6-1

WEDGE FAILURE

Lesson 6

6-2

LESSON 6 - WEDGE FAILURE

Learning Outcomes -

Identify Geometric Conditions for Wedge

Failure;

Analyze for Wedge Failure using Design Chart;

Apply Wedge Stability Conditions to Rock

Slope Design for Highways.

6-3

Wedge failure in very

strong granite with

widely spaced joints

(Upstate New York)

6-4

Wedge formed by

bedding and

orthogonal joints

in sandstone

(US60, Globe, AZ)

Joints

Bedding

6-5

Conditions for Wedge Failure

Two Intersecting Planes Behind Face

Line of Intersection “Daylights” on Face

Line of Intersection Dips >

6-6

Wedge Failure Geometry

Flatter of the two

sliding planes is

Plane A

Plane A Plane B

Line of intersection

6-7

Stereoplot of Wedge Failure Geometry

Direction of sliding

Plane A Plane B

Friction cone Slope face

6-8

Analysis of Wedge Failure

Factor of Safety F, for Friction only

ForcesDisplacing

ForcesistingReF

i

BA

sinW

tan)RR(F

(6-1)

6-9

Wedge Stability Charts for Friction Only

Factor of Safety

Plane A is Flatter of Two Sliding Planes

BA tanBtanAF

6-10

Wedge Stability Chart A

6-11

Wedge Stability Chart B

6-12

Student Exercise – Wedge Stability Analysis

Student Exercises No. 1B and No. 5

6-13

Wedge failure in

sandstone with

orthogonal jointing

(Ankara, Turkey)

6-14

Wedge failure in shale with orthogonal

jointing; tension on right side (Helena, MT)

6-15

Potential wedges formed by

discontinuous joints (US23, Flag Pond, TN)

6-16

Analysis of Wedge Failure

6-17

Stability Analysis of Wedge using SWEDGE

6-18

SWEDGE analysis showing wedge geometry (red),

water forces (blue) and external force (purple).

6-19

Wedge formed by

five planes (I-5, Grants Pass, OR)

LOI

1: Plane A

2: Plane B

3: Upper slope

4: Face

5: Tension crack

6-20

Wedges

Planar

slides

6-21

Plane failure on bedding

6-22

Wedges formed

by bedding and

joints

6-23

LESSON 6 - WEDGE FAILURE

Learning Outcomes -

Identify Geometric Conditions for Wedge

Failure;

Analyze for Wedge Failure using Design Chart;

Apply Wedge Stability Conditions to Rock

Slope Design for Highways.