CCP 01-31-1994 - Laserfiche WebLink

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___ ___---.n ___ - __ ___n______ I AET #93-1379 - Page 7 I LABORATORY TESTING e, I To aid our judgment of soil stability properties, 5 of the split spoon samples were submitted to the laboratory for moisture content testing. The results of these tests appear on the boring logs I opposite the samples upon which they were performed (We column). I BeCause the granular layer at Keithson Drive appears to have been specifically placed as a sand layer within the subgrade, we combined samples from Borings #1 through #3 for a composite I sieve analysis test. The results of this test appears on the data sheet included in the appendix I (behind the boring logs). This sample had 19% by weight passing the #200 sieve. Therefore, this material would meet the gradation requirements for a Granular Borrow (MnDOT 3149.2A), I but not a Select Granular Borrow (MnDOT 3149.2B). ENGINEERING CONSIDERA nONS .. General I For roadway support, a high level of strength is quite important within the upper portion of the I soil subgrade. Bituminous pavements are "flexible" systems and wheel loads transmit high local stresses to the subgrade. However, the load intensity dissipates through the subgrade such that I the high level of strength is usually not needed below about 3'. This is the purpose of requiring a higher level of compaction within fill placed in the upper subgrade zone versus the lower I portion. Moderate compaction is usually desired below the upper critical zone, primarily to avoid settlements and sags of the roadway. I Long-term pavement performance is also dependent on the soil sub grade drainage and frost I characteristics. Poor draining soils tend to be susceptible to frost heave and subsequent ,-- weakening upon thaw. This condition can result in irregular frost movements and "popouts," I as well as a general softening of the subgrade. -- I -----------