Here is the Purple Line Section 3 Construction Approach Plan, prepared in March 2018:
https://www.dropbox.com/s/0pfz2nslxy...0Plan.pdf?dl=0
Unlike the earlier sections, the plan is for tunneling to start early, before station construction. The stations will be built by breaking through the already-completed tunnels.
Such a plan is intended to allow acceleration of the schedule for opening by the Olympics. I wonder if this approach will be adopted for future tunneling projects.
http://media.metro.net/projects_stud..._2018-0601.pdf
Quote:
Metro proposes advancing the construction schedule of Section 3 in order to have the system in operation by the 2028 Olympic Games that will be held in Los Angeles. To accomplish this goal, Metro must advance contracts concurrently and, therefore, anticipates that the tunnel and station contracts would overlap. In comparison, the Final EIS/EIR did not assume that these contracts would overlap.
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Note the estimated Notice to Proceed date of June 2018 has been delayed and still has not occurred due to the delay in the federal funding and the FTA requirements. They do not allow Metro to issue the Notice to Proceed until the FTA completes an environmental review of the project. The Notice to Proceed is estimated to be before December 3, 2018, according to this board box report:
http://boardarchives.metro.net/Board...ONP_Update.pdf
Some interesting excerpts from the plan:
Quote:
Ahead of tunneling, the Section 3 Tunneling Contractor is required to install end wall piles to the west and east end of the (future) stations. Minor utility relocations are anticipated to need to be undertaken to install the piles. At VA Hospital Station, a grout block must also be installed at the east pile wall. These activities should be performed prior to tunneling through those areas.
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Quote:
The Section 3 tunnels will be driven from an access shaft on the Army Reserve eastward towards Century City. This is consistent with the FEIS/EIR. The Section 3 tunnels will be driven approximately 10ft into an improved ground zone (grout block) installed by the Section 2 Contractor outside of the Section 2 tail track interface chamber west of the Century City / Constellation Station.
The Section 3 Tunnel Contractor will dismantle the tunnel boring machines (TBM’s) within the tunnels and remove the TBM components back through the tunnel to the Army Reserve. TBM’s arrive at the Constellation Station location before the Section 2 Contractor will have excavated the station box so “holing through” into the Constellation Station at that time will not be possible. When the Section 2 Contractor has excavated the Century City / Constellation Station box, the Section 3 stations contractor will then be able to connect the Section 3 tunnels to the Section 2 tail track tunnel.
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Quote:
Excavation of the stations is subject to the Contractor’s means and methods, however excavation may need to be undertaken in two phases if the Station Contractor expedites station excavation prior to handover of the tunnels from the Tunnel Contractor. If this were the case, then the first phase would to be excavate down to 20ft over the tunnel prior completion of tunneling. The second phase will continue excavation to final grade after the handover of the tunnels and will require the breaking out of the tunnel lining segments when excavation reaches tunnel depth.
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Quote:
Whereas Sections 1 & 2 included the tunnel construction with the station and track construction contract, for Section 3 tunnel construction will be a separate contract to enable advancement of the tunnel work ahead of the procurement of the station contract.
Key Dates:
Tunnel Contract NTP: June 2018
Temporary power for TBM operations required: July 2019
Commence TBM tunneling: May 2020
Complete TBM tunneling: August 2021
Handoff tunnels to Stations and Systems Contractor: July 2022
Following delivery of the TBM’s to the Army Reserve site, the TBM’s will be assembled and commissioned. The TBM’s are anticipated to be assembled sequentially, six weeks apart, to allow TBM 1 drive to commence as soon as possible. The tunneling operation will be carried out in advanced of the station construction and as such there is no skidding through station boxes and/or shafts for the tunneling contractor to consider. Use of a slightly larger bore for both tunnels is planned to accommodate the ends of the crossover trackwork within the tunnels. The larger bore tunnels in combination with a localized steel liner means there will be no need to oversize the tunnel through mining operations in the fault zone.
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Quote:
Provision has been made in the design for knock out panels in the access shaft for a future tie in to an extension of the Purple Line west. The timeline for any potential construction activity associated with this is beyond the construction schedule of Section 3 and as such a construction interface is not envisaged.
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Quote:
By adopting a separate contract for the tunneling work from the stations and systems work a low bid design‐build procurement method can be utilized for the tunneling, cutting down on the evaluation duration. This will enable tunneling to start sooner than if a single design build contract was let.
With splitting the tunneling work from the station and systems work the coordination effort must be increased on the client side rather than passing that interface to a single design build contractor, however as the overall Westside Program will have delivered two prior sections, these interfaces are known and understood.
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