written by: Melissa Carruthers
Follow Me on Twitter: @MelissaC_PFB
This week we delve right into the applications for commercial construction. To start, I will be covering a geotechnical application for compressible fill material.
I don’t normally write very technical blogs, I like to keep them more of an easy read. However my latest blog is by far my most technical one yet. Bear with me and my attempt. Let’s discuss compressible fill material, specifically Plasti-Fab’s GeoSpan compressible fill material. When looking for a compressible fill material Plasti-Fab GeoSpan Compressible Fill material is a closed cell expanded polystyrene (EPS) product. It is designed to act as a compressible fill material which will reduce the potential forces on structures in the event soil expansion occurs after construction is completed. It can be distinguished from other EPS materials because of its brownish earth tone.
Something to note, before construction begins a site review needs to be conducted by a geotechnical engineer. It is important to know what kind of soils are on the building site, because soil deposits which contain substantial proportions of clay mineral particles can have different expansion possibilities. Soil expansion may affect the performance of structural members even when pile foundations are used. The magnitude of soil expansion experienced will depend upon factors such as moisture loss during construction and new conditions imposed on the soil as a result of construction.
GeoSpan Compressible Fill material is intended to be used primarily as a compressible medium under concrete grade beams or heavier structural members supported on piles. GeoSpan compressible fill material is designed to support expected construction live loads and the weight of the structural member until the concrete has cured and gained enough strength to be self-supporting.
If reinforcing is to be supported directly on GeoSpan compressible fill material, reinforcing support chairs used must be of a type, and in a sufficient quantity, to ensure that point loads do not exceed 10 kPa (1.4 psi). Normally, deformation due to initial weight of freshly placed concrete can be ignored. (Check out Plasti-Fab’s graph of compressive stress versus deformation)
When choosing your compressive fill material a couple of advantages of Plasti-Fab’s GeoSpan compressible fill material are:
1. It is an engineered product designed to meet specific requirements for each application
2. The engineered properties of the product are not affected by the presence of water
3. The product does not depend upon a voided configuration (which may become filled during backfilling) to reduce stress on the structure
4. If required, dimensions can be adjusted easily on the job-site using a fine-toothed hand saw to accommodate job-site obstructions
5. The product does not support the growth of insects or vermin nor does it contain any ozone depleting chemicals (ODC free)
Application, design criteria and design example
GeoSpan is supplied to customers pre-cut to the required dimensions. The standard dimensions are: length 96” (8’), width up to 48” and thickness up to 24”.
Required thickness of GeoSpan is determined by the following information provided by the customer:
1. Self-Weight the structure member temporarily supported
2. Net structural uplift resistance capacity of the structure
3. Maximum GeoSpan compressive stress
4. Maximum anticipated soil swell
*Things to note*
• Maximum compressive stress (U) is equal to the maximum compressive stress anticipated on the long term after compression of the GeoSpan induced by soil swell
• The net structural uplift load (required uplift resistance capacity of the structure) is the maximum GeoSpan compressive stress less the self-weight of the structure
• The GeoSpan final strain (D) is determined from the graph of compressive stress versus deformation provided based upon the maximum GeoSpan compressive stress (U)
• The required thickness (T) of GeoSpan compressible fill material is then calculated based upon maximum anticipated soil swell (E) using the following formula
T=(E X 100) /D
Quality Control testing
Designers are cautioned that GeoSpan compressible fill material utilizes different manufacturing and testing criteria than standard EPS insulation board in order to obtain the engineered properties necessary for this application. The physical properties of GeoSpan compressible fill material are controlled within close tolerances during manufacturing.
There we go, hopefully this helps answer questions about GeoSpan, if not send me your questions and I will get you some answers.
For more on Geotechnical applications, visit plastifab.com