Weather induced panic part 2

[Fat Controller]

I'm always intrigued by the comments that tree roots stop banks from slipping. I'm no geotechnical engineer (probably a good thing) but I can't help wondering two things:

 

What effect does all the extra weight of the trees have on the slope?

 

and

 

What held them up before the trees grew?

 

Andy

I think it's not so much that the tree roots are holding the embankment up, but that their removal , with the attendant heavy machinery, causes the embankment/ cutting slope to become unstable. If I remember, I'll ask brother-in-law, who's a retired geotechnical engineer who actually worked with Network Rail's personnel on slope stability in the Bristol/Swidon/Gloucester triangle; he might just know..

[37410]

Vegetation management on earthworks is not unfortunately a simple issue. Dependent on the type of earthwork (cutting or embankment), the geology of the area as well as the drainage management of both the surface and groundwater (something else NR is grappling with at present), the type of vegetation and it's location on the earthwork, it can mean that in some cases vegetation has a positive effect on slope stability whilst in other places it has just the reverse.

 

NR and London Underground have both researched the issue, some of which is still ongoing. In very broad brush terms, earthworks which are composed of "clay rich" materials (which absorb water and thus swell in wet weather and shrink in hot weather) and which have heavy water demand trees ( such as oak, elm, Hawthorne, etc.) on them can cause quite large localised movements on slopes. In summer months during dry weather you can actually see track quality issues directly adjacent to such trees near the crests of embankments.

 

Keeping on top of vegetation management is becoming a real priority for NR as it enters Control Period 5 but it is a "work in progress".