1. Teaching Aids Service by KRRC Information Section

2. Tunnel A tunnel is an underground passageway, completely enclosed except for openings for ingress and egress, commonly at each end.

3. TUNNEL DESCRIPTION 1.Made into natural material (rocks) 2.Empty inside 3.Carry the loads itself 4.Both ends are open to atmosphere 5.Generally horizontal 6.Thick walled structure looks like cylinder

4. 1- Key stone 2- Arch 3- Wall 4- Floor 5- Bench 6- Bench line or plane 7- Top heading 8- Invert 9- Ano (unit)

8. Types of Tunnels A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers. Other uses include routing power or telecommunication cables, some are to permit wildlife such as European badgers to cross highways. Secret tunnels have given entrance to or escape from an area, such as the Cu Chi Tunnels or the smuggling tunnels in the Gaza Strip which connect it to Egypt. Some tunnels are not for transport at all but rather, are fortifications, for example Mittelwerk and Cheyenne Mountain.

9. EXPLORATION & INVESTIGATIONS RELATED of SLOPE STABILITY Geomorphologic maping and preparation of longitudinal & cross sections Geological maping & surveyings (aerial photographs) Geophysical surveyings Underground explorations, boreholes Ground water surveyings Laboratory tests Model studies

10. SUBSURFACE EXCAVATIONS GEOLOGY 1.Soil profile or hard rock geology 2.Structure 3.Ground water (hydrogeology) 4.Stability

11. INVESTIGATIONS 1.Mapping (Topographic, geologic, etc...) 2.Geophysical surveying (especially seismic velocity of rocks) 3.Trial pits & boreholes 4.General and local stability analysis 5.Decide to excavation method

12. FACTORS EFFECTING EXCAVATION of ROCKS Mineralogical composition of rocks Texture & fabric Petrographic features Structure Rock mass Strike & dip of beds in relation to face of excavation Intensity of tectonic disturbances Degreee of weathering

13. 1. Describe the following geological structures that influence the tunnel design, stability and cost. ( i ) Tunnels in Horizontal Strata (ii) Tunnel axis parallel to the dip direction. (iii) Tunnel axis driven parallel to the strike (iv) Tunnels in folded rocks

14. ( i ) Tunnels in Horizontal Strata Horizontal strata : Such a situation is rare in occurrence for long tunnels. When encountered for small tunnels or for short lengths of long tunnels, horizontally layered rocks might be considered quite favourable. In massive rocks, that is, when individual layers are very thick, and the tunnel diameter not very large, the situation is especially favourable because the layers would overbridge flat excavations by acting as natural beams. However, when the layers are thin or fractured, they cannot be depended upon as beams; in such case, either the roof has to be modified to an arch type or has to be protected by giving a lining.

15. Horizontal strata : Such a situation is rare in occurrence for long tunnels. When encountered for small tunnels or for short lengths of long tunnels, horizontally layered rocks might be considered quite favourable. In massive rocks, that is, when individual layers are very thick, and the tunnel diameter not very large, the situation is especially favourable because the layers would overbridge flat excavations by acting as natural beams.

16. Tunnel axis parallel to the dip direction When the tunnel axis is parallel to the dip direction (which means it is at right angles to the strike direction), the layers offer uniformly distributed load on the excavation. The arch action where the rocks at the roof act as natural arch transferring the load on to sides comes into maximum condition. Even relatively weaker rocks might act as self- supporting in such cases. It is a favourable condition from this aspect. However, it also implies that the axis of tunnel has to pass through a number of rocks of the inclined sequence while going through parallel to dip.

18. (iii) Tunnel axis driven parallel to the strike When the tunnel is driven parallel to strike of the beds, the pressure distributed to the exposed layers is asymmetrical along the periphery of the tunnel opening : one half would be bedding planes opening into the tunnel and hence offer potential planes and conditions for sliding into opening. The bridge action, though present in part, is weakened due to discontinuities at the bedding planes running along the arch.

19. Tunnels in steeply inclined strata In vertical beds when the tunnel axis is parallel to the dip direction the formation stand along the sides and on the roof as massive girders- an apparently favorable condition. Conversely in tunnels running parallel to the strike of vertical bed a number of bedding planes are intersected at roof and along the arch so the natural beam action gets considerably weakened.

20. Tunnels in folded rocks Folded rocks show bends and curvatures and store a lot of stain energy in the rock. Their influence on design and construction of tunnel is important at the their position of angles. Folded Rocks are under peculiar rock pressure when excavations are made the store energy is likely to be released causing the rock fall or rock burst.

21. Effect of the folds: While tunnel is excavated in an area that contains folded rocks, different stresses and conditions may occur depending on the fold type. Fold axis and the tunnel direction is vertical Fold axis and the tunnel direction is parallel

23. Effect of faults: the relation between the fault slope direction and the tunnel direction, width of the fault zone, type and thickness of the fill material and the hydrostatic pressures in both sides of the fault are some problems in the tunnelling. Relation between the fault zone and the tunnel

24. Tunnel excavations in the slopes: the discontinuities (layers, fissures) inclined inside or outside of the slope are very important regarding the stress and strength of the tunnel.