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Head of Department of Civil Engineering
Institute of Engineering
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Lalitpur, Kathmandu
Nepal
CERTIFICATE
The undersigned certify that they have read, and recommended to the Institute of Engineering
for acceptance, a thesis entitled “Design of Tunnel Support Systems and Study of Tunnel
Support Systems of Likhu IV Hydroelectric Project" submitted by Mr. Sagun Shrestha
in partial fulfillment of the requirements for the degree of Master of Science in Geotechnical
Engineering, Tribhuvan University, Nepal is a record of bonafide works carried out by him
under my supervision and guidance. In geotechnical engineering no part of his work has been
published or submitted for the award of any degree elsewhere.
_______________________________
Prof. Dr. Akal Bahadur Singh
Supervisor
Department of Civil Engineering
IOE, Pulchowk Campus
Tribhuvan University, Lalitpur
Nepal
April 12, 2011
CERTIFICATE
The thesis presented by Mr. Sagun Shrestha entitled “Design of Tunnel Support Systems
and Study of Tunnel Support Systems of Likhu IV Hydroelectric Project” has been
accepted as the partial fulfillment of the requirement for the degree of Master of Science in
Geotechnical Engineering.
Mr. Padam Khadka
Coordinator, M.Sc. Geotechnical Engineering
Department of Civil Engineering
IOE, Pulchowk Campus
Tribhuvan University, Lalitpur
Nepal
April 12, 2011
Er. Prakash Man Shrestha
External Ecaminer
Nepal Electricity Authority
Bhaktapur
Nepal
ACKNOWLEDGEMENT
My foremost thanks go to Pulchowk Engineering Campus, Tribhuvan University for accepting my
research proposal and allowing me to do my master’s thesis on “Design of Tunnel Support
Systems and Study of Tunnel Support Systems of Likhu IV Hydroelectric Project”
I would like to express my deep sense of gratitude to my thesis adviser Prof. Dr. Akal
Bahadur Singh for his constant inspiration and guidance throughout the study period. My
sincere appreciation goes to Mr. Padam Khadka, Coordinator of M.Sc. in Geo-technical
Engineering, Pulchowk Campus for his constant support and encouragement.
I again would like to express my sincere thanks and deep gratitude to Prof. Dr. Akal
Bahadur Singh for providing materials, datas, constant inspiration and guidance throughout
the thesis period.
I would also like to thanks to Green Venture Pvt. Ltd. Where I get detail information of
Detail Project Report (DPR) of Likhu IV Hydroelectric Project.
Finally. I am grateful to my family and friends who support and encourage me for this
research work, without which none of all might have been possible.
Sagun Shrestha
065/MSG/r/814
April 12, 2011
ABSTRACT
This thesis demonstrates the various methods of Design of Tunnel Support Systems and Study
of Tunnel Support Systems of Likhu IV Hydroelectric Project. Primary support system
constitutes the main support element of the tunnel system. This support must be design to take up all
the types of loads that may be induced during the life time of the tunnel. And temporary support has
to be provide for safety during construction. But accurate determination of various types of rock
pressure on linings is rather difficult because predication of the existing stress condition (primary
stress) in the non-uniform rock mass as well as that of the secondary stresses that develops after
excavation is very much complicated and these secondary stress are highly dependent on induced
deformations which themselves are difficult to assess.
This thesis carried out in three parts. In the first part, the aim of this study is to investigate the
implementation of rocksupport using Empirical Method for a Headrace Tunnel (HRT). A HRT
alignment in Okhaldhunga District of Nepal were selected; an HRT (4128m) at the Likhu IV
Hydroelectric Project which is preparing for its generation license from Department of Electricity
Development. Analysis of support system has been done by empirical methods. RSR, RMR and Qsystem has been used to classify the rock mass. Stand up time has been calculated using Q value and
RMR. The headrace tunnel (length=4213m) consist of four different types of rock mass classification
such as i) Good ii) Fair ii) Poor IV) Very poor quality rock mass of Gneiss and Phylit/shist. Hence the
support has been provided as per the three empirical methods.
In the second part, Rock-support interaction analysis is an analytical model used to explain a process
of rock mass support which occurs during rock excavation. This theory addresses one problem that
appears during any rock excavation. The problem is to achieve the optimal amount of support
required to maintain a safe and useable opening with allowable initial settlement. In this study also the
whole length of tunnel has been divided into four parts with respect to rock mass quality. Individual
analysis has been done for maximum rock cover of 300m for the alignment.
The author has collected secondary data from prepared DPR and field visit. Data comprised details of
rock mass quality, Rock cover and geometric parameter of HRT. The data available from the above
sources were analysed using a spread sheet, mathematical and numerical calculation. A closed-form
analytical model was constructed, based on a series of algorithms from Brown et al. (1983) and Hoek
and Brown (1980).Mathematical excel graph sheet was prepared to describe functions for ground
reaction and support availability, and to seeks an intersection point between the ground reaction and
support availability. The author also has introduced the Steel Fiber Reinforced Concrete (SFRC)
rather than using the wire mesh which can be assumed to save the time in placing the wire mesh on
the rock surface.
However, there are some limitations:
Rock-support interaction has failed to give an explanation for good quality rock mass
The calculation of the extent of a plastic zone around the opening was not supported by the
displacement data and the numerical calculation. However the existence of a plastic zone was
accepted.
A ground reaction curve cannot represent an entire opening. A ground reaction curve should be
generated in each location to indicate a condition of stability in that particular location.
In the third part it is assumed that all the external loads are known and can be quantified in terms of
some mathematical expressions and concrete linings placed immediately after excavation to take all
the loads and deformation, so that it acts as temporary support and primary support as well. The
Protodiakonov’s Theory of Rock Pressure is considered for finding rock pressure. After determining
the all external loads we can determinant the other design parameter like ground reaction, active rock
mass pressure, passive resistance etc. All tunnel linings are designed taking a design length of one
meter along the tunnel axis. Assuming that the thickness and rigidity of the tunnel is constant for the
whole of its cross-section and that the cross-section as well as the loading pattern is also symmetrical
with respect to vertical axis of the cross-section, only one of the half sections will be analyzed. The
half section is assumed to be free at top and fixed at bottom. To make the structure statically
determinate first applying the Method of Potential Energy we will find moments M0 and Horizontal
reaction H0 at crown of the arch lining. Once these values are known the relevant value of moments M
and normal force N at any given section due to external load can be calculated by superimposing
moments and axial loads due to M0 and H0 on those due to external. Finally the monolithic concrete
linings for tunnel will be proposed to will resist the all superimposed M and N obtained at each
section. The Bending moment for similar modal in different standard also studied and finally the
reinforced concrete by limit sate method and unreinforced concrete form ACI code has been designed.
Finally the three results are studied. The study has concluded that immediate support is needed
throughout the Headrace tunnel only for poor and very poor rock mass class. Though the empirical
method shows that the tunnel can stand without any support for some good rocks but minimum 50
mm shotcrete has to be provided for safety point of view.
Nevertheless, the rock-support interaction theory does give a better understanding of the process of
supporting an excavated rock mass. Using this theory, the principle of optimising the dimensions of
excavation of rock mass for an underground opening was clarified. But the tunneling can be assumed
to be more economical if the final lining is done just after excavation. New Tunneling method with
pressed concrete can be used for this process. Press concrete tunneling method has been revived
as a new method. New tunneling complexes with sliding shuttering have been launched
including tunneling complex “malachite” that has been developed and produced for very hard
hydro geological conditions. The complex contains a shield with compressive air chamber. In
this method it is assumed that no temporary support are required, the entire designed load are
taken by the finial lining. This thesis paper is able to give only basic introduction about this
method and the author is very positive about this method to be used in Nepal’s Tunnel.
References:
1. Underground Excavations in Rock, E. Hoek & E.T. Brown
2. Class notes on “Design of Concrete Lining”, By Prof. Dr. Akal Bahadur Singh
3. Guidelines for Design of Shield Tunnel Lining, ITA- Working Group Research
4. Indian Standard, Code of Practice For Design of Tunnels Conveying Water , IS:4880(Part V)
– 1972
5. Stability Evaluation And Design of Tunnel Openings In Brittle-Massive Rock Masses
Istanbul Technical University-Mining Engineering Dept., Istanbul, Turkey
6. New tunneling with monolithic press concrete lining, N. Bulychev & N. Fotieva,
Department of Underground Construction Tula State University Tula Russia.
7. Implementation of rock-support interaction Theory in assessing the stability of
Underground openings By: Wisnu sardjono soenarso, S-1 in mining engineering
(institute technology of bandung)
8. American Concrete Institute, ACI 318.