Embankments

The terrible problems caused by the June storms to the SVR have been well discussed elsewhere. The reports on their floodline clearly indicated that many drains were blocked and some collapsed embankments were poorly constructed originally. Other than replaceing all the rubbish fill material is there a way these embankemnts can be stabilised without recourse to piling.

 

Exactly what we are doing, build them up with rock!
The modern way of doing it is with what are called Rock Gabions, these are steel baskets, filled with rock (In our case, Granite, as it is much harder than our local sand stone), then landscape over the top to make it look pretty.

 

Granite; not good for the bunnies then!

 

an unexpected bonus then if the rail weavels get a headache and go elsewhere?

 

No, neither are the steel cages Brian! I know what s good for the bunnies thought, a big pot of boiling water, with some carrots, potatoes, leeks, etc!

 

Don't i'm hungry

 

Thank you everyone for you sometimes informative and sometimes amusing replies.

 

of course, there is always the, er, interesting method hit upon by the Cambrian Railways. They tried to pile the sand at Ynys Llas, but it was just too deep. The answer thay came accross was to plant conifer trees, then tip spoil over the top of them, the growing brancehes fo the trees held the bank together, in the same way that roots do!

 

Now that the SVR is back together again with trains running over the newly reformed embankments I wonder has there been any tendency for them to settle? In days of old it was a fairly common occurance or do modern methods stop this happening.

 

double post...

 

Not happened yet... All bar one of the SVR embankment repairs reopened at full line speed on day 1, the exception being Borle viaduct (15mph TSR, normally a 20mph PSR there). The rebuilt sections of line were thoroughly dug out back to solid ground/rock, and then mostly built up with layers of rolled stone, and as such are much better that the remaining bits, which the Victorians choose mainly to build out of ash...

 

Indeed, I'll second that, the reparied sections appear as solid, if not more so, as the rest of the line

 

Give it time it will settle,

But due to the construction it is likely to be less severe, rock fill and gabions are stiffer than ash or much and spread the load over a wider area. Anyone who wants to see what settlement can do, then just go to Anglesey and travel the A55.

Incidentally the railways use of ash is a good one, ash being cementitious to a degree. It is also still widely used as a cheap fill, though it has to be said, not fun to use in the wet.

 

Settlement can be accelerated during the construction stage so that once in use, the remaining settlement is negligible. Temoporary surcharges may be placed on top of the fill to cause it to settle (or consolidate) to typically around 85-90% of total, the speed of this remaining settlement being very slow and almost unnoticeable. Though this method is typically employed for building foundations it can be used elsewhere.

Talking of gabions, go to Chiswell at the Portland end of Chesil beach. The bulk of the 'beach' there is made up of gabions to prevent it collapsing into the houses built behind. Gabions have been used for a considerable length of time for highways embankments/cuttings (obviously the guys on the A55 didn't use them (*,) ), especially where high drainage properties, as well as firmness, is required.

Gabions is one way of avoiding settlement or accelerating settlement in the construction stage; there are several others.

Cheers,

Dom Greenop
DMR

 

What happens when the wire cage rusts through? Does this generally cause a failure of the embankment or is the rock stable enough and compacted enough by that stage to not be a problem?

Keith

 

At one time cavity tie irons were galvanised. Now they are stainless. Perhaps gabion baskets have gone the same way.

 

.....

 

I think that a combination of the two above posts is the theory, though mainly Boldfords... ...

I've yet to work with Gabions close-up and personally; the only time I've seen them right up was on a visit to Chesil beach some years ago, and whilst seeing them on the roadside I have of course been going too fast to notice whether they are galvanised or not.

Cheers,

Dom Greenop
DMR

 

Gabions are basically lots of little cages with stones in them, yes if they break/rot you can loose fill, however only from the cage that has 'gone'

Modern Gabions are made from various sizes of steel wire usually coated with an all singing all dancing coating called 'Galfan', basically a newfangled galvanising with superior qualities. Also they can be PVC coated in addition. You can get stainless, but it costs lots of wonga.

Typical design life can be anywhere between 40 years to 120years dependant on spec.

 

The scenario I was thinking of was on the SVR where a quantity of gabions were placed very close to a river. Over time these will corrode and if one breaks open and causes a rock fall, the gabion above could then break because of the corrosion and the additional stress it is under.

Thanks to all for the info

Keith