Advanced Soil Mechanics

Preface

These lecture notes are part of a collection of study materials prepared for the students of my lectures ''Advanced Soil Mechanics'' and ''Numerical Simulations in Geotechnical Engineering'' at the Institute of Geotechnics of the Technical University of Darmstadt. These notes have evolved during the preparation of the lecture and are still under development. The tone is deliberately kept colloquial. If you find any errors (and there are certainly some) or have any comments / suggestions for improvement, they are very welcome and appreciated: contact me. -- Jan Machaček

Many thanks to Dr.-Ing. Merita Tafili (RUB) and Prof. Dr.-Ing. Carlos Grandas (BTU) for the discussions and the critical review of the content. I'd also like to thank my students Johannes Otte and Amira Thau for their comments during their critical study of the script.

Welcome to the Advanced Soil Mechanics course. As the name suggests, this course is designed to transition you from fundamental concepts of soil learned in your undergraduate studies to a more detailed exploration of advanced topics.

Scope of the Course: Throughout this course, we'll be focusing on several key areas in soil mechanics:

• Stress and strain: We'll delve into effective stress, stress invariants, and principal stresses.

  • Stress tensor
  • Strain tensor
  • Invariants
  • Simplified stress conditions
  • Effective stress in saturated soils

• Triaxial tests (on sand): This section deals with a repetition of triaxial tests on soils, in particular sand. In addition to the influence of different drainage conditions, the effects of density and mean effective pressure on soil behaviour are discussed. This section serves as a preparation for the introduction to Critical State Soil Mechanics.

  • Consolidated drained monotonic triaxial tests on sand
  • Consolidated undrained monotonic triaxial tests on sand
  • Consolidated undrained monotonic triaxial extension tests on sand
  • Influence of mean effective pressure

• Critical State Soil Mechanics: This section will touch upon dilatancy, soil failure mechanisms, and nuances of stress- and density-dependent stiffness.

  • Observations (Sand)
  • Observations (Clay)

• Cyclic and dynamic loading: Here, we'll study the properties of soil under dynamic conditions, looking at topics like small strain stiffness, the stiffness degradation curve, strain accumulation, and liquefaction.

  • Soil behaviour under undrained cyclic shearing
  • Earthquakes and assessment of liquefaction risk
  • Basics of Soil Dynamics – soil behaviour under dynamic loading / at (very) small strains

• Unsaturated Soils: This will involve an exploration of partially saturated soils, the soil-water-retention curve, and how permeability, stiffness, and strength are influenced by saturation levels.

• Constitutive Modelling: We'll introduce the importance of constitutive models in geotechnical engineering, key features to be addressed by constitutive models for geotechnical engineering and covering basic constitutive models such as (linear) elasticity, Mohr-Coulomb and Hardening Soil:

  • Features of constitutive models for soils
  • Elasticity

Information on the notations used and a refresher on the basics of index notation are provided in the Notation chapter.

Our Goals: By the end of this course:

• You should have a deeper understanding that connects basic soil mechanics with more advanced topics.
• You'll gain insights into the effects of drainage conditions and partial saturation on soil behaviour.
• We aim to clarify any lingering misconceptions about the stress-strain behaviour and strength of soils.
• You'll be better positioned to analyse and describe soil mechanical relationships both mathematically and physically.
• We'll highlight the limitations of basic engineering models and introduce you to the foundational principles of constitutive modelling in geotechnical engineering.
• This course serves as an entry point to more advanced topics in soil mechanics. It's a gradual step up from what you've learned previously, designed to provide you with a broader perspective on the field. We encourage active engagement, questions, and an inquisitive mindset as we journey through these topics together.