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 JOINTS
Rekahan dan Sesar FRACTURED ROCKS 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 bukti pergerakan (shear displacement) atau off-set Sesar (fault) dapat berbentuk satu bidang diskrit yang planar atau membentuk suatu zona (fault zone) yang terdiri dari banyak bidangbidang sesar yang sejajar dan saling berhubungan (net-work) Rekahan (Fractures) Rekahan (fractures) adalah suatu bidang diskontinuitas dalam batuan Fracture Types FRACTURES FORMATION Jenis-jenis fractures : extension fractures dan shear fractures Extension fractures (mode I) Shear fractures (mode II) Shear fractures (mode III) A. Extension (Mode I) B. Shear (Mode II) C. Shear (Mode III)
Rekahan (Fractures) Joint atau kekar (sistematik dan nonsistematik) Kekar kolom Kekar release dan kekar pembebanan (loading) Kekar yang terbentuk akibat perlipatan (cross-joint, longitudinal joint dan stretching joint) Veins (tension gash) SYSTEMATIC JOINT Nomenclatures (Joint vs. Fault) Shear vs. Extension Fractures Hybrid Fractures FRACTURES AND JOINTS FRACTURES & JOINT SETS
FRACTURED ROCKS KEKAR PALING SUKAR DIANALISA KARENA : PEMBENTUKANNYA TIDAK TERBATAS WAKTU Sejak sedimen diendapkan Batuan beku mendingin Mengalami diagenesa Sampai mengalami gangguan oleh gaya Kekar Non Tektonik Kekar Tektonik TIDAK MEMPERLIHATKAN ADANYA PERGESERAN PRINCIPAL STRESS STRESS vs. STRAIN Stress Tensor Notation σ 11 σ 12 σ 13 σ = σ 21 σ 22 σ 23 σ 31 σ 32 σ 33
Unstable σ S σ S σ S Stable Formation of Fractures σ n σ n T 0 σ n σ 1 σ 3 σ 3 Tension fracture envelope A. Stable states of stress B. Critical states of stress C. Unstable states of stress σ 1 σ 1 σ 3 σ 3= T0 σ s σ 1 Normal to fracture plane Tension fracture θ f = 90º α f = 0º x 1 2θ f = 180º σ 1 = 0 σ n A. Tension fracture B. Longitudinal splitting C. Extension fracture D. Conjugate shear fracture D. Physical diagram E.Critical uniaxial tension Relationship between fracture types and stress from rock experiments Effect of Anisotropy on Fracture Orientation Compressive Fractures The Coulomb Law of Failure σ c = σ o + tan θ (σ n ) σ c σ o = critical shear stress = cohesive strength tan θ = coefficient of internal friction = normal stress σ n (Modified from Davis and Reynolds, 1996)
COMPRESSIVE MOHR DIAGRAM FOR BRITTLE DUCTILE TRANSITION TENSILE Frictional Sliding Behavior (Byerlee s law) σc = tan θf (σn) σc = critical shear stress υf = tan θf υf = coefficient of sliding friction σn = normal stress (Davis and Reynolds, 1996)
THE CONCEPT OF EFFECTIVE STRESS EFFECT OF PRE-EXISTING FRACTURE Coulomb Failure Envelope σ N = normal stress σ τ = shear stress (σ s ) P f = pore fluid pressure σ 1 = maximum principal stress σ 3 = minimum principal stress ROLE OF FLUID PRESSURE (P f ) Effective stress (σ*) Slip and Fracture Condition σ n * = σ n -P f σ c = σ o + tan θ (σ n -P f ) σ c = σ o + tan θ (σ n *) If σ n * = 0 σ c = σ o σ c = Critical stress σ o = Tensile strength of rock (Twiss and Moores, 1992) Relationship between Differential Stress and Shear Displacement (Twiss and Moore, 1992) Mohr diagram showing variation of fracture condition resulting from the effect of differential stress and pre- existing fractures
Failure Envelope and Development of Fracture at Different Condition The Development of Through Going Fracture (Fault) σ s Brittle-ductile transition Von Mises ductle failure criterion Griffith Crack Yield stress Parabolic fracture envelope T 0 Coulumb fracture criterion A B C n σ 1 θ f α f D σ 3 E σ n τ 2 = 4σ t (σ t +σ) σ t = tensile strength I. Pre-existing crack II. Crack closed III. Crack propagation IV. Crack begin to interact V. Fault forms (Twiss and Moores, 1992) Twiss and Moores (1992) TWO TYPES OF FRACTURE MECHANISM FRACTURES AND FAULTS Fracture strongly dependent on: Confining pressure (σ 3 ) and Fluid Pressure (P f )
FRACTURES MECHANICS
FRACTURES AND FAULTS FRACTURES 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 bidang diskrit yang planar atau membentuk suatu zona (fault zone) yang terdiri dari banyak bidang-bidang sesar yang sejajar dan saling berhubungan (net-work) Anderson s s Dynamic Fault Classification Extensional Compressional
FAULT GEOMETRIES AND CLASSIFICATION Anderson s s Dynamic Fault Classification Separation Classification Slip Classification Dip-slip faults Hanging wall block Hanging wall block Dip-slip faults Foot wall block Foot wall block A. Normal B. Thrust C. Right-lateral, or dextral D. Left-lateral, or sinistral Obliqueslip faults Rotational faults E. Sinistral-normal F. Sinistral-reverse G. Classification of Fault Rocks (Sibson, 1977)
Model of a Shear Zone Brittle Ductile Deformation in The Earth Crust The strength of brittle rocks increases with confining pressure,, but decreases with temperatures. Cataclasis Deformation Lithospheric Strength Profiles (Scholtz, 1990) Oceanic Continental FAULT ROCKS AND DEFORMATION MECHANISM FAULT AND FAULT ZONES Surface trace of fault Incohesive cataclasites 1-4 km. Clay Gouge 0.1 m Cataclastic fault rocks Fault zone Cohesive cataclasites 4-10 km. Temperature 250º-350º C Myloniteic fault rocks Mylonites 1 m Fault zone on Pre-Tertiary sandstone, Central Sumatera
Strike-slip Oblique-slip Dip-slip Fault plane Horizontal component Obliq ue-slip Dip -slip Strike-slip comp onent Heave FAULT AND FAULT ZONES Fault Gouge Earthquake Focal Mechanism First Motion Study FAULT ATTRIBUTES Throw Vertical comp onent