Millennium Tower (Filene's) | 426 Washington Street | Downtown

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NEUcivENG said:
Foundation is scheduled to be a mat.
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How is that physically possible? Can you build a high-rise on a mat? Is it because bedrock is close to the surface in Downtown Crossing (which sits on a cut-down hill, IIRC)?
 
Equilibria said:
Is it because bedrock is close to the surface in Downtown Crossing (which sits on a cut-down hill, IIRC)?
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Before you get to any bedrock, there's this little thing called... the Orange Line subway tube and the Red Line subway tube. Wouldn't they play a significantly greater factor than any bedrock in terms of building the base? Or so I'd assume...
 
I don't pretend to have any construction/engineering knowledge but I am very curious about these processes and I am fortunate to have a pretty good view of the tower construction site. Someone mentioned upthread that they are doing soil mixing on site. I was curious about this process and came across this link that I found interesting and others with a similar lack of knowledge may as well. From my (untrained) vantage point, this is precisely what is going on at the site now and has been for at least a week or two. http://www.haywardbaker.com/WhatWeDo/Techniques/GroundImprovement/DrySoilMixing/default.aspx
 
Equilibria said:
How is that physically possible? Can you build a high-rise on a mat? Is it because bedrock is close to the surface in Downtown Crossing (which sits on a cut-down hill, IIRC)?
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The worlds tallest buildings are built on mat foundations. The mat is used to tie together all the caissons and to evenly distribute the load.
 
Scalziand said:
The worlds tallest buildings are built on mat foundations. The mat is used to tie together all the caissons and to evenly distribute the load.
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Thanks! So, they are drilling for caissons as well.
 
Equilibria said:
How is that physically possible? Can you build a high-rise on a mat? Is it because bedrock is close to the surface in Downtown Crossing (which sits on a cut-down hill, IIRC)?
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Equilib -- There is Bedrock close to the surface in the Boston Basin {esentially everything inside Rt-128) in only a very few locations -- places where you see it such as:
the Rt-2 cut from Arlington through Lexington
Hammond Pond Parkway
Quincy Quarries
Schoolmaster Hill in Franklin Park

In the Downtown area even most of the Big Hills such as Beacon are mostly loose Glacial deposits

There is Bed Rock under Cambridge and downtown Boston -- but you need to go down a long way

Here's a fairly generic slice through DTX -- not including the filled areas in the area around the Custom House and the former Mill Pond from a thoroughly documented very deep excavation Post Office Square parking Garage

http://www.deepexcavation.com/en/post-office-square-garage-boston-ma


SLURRY WALL EXCAVATION CASE STUDY #2:
Post Office Square Garage, Boston, MA

The Post Office Square Garage includes a 7-level, 75'-deep underground garage, constructed with the top/down method, bounded by Franklin, Milk, Pearl, and Congress Streets. Existing buildings up to 40 stories tall are located adjacent to the site. Basement excavation was completed in 1990.

Calculations for this project were done by DeepXcav. Click here to download it or arrange a FREE online demonstration to know more about DeepXcav 2011 performance and features

A perimeter slurry wall, 3.0' thick, extended approximately 10ft into bedrock, provided both the temporary and permanent earth pressure support for the excavation. The diaphragm wall is internally braced by the garage floor slabs (LL1-LL7), which are supported by interior steel H-section columns founded on bedrock at depths 85' to 96' below the ground surface. The interior columns, installed using slurry trenching methods, were concreted into till and rock to form load bearing elements (LBE).

Most of the site is located within the old Boston peninsula; however, the northwestern section is located in an area reclaimed from the sea. Soils in the two sections (3: E-E, D-D) comprise 15' of fill, local pockets of organic silt, 30' to 40' thick clay (Boston Blue Clay, BBC), 0' to 16' of sand, 3' to 20' of glacial till, weathered bedrock, and sound bedrock.
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There's a nice (albeit graphically ancient) section on that website:
excavation_sketch_1.jpg
 
datadyne007 said:
There's a nice (albeit graphically ancient) section on that website:
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Data -- that same URL also includes some information on the excavation for 75 State St.

Now apparently according to some test boring done when the Orange Line was dug -- there is some sort of a ridge of the bedrock or at least fractured bedrock that runs right through the immediate area bounded by Washington between Franklin and Summer -- so the bedrock might be actually significantly closer to the surface

casestudies75statefig2.JPG
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And another one for "Millennium Place"

The Millennium Place project includes a 55'-deep excavation with five underground parking levels constructed by the up/down method. The excavation has just been recently completed. Numerous buildings are right next to the excavation along the northern, western, and southern sides of the project. The MBTA Orange Line runs under Washington Street to the east of the excavation. Thus, slurry walls were selected to protect adjacent structures from excavation induced damage. The figure on the left displays a typical excavation section while the following figure shows the site plan.
Calculations for this project were done by DeepXcav. Click here to download it or arrange a FREE online demonstration to know more about DeepXcav 2011 performance and features


Soils at the site are representative of profile B as classified by Johnson 1989. The soil profile consists of fill, organics, outwash deposits, marine deposits, outwash deposits, glacial till, and bedrock.


The diaphragm walls are 3.0'-thick and have their toe embedded 40' beneath the base of the excavation, into the marine and glacial till deposits. Load bearing elements and caissons were constructed to carry the vertical loads from the basement floors and the superstructure.


Measured wall deflections are in the order of 0.3" to 0.8" towards the excavation, with some bending evident. Measured settlements are in the same order as wall deflections but at some localized points settlements were larger probably because of other construction activities.


casestudiesmillenium2.JPG


casestudiesmillenium1.JPG
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I'm not typically downtown, but I walked by this site tonight around 7:30pm and the work was still going strong. Two diggers and a drill working, horns honking, elevator moving, fence open, lots of guys on site. Has this level of activity this late been consistent for this project? Or does construction typically run into the evening for any project?
 
timsox6 said:
I'm not typically downtown, but I walked by this site tonight around 7:30pm and the work was still going strong. Two diggers and a drill working, horns honking, elevator moving, fence open, lots of guys on site. Has this level of activity this late been consistent for this project? Or does construction typically run into the evening for any project?
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Yes for consistency on this project. I work next door and the people in our office have noticed that most of the heavy work actually happens after 4 when we feel our building start to shake a bit. I think they are trying to minimize noise and vibration impact during the day or something. Even yesterday night when it was pouring at 5, they were still working.
 
A bunch of concrete trucks at the pit this week. Looks like they are filling up the caisson tubes? The trucks are right next to the drill rigs.
 
By your estimation, how active is this site? I don't get to go by that often anymore so I am not seeing things too often.
 
mass88 said:
By your estimation, how active is this site? I don't get to go by that often anymore so I am not seeing things too often.
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EXTREMELY. Work starts early in the morning and goes past 7 at night.
 
Why are they filling the hole with dirt/sand? No basement levels under the tower portion of the project? How many floors are below ground in the Burnham Building?
 
BostonUrbEx said:
Why are they filling the hole with dirt/sand? No basement levels under the tower portion of the project? How many floors are below ground in the Burnham Building?
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There are three basement levels with parking under the whole site. I think they filled in with dirt to get the cassion tubes in and get the foundation walls done. Make the walls for the hole before they dig it.
 
I also notice some work being done at the place next to the old Barnes and Noble...sign of things to come?
 
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