This document discusses geological data collection and stereographic plotting. It defines important parameters for characterizing discontinuities in rock masses, including rock type, discontinuity type, orientation, spacing, persistence, roughness, strength, weathering, aperture, filling, seepage, number of joint sets, and block size/shape. These parameters should be defined consistently using standard procedures to facilitate communication between parties and allow for quantitative engineering analysis. Methods of data collection discussed include surface mapping, geotechnical drilling, core orientation, and borehole imaging.

1. 2-1
LESSON 2 – GEOLOGICAL DATA
COLLECTION and STEREOGRAPHIC
PLOTTING
Learning Outcomes -
List important geological parameters of
discontinuities;
Plot and analyze structural orientation
(stereonet) data.

2. 2-2
Range of rock mass characteristics.

3. 2-3
Scale

4. 2-4
Pervasive discontinuities
Favorably oriented

5. 2-5
Strong rock widely spaced
joints.

6. 2-6Unfavorably oriented discontinuities control

7. 2-7
Definition of Geological Terms
Standard Definitions/Procedures Necessary for:
- Consistency and Compatibility Between Different
Data Collectors
- Facilitate Communication Between Different Parties
- Quantitative Basis for Engineering Evaluation and
Analysis
- Completeness in Data Collection

8. 2-8
Definition of Discontinuity Parameters
Figure 2-2
Page 2-6

9. 2-9
A. - Rock Type
Deere and Miller
Colorado School of Mines Quarterly
(Russell B Travis)

10. 2-10
B Discontinuity Type
Contact - (Continuous and Sometimes Low
Shear Strength e.g. Weathered Paleosurface
Dipping into Cut)
Fault/Shear - (Continuous, Potentially Low
Shear Strength)
Joint - (Cooling in Basalt, Tectonic Effects
Sedimentary/Igneous)
Bedding - (Sedimentary Layering)

11. 2-11
B Discontinuity Type (cont’d)
Flow Banding - (Igneous Flows; May Not be
Weakness)
Foliation/Schistosity/Cleavage - (Metamorphic
Layering)
Vein - (Includes “Healed Joints” - May Not be
Weakness)

12. 2-12
Joints are controlling discontinuities

13. 2-13
Bedding is
controlling
discontinuity
I40, NC/TN

14. 2-14
C Discontinuity Orientation
Dip - Angle of Steepest Inclination of Plane,
Measured Below Horizontal (two digits 00 to 90)
Dip Direction (Dip Azimuth) - Azimuth of the
Line of Dip (three digits 000 to 360)
Strike - Azimuth of a Horizontal Line (90
Degrees to Dip Direction) - Unsuitable for Rock
Slope Engineering

15. 2-15
Definition of Dip, Dip Direction,
Strike

16. 2-16
Structural Compass

17. 2-17
D Discontinuity Spacing
Measure True Spacing in Surface Mapping
Range:
Extremely close spacing (<20 mm)
Extremely wide spacing (>6000 mm)
Line Mapping or Coreholes: Use Terzaghi
Correction for True Spacing

18. 2-18
True and Apparent Spacing
Fracture Set Rock Face
Sapp SappSapp
S
S
S
θ

19. 2-19
Extremely close foliation
spacing
Will strongly influence rock
mass:
• strength
• deformability
• permeability
• excavatability

20. 2-20
E Persistence
Document Visible or Inferred Length
- Range:
Very low (<1 m)
Very high (>20 m)
Document Termination of Joints (0, 1, 2)
Statistical Estimates of Length Distribution (e.g.
Pahl, page 2-8)
Persistence cannot be Measured in Core

21. 2-21
Measurement of Persistence
L
H
(t)
(t)
(t)
(t) (t)
(t)
(c)
(c)
(c)
(c)(c)(c)(c)
(c)
s
S’
Scanline
Í
ś


22. 2-22
Persistence of family of
faults will control abutment
design

23. 2-23
F Irregularity/Roughness
Descriptive
Shape: Roughness:
Stepped Rough
Undulating Smooth
Planar Slickensided
Semi Quantitative - Joint Roughness Coefficient
(JRC)
Rough Undulating JRC 20 e.g. Tension Joints
Smooth Undulating JRC 10 e.g. Foliation/Joints
Smooth Planar JRC 5 e.g. Bedding

24. 2-24
Discontinuity Roughness
Measurement
i2d i8d
id i4d
4d8d
2d
d
Mean dip
1
2
Quantitative approach

25. 2-25

26. 2-26
G Wall Rock Strength - (Joint
Compressive Strength - JCS)
Estimate Compressive Strength Based on:
- Field Classification (ISRM) - Table 2-1:
Range:
Extremely weak (0.25-1MPa)
Extremely strong (>250 MPa)
- Field Testing (Point-Load Test or Schmidt Hammer)
- Laboratory Testing

27. 2-27
H Weathering
ISRM Weathering Classification - Table 2-2
- Fresh
- Slightly weathered
- Moderately weathered
- Highly weathered
- Completely weathered
- Residual soil

28. 2-28
Differential shale weathering

29. 2-29
Chemical decomposition

30. 2-30
I Aperture
Measure Directly, Table 2-1:
Range:
- Very tight (<0.1 mm)
- Cavernous (>1000 mm)

31. 2-31
J Filling/Width
Measure Width (Table 2-2)
Characterize Wall Rock
Infilling Characteristics
- Mineralogy
- Particle Size
- Water Content
- Stiffness

32. 2-32
25 mm thick, continuous clay
infillings (bedding plane shears)

33. 2-33
Controlling structure for slope design
Rocky Point Viaduct, OR

34. 2-34
K Seepage
Document According to Field Sheets
- Tight and dry
- Dry
- Dry, rust staining
- Damp
- Seepage, drops
- Continuous flow

35. 2-35
L Number of Joint Sets
Number of Systematic Joint Sets
- Often three orthogonal sets
- Maximum four or five sets
- Record faults and shears separately from joints and
bedding

36. 2-36
M Block Size/Shape
Use code on Data Collection Sheet
SHAPE SIZE
- Blocky Very large (>8 m3)
- Tabular Large (0.2 – 8 m3)
- Columnar Medium (0.008-0.2 m3)
- Shattered Small (0.0002 – 0.008 m3)
Very small (<0.0002 m3)

37. 2-37Blocky structure

38. 2-38
Refer to Figure 2-2 of Reference Manual on page
2-6

39. 2-39
Geotechnical Mapping
Line Mapping
- Documenting All Structures that Intersect a Tape or
Painted Scan Line
Window (Cell) Mapping
- Document All Structures Within a Representative
Areas or “Windows”

40. 2-40
Geotechnical Drilling

41. 2-41
Diamond Drilling
Triple Tube or Double Tube with a Split Inner
Tube
 Geotechnical Logs - RQD, Recovery, Fracture Frequency, Joint
Angle (Cornerstone of Communication !!!)
Core Photographs & Core Handling
Structural Orientation Data from Drilling
- Oriented Coring - Clay Impression Method
- Borehole Imaging

42. 2-42
Core Photographs

43. 2-43

44. 2-44
Core Orientation – Reference Line
Dip
Side View
Dip Joint
Dip Vector
Top of Core
(In Situ)
End View
Reference Angle

45. 2-45

46. 2-46

47. 2-47
Borehole Televiewer Logging

48. 2-48
Core Orientation – Borehole Camera
Core Unwrapped Core
Dip
Direction
0 90 180 270 360
Dip
Trace of
joint

49. ProjectNo.052-2005Date:May2008
Comparable section of core quality and televiewer data.
Acoustical
Log
Optical
Log
id# Dip DDR
DDR = dip directionBorehole Televiewer Logging