Pattern of Neurologic Emergencies in Tikur Anbessa Specialized Hospital, Addis Ababa, Ethiopia

145 Pages·2017·10.65 MB·English

Engineering rock mass characterization -
An integrated approach through Rock Mass Classification
and Seismic Refraction -A case of TAMS Hydroelectric Power
Dam Project In Gambella, Ethiopia
Daniel Gebremichael
A Thesis Submitted to
School of Earth Sciences
Presented in Partial Fullfillment of the requirements for the Degree of
Masters of Science (Engineering Geology)
Engineering rock mass characterization·
An integrated approach through Rock Mass Classification
and Seismic Refraction, A case of TAMS Hydroelectric Power
Dam Project in Gambella, Ethiopia
Daniel Gebremichael
A Thesis Submitted to
School of Earth Sciences
Presented in Partial Fullfillment of the requirements for the Degree of
Masters of Science (Engineering Geology)
ADDIS ABABA UNIVERSITY
Addis Ababa, Ethiopia
May, 2017
DECLARATION

I, the undersigned, declare that this thesis is my original work and has not been presented for
a degree on any other university and all sources of materials used for the thesis have duly
acknowledged.

DANIEL GEBREMICHAEL
Signature_________________________

Place and data of submission:
School of Graduate Studies, Addis Ababa University.
May, 2017
Signature Page

Addis Ababa University
School of Graduate Studies

This is to certify that the thesis prepared by Daniel Gebremichael entitled: Engineering rock
mass characterization – An integrated approach through Rock Mass Classification and
Seismic Refraction a case of TAMS Hydroelectric power Dam Project in Gambella, Ethiopia
and submitted in partial fulfillment of the requirements for the Degree of Master of Science
(Engineering Geology) complies with the regulations of the University and meets the
accepted standards with respect to originality and quality.

Signed by the Examining Committee:

Examiner _______________________ Signature ______________ Date _______________

Examiner _______________________ Signature ______________ Date _______________

Advisor _________________________ Signature ______________ Date _______________

Co-Advisor ______________________ Signature ______________ Date _______________

________________________________________________
Chair of School or Graduate Program Coordinator
Engineering rock mass characterization – An integrated approach A case of TAMS Hydroelectric power
through Rock Mass Classification and Seismic Refraction Dam Project in Gambella, Ethiopia

ABSTRACT

Engineering rock mass characterization – An integrated approach through Rock Mass
Classification and Seismic Refraction; a case of TAMS Hydroelectric power Dam
Project in Gambella, Ethiopia.

Daniel Gebremichael
Addis Ababa University, 2017
In the present study, an integrated geotechnical and geophysical approach was followed to
characterize the dam foundation of TAMS Hydropower dam, situated in South-western
Ethiopia, in Gambella National Regional State, Gambella Woreda, 721 km south-west of
Addis Ababa. The dam is being constructed for the purpose of hydropower generation and
will have a height of 265 m. A systematic methodology was followed for the present study.
This includes review of secondary reports on investigations and design and collection of
primary data from surface on geological and geotechnical parameters at the dam site. The
investigations carried out in this regard includes; surface mapping, Rock mass rating (RMR)
data collection, insitu testing on rock properties, and laboratory testing on representative
samples. Besides, secondary raw data on drill hole logs, water pressure test and Seismic
refraction survey data was also utilized to analyze and characterize the rock mass at the dam
foundation.

Surface rock mass classification at exposed rocks have been conducted to characterize the
rock mass at the dam foundation, accordingly, 50% of the foundation rock mass falls in RMR
class 66 – 70, 40% falls in 61 – 65 and the rest 10% falls in class 70 – 80. The data analysis
from the geological logs and the seismic refraction survey suggests that the bedrock in the
dam foundation is fresh granite, granodiorite, metagranite and schist of different types which
can be characterized as fresh, massive, strong, slightly fractured to unfractured rocks of high
quality, represented by very high seismic velocities (>4500m/sec) from seismic refraction
survey. With the exception of some very soft rocks and heavily jointed media, the majority of
the rock mass can be classified as an excellent foundation material. Further, the permeability
results from water pressure tests conducted in boreholes at both the abutments indicate very
low to medium permeability. The permeability value on right abutment, in BH-3 borehole,
demonstrated high to very high permeability in the top part of the dam foundation. The
permeability in the intermediate reach on the right abutments is again high as the Lugeon
value is more than 65. Therefore, the most effective means of checking seepage through the
abutments and the river section would be a provision of a grout curtain.
Finally, on the basis of findings of the present research, recommendations are forwarded to be
adopted as solutions against geotechnical problems identified at the proposed dam site.
Key Words: Rock Mass Rating, Seismic refraction, Lugeon, Permeability, Rock Quality
Designation.
*****
MSc Thesis, Daniel Gebremichael i School of Earth Sciences, AAU
Engineering rock mass characterization – An integrated approach A case of TAMS Hydroelectric power
through Rock Mass Classification and Seismic Refraction Dam Project in Gambella, Ethiopia

ACKNOWLEDGMENT

First and for most, God must be thankful for being with me all the time in my life and putting
those spectacular people around me who had played magnificent role in diverse ways to the
success of this work.
I deeply thank Dr. Tarun K. Raghuvanshi, Associate Professor, School of Earth Sciences,
College of Natural Science, Addis Ababa University who advised the present research work.
He often went beyond the call of duty in encouraging, participation and supporting the goals
of the research and providing his expertise. His devotion for guidance and constant
encouragement strongly supported me to complete the present research work in this manner.
I would like also to express my gratitude to my Co-advisor Prof. Tilahun Mamo, School of
Earth Sciences, College of Natural Science, Addis Ababa University for providing timely
advice and comments that require time and patience.
I am thankful to Head and staff of School of Earth Sciences, College of Natural Science, and
Addis Ababa University for providing a nice working environment and its entire supportive
staff who helped me by providing support what I needed on time.

I would like to present my deepest gratitude to Ewnetu Tessema (Engineering Geologist) for
his valuable comment, encouragement and cooperation which gave me enough strength to
carry out the present research study and the Ethiopian Construction Design and Supervision
Works Corporation for funding the research, letting me free access to inquired data,
encouraging me and willingly putting their technical support for the fertility of the work.
Special thanks are due to Dr. Tesfaye Kebede (Geotechnical Investigation Sub-process
Manager) and Ato Getinet Asfaw (Senior Engineering Geologist and Project Manager).

Special thanks are due to all my wonderful workmates, my friends and my family. In
particular, I am grateful to my parents for their support and encouragement throughout my
life, to my wife, mother, father, brother and sister, whose constant challenge always made me
work harder.

MSc Thesis, Daniel Gebremichael ii School of Earth Sciences, AAU
Engineering rock mass characterization – An integrated approach A case of TAMS Hydroelectric power
through Rock Mass Classification and Seismic Refraction Dam Project in Gambella, Ethiopia

TABLE OF CONTENT

ABSTRACT ………………………………………………………………………………….…………i
ACKNOWLEDGMENT …………………………………………………………………….………...ii
TABLE OF CONTENT...……………………………………………………………………………...iii
LIST OF TABLES ………………………………………………………………………………...…..vi
LIST OF FIGURES ………………………………………………………………………...……...…vii
LIST OF PLATES …………………………………………………………………………….……......x
LIST OF ANNEX ……………………………………………………………………………..…….…x
ABBREVATIONS ………………………………………………………………………………...…..xi
CHAPTERS Page

1. INTRODUCTION …………………………………………………………………………………………………….………1
1.1 Overview ………………………………………………………………………………….1
1.2 Problem Statement ………………………………………………………………………..3
1.3 Previous works ………………………………………………………………………….3
1.4 Research Objective ………………………………………………………………………..4
1.4.1 General …………………………………………………………………….…4
1.4.2 Specific ………………………………………………………………………4
1.5 Significance of the Research ………………………………………………………...……4
1.6 Methodology ………………………………………………………………………...……5
1.7 Limitation………………………………………………………………………….………6
1.8 Chapter structure ………………………………………………………………….…….7

2. THE STUDY AREA ….……………………………………………………………………………………………………8
2.1 Location and Accessibility ……………………………………………………………….8
2.2 Salient features of the Project……………………………………………………………..8
2.3 Climate …………………………………………………………………………………...9
2.3.1 Temperature ……………………………………………………….………..10
2.3.2 Rain fall ………………………………………………………….………….10
2.3.3 Evaporation and Relative Humidity …………………………….………….13
2.4 Hydrology………………………………………………………………………………..14
2.4.1 Runoff data and Observed Discharge……………………………………….14
2.4.2 Catchment characteristics …………………………………………………..14
2.5 Physiography …………………………………………………………………………….16
2.6 Geomorphology ………………………………………………………………………….19
2.7 Land use and land cover …………………………………………………………………21
2.8 Soil and Vegetation …………………………………………………………..………….21

3. LITERATURE REVIEW ….………………………………………………………….……………………………….25
3.1 Rock mass characterization ……………………………………………………..…..25
3.1.1 Rock mass classification ……………………………………………..…….25
3.1.1.1 Rock Quality Designation (RQD) classification method ………….26
3.1.1.2 Rock Mass Rating (RMR) rock mass classification
System……………………………………………………………....27
MSc Thesis, Daniel Gebremichael iii School of Earth Sciences, AAU
Engineering rock mass characterization – An integrated approach A case of TAMS Hydroelectric power
through Rock Mass Classification and Seismic Refraction Dam Project in Gambella, Ethiopia

3.1.1.3 The Q- rock mass classification System ………………….………..28
3.1.1.4 Rock Structure Rating (RSR) classification System ………………29
3.1.1.5 Geological Strength Index (GSI) …………………………………..30
3.1.1.6 Rock Mass index (RMi) ……………………………………………31
3.1.2 Rock mass Failure criteria ……………………………………..…………..31
3.1.2.1 Failure Criteria ………………………………………….………….31
3.1.2.2 Mohr-Coulomb …………………………………………………….31
3.1.2.3 Hoek and Brown Criteria …………………………….…………….33
3.1.2.4 Rock Mass Deformation ……………………………………...……34
3.1.2.5 Empirical Methods to determine shear strength of the rock mass ...35
3.1.3 Application of RMR in determination of Rock Slope Stability
Condition…………………………………………………………………...36
3.1.3.1 Slope Mass Rating (SMR) …………………………………………36
3.1.4 Seismic Refraction and its role in characterizing the rock mass ……...……37
3.1.4.1 General about Seismic refraction ………………………………….37
3.1.4.2 Characterization by Seismic refraction ……………………………38
3.1.5 Integration of Geotechnical and Geophysical Techniques …………………40
3.1.6 Genesis of Methodology for the Present Study …………………………….42

4. GEOLOGY AND STRUCTURES ….………………………………………….…………………………………43
4.1 Regional Geology and Structures ………………………………..…………………43
4.1.1 Regional Geology …………………………………………………………..43
4.1.2 Rocks and Stratigraphy ……………………………………………….…….43
4.1.3 Regional Structures …………………………………………………………47
4.2 Local Geology and Structures ……………………………………………..…,……..48
4.2.1 Local Geology ………………………………………………………,….…..48
4.2.1.1 Mildly deformed to non-deformed granite …………………..,……49
4.2.1.2 Foliated Granitoids ……………………………………………,…..49
4.2.1.3 Gneiss (both ortho and para –gneiss) …………………………,…..50
4.2.1.4 Schists ……………………………………………….…………,….50
4.2.1.5 Amphibolites ………………………………………………….,…..50
4.2.1.6 Quaternary Deposit …………………………………………….….51
4.2.2 Local Structures ………………………………………………………..…..51
4.3 Dam site Geology and Structures …………………………………………………..51
4.3.1 Geology of the Dam site ……………………………………………….…..51
4.3.1.1 Granite ………………………………………………….…………51
4.3.1.2 Pegmatite Intrusion ……………………………………….……….52
4.3.1.3 Residual and Colluvial Deposit …………………………….……..52
4.3.2 Structures of the Dam site …………………………………………………52
4.4 Seismicity ………………………………………………………………..…………56
4.5 Hydrogeology ………………………………………………………………………59

5. METHODOLOGY AND DATA COLLECTION ………………..………………………………………61
5.1 Preamble ……………………………………………………………………………61
5.2 Primary Data Collection ……………………………………………………….……62
5.2.1 Geological and Structural Data collection at the Dam Site ……………...…62
5.2.2 RMR Data Collection at surface outcrops …………………………….……62
MSc Thesis, Daniel Gebremichael iv School of Earth Sciences, AAU
Engineering rock mass characterization – An integrated approach A case of TAMS Hydroelectric power
through Rock Mass Classification and Seismic Refraction Dam Project in Gambella, Ethiopia

5.2.3 RMR Data collection at drilled boreholes ...………………………………..64
5.2.3.1 Descriptive rock Core Logging ………………………...………….64
5.2.3.2 Discontinuity Description …………………………………………64
5.3 Secondary Data Collection …………………………………………………….……65
5.3.1 Boreholes Data ………………………………………………………..……65
5.3.2 Insitu permeability Data …………………………………………….…..….67
5.3.3 Seismic Refraction Data ……………………………………….…….……..67
5.4 Sampling and Laboratory analysis ……………………………………………….68
5.5 Rock mass characterization Methodologies ……………………………….….….…68
5.5.1 Preamble …………………………………………………………...….……68
5.5.2 Foundation Characterization …………………………………………...…..69
5.5.2.1 Rock mass classification …………………………………….…….69
5.5.2.2 Rock mass strength and failure criteria approach ……………...….69
5.5.2.3 Deformability Assessment…………….,.…………………………..69
5.5.2.4 Foundation Permeability …………………………….…………….70
5.5.2.5 Bearing Capacity estimation ………………………………………70
5.5.2.6 Seismic Refraction in characterizing the rock mass ………………71

6. RESULTS, INTERPRETATIONS AND DISSCUSION…………………………………………72
6.1 Preamble …………………………………………………………………………….72
6.2 Rock mass classification …………………………………………………………….72
6.2.1 Rock mass classification from exposed rocks ……………………….………72
6.2.1.1 Intact Rock Strength ……………………………………………….72
6.2.1.2 Rock Quality Designation (RQD) …………………………..……..73
6.2.1.3 Condition and Spacing of Discontinuity ……………………….….73
6.2.1.4 Ground water Condition ……………………………………….…..73
6.2.1.5 Orientation of Discontinuity ……………………………………….73
6.2.2 Rock mass classification from boreholes ……………………………….….74
6.2.2.1 Preamble ……………………………………………….…………..74
6.2.2.2 Intact Rock Strength ………………………………………….……75
6.2.2.3 Rock Quality Designation (RQD) …………………………………76
6.2.3 Estimation of Rock mass quality ……………………………………….…..76
6.2.3.1 Rock Formations Intercepted ………………………….…………...76
6.2.3.2 Rock mass quality Estimation using Geological Strength Index ….77
6.2.3.3 Weak Zones ……………………………………………….……….80
6.2.3.4 Overall quality of the rock mass ……………………………….…..81
6.3 Engineering Geological Mapping ……………………………………………...……82
6.4 Estimation of Deformability ………………………………………………….…….83
6.5 Estimation of Shear strength ……………………………………………….……….83
6.5.1 Hoek and Brown failure criteria ……………………………………………83
6.6 Abutment Slope Stability ……………………………………………………...…….86
6.6.1 Preamble …………………………………………………………………….86
6.6.2 Discontinuity Analysis …………………………………………..…………88
6.6.3 Kinematic Check ……………………………………………………………91
6.6.4 Slope Stability Analysis using Slope Mass Rating (SMR) ……….….…….92
6.7 Assessment of Permeability …………………………………………………..…….93
6.7.1 Foundation Permeability …………………………………………….….….93
MSc Thesis, Daniel Gebremichael v School of Earth Sciences, AAU
Engineering rock mass characterization – An integrated approach A case of TAMS Hydroelectric power
through Rock Mass Classification and Seismic Refraction Dam Project in Gambella, Ethiopia

6.7.2 Seepage and Leakage Condition ………………………………….….….100
6.8 Assessment of Bearing capacity of foundation rocks ……………………….…...100
6.9 Seismic Refraction Results and Discussion …………………………………….….102
6.9.1 Preamble …………………………………………………………….….…102
6.9.2 Line ST-06 (Dam axis) ……………………………………………………102
6.9.3 Line ST-05(left of dam axis) ……………………………………….……..104
6.9.4 Line ST-03(upstream of dam axis)………….……………………….…..104
6.9.5 Lithology ……………………………………………………………....….105
6.10 Interpretation based on geotechnical and geophysical methods …………..107
6.10.1 General …………………………………………………………………….107
6.10.2 Seismic velocity and RQD relation at selected boreholes ……………...…110
6.10.2.1 Borehole- 14 …………………………………………...………110
6.10.2.2 Borehole 04 and 07 …………………………………………….110
6.11 Discussion on overall characterization ………………………..…………..111
6.12 Foundation Treatment ………………………………………………….…113
6.12.1 Grouting works ……………………………………………………..…….113
6.12.1.1 Consolidation Grouting ………………………………………..114
6.12.1.2 Curtain Grouting ……………………………………..…..…….115
6.13 Foundation Excavation ……………………………………...…...………..116

7. CONCLUSIONS AND RECOMMENDATIONS………………………………………………………118
7.1 Conclusion …………………………………………………………………………118
7.2 Recommendation ………………………………………………………………..…120

REFERENCES…………………………………………………………………………………………………………………122

MSc Thesis, Daniel Gebremichael vi School of Earth Sciences, AAU