- Slides: 44
• Tunnel Is an underground or underwater passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods.
• Tunnel A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. The central portions of a rapid transit network are usually in tunnel. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or sewers. Utility tunnels are used for routing steam, chilled water , electrical power or telecommunication cables.
• Parts of a tunnel
• Two main types of tunnelling Hard Rock Tunnelling Soft Rock/Soil/Ground Tunnelling
• Hard Rock Tunnelling In Scandinavian hard rock conditions, most tunnels are excavated by drill & blast technique in softer rock, other excavation methods such as road.
• Types of hard rock tunnelling Bored Tunnelling Method (sometimes called Tunnel Boring Method) Drill and Blast Method
• Soft Rock/Soil/Ground Tunnelling Workers generally use two basic techniques to advance a tunnel. In the full-face method, they excavate the entire diameter of the tunnel at the same time. This is most suitable for tunnels passing through strong ground or for building smaller tunnels. The second technique, shown in the diagram below, is the topheading-and-bench method. In this technique, workers dig a smaller tunnel known as a heading. Once the top heading has advanced some distance into the rock, workers begin excavating immediately below the floor of the top heading; this is a bench. One advantage of the top-heading-and-bench method is that engineers can use the heading tunnel to gauge the stability of the rock before moving forward with the project.
• Types of Soft Rock/Soil /Ground Tunnelling Cut and Cover Tunnelling Method Immersed Tube Tunnelling (for underwater tunnels) Shield Tunnelling
• Purpose of a tunnel Original purpose Ø Ø Ø In Military In Sewers In Mining In Rail traffics In Hydroelectric station and etc.
• Tunnel Construction Method Ø Ø Ø Ø Cut-and-cover Drill and blast Tunnel boring machines ( TBM ) Immersed tunnel Tunnel jacking Shield tunnel Other methods
Construction Methods Circular Cut and Cover Shield Driven Horseshoe Rectangular X X Bored X Drill and Blast X X Immersed Tube X X Sequential Excavation X Jacked Tunnel X X
• Cut -and -Cover Ø Simple method of construction for shallow tunnels where a trench is excavated and roofed over with an overhead support system strong enough to carry the load of what is to be built above the tunnel. Ø Two basic forms / methods of cut-and-cover tunnelling: 1. Bottom-up 2. Top-down
• Bored (tunnel boring machine ) Ø is a protective structure used in the excavation of tunnels through soil that is too soft or fluid to remain stable during the time that it takes to line the tunnel with a support structure of concrete, cast iron, or steel. In effect, the shield serves as a temporary support structure for the tunnel while it is being excavated.
• Drill and Blast Ø An alternative to using a TBM in rock situations would be to manually drill and blast the rock and remove it using conventional conveyor techniques. This method was commonly used for older tunnels and is still used when it is determined cost effective or in difficult ground conditions.
• Immersed Tube Ø When a canal, channel, river, etc. , needs to be crossed, this method is often used. A trench is dug at the water bottom and prefabricated tunnel segments are made water tight and sunken into position where they are connected to the other segments. Afterward, the trench may be backfilled with earth to cover and protect the tunnel from the water-borne traffic, e. g. , ships, barges, and boats.
• Sequential Excavation Method (SEM) Ø Soil in certain tunnels may have sufficient strength such that excavation of the soil face by equipment in small increments is possible without direct support. This excavation method is called the sequential excavation method. Once excavated, the soil face is then supported using shotcrete and the excavation is continued for the next segment. The cohesion of the rock or soil can be increased by injecting grouts into the ground prior to excavation of that segment.
• Jacked Tunnels Ø The method of jacking a large tunnel underneath certain obstructions (highways, buildings, rail lines, etc. ) that prohibit the use of typical cut-andcover techniques for shallow tunnels has been used successfully in recent years.
• Shield Tunnelling Ø This 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.
• Local tunnels Ternate-Nasugbu Tunnel (Kaybiang Tunnel) Ø longest tunnel in the Philippines (300 m); constructed for 4 years.
• Local tunnels Malinta Tunnel (Corregidor) Ø initially used as a bomb-proof storage, but later used as a 1000 -bed hospital; 831 feet (253 m) long, 24 feet (7. 3 m) wide and 18 feet (5. 5 m) high. Branching off from this main shaft are 13 lateral tunnels on the north side and 11 lateral tunnels on the south side.
• Local tunnels Fort Bonifacio Tunnel (Bonifacio Global City, Taguig) Ø The tunnel was initially used as a passageway for military supplies and war materials. It was first constructed around 1936 with the help of Igorots. It stretches 2. 24 kilometers (1. 39 mi) (from Pasig River to Villamor Airbase in Pasay) at an average depth of 70 feet (21 m).
• Intact rock contains neither joints nor hair cracks, and thus breaks across sound rock. Spalling conditions, which is when thin slabs of rock fall off the roof or walls of the tunnel, , and popping conditions, where rock slabs on the sides or roof of the tunnel spontaneously and violently detach, may occur for several hours or days after blasting.
• Stratified rock consists of individual strata with little or no resistance against separation along strata boundaries. Spalling conditions are quite common.
• Moderately jointed rock contains joints and hair cracks, but blocks between the joints are locally grown together or so intimately interlocked that vertical walls do not require lateral support. Again, spalling and popping conditions may be encountered.
• Blocky and seamy rock This consists of chemically intact or nearly intact rock fragments which are entirely separated from each other and imperfectly interlocked. The vertical walls of the tunnel may require support.
• Crushed rock is chemically intact, but extensively fractured. If the crushed rock is small-grained and below the water table, it will exhibit the properties of a water-bearing sand.
• Squeezing rock slowly advances into the tunnel without a perceptible volume increase. This condition requires a very high percentage of microscopic and submicroscopic micaceous minerals or clay minerals with a low swelling capacity.
Thank you for listening Reporters: Julienne Ruzell Andrade Eugene Miranda Ivan Reyes