Green Line Extension to Medford & Union Sq

BosMaineiac

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yup, so nice, I'm expecting that lot to be empty for a long time.
If the mound of dirt is for soil surcharging (which it appears it is) then they'd be prepping the soil for shallow foundations (footings). Doing so negates the need for deep foundations (piles) which are very costly, as long as the building isn't too tall or heavy. I would say having the ability to build this way makes the lot very attractive for developers and I expect it will not be long before something's getting built there.
 

RandomWalk

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All the sculptural lights on the bridge at Magoun aren’t working. I really hope that is covered by the warranty.
 

Semass

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If the mound of dirt is for soil surcharging (which it appears it is) then they'd be prepping the soil for shallow foundations (footings). Doing so negates the need for deep foundations (piles) which are very costly, as long as the building isn't too tall or heavy. I would say having the ability to build this way makes the lot very attractive for developers and I expect it will not be long before something's getting built there.
Interesting. So the idea is to put a huge amount of weight on the ground to compress the soil, then truck away what isn't needed? The compressed ground then serving as a more stable base?
 

RandomWalk

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Interesting. So the idea is to put a huge amount of weight on the ground to compress the soil, then truck away what isn't needed? The compressed ground then serving as a more stable base?
Exactly. Think of it like squeezing a sponge. The compressed sponge can better support a building than a sopping wet one.
 

BosMaineiac

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Interesting. So the idea is to put a huge amount of weight on the ground to compress the soil, then truck away what isn't needed? The compressed ground then serving as a more stable base?
That’s correct. It’s a more time consuming process than building deep foundations, but results in increased bearing capacity for the soil due to the compaction. DivcoWest/CX probably came to the clever solution of doing this after excavating all the soil from their neighboring properties. Rather than shipping it out for sale, it’s likely they decided to divert it for the surcharge load on this plot. You don’t see it very often around here as developer’s rarely are willing to wait months for the surcharge to compact the foundation to make a meaningful difference. The excess would then be trucked off for other uses leaving a much stronger foundation to build on. Obviously, the conditions have to be right to make this all work. I’m also speaking with no knowledge of the project and it’s possible that it’s just a pile of dirt, but I’m leaning toward this being a soil surcharge effort.
 

as02143

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That’s correct. It’s a more time consuming process than building deep foundations, but results in increased bearing capacity for the soil due to the compaction. DivcoWest/CX probably came to the clever solution of doing this after excavating all the soil from their neighboring properties. Rather than shipping it out for sale, it’s likely they decided to divert it for the surcharge load on this plot. You don’t see it very often around here as developer’s rarely are willing to wait months for the surcharge to compact the foundation to make a meaningful difference. The excess would then be trucked off for other uses leaving a much stronger foundation to build on. Obviously, the conditions have to be right to make this all work. I’m also speaking with no knowledge of the project and it’s possible that it’s just a pile of dirt, but I’m leaning toward this being a soil surcharge effort.
I believe some of the other photos showed some sort of storm water retention structure going in under the smaller triangle plaza/traffic island, so, seemingly they had a bit more extra soil and fill to work with too.

I think someone told me that surcharging is fairly common in the Netherlands not just for building foundations but also for infrastructure supports too. Would make sense that with their fairly water logged lands. Wonder why this isn't more popular on our coastal developments though. Other than time is there some other tradeoff in the construction process that makes it less appealing here?
 

BosMaineiac

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I believe some of the other photos showed some sort of storm water retention structure going in under the smaller triangle plaza/traffic island, so, seemingly they had a bit more extra soil and fill to work with too.

I think someone told me that surcharging is fairly common in the Netherlands not just for building foundations but also for infrastructure supports too. Would make sense that with their fairly water logged lands. Wonder why this isn't more popular on our coastal developments though. Other than time is there some other tradeoff in the construction process that makes it less appealing here?
That would make sense.

TBH I’m not really sure why it isn’t done here more often. I would think it’s because the soil around here is either really good so that surcharging doesn’t make a difference or it’s very poor fill that has little bearing capacity. This lot may be somewhere in between in that it’s fill that was placed here long ago but 100+ years of trolleys being parked over it resulted in a more compacted soil. Maybe we’ll see more of this going forward as the fill has been compacted quite a bit to result in the “sweet spot” where only about 10 feet of surcharge results in a large enough bearing capacity to meaningfully build on.
 

RandomWalk

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The Big Dig made use of soil mixing to increase its strength. That process basically involved mixing concrete into the muck and letting it harden.

I expect some combination of time constraints on construction financing and our clay soils mean that surcharging isn’t done.
 

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