A new subway station is being dug at the intersection of Pape and Danforth in Toronto. Few people understand how this underground station is being made. We are expecting a deep hole but all we see are a number of tanks and cranes on the surface.
My almost 3-year-old nephew, Nate, is excited by the machines but can't come to the City to see the construction site. I've been waiting for someone to get as excited about this as me! By taking daily pictures and sending short stories I'm trying to explain it all to him.
Dear Nate,
I hope you can come and see these machines sometime. Until then let me tell you some stories about them.
These are called “Slurry Wall Cutters”. Isn’t “slurry” a funny word? It means a mixture of gross watery stuff. In this case, a gross mixture of mud.
The Slurry Wall Cutters are cutting very deep and very narrow rectangle-shaped holes in the ground. The workers fill these holes with cement and when the cement dries it makes a tall wall. But the wall is underground. They build these walls around the outside of the future building and then dig out the dirt to make the basement.
The slurry mud keeps the narrow deep hole from collapsing before they can get the cement in. Have you ever dug a hole in sand? You know how when it gets deep the sand falls off the side and fills in the hole? Well the slurry keeps the filling in from happening.
It is all backwards. They use cranes to lower the digger teeth down instead of lifting things up. They build the wall before scooping out the hole to the basement.
Tomorrow I’ll tell you more. What questions do you have? Is there anything you’d like me to take a picture of?
Love from,
Uncle Jagger
Learn more about Slurry Wall Cutters from the people who build the machines Liebherr
Hello Nate,
I forgot to tell you about a step in building Slurry Walls.
After they dig the hole, but before they put in the cement, they have to put in a steel cage. This kind of steel is called “rebar” and it makes the concrete more sturdy.
Look at these workers. The rebar is being lowered by a crane but it takes 5 or 6 muscle-man workers pushing and pulling to guide it into place.
Notice their vests? Those are life jackets. They wear them so that they could float if they fell into the deep hole full of slurry. Can you imagine having to swim in that mud water?
What colour is your life jacket?
Love from,
Uncle “Danger” (that’s what my other nephews call me, but it is just me, Jagger)
Hello Nate,
Thanks for the video reply and telling me about your life jacket. You are welcome for the videos. There are lots more! I’ll take a break on the weekend though. So more on Tuesday.
What do they do with what they dig up? It is a mixture of dirt and slurry. The dirt they need to get rid of. The slurry they can re-use for the next hole. How do they get it apart?
Well… do you have an idea?…
You are right! The dirt sinks and the slurry floats.
They have another machine called a “Slurry Plant” -- they mean plant like factory not plant like with a flower. They dump the mixture in and the Slurry Plant sucks the water off the top and shakes the dirt and stones out of the bottom. It is very loud and shakes the whole ground. Then they put it in dump trucks. The dump trucks take it down my street to the lake. (I’ll tell you more about the lake another time.) What colour are the trucks in the lineup for the scoop? Can you see in the picture?
Sometimes the dirt falls off the trucks onto the street. Today there was a lot of dried dirt on the street and in the wind and traffic it made my whole neighbourhood dusty. I was mad. I’m wearing my nice office clothes, they can’t get dirty on my way to the office. So I called Metrolinx to complain. Metrolinx is the group of people that are the big bosses of this whole project. And I told them I wanted them to send street sweepers today. If I see the street sweepers I’ll take a video of them for you too.
That’s all I have for this weekend.
Love from,
Uncle Danger
Hello Nate,
How was nursery school today? First day!
Today I want to tell you about the cement trucks.
It takes a lot of cement to fill in those deep and narrow holes made by the slurry wall cutters. Good thing we have a cement factory just a few kilometres away. All day we have cement trucks driving up Pape Ave, our major street, carrying cement to build the new station.
Cement trucks have that big barrel on the back that spins all the time. It spins to keep the cement from drying and hardening while it is in the truck.
There must be 50 cement trucks a day on a busy day.
Love from,
Uncle Danger
