PRESENTED BY- Namrata M. Lolge (09CM16F) M. Tech. 1 st sem NITK

A definition of Conventional Tunnelling can be the construction of underground openings of any shape with a cyclic construction process of- 1. excavation, by using the drill and blast methods or mechanical excavators (except any full face TBM) 2. mucking 3. placement of the primary support elements such as- -steel ribs or lattice girders -soil or rock bolts -sprayed or cast in situ concrete,

 Conventional Tunnelling is carried out in a cyclic execution process of repeated steps of excavation followed by the application of relevant primary support, both of which depend on existing ground conditions and ground behaviour. An experienced team of tunnel workers (miners), assisted by standard and/or special plant and equipment shall execute each individual cycle of tunnel construction.

 The Conventional Tunnelling Method mainly using standard equipment and allowing access to the tunnel excavation face at almost any time is very flexible in situations or areas that require a change in the structural analysis or in the design and as a result of this, also require changes in the support measures.

 The processes involved in the cyclic operation of conventional tunnelling are 1. Drilling 2. Charging 3. Blasting 4. Ventilation 5. Supporting 6. Loading/Muck removel 7. Transporting

 A standard set of equipment for execution of conventional tunnelling may consist of following items  Drilling jumbo to drill holes for blasting, rock bolting, water and pressure release, grouting etc.  Road header or excavator in cases where blasting is not possible or not economic  Lifting platform allowing the miners to reach each part of the tunnel crown and of the tunnel face.

 Lifting equipment for steels sets  Loader or excavator for loading excavated ground into dump trucks.  Dump trucks for hauling excavated ground.  Set of shotcrete manipulators for application of wet or dry shotcrete.

 Conventional tunnelling enables :  A greater variability of the shapes.  Better knowledge of the ground by systematic exploratory drilling at the tunnel level ahead of the face.  Greater variability in the choice of excavation methods according to the ground conditions.  Easier optimisation of the primary support using observational method in special cases.  A greater variability in the choice of auxilliary construction methods according to the ground conditions

 Conventional tunnelling is specially convenient for:  Difficult ground with highly variable ground conditions.  Projects with highly variable shapes of cross sections.  Projects with a higher risk of water inflow under pressure.  Projects with difficult access.  Short tunnels.

 The conventional method for tunnelling entails the use of “shield mill”, which bores the entire cross section of the tunnel, the final supporting structure being produced behind said mill.  This method has limitation due to the need to have a shield which has exactly the dimension of the tunnel to be bored and can not therefore used in tunnels with different geometry.  Considerable excavation power furthermore required.

 Another disadvantage is to be seen in the fact that in the loose soil a downward thrust component is introduced which is due to the weight of the excavation tool and is difficult to control.

KONKAN RAILWAY:  Broad Gauge line for 760 km from Mangalore to Roha.  Mangalore to Bombay- 914 km

 The line passes through the States of Karnataka, Goa and Maharashtra and the distance in the 3 States are given below:  Karnataka -273 km  Goa -105 km  Maharashtra -382 km  Total -760 km

 Length- 2 km  Distance from Mangalore- 136 km (Northern End of Dakshina Kannada district)  Proposed tunnel passes through a lateritic plateau for a length of about 2 km.

 The total area around Byndoor Tunnel alignment is plateau designated as Paduvare plateau.  The plateau rises to an elevation of 70 to 110m and extends from the Arabian Sea Coast.  This plateau forms a thick sheet of laterite and has a hard petted crust.  Within the laterite profile, the upper 5 to 8m is comparatively rich in alumina and lower portion is ferruginous and clayey (lithomargic).

 Vertical Electrical Resistivity Soundings (VES) were conducted along the proposed tunnel alignment.  A total no. of 170 soundings were conducted to establish the strata and ground water conditions at 10m interval.

 The average depth to the bed rock along the tunnel alignment is as follows: CHAINAGEAVERAGE DEPTH TO BED ROCK (M) TO TO TO TO TO TO

 The work was commenced from both the faces.  However due to soft soil condition serious problems are met with on both the faces. There is heavy flow of lithomargic clay with water.  The work was stopped a number of occasions.  Finally at the Bombay end a n audit is cut opened from eastern side and entered the face where hard rock is met with.

 Total no. of holes- 74  Dia of hole- 32mm  Explosive- Ammonium Nitrate + Gelatine  Average pull for blasting- 2.2m  Yield- 75 cum.  Cross sectional area of tunnel- 35 sqm.  Powder factor- 1.5 cum/kg of gelatine.

 The cycle time is about 16 hrs as per datails given below: The alignment marking and location of bore holes 1hr Drilling holes5hrs Charging2hrs Blasting and defuming1hr Scaling1hr Muck removel6hrs TOTAL16hrs

 ITA Report on Conventional Tunneling Method, April 2009, pp  Advances in Drilling and Blasting, V. R. Sastry.