Soil-Structure Interaction Seminar - Foundation Performance ...

8. The subgrade and fill moisture content and density must be maintained until paving or
floor slabs are completed. We recommend that these parameters be verified by field
moisture and density tests at the time of construction.
9. In the areas where expansive soils are present, rough grade the site with structural fill
soils to insure positive drainage. Due to their high permeability of sands, sands should
not be used for site grading where expansive soils are present.
10. We recommend that the site and soil conditions used in the structural design of the
foundation be verified by the engineer's site visit after all of the earthwork and site
preparation has been completed and prior to the concrete placement.
Other Construction Considerations
1. Grad6 beam excavations should be free of all loose materials. The bottom of the
excavations should be dry and hard.
2. Surficial sub grade soils in the floor slab areas should be compacted to a minimum of 95%
of standard proctor density (ASTM D 698-78). This should be confirmed by conducting
a minimum of four field density tests per slab, per lift.
3. Minimum concrete strength should be 2,500 psi with a maximum slump of 5-inches.
Concrete workability can be improved by adding air to the concrete mix and the use of
a concrete vibrator. The concrete slump and strength should be verified by slump tests
and concrete cylinders.
4. The Visqueen, placed under the floor slabs, should be properly stretched to maximize
soil-slab interaction.
5. In the areas where expansive soils are present, the backfill soils for the underground
utilities under the floor slabs should consist of select fill and not sands or silts. The
cohesionless backfill can act as a pathway for surface water to get under the foundation
and resulting in subsoil swelling.
6. Tree stumps should not be left under the slabs. This may result in future settlement and
· termite infestation.
GEOTECH ENGINEERING AND TESTING, INC. ____________ ...
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