Lesson 2a rev 6-6-09

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

Range of rock mass characteristics.

2-3

Scale

2-4

Pervasive discontinuities

Favorably oriented

2-5

Strong rock widely spaced

joints.

2-6 Unfavorably oriented discontinuities control

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

2-8

Definition of Discontinuity Parameters

Figure 2-2

Page 2-6

2-9

A. - Rock Type

Deere and Miller

Colorado School of Mines Quarterly

(Russell B Travis)

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)

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)

2-12

Joints are controlling discontinuities

2-13

Bedding is

controlling

discontinuity

I40, NC/TN

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

2-15

Definition of Dip, Dip Direction, Strike

2-16

Structural Compass

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

2-18

True and Apparent Spacing

Fracture Set Rock Face

Sapp Sapp Sapp

S

S

S

θ

2-19

Extremely close foliation

spacing

Will strongly influence rock

mass:

• strength

• deformability

• permeability

• excavatability

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

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

2-22

Persistence of family of

faults will control abutment

design

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

2-24

Discontinuity Roughness Measurement

i2d i8d id i4d

4d 8d

2d

d

Mean dip

1

2

Quantitative approach

2-25

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

2-27

H Weathering

ISRM Weathering Classification - Table 2-2 - Fresh

- Slightly weathered

- Moderately weathered

- Highly weathered

- Completely weathered

- Residual soil

2-28

Differential shale weathering

2-29

Chemical decomposition

2-30

I Aperture

Measure Directly, Table 2-1: Range:

- Very tight (<0.1 mm)

- Cavernous (>1000 mm)

2-31

J Filling/Width

Measure Width (Table 2-2)

Characterize Wall Rock

Infilling Characteristics - Mineralogy

- Particle Size

- Water Content

- Stiffness

2-32

25 mm thick, continuous clay

infillings (bedding plane shears)

2-33

Controlling structure for slope design Rocky Point Viaduct, OR

2-34

K Seepage

Document According to Field Sheets - Tight and dry

- Dry

- Dry, rust staining

- Damp

- Seepage, drops

- Continuous flow

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

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)

2-37 Blocky structure

2-38

Refer to Figure 2-2 of Reference Manual on page

2-6

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”

2-40

Geotechnical Drilling

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

2-42

Core Photographs

2-43

2-44

Core Orientation – Reference Line

Dip

Side View

Dip Joint

Dip Vector

Top of Core

(In Situ)

End View

Reference Angle

2-45

2-46

2-47

Borehole Televiewer Logging

2-48

Core Orientation – Borehole Camera

Core Unwrapped Core

Dip

Direction

0 90 180 270 360

Dip

Trace of

joint

Pro

jec

t N

o. 0

52

-20

05

D

ate

: M

ay

2

00

8

Comparable section of core quality and televiewer data.

Acoustical

Log

Optical

Log

id# Dip DDR

DDR = dip direction Borehole Televiewer Logging