Excavation and base preparation
Once initial planning is completed, the next crucial step is excavation and base preparation. The deck will only be as good as the base it is built on. Thanks to initial planning, it should already be determined where and how the excavated material will be handled. During excavation, however, soil characteristics should be examined carefully, as this will help identify and predict not only drainage, compaction, geo-textile and load bearing capacity requirements, but also forecast time and money.
Aggregate base compaction
Aggregate base compaction is integral to deck and patio construction. This procedure rearranges soil particles to remove air and water pockets to achieve a higher base density. Various tools exist to complete soil compaction; when selecting the proper equipment, consider the project and use what is appropriate for each application. For example, a drum roller may not be the logical choice when attempting to compact a trench in an area with poor accessibility.
Compaction should be completed in multiple layers (or lifts) in order to achieve the required density results. Generally accepted industry standards require a minimum compaction of 98 per cent standard proctor density. (This is a method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density.) To check this, and the effectiveness of the equipment being used, a nuclear density test should be performed. This will help calibrate the equipment being used and understand what is required to achieve the recommended results.
A trained technician from a local soil testing company can conduct this test to provide the associated costs and results. The initial cost of having someone onsite to perform these tests can be recovered quickly when considering the costs associated with over or under compaction, wasted install time or failures and call backs.
Geo-textiles
When building on poor soil conditions, the addition of geo-textiles can improve base performance. Geo-textiles are used for soil separation and can increase the load bearing capacity of the compacted soil subgrade. While not always necessary, the use of geo-textiles should be considered in areas containing clay or silty soils as they will prevent the migration of finer aggregates from the in situ soil (i.e. soil in the original, natural or existing place or position) up into the base material.
This migration can negatively impact the long term structural integrity of the project. Along with compaction of the aggregate base, the subgrade may need to be stabilized or amended prior to its compaction in order for the base materials to subsequently perform correctly. By amending soil conditions, it essentially changes the soil’s composition to perform to the project’s requirements. Chemical and gradation amendments can be used separately or in unison. If poor soil conditions are not amended, the potential for base failure increases.
Base depth is also unique to every project and is determined by site conditions and available materials. For instance, frost lines should be considered when excavating and installing base materials. Other aspects such as installing drainage pipes and locating utility connections should also be considered. Finally, be sure to check local regulations and building codes to ensure compliance.
