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Re: cut and cover-not cheaper, if you have the right conditions to bore.
Author: BOB2
Date: 01-26-2017 - 17:40
Cut and cover is historically way more disruptive and costly in the days of tunnel boring machines, if you have decent geology..... ELA Gold Line competitive "turn key" bids were the ultimate test of that nonsense. Zev Yaroslavsky was even forced to rescind his no "bored" subway with "local" dollars nonsense.
If I recall correctly, almost all of turnkey bidders wanted to use boring machines (LA has good tunnel "goldilocks" geology for boring machines in that area, not too hard, and not too soft), and those bidders that considered a cut and cover alternative, wanted a lot more money for the cut and cover uncetainties (lawsuits from businesses and public exposure to accidents, more utilithy relocations, more potential for damage to surface buildings, all of the potential delays from things like that).
SCAG staff (in spite of Mark Pisano's years of "maglev madness") saved that corridor when the Feds refused to consider the 3 station Red Line extension a mere 3 miles at nearly 1.4 billion dollars for ELA, which modeled at only about 3,000 riders per day. Jim Gosnell, SCAG's Deputy Executive Director, had Barry Samsten lead a team that scouted the corridor and found the current route that took the line all the way out to Atlantic and ELA College as an LRT for just under $900 million, including the bored tunnel under Boyle Heights. Then the MTA hired Rick Thorpe and used a construction authority model to build it on time and on budget, like all of the Gold Line phases, which have followed that more efficient contracting model.
Cut and cover is required at most station boxes, and on the cross town connector now under constructino, those are also used to drop in the boring machines. This project has run into cost overruns due to poor planning and inadequate investigations into the state of utilities, many never properly located, many not even properly located in City plots or utility records. Hopefully, with the boring machines now down below that "can of worms" costs will not "bloat", as fast as they have until now.
It is my experience that there are many geological conditions that can make bored or excavated tunnels more expensive, including poor geology (too hard/too soft) which adds to costs, like the need to "support" the tunnel through water soaked clays or muds, and dealing with ground water or saturated soils, which could even require pressurization to keep the water out while boring, and immediate support and sealing, to keep them from flooding or collapsing.
Cut and cover is "cheaper", may be true true in this case, if the geology, or economies of using a boring machine are not there.
If I recall correctly, almost all of turnkey bidders wanted to use boring machines (LA has good tunnel "goldilocks" geology for boring machines in that area, not too hard, and not too soft), and those bidders that considered a cut and cover alternative, wanted a lot more money for the cut and cover uncetainties (lawsuits from businesses and public exposure to accidents, more utilithy relocations, more potential for damage to surface buildings, all of the potential delays from things like that).
SCAG staff (in spite of Mark Pisano's years of "maglev madness") saved that corridor when the Feds refused to consider the 3 station Red Line extension a mere 3 miles at nearly 1.4 billion dollars for ELA, which modeled at only about 3,000 riders per day. Jim Gosnell, SCAG's Deputy Executive Director, had Barry Samsten lead a team that scouted the corridor and found the current route that took the line all the way out to Atlantic and ELA College as an LRT for just under $900 million, including the bored tunnel under Boyle Heights. Then the MTA hired Rick Thorpe and used a construction authority model to build it on time and on budget, like all of the Gold Line phases, which have followed that more efficient contracting model.
Cut and cover is required at most station boxes, and on the cross town connector now under constructino, those are also used to drop in the boring machines. This project has run into cost overruns due to poor planning and inadequate investigations into the state of utilities, many never properly located, many not even properly located in City plots or utility records. Hopefully, with the boring machines now down below that "can of worms" costs will not "bloat", as fast as they have until now.
It is my experience that there are many geological conditions that can make bored or excavated tunnels more expensive, including poor geology (too hard/too soft) which adds to costs, like the need to "support" the tunnel through water soaked clays or muds, and dealing with ground water or saturated soils, which could even require pressurization to keep the water out while boring, and immediate support and sealing, to keep them from flooding or collapsing.
Cut and cover is "cheaper", may be true true in this case, if the geology, or economies of using a boring machine are not there.
