Dear Sudarshon

It is not easy to fix the tunneling alignment in such fragile geological terrain. Despite of the many challenges arising during the tunneling design, we should choose on option that is comparatively stable and having least risk factor. I think we should consider the following during the selection of  tunnel alignment.

1. You need to have detail geological and Geo-technical investigation of the site.

2. Detail information about rock type, strength of rock, detail joint set analysis, fault system,orientation of the rock, topography, associated hazard, ground water condition, mineralogy of the rock

I think it is useful to you.

Regards

Ishwor Thapa

Dear ishwor

Definitely, it is useful. but it is the very common and board things for investigation of tunnel site. Now, actually, we dealing with large landside and fragile Geology within the project area. 

 many thanks for your time to write this comment and suggestion. 

Regards

S.Sapkota

Dear Sudarshon Sapkota,

Alignment depends on,

Nature of the project and its need.

Surface and subsurface investigation. The rock investigation (Joint, fault,fold,strength, classification) is a must as you are in mountain region.

Survey of the area.

Further you can refer following

https://link.springer.com/chapter/10.1007/978-1-4613-0449-4_3

http://www.alignmentsurveys.com/tunnel-alignment/

http://www.gzconsultants.com/documents/selection-of-alignment-and-tunnelling-methods-in-urban-settings/

http://www.sciencedirect.com/science/article/pii/S088677980800076X

Mr Sudarshon 

you have raised very important issue.

Friends have given generic answers to the  practical problems, but in field, apart from the geological weaknesses, structure and rock conditions etc  the following are some of the key points

1, the rock cover over the prospective alignment  needs to be ensured i.e.  a concept of  3D cover.

2. the cross drainages and the depth of cover over drains.

3. landslides all along the alignment to ensure that the plane of failure does not affect the tunnel section in any way.

4. orientation of geological structure and bedding/foliation with respect to tunnel alignment.. A care where foliation / bedding follow the alignment is  generally a 'no-no situation', then obliquity is to be seen.

5. Projection of surface geology on the prospective tunnel alignment is to be precisely developed.

In order to answer some of these questions , a well planned geological, geophysical and exploratory programme needs to be evolved..

Hope this gives an overview of your inquiry, should you seek some specifics I will be glad to revert to you

best

Dr VK Sharma

India

+ 8004915833

I am very thankful to you both Dr. VK Sharma and Mr.Velusamy Gobinath for your valuable time and useful suggestions. 

Best Regards

Sudarshon Sapkota

A complex problem has been posed. Personally in such a complex area I would have avoided tunnelling, unless there is no other alternative or unavoidable. All the parameters you have given about the area such as fragile rocks (mostly with foliations/fractures/joints, etc); unfavorable slope; landslide prone; etc; indicate the high risk factor. Only based on the detailed field observations, one can come out with solution. It is better to consult a local geologist for guidance to deal with the geological condition and there after a tunneling engineer. I think you can also consult the scientists from Geological Survey of India or Wadia Institute of Himalayan Geology in Dehradun, who are doing research in Himalayan region. Good luck.

Thank you, N B Narasimha Prasad for your valuable comment.

Yes.Mr. Neil Bar, Himalayas are a challenging geotechnical environment! I am thankful for your suggestions. Your suggestions will be useful for us.

Thank you

Best regards,

Sudarshon