1. ROCK SLOPE ENGINEERING

2. ROCK MASS
Rock mass is a non-homogeneous, anisotropic and discontinuous medium ; often it is a pre- stressed mass

3. ROCK MECHANICS
Rock mechanics is defined as “ the theoretical and applied science of mechanical behavior of rock; it is that branch of mechanics concerned with the response of rock to the force field of its physical environment “ - As per ASEG (American Society of Engineering Geology )

4. Applications of Rock Mechanics
Rock mechanics is primarily applied in
Civil Engineering
Mining Engineering
Petroleum Engineering

5. CIVIL ENGINEERING APPLICATIONS
The Civil Engineer is mainly concerned with
Competency of the rock mass to carry the loads of the structures built on it
Stability of the excavations undertaken involving a rock mass, whether surface or underground

6. STRENGTH OF ROCK
Rock should be classified and its strength to be assessed in its simple state of existence i.e unconfined condition
Rock can be either “intact “ or “ jointed”
Parameters for assessing the rock strength/stability
In-situ stress/confining conditions
Environmental factors eg. seepage pressure etc.

7. INTACT ROCK Vs ROCK MASS
No through going fractures
ROCK MASS
Intact rock + Discontinuities

8. INTACT ROCK Vs ROCK MASS (Contd.)
Discontinuity
Joints
Fractures
Faults
Shear zones
Makes the rock discontinuous
Makes the rock anisotropic
Makes the rock stress dependent

9. FACTORS AFFECTING ROCK STRENGTH
Nature of discontinuities
Location of discontinuities
Orientation of discontinuities
Deformability
Strength
Permeability

10. ROCK MASS DESCRIPTION MASSIVE ROCK Rock mass with few discontinuities
Excavation dimension < discontinuity spacing
BLOCKY/JOINTED ROCK
Rock mass with moderate number of discontinuities
Excavation dimension > discontinuity spacing
HEAVILY JOINTED ROCK
Rock mass with a large number of discontinuities
Excavation dimension >> discontinuity spacing

11. DISCONTINUITY PARAMETERS
Spacing & frequency
Orientation & dip/dip direction
Persistence, size & shape
Roughness
Aperture
Discontinuity sets
Block size

12. AFFECT OF DISCONTINUITIES
Permeability – Grouting
Blast design
Stability of slopes

13. ROCK CLASSIFICATION Intact rocks are classified on the basis of
Uni axial compressive strength (UCS)
Modulus of deformation
Modulus ratio
Rocks are classified as of very high strength, high strength, medium strength, low strength and very low strength based on the above classifications

14. ROCK MASS CLASSIFICATIONS
Terzaghi’s in situ rock classification
Intact
Stratified
Moderately jointed
Blocky and seamy
Crushed
Squeezing
Swelling

15. ROCK MASS CLASSIFICATIONS (Contd.)
Rock quality designation (RQD)
Very Poor ( 0-25)
Poor (25-50)
Fair (50-75)
Good (75-90)
Excellent (90-100)
RQD , expressed as % , is the summation of all the cores larger than 10 cm from the preferred 150 cm drilled core run.
RQD = Jn

16. ROCK MASS CLASSIFICATIONS (Contd.)
Geomechanics classification (RMR)
Based on the following parameters
UCS of Intact material/rock
RQD
Spacing of discontinuities
Condition of discontinuities
Ground water condition
Orientation of discontinuities

17. ROCK MASS CLASSIFICATIONS (Contd.)
Q-System (Norwegian geo.tech classification)
Based on i) RQD ii) No.of joint sets
iii) Joint Roughness iv) Degree of alteration or filling v) Water inflow vi) stress condition.
Based on these parameters Q is expressed as (RQD/Js)x (Jr/Ja) x (Jw/SRF)

18. ROCK MASS CLASSIFICATIONS (Contd.)
RMR (Rock mass rating ) proposed by Bieniawsky (1973,19888 & 1993) based on shear strength parameters (Cohesion c and Ф (angle of friction) ). The rock mass is classified at five levels.

19. ROCK QUALITY
(Massive Rock) (Jointed Rock) (Massive Rock) (Heavily Jointed Rock)

20. ROCK QUALITY Q=100(Massive Rock) Q=3 (Jointed Or blocky Rock)
Rock mass with few discontinuity
Excavation dimension< discontinuity spacing
Q=3 (Jointed Or blocky Rock)
Rock mass with moderate nos. of discontinuity
Excavation dimension> discontinuity spacing
Q=0.1(Heavily Jointed Rock)
Rock mass with large nos. of discontinuity
Excavation dimension >> discontinuity spacing.

21. SLOPE FAILURE MECHANISIM
CONTINUUM
MANY CONTINUTIES
WEAK ROCK
EFFECTIVELY CONTINUUM
DISCONTINUUM
FEW CONTINUTIES
STRONG ROCK

22. TRANSITION FROM INTACT ROCK TO HEAVILY JOINTED MASS
IDEALISE ILLUSTRATION OF TRANSITION FROM INTACT ROCK TO HEAVILY JOINTED MASS WITH INCREASING SAMPLE SIZE (AFTER HOEK AND BRON,1980)

23. JOINTS PROBLEM IN CIVIL ENGINEERING
ROAD CUTTING ARE CONSTRUCTED, WHERE POSSIBLE AT RIGHT ANGLE TO STRIKE OF THE MAIN, GENTLY TO MODERATLY DIPPING PLANES OF WEAKNESS IN THE ROCK.

24. JOINTS PROBLEM IN CIVIL ENGINEERING (Cont.)
RESERVOIR AND DAMS: THE AXIS OF THE DAM SHOULD BE CONSTRUCTED PARALAL TO MAIN FACTURE SET AND THE LATER SLOULD DIP UPSTREAM TOWARDS THE RESERVOIR.

25. Rock “Material”-STRONG, Stiff, Brittle
ROCK ENGINEERING
Rock “Material”-STRONG, Stiff, Brittle
WEAK ROCK> STRONG CONCRETE.
STRONG IN COMPRERSSION, WEAK IN TENSION
POST PEAK STRENGTH IS LOW UNLESS CONFINED.
Rock “Mass”-behavior controlled by discomfitures.
ROCK MASS STRENGTH IS ½ TO 1/10 OF ROCK STREGTH.
Discontinuities give rock masses scale effects

26. ROCK ENGINEERING (Contd.)
ROCK STRESSES IN SITU
VERTICAL STRESS ≈ WEIGHT OF OVERLYING ROCK
~27 KPA / M => 35.7 MPA AT 1300 M
HORIZONTAL STRESS CONTROLLED BY TECTONIC FORCES (BUILDS STRESSES) & CREEP (RELAXES STRESSES)
AT DEPTH, σv ≈ σh UNLESS THERE ARE ACTIVE TECTONIC FORCES

27. ROCK SLOPES SLOPES CAN BE NATURAL SLOPES
MAN-MADE OR CUT SLOPES EXCAVATED FOR
ENGINEERING CONSTRUCTION LIKE BUILDINGS, ROADWAYS, WATER WAYS, WATER RESOURCES/HYDRO-ELECTRIC PROJECTS ETC.
OPEN CAST MINING

28. FAILURE OF SLOPES The extraneous factors can be
Failure of natural slopes is common geological phenomenon
Reasons for failure are
Imbalance between shear strength and the shear stress in the ground/rock mass
Failure can be either slow-time dependent process or by extraneous factors in an abrupt manner.
The extraneous factors can be
Increased shear stresses due to surface loadings
seepage pressure due to built up of hydro static pressure.

29. SLOPE FAILURE MECHANISMS
Rock falls due to dislocation of blocks (Mostly occur on steep slopes - with out sliding)
Fractures/weathered rock slope fails along a curved surface with a rotational slide
Translational slide to be planar along weak bedding/shear plane/fault zone
Movement initiates rotational slides where as imbalance in forces results in translational movements.

30. MODES OF FAILURES Rotational or circular/arc failure
Sliding /planar failure
Wedge failure
Toppling failure (without sliding mechanism)
Buckling failure
In any open/surface rock excavation, one mode or a combination of several modes of failures can occur

31. FAILURE MECHANISMS HAVE GENERALLY BEEN DESCRIBED AND ANALYZED IN TWO DIMENSIONS

32. MAIN LANDSLIP TYPES

33. SLOPE MASS RATING
A practical approach proposed by ROMANA (1985) to evaluate the slope stability. SMR is expressed as SMR = RMRbasic – (F1,F2,F3) + F4 Where RMR basic is evaluated according to Bieniawsky (1979,1989) F1= Square (1-Sin A) Where A denotes angle between strikes of slope face and that of the joints

34. SLOPE MASS RATING (Contd.)
F2 = Tan (βj) where βj is the joint dip angle in planar failure mode. Both F1 and F2 vary from 0.15 to 1.0. For toppling mode of failure value of F2 becomes 1.0 F3 = Measure of relationship between the slope face and joint dips.In planar failure mode F3 refers to the probabilty of joints day-lighting in the slope face.

35. SLOPE MASS RATING (Contd.)
F4 pertains to adjustment for the method of excavation. Values of F4 are as follows:
Natural slope
Pre splitting
Smooth blasting
Normal blasting or
mechanical excavation
Poor blasting
SMR value ranges from 0 to 100

36. FOUNDATIONS ON ROCK

37. STABILITY OF SLIDING BLOCK RELATED TO DIP OF SLIDING SURFACE.

38. POTENTIAL FAILURE PATH

39. ANALYSIS OF ROCK SLOPES
Rock mass or the proposed slope needs to be analyzed for the possible mode of failure
Rock slopes can be analyzed by
Conventional limit equilibrium methods/closed form solutions
Numerical approximation methods
Discrete element methods
Finite element methods

40. SLOPE STABILITY / PROTECTION
Decreasing the seepage pressure
Flattening the rock slope as much as possible
Reducing the height of slope/excavation depth (may not be possible in some situations)
Rock support measures
Rock bolts/rock anchors/soil nailing
Shotcrete with or without wire mesh (mainly to improve/protect the surface stability)

41. SLOPE STABILITY / PROTECTION (Contd.)
Toe protection – Retaining walls/butress with weep holes
Tree plantation/grass turfing
Catch water drains
Nailing wire mesh/geo-grids ( in to steep slopes)
Drainage gallery behind toe ( in special circumstances)

42. Rock Slope Stability Problems In Himalayas

43. Slope Protection Using Soldier Piles/Shotcrete Retaining Wall

44. Slope Protection Using Soldier Piles/Shotcrete Retaining Wall

45. Use of Soil Nail in Slope Protection

46. Use of Soil Nail in Slope Protection

47. Use of Soil Nail in Slope Protection

48. Use of Rock Anchors/Shotcrete in Slope Protection

49. POINT TO PONDER
“…… Care has to be taken that the design is driven by sound geological reasons and rigorous Engineering Logic rather by the very attractive images that appear on the Computer screen.”
by Hoek, 1999

50. POINT TO PONDER
The innocent rock mass is often blamed for insufficient stability that is actually the result of rough and careless blasting. Where no precaution have been taken to avoid blasting damage, no knowledge of the real stability of undisturbed rock can be gained from looking at the remaining rock wall. What one sees are the sad remains of what could have been perfectly safe and stable.
by Holmberg and Persson,1980

51. THANK YOU