Agenda - Council - 10/26/2021 - Laserfiche WebLink

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4.2 Discussion Roadways Based on a brief review of historical aerial photographs available on Google Earth and the Anoka County GIS website it appears that the streets were originally built sometime around 1990 thru about 1997 and based on that they appear to be approaching or have exceeded their assumed 20-year design life. Observations of the bituminous cores appears to indicate that the roadways were seal coated/chip coated as evidence by smaller sized aggregate at the surface of the cores. It further appears that some of the roadways may have been overlaid, especially near soil boring / core 06. The core at SB-06 was about 61/2 inches thick or about 11/2 inches thicker, or more, that the cores at soil borings SB-01 thru SB-05 . We observed longitudinal and transvers cracks with some "alligator" or fatigue cracking of the pavement surfaces. The cracking observed could be the result of a combination of factors including; inadequate pavement thickness, pavement age and possibly frost action/frost heave. Longitudinal cracking are cracks parallel to the pavement centerline or laydown direction. These can be caused by poor joint construction, reflective cracking from an underlying layer, fatigue cracking or top -down cracking resulting from the age of the pavement or due to expansion and contraction of the pavement surface or increased loads/traffic on the pavements. Transverse cracking are cracks perpendicular to the roadway centerline or laydown direction. These are often caused by shrinkage of the pavement surface, reflective cracking from an underlying layer or top -down cracking. Alligator or fatigue cracking can be symptomatic of poor subgrade soils and/or inadequate pavement thickness. Aggregate Base An apparent aggregate base layer was observed below the pavements at each boring location. The aggregate base appeared to contain little gravel and because of that it is identified as Possible Aggregate Base on the boring logs. Based on our observations the aggregate base or Possible Aggregate Base may not meet MN/DOT gradation specifications for Class 5 aggregate base. It is possible that the Possible Aggregate base was initially placed as new or virgin Class 5 aggregate base but has degraded over time due to traffic or possibly due to frost action. Soils The borings encountered sandy subgrade soils consisting of poorly graded sand corresponding to the ASTM Classification SP. These soils are considered non -frost susceptible and are also free draining materials and are well suited for pavement support and. Where spot fixes of the utilities will occur, we anticipate that the soils excavated for utility repairs will be reused to the greatest extent possible. The soils encountered in the borings in our opinion is suitable for reuse. We recommend that any unsuitable materials such as buried topsoil, organic soils and any soft or otherwise unsuitable materials, if encountered, be removed and replaced with suitable compacted engineered fill. 6