Jacking a tunnel and the budget

The Belmont Community Path project #609204 is currently in Phase 1. This phase consists of  project 1A - a commuter rail underpass and project 1B - a multi-user path aka linear park extending from Brighton Rd to Clark St.

The pedestrian underpass was originally envisioned to be 10' wide.  However, in late 2020, Nitsch Engineer Michalak revealed that the underpass had morphed into a gargantuan 1-2 lanes wide tunnel to allow passage of emergency vehicles.   From the moment Nitsch came on the scene, tunnel jacking became the preferred choice over cut-and-cover (dig a hole and cover it) to built this tunnel.

What is tunnel jacking? it is using a giant jackhammer or boom to punch a hole through the soil at the pace of no more than 2-3" per punch, according to Michalak.  This process, as you can imagine, takes weeks and there is a likelihood that the jacking will damage neighboring homes' foundations and be deleterious to people's well being.   (To top that, a Nitsch report reveals that the jacking is preferentially done at night time).

The jacking entails digging large, deep pits in which to lay the giant jackhammer.    Last July, Michalak wrote that it would take 2 weeks of preparation (digging the giant pits and placing the equipment) and 3 weeks of jackhammering but that was before the tunnel was enlarged to accommodate vehicles.  A tunnel for vehicles would probably require the largest made jack which is ~14'.  As you can imagine, it is a very, very expensive method.

 

 

What's the story behind jacking?  Nitsch’s Engineering proposal to Belmont consisted almost entirely of tunnel jacking and, at the initial meeting with the town (~Sept 2019), Engineer Michalak insisted on tunnel jacking without any soil boring data on which to base his recommendation.  (This insistence is not surprising now since jacking seems to be the one note that Nitsch plays.)



Surprised, at the time, I consulted with Pare’s Engineer Amy Archer (author of Proj. #609204’s feasibility study) who also expressed surprise at tunnel jacking and told me that, in her opinion, cut-and-cover was the best approach if supported by soil data: the tunnel could be installed in days instead of weeks; there was less probability of damage to nearby homes and to homeowners’ health* and well-being*; the method was far less expensive.  

 * Now, a few years later, I still cringe when I recall the agonizing booming that we had to endure for weeks at the beginning of the new HS construction.  Now I know that it was due to jacking.

 A few months later, tunnel jacking evolved from being Nitsch’s recommendation into Belmont’s choice, according to Michalak’s statement at a public meeting, although soil borings still had not been done.  Fast forward to mid-late 2020: Michalak informed the public that the MBTA  had recently announced a preference for tunnel jacking for all installations going under the rails.  Mr. Michalak explained that the MBTA was dissatisfied with cut-and-cover’s soil settling/compaction as observed in other projects and that as a result, the MBTA had made it clear it preferred jacking to cut-and-cover.  In a few years, I had seen the choice of jacking hopping from Nitsch to Belmont to now the MBTA!

Since my suspicion has been that the choice of tunnel jacking is all about budget inflation and not necessarily about engineering,  I sought to inquire about the MBTA’s stance with regard to tunnel jacking for a long time without success. However, this past week I did succeed in contacting the relevant person at the MBTA: Chief Engineer Erik J. Stoothoff, PE

 My question:  "In general, does the MBTA have a preference for constructing a tunnel under the RR by tunnel jacking or by cut-and-cover?"

Chief Engineer Stoothoff's answer: "All infrastructure that gets installed below our tracks is evaluated on a case-by-case basis.”  

As far as we can see, these words - "on a case-by-case basis" - demolishes the latest excuse for choosing tunnel jacking for this project. 

Tunnel jacking concerns us because of all of our homes sit on “bad soil” i.e. clay either adjacent to or near the proposed tunnel.    We suspect that the jacking recommendation is primarily due to the fact that it is far more an expensive method than the standard method of cut-and-cover and that there is a bounty of Federal funds made available via the Boston MPO. The fact that jacking is more expensive fits in with the persistent and surprising effort to inflate the project’s budget that I have witnessed at various CPPC public meetings.   We trust that, if this 25% design plan is accepted, the MPO and MassDOT will access very carefully whether the soil boring data truly warrant  a choice  that has the greatest potential to be damaging to our homes and health ... and to be the most costly at a time of a budget crunch.


 

CPPC: Community Path Project Committee; MassDOT: Massachusetts Department of Transportation; MPO: Metropolitan Planning Organization. In reality, it is the Boston MPO that is in charge of our area.


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