basics of groundwater hydrology in geotechnical engineering oh ga01
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Introduction to geotechnical engineeringTRANSCRIPT
Basics of groundwater hydrology and geotechnical engineering Dr. O Hamza
Prepared by Dr O. Hamzao_hamza at hotmail dot com
Lecture reference: OH_GA01
1. Basic groundwater hydrology
2. Basic forms of geotechnical structure
3. Basic problems in geotechnical engineering
4. Basic mechanics of soil
5. Summary
6. Example problems
Content
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Basic groundwater hydrology
Hydrologic Cycle
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Basic groundwater hydrology
Subsurface water occurs in two different zones: saturated and unsaturated
Saturated zone
Unsaturated zone
Hydrologic cycle
Groundwater flow
Precipitation
Water table
aquiferDischarge area
Hydrologic cycleHydrologic cycle
Groundwater flow
Precipitation
Water table
aquiferDischarge area
Hydrologic cycleHydrologic cycle
Groundwater flow
Precipitation
Water table
aquiferDischarge area
Hydrologic cycleHydrologic cycle
Groundwater flow
Precipitation
Water table
aquiferDischarge area
Hydrologic Cycle
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Basic forms of geotechnical structure
Natural slope Cut
slope Embankment dam
Building foundation Supported
excavation
Tunnel
Road embankme
nt
Construction on soft soil
Offshore foundation
Study of groundwater is essential for engineers who construct dams, tunnels, water conveyance channels, mines, and other structures.
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Basic problems in geotechnical engineering
Water may contribute to both types of problem. Therefore, successful designing requires adequate consideration of groundwater effects.
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
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Basic mechanics of soil Analysis of stress and strain
Stresses Strains
Load
s on
soi
l
Inst
abili
ty &
Set
tlem
ents
What is stress and strain?
Why the relation between stress and strain is so important?
normal stress = Fn / A
shear stress = Fs / A
normal strain = z / zo shear strain = h / zo
normal strain = z / zo shear strain = h / zo
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
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.
principal stresses '1 and '3
Basics of groundwater hydrology and geotechnical engineering Dr. O Hamza
stress strain
meanp' = (s'a + 2s'r) / 3s' = (s'a + s'r) / 2
ev = DV/V = (ea + 2er)en = (ea + er)
deviatorq' = (s'a - s'r)t' = (s'a - s'r) / 2
es = 2 (ea - er) / 3eg = (ea - er)
GA01
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
Basics of groundwater hydrology and geotechnical engineering Dr. O Hamza
Uniaxial compression Uniaxial extension
Shearing
GA01
Basic mechanics of soil Analysis of stress and strain
Do you think of any material parameter?
Stress-strain relation, stiffness and strength
Stresses StrainsConstitutive 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
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Basic mechanics of soil
Rigid mechanics
When soils fail they develop distinct slip surfaces
retaining wall
Soil
Analysis of stress and strain
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Equilibrium is examined by construction of a polygon of forces.
Basic mechanics of soil
Rigid mechanics
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W PT
N
W
P T
N
W
P T
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W PT
N
W
P T
N
W
P T
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W PT
N
W
P T
N
W
P T
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W PT
N
W
P T
N
W
P T
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W PT
N
W
P T
N
W
P T
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W
P T
N
Polygon of forcesForces on a body
W PT
N
W PT
N
W
P T
N
W
P T
W
P T
N
Polygon of forcesForces on a body
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
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Basic mechanics of soil
Special stress and strain states
The state of stress in the ground is complex.
These are simple theories for two special cases: • Isotropic• One-dimensional
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
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 / Vo = volumetric strain
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
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 / Vo = volumetric strain
Basic mechanics of soil
Special stress and strain states
where e0 is the initial void ratio (before stress increment)
00 e1
Δe
H
ΔH
GA01 Basics of groundwater hydrology and geotechnical engineering Dr. O Hamza
Summary
• 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.
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
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.
W
PT
N
W
PT
N45o
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Example problems
Consider a suitable scale e.g. 1cm=20kN
Problem 1
W=160 kN~ 8cm
45o
T=60 ~ 3cm
Polygon of forces –scale 1cm=20kN
W=160 kN~ 8cm
45o
T=60 ~ 3cm
Polygon of forces –scale 1cm=20kN
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.
W
PT
N
W
PT
N45o
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
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.
Basics of groundwater hydrology and geotechnical engineering Dr. O Hamza
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.
Mohr circle
-400
-300
-200
-100
0
100
200
300
400
0 100 200 300 400
Normal stress, ' [kPa]
Sh
ea
r st
ress
, '
[kP
a]
max
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
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 ef if
the soil consolidated by 3.52mm (i.e. H).
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
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 ef if
the soil consolidated by 3.52mm (i.e. H).
000v e1
Δe
H
ΔH
V
ΔVεstrain Volumetric
Void ratio change = e = eo – ef We have H=3.52mm, initial void ratio e0=0.891 and
initial thickness H0=0.891mm
19
52.3
891.01
891.0
fe
Thus, the final void ratio of the soil ef =0.54
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01
Basics 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
Basics of groundwater hydrology and geotechnical engineering Dr. O HamzaGA01