5 ms·

I haven't been able to tell from any reports yet. What is it about this object that they weren't able to discern existing through sonar/ultrasound/core samples/

I haven't been able to tell from any reports yet. What is it about this object that they weren't able to discern existing through sonar/ultrasound/core samples/whatever pre-engineering I imagine these sorts of projects do? Is it that it's just so far down? Or do we not even know?

abduhl 13y ago
A couple things: 1. We generally do a boring every couple hundred feet along an alignment for tunnels. The bore hole is about 2" in diameter. You can imagine that we miss white a bit of subsurface detail. We rely on experience and local geological history for fleshing out the details and putting things in context. Sometimes we just flat out miss things. 2. Geophysics methods (sonar essentially) is not very good at telling you what something is past "hard", "soft", or "void". In a glacial till you get a lot of all three.
- 001sky 13y ago
  Is inconsistency of substrate enough to be a problem? Like if you put marbles in a food processor?
  - abduhl 13y ago
    I don't understand your question. A problem for what? For the geophysics methods or for the TBM? Geophysics methods give a measure of density based on wave reflection/refraction and are therefore at the mercy of energy absorption of a given material. Resolution is a function of energy and so the ground smears in your results. The variability of the ground may or may not pose a problem to the geophysics methods used, it depends on how they do it. For the TBM, inconsistency in the ground can obviously pose problems. Based on what I know about this project (which is not much), Bertha has mixed face tooling on its cutter head but is primarily a soil machine. This means that large boulders can pose a problem as the cutter head isn't designed to deal with massive, hard objects most likely. The way most of these soil machines work is that they have a cutter head with tooling that essentially scrapes the soil and there are windows in the head that open to an area behind the cutter head which the soil moves through before being spit out as muck from a conveyor or screw jack. This area behind the cutter head generally has a system to crush large rocks that enter this area into sizes that are fit for the muck system. The problem arises when you have a rock too large to fit through the window as the cutter head isn't really equipped to bust up rocks (for multiple reasons). Let me know if that didn't answer your question.
    - dreen 13y ago
      So what is the typical procedure when encountering a large boulder? Get people there and just drill through it manually? Or would they have to completely remove the entire boulder? (how?)
      - abduhl 13y ago
        Access the face and bust up the obstruction so that it can be ingested or sink a shaft and remove the obstruction vertically.

abduhl 13y ago

A couple things: 1. We generally do a boring every couple hundred feet along an alignment for tunnels. The bore hole is about 2" in diameter. You can imagine that we miss white a bit of subsurface detail. We rely on experience and local geological history for fleshing out the details and putting things in context. Sometimes we just flat out miss things. 2. Geophysics methods (sonar essentially) is not very good at telling you what something is past "hard", "soft", or "void". In a glacial till you get a lot of all three.

001sky 13y ago
Is inconsistency of substrate enough to be a problem? Like if you put marbles in a food processor?
- abduhl 13y ago
  I don't understand your question. A problem for what? For the geophysics methods or for the TBM? Geophysics methods give a measure of density based on wave reflection/refraction and are therefore at the mercy of energy absorption of a given material. Resolution is a function of energy and so the ground smears in your results. The variability of the ground may or may not pose a problem to the geophysics methods used, it depends on how they do it. For the TBM, inconsistency in the ground can obviously pose problems. Based on what I know about this project (which is not much), Bertha has mixed face tooling on its cutter head but is primarily a soil machine. This means that large boulders can pose a problem as the cutter head isn't designed to deal with massive, hard objects most likely. The way most of these soil machines work is that they have a cutter head with tooling that essentially scrapes the soil and there are windows in the head that open to an area behind the cutter head which the soil moves through before being spit out as muck from a conveyor or screw jack. This area behind the cutter head generally has a system to crush large rocks that enter this area into sizes that are fit for the muck system. The problem arises when you have a rock too large to fit through the window as the cutter head isn't really equipped to bust up rocks (for multiple reasons). Let me know if that didn't answer your question.
  - dreen 13y ago
    So what is the typical procedure when encountering a large boulder? Get people there and just drill through it manually? Or would they have to completely remove the entire boulder? (how?)
    - abduhl 13y ago
      Access the face and bust up the obstruction so that it can be ingested or sink a shaft and remove the obstruction vertically.