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Tim Lewis

Aylesbury Arm Stoppage

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Aylesbury Arm Closure Lock 11 to Lock 13

 

Thursday 28 March 2013 until further notice

Locks 11 to 13 on the Aylesbury Arm are closed with immediate effect

due to a collapse on the towpath side at Lock 12 which has resulted in

the lock chamber being unstable and unsafe for navigation.

 

The towpath is also closed

Enquiries: 0303 0404040

 

 

How long to rebuild a lock?

 

Tim

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Aylesbury Arm Closure Lock 11 to Lock 13

 

Thursday 28 March 2013 until further notice

Locks 11 to 13 on the Aylesbury Arm are closed with immediate effect

due to a collapse on the towpath side at Lock 12 which has resulted in

the lock chamber being unstable and unsafe for navigation.

 

The towpath is also closed

Enquiries: 0303 0404040

 

 

How long to rebuild a lock?

 

Tim

 

From Yesterday:

 

IMG_0477-L.jpg

 

Tim

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From Yesterday:

 

IMG_0477-L.jpg

 

Tim

6-8 weeks on site. How long is a piece of string to get all the ducks in a row to get on site:

 

Money

contract (though maybe this will fall under the Galliford umbrella contract)

design

materials

manpower

machinery

permissions

etc..

 

 

 

N

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Take a good while to fix this

Maybe they could use the crane they fished out the canal up north

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Having seen a very poor engineering description of the reason for this collapse on another canal website, I think it worthwhile putting the record straight. Lock walls should be designed to take an alternate load - pushing outwards when full and pushing inwards when empty. As the inward pressure comes from the earth fill behind the wall, this was perceived by early engineers to have been significantly less, particularly after the collapse of a straight-sided lock wall on the Canal du Midi shortly after that canal opened in the 1680s. All locks on that canal now have curved sides as that was thought the best solution. However, it could make the walls more liable to distortion when the lock is full, as it is difficult to make the ends of the lock wall by the gates strong enough - they would tend to be pushed outwards when the lock was full. Subsequently almost all locks have been built with straight sides. The earth backing to the lock wall gives it the static load needed to resist the force created by the water when the lock is full. When empty, the restraint of that static load forcing the wall out is reliant upon the way the wall is connected to the brick or stone invert at the bottom of the lock. Some early canal locks, such as those on the L&LC in Yorkshire, were built on wooden foundations where creep of the bottom of the lock wall could be a problem, and that was why brick or stone inverts became universal on canal locks from around 1790.

 

What has happened here is a failure to stop leakage through the lock wall. This leakage can create a void behind the lock wall which becomes filled with water when the lock is filled, as well as just from land drainage, particularly in wet weather. This creates a force on the joint between invert and wall which it is not designed to take, and hence the movement of the wall. Keeping the lock full or empty would have made little difference to the result.

 

On some canals, locks were supposed to be kept full because they had no bywash, and excess water was fed through the lock. Keeping the lock full has the added advantage of keeping the bottom gates wet, and so tight, and of keeping any puddle behind the lock walls wet, and so in good condition. If puddle becomes dry, it cracks and can cause leakage, with leakage removing material and hence creating a void. On old or poorly-maintained locks, this does give a reason for emptying the lock after use, though they should be emptied slowly to allow any water in voids behind the wall to flow out and not to create excess pressure on the back of the lock wall.

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Will the new lock be a cast concrete trough or will they rebuild it to the original spec.

 

Darren

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Will the new lock be a cast concrete trough or will they rebuild it to the original spec.

 

Darren

This lock at Kidsgrove is a good example of what can be done with concrete. I suspect it was built because of subsidence around 1950/60, with local canal men doing the work as it is an almost exact copy of the earlier brick locks, with all the curves and slopes necessary for working a boat through without lines catching. Concrete doesn't have to result in a non-traditional shape.

8616503626_d90bbb59a0_b.jpg

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Will the new lock be a cast concrete trough or will they rebuild it to the original spec.

 

Darren

 

I don't know what CRT will do but this is how I'd deal with it.

 

Drain the lock completely,

 

Demolish the wall (most of the job has already been done!)

 

Remove unstable earth, this may cut back a lot further than people expect

 

Build a RIC retaining wall, as well as foundations anchor it back into the stable soil

 

Fill the gap, ideally with hardcore so grout can then be added

 

Build a face to the retaining wall in suitable brick

 

grass the lockside

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I don't know what CRT will do but this is how I'd deal with it.

 

Drain the lock completely,

 

Demolish the wall (most of the job has already been done!)

 

Remove unstable earth, this may cut back a lot further than people expect

 

Build a RIC retaining wall, as well as foundations anchor it back into the stable soil

 

Fill the gap, ideally with hardcore so grout can then be added

 

Build a face to the retaining wall in suitable brick

 

grass the lockside

 

You are a wise man - this is what BW did on a direct labour basis when they rebuilt a couple of locks on the Marsworth flight some years ago. One of them was the lock which was open for public inspection a few weeks ago.

 

Leo.

 

PS - It's how I would do it as well.

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You are a wise man - this is what BW did on a direct labour basis when they rebuilt a couple of locks on the Marsworth flight some years ago. One of them was the lock which was open for public inspection a few weeks ago.

 

Leo.

 

PS - It's how I would do it as well.

 

 

I believe CART's national engineers are proposing a 'piled solution'.

 

N

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I believe CART's national engineers are proposing a 'piled solution'.

 

N

A possible way of fixing it but piling normally requires fair sized machinery, could be access problems here.

 

L.

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Will English heritage have to be involved I wonder? As they do like to try and keep things where possibly the same as what was there originally.

 

Darren

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Will English heritage have to be involved I wonder? As they do like to try and keep things where possibly the same as what was there originally.

 

Darren

 

 

I understand that EH had to be involved when Lock 4 on the Arm was rebuilt last winter but that Lock 12 is not Listed in any way.

 

Access is not bad- there is a decent sized road to Lock 13, with good connections to the Aston Clinton bypass and a gate from that road to the towpath. The 300yds of towpath from lock 13 to lock 12 is not piled but does have a decent edge to it and reasonable width. Whether its good enough for a big digger and a vibrating piling rig I do not know. The towpath along the arm is supposed to be being improved on the back of the Arla dairy construction so maybe this bit will be an early stretch. There is also the possibility of access from the bridge above, though the road is pretty narrow and would involve going through Aston Clinton. The towpath to this bridge is again quite wide, and has been piled, though there is no easy access to the towpath at the bridge for big kit. I have also heard rumour that access across a field might be needed.

 

N

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I understand that EH had to be involved when Lock 4 on the Arm was rebuilt last winter but that Lock 12 is not Listed in any way.

 

Access is not bad- there is a decent sized road to Lock 13, with good connections to the Aston Clinton bypass and a gate from that road to the towpath. The 300yds of towpath from lock 13 to lock 12 is not piled but does have a decent edge to it and reasonable width. Whether its good enough for a big digger and a vibrating piling rig I do not know. The towpath along the arm is supposed to be being improved on the back of the Arla dairy construction so maybe this bit will be an early stretch. There is also the possibility of access from the bridge above, though the road is pretty narrow and would involve going through Aston Clinton. The towpath to this bridge is again quite wide, and has been piled, though there is no easy access to the towpath at the bridge for big kit. I have also heard rumour that access across a field might be needed.

 

N

 

I'm no expert but as the canals were mostly dug by hand to start with I can't see why they can't just get a crew of navvies in to do the job ... it certainly wouldn't cause any damage to the surrounding environment and might even be quicker

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Access is not bad- there is a decent sized road to Lock 13, with good connections to the Aston Clinton bypass and a gate from that road to the towpath. The 300yds of towpath from lock 13 to lock 12 is not piled but does have a decent edge to it and reasonable width. Whether its good enough for a big digger and a vibrating piling rig I do not know. The towpath along the arm is supposed to be being improved on the back of the Arla dairy construction so maybe this bit will be an early stretch. There is also the possibility of access from the bridge above, though the road is pretty narrow and would involve going through Aston Clinton. The towpath to this bridge is again quite wide, and has been piled, though there is no easy access to the towpath at the bridge for big kit. I have also heard rumour that access across a field might be needed.

 

No doubt CRT thought the access to Apperley Bridge was "not bad" and the towpath had a "decent edge to it". :)

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£500K to repair this lock, that's a lot more that I thought it would be.

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