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Fracture Analysis - 2

Fractures & Stress Orientation

7/25/2019 Fracture and Stress Orientation.ppt

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Fracture orientations relative to the

 principal stress orientations•  Stress = Gaya per satuan area yang

mengenai suatu bidang

• Kondisi stress yang mengenai suatuobjek misal batuan,memperlihatkan orientasi dan

 besaran dari tiga stress, meruakan“principal stresses”

• !he principal stresses terorientasitegak lurus satu terhadap lainnya ,untuk ketiga bidang tidak ada shearstress yang mengenai

•

Suatu blok batuan dengan stress yang mengenainya, simbol "sigma#menunjukkan “compressi$e ortensile stress”

• !he principal stresses menunjukkan bah%a ' ( ) ( *

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Fracture orientations relative to the

 principal stress orientations• +ompressi$e stress dan shortening

strain adalah sesuatu yang penting didalam “rock mechanics and structuralgeology” karena di bumi, ketiga“principal stresses” selalu bersiat“compressi$e” "kecuali disekitar“underground $oids” seperti ca$esatau karena dengan denganpermukaan

• -oints "e.tensional ractures#memperlihatkan pertentangan karenamerupakan salah satu kekar batuanalami, namun memerlukan suatu“eecti$ely tensile dri$ing stress”

"tensile stress = tegasan tarik#• !ekanan luida pori "/ore0luid

pressure# mendorong terbentuknya“tensile eecti$e stress” melalui“poroelastic loading o la%s” denganperingkat magnitude lebih besar daritipikal ractures

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Fracture orientations relative to the

 principal stress orientations• -oints "G1223#• !he tip o a gro%ing joint is al%ays perpendicular

to * at the joint tip during propagation• +ur$ed joints indicate temporal and4or spatial

 $ariations in the orientation o * during joint

gro%th• Faults "125#• 3e% aults in $irgin rock orm in each lithology

 %ith an appro.imately constant acute angle bet%een ' and the t%o conjugate aultorientations !his angle ranges rom )67 to 897 but is normally about *97

• /re0e.isting discontinuities %ith a %ide range oorientations can be acti$ated as aults, pro$ided

they are not oriented perpendicular to aprincipal stress• 5eormation bands "aults %ith an anti0mode :

component# also tend to orm at *97 to ' but canorm at any angle ;<97

• Stylolites ">?2# and compaction bands "notsho%n# orm perpendicular to '

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Regional Fracture Orientations

@ Gambar ', ) and * menunjukkan tiga “regionalearth stress regimes” " Andersonian stressregimes#

@ erdasarkan “Andersonian regimes”, satu“principal stress” menunjukkan $ertikal, sedang

dua lainnya adalah horiBontal

http://www.naturalfractures.com/1.1.3.htm

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Regional Fracture Orientations

http://www.naturalfractures.com/1.1.3.htm

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Regional Fracture Orientations

http://www.naturalfractures.com/1.1.3.htm