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Geotechnical Engineering–I [CE-221]
BSc Civil Engineering – 4th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/forum/#!forum/geotech-i
Lecture # 2
27-Jan-2017](https://image.slidesharecdn.com/2-180923175525/85/Geotechnical-Engineering-I-Lec-2-Introduction-2-1-320.jpg)
Geotechnical Engineering-I [Lec #2: Introduction-2]
- 1. 1 Geotechnical Engineering–I [CE-221] BSc Civil Engineering – 4th Semester by Dr. Muhammad Irfan Assistant Professor Civil Engg. Dept. – UET Lahore Email: mirfan1@msn.com Lecture Handouts: https://groups.google.com/forum/#!forum/geotech-i Lecture # 2 27-Jan-2017
- 2. 2 SOIL FORMATION Soil is formed due to the weathering of rocks. Weathering Weathering is a process whereby an intact rock mass is decomposed or broken into a loose material by the action of various atmospheric agents. Types of Weathering 1. Mechanical/Physical Weathering 2. Chemical Weathering
- 3. 3 MECHANICAL WEATHERING Mechanical weathering agents; • Soils formed by mechanical weathering have the same composition as that of the parent rock. • Soils formed by mechanical weathering retains the minerals and material fibers as that of the parent rock. • Coarse grained soils (gravels, sands and their mixtures) are the examples of mechanical weathering. 1. Temperature changes 2. Freezing & Thawing 3. Erosion/Abrasion due to flowing of water/wind 4. Natural disasters (landsides, earthquakes, etc) 5. Activities by plants, animals, humans, etc.
- 4. 4 CHEMICAL WEATHERING • Weathering caused by decomposition of rock mineral by different chemical processes such as oxidation, hydration, carbonation, leaching, solution, etc is known as chemical weathering. • Different types of clays and organic soils are the common soils formed by chemical weathering. Chemical weathering processes; 1. Oxidation 2. Carbonation 3. Hydration 4. Leaching 5. Solution (Search for single line definition of the these + major problems associated with them)
- 5. 5 ROCK-SOIL CYCLE Igneous Rocks SOIL Sedimentary Rocks Metamorphic Rocks Weathering Weathering Weathering compression + cementation Heat + Pressure + Solution
- 6. 6 SOIL DEPOSITS 1. Residual soil deposits i. Coarse grained ii. Fine grained 2. Transported soil deposits i. Alluvial deposits ii. Aolean deposits iii. Colluvial deposits iv. Glacial deposits v. Lucastrine deposits vi. Marine deposits vii. Pyroclastic deposits 3. Organic soil deposits i. Peat (partially decomposed organic matter) ii. Muck (completely decomposed organic matter)
- 7. 7 RESIDUAL vs TRANSPORTED SOILS Residual soils Deposited at the place of decomposition. • Properties of coarse grained soils generally depend upon size of particles. • Properties of fine-grained soils are greatly influenced by mineral content, moisture content, etc. • The knowledge of "classical" geotechnical engineering is mostly based on behavior of transported soils. The understanding of residual soils is insufficient in general. Transported soils Moved and deposited at other places. Particle size generally depends on mode of transportation Transported soils can be categorize based on the mode of transportation and deposition.
- 8. 8 TRANSPORTED SOILS 1. Glacial soils: formed by transportation and deposition of glaciers. 2. Alluvial soils: transported by running water and deposited along streams. 3. Lacustrine soils: formed by deposition in quiet lakes. 4. Marine soils: formed by deposition in the seas. 5. Aeolian soils: transported and deposited by the wind. 6. Colluvial soils: formed by movement of soil from its original place by gravity, such as during landslide. 7. Pyroclastic soils: materials ejected from volcanoes, and transported through gravity and wind, etc.
- 9. 9 SOIL TEXTURE & SOIL STRUCTURE Soil Texture → Appearance /feel of soil. 1. Coarse textured soils (sands, gravels, etc) 2. Fine textured soils (silts, clays) Fg α (Dia)3 Fs α (Dia)2 Fg/Fs α Dia Inter-Particle Forces 1. Weight of soil particles, Fg 2. Particle surface forces, Fs • In case of coarse textured soils Fg is dominating. • In case of fine textured soils Fs dominates. Soil Fabric: geometric arrangement of soil particles. Soil Structure: geometric arrangement + inter-particle forces
- 10. 10 TYPES OF SOIL STRUCTURES 1. Single grained structure 2. Honey-combed structure 3. Flocculent structure Single-grained soil structure Honey-combed soil structure Flocculant structure
- 11. 11 TYPES OF SOIL STRUCTURES (contd…) Single Grained Structure • Formed by the suspension of coarse-grained particles in a soil-fluid suspension. • Generally formed by cohesionless particles (e.g. sands) • In loose form soils may be weak and unstable but quality can be improved by compaction. Single-grained soil structure
- 12. 12 Honey Combed/Cellular Structure • Formed by the particles having inter-particular attraction (cohesion) greater than their weight. • Structure having large voids inside. • Meta-stable structure. • May be stable under static loads but can fail upon vibrations or dynamic load application. TYPES OF SOIL STRUCTURES (contd…) Honey-combed soil structure
- 13. 13 Flocculent Structure • Formed by very small sized particles (< 5x10-4cm) • Soil particles floating at the surface join together and form flocs. Settling down of flocs give rise to flocculent structure. • Double honey-combed structure. TYPES OF SOIL STRUCTURES (contd…) Flocculant structure
- 14. 14 COMMON CLAY MINERALS 1. Kaolinite 2. Illite 3. Montmorillonite (details from An Introduction to Geotechnical Engineering by Holtz & Kovacs; Chapter #4)
- 15. 15 CONCLUDED REFERENCE MATERIAL An Introduction to Geotechnical Engineering (2nd Edition) By R. D. Holtz, W. D. Kovacs and T. C. Sheahan Chapter #2; Chapter #4 Fundamentals of Soil Mechanics By M. S. Qureshi & Aziz Akbar Chapter #1; Chapter #2