Lecturer: Carlo Giovanni Lai  

Course name: Geotecnica
Course code: 500157
Degree course: Ingegneria Edile-Architettura
Disciplinary field of science: ICAR/07
The course relates to:
University credits: CFU 6
Course website: http://www-3.unipv.it/webgeotk/geotecnica.html

Specific course objectives

Scope of the course is to provide students with the theoretical foundations on the hydro-mechanical behaviour of soils which is propaedeutic to the solution of the main problems associated to geotechnical engineering like design and assessment of foundation systems and earth-retaining structures. Special emphasis will be given during the course to the subject of geotechnical characterization of construction sites through field and laboratory investigations. The course will comprise lecturing hours dedicated to the illustration of the theoretical topics and hours of exercising dedicated to problem-solving and/or deepening some of the themes treated during the lectures. The course subdivision in didactic modules with lecturing hours (L) and tutoring hours (T) is illustrated in the following.

Course programme

First didactic module (4L+2T) – Origin, description, fabric and classification of soils.
Origin of soils and macro-structural characters of natural deposits. Phase relations. Clay minerals and the chemism of clays. Identification and systems of classifications of soils. Grain size distribution curves. Atterberg limits. Casagrande plasticity chart. Initial state soil parameters. Interaction between fluid phase and solid skeleton. Burland intrinsic compressibility curve.

Second didactic module (4L+2T) – Fundamentals of continuum mechanics. Introduction to particulate systems.
Analysis of the state of stress and state of strain within the small-strain theory. Principal and octahedral stresses. Use of invariants. Decomposition of stress tensor. Mohr circle. Equilibrium and compatibility equations. The constitutive relation. The assumption of a linear elastic medium. Isotropy and cross-anisotropy media. Application of the theory of elasticity to the computation of the state of stress and strain induced in a homogeneous medium by external loadings. The Boussinesq and Mindlin problems and their relevance in solving engineering problems. Limits of applicability of elastic theory. Introduction to Hertz theory and to the intrinsic non-linearity in the mechanical behaviour of particulate materials. The phenomenon of dilatancy and its practical implications.

Third didactic module (4L+2T) – The porous medium: peculiarities and general characteristics of natural deposits.
Particulate nature of soils. Limits of applicability of the continuous model. Principle of effective stresses and its physical significance. Total and effective geostatic stresses, pore water pressures. Partially saturated and saturated soil deposits. Phenomena of capillarity. Geologic history and stress history. The notion of pre-consolidation pressure. The at-rest coefficient of lateral earth pressure. Normally-consolidated and over-consolidated soils. Pre-consolidation from diagenetic and aging processes.

Fourth didactic module (6L+3T) – Water in soils: fundamentals of water flow in porous media.
Kinematical aspects of fluid motion. Review of the fundamental equations of fluid mechanics. Forms of energy and Bernoulli’s equation. Flow of water in porous media. Darcy’s law. Equilibrium conditions under the presence of seepage forces. Hydrodynamic pressure and critical hydraulic gradient. The problems of seepage and piping. Assessment of safety conditions of an excavation. Undrained conditions and definition of Skempton pore pressure parameters. Steady state flow. Derivation of Laplace’s equation. Graphical and analytical solutions of boundary value problems associated to Laplace’s equation.

Fifth didactic module (6L+4T) – Theory of consolidation.
Terzaghi one-dimensional consolidation equation. Structure and formal analogy with heat equation. Analytical and numerical solution of Terzaghi equation. Consolidation/oedometer test. Determination of pre-consolidation pressure. Deformability parameters under oedometric conditions: the constrained modulus. Primary and secondary (aging) compression. Experimental determination of the coefficient of consolidation. Influence of sampling disturbance on the results of oedometer testing. Limits of applicability of the Terzaghi one-dimensional consolidation theory. Introduction to radial consolidation theory and design of vertical drains.

Sixth didactic module (10L+6T) – Mechanical behaviour of soils: experimental evidences and mathematical-physical modeling.
Premises. Representation of states of stress and of stress and strain paths through the Mohr circle. Representation through the t-s plane, the triaxial plane and the q-p plane. Drainage conditions. Stability analyses under drained and undrained conditions. Mohr-Coulomb failure criterion. Main laboratory equipments: triaxial apparatus, direct shear device or Casagrande box, simple shear and plane strain apparatuses, the resonant column device. Mechanical behaviour of coarse-grained soils. Shear strength and deformability. Some peculiarities in the mechanical behaviour of sands. Dissipation of mechanical work. Constant volume friction angle. Mechanical behaviour of fine-grained soils. Shear resistance and deformability of NC and OC clays. Consolidated undrained and unconsolidated undrained triaxial tests. Undrained shear strength. Peak and residual shear strength. Sensitive clays. Selection of shear strength parameters in stability analyses. Introduction to advanced constitutive models of hydro-mechanical behaviour of soils. Unified approach in soil constitutive modeling. A brief account on Cam-Clay model.

Seventh didactic module (6L+3T) – Field site investigations.
Exploration programme, objectives and extension of the survey. Boreholes and sampling techniques. Undisturbed sampling. In-situ static and dynamic penetration tests. Empirical correlations for the interpretation of CPTU and SPT test results. Vane shear test. Plate test. Introduction to pressuremeter and flat-dilatometer tests. Field measurement of pore water pressure. Installation of piezometers. Introduction to seismic geophysical testing. Cross-hole, down-hole and SASW tests.

Eighth didactic module (12L+8T) – Foundation systems and earth-retaining structures.
Typologies of foundations. Shallow and deep foundations. Limit bearing capacity of shallow foundations. Settlement calculation. Piled-foundations. Classification of foundation piles. Driven and bored piles. Limit bearing capacity of a single pile subjected to axial loads. Base and side resistance components of piles. Overview of earth-retaining structures. Computation of active and passive earth pressures according to the classical theories of Coulomb and Rankine. Effects of water pressure and of surcharge live loads. Drainage systems. Introduction to flexible earth-retaining structures.

Course entry requirements

Basics of Calculus and Mechanics of Deformable Body.

Course structure and teaching

Lectures (hours/year in lecture theatre): 54
Practical class (hours/year in lecture theatre): 30
Practicals / Workshops (hours/year in lecture theatre): 0
Project work (hours/year in lecture theatre): 0

Suggested reading materials

Lancellotta, R. (2009). Geotechnical Engineering. Second Edition, Taylor & Francis, pp. 499. Recommended basic textbook.

Atkinson, J. (2007). The Mechanics of Soils and Foundations. Second Edition, Routledge, Taylor & Francis, pp.442. Reference textbook. It treats both soil mechanics and design of foundations and earth-retaining structures though at a basic level.

Holtz, R.D. & Kovacs, W.D. (1981). An Introduction to Geotechnical Engineering. Prentice-Hall, pp.733. Excellent book to deepen the study on the hydro-mechanical behaviour of soils. Pragmatic and of easy comprehension.

Lambe, T.W. (1991). Soil Testing for Engineers. BiTech Publishers, pp. 165. Reference monograph for geotechnical laboratory tests.

Lambe, T. W. & Whitman, R. V. (1990). Soil Mechanics. John Wiley & Sons, pp. 576. Classical textbook to deepen the study of soil mechanics.

Nova, R. (2002). Fondamenti di Meccanica delle Terre. Mc Graw Hill, pp.373. Reference monograph to deepen the study on the hydro-mechanical behaviour of soils and of soil constitutive modeling. Advanced theoretical approach.

Wood, D.M. (1990). Soil Behaviour and Critical State Soil Mechanics. Cambridge University Press, pp. 462. Reference monograph to deepen the study on the hydro-mechanical behaviour of soils and of soil constitutive modeling. Advanced theoretical approach.

Mitchell, J.K. & Soga, K. (2005). Fundamentals of Soil Behavior. Wiley & Sons, pp. 592. Reference monograph to deepen the study on the chemism of clays and on the interaction between solid and fluid phases of the porous medium.

Salgado, R. (2006). The Engineering of Foundations. McGraw-Hill, 928 pp. Reference monograph to deepen the study on the engineering of foundations and of earth-retaining structures.

Reese, L.C., Isenhower, W.M. & Wang, S.T. (2005). Analysis & Design of Shallow & Deep Foundations. Wiley & Sons, pp. 608. Reference monograph to deepen the study on the engineering of foundations.

Testing and exams

The final exam consists of a three hours written assessment. The test is split in two parts: the first based on theoretical questions while the second on problem-solving. The final grade will be the arithmetic mean of the two parts each of which should be successfully passed with a score greater or equal to 18/30. The test format is closed-book. Problems and/or reading assignments will be given during the course but they will not be collected. However, at the final exam students will be asked to turn in their work for an evaluation. Students are strongly recommended to attempt all the assigned homeworks in order to have a positive outcome at the final examination.