Some Thoughts About Rock Mechanics Aspects of Mars

Ömer Aydan

University of the Ryukyus, Department of Civil Engineering

Nishihara, Okinawa, Japan

3rd Off Earth Mining Forum - 2017OEMF

Opportunity Curiosity Spirit

Courtesy of NASA

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

Contents

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

(Rock Mechanics in Other Planets)

(Contents)

2) General Characteristics of Mars

Gravitational acceleration is 0.377g of the Earth

Radius is 3389 km

Mean density is 3.933 g/cm3

3-1) SURFACE TOPOGRAPHY From NASA

3-2) SURFACE GEOLOGY OF MARS

c) TEMPERATURE VARIATIONS

Temperature difference is more than 80 degrees

Subjected to Harsh Freezing and Thawing Environment provided rock is saturated

From NASA

Earth is 20-40 degrees

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

Volcanic Activity & Columnar Jointing Folding and metamorphism

Seismicity - Mars-quakes

Mars-quakes (?)

No Doubt that Mars-quakes should exist as it happens in Moon Possible Causes of Quakes

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

InSighter Module

No Instrumentation yet

0 100 200 30029

30

31

5.6

5.8

6.0

6.2

TIME (DAYS)

VE

LO

CIT

Y (

km

/s)

AC

CE

LE

RA

TIO

N (

mm

/s2)VELOCITY AND ACCELERATION OF EARTH

Acceleration Velocity

5) Stress State of Earth & Mars

s1 = s3 + S¥ - (S¥ -s c )e-b1s3é

ëùûe

-b2T

Case 1: Hydrostatic-fluid

Case 2: Mantle-crust are elastic & solid; core fluid

Case 4: Same condition as above, thermo-plasticity

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

• Overcoring Method

• Stress Relief & Restoration Method (Flat jack Method)

• Hydraulic Fracturing Method

• Sleeve Fracturing Method

• Acoustic Emission Method (AEM)

Compiled by Aydan and Kawamoto, 1998

Direct Techniques

InDirect Techniques

• Borehole-breakout Method

• Fault-Striation Method

• Focal Mechanism Solution Method

• Blasthole Damage Method

Stress State of Mars Constitutive Law and

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.

Before

After

Motion of dry granular deposits before and

after shaking

From Aydan & Ulusay (unpublished 2000)

10 20 30 40 50

10

20

-1000

0

1000

0

TIME (sec)

SE

TT

LE

ME

NT

(m

m)

CU

MU

LA

TIV

E A

E C

OU

NT

(x 1

0)

BA

SE

AC

CE

LE

RA

TIO

N (

gal)Sand4- dry1

Travel length: 675 cm

Inclination: 23.5 degrees

Maximum Acceleration: 42.13 cm/s2

Maximum Velocity: 238.5 cm/s

Basalt friction angle: >30 degrees

)tan( m

gaMaximum Acceleration

)tan(2max

m

gv

Maximum Velocity

SOME INFERENCES FROM SLIDING OF BLOCKS

0 10 20 30-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

TIME(sec)

FR

ICT

ION

CO

EF

FIC

IEN

T(S

/N)

NO

RM

ALIZ

ED

AC

CE

LE

RA

TIO

N(a

/g)

S/N

Upper Block Acceleration

Mt.Fuji Basalt Saw-cut Surface

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.

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

ACKNOWLEDGEMENTS

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