The same can be said for drainage; tree and shrub roots can damage pipes and channels in the cess, as well as flumes on embankments. In the most severe cases, roots can crack and deform the drains to the extent that they don't work, very often resulting in wet beds for example.
In your experience, how many of those drains damaged via
direct penetration of roots were in a poor condition to start with? I know there is contradicting research, but a lot of what I have read suggests that roots will only directly penetrate a drain where there is a leaking/failed joint; in this case the roots, being hydrotropic, grow along the moisture gradient and enter the drain run via the leaking joint to proliferate once inside, subject to oxygen levels being sufficient. An answer that has been suggested is to line trenches with non-woven geotextiles (Terram) which acts as a root barrier, although this is only any good on new installations obviously.
But yes you're quite right, tree root damage to drains can be as a result of lateral forces from the wind acting on the crown being translated via the roots onto the pipe. Claus Mattheck has researched this extensively, many of the findings can be found in '
Tree Roots in the Built Environment', which I recommend as a very good read on this subject. And there is indirect damage in shrinkable clays as a result of tree-related soil drying leading to soil movement.
Tree roots can be very destructive. Although not a 'tree', things like Japanese Knotweed do nothing but damage to wherever they grow; their roots grow through reinforced concrete, so just imagine the damage done to an earth embankment...
Some trees (e.g., poplar, willow, cherry) but not all species by any means. And while I agree that Knotweed can cause extensive damage to structures/hard surfaces, surely in the case of an earth embankment the (extensive) root system will help to bind the soil horizons together, preventing shear/slump? (Not that I'm advocating retaining Japanese Knotweed on embankments, because of its hugely detrimental effect on biodiversity).
The problem is, the only way to really remove it is to spray it (which can sometimes be ineffective) or to inject it. As you can image, to inject all the Knotweed on the 20,000 mile network would be astronomically costly! (Bearing in mind that the chemical used is strong enough to burn your skin, so doesn't come cheap!)
The chemical mostly used is glyphosate (which you can buy in the garden centre as Round Up), which doesn't burn the skin. If a contractor is using something else that burns the skin, then they really need to revisit their COSHH assessment! You're right though, stem injection is hugely time consuming and not always effective at 'first strike' (speaking from experience here).
--- old post above --- --- new post below ---
On the flip side, from a safety point of view, the actual felling of trees would have to be carried out in a controlled manor which prevented any branches falling on the track - this would either require a possession or other safe system of work. On top of that, you can't go cutting trees down that are next to live OHLE...
Do NR not allow any live line cutting? In theory it's perfectly possible, as all the electricity companies allow it (with the exception of National Grid - 400 and 275kV is too high a voltage) using insulated rods and/or cutting from a cherry picker using insulated tools and suitable PPE, depending on the voltage. (I suppose though that if treework on the railway requires a possession, you may as well have a current isolation too, much less hassle than that associated with a DNO taking 100s of customers off supply for a power outage)
