MKAJ 1023
ANDVANCED GEOTECHNIICAL
ANALYSIS AND DESIGN
ASSIGNMENT : TUNNEL CONSTRUCTION METHOD
NAME :
MUHAMMAD AMEER ZAHID BIN MOHD ZAFRULLAH
MATRIC NO. :
MKA191024
LECTURER :
DR.NORAFIDA
REVISION
What is difference between hard and soft ground tunneling?
Soft Ground Tunneling
Hard Ground Tunneling
Shallow tunnel (cover less or equal to 2
times diameter of tunnel)
Deeper depth of tunnel
Complex due to ground water level
Complex due to rock conditions
Soil-structure interaction
Rock-structure interaction
More settlement especially for shallow
depth
More stable, long stand up time
Excavation stages must be sufficiently
short, both in terms of dimensions and
duration.
Deeper depth of tunnel
Erection of the ‘full ring’ of initial ground
support must be completed immediately
after excavation.
Do you know shallow tunneling?
Yes. Shallow tunnel has a cover less or equal two times the diameter of the tunnel.
What suitable tunnel for clay/saturated/high water condition?
Earth Pressure Balance Machine
TUNNEL BORING MACHINE: A GENERAL
REVIEW ON SOFT GROUND TUNNELING
Muhammad Ameer Zahid Bin Mohd Zafrullah
Introduction
Mechanized tunneling is an alternative to method to the classic drill and blast, New
Austrian Tunneling Method (NATM) and New Italian Tunneling Method. Tunnel Boring
Machine (TBM) is a well-known tunneling machine that bore through variety of soft and hard
ground with circular-cross section in shape. The TBM are divided into two group which is
shielded TBM and non-shielded TBM. The shield resist surrounding pressure and hold back
ground water from the excavated cavity priorly before the temporary support and final lining
installed as the tunnel continues to advance. Three most common shield TBM in soft ground
tunneling is Slurry Shield TBM, Earth Pressure Balance (EPB) Machine, and Variable Density
Machine.
Slurry Shield TBM
Slurry Shield TBM is one of the common closed shield TBM that uses slurry face
support method. Depending on the soil condition the slurry which is a fluid support medium
can be a suspension of water and bentonite or clay (sometimes with additives).
The functional of the slurry is to form a “filter cake” which can be describe as an almost
impermeable layer of bentonite or clay particle that formed as the suspension is filtered under
flow gradient at the surface face. The filter cake enables the pressurized suspension in the
excavation chamber to equilibrium against ground and water pressure. In order to from the
filter cake, the slurry is pumped into the closed excavation chamber against the face, where it
penetrates under pressure into the soil, seals it and form the filter cake.
The slurry purpose as a support medium also undertakes the role as a transport medium
by mixing with the excavated material before being pumped out back to a slurry separation
plant, usually outside of the tunnel. Slurry separation plants are multi-stage filtration systems,
which remove the soil from the slurry so that it may be reused if required and pump back down
to the face. The removal of the excavated soil as a suspension in a fluid pumped by a centrifugal
pump can be characterize as hydraulic mucking.
The method of soil excavation is full-face machine with cutting wheel. The cutting
wheel of a slurry shield is flat and almost closed, which provide a certain degree of mechanical
support in addition to the action of the pressurized slurry. The excavation tools, in general
scrapers or teeth, are fitted in two rows radially so that the machine can excavate while rotating
in either direction. The soil can pass through slots in the cutting wheel parallel to the excavation
tools; the width of the slots has to be suitable for the expected maximum grain size
The main disadvantage of slurry shield TBM are the space and energy required by the
slurry separation plant. However, the most crucial part is the difficulties with encountering fine
grained material. Separated fine grained material are difficult to disposed and any bentonite
suspension loaded with fine material cannot be separated. The cost-effectiveness of a slurry
shield in comparison with other processes is essentially determined by the cost and difficulty
of separating the transport suspension. The technical limits to its application are set by the
permeability of the soil encountered. For this reason, slurry shield TBMs are not suitable for
silts and clays as the particle sizes of the spoil are less than that of the bentonite clay from
which the slurry is made (Maidl et al., 2013).
Earth Pressure Balance (EPB) Machine
Earth Pressure Balance (EPB) Machine is one of the common closed shield TBM that
distinct from other closed shield TBM that does not mainly rely on additive for the support
medium as the role was taken by the excavated soil by the cutting wheel. However, it depends
on soil condition to increase the stability of the ground.
Unlike slurry shield the soil cut from the face by the tools on the cutting wheel squeeze
through the opening in the cutting wheel into the excavation chamber mixes with the already
remoulded earth mud. To reach the state of equilibrium between the support pressure of the
earth mud and the face pressure, the earth mud in the excavation chamber is compacted by the
thrust cylinder. Thrust cylinder provide thrust to the earth slurry through the pressure bulkhead
and avoid uncontrolled penetration. The quantity of soil taken from excavation chamber is
regulated by the screw conveyor rotational speed which is match to the advance speed. The
aim is to maintain the state of equilibrium between the quantity of soil removed by the screw
conveyor and the quantity of soil accumulated from the shield tunneling process. The
requirement for the excavated material to be used as support medium:
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Good plastic deformability
Plastic consistency
Low internal friction
Low water permeability
Good elasticity by being compressible
Good plastic deformation properties and a pasty consistency ensure that the support
pressure is as evenly distributed across the face as possible, a continuous flow of material to
the screw conveyor inlet and that blockages are avoided in areas with little pressure gradient.
The internal friction of the soil should be as low as possible to minimize wear and energy
consumption. A low permeability is necessary to transfer the material to the transport conveyor
at the outlet of the screw conveyor without an air lock. Good compressibility simplifies the
control of support pressure by regulating the screw conveyor.
Soil conditioning is needed when natural excavated soil does not meet the required
properties. Therefore, selection of conditioning process must compliment the type of soil
encountered and depended on the parameter grading curve, water content 𝑤(%), liquid limit
𝑤𝐿 (%), plasticity index (𝐼p) and liquidity index(𝐼c). These parameters can be influenced by
the addition of:
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Water
Bentonite, clay or polymer suspensions
Tenside or polymer foams
Several main disadvantage EPB is the increasing of sand content from initial condition
of the soil in which addition of water no longer effective. The increased water permeability
also makes sealing of the screw conveyor difficult. The absence of fines content has to be
supplemented with the addition of clay or bentonite suspension (Maidl et al., 2013)
Variable Density TBM
Classic shield TBM have certain limits encountering variable geologies in term of
technical and economics. A new generation of multi-mode TBM, the Variable Density TBM
have been introduced to the industry. The technology combines the slurry-supported mode
(Mixshield method) and earth pressure balance mode (EPB method) thus combining their
advantages in a single machine without any major mechanical changes. Operational of the
machine is control by mode it is use in. In earth pressure balance mode, the face support
pressure is control through the screw conveyor speed and the advance rate of the TBM.
Meanwhile, in slurry mode the face support pressure is automatically controlled by an air
cushion. (Release, 2015)
Varied from Mixshield TBM the submerged wall opening is replaced by
communicating pipes. Excavated material from both modes will be removed from the
pressurized excavation chamber through the screw conveyor. In EPB mode, the screw
conveyor drops the excavated material onto a belt conveyor. An additional slurryfier box at the
end of the screw conveyor makes it possible to drive the TBM with a hydraulic slurry circuit
in slurry mode.
This makes the range of application of the Variable Density TBM even larger and makes the
machine the all-rounder for loose soils of all kinds (Gripper TBM – Herrenknecht AG, n.d.).
From your point of view, why advancement of tunnel different from one country /case
study to the other
The term advancement in tunnel is quite broad. In terms of advancement of a country
in developing experts in tunnel engineering really depends on how that country had been
involve in tunneling projects in which shaping and developing engineer and workers involve
in it. Malaysia’s SMART tunnel can be considered the pioneer of the country’s involvement in
tunneling project. Compared to other countries like China and Germany that have large number
of tunneling project have produce large number of experts and specialize workers related to
tunnel engineering.
In terms of how the advancement of a country embracing the development of tunnel.
Every country has different geological profile even from one city to another. Government funds
are often required for the creation of tunnels. When a tunnel is being planned or constructed,
economics and politics play a large factor in the decision-making process.
Civil engineers usually use project management techniques for developing a major
structure. Understanding the amount of time, the project requires, and the amount of labor and
materials needed is a crucial part of project planning. The project duration must be identified
using a work breakdown structure (WBS) and critical path method (CPM). Also, the land
needed for excavation and construction staging, and the proper machinery must be selected.
Large infrastructure projects require millions or even billions of dollars, involving long-term
financing, usually through issuance of bonds.
Reference
Gripper TBM – Herrenknecht AG. (n.d.). Retrieved May 16, 2020, from
https://www.herrenknecht.com/en/products/productdetail/multi-mode-tbm/
Maidl, B., Thewes, M., & Maidl, U. (2013). Handbook of Tunnel Engineering. In Handbook
of Tunnel Engineering (Vol. 1). Wiley Blackwell.
https://doi.org/10.1002/9783433603499
Release, P. (2015). HERRENKNECHT Variable Density Technology : Game Changer for
Kuala Lumpur. 1–8.
https://www.herrenknecht.com/en/newsroom/pressreleasedetail/variable-densitytechnology-game-changer-for-kuala-lumpur/