CCP 11-12-1996 - Laserfiche WebLink

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I '. AET #96-2601 - Page 6 I It is our judgment the subgrade soils for the Snelling A venue Service Road are of poorer quality, I in terms of soil support value, frost/drainage properties and ease of stability improvement. From I a soils standpoint, this street appears to have the greatest need for a sand subbase. Although the silty sands in the upper zone at Boring #11 are relatively stable, the silty sands are fme grained I and have a relatively high silt content (approaching a silt classification) and these soils could potentially have the highest frost susceptibility of all soils encountered. I I Sub grade Preparation I To prepare the subgrade for new base and bituminous placement, we recommend removal of the Ie existing pavement materials, thereby exposing the existing subgrade. It may be possible to reuse the old pavement materials, if they are crushed to a base-like gradation. With recycled bituminous , materials, it is usually preferred that they be blended with soiIlgravel materials (to reduce asphalt content) if they are to be reused as base; or that they be reused as sub grade materials (recycled , bituminous will not meet a "Select Granular Borrow" specification). , Based on the reconstruction approach of using a subbase layer, it is our judgment that ai' thickness of sand should be sufficient. The in-place soils prior to subbase placement (or prior to , base placement if no subbase is used) should be test rolled to determine stability suitability. If the in-place soils within the subgrade are unstable (based on the test rolling or if induced by , construction traffic), stability should be improved by means of in-place scarification, drying and , recompaction until a test roll can be passed. An alternate to in-place soil reworking would be to place a geotextile fabric (MnJDOT Specification 3733, Type V) below a sand subbase. A , geotextile fabric would not be considered an equivalent offset in cases of excessive instability. If it is necessary to vary the thickness of the subbase, we recommend the thickness have gradual ,- transitions of no steeper than 20 (horizontal):! (vertical). The subcut and sand layer placement , H