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CE2004 earth pressure&liquefaction_handout0

Course: ENGINEERIN H203, Spring 2011
School: Brunel University
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Word Count: 474

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Pressure, Ground Lateral Movement and Liquefaction CE2004 What well cover Soil at rest and overconsolidation Lateral earth movement Lateral spreading Liquefaction Soil at rest Point at which lateral strain in a soil = Represents transition between active and passive pressure states p0 = k0 z Kp K0 expansion Ka compression Where: p0 = pressure at-rest; k0 = coefficient of earth pressure at rest = unit weight; z = depth Determining K0 Influenced by ..events Is soil loose or .. Present stress = maximum experienced Soil is normally consolidated (nc) Present stress is < maximum experienced Soil is overconsolidated (oc) Overconsolidation ab load applied, void ratio reduces a Void ratio e e.g. a clay soil bc load removed, void ratio does not change - overconsolidated cb load applied, void ratio does not change until stress at point b exceeded - recompression c b d Stress Soil cannot return to its original state Ratio of maximum stress in past to present stress = overconsolidation ratio OCR (or Roc) OCR>1 = overconsolidated OCR=1 = normally consolidated KaK0Kp K0 normally quite close to Ka Kp decrease in 3 leads to plastic deformation Small K0 normally quite far from Kp increase in 3 needed to cause plastic Greater K0 expansion Ka compression Determining K0 Use shear angle Kp Where Roc = 1 K0 = 1 sin Where Roc > 1 K0 = (1 sin ) (Roc)sin expansion Or, K0 = (1 sin ) (Roc)0.5 K0 Ka compression [Eurocode 7 ] Lateral earth movement Plastic deformation to .. Major hazard Component of . What is liquefaction? Transformation of sediment/soil into a .mass Sudden loss of shear strength due to increased pore-fluid water pressure Causes: Excess supply Loading .. LapidusD.R.1987.DictionaryofGeology.Collins,London. Liquefaction: what happens Liquefaction results Subsurface mobilisation/.. Sediment venting at surface Lateral movement Requirements for Liquefaction Suitable Sands, Helike core: HR010708-2 0 5 10 15 0 silts, gravels 100 Suitable .. loose material high water content enhanced by overlying .. 200 Depth cm 300 400 Bearing 500 600 Shear Where can Liquefaction occur? Seismically induced liquefaction NeedM>5.56.0 (sometimesM5.0) Obermeier1998 Pore water pressure increase with shaking Holzeretal.1989 Magnitude and liquefaction Obermeier1998 Influence of surface conditions Obermeier1998 Lateral spreading Spatialvariationsinsurfacecovertype/thickness Obermeier1998 Sand dykes and sills Obermeier1998 Sub/ surface disruption Rodriguezetal.2000 Intensity and sediment contortion Hibschetal.1997 Surface features Vented Sediment Sand/mud volcanoes .ground Pit in sand volcano with feeder sand dike Nonseismicsand volcanoestendtobefed bypipes Mima mounds: seismic origin? Summary Resistance of soil to deformation/failure reflects what has happened to it in the . Lateral earth movement can be a major Liquefaction can occur ..within a soil and enhance lateral movement Sources Craig R.F. 2004. Craigs Soil Mechanics. 7th Ed. Spon, London. Chapter 6. McCarthy, D. F. 2007. Essentials of soil mechanics and foundations : basic geotechnics. Pearson. London. Chapter 17 Tomlinson M.J. 2001. Foundation Design and Construction. 7th Ed. Pearson, London. Ch 5. Check paper by Obermeier in Engineering Geology, vol 76, published in 2005

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