After graduation, it made reasonable sense to go work for a bank. I had my finance and economics degrees, strongly believed in the importance of fiscal independence and honestly, really enjoyed wearing the suits. It wasn’t long however before I found myself on a mission to discover a more challenging career, one that provided me with a greater variety of tasks in a day and where my efforts ultimately contributed to the creation of a tangible product. This is the story of a girl from Montreal, who made the big move out West and joined a real estate development team in Vancouver. A complete newbie to the construction world and the countless associated particulars, this will be an account of my journey through my very first project. If you have ever wondered just what goes into creating Home Sweet Home, you will likely enjoy this.
Blog Post #2
April 12th, 2012
“Wow, that is some great dirt” my boss John tells me as we take a casual stroll through the depths of Bloom’s construction site. “Really? Great dirt?” I reply, clearly skeptical, as we make our way through a never ending puddle of sludge. The geotechnical report indicates that a variety of subsurface materials including topsoil, weathered till, and glacial till are presumed to be on site. I didn’t know it at the time, but the latter is what both I and my boss were referring to. You see, the glacial till found onsite is quite dense and is primarily comprised of a very fine silty sand. When dry, it is firm and easily maintains its form- a developer’s dream when it comes to digging a 16,000 cubic metre hole. “Yes, excellent dirt…Check it out” as he points to what will eventually be Bloom’s parkade ramp. Shifting my gaze from the muck at my feet, I was surprised to see that the access ramp was completely self sufficient. Consisting of nothing other than a pile of compacted dirt, it is interesting to note that up to sixty tandem trucks weighing approximately 12.5 tonnes utilize this ramp each day. Now don’t be fooled by the steel bars lining the bottom of the ramp as these are actually a few feet from the slope and provide zero support. In fact, this line of Reinforcing Steel or Rebar is set to become a parkade wall, but we will get to that a bit later.
The presence of glacial till also influences our strategy when it comes ensuring the stability of the site’s retaining walls. Depending on the spot, our excavation efforts can extend over 18ft vertical feet and it is always nice when a periphery wall of this magnitude does not collapse on us or the development itself. Shoring is a process that is required when you dig a hole that results in a vertical wall. For Bloom, this is practically the entire circumference of the site as the parkade footprint extends within feet of our property line. In order to ensure the stability of the wall, 20ft. long metal rods known as anchors are shot into the dirt wall using an air track drill and then secured in place.
Wire meshing is then fastened to the wall to eliminate any loose dirt from falling and a thin layer of concrete is sprayed to complete the process. When a site consists of glacial till, the exterior dirt periphery is significantly sturdier and more reliable. This is the conclusion our Geotechnical Engineer came to after conducting his site inspection. A certified professional when it comes to the engineering of earth materials, the Geotech, like most engineers, is responsible for conducting site inspections to ensure that we are building according to his requirements. Luckily for us, the presence of the glacial till eliminated the need for shoring in certain areas and as a result we were able to cut back on 3000 square feet of shoring which resulted in notable cost and time savings.
So now that you have been brought up to speed about the benefits of this great dirt, let’s take a look at what happens when it gets wet. Provided that the soil is left to its own devices and not disturbed, it manages to maintain its form quite well. It is a different story however once the trucks and excavators get to work. When disturbed, glacial till essentially transforms into liquid dirt. It is more difficult to excavate and due to the additional weight from the water, creates heavier truck loads. Most trucks that we use can carry up to 14 tonnes and as a result, this additional water weight could results in more trips to the dumping ground.
The primary concern for us however, is where the runoff from all this water goes. The silt has such a fine texture that it combines effortlessly with flowing water and the result is a cloudy liquid that is not suitable to flow into the city’s storm sewer. Many of these sewers empty into rivers and lakes and it is important that this water be properly filtered in order to ensure that the ecosystems of these bodies of water are protected. The solution for this was a sediment control system powered by a 2.5 kilowatt generator. Presented to us by our civil engineer, this is quite the sophisticated setup and consists of four primary steps. The first is a pump-out storage basin. It is essentially a sump, surrounded by crushed rock in order to filter out any large dirt particles right from the get go. This is where the runoff is held until it is ready to be pumped through the Flocculent Tube. Once in the tube, the water goes through a process known as flocculation where a chemical is bound to the sediment in order to make it larger and heavier. Once pumped into the settling tank, this additional weight facilitates the filtration process as the dirt tends to settle and be caught by the straw curtains (AKA filters) a lot easier. This tank also boasts a weir setup, which is essentially high and low level barriers that serve to alter the flow of the water. These barriers maximize the distance the water must travel in order to further increase the settling efficiency.
Once through the tank, the final step involves using a sand filter to eliminate any remaining fine sediment before the water is transferred to the city storm sewer. Now, you might be thinking that this system seems powerful enough to filter water runoff from a large industrial site and initially, in all truthfulness, we did think it seemed a bit extreme. However for those of you who have been here in the winter, you know that British Columbia experiences its share of rain and when combined with an 80 gallon per minute underground stream, you can be sure that we were thanking our lucky stars that we had this setup on-site. Yes, you heard me…a stream and a powerful one at that! To put it into perspective for you, this stream could fill an average bathtub to the brim in less than one minute and that is a lot of water to find consistently flowing through your site.
Primarily stemming from the South East corner of the site, our approach has been to pump the clear, untouched water through a filter and directly into the closest storm sewer. Dirty water that we are unable to catch before it travels the length of the site is then passed through our sediment control system to ensure that all dirt particles are removed before being transferred to the storm sewer. To ensure that the system is functioning in accordance with city standards, bylaw inspectors as well as our civil engineer periodically pop by for an inspection. From the photo above, you can get an idea of just how efficient the system really is. This photo was taken after a rainy week and required two full truck loads to remove all the sediment. Moving forward, our hope for this stream is to be able to free flow it through an underground pipe along Langside Avenue all the way down to the storm sewer at the edge of Burquitlam Park. Given that our site slopes roughly 28 feet from the East to West, our goal is to use the incline and avoid using a pump to get the water up to the manhole, which is located at street level. This design is still a work in progress, but I will be sure to keep you posted on our final solution. I have included a site plan below meant to provide you with a better understanding of what I am referring to from a bird’s-eye view. The buildings along the top of the image represent an elevation of Bloom from a Southerly point of view. In order to envision the final development, imagine these buildings being transposed onto the parkade footprint. Click to enlarge.
Did you know that in total 35,000 tonnes of dirt were removed from the site during excavation? This dirt was transferred to an unproductive lowland site in Port Moody and will be used to infill the area, which is set to eventually become a park.