CCP 01-31-1994 - Laserfiche WebLink

Home Browse Search

------- ---- -------- ------- I AET #93-1379 - Page 11 -: subcuts of existing roadways would need to extend a minimum of I' beneath the bottom of the proposed aggregate base layer. If soils at this depth are "stable," no further subcutting should I be needed. To judge stability, we recommend the exposed subgrade soil be subjected to a test rolling program. Test rolling should be performed with heavier rubber-tired construction I equipment, such as a loaded dump truck. In general, soils which deflect or rut less than I" can be considered "stable". I - Soils which are not stable at the I' depth should be further subcut to 2' deep. However, we I recommend subcutting be continuous laterally such that subsurface drainage can be controlled. I Subcuts should be transitioned at 20: I or flatter. Based on the borings, it appears that you should plan for the 2' subcuts in at least the northern half of Amble Drive and the western I portion of Bussard Court. If the soils at the bottom of the 2' subcut are still not "stable," we recommend that soils be .. scarified, dried, and recornpacted to a higher level of stability until a test roll is passed; or an I appropriate geotextile fabric be placed to aid in offsetting the subgrade instability. We recommend new fill used to replace the excavated clayey soils be a "Select Granular I Borrow" which is describerl by MnDOT Specification 3149.2B. If cost savings are substantial, I you could consider the use of "Granular Borrow" (MnDOT Specification 3149.2A), although drainage properties would be rerluced, which would tend to rerluce longer term performance and I affect maintenance costs. I Placement and compaction of subgrade fill should meet the minimum requirements outlined in Mn/DOT Specification 2105.3FI (Specified Density Method). This specification requires soils I placerl within the upper 3' zone of the subgrade be cornpacterl to a minimum of 100% of the Standard Proctor density (ASTM:D698). Soils placed below this level can have a reduced I minimum compaction level of 95% of the Standard Proctor density. .. I