Parameters and Methods For Quantitative Description of Discontinuities in Rock

JOINT ANALYSIS PART I to

Parameters and Methods For Quantitative Description of Discontinuities in Rock

Masses IS 11315 Part 1 To 4 FOR CE 427, CE635 and CE 6540

PROFESSOR M. MASROOR ALAM

mmalam.cv@amu.ac.in

DISCONTINUTIES

• Different level of discontinuities are found in nature in and around rock masses.

• In ascending order of their size they are:

• Grain and Mineral Boundaries

• Layers (Lamination, Foliation, Bedding and Flowage Plains)

• Joints

• Contacts

• Shear Zone

• Fault

• Unconformity (Non-, Angular-, Blended-, Dis-, Para- Conformity)

• Plate Boundary (Divergent, Convergent, Translational)

FOREWORD

• In view of advancement of Rock

Mechanics, the expert group of Rock Slope, Rock Foundation and Rock

Mass Improvement has worked out careful description of discontinuities in rock masses.

• The majority of rock masses on the surface and within few hundred

meters below the surface, behave as discontinuous ground mass.

• It is the discontinuities which

determine the mechanical behaviour of rock mass.

DISCONTINUITIES (Grain Boundaries)

DISCONTINUTIES (Layers)

Siw alik Sa ns to ne Sur endr ana ga r Po rc el la ni tes , O br a, U P

TWO DIFFERENT ROCKS

QUARTZITE &

CONGLO- -MERATE, Aravalli Bayana, Raj.

Contact

&

Foliation Quartzite

&

Phyllite

Nainital

Lava flow from

#Kilauea volcano in Hawaii

continues to advance

towards small town of #Pahoa ... thousands

affected—

Mario Picazo

(@picazomario) October 24,

2014

8 Prof. M M Alam, CED, AMU, Aligarh

FLOWAGE PLAIN

J O I N T S Y S T E M, L A L I T P U R

SHEAR ZONES

(“Fused” in Augen Gneiss, on a rock slab)

SHEAR ZONE IN SANDSTONE AT RASUL PUR < FATEHPUR SIKRI

SHEAR ZONE

In Limestone

Incorporating

a FAULT

FOLDED SHEAR ZONE, SOHNA, HARYANA

F A U L T

FOLD AND FAULT

FAULT,

QUARTZITE, MANDWARA LALITPUR

Bijawar Formation 2000 My Old

U N

C O

N F

O R

M I

T Y

DESCRIPTION AND QUANTIFICATION OF DISCONTINUITIES

• To get the unified description of rock mass and

discontinuities, it is essential that the structure in rock mass and discontinuities are carefully described and quantified.

• So that it may become possible to design Engineering Structure on or in the rock mass with a minimum

expense in insitu testing.

• Careful description will enhance the value of the insitu

tests that are performed as well as the interpretation

and extrapolation will be more reliable.

D I S C O N T I N U I T I E S

• Discontinuity is a general term for any mechanical break in rock mass along which the rock mass has “ZERO” or negligible tensile strength.

• It is a collective term for most of the JOINTS, weak

BEDDING PLANES, weak SCHISTOSITY PLANES, SHEAR ZONES and FAULTS

• Why not FOLIATION, CONTACTS and UNCONFORMITIES

• Ten parameters are essential of discontinuities for rock mass survey: Orientation, Spacing, Persistence,

Roughness, Wall Strength, Filling Material, Seepage,

Number of Sets and Block Size

Four Set plus Random joints

J O

I N

T

A N A L Y S I S

F O

R R O C K M

A S S

C H A R A C T E R I Z A

T I O N

JOINTS (Systematic)

JOINTS (Systematic & Non Systematic)

PART – 1 ORIENTATION

• The orientation of discontinuities relative to an

engineering structure largely controls the possibility of UNSTABLE conditions or any kind of deformation,

slippage.

• The discontinuities orientation becomes more

important when few other parameters are not in good condition i.e. presence of Shear Zones, Multiple

number of Joint Sets

• The mutual orientation of different discontinuity sets

will determine shape and size of blocks, the mosaic a

rock mass is comprise of.

• Orientation defines the attitude of discontinuity in space

• Described by Strike of Azimuth (α) and Dip in terms of direction and amount of maximum inclination (β).

• It can be measured by using Brunton Clinometer Compass by reading clockwise from True North.

• When rock is strongly magnetic then a CLINO-RULE, and AZIMUTH PROTACTOR should be used.

• The STRIKE or AZIMUTH may be recorded in three digits

(010

, 115

, i.e. 000

to 360

), dip direction in three digits

and amount in two digits (05

, 45

, i.e. 00

to 90

) with a

slash in between (030

/225

)

JOINT SPACINGS – Part 2

JOINT SPACING CLASSES

BEDDING PLANE

SPACING JOINT PLAIN SPACING LIMITS OF SPACINGS MASS FACTOR (j) Very Thickly Bedded Extremely Wide Over 2.0 m 0.8 to 1.0

Thickly Bedded Very Wide 0.6 to 2.0 m 0.6 to 0.8

Moderately Bedded Wide 20 to 60 cm 0.4 to 0.6

Thinly Bedded Moderately Wide 600 to 202 mm 0.2 to 0.4 Very Thinly Bedded Moderately Narrow 200 to 60 mm 0.1 to 0.2

Laminated Narrow 60 to 20 mm 0.08 to 0.1

Thinly Laminated Very Narrow

Extremely Narrow 20 to 6 mm

Less than 6mm 0.06 to 0.08 < 0.06

DISCONTINUITY RECURRENCE & SPACINGS

Line No. Trend

of Line Plunge

of Line Length

of Line No. of

Fractures Spacing (s) Ave.

Spacing REMARKS

Line 1

Line 2

Line 3

Discontinuity Spacings (m) - [ ]

1- Ext. Wide >2 m, 2- Very Wide 0.6 – 2 3- Wide 0.2- 0.6

4- Mod. Wide 0.06 – 0.2

5- Mod. Narrow 0.02 – 0.06 6 - Narrow 0.006 – 0.02,

7 - Very Narrow < 0.006

JOINT PERSISTENCE - Part 3

• Very Low Persistence < 1 m Low Persistence 1 to 3 m

• Medium Persistence 3 – 10 m High Persistence 10 to 20 m

• Very High Persistence 20 – 100 m Extremely High Persistence >100m

• Massive – Few joints with vey wide spacings

• Blocky – Approximately Equi-dimensional

• Tabular – One dimension considerably shorter than other two

• Columnar - One dimension considerably larger than other two

• Irregular – Wide variation in block size and shape

• Crushed – Heavily jointed to “Sugar Cube”

JOINT SURFACE ROUGHNESS OR ASPERTIES – Part 4

• Polished Slickensided Decreasing

• Slickensided PLANAR Smooth Shear

• Smooth Rough Strength

• Rough

• Ridges and Furrows Slickensided

• Small Steps UNDULATING Smooth

• Very Rough Rough

Increasing Shear Strength

Annon 1977 Slickensided

STEPPED Smooth

Rough Barton 1978

PL UM O SE M ARKI NG S

ST EPP ED SL IKE NS ID ED

PL AN AR SL IKE NS ID ED

ST EPP ED SL IKE NS ID ED

PL ANAR SM O OT H

RIDGE S A N D FURR O W S

JOINT WALL STRENGHT Part - 5

• When the rock walls are in direct contact with each other along a discontinuity shear displacement in response to shearing

stresses become important.

• Rock Masses are frequently weathered along the discontinuity plains

• It is a relatively “thin skin” of wall rock which affect the shear strength of discontinuity of other wise strong rock away from the wall

• Mineral Coating can also affect the shear strength to a mark degree. Extent and thickness of coating should be worked out

• Type of mineral coating is important which can be Calcareous, Ferruginous, Siliceous, Carbonaceous, Talcy, Chloritic, Kaolinitic

THANKS