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B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza Basics of groundwater hydrology and geotechnical engineering Prepared by Dr O. Hamza o_hamza at hotmail dot com Lecture reference: OH_GA01
Content B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
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Basic groundwater hydrology Hydrologic Cycle B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
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Basic groundwater hydrology Subsurface water occurs in two different zones: saturated and unsaturated Hydrologic Cycle B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 Saturated zone Unsaturated zone
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Basic forms of geotechnical structure Study of groundwater is essential for engineers who construct dams, tunnels, water conveyance channels, mines, and other structures. B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 Natural slope Cut slope Embankment dam Building foundation Supported excavation Tunnel Road embankment Construction on soft soil Offshore foundation
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Basic problems in geotechnical engineering Water may contribute to both types of problem. Therefore, successful designing requires adequate consideration of groundwater effects. B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
1. Problems of equilibrium or stability
The load imposed on the soil
The magnitude & distribution of stress
The resistance that can the soil afford
2. Problem of deformability or settlement
Value of the total settlement that will occur
The rate at which this value will be achieved
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Basic mechanics of soil Analysis of stress and strain Stresses Strains What is stress and strain? Why the relation between stress and strain is so important? B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 Loads on soil Instability & Settlements
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Basic mechanics of soil Analysis of stress and strain Stresses and strains occur in all directions and to do settlement and stability analyses it is often necessary to relate the stresses in a particular direction to those in other directions. B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 stress strain mean p' = (s' a + 2s' r ) / 3 s' = (s' a + s' r ) / 2 e v = DV/V = (e a + 2e r ) e n = (e a + e r ) deviator q' = (s' a - s' r ) t' = (s' a - s' r ) / 2 e s = 2 (e a - e r ) / 3 e g = (e a - e r )
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Basic mechanics of soil Analysis of stress and strain To visualise the stresses on all the possible planes, a graph called the Mohr circle is drawn by plotting a (normal stress, shear stress) point for a plane at every possible angle. Mohr circle B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza Uniaxial compression Uniaxial extension Shearing GA01
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Basic mechanics of soil Analysis of stress and strain Do you think of any material parameter? Stress-strain relation, stiffness and strength B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 Stresses Strains Constitutive law Material properties/ parameters Stiffness parameters Strength parameters Change of size: bulk modulus K Change of shape: shear modulus G Change of 1-dimension: Young’s modulus E
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Basic mechanics of soil Rigid mechanics When soils fail they develop distinct slip surfaces Analysis of stress and strain B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 retaining wall Soil
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Equilibrium is examined by construction of a polygon of forces. Basic mechanics of soil Rigid mechanics Similarly Compatibility of displacements is examined by construction of a displacement diagram Slip surfaces divided soil or rock into blocks, so the principles of rigid body mechanics can be applicable . Analysis of stress and strain B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
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Basic mechanics of soil Special stress and strain states
These are simple theories for two special cases:
Isotropic
One-dimensional
B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 The state of stress in the ground is complex.
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Basic mechanics of soil Special stress and strain states Isotropic: Equal stress in radial direction. Applicable to triaxial test before shearing. p' = ( ' a + 2 ' r ) / 3 = mean stress v = V / V o = volumetric strain B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
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One-dimensional: Horizontal strains are zero. Applicable to oedometer test and in the ground below wide foundations, embankments and excavations. ' z = vertical stress v = V / V o = volumetric strain Basic mechanics of soil Special stress and strain states GA01 B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza where e 0 is the initial void ratio (before stress increment)
Geotechnical engineering is a branch of engineering that deal with the analysis and design of foundations, slopes and structures made from soils and rocks.
Problem in geotechnical engineering can be broadly divided into stability and serviceability/deformation.
Many problems in geotechnical engineering require the solution of a flow in porous media.
The theories of basic mechanics (equilibrium and compatibility) and of material behaviour (stiffness and strength) apply equally in geotechnical engineering.
The state of stress (including pressure induced by water) in the ground is complex, therefore simple one-dimensional theories may be employed to analyse soil behaviour.
B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
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Example problems Problem 1 The figure shows a rigid triangular block of soil with a slip surface. Two of the forces, acting on the block, are known to be W=160kN and T=60kN. Determine the value of P to ensure the equilibrium of the block. B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 45 o
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Example problems Consider a suitable scale e.g. 1cm=20kN Problem 1 The figure shows a rigid triangular block of soil with a slip surface. Two of the forces, acting on the block, are known to be W=160kN and T=60kN. Determine the value of P to ensure the equilibrium of the block. B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 45 o
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Example problems Problem 2 An element of soil behind a retaining wall; the effective vertical and horizontal stresses are z =300kPa and h =100kPa and these are principal stresses. Draw Mohr's stress circle and determine the maximum shear stress. B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza
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Example problems Problem 2 An element of soil behind a retaining wall; the effective vertical and horizontal stresses are z =300kPa and h =100kPa and these are principal stresses. Draw Mohr's stress circle and determine the maximum shear stress. B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01 max
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Example problems Problem 3 At the beginning of odeometer test, the void ratio and thickness of the specimen was 0.891 and 19mm respectively. Find the final void ratio e f if the soil consolidated by 3.52mm (i.e. H). B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
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Example problems Problem 3 At the beginning of odeometer test, the void ratio and thickness of the specimen was 0.891 and 19mm respectively. Find the final void ratio e f if the soil consolidated by 3.52mm (i.e. H). Void ratio change = e = e o – e f We have H=3.52mm, initial void ratio e 0 =0.891 and initial thickness H0=0.891mm Thus, the final void ratio of the soil e f =0.54 B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
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B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza
Weblinks
Electronic journal of geotechnical engineering, Available at http://www.ejge.com/index_ejge.htm
GeotechniCAL on the web, 2000, Educational technology for Ground Engineering. Swiss Federal Technical Institute and many UK universities. Available at http://fbe.uwe.ac.uk/public/geocal/index.htm
References
Smith G.N. and Smith I.G.N. 1998. Elements of soil mechanics. Seventh edition
Verruijt A. 2001. Soil Mechanics, Delft University of Technology
GA01
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End of Unit B asics of groundwater hydrology and geotechnical engineering Dr. O Hamza GA01
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