Sunday, 19 August 2018

On Soft Ground

Building paths is no different to building motorways, it's just the order of magnitude which is different.

Motorway building attempts to be as economic as possible (relatively speaking) and this is very apparent when we consider the use of materials. Excavation, transportation and especially disposal. The motorway builders try and use as much "site won" material as possible in order to keep costs down. Topsoil is stripped to be reused for landscaping, subsoil of a useful quality is reused as bulk fill and any aggregates are used to make concrete and asphalt.

One problem which is often faced by engineers is dealing with ground with poor bearing capacity; that is ground which cannot cope with holding up the mass of road being built, let alone the traffic it's being built to carry. It would be economically viable to keep digging until decent ground is found as it could be many metres down and so some sort of improvement to the bearing capacity is required.

Even a humble path can find itself being built on poor ground and so rather than just spending the minimum knowing full well it's going to move and settle leading to cracking and a poor surface, there are some bits of technology out there which can help.

Some years ago now, I was involved in the construction of a couple of 'rural' paths. One was along a boggy old bridleway and one was through some woods. In both cases, the subsoil was pretty soft clay and especially through the woodland, we couldn't dig too deep for fear of damaging tree roots. Our way to provide a stable base was to use geotextile membranes and a cellular containment system.

The photograph above shows the boggy old bridleway which was pretty much impassible in the winter. Under the thin layer of topsoil was soft yellow clay. Even just building a path to take horse and human traffic would have taken some pretty hefty construction.

The first job was to roll out our geotextile membrane - essentially a synthetic cloth. In this case, we chose a non-woven version for superior performance. It's doing two jobs - first, it will stop the granular foundation to the path mixing into the clay below and it resists getting holed by stones below. On some parts of the path we didn't even bother clearing the topsoil as we wanted to raise the path out of the ground for better drainage.

With the geotextile installed and a thin layer of granular material installed and rolled (above) to provide a working platform (recycled concrete in this case) it was time for the next clever material to be installed, the cellular confinement system.

The system is essentially a plastic mesh which comes in rolls.  When the product is stretched out (above) it forms a grid of 'cells' into which granular material is placed and compacted. Notice the holes in the sides of each cell - they are there to allow sharp points from the granular material to lock into place. This particular version is made by Geoweb and was 75mm thick (i.e. the depth of the material when stretched out).

The way in which the granular material interacts with the cells means the thickness of material used can be far less than a conventional design. It's also helpful as the layer as a whole acts like a raft which can make it more forgiving over the odd soft spot. As can be seen on the section being tested above, you can run heavy kit over the system without a problem.

For this scheme, the client would not allow an asphalt surface and instead we had to use a self-binding gravel because it was considered to be more in keeping with the rural nature of the path. In my view, this was a mistake because self binding gravel requires a great deal of aftercare from a maintenance point of view to keep the edges weed-free and the surface compacted (especially with horse riding). However, nothing would have stopped us laying an asphalt surface - it wouldn't have need any edging or kerbs either.

As suggested above, the system can be used near trees as shown in the photograph above. Again, the client wanted a self-binding gravel surface and you can see how we picked a route through the woodland.

Sunday, 12 August 2018

Ramps and Steps

Inclusive design is about more than just giving people options, it's about enabling people to take the same options as everyone else. How we deal with changes in level is perhaps one area which shows this off in sharp relief.

It is a certainty that we'll have to design for level changes because the world isn't flat However, they way in which we deal with those changes can make all the difference. Consider this example from Great Yarmouth;

There's nothing revolutionary or flash about the layout and one can even ask why there are steps at all. However, some people do prefer to use steps and so having a ramp and steps next to each would allow a group of people to broadly stay together as they change level and so in my book, this is a pretty inclusive layout.

The photograph above is a ramp and step combination which I saw recently in Manchester. It works hard to fit into limited space and again (as far as possible) allows a group of people to keep together whether they use steps or ramp.

Ramps do need a heck of a lot of space and the greater the change in level, the greater the length of ramp needed. In the UK, it's something of a tragic design classic that we end up building bridges and underpasses with twisting ramps to fit them into as smaller space as possible like this dystopian mess of an example from the many footbridges crossing the High Speed 1 railway.

This sort of outcome is often because the desire line isn't considered. Bridges like this will often have the desire line for people placed perpendicularly to the obstruction to be crossed and unless space is provided either side to simply lift and drop the desire line, we get convolution. In terms of inclusive design, this bridge is nothing like the elegant solution of the Yarmouth example as people cannot cross as a group. 

Compare the HS1 bridge with this bridge in Cambridge which doesn't bother with steps, as the gentle ramp allows people to pass in groups whether as pedestrian or cyclist

Much of the design thought depends on the context of course. Whilst we can have surface level pedestrian (and cycle) crossings over busy high speed roads, we don't provide them in the UK in general unless they are associated with a junction. Bridges require a greater change in level to get the lorry headroom, whereas underpasses for people require less, even if designed for people riding horses. In this photograph, the Dutch ably show how to get a cycle track under a road;

Crossing rivers will depend on whether or not they are navigable or what is needed in terms of coping with flood events. Railways need certain headroom for the trains (obviously) and whether or not they have overhead power cables.

The key to much of this goes back to the simple provision of infrastructure which follows the desire lines for those people for whom the use of energy to move is the most critical. Get it right and the experience will be better for everyone.

Saturday, 4 August 2018

300th Blog Post: So Where Next?

Rather astonishingly, this is my 300th post to this blog which I started in November 2012 and what a journey I have been on (goodness knows how many words I have written).

In my very first post, I asked the question "what do we really want" in response to the various articles in the CIHT's Transpro magazine for the month. I also made the following comment;

What this single month's magazine shows me is that the UK really doesn't seem to want to get a grip on running its highways properly and doesn't do long-term planning.

It's now the middle of 2018 and I am not sure that as a country, we have changed (well apart from the continuing fallout from *that* referendum). We still want to predict and provide for motorways under the guise of being nationally significant projects, whereas local active travel is stupendously patchy and often reliant on budgets which wouldn't even buy a modest motorway junction - Highways England is currently running at a £2.9bn overspend, a sum which could transform dozens of towns and cities.

We have expensive and often unreliable railways, a big push to move car fuelling from the petrol station to our streets with EV charging and endless studies and reviews whenever we're dealing with local transport and especially active travel.

My most popular post is from 2013 and it was heartening to see that it was Kerb Your Enthusiasm, which has remained my top post for a long time. It's great that people are interested in perhaps the most ordinary element in our streets toolkit because in fact, they are extremely powerful in how they shape space, safety and accessibility. The post actually inspired me to write an entire design guide as part of developing my fledgling micro-consultancy, City Infinity. By the way, The Joy of Kerbs is available for free.

This blog has hit over half-a-million views and I like to think this is more about people being interested in how our highways are designed and managed, rather than my writing skills. Certainly I have been humbled when people have told me they have used my posts as either campaigning tools or as reference materials when they have been undertaking design work. I have even seen my photos appear in consultants' documents when they are trying to get a point or cross. I don't always get the credit, but I am glad the message is spreading.

So, where next? I don't know if blogging is going out of fashion because I am seeing fewer posts from other people I have followed for a long time, but I continue to find writing enjoyable and so I'll carry on for now. I set myself a crazy target of a post a week and while I have ideas, it'll continue. If there is a subject you think I should cover or if there is a problem you want looked at, then please let me know.

It just remains for me to say thank you for reading and let's continue with these adventures in time and space in the strange universe of highways and transport!

Saturday, 28 July 2018

Ride London Freecycle: We Were Lucky With The Weather Edition

So today saw the annual Ride London Freecycle event in central London with it's 8 miles of roads open to cycle traffic and as with previous years, there were some slight tweaks to the route and I thought it was better - the earlier start at 9am was also good.

Anyway, aside from the usual observation about how hostile most of London is for the other 364 days a year, it's nice to let the photos of people having fun speak for themselves. I bring you Ride London Freecycle: We Were Lucky With The Weather Edition (mainly because it was raining for my journey to the start!)