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Geotechnical Engineering - Vol 2
Explore and master the fundamentals of Geotechnical Engineering - Vol 2
You've not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.Chapter 1
CONSOLIDATION
Civil engineering involves understanding soil behavior under load conditions, particularly the settlement that occurs in saturated soils. This chapter discusses the various types of settlement: immediate, primary consolidation, and secondary consolidation. Each type is influenced by factors such as soil compressibility and permeability, which dictate how soil responds to increased load over time.
Chapter 2
Terzaghi’s Spring Mass Analogy
The chapter discusses Terzaghi’s Spring Mass Analogy as a model for understanding the consolidation process in saturated clay under external load. It highlights the differences in behavior between coarse-grained soils (like sand) and fine-grained soils (like clay) during compression and consolidation due to applied pressure. The role of effective stress and pore water pressure in these processes is examined, shedding light on the time-dependent nature of compression in fine-grained soils compared to immediate compression in sands.
Chapter 3
Compression of Fine Grained Soil
Fine-grained soils exhibit varying compressibility based on their void ratio and effective stress. Experimental analysis reveals distinct behavior during loading and unloading phases, highlighting virgin compression paths and elastic recovery processes. Understanding these behaviors is critical for predicting soil performance in engineering applications.
Chapter 4
Terzaghi’s 1D Consolidation Equation
The chapter discusses the principles of Terzaghi's one-dimensional consolidation theory, focusing on the assumptions that the soil medium is saturated, isotropic, and homogeneous while following Darcy's law. It explains the concept of volume change in soil due to consolidation and outlines limitations of the one-dimensional model such as constant permeability and assumptions of three-dimensional flow. The chapter concludes with Terzaghi's solution indicating consolidation progress with time and depth, emphasizing the importance of average degree of consolidation in practical applications.
Chapter 5
Compressibility Properties
The chapter discusses compressibility properties and their significance in various scientific and engineering applications. It delves into the relationships between different materials under pressure and how these relationships can be quantified effectively. A thorough examination of swelling indexes and other related measurements provides essential insights into material behavior under stress conditions.
Chapter 6
Preconsolidation Pressure
The chapter provides an overview of preconsolidation pressure, the maximum effective stress experienced by soil throughout its stress history, and classifies soils based on their stress history: normally consolidated, over consolidated, and under consolidated soils. The behavior of these soils under various loading conditions and their implications for structural integrity are emphasized.
Chapter 7
Determination of coefficient of consolidation (Cv) from laboratory data
The chapter discusses the determination of the coefficient of consolidation (Cv) using three graphical methods: the logarithm of time method, square root of time method, and hyperbola method. It elaborates specifically on the log-time curve fitting approach, detailing the necessary steps for plotting and analyzing consolidation data. The overarching goal is to facilitate understanding of how to interpret laboratory data relevant to soil consolidation and its implications in engineering applications.
Chapter 8
Square-root – time curve fitting method
The chapter discusses the square-root and log-time curve fitting methods related to pressure increment and consolidation processes in geotechnical engineering. Key steps of the square-root time curve fitting method include plotting the dial reading against the square root of time and determining points of tangency on the curve. Additionally, it explores the time rate of consolidation in laboratory samples compared to field deposits, underscoring the importance of drainage paths in consolidation predictions.
Chapter 9
Settlement Calculations
Settlement calculations involve understanding the processes and methodologies to assess how various factors affect the compression of field deposits. Practical exercises and activities guide students in applying theoretical concepts, reinforcing the importance of accurate calculations in geotechnical engineering. The chapter emphasizes the need for proper analysis and interpretation of data to ensure safe and effective engineering practices.
Chapter 10
Shear Strength Of Soil
Understanding shear strength is crucial for evaluating soil stability and ensuring the safety of geotechnical structures. It involves the resistance of soil to shearing stresses, influenced by factors such as cohesion and internal friction between particles. Shear strength plays a vital role in foundational stability, slope integrity, and the management of lateral earth pressures.
Chapter 11
Factors Influencing Shear Strength
Shear strength is influenced by various factors including soil composition, initial state, and structure. The Mohr-Coulomb failure criteria offer a framework to understand when materials fail due to specific combinations of normal and shear stress. Understanding these factors is essential for geotechnical engineering and soil mechanics.
Chapter 12
Direct Shear Test
The direct shear test is a crucial procedure for assessing the shear strength of dry sand by applying normal loads and shear forces to a specimen in a controlled environment. This method allows for the determination of normal and shear stresses at failure, thereby enabling the calculation of the friction angle associated with the material. Understanding the relationship between relative density and the angle of friction for coarse-grained soil is also essential for effective analysis and application in geotechnical engineering.
Chapter 13
Triaxial Tests
The chapter discusses triaxial compression tests used for soil analysis, highlighting procedures for conducting these tests on sands and clays. Various types of triaxial tests are outlined, along with their methodology for determining shear strength parameters using Mohr’s circles. Significant equations and principles related to effective and total stress are presented to aid in understanding soil behavior under applied pressures.
Chapter 14
Unconfined Compression Test
The chapter discusses the unconfined compression test, detailing its significance in determining the unconfined compression strength of soil specimens. It describes the conditions under which the test is performed and how the results, indicated by the axial stress at failure, can be utilized to assess soil consistency. The relationship between the degree of saturation and unconfined strength is also emphasized, presenting an essential aspect of testing for both saturated and unsaturated soils.
Chapter 15
Vane Shear Test
The vane shear test is a method used to determine the undrained shear strength of cohesive soils, particularly in very soft to medium conditions. The test involves inserting a vane into the soil and applying torque to measure resistance until failure occurs. Various distributions of shear strength mobilization are proposed, affecting the calculation of torque necessary for soil failure.
Chapter 16
Stabilization Of Soil
The chapter discusses the stabilization and modification of soils in road construction, emphasizing the importance of creating a stable subgrade to support construction activities and enhance pavement effectiveness. It differentiates between soil modification, aimed at creating a working platform, and soil stabilization, which increases the strength of subgrades for long-term pavement performance. Various techniques are explored, including mechanical stabilization and geosynthetic reinforcement, alongside requirements and guidelines for implementation in engineering practices.
Chapter 17
Chemical Modification or Stabilization
Chemical modification and stabilization of soil significantly alters its index properties through the addition of materials such as cement and lime. The primary mechanisms of change include increases in particle size and moisture binding. Proper criteria for selecting these chemicals based on soil properties, as well as quantifiable strength gains required for effective stabilization, are crucial for successful application.
Chapter 18
Lime Stabilization
Lime stabilization is an effective method for enhancing the properties of medium, moderately fine, and fine-grained soils by reducing plasticity and increasing strength and workability. The process involves determining the optimal lime content through mechanical tests, pH measurements, and compaction tests. Key test procedures include the Eades and Grim pH test, unconfined compression tests, and California Bearing Ratio tests to evaluate soil stabilization efficacy.
Chapter 19
Cement Stabilization
Cement stabilization techniques for soil treatment involve performing tests to determine the appropriate cement content based on soil properties. The methodology emphasizes quality control through mechanical and physical property tests, with specific recommendations for cement percentages and testing methods to ensure adequate stabilization. Thermal stabilization methods are also mentioned but are currently under revision.
Chapter 20
Grouting
Various soil improvement techniques are crucial for enhancing liquefiable ground stability, particularly with low vibration methods that include compaction, permeation, and jet grouting. Each technique addresses specific needs such as increasing soil density, waterproofing, and reducing liquefaction risks, thereby ensuring structural safety in urban environments and under existing infrastructure.