P5_MEKANIKA_BATUAN_Stress_&_Srain

1Mekanika Batuan(Stress & Strain)

Oleh :Irvani

Universitas Bangka Belitung Jurusan Teknik Pertambangan

Referensi : Goodman, R.E. 1989. Introduction to Rock Mechanics. 2nd Edition. John Wiley &

Sons., Canada. De Vallejo, L.I.G. And Ferrer, M. 2011. Geological Engineering. Taylor & Francis

Group, London, UK. Hudson, J.A. and Harrison, J.P. 1997. Engineering Rock Mechanics : An Introduction

to The Principles. Elsevier Science Ltd., Oxford. Hudson, J.A. and Harrison, J.P. 2000. Engineering Rock Mechanics : Illustrative

Worked Examples. Elsevier Science Ltd., Oxford. Hoek, E. 2007. Practical Rock Engineering. Notes, Evert Hoek Consulting Engineer

Inc., Canada. http://www.rockscience.com. Giani, G.P. 1992. Rock Slope Stability Analysis. A.A. Balkema Publishers, Rotterdam,

Netherlands. Bieniawski, Z.T. 1989. Engineering Rock Mass Classification. Mining and Mineral

Resources Research Institute. Pennsylvania State University. Bell, F.G. 2007. Engineering Geology. 2nd Edition. Elsevier Ltd., Burlington, USA. Singh, B. and Goel, R.K., and Hudson, J.A. 2006. Tunneling in weak rocks. Imperial

College of Science, Technology and Medicine, University of London, UK. Singh, B., Goel, R.K. 2011. Engineering Rock Mass Classification: Tunneling,

Foundation, and Landslides. Butterworth-Heinemann, Elsevier Inc., USA. Wyllie, D.C. 1999. Foundations on Rock. 2nd Edition, E & FN Spon, London. Wyllie, D.C. and Mah, C.W. 2004. Rock Slope Engineering. Civil and Mining

Engineering, 4th Edition, Spon Press, New York. Bates, R.L. and Jackson, J.A., 1987. Glossary Geology. 3th Edition. American

Geological Institute Elexandria, Virginia. DLL.


2Pokok Bahasan :I Pendahuluan (P.1)

II Klasifikasi & Sifat Indeks Batuan (P.2-4)a. Batuan & Perilaku Batuanb. Diskontinuitasc. Sifat Indeks & Mekanik Batuan

III Stress & Strain (5)

IV Kekuatan, Deformability & Kriteria Runtuhan Batuan(P.6-7)a. Kekuatan Batuan & Deformabilityb. Kriteria Mohr-Coulomb & Hoek-Brown.

V Klasifikasi Massa Batuan (P.8-10)

VI Aplikasi Mekanika Batuan pada Lereng (P.11-12)

VII Aplikasi Mekanika Batuan pada Terowongan (P.13-14)


Pluijm & Marshak (2004)

I. FORCEUniversitas Bangka Belitung Jurusan Teknik Pertambangan

3Newtons first law of motion (Law of Inertia) : In the absence of a force a body moves either at constant velocity or is at rest.

Change in velocity (acceleration [a]) :



Body forces : Forces that result from action of a field at every point within the body.Surface forces : Forces that act on a specific surface area in a body.

Natural processes can be described with four basicforces: (1) The gravity force (2) The electromagnetic force (3) the nuclear or strong force(4) the weak force



4Pluijm & Marshak (2004)

II. STRESS




5TWO-DIMENSIONAL STRESS: NORMAL STRESSAND SHEAR STRESS





6THREE-DIMENSIONAL STRESS: PRINCIPAL PLANES AND PRINCIPAL STRESSESStress at a Point



The Components of Stress



7Stress States



DERIVING SOME STRESS RELATIONSHIPS



8Some Common Stress States



MEAN STRESS AND DEVIATORIC STRESS



9STRESS TRAJECTORIES AND STRESS FIELDS



METHODS OF STRESS MEASUREMENT



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Response to StressTemperature has a role in the response of a material to stress,

but so does composition.

In general rocks with more water in them and which contain

more platy minerals (micas, clays) are more prone to

ductile deformation.

That is why sedimentary rocks in the shallow crust frequently

form fold belts, large provinces dominated by folded strata.


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Types of StressThere are three principal types of stress

(as are demonstrated on large scale by the three

plate tectonic boundaries):

compressive, tensional and shear.

Compression occurs when material is squeezed, when

bodies are pushed straight together.Tension (or extension) is when material is pulled apart.

Shear deformation occurs as two bodies

slide past one another.


..Types of Stress


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Traces of Stress in Rocks

By measuring objects of know

undeformed dimensions, we

can estimate the nature and magnitude of deformation.


..... Traces of Stress in Rocks

Orientation of slaty cleavage is another tool to estimate the nature and magnitude of stress on a rock.


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Goodman (1989)



II. STRAIN


Strain describes the changes of points in a bodyrelative to each other; it describes the distortion of abody.

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HOMOGENEOUS STRAIN AND THE STRAIN ELLIPSOID



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COAXIAL AND NON-COAXIAL STRAIN ACCUMULATION



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THE MOHR CIRCLE FOR STRAIN


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STRAIN STATES



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Elastic Behavior



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Confining Pressure



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Temperature


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Pore-Fluid Pressure


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Brittle Deformation

The permanent change that occurs in a solid material due to the growth of fractures and/ or due to sliding on fractures. Brittle deformation only occurs when stresses exceed a critical value, and thus only after a rock has already undergone some elastic and/or plastic behavior.


Rocks that respond brittlely to stress

break. Where a rock breaks and no

movement takes place is called a

fracture or joint.

Fractures in the shallow crust are

commonly evidenced by quartz

veins, where fluid once flowed and

later crystallized.


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A fracture along which movement takes place is a fault. Ex : Faults

We classify faults based on direction of movement of individual blocks, with reference to a horizontal plane.

acute angle = hanging wall

obtuse angle = foot wall

fault p

lane



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Ductile Deformation

A general term for the response of a solid material to stress such that the rock appears to flowmesoscopically like a viscous fluid. In a material that has deformed ductilely, strain is distributed, i.e., strain develops without the formation of mesoscopicdiscontinuities in the material. Ductile behavior can involve brittle (cataclastic flow) or plastic deformation mechanisms.


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Ductile and Brittle Deformation Features

Ductile

Brittle


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Many deformation structures are composite in nature. Fold belts (compressional) commonly contain numerous reverse faults.

Composite Brittle + Ductile Features


A vein such as this may have formed in a fracture, but subsequent ductile deformation caused its wiggly appearance.

Brittle + Ductile Features (small scale)Universitas Bangka Belitung Jurusan Teknik Pertambangan

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Terima Kasih


P5_MEKANIKA_BATUAN_Stress_&_Srain

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