Extension of Metro’s Extension of Metro’s Purple LinePurple Line

Presented By:Presented By:Eric ChristensonEric Christenson

Engineering Challenges and Engineering Challenges and MitigationsMitigations

Building a subway under a major city Building a subway under a major city that is already established.that is already established.

Sustaining a tunnel through two Sustaining a tunnel through two active fault zones.active fault zones.

Most of construction is under the Most of construction is under the ground water table.ground water table.

Area has scattered natural deposits Area has scattered natural deposits of tar, toxic gasses, and oil.of tar, toxic gasses, and oil.

First, Some Fun FactsFirst, Some Fun Facts Project started in Project started in

November 2014.November 2014. Largest public works Largest public works

project and program project and program in the nation right in the nation right now.now.

Already raised 1.2 Already raised 1.2 billion for phase two.billion for phase two.

To the right: To the right: Hollywood and Hollywood and Highland station so Highland station so far.far.

Construction of TunnelsConstruction of Tunnels

Tunnels are 20’ in Tunnels are 20’ in diameter.diameter.

They are parallel They are parallel and separated and separated about 20’ from about 20’ from each other.each other.

Varying depths Varying depths throughout project throughout project from 50’ to 130’.from 50’ to 130’.

Tunnel Boring MachinesTunnel Boring Machines TBM’s are huge cylindrical TBM’s are huge cylindrical

machines that drill into the machines that drill into the earth around 40’ per day.earth around 40’ per day.

TBM’s on this project keep TBM’s on this project keep pressure on the face and walls pressure on the face and walls of the tunnel while installing of the tunnel while installing tunnel liners to support the tunnel liners to support the tunnel.tunnel.

Different tunnel liners can Different tunnel liners can accommodate special accommodate special conditions.conditions.

Under groundwater table there Under groundwater table there will be secondary tunnel liners, will be secondary tunnel liners, gaskets, and drainage systems.gaskets, and drainage systems.

Metro Tunnel Design Metro Tunnel Design

Metro design criteria uses two levels of Metro design criteria uses two levels of ground shaking hazard and fault offset: ground shaking hazard and fault offset: the operating design earthquake (ODE), the operating design earthquake (ODE), having a 50-percent probability of having a 50-percent probability of exceedance in 100 years exceedance in 100 years

Maximum design earthquake (MDE), Maximum design earthquake (MDE), having a 4-percent probability of having a 4-percent probability of exceedance in 100 years exceedance in 100 years

Basically it is not feasible to design to last Basically it is not feasible to design to last over 100 years in this environment.over 100 years in this environment.

Through Two Active Fault Zones?Through Two Active Fault Zones?

The tunnel alignment options in the Century The tunnel alignment options in the Century City/West Beverly Hills area cross two mapped City/West Beverly Hills area cross two mapped fault zones—the Santa Monica fault zone and the fault zones—the Santa Monica fault zone and the West Beverly Hills Lineament (WBHL) fault zone. West Beverly Hills Lineament (WBHL) fault zone.

Mitigate by minimizing area of tunnel that Mitigate by minimizing area of tunnel that intersects faults.intersects faults.

Make flexible tunnel liners and excavate a wider Make flexible tunnel liners and excavate a wider tunnel by faults to allow for shear stress.tunnel by faults to allow for shear stress.

Exploration Plan Around Both Fault ZonesExploration Plan Around Both Fault Zones

7 rotary-wash continuous core 7 rotary-wash continuous core boreholes boreholes

49 hollow stem auger continuous 49 hollow stem auger continuous core boreholes core boreholes

192 CPTs192 CPTs 5 P-wave seismic reflection profiles 5 P-wave seismic reflection profiles 5 S-wave seismic reflection profiles 5 S-wave seismic reflection profiles 5 down hole suspension PS velocity 5 down hole suspension PS velocity

measurementsmeasurements

Cannot Avoid FaultsCannot Avoid Faults The Santa Monica fault zone is capable of The Santa Monica fault zone is capable of

generating earthquakes in the magnitude range generating earthquakes in the magnitude range M6.9 to M7.2, with average surface M6.9 to M7.2, with average surface displacements of approximately 3 to 6 feet. displacements of approximately 3 to 6 feet.

A major event on the WBHL might be between A major event on the WBHL might be between M6.4 (generally the lower end of the magnitude M6.4 (generally the lower end of the magnitude range for surface rupture) and M7.2, also with range for surface rupture) and M7.2, also with average surface displacements of up to 3 to 6 average surface displacements of up to 3 to 6 feet, depending on the length of rupture on the feet, depending on the length of rupture on the northernmost portion of the Newport Inglewood-northernmost portion of the Newport Inglewood-WBHL fault zone.WBHL fault zone.

Designing for this maximum displacement was Designing for this maximum displacement was not feasible, so the minimal cross sections are not feasible, so the minimal cross sections are crossing faults, repairs will be made when a fault crossing faults, repairs will be made when a fault ruptures.ruptures.

Liquefaction and Seismic Liquefaction and Seismic Settlement Settlement

Based on the magnitude of evaluated Based on the magnitude of evaluated liquefaction, a suitable mitigation will be liquefaction, a suitable mitigation will be selected, either structural design, or selected, either structural design, or ground improvement (such as deep soil ground improvement (such as deep soil mixing) or deep foundations to non mixing) or deep foundations to non liquefiable soil (such as drilled piles). liquefiable soil (such as drilled piles).

Most of the project will be under the layers Most of the project will be under the layers of threatening liquefaction so this does not of threatening liquefaction so this does not pose a big threat.pose a big threat.

Hazardous Subsurface Gas Hazardous Subsurface Gas Operations Operations

Measures will include the following for Measures will include the following for both tunnel and station operation:both tunnel and station operation:

High volume ventilation systems with High volume ventilation systems with back-up power sources.back-up power sources.

Gas detection systems with alarms.Gas detection systems with alarms. Emergency ventilation triggered by the Emergency ventilation triggered by the

gas detection systems.gas detection systems. Automatic equipment shut-off.Automatic equipment shut-off. Maintenance and operations personnel Maintenance and operations personnel

training training

Tar Sand Disposal Tar Sand Disposal

Based on results, tar sands may also Based on results, tar sands may also be transported to a facility where be transported to a facility where they can be re-cycled and they can be re-cycled and incorporated into the asphalt incorporated into the asphalt pavement manufacturing process.pavement manufacturing process.

If not recyclable, they will go to If not recyclable, they will go to an an appropriate waste manifest to a local appropriate waste manifest to a local landfill that accepts petroleum-landfill that accepts petroleum-impacted soils.impacted soils.

Beverly Hills High SchoolBeverly Hills High School 1. Tunneling can be safely carried out beneath the Beverly 1. Tunneling can be safely carried out beneath the Beverly

Hills High School (BHHS) campus; Hills High School (BHHS) campus; 2. Tunneling would not prevent future development of the 2. Tunneling would not prevent future development of the

BHHS campus; BHHS campus; 3. Tunneling would not impact the use of the BHHS campus 3. Tunneling would not impact the use of the BHHS campus

as an emergency evacuation center; as an emergency evacuation center; 4. Vibration and noise levels are within the FTA 4. Vibration and noise levels are within the FTA

requirements and tunnel operation is not anticipated to requirements and tunnel operation is not anticipated to have adverse impacts. The tunnel construction may cause have adverse impacts. The tunnel construction may cause some low levels of noise and vibration for a day or two;some low levels of noise and vibration for a day or two;

5. Tunneling can be constructed and operated safely in 5. Tunneling can be constructed and operated safely in gassy ground; gassy ground;

6. Oil wells do not pose an unmitigable risk to tunneling. 6. Oil wells do not pose an unmitigable risk to tunneling. Should they be encountered, procedures will be in place for Should they be encountered, procedures will be in place for their safe removal and reabandonment; their safe removal and reabandonment;

Beverly Hills High SchoolBeverly Hills High School 7. In Century City, Constellation Boulevard is a viable 7. In Century City, Constellation Boulevard is a viable

option for a station location, but Santa Monica Boulevard is option for a station location, but Santa Monica Boulevard is not due to unacceptable seismic risk; not due to unacceptable seismic risk;

8. Tunneling through fault zones can be done safely; 8. Tunneling through fault zones can be done safely; 9. MTA's approach to risk management is correct; 9. MTA's approach to risk management is correct; 10. Further site investigations will be conducted and 10. Further site investigations will be conducted and

measures will be implemented to reduce risks to levels that measures will be implemented to reduce risks to levels that are as low as reasonably practicable; are as low as reasonably practicable;

11. MTA and its engineering consultants have expertise 11. MTA and its engineering consultants have expertise designing and building tunnels and subway stations in Los designing and building tunnels and subway stations in Los Angeles; andAngeles; and

12. The Constellation Station will attract more riders than 12. The Constellation Station will attract more riders than the station locations along Santa Monica Boulevard.the station locations along Santa Monica Boulevard.

In Recent NewsIn Recent News

As of late 2014 Beverly Hills is still As of late 2014 Beverly Hills is still trying to appeal the decision to trying to appeal the decision to tunnel under BHHS, recruiting tunnel under BHHS, recruiting students to make anti metro subway students to make anti metro subway films...films...

The current ruling still stands and The current ruling still stands and plans have been made to bore under plans have been made to bore under the high school.the high school.

Possible Routs Through Century CityPossible Routs Through Century City

SourcesSources

http://www.metro.net/projects/westside/http://www.metro.net/projects/westside/#constructionimpacts#constructionimpacts

http://thesource.metro.net/2011/10/19/ehttp://thesource.metro.net/2011/10/19/experts-speak-to-metro-board-about-xperts-speak-to-metro-board-about-westside-subway-extension-seismic-westside-subway-extension-seismic-issues-in-century-city-a-constellation-issues-in-century-city-a-constellation-station-is-recommended/station-is-recommended/

http://media.metro.net/board/Items/2012/05_may/20120524RBMItem58.pdfhttp://media.metro.net/board/Items/2012/05_may/20120524RBMItem58.pdf