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Any body who is envolved in tunneling worsk, my question lies in water inflow criteris; what is the best limit of water inflow to execute grouting works in soft ground using canopy pipes... consider big section of tunnel say 16m x 20m... Thanks in advance.

RE: Tunneling

Im confused. The act of grouting is one of the best limits of water inflow, so what exactly is it that you are asking. 16x 20 is a big tunnel, ESPECIALLY in soft ground, and I'll predict that with any water inflow, your tunnel will cave in before you have a chance to mobilize your grout pump. What is your ground support regime ??? When you have answered that , maybe grouting can be discussed.

RE: Tunneling

The Mode of support shall be a Rib Reinforced shotcrete at 1m distance with canopy pipe on the crown, the excavation shall be done by NATM, my question is the critical water inflow that shall be considered for Pre-excavation grouting be done before advance.

RE: Tunneling

Im still,confused. If we are talking about pre excavation grouting, then by definition the water flow rate is zero. Are we talking dewatering wells or what is it that I am missing?

RE: Tunneling

Mode of excavation is now being reconsidered, The main point that i'm asking is with the given size of tunnel and mode of excavation, how many probhole is needed to drill and what is the water inflow limit that is considered to do pre excavation grouting and or when to say Pre excavation grouting is not needed.Tunnel is at estiamted 40m above see level.

RE: Tunneling

Acerians , please accept these comments as a desire to help, rather than outright criticisms which I am sure they will appear to be. You appear to be in well over your head, and the answers to your general questions are well beyond what could be supplied in a forum like this. Your reference to project elevation above sea level is irrelevant unless you are close to the shore, and if so this is an important detail. The fact that the mode of excavation is being reconsidered is probably a positive........ some members of your team are starting to comprehend the scope of this project. I have driven tunnels in relatively competant ground , at moderate size , with 100 gallons per minute inflow, but I were trying to do full face at 20 metres wide, in poor ground , I would be horrified at the thought of even 5 gallons per minute. NATM has a number of variations and I suggest you really need the advice of competant geotechnical engineers, who have tunnelling experience, and provide them with ALL the facts rather than the selective dissemination that appears on this thread. This project appears to be one of those "pay me now, or pay me later" jobs and I predict that your existing budgets are nowhere near adequate to cover the required engineering , test holing and possible grouting after evaluation of the test results.. Of course my definition of soft ground may be different to yours and I may be reading too much into your apparent plans.

RE: Tunneling

Thanks miningman, no negative feeling here on my side, I am glad to have your advice, They considered to push through with the method, These is really my first time to work with these huge size of tunnel, I had work on HATS 2 in Hongkong and had huge volume of water as grouting engineer but we had manage to stop those volumes of water coming out(tunnel under sea), soft ground with vibration is really challenging and safety is a big issue. project starts October...Soon to read the investigation, specs and contract...

RE: Tunneling

In the end, make sure you contractor is very experienced in soft ground tunneling and that he is supplying staff who have the experience. Many times a contractor may but then may not staff it with the right people.

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