GFM 1
lectures 1 and 2
lectures 1 and 2
variations in normal and shear stress with changes in orientation graph
.
variations in normal and shear stress with changes in orientation graph, which is the top and bottom line?
.
at what angle to the principal stress does maximum shear stress accur
45 degrees
the value of maximum shear stress is always (relationship)
half the differential stress
where is 2 theta measured from on a mohrs circle
clockwise (when tensile stress is negative)
centre of a Mohrs circle is
mean stress
diameter of a Mohrs circle is
differential stress
Hookes Law
e=kF
hydrostatic value
lamda = (pore-pressure)/(geostatic pressure)
lamda on a graph?
.
v
Poissons ratio
poissons ratio range
0 to 0.5
Poissons ratio
compressibility
v=0.5 means
v=Poissons ratio
v=0.5=incompressible
2 Lamé parameters
lamda and G
deformation rate
symbol and values
e or squiggly e
1=recognisable
0.1=unrecognisable
10=too big
deformation rate and strain ratio
deformation rate=squiggly e
strain ratio=squiggly e with a dot
Byerlee's Law
tau=0.5+0.6thetan
when pressure is >200MPa
what does Byerlees Law not take into account
pore fluid pressure
Amonton’s Law
tau=mu.thetan
Pc
defined and equation
confining pressure
Pc=rho.g.h
typical rock density
2500kg/m3
typical lithostatic gradient is
100MPa per 3km
stable continental crust T increase with depth
.
what can affect gradient of T with depth
stretching and shortening
natrual or logarithmic strain in defined by
e = ln(l/l0)
Sqiggly e
l is deformed length and l0 is the undeformed length
sqiggly e with a dot above it
deformation rate
squiggly e
stretching ratio
time to reach a strain rate of 1
t* = 1.0/squiggly e with dot
differential stress
difference in maximum and minimum principal stresses (sigmamax-sigmamin)
two lines on strength depth diagram
.
hydrostatic pressure equation
P=rho.g.h
rho=103 (water)
graphs of the variations of confining pressure and pore fluid pressure
.
on graphs of the variations of confining pressure and pore fluid pressure:
what are the three lines called
hydrostatic pressure
geostatic pressure
pressure of interstitial water
Ks
Shear force
Kcos(angle of force)
Kn
normal force
Ksin(angle of force)
symbol of stress acting parallel to the surface
tau
symbol of stress acting normal to a surface
.
way of visualising stess and strain
you feel stress but you see strain
Heims rule
SV = SH = Sh (or, S1 = S2 = S3)
SV=principal stress
SH and Sh = maximum and minimum horizontal stress
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Cartes-fiches
what does Byerlees Law not take into account
pore fluid pressure
Amonton’s Law
tau=mu.thetan
