Stability of Historic Monuments in Rocks: Case Studies ... Monuments_Hatzor.pdf · Rock Mechanics...

Stability of Historic Monuments in Rocks: Case Studies from Israel

Yossef H. HatzorRock Mechanics Laboratory of the Negev

Dept. of Geological and Environmental Sciences

Ben-Gurion University of the Negev, Beer – Sheva, Israel

Rock Mechanics Laboratory of the Negev, Dept. of Geological and Environmental Sciences, Ben-Gurion University 2

The Rock Mechanics ChallengeHistoric monuments of great cultural importanceVery long life span: 1000 – 3000 yearsLong term exposure to severe environmental impacts:

Seismic loadingClimatic fluctuations (temperature, relative humidity, sun radiation)

Variable rock mass conditions:Weak and continuous (Beit Guvrin)Strong and discontinuous (Masada).

Challenging structural constructions:High span underground openingsSteep natural rock slopes

Safe and aesthetic preservation are key issues


Case Studies• Tel Beer Sheva: a 3000 year old underground water reservoir

in a horizontally bedded and vertically jointed rock mass

• The Cave of Zedekayah: a 2000 + year old underground quarry in strong and discontinuous rock

• Bet Guvrin: a 1000 year old system of underground openings in a weak and continuous rock mass

• Masada: Civil structures on top of natural rock slopes in a strong and discontinuous rock mass which has been subjected to intense seismic activity over the past 2000 years


Tel Beer Sheva

Project funded by: Israel Nature and Parks AuthorityProject funded by: Israel Nature and Parks AuthorityGraduate Students: Ron Benary, Michael TsesarskyGraduate Students: Ron Benary, Michael Tsesarsky


Artist Conception of the Water System

Drawing courtesy of TBS national park


The Challenges• Rock Mechanics Challenge:

An ancient water reservoir excavated in a relatively weak, horizontally bedded and vertically jointed rock mass

• Preservation challenge:Stabilization of the roof but with minimal interference with original design and maximum preservation of original rock face

• Approach:– Geometrical Model– Mechanical Properties of

Rock– Stability Analysis

(Numerical Methods - DDA)


The Geological Cross Section at the Site


Inside View – The Discontinuous Roof


System Layouta a

b b


Influence of Rock Structure on Excavation


Compressive Rock Strength

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2Strain (%)

0

5

10

15

20

25

30

35

Axi

al S

tress

(MP

a)

β = 90ο

β = 0ο

AxialRadial


Shear Strength of Discontinuities

0 2000 4000 6000 8000Normal Stress (kPa)

0

10

20

30

40

50

φ (d

eg.)


Kinematics of a Jointed Beam (Voussoir)

φ = 30οφ = 45οφ = 75οφ = 80ο

Initial Geometry

Deformed state

S = 8m, t = 0.5m, Sj = 0.25m


Kinematics of a Layered, Jointed Beam(Laminated Voussoir)

φ = 30οφ = 50οφ = 60οφ = 70ο

(S = 8m, t = 0.5m, T = 6m, Sj = 0.25m )


The Influence of Joint Spacing and Friction on Beam Stability

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800

Vertical joint spacing (cm)

Fric

tion

angl

e re

quir

ed fo

r st

abili

ty

From Hatzor and Benary, 1998. Int. J. Rock Mech. Min. Sci.


The Cave of Zedekayah, Jerusalem

Project Funded by: The National Quarry Restoration FoundationProject Funded by: The National Quarry Restoration FoundationGraduate Student: Graduate Student: CarolaCarola ImermacherImermacher


System Layout

Maximum Length – 230 mMaximum Width – 100 mAverage Height – 15mEstimated Area - 9000 m2

Map courtesy of Z. Temkin - Tik Projects


The Challenges• Rock Mechanics Challenge:Extremely high span opening (40

meters) excavated in bedded and jointed rock

• Preservation Challenge:Minimum interference with original

excavation faces while ensuring maximum visitor safety

• Approach:Geometrical ModelMechanical PropertiesStability Analysis


Rock Strength:Point Load and Brazilian Tests


Summary of Mechanical and Physical Properties

• Dry Density = 1973 kg/m3• Bulk Porosity = 27%• Elastic Modulus = 8 GPa• Poisson’s Ratio = 0.14• Uniaxial Compressive Strength Normal to Bedding = 11 MPa• Uniaxial Compressive Strength Parallel to Bedding = 16 MPa• Tensile Strength (Brazilian) = - 2.8 MPa


Failure Mode of Roof Assuming Continuity and Linear Elasticity (L = 30m)

Maximum Tensile Stress at Roof = 10.5 MPaMaximum Deflection = 7.37 cmMaximum Shear Stress = 450 kPa


The (Important) Role of Discontinuities

Bedding planes

Oblique Joints

Vertical Joints


2D Discontinuous Deformation Analysis

1st realization: horizontal beds and inclined joints

2nd realization: horizontal beds and vertical joints


Expected Deformation


Proposed Solution: Rock Bolting


The Bell – Shaped Caverns at Beit Guvrin

Project Funded by:Project Funded by:1)1) Israel Nature and Parks AuthorityIsrael Nature and Parks Authority2)2) Ministry of National Infrastructure Ministry of National Infrastructure –– The National Quarry Restoration FoundationThe National Quarry Restoration FoundationGraduate Student: Michael TsesarskyGraduate Student: Michael TsesarskyCoCo--PI: Dr. Mark PI: Dr. Mark TalsenickTalsenick, The , The TechnionTechnion


The Challenges• Rock Mechanics Challenge:Extremely high span and height

opening (40 meters/ 20 meters) excavated in a discontinuous and very weak rock that exhibits time dependency

• Preservation Challenge:The system is at an advanced stage

of disintegration – can it be saved without ruining it?

• Approach:Geometrical ModelMechanical PropertiesStability Analysis


System LayoutNorthen System

The “Yard”

Southern System

0 40 m

Collapsed Pillar

� 6

5

1

�

��

11

8

9

1412

10

13

16

13

14

11

10

�

�7 4

32

9

8

1

12

Single bell shaped cavern which collapsed

in winter 1995

�

3

4a

2

4b

4c

Legend

Boundary ofcollapsed system

Existing Cavern Wall

Vertical shaft

Inner Pillar

LVDT Transducer

2 Location of photograph


Determination of Mechanical Properties of Rock

Sampling

Rock Testing

Continuous Members Discontinuities

Test Preparation


Influence of Rock Anisotropy on Rock Strength

0123456789

10

-1.5 -1 -0.5 0 0.5 1 1.5 2 2.5Strain (%)

Stre

ss D

iffer

ence

(MPa

)Pc = 0 MPa β = 900

β = 00

Axial StrainRadial Strain

σ1β

σ1

From Tsesarsky, Hatzor, and Talesnick, 2000. Isr. J. Earth Sci.

ε R1ε R2

n̂

σ 1

σ1

900


Influence of Water Content on Compressive Strength

0123456789

10

0 5 10 15 20 25 30 35 40 45 50

Water Content (%)

Uni

axia

lStr

engt

h (M

Pa)

β = 0 0

β = 90 0

From Talesnick, Hatzor, and Tsesarsky 2001. Int. J. Rock Mech. Min. Sci.


Summary of Mechanical Properties

• Peak compressive strength parallel to bedding 9 MPa

• Peak compressive strength normal to bedding 5 MPa

• 50% reduction in rock strength with water content increase from 3% to 50% in both states

• Peak tensile strength parallel to bedding = 1 MPa• Decrease in tensile strength due to water content

same as in compression


Stress Distribution AnalysisSingle Opening, Maximum Free Span 24m

x

y

40 kPa

ghyy ρσ −=

yyxx σννσ−

=1

x

y

40 kPa

ghyy ρσ −=

yyxx σννσ−

=1

x

y

40 kPa

ghyy ρσ −=

yyxx σννσ−

=1

Vertical stress distribution

Horizontal stress distribution

Factor of safety against crushing at roof = 40

Factor of safety against crushing at abutments = 17


Two Overlapping Openings Maximum Free Span 34 meter



Factor of safety against crushing at roof = 13

Factor of safety against crushing at abutments = 6


Two Adjacent Openings

Factor of safety against crushing at common side wall:F.S. = 3 (Wall thickness = 3m)F.S. = 2 (Wall thickness = 2m)




Stress Re-Distribution after Collapse of Common Side Wall: Free Span = 64 meter

• Factor of safety against crushing at roof = 2• Factor of safety against crushing at abutments = 4• Factor of safety against tensile rupture in roof = 0.5!


Monitoring In Situ Cavern Wall Performance (Transducers By DINA Elc.)


Monitoring Results – Southern SystemMonth

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6 9 11 1 2 4 5 7 8 10 12 1 3 5 6 8 10 12 1

8.9.1996 - 26.1.1999

Rel

ativ

e D

ispl

acem

ent (

mm

)

SF4

SF9

SF1

SF12

SF5


Monitoring Results – Northern System

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1 9 11 1 3 4 6 9 11 1 6 8 10 12

12.9.96 - 22.1.99

Rel

ativ

e D

ispl

acem

ent (

mm

)

NF11

Month

NF16

NF6

NF1


Masada

Project Funded by Israel Nature and Parks AuthorityProject Funded by Israel Nature and Parks Authority


Failure Modes in Masada Rock Slopes

East Face – Failure of large, individual blocks North Face – Disintegration of entire slope due to interaction of many, small,

blocks (different talk)


The Challenge• Reinforcement of a

fractured rock mass• Consideration of

dynamic loads• Ensuring maximum

visitor safety• Minimum damage for

restoration efforts• Preservation of original

rock slopes wherever possible


Key block Displacements – East Face


Monitoring Installation Program

Block 1Block 2

Block 3


Typical Displacement Output – Block 3

-1

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

14 / 1

/ 98

18 / 1

/ 98

23 / 1

/ 98

27 / 1

/ 98

31 / 1

/ 98

4 / 2

/ 98

8 / 2

/ 98

12 / 2

/ 98

16 / 2

/ 98

21 / 2

/ 98

25 / 2

/ 98

1 / 3

/ 98

5 / 3

/ 98

9 / 3

/ 98

13 / 3

/ 98

18 / 3

/ 98

22 / 3

/ 98

28 / 3

/ 98

02/04

/9814

/ 4 / 9

827

/ 4 / 9

8 9

/ 5 / 9

8 21

/ 5 / 9

8 3

/ 6 / 9

8 15

/ 6 / 9

8 28

/ 6 / 9

8

Date

Rel

ativ

e D

ispl

acem

ent

0

50

100

150

200

250

Flat

jack

Pre

ssur

e

FJ 3

JM 10

JM 11

JM = Joint Meter(LVDT) FJ = Flat Jack

Displacement in mm, pressure in kPa


Superposition of outputs from 3 Blocks

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

14 / 1

/ 98

18 / 1

/ 98

23 / 1

/ 98

27 / 1

/ 98

31 / 1

/ 98

4 / 2

/ 98

8 / 2

/ 98

12 / 2

/ 98

16 / 2

/ 98

21 / 2

/ 98

25 / 2

/ 98

1 / 3

/ 98

5 / 3

/ 98

9 / 3

/ 98

13 / 3

/ 98

18 / 3

/ 98

22 / 3

/ 98

28 / 3

/ 98

02/04

/9814

/ 4 / 9

827

/ 4 / 9

8 9

/ 5 / 9

8 21

/ 5 / 9

8 3

/ 6 / 9

8 15

/ 6 / 9

8 28

/ 6 / 9

8 12

/ 7 / 9

8

Date

Rel

ativ

e D

ispl

acem

ent

Bedrock

Block 1

Block 3

Block 2

Displacement in mm


Influence of Climatic Changes on Block Displacement


2D Stability Analysis – Block 1

ψ

H = 15mV

U

W

b

J1J3

J2

A A’

A

A’

Plan view of Block 1

N

5 m

α=2oo

DDATUM, Zw = 0


3D Stability Analysis – Block 1


Total Required Support Force (Ton) for Block 1

0

500

1000

1500

2000

2500

3000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7PEAK HORIZONTAL GROUND ACCELERATION (g)

SU

PPO

RT

FOR

CE

Dry Case

Saturated Case

FACTOR OF SAFETY = 1 . 5

From Hatzor 2003. Journal of Geotechnical and Geoenvironmental Engineering, ASCE.


Support Installation


The Final Product


King Herod Palace


The Problem – Highly Discontinuous Rock


Mesh Generation Philosophy:Synthetic or Deterministic?

Synthetic joint trace generation

Deterministic joint trace generation


The Resulting Deterministic DDA Mesh- W -- E -


The Dynamic Loading Input Function

0 10 20 30 40 50 60Time (sec)

-0.08

-0.04

0

0.04

0.08

0.12

Accl

. (g)

-0.08

-0.04

0

0.04

0.08

0.12

Accl

. (g)

Vertical

E - W

-0.12

-0.08

-0.04

0

0.04

0.08

0.12A

ccl.

(g) N-S


Predicted Damage by DDA

No Energy Dissipation

2.5% Kinetic Damping5% Kinetic Damping


Rock Bolt Reinforcement:Modified Record Normalized to a 0.6g PGA

Sparse Bolting Pattern: L = 6m, s = 4m

Dense Bolting Pattern: L = 6m, s = 2m

Stability of Historic Monuments in Rocks: Case Studies ... Monuments_Hatzor.pdf · Rock Mechanics...

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