Why the Green Matting?

 All throughout the lanes of the California Villa Apartments in the Hui Shan District of Wuxishire, China, the above-pictured matting can be seen.

What is it covering?  A month or so ago, the pipes under the cobblestones were repaired.  The pipes were covered with gravel.

Residents are annoyed that the lanes have not been properly resurfaced and they want the property managers to be fired.