tunnels near a bridge pile foundation.

[newbuilder]

What are the common techniques used to deal with new tunnels next to pile foundations.

I am thinking of designing the tunnel to transfer the pile lateral loads through the lining structure. Is this the best way?

Another option is to investigate by calculation, the redundancy of part of the pile near the tunnel. If possible to form a soft zone near the tunnel to avoid load tranfer. I foresee many problems with this approach and prefer the former.

NB

 

[dimitrios]

hello newbuilder,

this is a very serious problem. Is it possible to have some more information for the case ? Distance from piles, depth of piles and tunnel depth and section area would be helpfull to form the picture.

Generally speaking I think the first thing would be to try to transfer the tunnel out of the area of influence of the piles, but I suppose this is not possible as you would have done it already, but is there any possibility of moving the tunnel axis ?

Loading the lining from the piles would cause assymetry, which generates many problems difficult to calculate and with not much experience on the subject. Perhaps a reinforcement of the piles in a way to hinder lateral movement is possible, but anyway we could exchange some ideas after more data is available, if possible.

Regards
Dimitrios

 

[newbuilder]

dimitrios,

thanks for the brave reply! Actually, since making the posting I have done more research and seen the calcs and as-built plans.

Yes my first thought was to transfer the alignment but that option, "is not an option".

The design assumes that the lateral loads from the pile are transferred to the soil several metres above the tunnel. As such there is little pressure and movement at the level of the tunnel.

Short of digging a big hole to sleeve the pile there may not be much we can do that is practical. I believe that we will be able to have a geotechnical engineer produce some calculations based on soil structure interaction which show that the lining will not be adversely affected by the adjacent foundation. That together with some monitoring system and proper SI should deal with the problem.

NB

 

[dimitrios]

new builder,

I understand that you have already put the problem in its way to be solved, and since there are no geometrical data available, you probably have made up your mind.

My only point just to complete my answer is that transef of loads is done through the bending of the adjacent pile. This may be influenced by soil softening that occurs before the tunnel front reaches the pile arean and a kind of stiff lining is constructed. Putting a sleeve around the existing pile is both difficult in depth and due to the poor behavior in bending of the circular section of the pile may not be adeaquate. Perhaps if in addition to the measure you consider to take, boring a second pile near the existing one but on an axis perpendicular to the tunnel axis and in the opposite direction (from the other side of the pile) tying its collar to the existing pile and properly reinforcing the body of the existing pile near the surface (where most of the displacement occurs) may produce more and even adequate bending stiffness to the system so as to produce little effect on the tunnel construction.

Good luck
Dimitrios

 

[emmgjld]

I do not know the geometry of the problem but, would Compaction Grouting of the Tunnel /Pile area prior to driving the tunnel be part of the answer? If grouting is feasible, the soils may be stiffened/cemented and the tunnel driven through the grouted area. Loads area transferred through the improved soil mass and lateral loading of the tunnel may be accomodated.

 

[Ginger]

Emgild has a good point. Compaction or jet grouting ahead of the tunnel drive is a possible answer for transferring the pile loads away from the tunnel lining. Provided you know what the pile loads are it may be possible to design the lining to carry these loads but this will induce extra moment into the lining and therefore probably increase the lining thickness or the rebar content.

The other problem you will have to consider is the settlementeffect on the piles caused by tunnel volume loss. This will obviously affect the piles and may induce additional load in the piles themselves.

Regards Andy Machon

 

[newbuilder]

Thanks for the tips.

The pile is end bearing. I am now discussing the problem with the specialist tunneling company.

nb