Kelly Panteluk Construction Ltd. (KPCL), a Saskatchewan-based heavy civil contractor, focuses on construction activities that are on or below the earth’s surface requiring the use of a wide array of earth-moving equipment associated with the building of dams, dykes, tailing ponds, canals, roads, and rail spurs to name a few. While KPCL is highly proficient at moving large volumes of earth materials to build earth structures, it also has in-house expertise in several specialized areas of earthworks construction. Nowhere is this more evident than KPCL’s proficiency in constructing cut-off walls.
Cut-off walls are non-structural underground barriers with extremely low permeability that are used by engineers as a control to prevent the migration of groundwater between controlled and uncontrolled groundwater systems. In Saskatchewan, cut-off walls are typically constructed at mine sites looking to contain the long-term migration of potentially impacted groundwater within the mine’s footprint.
Soil-bentonite cut-off walls are the most common type of wall construction in North America and have been used extensively throughout Saskatchewan to control groundwater migration. Conventional wall construction consists of excavating a vertical walled trench with a long reach excavator and stabilizing the trench walls during construction by maintaining a thick bentonite slurry (mud) within the trench. The trench is subsequently backfilled by displacing the slurry in the trench with a low permeability material usually consisting of native soils excavated from the trench that have been mixed thoroughly with bentonite clay – an absorbent highly swelling clay. A few of the keys to successfully constructing a cut-off wall include: selecting an appropriate location, physical parameters such as trench width and depth required to tie the wall into an impermeable layer of soil, slurry and backfill specifications, and installation methods.
As noted, specially-equipped long-reach excavators are required to excavate deeper slurry walls to a maximum depth of about 26 metres (85 feet). Trench depths beyond this are achieved using a hydraulic clam shell bucket attached to a large crane. The bentonite slurry is typically prepared using an onsite mobile batch plant that produces the required mud consistency, and the slurry is subsequently pumped into the trench. The soil bentonite backfill is normally prepared on the surface adjacent to the trench using a combination of small hydraulic excavators and dozers to mix the bentonite and native soils together until the desired homogeny is achieved before placing the mix into the trench and displacing the slurry.
Over time, KPCL has built up a wealth of knowledge and expertise in cut-off wall construction methods with the successful completion of a number of Saskatchewan installations. While every wall construction is unique, some of the challenges remain the same from project to project such as consistently maintaining the main excavation tool to maximize up-time due to excessive wear and tear, extracting large boulders within the confines of the trench excavation that are larger than the dimensions of the trench, ensuring high-quality slurry consistency during excavation, and maintaining a safe work site.
For each project KPCL undertakes it brings a client perspective, getting the project completed efficiently, economically, and safely. By way of a recent example, KPCL combined two cut-off wall construction methods to overcome a few site-specific challenges, utilizing the strengths of each methodology to complete the project. For this project, KPCL first conventionally excavated a slurry wall to a depth of nine metres, successfully removing a layer of boulders from the trench. Once the boulder lag was removed, a large, specialized chain trencher was inserted into the trench to complete the cut-off wall to the design depth which extended up to 30 metres (100 feet) below the surface. The trencher was utilized to cut through a very hard soil formation below the boulder lag and in which a conventional long-reach excavator or hydraulic clam shell would have significantly reduced productivity. The combination of these two methods ultimately saved the client time and money as the trencher was faster and more efficient than if the entire trench was excavated conventionally, while the upper nine metres of trench was conventionally excavated as the trencher could not contend with the boulders.
KPCL – Building Today for Tomorrow.
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