What is Shoring Wall Blindside Waterproofing?
Below-grade waterproofing is a fundamental construction practice implemented in areas below ground level where there may be a high risk of flooding and/or increased moisture levels. It is implemented in all projects that have subsurface structural features like basements, underground garages, and underground wineries. The two main below-grade waterproofing systems are positive-side applications and negative-side applications. Blindside waterproofing is a positive-side application and is commonly used when there is limited real estate.
When developing an underground feature, Contractors may implement Shoring and wooden lagging to hold back soil while excavating the underground features (This is often termed Shoring Walls). Another common construction technique is to excavate at a 45-degree angle in the soil to minimize the risk of soil collapsing (This is often termed Retaining Wall).
Why and How is Shoring Wall Blindside Waterproofing Installed?
If a retaining wall approach is taken, excavation of the area will come first, then formed walls or block walls with steel reinforcements will be placed, followed by the concrete pour. Block walls are generally lower costs but sometimes require higher skill and a more labor, but the material cost will be significantly reduced. A substantial amount of space would be required to allow for a 45° taper at a maximum vertical height of 5 feet. The required width to accommodate that will consume a huge space on the lot area.
Oftentimes in Los Angeles, where property is extremely valuable, there is motivation to install shoring with back lagging conditions so that the amount of the property that is used is maximized. This is why you commonly see structures being built right on the property line.
The construction approach that would be taken will depend on the application and how the architectural and structural engineer decided to proceed with the design. If Shoring Wall application to be used, the membrane is first applied to the lagging and then concrete is applied against the membrane creating a bond.
When dealing with waterproofing projects, another consideration is level. Some areas in Los Angeles have an extremely high groundwater table wherein water gets as shallow as 10 feet below the ground surface.
As you could assume, if you decide to install a subterranean garage in these instances, your project will be floating inside the water table. When this occurs, the design and construction approach will differ significantly from a non-water table project. Your building now needs to be able to resist the hydrostatic pressure induced on the structure. The geotechnical engineer will most likely defer to a design approach of installing a mat slab foundation in order to create enough weight to resist that hydrostatic pressure. This is commonly referred to as the boat design approach.
The waterproofing and methane barriers also need to be able to withstand the hydrostatic pressure. This is why reinforced and oftentimes hot seam welded methane barriers and waterproofing are installed to ensure that water will not seep through the seams and gaps in the masonry.
Waterproofing and Methane Vapor Barriers
Just like how methane can diffuse through the slab’s foundation, the methane vapor gas can also diffuse through the sides of the building and enter through the walls of a basement. Similar to being exposed to carbon monoxide, when methane vapor gas is constantly inhaled, it will deprive the body of oxygen. This is why in this type of construction, it’s important to install waterproofing and methane vapor barriers considering the methane mitigation requirements and water table height.
There are several manufacturers that have developed technologies to install waterproofing and vapor barrier membranes on shoring walls. Some of these technological options are spray-applied, bentonite-based sheet, asphaltic sheet, plastic, and synthetic-rubber sheet membranes. Some use HDPE sheets with spray-applied asphalt emulsion that bond to concrete while others use HDPE sheets with self-adhering chemicals that bond to concrete. All methods are sufficient and will act accordingly for waterproofing and prevention of the diffusion of methane.
The biggest concern is the installation of quality control for these systems. Waterproofing and Methane Mitigation are extremely detail-oriented type of work, especially in Shoring Wall Blindside Waterproofing. If work is not done correctly, significant failures can occur. That’s why it’s important to install the barriers according to the manufacturers and designers’ specifications.
How much is the cost of the installation of Shoring Wall Blindside Waterproofing?
Shoring is generally more costly due to the required drilling and lagging installation. A project will start with drilling the holes for the I-beams along the lines in which the building walls will be built. Then, the installation of rebar and concrete caissons will take place. Some projects don’t have caissons, they just have I-beams sticking out with a structural foundation.
Once the drilling and I beam installation is completed, the excavation begins. Shoring wood will get installed slowly but surely until ultimately all the dirt is removed from the middle space and the shoring walls are held up by the I-beams and the wood lagging. The next steps are to install the waterproofing systems and methane barrier per the manufacturer’s recommendations. Drainage mat and the waterproofing membrane will be applied to the shoring wood, the walls will then be shotcrete to provide the final product.
The cost of the installation of Waterproofing products can range from $5 to $50 per SqFt, their cost is highly dependent on the size of the area along with the preferred material manufacturer.