Dear Rouhollah Basirat,

As per my experience in tunneling by TBM in fault zone the following steps must follow:-

1. Go for probe hole drilling, it will help you to assess the nature of fault, infilled material (fault Breccia), its width and dip direction, this is the direct method to investigate about the fault.

2. Second is Tunnel seismic prediction method, by this you can get the extent of fault in less time but won't be able to assess the nature of fault breccia.

3. As you have stated that there is  water inflow in tunnel through the tunnel face then to counter this the grouting should be done to stop the water and the drainage holes must be provided at inverts level to allow the water seep through a proper channel. Before going for the grouting the pressure of water should be checked by using the pressure gauge by doing this you can decide the grout mix and the pressure at which you have to inject the grout into the holes.

4. The grouting should be done in umbrella shape by keeping the drill holes direction slightly ~10 to 15 degree upward. This umbrella will help as a roof for your TBM and will also prevent the tunnel from problem of collapse etc.

5. Before doing these all the surface geological mapping of the area should be referred for the tectonic settings.

I have attached herewith a file of umbrella grouting for your reference.

Thanks & Regards

Naveen 

Thanks Dr. Sharma!

The forpoling method is used more for conventional method like NATM and it is hard for mechanized tunnels which are excavated by TBM, especially when we use a Open TBM or Single shield TBM that this equipment in not considered. Is there any solution else?

Best Regards

HI

One method is to inject cement slurry into crack and fault zones and then continue the rest of excavation.

regards

MJM

Dear Mr. Rouhollah Basirat,

Then try to inject the grout slury into the drill holes this is the only method or you can go for the conventional tunneling method in the fault affected zone and once it cross then continue the TBM because the fault zone could be charged with water and the TBM will not work in the squeezed ground conditions, go for conventional method install ISB ribs in the affected stretch.

Regards

Naveen 

Thanks Dr. Sharma,

But there is a problem here, because the fault zone is located in the middle of tunnel, how we can access to this zone? It is necessary TBM is gone back and then we inject grouting, in this situation. Is it possible?

 Dear Mr. Rouhollah Basirat,

There is a option to excavate a pilot access tunnel by passing the TBM parallel to your tunnel by conventional method and once you will reach to the fault zone then the grouting can be done and also can excavate the pilot tunnel through the fault affected zone.

I have attached herewith a sketch please discuss with your tunnel designers before proceed.

Regards

Naveen

Being biased - sorry (!) you might find some useful explanations, even an equation about why fault zones are likely to delay TBM - in case 'justification' of your difficulties could be helpful? (see www.isrm.net, 11th on-line lecture re TBM. Go beyond the 4 minutes introduction). You will get to fault zone challenges half-way through. Otherwise, probe drilling, drainage holes, some pre-injection if configured for that, and finally a bypass with grouting, all as suggested by others. Note the potential adverse effect of TBM with-drawal.

Regards, Nick Barton

Thanks a lot Prof. Barton,

Do you have any schematic figure and executive map? 

Some slides in the lecture - or go to Barton, 2013 in www.nickbarton.com - some problem

solutions are shown.

Regards,  Nick Barton

Thank so much Prof. Barton!

Most of Fault Zones are experienced Nightmare for many projects. Though during construction such a very critical reaches are proving existence of adverse condition in further advance but most management decides to provide higher support solution or to improve the ground strength.In such critical tunnel front re rooting and alternate alignment if seems feasible should be opted in consultation with Design people.Otherwise though by very expensive tunneling methodology are helping a lot but the impact of such critical zones on project schedule,Budget ,contractual disputes and structural stability are out of envelop.