Alignment of tunnel useful for engineering exams
- 1. ALIGNMENT OF TUNNEL 1) Preliminary setting of tunnel on topographical survey of Indian maps 2) Marking tunnel obligatory points 3) Driving lines between obligatory points 4) Marking points with concrete pillars Note : Rotary or rotary percussion methods used for investigating loose soil while rotary drilling method used for rocky soil
- 2. INVESTIGATION AT TIME OF CONSTRUCTION 1)Heading : It is part of tunnel c/s excavated for small length.It may be top , bottom and side 2)Driving Drift :Excavated for entire length of tunnel Heading give information at time of construction while drift give complete information prior to construction of tunnel When length of tunnel is small ,centre line located by means of theodolite When length of tunnel is sufficient , triangulation is used for locating centre lines.
- 3. TUNNEL ALIGNMENT AND GRADE 0.2% grade for proper drainage Straight alignment sold be provided Side drain have slope of 1 in 500 Ventilation more effective if grade is in one direction In underground compound levelling BS & FS must be made same Grade in tunnel should be less then surface grade For tunnel greater than 300m length grade provided below 75% of ruling gradient In order to maintain desire shape off tunnel c/s is check @interval at 2m to 3m