Waterlogging on Construction Sites – 22/11/2012Leave a Comment
This year is the worst I have experienced in all my career of landscaping.
It has,as always been aggravated on sites where Contract Managers, Area Managers and Site Managers see the building of a structure through to it’s high spec finish. Then draw a sigh of relief “job done”. But is ” job done” the ambiance of a magnificent building? Can it then be destroyed 6 months or a year later by a lack lustre, struggling, waterlogged landscape?
Bits of light kit to break up pan, as used on our compact tractor and mini digger.
But of course, we do use heavy gear as needed. Mick George is always quick off the mark and has often been on-site for us within 24 hours with a D8 and multi tyned ripper.
The only trees that had to be replaced, on the whole park, were Jugalans Rega, as you can see, they have been replaced by the water tolerant Alnus near the main building, originally a well drained area, but, a temporary bund had stopped the drainage, the Jugalans Rega (Walnut) started to die, not liking its feet in the waterlogged ground.
All the other planting on rest of park was earth sculpture mounds which of course drained.
When I came out of a pre-contractural meeting my heart sank. Damien Debski the Halcrow consultant Chief Engineer said this project will be different to any project you have ever had, then you said one problem after another will occur.
I looked across the potential park we had taken ownership of, it was waterlogged as far as the eye could see.
The extensive earth sculpture mounds, of pure subsoil, were heavily compacted on the famous Gunpowder Park at Enfield, due to wet conditions at the construction phase.
We double dug these areas with a 20 ton 360 digger, to a metre deep, to de-compact them. We then turned Bio Gram (heat treated sewage sludge) in, with a heavy duty land reclamation spading machine to 400 mm. We then got top results planting trees and shrubs straight into the sub soil by putting fungus mycorrhizings in the soil to assist with the establishment of the soil population.
Gunpowder Park – After:
Above is a view of the park to the left of the main gate.
Some areas were left unseeded and ended up like this.
Above is a seeded wildflower area, much of the park was seeded by a Emorsgate’s Seeds, Lea Valley Park indiginous mix.
I was introduced to HRH the Duke of Edinburgh by my client David Thompson of LDA – the landscape architect for Gunpowder Park (David is standing next to me in the last photo). None of us knew it at the time but David was to go on to be a big player in the design process of the Olympic site just down the road from Gunpowder Park.
If you scroll down, the first thing you will see is the Gun Cotton Grinding Wheels.
Because of the precise procedures required to safely produce armaments, strict health and safety systems were written and this was the beginning of ISO9000.
Continue to scroll down to see the original gates to the site and various stages of seeding and planting throughout the project.
Our very resourceful agricultural team of Ray and Russel were having trouble with equipment being smashed. They worked 24/7, cut up an articulated lorry and used it as a levelling bar to help with final preparation.
Read on for symptoms, cures and case studies re Compaction and Water-logging (especially on construction sites that is in most cases so easily avoided at the onset).
The symptoms of anaerobic and waterlogged damage are many. The effects can be brought on by waterlogging caused mainly by no attention to ripping through the site pan prior to the spreading of top soil. A little bit of preparation before top soiling takes hardily any time. Of course, the normal checking for cables and drains etc. prior to ripping is essential. What can happen if these normal good husbandry techniques are not catered for?
When it has a nice open structure, preferably with some humus in the soil, it is then populated by aerobic bacteria and other microbial fungus type organisms, often pertinent to the development and well being of certain plants. Plus worms and the plethora of other creatures flourish working the soil, keeping it well and truly open and alive. When it is waterlogged, it is only populated by anaerobic souring bacteria. It then becomes dead and inert: inhospitable to most life and plants. What are the symptoms? Often very much the same as drought. Some plants die, with others having yellow leaves and droop.
Root balled, semi mature trees, struggle when the bottom of the root ball is waterlogged, killing all the lower roots. The few roots near the top of the ground, that are left, struggle to serve the tree in drought. To test anaerobic inert soil, dig out a spit or two. There will be a sour rotten smell and often, a short way down, the profile of the soil will be mottled and lacking any noticeable form of life.
The effect on turfed rear gardens that have to be installed at certain dates to co-incide with clients moving into a property:
These often have to be turfed in less than ideal conditions on building sites. If the subsoil has been scraped out evenly and drainage is good, as well as there being a good depth of topsoil, there will only be slight shrinkage across the whole area and the garden will keep its level as it dries out.
However, if the topsoil has been intermittently spread across undulating, non-ripped, compacted undersoil the chances are, as the top soil settles, the garden will follow the underlying contours and swales and hollows will appear.
2. If the topsoil has been taken up without care and includes chunks of subsoil, it is sometimes up to 2 years later (if there is an exceptional dry period) that undulations may appear, as the different types settle.
3. Cambridge clays, but mainly Milton Keynes type soilers are the landscaper’s original nightmare! When Milton Keynes’ soil is put into a topsoil pile slightly wet, I have seen it come out in lumps; some as big as footballs, that get tipped in rear gardens on sites, blinded over with finer soil that looks great but store up problems because, as the years go by the topsoil migrates into the hollows below. We can all do our best to make it work, but, with the best will in the world, if it suddenly becomes very dry, 6 months later or so, the chances are that Customer Services get a call stating ‘Our garden has hollows, dips and subsidence etc.’
Some case history on how Giles Landscapes started getting main landscaping projects by trouble shooting on waterlogged sites….
1. A LARGE SUPERMAKRET OUT IN NORFOLK, ON VERY FINE SANDY LAND.
I visited the site and met the project manager.
I told him I had local knowledge of the soil conditions, having just planted up the adjacent motorway on the same type of soil.
I was sent away with a flea in my ear. I got the same when I rang the developer. I was told ‘we have a top class landscape architect running the project, your outfit does not have the credentials we need’. I did not agree with him, but left my card with the developer and the project manager. However, we did did not get invited to price for the project.
About a year later, Author Amos, a landscape architect who specialized in pulling problematic sites round, had been retained by the developer for the sole purpose of getting their client to accept a failing planting scheme and to get their project signed off.
The original project was £250,000 for the landscaping scheme. The building project had run over its deadline, the weather was diabolical and wet. Three sides of the building were heavily landscaped with trees, shrubs and ornamentals. This area co-incided with the Tempery Hall Road, so that most of the materials were carted round the building. The deadline for the store to open was fast approaching, the developer pushed the top soil in (probably not paying much attention to the drainage and ripping), the heavens opened; the plants went in badly, as landscapers struggled to meet the dates of opening the store. The very wet site then suffered from a heat wave. The fine black sandy soil set like concrete, the plants started to droop and die. Bark mulch was added, containing a high percentage of fines. The plants appeared to be drying out, but the fines compounded the problem, not letting the soil breath. Auther Amos, the trouble shooting Landscape Architect, had been given our card as a landscape company with local knowledge. Another consultant had been originally called in by the developer to give their opinion, which was “apparently”, that the top soil had been originally stored in larger piles for a period of time, thus becoming inert; losing it’s soil population. Thus the cure was, rip everything! Bring in new topsoil and replant. This new scheme was priced at £250,000 to rip it all out, dispose of the waste, plus bring in new soil, then, possibly another £250,000 making it half a million. Plus, it was bandied about that the store would want compensation for the disruption, bringing the rescue project to about £1 million”.
As you can imagine, the developer did not like this whatsoever, so chose Author Amos to lead our team into battle. First of all, I went round with Auther, he stuck his little probe in everywhere and it was all stinking rotten! The plan was devised as follows;
1. A Terra lift machine was brought in. This banged a hefty charge of air into the ground about a metre down, cracking fissures in the sub arrears. If I remember, each charge was inserted every 15 metres, filling the fissures with graduals to keep them open.
2. The fine bark mulch was scraped into rows, to let the ground breath.
3. A breaking bar was used down, to about 400 t0 450 mm, to further heave the ground. The rest of the gaps between the plants was heaved with heavy fork dissipating with a bit of bark back into the ground. Well before we had finished, the improvement became apparent. The Store Manager got a smile back on his face and even invited the lads to lunch in the store canteen.
The final operation was to replace the dead plants and trees. This was easy, as most of them amazingly recovered once the ground was opened up and aerated. The cost from us to the client was £45,000 on top of whatever Author Amos charged them. The bonus to us was, it gave our struggling little outfit credibility. The Store Manager moved on, but if we needed references for new clients, he would sing our praises when they rang.
We were then awarded a couple of similar schemes putting us right on track.
The 2 projects gave us over £400,000 of work.
On one of these projects, we knew exactly what to do, it was so simple. We had noted a few acres of sloping sandy land had been used by main developer, who built a bypass by a market town, to store all the heavy plant and machinery. When this was top soiled and planted by the original landscapers, the under pan was just as good as a pond liner. Consequently, every time it rained a black stinking mess ran over the pavement across the road to the horde of hoteliers opposite! Once the soil pan was cracked, it drained easily. Under the pan, a metal spike could be pushed in by hand into well drained soil. Why do only people from farming back grounds understand how to rectify these so simple and unnecessary problems?
Just as the last recession was finishing, we looked after about 15 sites for a NATIONAL BUILDER. This builder had stored up quite a few problems and the NHBC were on his back. Waterlogging occurs mainly were there are rows of houses which have attracted a bit of compaction from machinery hauling equipment along the back of sites. Some builders and developers when they finish sites, spread topsoil on top of the compaction, then fence the site. Then the landscaper comes in who rotavates, levels and turfs the gardens in a dry times and often it can look good. However, we then get the wet season and every house owner is onto the builder’s Customer Services that the garden appear to be waterlogged!
Despite being paid by the builder to put in land drains to all the gardens, it was a miserable job. I became frustrated and had a row with a few site agents; trying to convince them to do somthing about compaction and finished up meeting the main contracts manager at head office and after an insalubrious meeting, we parted company.
To cut a long story short, we were back working for the company again after a couple of years.
The contracts manager & I shook hands, both apologised to each other; agreeing we had been pointlessly arrogant.
It tuned out that he had engaged a couple of farm boys as site managers who undestood soil, we then developed a team with build area managers, sales area managers, public open space technical managers and customer service staff. We put on PowerPoint presentations at site manager level on soil and compaction, we worked as a great team then for 15 years helping to give the builder presentations with his show houses and public open spaces forging links with councils etc.
If you scrowl right down on our Awards page, the sites run by the farm boys won a few NHBC awards.
This year, we all know there will be complaints about waterlogging. Even when site conditions are well drained and perfect.
All this jargon I have preached about is because, I would hope to encourage developers to put in their specifications a tick box for site managers to check; mot, tempory base has been removed, site has been leveled and tyne riped prior to spreading topsoil.
I now see the original customer service man we used to work with, he is a poacher turned game keeper inspector for NHBC.