West Lake Taking Shape
Thursday, July 9, 2015
Today Brendan took me out to see the progress at West Lake. Progress is an understatement. I would describe it more as a transformation. As soon as we arrived at the site, Cody, the project supervisor for GW Tatro, pulled up. This meant that I got to try and keep up with engineer-speak for the next hour. Luckily, the guys are superb teachers and had no problem taking the time to define all the stuff that was above my head. So here goes - how to build a 120 mgal snowmaking pond in 600 words!
Let's get oriented! Above: To your far right are two lines coming into the middle of the lake. Those are the (2) 24" pipes that will pump the water in and out. The dam is on the southern end (right). The bottom edge is west. This is a cut and fill construction. Meaning, material is pulled from the high spots and moved into place to create the dam and banks. And with a maximum depth of 55 ft, much of the cut comes from the bottom of the pond. On your left, the back corner (north) requires the least amount of work as it is a little high and does not need to be built up.
Above: Those are the (2) 24" ductile pipes, 600 ft in length, installed all the way up to the pond site and are in place underground.
Above: I’m currently standing at elevation 1730. When the South embankment is fully built, there will be 35’ of dirt on top of me.
Above: This is where the middle of the lake will be - that standing water is about 15ft deep. The elevation at the bottom of the pond will be 1710'.
Above: At the back (north end) of the pond I was introduced to our upscale (aka - pricey) erosion control. In many cases you will see hay but this is a coconut fiber mulch or mat to stabilize after work is finished. I left that area having a sudden thirst for a Pina Colada.
Eastern bank above.
I learned a lot about compaction. As I mentioned in an earlier blog, the trick to this build is getting the correct compaction, layer by layer to provide stability. Here are the 5 abridged steps to getting it right.
1) Each layer is 1 foot thick (think of building up a layer cake). First, the haul truck (below, left) brings in the material.
2) The dozer spreads the material
Above: GW Tatro has a fleet of impressive machinery but two pieces are super impressive because they are set up with GPS. On the front blade you can see the two GPS units. This allows the operator to know exactly what elevation they are at. Amazing!
3) Next the 8" rake pulls out any rocks larger than 8". And there is a lot of hand-picking that goes along with this step.
4) A Sheep's Foot Roller is used to start the compression process. Yes, inspired by a flock of sheep.
Brendan explaining to me that the 825G weighs in at about 70,000 lbs and qualifies for the heavy-weight category!
A closer look of the 825G
This Sheep's Foot is smaller
The smaller Sheep's indent
5) The smooth roller drum goes last
Above: At the south end of the project, Jim, the site foreman is doing a little hand compaction and picking rocks as he goes.
If all goes well, the end result is a compaction rate of 95% or better. If the work does not make the grade, it is back to the drawing board.
Above: This is the western bank and toe drain construction. The toe or blanket drain runs along the entire outer edge of the pond, with the exception of the back section. The back corner (North) requires the least amount of fill as the existing grade is around 1760 – final is 1765. This drain allows for normal seepage (think perimeter drain at your home) and is a safety signal in the event of a breach. The green PVC you can see is connected underground by horizontal sections.
Chimney sand is filled in around the PVC pipe and then a 2" screening bucket is used for the next layer of filtered material. A double-guarantee, so-to-speak, to eliminate undermining. And of course, the 5-step compaction process.
In the photo above, all the way to the left, a road will be constructed for access to the pond.
View of toe drain taken from the north side.
Above: Toe Drain T to the outlet.
Above: The 320G is also equipped with GPS. See the (2) back stack mount position? Brendan explained to me that three sensors monitor hydraulics in the bucket (1 for the bucket, 1 for the stick and 1 for the boom) to determine the exact location of the bucket - amazing technology.
As you can see, there is a lot going on out at the site. Brendan and a few others will write some of the future blogs and I know you will enjoy their expert descriptions of the work. But for this week they are very busy so I volunteered to blog. Feel free to ask questions. I will find the answers for you.