HS2 at Fosse Way and Offchurch Greenway April 2026

This film shows HS2 construction at the B4455 Fosse Way and the Offchurch Greenway near Leamington Spa.
Does anybody know what the grey / white stone areas are for on the grass cutting sides, as seen in the thumbnail view?
Filmed in April 2026.

Chapters
0:00 Fosse Way
3:10 Long Itchington Road
6:13 Offchurch Greenway
March 2025
https://youtu.be/9Yh45ub3F58

Fosse Way October 2025
https://youtu.be/5084paeATZw

Offchurch Greenway October 2025
https://youtu.be/kqKUTJI4TRg

Видео HS2 at Fosse Way and Offchurch Greenway April 2026 канала Jim H24