Research
Research Objectives and Thematic Focus
The primary research objective is to investigate the geotechnical behavior of granular soils that are susceptible to time-dependent degradation, commonly known as "negative aging," due to water-induced particle disintegration. This study seeks to understand how the deterioration of soil grains affects the static and dynamic strength and deformation characteristics of non-conventional granular soils, such as crushed soft rocks, compared to durable conventional sands.
- Mechanisms of water-induced soil grain disintegration and particle breakage.
- Evaluation of strength and deformation properties using consolidated drained torsional shear tests.
- Development of a degradation index to quantify the degree of grain disintegration.
- Influence of saturation, effective confining stress, and loading cycles on soil behavior.
- Comparative analysis of the dynamic shear stiffness and damping ratios of various granular materials.
Excerpt from the Book
1.2 PROBLEM STATEMENT AND ITS SIGNIFICANCE
The geologic changes in soil composition and its engineering properties may require hundreds of thousands of years and over this time the process of soils turning into rocks as well as rock weathering to form soils takes place. In last few decades, it has been realized that there are also changes in the soil properties over a shorter period of time, like few months or years, which are more relevant to engineers. These changes are called aging effects as schematically described in Figure 1.2.
Conventionally, the aging effects have been believed to be positive as shown in Figure 1.3, that is, the increase in strength and stiffness of soils over time under constant effective stresses after deposition. Moreover, in practice of geotechnical laboratory testing on conventional granular soils, the soil grains are usually considered as durable under working stress-strain conditions. However, naturally occurring sedimentary and residual deposits which are generally treated as granular soils in geotechnical engineering, experience time-dependent disintegration of grains due to different environmental conditions associated with loss of strength and stiffness parameters, hereafter referred to as negative aging as shown in Figure 1.4. Such characteristics are common in natural geological materials and have a strong influence on the engineering behavior of granular soils and the description of such effects needs to be included in the conventional concepts of soil mechanics.
Summary of Chapters
CHAPTER 1 Research Curriculum: This chapter introduces the problem of time-dependent geotechnical property changes and outlines the thesis objectives, scope, and limitations regarding the study of granular soil deterioration.
CHAPTER 2 Literature Review: This chapter reviews existing knowledge on granular soil behavior, focusing on time-dependent characteristics, particle breakage, and the impact of saturation on strength properties.
CHAPTER 3 Experimental Setup: This chapter describes the specialized hollow cylinder torsional shear apparatus used for the experimental program, including calibration procedures and the calculation of stress and strain components.
CHAPTER 4 Materials and Methodology: This chapter details the characteristics of the test materials, the preparation of soil specimens, and the overall experimental methodology, including the definition of the proposed degradation index.
CHAPTER 5 Experimental Phase - I: Monotonic Torsional Shear: This chapter presents results from monotonic tests on Toyoura sand and several crushed soft rock specimens, examining saturation effects, consolidation, and failure envelopes.
CHAPTER 6 Experimental Phase – II: Cyclic Torsional Shear: This chapter provides data from multi-stage cyclic loading tests, focusing on the hysteresis behavior and stiffness degradation of the tested soils.
CHAPTER 7 Data Analysis and Interpretation: This chapter synthesizes the results, providing a detailed analysis of the correlations between the degradation index and the mechanical properties of the tested soils.
CHAPTER 8 Conclusions and Recommendations: This chapter provides the final conclusions of the study and proposes potential directions for future research in the field of geotechnical engineering.
Keywords
Torsional shear, Saturation, Time effects, Particle breakage, Soil structure, Shear strength, Crushed soft rocks, Negative aging, Degradation index, Consolidation, Cyclic loading, Geotechnical failures, Mudstone, Stress-strain response, Soil mechanics.
Frequently Asked Questions
What is the core focus of this research?
The research focuses on the "negative aging" of granular soils, where the disintegration of soil grains upon water exposure leads to a loss of strength and stiffness over time.
What are the primary thematic fields covered?
The thesis covers geotechnical engineering, soil mechanics, weathering processes, soft rock geotechnics, and laboratory experimental testing of granular materials.
What is the primary objective of this thesis?
The objective is to elucidate the mechanisms behind the deterioration of non-conventional granular soils and to provide a quantitative index for assessing their strength loss upon submergence.
Which scientific method is employed?
The study utilizes a hollow cylinder torsional shear apparatus to conduct both monotonic and cyclic drained tests on reconstituted soil specimens.
What topics are discussed in the main body?
The main body details the experimental methodology, presents results of monotonic and cyclic tests for various soil types, and provides a comprehensive data analysis of grain deterioration effects.
Which keywords characterize this work?
The work is characterized by terms such as Torsional shear, Negative aging, Particle breakage, Shear strength, and Degradation index.
How is the degradation index defined?
The degradation index (ID) is defined based on the area under initial and final grain size distribution curves, quantifying the change in particle size composition after testing.
How does the presence of water impact the tested crushed rocks?
Water-induced deterioration leads to significant loss of grain strength, resulting in different stress-strain responses compared to dry conditions, including increased volume contraction and reduced shear resistance.
- Quote paper
- Mubashir Aziz (Author), 2010, Experimental Study on Effects of Deterioration of Grains on Deformation and Strength Characteristics of Soils, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/178063
