Running Track Replacement/Compaction 1

[GZ2001]

Another compaction type question--the contractor is replacing an existing asphalt running track as part of a project to provide an artificial turf field--the design (by a consultant no longer associated with the project) calls for a compacted subgrade (without giving any percent requirement--though we would expect it to be at least 95%), 6 inches of dense graded aggregate, a 3-inch MABC I-2 stabilized base course, a 1.5 inch FABC I-5 surface course, a 0.5 inch non-porous track surface, topped with a rubberized running surface. The contractor has milled out the top 4 inches of the existing track leaving a 1-inch thick base course. He claims this will give a good starting base for the new asphalt layers and also he is afraid if he takes out that last inch that he might "expose some soft ground." The existing track while old, worn, and cracked in a few places did not exhibit any areas of subsidence. Presumably there is stone under the bituminous base (this site is within a flood hazard area, but has not flooded as far as anyone could remember). Presumably again, the subgrade was compacted when the original track was placed down (30 or 40 years ago). Of course, without removing that last inch it is unknown what lies underneath. So, does it all need to be removed, the subgrade "re-compacted" and the stone and pavement sections placed as shown on the civil drawings? Should a few test pits be punched through to see what is underneath, or is it reasonable to assume the relatively good shape of the existing track indicates that the base is acceptable and leaving the one inch base in place and working from there is a reasonable solution? Thanks!

 

[Ron]

Using post-hole diggers, cut a few holes in and see what's below. Cheap and easy. Then you can decide. I don't like 1-inch of anything under asphalt. Constructability has to be considered and you need a stable material to achieve that. The loads from use are irrelevant.