Wednesday, 25 November 2015

Bending steel

After some spraying of blue marker paint on the ground and lots of measuring, we've specified the steel reinforcing bar for the concrete beam to support the gate posts of the field gate. In an earlier post on here we mentioned the reasoning for constructing a concrete beam. Now we've taken a view on the likely forces that will be imposed on the concrete. We've also considered how the posts will be replaced in future if significant repairs are required.

Some research on YouTube has made us instant experts on how to set out rebar (Steel reinforcing bar) and to create shuttering to hold the concrete used to form the beam. We've had to understand the British Standards for common rebar shapes used in the construction industry. This allowed us to produce specifications for the amount and shape of rebar required for the concrete beam to support the orchard field gate. It is a cantilevered design to prevent the gates from sagging in use. We requested a quotation from a local steel supply firm Twiggs for rebar bent to our custom requirements. The price was so reasonable I actually rechecked they'd included the cost of bending within their price. We've placed the order and await delivery.

The beam will be approximately 200 cm long by 90 cm wide with a depth of approximately 40 cm. It will be capable of withstanding the weight of heavy agricultural machinery which might pass through the gateway. It will be buried from view once the posts are installed.

The reinforced beam will provide reinforced sockets for the gate post (200 mm diameter) and a fence post (100mm). When we're casting the beam we'll mount the gate and fence post in position in the beam. We'll pre-wrap the end of the posts in plastic bubble wrap so we can lift them out once the concrete has hardened. The sockets are also designed to prevent the accumulation of water under the base of the posts. After removing the bubble wrap we'll re-install the posts in the beam using sand to pack the gap between the beam sockets and the posts. This installation method allows the post to be securely mounted, free from rocking/tilt, but allowing for easy removal for future maintenance. If you just mount the posts directly in the concrete when it is poured subsequent maintenance of post removal is difficult.

We are also practising the art of wire tying to fix the rebar in place before pouring concrete. Youtube helps again.  All that remains now is to trick the volunteer team into agreeing to, dig the trench and to mix the concrete when the management team are ready to construct the beam. We'll be incorporating reinforcement fibre into the concrete mix to provide extended life.

Little did we realise when we started the orchard project that we'd become involved in civil engineering and reinforced concrete design.

Sunday, 15 November 2015

Heavy rain, river is high

I popped up to the Orchard today to measure up for the new roadside gate. The work was soon done and I'll now be able to order some timber to build the new gate(s). We've had a lot of rain over the past week and the river Ecclesbourne has swollen accordingly. From what was a gentle brook after a relatively dry early Autumn it is now a fast flowing muddy torrent at least 75 cm deep. It would be difficult to stand in the water. 

Clearly our work earlier in the year to clean up the river bank and remove fallen trees and river bed obstacles has paid off. The water flows have less turbulence, swirling and scour. The accumulated bank of silt, where a fallen tree had been laying, has now washed away.

Wednesday, 11 November 2015

Fixing the main gate

One of the first things I noticed when we acquired the site for the Turnditch Orchard is that the main gate at the roadside is broken. The old sandstone hinge post is fractured and the gate no longer swings from it. The latch post, again old sandstone, has a substantial lean from the vertical. The latch post was probably displaced when the river bank collapsed near the bridge and was rebuilt by the local authority. The iron tube gate itself is heavily rusted and the bottom bar corroded through. Steel chains attached to an elm tree stump currently provide hinges for the gate.

We've decided the best way of repairing the gate is to install new posts behind the the old original posts. This approach will preserve the historical stone posts, but it does present some problems. The latch post is at the top of a relatively unstable river bank and also close to the historic stile "gate" for the public footpath. If we are careful in positioning the new post we can avoid blocking the footpath stile, as required by law. However the new gate would effectively block the route to dogs accompanying people using the footpath as we need to be able to lock the new main gate.

We also need to be sure the installation of a post does not create long term potential for damaging the riverbank close to a public road bridge. It is inevitable that walkers will swing on the new gate post as they pass through the stile. Some form of reinforcement will be required to prevent damage to the river bank. We are already planning a hidden steel reinforced concrete beam to support the fence post for the riverside stock fence. We'll extend that beam to provide support for the gate post on the river bank. Once the works are complete the concrete beam will be buried and unobtrusive, but it will prevent the gate post and fence post from toppling and damaging the riverbank.

We'll design the concrete reinforced beam with post sockets so that the gate and fence posts can be replaced in future without disturbing the beam.

There's no legal requirement to provide access for dogs on the public footpath at the end of the orchard by the river, but it is a popular route for local dog walkers. Currently dog owners just lift the old rotten metal gate to get their dogs through. So we are planning to introduce a dog gate which will allow passage to dogs. We've looked at various configurations because near the footpath stile space is quite cramped. There's not enough space at the top of the river bank to safely install a swinging stile gate. We can't reduce the width of the gateway, it has to be wide enough to allow the passage of farm machinery. Our current plans are to build a bespoke main gate which will have an integral dog gate built into the design. Dog owners will be able to open/close the dog gate without the need to unlock the main gate.

Monday, 2 November 2015

Wildlife in Turnditch Orchard

We were working at the weekend to tidy some of the piles of branches left over from the river clearance and also starting to expose the electric fence ready for removal. As I wandered past the river bank I managed to surprise an adult heron fishing in the water. It took off in a hurry. I'd guess now we have removed most of the bank side vegetation the heron found access to the water more attractive.

As we worked we were often interrupted by the sight and sound of wild male pheasants flying in and out of the other end of the orchard.  It's good to see our work hasn't really disturbed the local wildlife.