Basics of groundwater hydrology in geotechnical engineering oh ga01

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


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



Groundwater flow

Precipitation

Water table



Groundwater flow

Precipitation

Water table


Hydrologic Cycle


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.


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


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



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


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


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


Uniaxial compression Uniaxial extension

Shearing

GA01


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


Basic mechanics of soil

Rigid mechanics

When soils fail they develop distinct slip surfaces

retaining wall

Soil

Analysis of stress and strain


Equilibrium is examined by construction of a polygon of forces.


Rigid mechanics

W PT

N

W

P T

N

Polygon of forcesForces on a body

W PT

N

W

P T

N


W PT

N

W PT

N

W

P T

N

W

P T

W

P T

N


W PT

N

W

P T

N


W PT

N

W

P T

N


W PT

N

W PT

N

W

P T

N

W

P T

W

P T

N


W PT

N

W

P T

N


W PT

N

W

P T

N


W PT

N

W PT

N

W

P T

N

W

P T

W

P T

N


W PT

N

W

P T

N


W PT

N

W

P T

N


W PT

N

W PT

N

W

P T

N

W

P T

W

P T

N


W PT

N

W

P T

N


W PT

N

W

P T

N


W PT

N

W PT

N

W

P T

N

W

P T

W

P T

N


W PT

N

W

P T

N


W PT

N

W

P T

N


W PT

N

W PT

N

W

P T

N

W

P T

W

P T

N


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



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




Isotropic: Equal stress in radial direction. Applicable to triaxial test before shearing. p' = ('a + 2'r) / 3 = mean stress

v = V / Vo = volumetric strain


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



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.


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


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



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.



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



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).



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



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

http://www.ejge.com/index_ejge.htm

http://fbe.uwe.ac.uk/public/geocal/index.htm

Basics of groundwater hydrology in geotechnical engineering oh ga01

Education

Transcript of Basics of groundwater hydrology in geotechnical engineering oh ga01