Case study: rock mass in a sub-urban road, north of Lecco, near Varrena, on a road between Esino and Parlasco, (North Italy, Lombardia)

1. Team Members:
Maryam Izadifar, Alireza Babaee, Budiwan Adi Tirta
GETUS
Geo-Engineering Techniques for Unstable Slopes
July 2015
Characterization of a rock mass by integrated study of geology,
geophysics, and photogrammetry
Professors:
Laura Longoni, Marco Scaioni,
Stephene Garambois

2. Table of Contents
1- Introduction
2- Geological Study
3- Photogrammetry and Laser Scanning
4- Geophysical Study
5- Block Volume Evaluation

3. 1- Introduction
Area of interest
• North of Lecco
• Slope is adjacent to sub-urban road
near Varrena
• The rock is typically hard sedimentary
rock, which is classified as limestone
• The slope itself is quite regular with
average height of 9-10 m, dip and dip
direction 65° and 220

4. Geological Study
Joint Orientation

5. Geological Study
Sets of joint family
Joints and Families Orientation
In order to have final classification, we made stereo plots
of poles using an equal area projection streoronet of each
discontinuity. Therefore, we were able to see classification
of families of discontinuity as shown
Family
Joint Code
Dip Direction
(°)
Average
Dip
Direction
(°)
Dip (°)
Average
Dip (°)
A
A1 220
222
65
63
A2 230 65
A3 210 65
A4 210 65
A5 210 65
A6 210 65
A7 235 60
A8 230 55
A9 240 60
B
B1 110
124
75
74
B2 110 75
B3 110 75
B4 120 75
B5 130 70
B6 140 80
B7 130 75
B8 130 75
B9 110 75
B10 110 80
B11 150 70
B12 140 65
C
C1 340
333
10
17C2 320 10
C3 340 30

6. Geological Study
Joint Surface roughness
• JRC number is obtained by directly comparing the
actual joint surface profile with the typical profile in
the given chart.
• The measurement of the surface roughness was not
measured for all the joints, but it almost covers all
the measured joints. In this case the average JRC for
three families are:
• Family A = 8.75; Family B = 15; Family C = 13.7
Joint Roughness Coefficient chart
Joint surface roughness of the measurements and JRC numbers

7. Geological Study
Uniaxial compressive strength of intact rock
• For determining the uniaxial compressive strength of rock we can
use the Schmidt hammer (L-hammer).
• Obtain a direct estimate of the compressive strength by knowing
the density of rock.
• at least ten readings that are taken at various locations on each
surface
• the five lowest reading are discounted, and the five highest
readings are used to obtain uniaxial compressive strength
• Considering the unit weight of 26 kN/m3 and the five highest
readings, it gives us the uniaxial compressive strength (average
value of the strength of the five highest reading) for three
families

8. Geological Study
Uniaxial compressive strength of intact rock
Family A
Uniaxial Compression
Strength (MPa)
Family B
Uniaxial Compression
Strength (MPa)
Family C
Uniaxial Compression
Strength (MPa)
45 25 20
140* 25 65*
38 70* 37
28 38 60*
38 45* 42
80 50* 37
110* 35 80*
145* 30 65*
90* 52* 50
110* 48* 85*
Average for 5 Highest
Records
119
Average for 5
Highest Records
53
Average for 5 Highest
Records
71
* Five highest records are considered.
Schmidt hammer test results

9. Geological Study
Shear strength of discontinuity
Shear strength of the joints can be computed by empirical Barton’s
criterion:
Where:
• τ is shear strength of the joint;
• JCS is Joint Compressive Strength (wall). This value is the
uniaxial compressive strength based on Schmidt’s hammer
tests;
• σ_n is normal stress;
• JRC is Joint Roughness Coefficient according to Patton;
• ф_b is basic friction angle (assumed 30° in this case) ;
• ф_a is overall friction angle.
Three values for JRC (minimum, average and maximum) used for
each family group. Results are depicted in the following graphs.

10. Geological Study
Slope stability analysis ( Markland Tests)
Planar failure
When a single plane of rock slides, a planer failure will occur. In
order to have that sliding, the following geometrical conditions
must be satisfied:
• The plane on which sliding occurs, strike must be parallel or
nearly parallel (within approximately ± 20°) to the slope face
• The dip of the plane must be smaller than the dip of the slope
face
• The dip of the failure plane must be greater than the angle of
friction of this plane
Joint Family
Average value of
dip direction
Average value of
dip
[°] [°]
A 222 63
B 124 74
C 333 17
Slope 220 65
Stereograph representation of joint families
and the slope with great circle for planar failure
evaluation
Planar failure
Criterion Description Family A Family B Family C
1 Slope dip > joint dip
YES
(65°>63°)
NO
(65°<74°)
YES
(65°>17°)
2
Difference between dip directions of
slope and joint < 20°
YES
(2°<20°)
NO
(96°>20°)
NO
(113°>20°)
3 Joint dip > friction angle
YES
(63°>30)
YES
(74°>30)
NO
(17°<30)
Based on the test, joint family A has all the criteria to
have planar failure.

11. Geological Study
Slope stability analysis ( Markland Tests)
Wedge failure
Wedge failure occurs where sliding takes place along the line of
intersection of two planes. The following geometrical conditions
must be satisfied:
• The dip of the slope, must exceed the dip of intersection line
• The dip of the intersection line must higher than friction angle
• Dip direction of intersection line should be almost similar to the
dip direction of slope
To check wedge failure, a circle that shows friction angle on the
stereograph has been considered with dip and dip direction of joint
families. Intersection of friction angle circle and slope great circle
creating an intersection area that is mentioned as a critical area (red
zone in Figure ‎).
Stereograph representation of great circles of
joint families and slopes, intersections, and also
cohesion=30° for wedge failure evaluation
the intersection of joints A and B sets
satisfied the criteria. Moreover, as shown in
the stereoplot of wedge failure’s test, it can
be observed that the A-B intersection
located inside the critical area
Wedge failure
Criterion Description Intersection AB Intersection AC Intersection BC
1 Slope dip > intersection dip
YES
(65°>58°)
YES
(65°>14°)
YES
(65°>10°)
2 Intersection dip > friction angle
YES
(58°>30°)
NO
(14°<30°)
NO
(10°<30°)
3
Similarity between dip direction of
intersection line and slope (220°)
YES
(190°)
NO
(308°)
NO
(48°)

12. Geological Study
Slope stability analysis ( Markland Tests)
Toppling failure
Toppling failure involves rotation of columns or blocks of rock about fixed base. In the following there
are geometrical conditions that must be satisfied.
• The plane on which toppling occurs must have the same strike of the slope but in opposite direction
• The dip of the plane must be greater than 70°
Therefore, there would be no possibility to have toppling failure in this slope, since all the joint
families did not satisfy the failure conditions of toppling
Toppling failure
Criterion Description Family A Family B Family C
1
similar strike , opposite dip direction
with slope
NO
(YES and NO)
NO
(NO and NO)
NO
(NO and NO)
2 Joint dip > 70°
NO
(63°< 70°)
YES
(74°> 70°)
NO
(17°< 70°)

13. Geological Study
Unitary Rock Volume (URV)
Joint family Spacing, (cm)
Code Minimum Medium Maximum
A 0.06 0.167 0.3
B 0.5 2.145 6.5
C 2.4 2.7 3

14. Geological Study
Unitary Rock Volume (URV)
Empirical method

15. Photogrammetry
Data Acquisition
Objectives:
1) To generate point clouds and orthophotos; [PhotoScan]
2) To get some representative trace for the profiles of geophysical survey; [CloudCompare]
3) To define dip and dip direction of the face derived from point clouds. [CloudCompare]
Images:
- Two groups of images;
- 80% overlapping + random images
Camera:
 Model: Canon EOS-1D Mark IV;
 Lens: focal length 20 mm;
 Resolution of image: 4896x3264
pixels.

16. Photogrammetry
Geodetic Network and GCPs
Ground Control Point (GCP)
geodetic network for photogrammetry and location of 4 stations
- to geo-referencing the images
Geophysical Points
- to extract topography of
geophysical profiles
Local RS
+
2 GPS stations
=
Global RS

17. Photogrammetry
Processing Images (PhotoScan)
Steps for each chunk:
1- Aligning the photos (tie points);
2- Marking some GCPs for geo-referencing (already in Global System);
3- Camera Calibration (automatically in the software);
Residual error in tie points = 0.5 pixel (3 mm)
Before calibration After calibration
C, XP, YP: Inner orientation parameters
K1, K2, K3, K4: Radial distortion parameters (very small)
p1, p2: decentering distortion coefficients (very small)
B1, B2: affine distortion coefficients (very small)

18. Photogrammetry
Processing Images (PhotoScan)
4- Merging two chunks;
5- Building Dense Cloud;
6- Building Mesh;
7- Texture construction;
8- Exporting the point cloud;
[CloudCompare]

19. Photogrammetry
Orthophoto (PhotoScan)
After building the texture:
- Export the Orthophoto
XZ-Front
Orthophoto from Canon images
Orthophoto from iPhone 4 images (lower resolution and quality)
pixel size = 0.5 cm

20. Photogrammetry
GPR profiles (CloudCompare)
After Importing Point Cloud:
- Segmentation / Extract Sections
- Save Vertices of profiles in text file
- Represent profile in Excel
Distance calculation (comparing with geophysical
and geological results)
H2 profile (exported to Excel)
Topography effect in geophysical results

21. Photogrammetry
Dip and Dip Direction Extraction (CloudCompare)
Option 1:
RANSAC (RANdom SAmple Consensus) Shape Detection plug-in -- Poor results
Option 2:
- Defining block segments with same orientation [by Professor Scaioni]
- Segmentation / Cross section for each block segment
- Manually extracting d and dd (by fitting a plane for each cross section)
Remove vegetation:
Edit / Segment/ Segment Out

22. Photogrammetry
Dip and Dip Direction Extraction (CloudCompare)
Results:
(Comparing photogrammetry and classic geological survey)
Slope and A joint family from
Geological survey
15 planes from photogrammetry
Methods
Average dip
direction [deg]
Average dip angle
[deg]
Geological Survey 222 63
Photogrammetry 209 53
Slope = 220 / 65

23. Terrestrial Laser Scanning
Alignment (CloudCompare)
Two TLS recorded in Local RS
1- Segmentation of two data sets (removing road and trees, etc.)
2- Aligning by ICP (Iterative Closest Points)
- residual error < 1 cm

24. Photogrammetry vs Laser Scanning
Alignment (CloudCompare)
3- Aligning by ICP (Iterative Closest Points)
Point cloud of photogrammetry as reference (will not move during ICP)
Merged point cloud of LS as model (will move during ICP)
- residual error << 1 cm
- higher residual error
Canon
iPhone4

25. Geophysical Study
Introduction
Methods:
 Ground Penetration Radar (GPR).
Objectives:
 a seduo 3D sketch of the main discontinuities
considering areal persistance;
 1D velocity-depth (validation with the thickness layers
based on other surveys);
 Water content (an empirical formula).

26. Geophysical Study
Data acquisition
 GPR with frequency of 1 GHz;
 The resolution (/4) of the GPR measurement is around 2.5 cm considering
typical velocity of limestone (10 cm ns-1);
 Two horizontal profiles (H1, H2) and four vertical profiles (V1-V4);
 One common-mid-point (CMP) profiling;
 Total length of the profiles is about 20 m

27. Geophysical Study
Velocity analysis (stacking velocity)
n 1/v0:n
2 v0:n
2 v0:n t0:n
2 t0:n
[-] [(ns/cm)2] [(cm/ns)2] [cm/ns] [ns2] [ns]
1 0.014 71.43 8.45 71 8.43
2 0.012 83.33 9.13 173 13.14
3 0.011 90.91 9.53 643 25.35
4 0.012 83.33 9.13 1289 35.90

28. Geophysical Study
Interval velocity (Dix’s formula)
n v0:n t0:n (v0:n)2
t0:n-
t0:n-1 Vint thickness elevation
[-]
[cm/ns
] [ns]
[(cm/ns)2
] [ns] cm/ns [cm] [cm]
1 8.45 8.43 602 - 8.45* 35.61 35.61
2 9.13 13.14 1095 4.71 10.23 24.09 59.70
3 9.53 25.35 2305 12.21 9.95 60.77 120.47
4 9.13 35.90 2992 10.55 8.07 42.59 163.06
0
20
40
60
80
100
120
140
160
180
8 9 10 11
Elevation,cm
Velocity, cm.ns-1
Interval velocity
average of interval velocity

29. • Based on the 1D
velocity analysis from
CMP;
• Assuming:
where c is the air velocity (30 cm.ns-1).
29
Vint elevation c Ka qv
[cm/ns] [cm]
[cm/
ns] [-] [-]
8.45 35.61 30 12.6 0.24
10.23 59.70 30 8.6 0.16
9.95 120.47 30 9.1 0.17
8.07 163.06 30 13.8 0.26
Geophysical Study
Water content (Topp, 1980)

30. Geophysical Study
Reflective layers
V1
V2
V3
V4

31. • Profile at normal direction
with respect to dip
direction of surface;
• Areal persistence;
– Persistence based on
reflective profiles ;
– Linear interpolation
between two data;
31
4- Geophysical Study
4-7 Sketch of a Pseudo-3D of discontinuity

32. 5- Block Volume Evaluation
3DEC calculation
Three sets of joints (A, B, C) and the surface are introduced in the 3DEC software in order to
compute block size. Two different models according to persistence of the joints are introduced in
order to have comparison the block size in 3DEC software.
• Model 1, with 100% persistence for all the discontinuities
• Model 2 with real persistence for all joint families.
model of the rock mass built up
with 3DEC software

33. Thank You For Yours Attention