JWC – JW Clark

Aftercare for Treatment Plants

Aftercare for treatment plants, servicing, what JW Clark can help with afterwards… and what we can’t help with…..!

The Three Ps

With any sewerage system, including when you are connected to the public sewer, you should never be putting any waste into your system apart from Pee, Poo and Paper…..! But with a Treatment Plant in particular, if you don’t observe the Three Ps (see here) then you’re quickly going to run into trouble – and avoidable cost – with your Treatment Plant. You might have to do a bit of educating the rest of the household, including kids and teenagers in particular. They may well be used to throwing wet wipes, sanitary towels and many other prohibited items down the toilet, and it’s difficult to change habits, but if these naughties end up in your treatment plant then it’s going to cause you trouble and cost you money. You may need to put signs up at each toilet for a period, to get people used to these basic rules.

Treatment Plant Servicing

Having had your treatment plant installed, it’s important to keep on top of maintenance and servicing. The Environment Agency dictates that Treatment Plants should be serviced in accordance with Manufacturer’s Guidelines, and this is normally once a year. We don’t service Treatment Plants ourselves, but we generally recommend https://www.ukpumpmaintenance.com/ Otherwise you can find a list of service engineers at https://www.britishwater.co.uk/page/ListofAccreditedServiceTechnicians

Regular checks

In between regular services done by a third party, you’ll also have to keep an eye on the plant yourself, in particular with regard to the ‘blower’.

Your ‘blower’, whether it be internal (inside the Treatment Plant) or External (in a green hood outside the Treatment Plant) should be humming away permanently, blowing a steady stream of oxygen into the plant.

To check that an internal blower is working, you should normally be able to hear it when stood right next to the manhole cover central to the Treatment Plant – normally square, and 2ft square. If you can’t hear it, then you should normally be able to feel some vibration by putting your foot on the manhole cover, or by putting your hand on it.

To check that an external blower is working, simply put your hand on the green hood instead, which houses the blower. You should hear or feel the blower working even more so with an external blower within a hood, than with an internal blower.

This ideally needs doing once a week, maybe do it on a Saturday morning, for example, or if you have a gardener or a handyman, make it their job to do it. But it’s your duty to make sure the Treatment Plant is cleaning the waste to the required standard to discharge into land drainage or into a watercourse, and if the blower isn’t working, then this is going to quickly reduce the extent to which the Treatment Plant is working effectively.

If you don’t think the blower is working, or if you can’t feel or hear it from outside, then take the main lid* off the Treatment Plant, and you should see the liquid fizzing or bubbling towards the top. If the liquid is still and undisturbed, then the blower is likely not working.

In the first instance, check that the electric feed to the Plant is working, consult an electrician if you need to, and if the feed is not the problem, then you will need a service engineer to attend, to fix or more likely to replace the blower. If the blower is less than 2 years old, then it will be under warranty, in which case please get in touch with us and we’ll contract the manufacturer for a replacement, in the event that we supplied the Treatment Plant as part of our service to you.

*When taking the manhole cover off a treatment plant, never do this on your own, always have another person with you. It goes without saying, that you should never enter a Treatment Plant, this is a confined space, and every care should be taken when taking off the cover.

Pump checks

If you have a pumped outlet, the the ‘pump’ is a secondary thing that you are going to have to check regularly. This is not as easy as checking the blower, as the pump for the outlet only makes a noise when the level in the plant gets to a certain point, and when the pump kicks in for a short period.

On most Treatment Plants, we will normally install a ‘final manhole’ just before the waste enters the Treatment Plant. In the bottom ‘channel’ of this manhole, the waste where it flows into the Treatment Plant should be at a minimum level where it flows through the bottom fo the manhole – the ‘channel’ – nothing more than an inch or so. If it’s particularly deep, a few inches deep or more, then it’s quite likely that the effluent isn’t pumping out. You’ll need a service engineer as quick as you can get somebody out, and again, if the system is less than two years old, then speak to us, as the pump will be under warranty.

Alarms

Both the blower and the pump (in a pumped unit only) can be fitted with alarms, and we will normally give you the optional extra of having an alarm fitted to each. The problem with alarms though, is that they are often dependent on batteries, or on the electric feed itself, so if the reason for the blower or pump not working is a problem with the electric feed, then the alarm itself – dependent on type – may not work either. We particularly recommend you have an alarm fitted for a ‘pumped’ unit. If your pumps stops working, then your Treatment Plant is going to fill up particularly quickly, and the pump – that has failed – is inside the Plant, drowning in an ever-rising of sewerage.

So to summarise… we can help with:

Replacement of blowers and pumps within 2 years of installation – but if any of these have failed, always check the electric feed first, it’s more likely to be an electrical failure in the early days than a failed part.
Any problems relating to underground drainage pipework that we laid as part of your project
Problems with reinstatement, i.e. ground settling around the Plant within our original excavation

We cannot help with:

Regular servicing
Replacement of blowers and pumps after the initial 2-year warranty has expired
Problems with underground drainage pipework that we didn’t lay as part of your project
Electrical problems – except whereby we instructed the electrician to make the connection to the plant and the problem is with this small amount of electrical installation, as opposed to electrics within the property as a whole – and this is usually where the problem lies.

Of all the problems we have ever encountered with Treatment Plants after we’ve fitted them, by far the vast majority of them relate to lack of servicing, in particular when blowers or pumps fail and have been left unserviceable for a long period of time. Several Treatment Plants we have fitted, have had never been serviced, many years after we complete the install. We’ve seen some real horror shows over the years, but if you can keep on top of those regular checks detailed below, and if you have your Treatment Plant serviced once a year, then you shouldn’t have any problems.

Treatment Plant Installation, Finedon

Projects

Treatment Plant, Finedon, Case Study

We were approached by our customer in Finedon, Northants, who had a treatment plant already, but it was borderline-compliant, and in any case he wanted to move it as part of an extensive reorganisation and redesign of his garden.

Survey work in advance

As part of the initial survey we downloaded the local Water Authority Asset Plan to make sure there wasn’t a public sewer in the Highway, within the vicinity of the property. Quite often a customer will have a septic tank or treatment plant dating back many years, but a public sewer may have been laid in the Highway since. Under a new law that came into force in 2020, if a public sewer exists within a reasonable distance, you cannot install a treatment plant instead.

We also took some levels on site to ascertain the proposed treatment plant inlet and outlet depth, as these are determined by the levels of the existing underground drainage on site. With these to hand, we ordered the treatment plant from Marsh Industries, we’ve had a relationship with Marsh for over 20 years, and they are our go-to supplier for all treatment plants & pump chambers etc.

With the treatment plant dispersing into a watercourse, we had to make sure that we could get the fall by gravity, from the outlet on the treatment plant, to the watercourse. Unfortunately our survey put the outlet level at the very bottom of the watercourse, which would not have been suitable – in the event that the watercourse rises during wetter months, water from the watercourse would have flooded the treatment plant and put it beyond use until the water level went down again.

We installed an 8-person treatment plant, with the property being a 5-bed house. We were lucky enough to find the ground to be very dry, despite us being at the bottom of a hill and next to the stream. The excavation work was done on Day 1, and the treatment plant was delivered on Day 2. We concreted a base for it and installed the plant with a full concrete surround. The customer did not want to lose use of his sewerage system, and therefore we kept his old septic tank in operation for as long as we could whilst the work was being undertaken. The plant was in and concreted by the end of Day 4, after which we did the switchover and laid the pipework to the watercourse. On Day 5 the customer had his septic tank emptied one last time, after which we put it beyond use by filling it with inert material from the treatment plant excavation, and capping it off.

We instructed an electrician to commission the new plant, and as a pumped-outlet unit, it had an external blower under a green hood, for which we had to form a small concrete base. The electrician installed a feed to this concrete base, which in turn fed the blower within the hood arrangement. From here a second feed was laid into the plant, for the pumped outlet – when the level in the final chamber of the plant gets to a certain level it pumps out to the watercourse.

We installed a carbon vent for the plant, which we fixed vertically adjacent to the blower housing. With the new plant connected up and working, and the old septic tank decommissioned, we set to reinstate the areas of the garden where we had been working. The garden was being landscaped after this phase of the project, and so minimal reinstatement was required.

Our customer was kind enough to leave us a 5-star review on Google afterwards. Click here to see our Google reviews

Riverside Park, Higham Ferrers

Projects

Riverside Park, Higham Ferrers, Case Study

We were delighted to undertake these works for Higham Town Council in conjunction with North Northants Council

Objective

Our objective was to rejuvenate 400 metres of pathways that had become uneven and unsafe. The paths were put down many years ago with road plainings, and our job was to resurface with Type 1 MOT granite and granite dust

About the project

It was very important to the Council that we keep the park open for the duration of the works. The park sits between two housing estates and is used for more than just recreational use. With the weather being reasonably dry at the time, we opted to close short sections of the paths at a time, and divert people onto the grass. We put signage up and offered to assist people around our works should they require.

The paths had been laid at 1.5m wide originally, but some were down to less than a metre wide, with grass and vegetation having encroached in from both sides. Our first job was to scrape off the vegetation, and to hopefully find an existing path underneath, which hadn’t been contaminated too much. Generally the paths were okay, and in the main they just needed blinding with Type 1 MOT to smoothen out the levels.

We then applied a thin layer of 0-4mm granite dust to the paths, which we compacted in, with a ride-on roller. Lastly we laid topsoil and grass seed to either side of the paths.

There was also a small ‘bridge’ formed with railway sleepers, where a natural stream ran underneath, during wetter weather. We replaced this using oak timbers, to give it a long lifespan going forward. And on top of the timbers we fixed wire mesh, to stop them becoming slippery when wet.

It was a pleasure to carry out these works, on behalf of North Northamptonshire Council and Higham Ferrers Council, we had plenty of compliments at the end of the works, and it was great to work on this project on our doorstep and to have made such a cosmetic difference.

Re-concreting of cemetery footpaths, Irthlingborough

Projects

Re-concreting of footpaths, Case Study

Objective

To break out and remove old concrete footpaths and road within the cemetery, and to completely renew.

We were delighted to be doing this work for Irthlingborough Town Council at the cemetery, so close to where we all live. And it was a tad emotional for a lot of us, who live in Irthlingborough, and found ourselves to be surrounded by so many familiar names. The concrete paths around the cemetery and the main road were full of trip hazards and the only remedy was to take them all up and start again. We kept the cemetery open whilst we were carrying out the work, and helped people get about the cemetery where we could.

The old concrete paths were well-made, and some of them laid at about 5” or 6” thick, but our 6-tonne excavator soon broke them out and we took the waste away on our own grab lorry. We dug out the old sub-base and laid Type 1 Granite MOT on a geotextile membrane. Some of the paths were curved, so we used plastic fascia board to create the curved sides.

On the majority of the paths we used 4×2 timber to create a shutter on either side. We lifted these a bit higher than the new sub-base to leave 5” (125mm) for new concrete.

A long 150-metre stretch of the path had to be pumped with an overhead ‘boom pump’, which pumps it in from above. For the remainder of the paths we used a dumper truck to move the concrete into place. And when we concreted the road to the old chapel, the concrete lorries were able to drive down the already-prepared road. In total we poured 80 metres of RC40 concrete with fibres, a total of approx. 180 tonnes. With the paths and road concreted, we finished the sides with topsoil and grass seed.

With the job finished after a bit less than 3 weeks, we completlely opened up the cemetery to the general public. We believe the old concrete was in excess of 60 years old, and of course we hope the new concrete paths and road will last a lot longer than that!

Installation of service ducts and pipes, new build, Stagsden

Projects

Installation of service ducts and pipes, new build, Case Study

Having done the groundwork for this pair of new builds 6 months prior, we were asked to come back and lay various service pipes and ducts to each of the two plots.

Objective

To lay services for two new builds, including water pipes, electric ducts & BT ducts

We were delighted to be asked to return to this site to excavate for and lay water pipes, electric ducts and BT ducts from the boundary with the Highway, to the two new builds that we had done groundwork for previously. The groundwork was done 6 months prior and a builder had since got the two shells up and built.

We brought a couple of diggers to site, our favourite 3.7 tonne Kubota digger, and also its younger brother, the 1.5 tonne. One for digging and one for backfilling.

We laid the water pipes first, as these were deepest. Anglian Water had specified barrier pipe, due to the possible risk of the ground being contaminated. Unfortunately, water authorities used to occasionally ask for barrier pipe to be used if they suspected contaminated ground, but now it’s becoming the norm, unless you can prove your ground is not contaminated. We suggested to our customer that he send AW a ground survey that he’d had done previously, which he did. Although AW relented and said they’d allow him to use standard 32mm pipe for half of the 70m run, the other half had to be barrier pipe, due to the site having an agricultural history. Unfortunately, barrier pipe is a lot more expensive than standard MDPE pipe.

We laid these water pipes at a depth of 800mm cover (750mm is the minimum), in sand surround and with warning tape to cover. AW inspected the depths that the pipes had been laid at etc. With these laid, we put in a 125mm ribbed electric duct from the boundary with the Highway, to a location near the first plot. At this point we left an open hole for an electric joint to be done later, and from here we laid smaller 32mm black duct to the meter box on each plot. These too were laid in a sand surround, and with a different warning tape on top.

Lastly we laid a BT duct, this was a 90mm duct from the boundary with the Highway, to a position near the first plot, where we built a ‘No 4’ BT Box with pre-cast plastic sections, and finished with a frame and cover supplied by BT. From here we laid smaller 50mm ducts from this box to each plot, and these ducts were finished with warning tape as well.

A nice simple job for us, and nice and local to us as well. It was a pleasure to return to this site having done the groundwork previously. Click here to read a case study on the original groundwork project for this site.

And we were delighted to have received a 5-star Google review from our customer for this job!

Sewer connection, Golder’s Green, London

Projects

Sewer connection, Golder's Green, London, Case Study

We were approached by a private customer, who had been referred to us by another private customer, to undertake both a foul and surface water connection for an existing property.

Objective

Our objective was to make two new connections onto the public sewer, both foul and surface water and connect to an existing property. The connections were made in the centre of the road, and pipes laid back to the boundary with private property. We connected the new pipework into the existing sewerage system within private property which included us making some alterations to the existing system.

In addition, we lifted an existing paved area and re-laid all the slabs.

About the project

Our customer already had a connection into a neighbouring property, but required two connections to be made into the public sewers in the Highway instead. This included both the foul and surface water sewers. The surface water sewer was in the centre of the road, at a couple of metres deep. The foul was closer to the pavement, but was in excess of 3m deep.

We facilitated to Section 106 to Thames Water, which included us putting together a basic drainage drawing, which detailed where the pipework was within the property, and also how we planned to connect to the two sewers and by which method. For the surface water we were able to fit a saddle connection and for the foul we had to fit a junction insertion.

If you need a sewer connection doing, please contact us as early as possible, there are many reasons why the lead-time for a sewer connection can be up to a year or more. For more information click here.

Our Section 50 application to Highways included some legal suspensions of parking spaces, in order that we could clear cars in advance of the work taking place. With the site set up on day one, we brought our own 3.7 tonne mini digger to site, complete with breaker.

As is the condition with a Section 50 Licence, we were obliged to source all drawings for utilities that might be present within the area to be excavated. We also sprayed up where we expected services to be, having done a CAT scan of the area.

We sawcut and broke out for the pit in the road, where we would make the two connections.

We were lucky to have very few services in the road and located both the foul and surface water sewers on day one. Over the next couple of days we carefully excavated around both sewers, breaking concrete away from the surface water sewer, as is of the case.

We sheeted the excavation as we went, using trench sheets, acrows and timbers.

We made the connections onto both sewers and these were inspected and passed by the Thames Water Inspector. We then proceeded to excavate further and to lay pipes towards the pavement.

In the pavement we encountered a lot more services, including a cast iron pipe which we think was a water main, also a couple of electric cables, BT ducts, a small BT cable which we were lucky to avoid, and also some fairly shallow Cable TV ducts. We had to hand dig around all of these services, after which we continued to lay pipework, for foul and surface water, into private property.

In private property we had to remove and reinstall the demarcation manhole for the foul, which included turning it to face the new direction out towards the Highway. From this new demarcation manhole we laid plastic 110mm pipework to connect up to the clay pipework we’d laid up to the boundary.

For the surface water we had to lay new 110mm plastic pipework from the downpipes on the house, to a new demarcation chamber that we installed, and from here will laid pipework up to that which we’d laid to the boundary in clay.

As part of the quote to our customer, we had included to lift and relay about 20 paving slabs which were uneven, creating a trip hazard. We re-laid these on a wet sand/cement bed, and pointed up around the two demarcation manholes.

With the excavations backfilled and compacted in the Highway, we reinstated with tarmac, and in the pavement we re-laid the large slabs that were there previously. The job took us 8 days from start to finish, including the work in private property. We finished by jet washing in private property and in the Highway, removing all signage and barriers from site, and taking our plant and machinery home for a well-earned rest!

Timeline

Time to quote for the works: Less than a week

Time taken to obtain Section 106 Licence from TW: 2 weeks

Time taken to obtain Section 50 Licence from Highways: 4 weeks – included talks between us and Highways regards traffic management, suspended parking bays, and we also had a site meeting with the representative from Highways

Leadtime to use S50 Licence: 6 weeks

Time taken to do the work: 8 days

Total time: 15 weeks

Do you need a sewer connection needs doing? Click here to enquire.

Don’t leave it too late for a sewer connection, most people do! Read our article here: How long does it take to do a sewer connection?

Click here to see more of our case studies.

Remediation Work, Warwick Academy, Wellingborough

Projects

Remediation Work, Warwick Academy, Wellingboro' Case Study

It was a pleasure to carry out our first job for Lion Academy Trust, at the Warwick Academy school in Wellingborough.

Objective

Our objective was to remove an existing sub-base from an old paved area, and reinstate with topsoil and grass seed, and revert the area back to grass.

At the request of the trust, we carried out the work on our last day in work before the Christmas break, and when the children were not in attendance at the school, with safety in mind of course. We brought a digger and dumper to site and used a breaker attachment on the digger to break out the old concrete base on which slabs had been laid previously.

We removed the broken up concrete from site, using our own 8-wheel grab lorry. On the same grab lorry we brought in recycled topsoil, screened down to 20-40mm. We compacted this in layers using the digger, thankfully the weather was dry despite the time of year.

We used a total of 40 tonnes in the void, which we brought across the school field in a 3 tonne swivel dumper truck. The topsoil was finished with grass seed which we raked into the top couple of inches of topsoil.

We had quite a distance to go with the dumper truck and we did make an impression on the grass, despite it being quite dry. It could have been a lot worse though, for the time of year.

It was a pleasure to have carried out our first job for Lion Academy Trust and we look forward to working with them again in the future.

Sewer connection, Waddesdon

Projects

Sewer connection, Waddesdon, case study

We were approached by Fitzgerald Building Services to connect one new property to the public sewer, on the main road running through the picturesque town of Waddesdon in Buckinghamshire.

Objective

Our objective was to make a new connection onto the public sewer in the main road running through the town. And then to lay pipework back to the boundary where our customer had terminated his pipework and built a demarcation manhole.

About the project

On this occasion our customer already had the Section 106 approval from Thames Water which was really handy, and enabled us to go straight to Highways and apply for the Section 50 application, which we always take care of on behalf of our customer. (You cannot apply for a Section 50 before you have the Section 106)

This required us filling out the Section 50 Application Forms, supplying our accreditations, insurance documents, a traffic management plan, utilities drawings for all other services (Highways have a duty of care to ensure we know where all other utilities are before we start excavating) and various other documents. For the traffic management, we opted for 2-way traffic lights, as this was quite a busy main road.

Our S50 application was rejected initially, as the road was a HS2 diversion route at the time, and traffic lights and road closures are prohibited on HS2 diversion routes. This created a huge problem for our customer as the house was pretty much finished, and waiting for HS2 to complete in the area would have meant a delay of over a year, before he could finish the project and sell the property.

If you need a sewer connection doing, please contact us as early as possible, there are many reasons why the lead-time for a sewer connection can be up to a year or more. For more information click here.

We appealed to Highways and they eventually agreed on ‘give & take’ traffic management for this job, if we were able to keep our excavation far enough over, that we could leave 7m of road remaining outside of the works, for two lanes of traffic to be maintained. We took measurements on site, and this was indeed possible.

The Section 106 approval letter from Thames water detailed connection to the public sewer by way of Junction Insertion, which is the most common method of connection for a single house. This is simply putting a Y-Junction onto the sewer – but of course it’s not that simple with it being a live sewer! It requires us to stop the flow upstream in order that our exaction is not flooded with sewerage whilst the connection is being made. We had all manner of other utilities in our excavation where the connection was made, which is usual, including a gas main and a water main.

We knew where these were in advance as we had the utilities drawings for existing utilities, but there are always services in the Highway that are not on any drawings!

The pipework was laid from the connection point and back to the site. The majority of the pipework, for about 8 metres, was in a wide parking layby. With the connection having been made at approximately 1.4m deep, it made the pipework back to the site a bit over a metre throughout, and of course becoming shallower as we worked back to the site. The carriageway and the layby had to be backfilled and made safe before we could extend our excavation into the footpath – the road was too busy for us to ask pedestrians to cross the road and use the other footpath. In advance of reinstating the carriageway and the layby, we used a ‘footpath board’ to enable pedestrians to cross our back-filled excavation in the layby, whilst we excavated in the footpath.

As usual, we found plenty of smaller utilities in the footpath, including electric cables, BT cables and ducts, and a water service pipe, all of which we had to hand-dig underneath.

The pipework was laid up to the boundary with the private property. A demarcation manhole is always required within 1 metre of the boundary with the Highway, but this was not within our remit, and the customer had already fitted this, and left a plastic 110mm spur from the demarcation manhole to the boundary, onto which we connected our clay pipework. With all pipework complete and tested, we prepared for tarmac reinstatement. We collected base course tarmac and 10mm tarmac ourselves on our own 4-wheel grab lorry and the reinstatement was completed just over a week after we started on site.

Timeline

Time to quote for the works: Less than a week

Time taken to obtain Section 106 Licence from AW: (Our customer already had this)

Time taken to obtain Section 50 Licence from Highways: 5 weeks – included talks between us and Highways regards traffic management

Leadtime to use S50 Licence: 5 weeks

Time taken to do the work: Just over a week

Total time: 12 weeks

Do you need a sewer connection needs doing? Click here to enquire.

Don’t leave it too late for a sewer connection, most people do! Read our article here: How long does it take to do a sewer connection?

Click here to see more of our case studies.

House Extension, Towcester

Projects

Conservatory demolition and groundwork for house extension, case study

We were approached by a long term customer of ours, a builder and developer, to do the groundwork for a reasonable sized house extension in Towcester.

Objective

Our objective was to demolish the existing conservatory. Then to dig and pour footings for the new extension and do the masonry up to underside of block & beam. Then some foul and rainwater drainage, followed by installation of block & beam.

About the project

We started by removing the conservatory from site, and we removed this to a skip in our own yard, due to limited space on site. We we’re only able to get a 1.5 tonne digger in to this back garden through a narrow gap between the existing house and the standalone garage. There were a few steps here as well, so we put some plastic down on the steps and then laid type 1 MOT to form a ramp for the digger and to enable easier access for wheelbarrows back and forth. With the digger in the back garden, we started breaking out the floor of the conservatory. This came out easily enough, as it was only about 150mm thick, and not reinforced.

The footings were a bit more difficult to remove. At about a metre deep, which is a bit unusual for a conservatory, we had to break with the breaker attachment on the machine, then put the bucket on the machine and dig out what we’d broken. Then we had to put the breaker back on, then the bucket back on, and so on. We got the footing broken out in a bit over a day, and then we were ready to set out for the new footings.

The drawings asked for a 1-metre deep footing, but this is standard, and final depths were subject to the Building Inspector’s decision. There were a few small trees within 10 metres, and ordinarily any trees within 15 metres will have an effect on the footing depth, subject also to ground conditions of course. The Inspector asked for slightly deeper footings on two sides, to a depth of 1.4 metres, and then stepped back up to 1 metre on the final stretch.

We poured the footings to a depth that would enable 300mm of masonry to be laid to the underside of the beams (block & beam floor on this one). There was 8 cubic metres of concrete required in the footing, so we used a ‘line’ pump to get the concrete round the back of the house. We dug the oversite off to the required depth the next day, so that we had 250mm clearance underneath the block and beam floor.

With the masonry done, we filled the cavity to the required level, with Gen 1 concrete. Due to the available access, we had no choice but to carry the concrete beams round, one by one. These were laid within 2 days nonetheless, and the infill blocks and splits done thereafter. The floor was sealed with cement slurry, to complete the block and beam.

There was some drainage to complete for the project including foul and also rainwater from the new roof. The extension was generally for a new kitchen, so we laid new drainage from the proposed drainage points, to the existing foul manhole within the patio. We dug out for and laid underground rainwater pipes from the new downpipe positions. We had planned to dig out for and form a soakaway, but we discovered there was a dedicated surface water sewer in the Highway, and the existing rainwater pipes were connected to this system. We spoke to the Building Inspector, and he was fine for the new rainwater pipes to connect into this existing system, within the confines of the property.

With all of this work complete, we handed over to our customer, who continued with the build. It was good to carry out a small domestic job, and locally as well. A lot of our work is far from home and often on much bigger sites. Please contact us should you have a similar project you’d like help with.

Culvert/Bridge Install, Stanwick

Projects

Culvert/Bridge install, Stanwick, Case Study

We had already been asked to do the groundwork for a new build on this site, but the existing bridge was not suitable for bringing multiple lorries across, to remove hundreds of tonnes of spoil from site and bring all the materials in etc. Therefore a new bridge in the form of a culvert was proposed and designed, and we were instructed to install this.

Objective

Our objective was to demolish the existing concrete bridge with its steel supports, install the culvert sections and then form a road on top including kerbs and tarmac etc.

About the project

We decided to carry out these works in the middle of the summer, as the flow of the stream would be at its lowest, as opposed to the wetter months, when the stream was significantly faster-flowing. We started by demolishing the existing bridge, taking care not to pollute the stream with debris from the old structure. The culvert sections could have been laid on consolidated type 1 MOT, but due to the stream being live, and the volume of water being considerable even during the drier months, we decided to lay a concrete slab instead.

By laying a concrete slab, we could envelop the shuttering in plastic and divert the stream around. However we were struggling with room, as the concrete culvert sections took up more than the width of the stream, there was not much room to divert the stream around. Therefore we installed a small catchpit ‘upstream’, and from here we ‘over-pumped’ the work area to reduce the flow of the stream.

With the flow significantly reduced, we were able to excavate for and form shuttering for a concrete pad, for the culvert sections to sit on. We put a double-layer of thick dpm plastic within the shuttering, and formed a concrete slab 200mm thick, with 2 layers of reinforcing mesh to the middle. The concrete was allowed to cure for two weeks before the concrete culverts sections were scheduled to be delivered.

We looked into different ways of lifting the concrete culvert sections into place. We originally planned to have a 13-tonne ‘track machine’ on site, this would lift the sections off the lorry and onto the concrete pad. But due to trees on either side of the site entrance, some of which had protection orders on, we had to look at bringing a crane onto site. The size of crane required meant that it would have to sit in the road, and this in turn would close half of the road off for many hours. This also had implications for pedestrians as they would be passing on the pavement underneath the crane and through a live site, in effect. We spoke to Northants Highways and it was decided that we would use 2-way traffic lights to control the traffic. And that the pedestrians would be diverted into a temporary pedestrian walkway around the crane as it sat in the road.

We instructed A-Lift Crane Hire from Northampton to assist us with these works. (A few other local crane companies told us this job couldn’t be done!) We had to co-ordinate the crane hire, the delivery of the culvert sections, and the traffic lights, and all other deliveries, all to happen on the same day. The crane lift was particularly difficult due a combination of various overhead BT cables and also the many trees that surrounded the front of the site, it was very tight as the 7-tonne culvert sections were lowered down amongst all these overhead obstacles! We decided on a strong sand and cement mix to bed the culvert sections onto, on top of the pre-formed concrete. There were only 3 culvert sections to go onto the concrete base, but at 7 tonnes each, we didn’t want to be lifting them on and off our screed too many times, so we spent a lot of time getting the screed exactly right, on top of the concrete slab.

The culvert sections interlocked where they met, and we had to seal them at this point as well, with bitumen and with thick flexible bitumen strips as well.

Looking down the culvert sections either side, we laid a double sand-bag wall 450mm thick, to retain the fill between the long edges of the culvert sections. We used 6F2 for the fill, which we compacted in layers with a heavy duty trench wacker, as the road above was to go on top of all this construction.

Before we could form the road on top of the new culvert, we had to lay services across to the proposed new build. These included electric, BT & Water. With these in, we brought type 1 in to form the sub-base of the new road. We laid kerbs either side to retain the tarmac and then laid 150mm of 20mm base course tarmac, to enable heavy traffic across the culvert/bridge for the duration of the build. The tarmac will be topped later on at the very end of the build, with a 6mm top coat.

Our last job was to lay oak sleepers at each end of the culvert, purely for cosmetic reasons. We finished these works just in time, as the wetter weather set in towards the end of September and the flow increased significantly. It was a pleasure to carry out this very exciting and challenging job for our customer, and from here we were ready to make a start on the groundwork for the new build. Case study coming soon for this.

Author: JWC

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