Tunneling(1)

I] TUNNELLING THROUGH SEDIMENTARY STRATA OR              TUNNELLING THROUG DIP AND STRICK DIRECTION.

                                                                                                                                 1) The relation between dip and strick of the rock with the centre line of tunnel is always a important factor for proper planning of the project.

                                                                                                                                   2) When central line of tunnel is right angle to the strike ie. Tunnel is parallel to dip direction. In this case there is no unsymmetrical pressure from the sides.

                                                                                                                                    3) The tunnel can be easily passing and smoothly even with little lining which may be required for downward pressure of roof.

                                                                                                                                    4) Therefore it is more convenient tunnel across the strike rather than along it.

                                                                                                                                    5) When centre line of tunnel is parallel to strike in this case there is a considerable unsymmetrical pressure from the sides as the blocks always tends to slide down into the tunnel. In this case heavy lining has to be provided for stability of tunnel. In both the cases through the beding planes the leakage of water may be takes place. Over break is much less when tunnel is across the strike lines than along it.

Ex:- In Lochabar tunnel in Scotland the rock type is mica schist. The over break is 40% along the strike and only 16% across the strike.