Earth Pressure for Deep Tunnel Shaft Design

[HB4775]

Hi All,

I was wondering if anyone has latest references/sources for earth presure for deep tunnel shaft design (more than 100 feet deep). Are people still using the Terzaghi/Peck method to come up with the pressure diagram (0.65*Ka*Gamma to certain depth and then go stright line down)?

TIA,

HB4775

 

[Ginger]

We use conventional Rankine theory for pressure at depth. This assumes that you are operating in soils and not in rock. You also need to generate the correct hydrostatic pressures applied to your shaft before you can determine the correct hoop thrusts etc

 

[HB4775]

Thanks for the reply, Ginger. But if I use Rankine theory then the pressure would be huge at the 150 feet depth. I am trying to develop the earth pressure for design of the tunnel portal shaft shoring.

 

[Focht3]

Where is your project?

 

[HB4775]

In Seattle, WA. My bad on the 2nd post.

 

[Focht3]

Try this link:

http://www.guideme.com/Bookstores/TUNNELS.HTM

This reading list should help you get started. Look for projects similar to yours, then search for any other papers written by those authors. If you still can't find what you need, make a personal phone call. You would be surprised how helpful people will be -

Let us know what you decide to do, and why.

 

[Ginger]

Yes the ground pressure is large!!! That's because you are 150 feet down!! The Terzaghi & Peck envelopes relate to empirical readings taken in braced excavations and are therefore only really applicable to similar support schemes. These structures had a fair degree of flexibility and will therefore have shed some load due to ground/structure interaction. A shaft ring is generally stiffer and will attract more load.

You are looking at the coefficient of lateral earth pressure loading the shaft . So, if you are in sands then this load will be around 30-35% of the effective overburden pressure, ka=0.33 say, (plus water). If you are in clays then k0 =1 or higher if the clay is overconsolidated.

Now, in clays you have to consider how quickly the load will "come on" to the shaft. This is a matter of experience and knowledge of the material you are tunnelling through. For temporary worksin some clays, up to 50% of the applied load can be removed as the ground load does not "come on" within the design life of the temporary works. Engineering judgement is required here.

 

[DBNodurf]

you could seek help from a mining engineer; try Univ KY or WV

D. Bruce Nothdurft, MSCE, PE, PG, M.ASCE, etc, etc,...
Principal Engineer/Geologist
Atlantic Geoscience & Engineering
Charlotte, NC