TUNNELINGMETHODS BY DEEPAK JAISWAL MOHAMMAD SALIK
CONTENTS INTRODUCTION REQUIREMENTS OF TUNNEL MAIN PURPOSES PROCEDURES INVOLVED METHODS OF TUNELLING METHOD TO SELECTION THE OTHER SIDE
INTRODUCTIONA tunnel is an undergroundpassageway, completely enclosed except foropenings for egress, commonly at each end.A tunnel may be for road traffic,roadtraffic,canal,hydroelectric station,sewer etc.The Delaware Aqueduct in New York USA is thelongest tunnel, of any type, in the world at 137 km(85 mi)
REQUIRMENTS OFTUNNEL IT IS VERY USEFUL WHERE BRIDGE FAIL TO FULFILL REQUIRMENTS LIKE IN SEA ,IN URBAN AREA ,AND IN MOUNTAINS. EFFICIENT COPARED TO BRIDGES. IN WAR TIME IT IS MUCH DIFFICULT TO DESTROY A TUNNEL BUT DESTRUCTION OF BRIDGE IS TOO EASY. LOTS OF LAND AND TIME IS SAVED.
MAIN PURPOSES 1.IN ROAD TRAFFICS 2.IN SEWERS 3.IN MININGS 4.IN RAIL TRAFFICS 5.IN HYDROELECTRIC STATIONS etc.
The process for bored tunnelling involves all or some of the following operations: Probe drilling (when needed) Grouting (when needed) Excavation (or blasting) Supporting Transportation of muck Lining or coating/sealing Draining Ventilation
PROBE DRILLING This type of drilling is done in order to find out suitable method for drilling . It consist of drilling in sample, by various method to find most suitable . It is necessary part of all drilling operation .
GROUTING Itis the process of providing additional support to drilled mine. Itis done by a liquid called grout ,consist of water ,cement ,color tint and sometime fine gravel . Good surface is achieved .
EXCAVATION Excavation is the digging and recording of artifacts at an archaeological site. Itis necessary to know the archaeological importance of a site before digging . This is performed by experts in a scientific way. Many governments grants permission for tunneling after finding a go certificate in excavation.
SUPPORTING Afterinitial mining , tunnel need supports for further processing . For the sake of life a perfect planning is needed for support. In ancient time timber and masonry were the main methods. Today support is provided by injecting final pipe or building it completely before further tunneling
TRANSPORTATION OF MUCK Inancient time transportation was done by steam engine and by Manual transport. Todayit is done by modern methods and process is automatic . TBMs are also come with proper arrangment for the transport of muck.
LINING OR COATING Lining of proper material is done by modern methods like polishing ,painting to prevent wear and tear and corrosion. Verynecessary part where corrosive metals are being used.
DRAINING Draining is the process to remove the water or other liquid from working site . Very important where water level is very high. Pumps and pipes are used for this purpose.
VENTILATION Proper ventilation is required for safety of workers. This is done by proper checking of oxygen and other parameters . Proper installations for exit of hazardous gasses coming out from tunneling .
tunnel construction methods: Classical methods Cut-and-cover Drill and blast Tunnel boring machines (TBMs) Immersed tunnels Tunnel jacking Other methods .
Classical Methods Among the classical methods are the Belgian, English, German, Austrian, Italian and American systems. These methods had much in common with early mining methods and were used until last half of the 19th century. Excavation was done by hand or simple drilling equipment. Supports were predominantly timber, and transportation of muck was done on cars on narrow gauge tracks and powered by steam. Progress was typically in multiple stages i.e. progress in one drift, then support, then drift in another drift, and so on. The lining would be of brickwork. These craft-based methods are no longer applicable, although some of their principles have been used in combination up to present day. Nevertheless some of the world’s great tunnels were built with these methods.
The English method (crown-barmethod, figure left) started from acentral top heading which allowedtwo timber crown bars to behoisted into place, the rear endssupported on a completed lengthof lining, the forward ends proppedwithin the central heading.Development of the heading thenallowed additional bars to beerected around the perimeter ofthe face with boards between eachpair to exclude the ground. Thesystem is economical intimber, permits construction of thearch of the tunnel in full-faceexcavation, and is tolerant of awide variety of groundconditions, but depends onrelatively low ground pressures.
The Austrian (cross-bar) method required a strongly constructed central bottom heading upon which a crown heading was constructed. The timbering for full-face excavation was then heavily braced against the central headings, with longitudinal poling boards built on timber bars carried on each frame of timbering. As the lining advanced, so was the timbering propped against each length to maintain stability. The method was capable of withstanding high ground pressures but had high demand for timber.
The German method (core-leaving method) provided a series of box headings within which the successive sections of the side walls of the tunnel were built from the footing upwards, thus a forerunner of the system of multiple drifts. The method depends on the central dumpling being able to resists without excessive movement pressure transmitted from the side walls, in providing support to the top key heading prior to completion of the arch and to ensuring stability while the invert arch is extended in sections. The Belgian system (underpinning or flying arch method) started from the construction of a top heading, propped approximately to the level of the springing of the arch for a horseshoe tunnel. This heading was then extended to each side to permit construction of the upper part of the arch, which was extended by under- pinning, working from side headings. The system was only practicable where rock loads were not heavy. The first sizeable tunnel in soft ground was the Tronquoy tunnel on the St Quentin canal in France in 1803, where the method of construction, based on the use of successive headings to construct sections of the arch starting from the footing, was a forerunner to the German system described above.
CUT & COVER METHOD The principal problem to be solved in connection with this construction method is to how to maintain surface traffic, with the least disturbance during the construction period. One method is to restrict traffic to a reduced street width, another to direct traffic to a bypassing street. Another way of supporting the sidewalls of open trenches is to substitute sheet-pile walls by concrete curtain walls cast under bentonite slurry (ICOS method), and using steel struts. This is especially a requisite in narrower streets trimmed with old sensitive buildings with their foundation plane well above the bottom level of the pit. This type of trench wall becomes a requirement for maintenance of surface traffic due to the anticipation of vibration effects potentially harmful to the stability of buildings with foundations lying on cohesionless soils.
DRILL AND BLAST 1.Before the advent of tunnel boring machines, drilling and blasting was the only economical way of excavating long tunnels through hard rock, where digging is not possible. 2.Even today, the method is still used in the construction of tunnels.
MECHANICAL DRILLING AND CUTTING-CRUSHING STRENGTHOF ROCK
TBM Invarious size Tunnel Boring Machines(TBM) are used for drilling a vast type of tunnels . Transportationof muck , supporting and all other actions are done automatically. Very useful in boring tunnel where all other methods fail.A main method in use in now a days.
IMMERSED TUNNELS 1.THIS TYPE OF TUNNELS ARE PARTLY OR WHOLLY ARE UNDERWATWER. 2.THEY DO NOT BLOCK THE ROOT FOR SHIPS SO THERE IS NO PROBLEM OF CONGESSION OF TRAFFIC AS IN CASE OF BRIDGES OVER RIVERS OR SEAS.
TUNNEL JACKING1.IT IS A PROCESS TO MAKETUNNELS IN ALREADY EXISTINGBOADIES SUCH AS ROADS,RAILWAYS.2.IN THIS METHOD ESPECIALLYMADE PIPES ARE PUSHED BY AHYDRAULIC RAM IN GROUND .3.MAXIMUM DIAMETER OF TUNNELBY THIS METHOD IS AROUND 2.4METER.
The choice of tunnelling method may be dictated by: geological and hydrological conditions, cross-section and length of continuous tunnel, local experience and time/cost considerations (what is the value of time in the project), limits of surface disturbance, and many others factors. Tunnel methods . Required speed of construction. Shape of tunnel. Managing the risk of variations in ground quality
THE OTHER SIDE Beside of many security measures , tunnelling is still not full proof. Failure of automatic system will cause deadly results as depicted in Hollywood flick Die Hard 4.0. Highcost than bridges , but more fruitful from previous.