FOUNDATIONS AND EXCAVATION SAFETY
Learning outcomes of the course unit
The course provides basic knowledge on the soil, on its mechanical characteristics and on the geotechnical characterization, aimed at addressing the issue of the safety of an excavation in a vertical or inclined wall, with notes on stability verifications and the main types of retaining structures.
Course contents summary
Particle structure of the soils, relationship between the phases and index properties.
Recognition and classification of soils: the single solid particle, the interaction between solid particles, interaction between solid particles and water. Natural aggregates. Classification: granulometric curve, Atterberg limits, types of soil according to the classification of S.I. The role of boreholes in the recognition of natural soil for design purposes.
From the particle system to continuous medium: concept of stress and strain for particle medium, the principle of effective stress of Terzaghi for the saturated means. Recalls of continuous mechanics applied to the soil. Stress tensor, Mohr's circle, invariants, tensional state in water, tensor of effective stress, tensor strain. Field equations: undefined equilibrium equations, congruence equations, stress strain bonds. Typical common stress states for the soils: axial-symmetrical stress state, plane strain. Natural soil conditions and stress history: geostatic stress state. Vertical geostatic tension state. Neutral water pressure in geostatic conditions. Capillarity phenomenon. The geostatic horizontal stress state, the k0 boost coefficient, the degree of overconsolidation, OCR.
The stress-strain relationship for the soil: at failure and in service conditions.
Soil shear strength: experimental behaviour of sands and clays. Mohr-Coulomb failure criterion, concept of undrained shear strength. Typical values of shear strength parameters for loose and dense sands, normally consolidated and over-consolidated clays. Soil compressibility under unlimited confinement, in axisymmetric conditions.
Geotechnical design, NTC 2018, Serviceability limit state and Ultimate Limit State SLU verification.
Analysis of the soil ultimate conditions. Rankine’s theory and the limit equilibrium method for earth pressure. Earth pressure at failure. Active and passive earth pressure.
The problem of excavation. Application of the Rankine’s theory. Verification in drained and undrained conditions, of vertical or inclined excavations in short- and long-term. Introduction to embankment and trench stability. Introduction to the main types of retaining structures.
Excavation safety according to NTC 2018. Introduction to slope stability and retaining structures.
Text adopted: Lorella Montrasio. Geotecnica. ed. Santa Croce
Other recommended texts:
Atkinson J. Bransby P.L. (1978). The Mechanics of Soils. Mc Graw Hill.
Bowles J.E. (1982). Foundation Analysis and Design. Wyley.
Burghignoli A. (1975). Lezioni di Meccanica delle Terre. Editoriale Esa
Chen. (1975). Limit Analysis and Soil Plasticity. Elsevier.
Colombo P., Colleselli F. (1996). Elementi di Geotecnica. Zanichelli.
Craig R.E. (1974). Soil Mechanics. Van Nostrand Reynolds.
Fredlund D.G, Rahardjo H. (1993). Soil Mechanics for Unsaturated Soils. Van Nostrand Reynolds.
Holtz R.D., Kovacs W.D. (1981). An Introduction to Geotechnical Engineering. Prentice Hall.
Lambe T.W., Whitman R.V. (1969). Soil Mechanics. Wiley.
Lancellotta R. (2004). Geotecnica. Zanichelli.
Nova R. (2002). Fondamenti di Meccanica delle Terre. Mc Graw Hill.
Nova R. (1979). Lezioni di Geotecnica. Clup.
Schofield A.N., Wroth C.P. (1968). Critical State Soil Mechanics. Wiley.
Terzaghi K., Peck R.B.(1967). Geotecnica. UTET.
Viggiani C. (1999). Fondazioni. Hevelius.
X ECSMFE. (1991). Deformation of Soils and Displacements of Structures. AGI.
The course consists of lectures and exercises carried out by students, consisting of practical applications of the concepts taught during the lectures.
Assessment methods and criteria
Verification of learning is achieved through a written test, which will consist of exercises based on practical tests by students during the year and a theoretical question on one of the topics presented during the lessons.