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1. Introduction Urban areas are increasingly grappling with the problem of traffic congestion, which not only leads to longer travel times but also results in excessive fuel consumption and harmful emissions. With cities growing in both size and population, efficient traffic management has become a priority for city planners. One of the most promising solutions to address this challenge is Adaptive Traffic Signal Control (ATSC). By adjusting traffic light timings based on real-time data, ATSC significantly reduces delays and improves traffic flow, thus offering a smarter way to manage urban mobility. 2. What is Adaptive Traffic Signal Control? Adaptive Traffic Signal Control (ATSC) is an advanced traffic management system designed to optimize traffic light timings in response to real-time traffic conditions. Unlike traditional systems that operate based on fixed schedules, ATSC uses real-time data to dynamically adjust traffic signals. This results in fewer traffic jams, smoother vehic
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TBM - TUNNEL BORING MACHINE


INDEX

  • INTRODUCTION

  • TYPES OF TBM

  • WORKING PROCESS OF TBM 

  • APPLICATIONS OF TBM

  • TBM ADVANTAGES/DISADVANTAGES 

  • REFERENCES






INTRODUCTION 

 


A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They can bore through anything from hard rock to sand.


Tunnel diameters can range from 1 meter to 17.6 meters to date. Tunnels of less than a meter or so in diameter are typically done using trenchless construction methods or horizontal directional drilling rather than TBMs.
TUNNEL BORING MACHINE FRONT VIEW


TUNNEL BRING MACHINE VECTOR DIAGRAM



Tunnel boring machines are used as an alternative to drilling and blasting (D&B) methods in rock and conventional "hand mining" in soil.


TBMs have the advantages of limiting the disturbance to the surrounding ground and producing a smooth tunnel wall. This significantly reduces the cost of lining the tunnel, and makes them suitable to use in heavily urbanized areas.


The major disadvantage is the upfront cost. TBMs are expensive to construct, and can be difficult to transport. Tunneling with TBMs is much more efficient and results in shortened completion times. Drilling and blasting however remains the preferred method when working through heavily fractured and sheared rock layers.


Modern TBMs generally consists of the rotating disc, called cutter head, followed by a main bearing, a trust system to give support against down thrust of the tunnel wall, and tailing support mechanism.


The type of machine used depends on the particular geology of the project, the amount of ground water present and other factors like formation of different soil strata and their extent.







TYPES OF TBM


Hard rock TBM


Hard rock TBMs excavate rock with disc cutters mounted in the cutter head. The disc cutters create compressive stress fractures in the rock, causing it to chip away from the tunnel face. The excavated rock (muck) is transferred through openings in the cutter head to a belt conveyor, where it runs through the machine to a system of conveyors or muck cars for removal from the tunnel.


The process of working of this type of TBM is very simple. As each operation of movement of cutter head to the follow back by gripper shoe, insuring the arrangements of supports like ring beams or conventional supports or concrete lining to the walls of bored tunnel including removal of muck generated and again starting the movement of cutting head to bore the tunnel for next distance is called One Complete Cycle of TBM.


Open-type TBMs have no shield, leaving the area behind the cutter head open for rock support. To advance, the machine uses a gripper system that pushes against the tunnel walls. The machine will then push forward off the grippers gaining thrust. At the end of a stroke, the rear legs of the machine are lowered, the grippers and propel cylinders are retracted. The retraction of the propel cylinders repositions the gripper assembly for the next boring cycle. The grippers are extended, the rear legs lifted, and boring resumes. 


Soft ground TBMs 

In soft ground, there are three main types of TBMs: Earth Pressure Balance Machines (EPB), Slurry Shield (SS) and open-face type. Both types of closed machines operate like Single Shield TBMs, using thrust cylinders to advance forward by pushing off against concrete segments. Earth Pressure Balance Machines are used in soft ground with less than 7 bar of pressure.


The EPB gets its name because it uses the excavated material to balance the pressure at the tunnel face. Additives such as bentonite, polymers and foam can be injected ahead of the face to increase the stability of the ground. In soft grounds unlike like hard ground the stability of ground is much more concern. 


In soft ground with very high water pressure or where ground conditions are granular (sands and gravels) so much so that a plug could not be formed in the Archimedes screw, Slurry Shield TBMs are needed. The cutterhead is filled with pressurized slurry which applies hydrostatic pressure to the excavation face.


Open face TBMs in soft ground rely on the fact that the face of the ground being excavated will stand up with no support for a short period of time.


Backup system


Behind all types of tunnel boring machines, are trailing support decks known as the back-up system. The back-up can include: conveyors, slurry pipelines if required, electrical systems, dust removal, ventilation mechanisms.







WORKING PROCESS OF TBM OF EPB (Earth pressure balance) TYPE IS EXPLAINED AS FOLLOWS.


Cutting wheel or cutting head rotates and breaks the material from the tunnel face and the material transferred to the belt conveyer in the rear of the shield through screw conveyer. Meanwhile the hydraulic cylinders press the machine forwards continuously.

The RCC work from segments of RCC known as lining segments are installed under the protection of shielding skin.
TBM PARTS IN VECTOR DIAGRAM



As the ring of lining completed the machine advances further cutting new soil.

Working method of EPB TBM can be categorized in two phases generally.

1.     Cutting phase (tunneling phase)

2.     Strengthening of walls phase (ring building phase) 


Cutting phase: -

Sometimes to control the direction and angle of penetration the excavated material is used to compensate the pressure of soil and water coming from tunnel phase and giving the same pressure from TBM by excavated material makes equilibrium of pressure and controls direction and angle of the penetration to insure the same pressure back from cutting face many sensors are used to monitor the geological uncertainty and pressure changes and adopting the rotation speed of cutting head and rotating screw to provide the same pressure resistance with every changing pressure of soil from tunnel face to optimize the tunneling process as much as it can.
 
CUTTING HEAD OF TBM


In ring building phase the method can be adopted as pre casted sections or cast in situ, generally pre casted sections method is adopted having more benefits, fast process and quality control over cast in situ method. In pre cast sections method the quality can be insured by fabricating the segments of the lining outside the tunnel in controlled environment and with high precision the cannot be controlled and guarantied in cast in situ method. With construction of each lining ring the TBM advances further.  
SEGMENTS OF RCC PRECAST FOR LINING OF TUNNEL





The excavated material is removed by belt conveyor. The cutting tools are constantly maintained and sometimes replaced as the getting wear and tear damage from abrasion with the material encountered and excavated time to time. 


The maintenance and replacement of cutting disc is done by removing partial loose material from rear of cutting head and providing air pressure to counter the soil pressure and providing man lock to work and replace the damaged cutting disk. 


The excavated material is transported out with the help of conveyor belt adjustable and long enough to transport the material even with increase in tunnel length.


The detailed view of this process is explained with help of animation in this video below. 

https://www.youtube.com/watch?time_continue=790&v=qx_EjMlLgqY&feature=emb_title













APPLICATIONS OF TBM 


1.     Urban subway tunnel

2.     Cross river roadway and railways

3.     Subsea tunnel

4.     Urban municipal engineering tunnel

5.     Oil gas pipeline tunnel

6.     Water tunnel 


Preferred in construction of tunnels in all types of geology with minimum disturbance/deterioration to environment. For example, metro rail projects in congested urban areas are difficult or rather unthinkable to construct without TBMs.







TBM ADVANTAGES


  • Protects on surface life
  • Zero impact on aesthetics
  • Minimum eco-disturbance
  • Zero seismic vibrations
  • Safe
  • Adaptable to changing topography
  • Tunnel length not a limitation
  • Cost efficient

 

 

TBM DISADVANTAGES 


  • The major disadvantage is the upfront capital cost. TBMs are expensive to construct, difficult to transport, require significant backup systems and power.
  • Large stones and boulders can be troublesome.









REFERENCES 


1.       https://www.wikipedia.org/ wiki/Tunnel_boring_machine

2.       http://www.railsystem.net/tunnel-boring-machine-tbm/


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