Stakeholders decided to move forward with the deep-bore tunnel. The 54-ft. diameter double-deck tunnel will stack two southbound lanes atop two northbound lanes. The structure is just under two-miles long with 9,000-ft. of bored tunnel.
A series of projects will construct the tunnel and access roads. During preconstruction planning, simulations of construction sequencing are proving valuable in managing the interfaces and shared construction spaces between the projects in a way that optimizes construction and shaves years off the project, Clark says.
Mexico City Metro Expansion
In Mexico City, BIM is facilitating the design and construction coordination of the $1.35 billion expansion of the Metro system. Gehry Technologies, Los Angeles, Calif., has used BIM for the 3-year project constructing a new 25-km line with 20 stations and a 9-km tunnel segment.
The project was well into design and development when Gehry started work on the model. �The biggest value has been bridging the gap between engineering that is still in process and construction that is initiated,� says Gehry�s Mendoza.
To track station construction, Gehry developed smart PDFs that can be filled out by people untrained in 3D modeling for subsequent entry into the system.
Simulations and collision reports were employed to devise logistical plans for delivering and assembling the tunnel boring machines and managing the movement of trucks and cranes at various insertion points along the length of the tunnel. �We went through a whole series of scenarios to coordinate the sequencing of these events,� Mendoza explains. 4D drawings guide the assembly process.
Tunnel sections are designed with precast concrete liners composed of seven segments. To design the rebar within each segment Gehry converted 2D drawings to 3D. �The goal was to optimize one segment and then replicate that segment over the length of the track with hopefully exponential savings,� explains Lucas Reams, Gehry�s lead project manager.
At the project�s conclusion the BIM will be turned over to the Metro Authority for use as an asset management tool to facilitate operation and maintenance.
New York Projects
On the Fulton Street Transit Center Project in Lower Manhattan PB employed BIM to provide constructability and scheduling reviews. �The team felt the best way to do our job as the CM was to build a BIM and tie it to the schedule for construction phasing,� explains Judith Kunoff, PB�s construction manager on the job who is now chief architect at New York City Transit (NYCT).
Different construction schedules were played out during meetings with NYCT operations and planning staff to analyze pedestrian flows through proposed barriers erected to enable safe passage around the construction areas. The schedules were refined until everyone was satisfied with the sequencing.
PB has also used BIM to model short segments of existing tunnels for rehabilitation projects. Construction sequencing and management is particularly important in these projects, explains Rachel Arulraj, PB�s director of virtual design and construction. �Knowing when someone is out of the way and the next contractor is coming in has huge repercussions on a project.�
Two years ago NYCT set a goal to use BIM internally on all projects moving forward, Kunoff explains. Currently 25 jobs in design are using BIM.
One of NYCT�s current projects is converting parts of an abandoned underground tunnel into a circuit breaker house. Laser scanning created a smart geocoded model of the space. Various configurations for equipment and infrastructure will be modeled along with the access route for linking the space to the existing electrical system.
Kunoff expects the use of BIM will speed up project reviews and the RFI process. Project teams will be able to meet in NYCT�s CAVE (Computer Analysis Visual Environment) to efficiently review progress and change orders. Once a project is completed contractors will provide as-built drawings and BIM models as asset management tools.
Technology Challenges?Using BIM requires organizations to think about software and hardware upgrades. At NYCT, software tasks such as producing renderings are running slowly on existing 32-bit operating systems. To speed rendering and other tasks, testing is underway on 64-bit systems that support more memory.
Server storage capacity has been upgraded to handle the data sets required for modeling. For example, laser scanning of a one mile tunnel segments, costing $15,000 to $50,000, generates 30-gigabytes of data.
Technologies applying BIM to civil and subsurface engineering are less mature than facilities design, Anunson says. At NYCT designers recently ran into problems using BIM electrical software to design a new lighting system for an existing tunnel. Lighting was specified to be centered of the top of the tunnel at specific intervals. The software could not layout the lighting system in a curved tunnel.
“The biggest challenge for us is interoperability,” Mezher says. Different software tools and data sets are required for the civil engineering, GIS, planning and urban design components. “Determining when to use which tools and how the tools communicate with each other was a challenge. But we are getting there.”
