Technical Report: Design Considerations for Microtunneling
Technical Report:
Design Considerations for Microtunneling
Successful design of microtunneling projects can be achieved by paying attention to the following:
1. Developing, understanding and defi ning project needs and requirements,
2. Exploring and defi ning ground conditions,
3. Superimposing the project “in the ground”, and
4. Creating a project “environment” that will allow for
Contractor success.
The design process has four stages: planning, risk assessment, design and contract documents. Each stage is discussed in detail in the rest of this paper.
Planning
Planning questions must begin with “Is this a microtunnel project?” There are many excellent trenchless construction methods to consider in addition to microtunneling: auger boring, pipe jacking, guided auger boring, pipe ramming, guided pipe ramming, horizontal directional drilling and conventional tunneling. Depending on the project length, diameter, ground conditions, groundwater conditions, access restrictions, allowable pipe material, permits, available right of way and available shaft locations, microtunneling may not be the preferred construction method. In fact, of the alternative trenchless methods, microtunneling represents
“the Cadillac” method: costly, but capable of successfully excavating within tight alignment tolerances in cohesionless soils below groundwater.
If it is determined microtunneling is the best alternative, the question “Can a microtunnel boring machine (MTBM) handle the project requirements and anticipated ground conditions?” must be answered. Experienced tunnel engineers are needed to evaluate the drive length, tunnel/shaft depth, hydrostatic head, anticipated ground conditions, potential for obstructions and contractor access and laydown areas to determine if the project can be designed and built using microtunneling methods. Contingencies must be considered to handle hard obstructions, mixed face ground conditions, hard rock or refuse fi
Design Considerations for Microtunneling
Successful design of microtunneling projects can be achieved by paying attention to the following:
1. Developing, understanding and defi ning project needs and requirements,
2. Exploring and defi ning ground conditions,
3. Superimposing the project “in the ground”, and
4. Creating a project “environment” that will allow for
Contractor success.
The design process has four stages: planning, risk assessment, design and contract documents. Each stage is discussed in detail in the rest of this paper.
Planning
Planning questions must begin with “Is this a microtunnel project?” There are many excellent trenchless construction methods to consider in addition to microtunneling: auger boring, pipe jacking, guided auger boring, pipe ramming, guided pipe ramming, horizontal directional drilling and conventional tunneling. Depending on the project length, diameter, ground conditions, groundwater conditions, access restrictions, allowable pipe material, permits, available right of way and available shaft locations, microtunneling may not be the preferred construction method. In fact, of the alternative trenchless methods, microtunneling represents
“the Cadillac” method: costly, but capable of successfully excavating within tight alignment tolerances in cohesionless soils below groundwater.
If it is determined microtunneling is the best alternative, the question “Can a microtunnel boring machine (MTBM) handle the project requirements and anticipated ground conditions?” must be answered. Experienced tunnel engineers are needed to evaluate the drive length, tunnel/shaft depth, hydrostatic head, anticipated ground conditions, potential for obstructions and contractor access and laydown areas to determine if the project can be designed and built using microtunneling methods. Contingencies must be considered to handle hard obstructions, mixed face ground conditions, hard rock or refuse fi