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File: Construction Methods Pdf 88897 | 99991103
types of tunnels construction methods a mountain tunnel drilling and blasting d b method natm new austrian tunneling method is the most common method it originates in hard rock tunneling ...

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                Types of Tunnels & Construction Methods 
       (a) Mountain Tunnel 
       -- Drilling and blasting (D&B) method: NATM (New Austrian Tunneling Method) is the most 
       common method. It originates in hard rock tunneling and utilizes rockbolts and shotcrete applied 
       immediately after blasting. This is often followed by a cast in-situ concrete lining using formwork. 
       -- Tunnel Boring Machine (TBM) method: TMB is used as an alternative to drilling and blasting 
       (D&B) methods. TBMs are used to excavate tunnels with a circular cross section through a variety 
       of  subterranean matter;  hard rock, sand or almost anything in between. As the TBM moves 
       forward, the round cutter heads cut into the tunnel face and splits off large chunks of rock. The 
       cutter head carves a smooth round hole through the rock -- the exact shape of a tunnel. Conveyor 
       belts carry the rock shavings through the TBM and out the back of the machine to a dumpster. 
       Tunnel lining is the wall of the tunnel. It consists of precast concrete segments that form rings, 
       cast in-situ concrete lining using formwork or shotcrete lining. 
        
       (b) Shallow-buried Tunnel or Soft Soil Tunnel 
       Shallow tunnels are of a cut-and-cover type (if under water of the immersed-tube type). Deep 
       tunnels are excavated, often using a tunnelling shield. For intermediate levels, both methods are 
       possible. 
       -- Cut-and-cover method: Cut-and-cover is a method of tunnel construction where a trench is 
       excavated and roofed over. Strong supporting beams are necessary to avoid the danger of the tunnel 
       collapsing. 
       -- Shield method: The Shield method uses one or two shields (large metal cylinder) to cut out a 
       tunnel through the soft ground. A rotating cutting wheel is located at the front end of the shield. 
       Behind the cutting wheel is a chamber where, depending on the type of the TBM, the excavated 
       soil  is  either  mixed  with  slurry  (called  slurry  TBM)  or  left  as  is  (earth  pressure  balance  or 
       EPB  shield).  Systems  for  removal  of  the  soil  (or  the  soil  mixed  with  slurry)  are  also 
       present. 
       Behind  the  chamber  is  a  set  of  hydraulic  jacks  supported  by  the  finished  part  of  the 
       tunnel  which  are  used  to  push  the  TBM  forward.  Once  a  certain  distance  has  been 
       excavated  (roughly  1.5-2  meters),  a  new  tunnel  ring  is  built  using  the  erector.  The 
       erector  is  a  rotating  system  that  picks  up  pre-cast  concrete  segments  and  places 
       them in the desired position. Behind the shield, inside the finished part of the tunnel, several 
       support mechanisms can be found that are part of the TBM: dirt removal, slurry pipelines if 
       applicable, control rooms, and rails for transport of the precast segments, etc. 
        
       (c)Underwater Tunnel 
       -- Immersed-tube method: The immersed tube tunnel technique uses hollow box sectioned tunnel 
       elements that have been prefabricated in reinforced concrete. These are floated out into the harbor 
       and  placed  into  a  trench  that  was  pre-dredged  in  the  harbor  bed.  When  in  position, 
       the elements are joined together to form a tunnel. The trench is then refilled and the harbour bed 
       returned to its original level. 
       -- Shield method: As previously stated. 
        
       Tunnel Construction Methods and their comparison 
       1. Introduction – This paper gives a general description of the tunnelling techniques such as cut 
       and cover, drill and blast, bored tunnelling and sequential mining construction, reviewed for 
       possible use in various projects. 
       A summary of environmental merits and demerits associated with these methods are also given. 
       Above tunnelling techniques are mostly used to construct small tunnels and find their applications 
       in utility projects to a great extent. 
       2. Construction Methods: 
       a. Cut and Cover Tunnelling – Cut and cover tunnelling is a common and well-proven technique 
       for constructing shallow tunnels. The method can accommodate changes in tunnel width and non-
       uniform shapes and is often adopted in construction of underground stations. Several overlapping 
       works are required to be carried out in using this tunnelling method. Trench excavation, tunnel 
       construction and soil covering of excavated tunnels are three major integral parts of the tunnelling 
       method. 
       Most of these works are similar to other road construction except that the excavation levels 
       involved are deeper. Bulk excavation is often undertaken under a road deck to minimise traffic 
       disruption as well as environmental impacts in terms of dust and noise emissions and visual impact. 
       b. Drill and Blast – This tunnelling method involves the use of explosives. Drilling rigs are used 
       to drill blast holes on the proposed tunnel surface to a designated depth for blasting. Explosives 
       and timed detonators (Delay detonators) are then placed in the blast holes. Once blasting is carried 
       out, waste rocks and soils are transported out of the tunnel before further blasting. Most tunnelling 
       construction in rock involves ground that is somewhere between two extreme conditions of hard 
       rock and soft ground. Hence adequate structural support measures are required when adopting this 
       method for tunnelling. 
       Compared with bored tunnelling by Tunnel Boring Machine (see below), blasting generally results 
       in higher but lesser duration of vibration levels. A temporary magazine site is often needed for 
       overnight storage of explosives. 
       c. Bored Tunnelling by Tunnel Boring Machines (TBM) – Bored tunnelling by using a Tunnel 
       Boring Machine (TBM) is often used for excavating long tunnels. An effective TMB method 
       requires the selection of appropriate equipment for different rock mass and geological conditions. 
       The TBM may be suitable for excavating tunnels which contain competent rocks that can provide 
       adequate geological stability for boring a long section tunnel without structural support. However, 
       extremely hard rock can cause significant wear of the TBM rock cutter and may slow down the 
       progress of the tunnelling works to the point where TBM becomes inefficient and uneconomical 
       and may take longer time than the drill-and-blast tunnelling method. 
       d. Sequential Excavation Method – This method is also known as the New Austrian Tunnelling 
       Method (NATM). The excavation location of a proposed tunnel is divided into segments first. The 
              segments are then mined sequentially with supports. Some mining equipments such as road-
              headers and backhoes are commonly used for the tunnel excavation. The ground for excavation 
              must be fully dry for applying the NATM and ground dewatering is also an essential process before 
              the excavation. Another process relates to the ground modifications such as grouting and ground 
              freezing is also common with this method in order to stabilize the soil for tunnelling. This method 
              is relatively slow but is found useful in areas where existing structures such as sewer or subway 
              could not be relocated. 
              3.  Environmental  Merits  and  Demerits  – Selection  of  the  techniques  to  be  adopted  for 
              construction of a tunnel section shall take into account the nature of the substrata and the levels of 
              the tunnel involved. A summary of the environmental advantages and disadvantages associated 
              with the construction methods is tabulated below: 
               
                 Tunnel Construction             Environmental advantages and disadvantages 
                 Methods                         (on relative terms) 
                                                 Disadvantages: 
                                                      More dust and noise impact may arise, though 
                                                       these can be mitigated through implementation 
                                                       of sufficient control measures; 
                                                      Temporary decks are often installed before bulk 
                                                       excavation to minimise the associated 
                                                       environment impacts; 
                                                      Larger quantity of C&D materials would be 
                                                       generated from the excavation works, requiring 
                 Cut and cover tunnelling              proper handling and disposal. 
                                                 Advantages: 
                                                      Potential environmental impacts in terms of 
                                                       noise, dust and visual on sensitive receives are 
                                                       significantly reduced and are restricted to those 
                                                       located near the tunnel portal; 
                                                      Compared with the cut-and-cover approach, 
                                                       quantity of C&D materials generated would be 
                                                       much reduced; 
                                                      Compared with the cut-and-cover approach, 
                                                       disturbance to local traffic and associated 
                                                       environmental impacts would be much 
                                                       reduced; 
                                                      Blasting would significantly reduce the 
                                                       duration of vibration, though the vibration level 
                                                       would be higher compared with bored 
                                                       tunnelling (with proper blast design & 
                                                       techniques vibration can be reduced); 
                                                   
                 Drill and blast 
                                                                       Disadvantages: 
                                                                                Potential hazard associated with establishment 
                                                                                 of a temporary magazine site for overnight 
                                                                                 storage of explosives shall be addressed 
                                                                                 through avoiding populated areas in the site 
                                                                                 selection process. 
                                                                       Advantages: 
                                                                                Potential environmental impacts in terms of 
                                                                                 noise, dust and visual on sensitive receives are 
                                                                                 significantly reduced and are restricted to those 
                                                                                 located near the launching and retrieval shafts; 
                                                                                Compared with the cut-and-cover approach, 
                                                                                 disturbance to local traffic and associated 
                                                                                 environmental impacts would be much 
                                                                                 reduced; 
                                                                                Compared with the cut-and-cover approach, 
                                                                                 quantity of C&D materials generated would be 
                        Bored tunnelling by TBM                                  much reduced; 
                                                                       Advantages: 
                                                                                Similar to the drill-and-blast and bored 
                                                                                 tunnelling methods, only localised potential 
                                                                                 environmental impacts would be generated; 
                                                                       Disadvantages: 
                                                                                As the method is relatively slow, duration of 
                        Sequential Excavation                                    potential environmental impacts would be 
                        Method                                                   longer than that of the other methods. 
                     
                     
                    Tunnel Excavation by Tunnel Boring Machine (TBM) & Parameters 
                    Major components of this Tunnel Boring Machine include: 
                    1. Cutter head, with cutting discs/tools and 
                    2. Muck buckets to carry and dispose excavated muck 
                    3. Power supply Systems 
                    4. Cutter head rotation & thrust 
                    5. Bracing system for the TBM during mining 
                    6. Equipment for ground support installation 
                    7. Shielding to protect workers 
                    8. Steeling system 
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...Types of tunnels construction methods a mountain tunnel drilling and blasting d b method natm new austrian tunneling is the most common it originates in hard rock utilizes rockbolts shotcrete applied immediately after this often followed by cast situ concrete lining using formwork boring machine tbm tmb used as an alternative to tbms are excavate with circular cross section through variety subterranean matter sand or almost anything between moves forward round cutter heads cut into face splits off large chunks head carves smooth hole exact shape conveyor belts carry shavings out back dumpster wall consists precast segments that form rings shallow buried soft soil cover type if under water immersed tube deep excavated tunnelling shield for intermediate levels both possible where trench roofed over strong supporting beams necessary avoid danger collapsing uses one two shields metal cylinder ground rotating cutting wheel located at front end behind chamber depending on either mixed slurry...

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