3 rd Off Earth Mining Forum - 2017OEMF Some Thoughts About Rock Mechanics Aspects of Mars Courtesy of NASA Opportunity Curiosity Spirit Ömer Aydan University of the Ryukyus, Department of Civil Engineering Nishihara, Okinawa, Japan
Contents 1) Motivation 2) General Characteristics of Mars 3) Surface Topography and Geology 4) Tectonics and Seismicity 5) Stress State of Mars 6) Rocks 7) Formation of Discontinuities and Their Surface Morphology 8) Rock Weathering 9) Slope Stability Problems 10) Sinkholes 11) Properties of Rocks, Discontinuities and Rock Masses 12) Conclusions Acknowledgements
1) Motivation Mankind is now exploring the ways to find out the characteristics of other planets and possibility of exploiting their mineral resources.. One of most impressive images from the Apollo Program of NASA to me is the man standing next to a fractured lunar rock mass. The images from recent Mars exploration rovers showed the striking similarities between rocks on Earth and those of Mars, which motivated me to bring together some of my thoughts about the aspects of rock mechanics and rock engineering in Mars and to compare them with those of the earth. In this presentation, I will specifically consider the stress state, the characteristics of rocks and their weathering, discontinuity formations, slope and cliff stability problems and natural caves.
Teaching Rock Mechanics and Rock Engineering in Space in my Rock Mechanics Classes in Tokai University since 2010 and University of the Ryukyus since 2014 (Contents) (Rock Mechanics in Other Planets)
2) General Characteristics of Mars Gravitational acceleration is 0.377g of the Earth Radius is 3389 km Mean density is 3.933 g/cm 3
3-1) SURFACE TOPOGRAPHY From NASA
3-2) SURFACE GEOLOGY OF MARS
c) TEMPERATURE VARIATIONS Earth is 20-40 degrees From NASA Temperature difference is more than 80 degrees Subjected to Harsh Freezing and Thawing Environment provided rock is saturated
d) INTERIOR CHARACTERISTICS From Sohl and Spohn (1997)
4) Tectonics and Mars-quakes From NASA
from USGS(?)
LARGE SCALE RIFTING TYPE MOTIONS AND ASSOCIATED FRACTURE ZONES
LARGE SCALE SHEARING, FAULTING, FOLDING AND ASSOCIATED METAMORPHISM FAULTING SHEARING & FAULTING FAULTING, FOLDING & METAMORPHISM
Sedimentation and Tilting Sedimentation and Discordance Folding and metamorphism Volcanic Activity & Columnar Jointing
Seismicity - Mars-quakes
Mars-quakes (?) No Doubt that Mars-quakes should exist as it happens in Moon Possible Causes of Quakes InSighter Module a) Impacts by Meteorites b) Thermal Contraction & Expansion c) Volcanic Activity d) Large Scale Mass Movements e) Plate-tectonic Type Movements f) Daily Rotation and Annual Solar Motion No Instrumentation yet 31 6.2 ACCELERATION (mm/s 2 ) VELOCITY AND ACCELERATION OF EARTH Acceleration VELOCITY (km/s) Velocity 6.0 30 5.8 29 5.6 0 100 200 300 TIME (DAYS)
5) Stress State of Earth & Mars Case 1: Hydrostatic-fluid Case 2: Mantle-crust are elastic & solid; core fluid Case 4: Same condition as above, thermo-plasticity s 1 = s 3 + S ¥ - ( S ¥ - s c ) e - b é 1 s 3 ù û e - b 2 T ë Tan. Stress Max, All Compressive: 6.3 GPa at surface. Basalt UCS is 0.6 GPa Upper Mantle is in plastic state. This was the main cause of tectonics in Earth
Direct Techniques • Overcoring Method • Stress Relief & Restoration Method (Flat jack Method) • Hydraulic Fracturing Method • Sleeve Fracturing Method • Acoustic Emission Method (AEM) InDirect Techniques Compiled by Aydan and Kawamoto, 1998 • Borehole-breakout Method • Fault-Striation Method Stress State of Mars Constitutive Law and • Focal Mechanism Solution Method • Blasthole Damage Method Thermo-plastic yielding characteristics are needed
Proper evaluation of stress state of Mars will enable us to explain Why mountains are high and Why tectonism is less pronounced in Mars Earth Mars
6) Rocks a) Igneous Rocks b) Sedimentary Rocks c) Metamorphic Rocks
a) Igneous Rocks
b) Sedimentary Rocks
c) Metamorphic Rocks
7) Discontinuities i) Tension discontinuities due to - Cooling - Drying - Freezing - Bending - Flexural slip - Uplifting - Faulting, and - Stress relaxation due to erosion or glacier retreation or man-made excavation ii) Shear discontinuities due to - Folding, and - Faulting iii) Discontinuities due to periodic sedimentation, and iv) Discontinuities due to metamorphism. Characterization of rock mass depends upon, intact rocks, discontinuities, weathering state etc.
Discontinuities
Filling of Discontinuities Healing of discontinuities
SURFACE MORPHOLOGY OF DISCONTINUITIES Shear strength of discontinuities are greatly affected by their surface morphology parameters
INDUCED CRACKING OR RE-CRACKING Bending Failure Torsion-induced Failure Re-opening of healed cracks
8) Rock weathering (Chemical or Physical)
9) Slope Stability Problems From Aydan 1989
a) Large Scale Slope Failures Partly from Bigot-Cormier & Montgomery, 2007
Some examples of Rock Slope Stabilities on Earth (compiled from various publications by Aydan)
b) Slope Failures in Layered Rock Mass
b) Slope Failures in Jointed Rock Mass
c) Actual or Potential Slope Failures in Discontinuous Rock Mass
EARTH MARS
d) Steep or Overhanging Cliffs in Layered Rock Mass Coogee
e) Failures of Overhanging Cliffs in Discontinuous Rock Mass Coogee
f) Stability of Precarious Rock Blocks Açıksaray -Cappadocia
g) Impact & Vibration Induced Mass Movements Before Drilling After Drilling
Rover’s Vibration Induced Mass Movements Some wrongly interpreted as the motion was caused by fluid flow, liquefaction etc. Motion of dry granular deposits before and after shaking Before 20 1000 Sand4- dry1 BASE ACCELERATION (gal) CUMULATIVE AE COUNT (x 10) SETTLEMENT (mm) 10 0 After -1000 0 10 20 30 40 50 TIME (sec) From Aydan & Ulusay (unpublished 2000)
SOME INFERENCES FROM SLIDING OF BLOCKS Travel length: 675 cm Inclination: 23.5 degrees NORMALIZED ACCELERATION(a/g) Mt.Fuji Basalt Saw-cut Surface 0.7 FRICTION COEFFICIENT(S/N) S/N 0.6 0.5 0.4 0.3 Maximum Acceleration 0.2 Upper Block Acceleration 0.1 tan( ) a g 0 m -0.1 Maximum Velocity 0 10 20 30 TIME(sec) 2 tan( ) v g max m Basalt friction angle: >30 degrees Maximum Acceleration: 42.13 cm/s 2 Maximum Velocity: 238.5 cm/s
10) Sinkholes (Impact, Solution or Rifting Induced)
11) Properties of Rocks, Discontinuities and Rock Masses
12) Conclusions The rock mechanics aspects of Mars are quite similar to those of the Earth. The differences result from gravitational acceleration, climatic conditions (temperature, humidity, winds), thickness of atmosphere and non or limited amount of ground water. The knowledge on the behaviour of rocks, discontinuities and rock masses acquired on the Earth can be easily used in Mars with the consideration of the differences resulting from gravitation acceleration, climatic conditions and fluid in rock masses.
ACKNOWLEDGEMENTS The author heart-fully thanks the organizing committee and the invitation to join the 2017 Off-Earth Mining Forum and to have chance to address you on my thoughts. The author gratefully acknowledges NASA and the people involved in the development and operation of Mars exploration programs, Mars rovers, namely, Opportunity, Sprit and Curiosity, and processing and releasing their images on related web-sites. The author is solely responsible for the content, statements and opinions made in this presentation Thoughts of the author are based on Images of Mars Rovers and mostly obtained from the following web-site: https://mars.nasa.gov/mer/gallery/images.html
THEMES ■ Laboratory tests on Dynamic Responses of Rocks and Rock Masses; Fracturing of Rocks and Associated Strong Motions ■ Estimation Procedures and Numerical techniques of Strong Motions Associated with the Rupture of Earth’s Crusts and Some Strong Motion ■ Dynamic Response and Stability of Rock Foundations, Underground Excavations in Rock, Rock Slopes Dynamic Responses and Stability of Stone Masonry Historical Structures and Monuments ■ Induced Seismicity ■ Dynamic Simulation of Loading and Excavation ■ Rockburst and Outburst ■ Blasting ■ Impacts ■ Nondestructive Testing Using Shock Waves ■ Case Histories of Failure Phenomenon in Rock Engineering ■ Rock Dynamics in Space
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