The importance of site preparation is paramount to the success of any below-grade waterproofing project not only from a quality perspective but also to keep the project on track and on budget. There are several steps to take to ensure proper site preparation is considered for below-grade projects. Today we will focus on dewatering, which is one of the most important activities in regard to preparing and maintaining a site where water is present during the below-grade construction process.
Dewatering is the intentional removal of groundwater or surface water from a site. This process is critical to keep groundwater from entering the site, controlling erosion, and therefore allowing construction activities. Dewatering is critical to the success of the waterproofing system as well as to ensure the structural integrity of the structure during construction. From a structural perspective, buoyant forces need to be mitigated, so there is no ability to lift the structure until enough of it is completed or sufficient dead load has been achieved. In relation to waterproofing, managing site water is imperative for a successful installation.
Waterproofing systems are not designed to be installed in the presence of ponded site water. Water during the installation impedes the ability to form laps, and complete details and can inhibit the ability of certain reactive technologies to perform long term. After the waterproofing installation is complete but before concrete placement for under slab or blindside walls, hydrostatic pressure can also exert stresses on laps and detail areas which may further compromise the system. Controlling site water and hydrostatic pressure until the concrete is in place and has achieved structural integrity is critical.
There are many methods or combinations of methods to mitigate water from entering or evacuating water from a site that can be temporary or permanent. The section of the shoring system is often driven by the dewatering needs, and the shoring system should also be considered when selecting the waterproofing system to ensure it is conducive to the site conditions. Shoring systems designed to act as water cut-off walls, such as sheet piles, slurry walls or soil/cement mix walls can be effective means for preventing water from entering a site and are more commonly used in permanent dewatering situations, generally having less of an effect on groundwater levels outside of the site. Dewatering methods within the excavation will typically be sumps, wellpoints, or large diameter wells to lower the water table or evacuate water from the site. All these methods can be used independently or in conjunction with one another.
It is critical to have a well-developed dewatering plan in place prior to construction based on the site-specific geotechnical considerations to ensure a successful waterproofing installation and overall project.
If you have any questions about site preparation or dewatering Polyglass has an experienced waterproofing team ready to support your questions and assist with your project needs. Contact us today to learn more.