Microtunneling in sand and gravel and then into limestone

[duckman]

Does any one know if a TBM or a MTBM can tunnel through sand and gravel with cobbles and boulders and then into lime stone, i.e., through an aluvial valley with bedrock on the other side?

 

[exploengineer]

Duckman,

I've seen small TBM's work in alluvial deposits, but its difficult becuase its hard for the machine to keep the proper pressure in the tunnel walls to make it advance.

Also, when starting into bedrock, we usually are called to blast the initial opening to start the machine.

Frank Frank Lucca

http://www.terradinamica.com

 

[daqingwa]

It can be done, a major problem is preventing your TBM from "kicking" upward along the boundary rather than digging into the rock.