Recommended texts

1. Recommended texts • Foundations of Engineering Geology • Tony Waltham (Spon Press) • Any Engineering Geology texts in the library • Practical Rock Engineering by Evert Hoek. Available free on the web: • http://www.rocscience.com/hoek/PracticalRockEngineering.asp

2. Mam Tor Fieldclass • Thursday 17th March • depart from Department at 8.45am • return approx. 6pm (depending on traffic) • You will need: • standard field gear • mapping board • notebook • compass-clinometer • ruler • stationary • camera? • LUNCH

3. Soil properties • Soil properties control their mechanical behaviour • 30 m of marine clay sits at a depth of 10 m below the surface of the tower’s foundations

4. Types of soil • Residual soils • Transported soils • glacial • alluvial • lacustrine • marine • aeolian • colluvial

5. Soil particle size • gravel >2 mm • sand 60 mm – 2 mm • silt 2 mm – 60 mm • clay <2 mm • not that clay defines clay sized particles, doesn’t necessarily contain clays

6. Soil particle size distribution Effective size, D10: Grain size at upper bound of the finest 10% fraction. Useful gauge of the hydraulic conductivity Uniformity coefficient, Cu: defined as D60/D10 Coefficient of gradation, Cz: defined as(D30)2/Cu

7. Soil particle size distribution • Well-graded: • gradient of curve constant over large grain size range • Poorly-graded: • variation from above

8. Clay chemistry • Main clay groups: • kaolinite • illite • montmorillonite

9. Clay chemistry • Carry negative charge on their surface • attract cations (e.g. Na+, Ca2+) • Also attract water (polarized molecule)

11. After Rutter, 1983

12. Soil consistency • Also known as the Atterberg Limits (1911) • Liquid limit (LL) • Plastic limit (PL) • Shrinkage limit (SL)

13. Liquid Limit (LL) • When soil stops acting as a liquid; becomes plastic • Measured in terms of Moisture Content (%)

14. Plastic Limit (PL) • When soil stops acting as a plastic solid; becomes brittle • Also measured in terms of Moisture Content (%)

16. Plasticity Index (PI) Plasticity Index (PI) = Liquid Limit (LL) – Plastic Limit (PL) • Range of water content where soil behaves plastically

17. Shrinkage limit (SL) • Where the soil ceases to decrease in volume on further drying • Below the SL the soil is partially saturated

18. Porosity and Void Ratio • Porosity, Φ = pore volume / total volume • Void ratio, e = pore volume / solid volume • Porosity and Void ratio affected by consolidation. Overconsolidation ratio

19. Effect of pore pressure on soil behaviour • Same mechanical effects as for hard rocks • Skempton’s pore pressure coefficients A and B: • Effect of Δσ3 on the Pf described by B • Effect of Δ(σ1 - σ3) on the Pf described by A

20. Skempton’s equations (1954) For a change in the mean stress: Fully saturated soil, B = 1 For a change in the differential stress:

21. Skempton’s equations • A can <1 or negative (when soil is dilatant) • overconsolidated soils • If A is positive • substrate weakest immediately after loading • If A is negative • substrate is strongest immediately after loading