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FRACTURES• Fracture : a break in rock due to brittle
behavior to stress• Joint : A fracture with no displacement
– Joint Sets : multiple joints oriented parallel to one another, in response to regional stress
– Groundwater flow, hydrothermal ore deposits
• Fault : A fracture with displacement
FRACTURES AND JOINTSFRACTURES AND JOINTS
FRACTURED ROCKSFRACTURED ROCKS
Rekahan dan Sesar• Rekahan (fractures) adalah suatu bidang diskontinuitas dalam
batuan• Jenis-jenis fractures : extension fractures dan shear fractures• Extension fractures (mode )• Shear fractures (mode II)• Shear fractures (mode III)
– Joint atau kekar (sistematik dan non-sistematik)• Kekar kolom• Kekar release dan kekar pembebanan (loading)• Kekar yang terbentuk akibat perlipatan
(cross-joint, longitudinal joint dan stretching joint)– Veins (tension gash)
• Sesar (fault) adalah rekahan yang memperlihatkan adanya buktipergerakan (shear displacement) atau off-set
• Sesar (fault) dapat berbentuk satu bidang diskrit yang planar ataumembentuk suatu zona (fault zone) yang terdiri dari banyak bidang-bidang sesar yang sejajar dan saling berhubungan (net-work)
• Rekahan (fractures) adalah suatu bidangdiskontinuitas dalam batuan
• Jenis-jenis fractures :extension fractures dan shear fractures
• Extension fractures (mode I)• Shear fractures (mode II)• Shear fractures (mode III)
Rekahan (Fractures) FRACTURES FORMATION
B. Shear (Mode II) C. Shear (Mode III)A. Extension (Mode I)
Fracture Types
Rekahan (Fractures)– Joint atau kekar (sistematik dan non-
sistematik)• Kekar kolom• Kekar release dan kekar pembebanan
(loading)• Kekar yang terbentuk akibat
perlipatan(cross-joint, longitudinal joint danstretching joint)
– Veins (tension gash)
SYSTEMATIC JOINT
• Nomenclatures (Joint vs. Fault)
• Shear vs. Extension Fractures
• Hybrid Fractures
FRACTURES & JOINT
SETS
FRACTURES AND JOINTSFRACTURES AND JOINTS
FRACTURED ROCKSFRACTURED ROCKS KEKAR PALING SUKAR DIANALISA KARENA :
PEMBENTUKANNYA TIDAK TERBATAS WAKTUSejak sedimen diendapkanBatuan beku mendinginMengalami diagenesaSampai mengalami gangguan oleh gaya
Kekar KekarNon Tektonik Tektonik
TIDAK MEMPERLIHATKAN ADANYA PERGESERAN
PRINCIPAL STRESS
Stress Tensor Notation
σ11 σ12 σ13
σ = σ21 σ22 σ23σ31 σ32 σ33
STRESS vs. STRAINSTRESS vs. STRAIN
Tensionfracture
D. Physical diagram E.Critical uniaxial tension
Normal tofracture plane
σ = 3 0T
σ = 1 0
σs
σn
α = f 0ºx1
θ = f 90º
2 180ºθ = f
Stable
C. Unstable states of stress
Unstable
B. Critical states of stressA. Stable states of stress
Tension fractureenvelope
σS σS σS
T0σn σn σn
D. Conjugate shear fracture
B. Longitudinal splitting
C. Extension fracture
A. Tension fracture
σ3
σ3
σ3
σ1
σ1
σ1 σ1
Formation of Fractures
Relationship between fracture types and stress from rock experiments
Effect of Anisotropy on Fracture Orientation
σc = σo + tan θ (σn)
The Coulomb Law of Failure
σc = critical shear stressσo = cohesive strengthtan θ = coefficient
of internal frictionσn = normal stress
(Modified from Davis and Reynolds, 1996)
Compressive Fractures
COMPRESSIVE TENSILE
MOHR DIAGRAM FOR BRITTLE –DUCTILE TRANSITION Frictional Sliding Behavior (Byerlee’s law)
(Davis and Reynolds, 1996)
σc = tan θf (σn)
σc = critical shear stress
υf = tan θf
υf = coefficientof sliding friction
σn = normal stress
EFFECT OF PRE-EXISTING FRACTURE
THE CONCEPT OF EFFECTIVE STRESS
σN = normal stress
στ = shear stress (σs)
Pf = pore fluid pressure
σ1 = maximum principal stress
σ3 = minimum principal stress
Coulomb Failure
Envelope
ROLE OF FLUID PRESSURE (Pf)
Effective stress (σ*)
σn* = σn - Pf
σc = σo + tan θ (σn- Pf)
If σn* = 0 σc = σo + tan θ (σn*)
σc = σo
σc = Critical stress
σo = Tensile strength of rock
(Twiss and Moores, 1992)
Relationship between Differential Relationship between Differential Stress and Shear DisplacementStress and Shear Displacement
((TwissTwiss and Moore, 1992)and Moore, 1992)
Mohr diagram showing Mohr diagram showing variation of fracture condition variation of fracture condition
resulting from the effect of resulting from the effect of differential stress and predifferential stress and pre--
existing fracturesexisting fractures
Slip and Fracture ConditionSlip and Fracture Condition
A
T0
σs
σn
Von Mises ductlefailure criterionBrittle-ductile
transition
B
CD
E
Coulumbfracturecriterion
Yield stress
Parabolicfractureenvelope
σ3
n αfθf
σ1
Failure Envelope and Development of Fracture at Different Condition
(Twiss and Moores, 1992)
Griffith Crack
I. Pre-existing crackII. Crack closed III. Crack propagationIV. Crack begin to interactV. Fault forms
Twiss and Moores (1992)
τ2 = 4σt(σt+σ)
σt = tensile strength
The Development of Through Going Fracture (Fault)
TWO TYPES OF FRACTURE MECHANISM
• Fracture strongly dependent on: Confining pressure (σ3) and Fluid Pressure (Pf)
FRACTURES AND FAULTSFRACTURES AND FAULTS
FRACTURES MECHANICS
FRACTURES AND FAULTSFRACTURES AND FAULTSFRACTURES AND FAULTSFRACTURES AND FAULTS
Sesar dan Rekahan Sesar dan Rekahan
• Sesar (fault) adalah rekahan yang memperlihatkan adanya bukti pergerakan(shear displacement) atau off-set
• Sesar dapat berbentuk satu bidangdiskrit yang planar atau membentuksuatu zona (fault zone) yang terdiri daribanyak bidang-bidang sesar yang sejajardan saling berhubungan (net-work)
Extensional Extensional CompressionalCompressional
AndersonAnderson’’s Dynamic Fault Classifications Dynamic Fault Classification
FAULT GEOMETRIES AND CLASSIFICATIONFAULT GEOMETRIES AND CLASSIFICATION
•• AndersonAnderson’’s Dynamic Fault Classifications Dynamic Fault Classification
•• Separation ClassificationSeparation Classification
•• Slip ClassificationSlip Classification
Foot wallblock
Rotationalfaults
Hanging wallblock
F. Sinistral-reverse
Foot wallblock
G.E. Sinistral-normal
Hanging wallblock
Oblique-slipfaults
Dip-slipfaults
Dip-slipfaults
B. Thrust D. Left-lateral, or sinistralA. Normal C. Right-lateral, or dextral
Classification of Fault RocksClassification of Fault Rocks
(Sibson, 1977)
Model of a Shear Zone Model of a Shear Zone
(Scholtz, 1990)
Brittle Brittle –– Ductile Deformation in The Earth CrustDuctile Deformation in The Earth Crust
OceanicOceanic ContinentalContinental
CataclasisCataclasis DeformationDeformation
The strength of brittle rocks increases with The strength of brittle rocks increases with confining pressureconfining pressure, but , but decreases with decreases with temperaturestemperatures. .
LithosphericLithospheric Strength ProfilesStrength Profiles
Myloniteicfaultrocks
Surface trace of fault
Mylonites
Cohesivecataclasites
Fault zone
Cataclasticfaultrocks
Incohesivecataclasites 1-4 km.
4-10 km.
250º-350º CTemperature
FAULT ROCKS AND DEFORMATION MECHANISMFAULT ROCKS AND DEFORMATION MECHANISM
1 m
0.1 m
FAULT AND FAULT ZONES
Fault zone on Pre-Tertiary sandstone, Central Sumatera
Clay Gouge
Fault Gouge
FAULT AND FAULT ZONES
Strike-slip
Fault plane
Oblique-slipDip-slip
Obliq ue-slipDip -slip
Heave
Horizontal component
Str ike-slip
component
Verticalcomponent
Throw
FAULT ATTRIBUTESFAULT ATTRIBUTES
First Motion StudyFirst Motion StudyEarthquake Focal MechanismEarthquake Focal Mechanism