GCL Overlaying

Q: Can you provide information about overlaying a new GCL on hydrated and damaged GCL?

A: This is more complex than one might first think—particularly from the standpoint of instability. The friction angle (ASTM D5321) of hydrated GCL to new GCL might be in the single digits (i.e., 8+/-2 degrees residual or less). Depending on the slope and filling sequence, this could create a slip plane. That is why many insist on removal of hydrated GCL before replacement.

Please note that if you proceed with the overlay scenario, the designer of record will have to verify (sign off on) this modification. Again, if you decide to go ahead with the overlay scenario, evacuate all the free water (puddles) and dry out the placed (pre-hydrated) GCL as much as possible.