The Great Wall – Part 2

We made an initial assessment of the Great Wall in our previous post on the subject. We have now had time to look at the proposal in a bit more detail and this post presents more of our analysis.

Height Profile and Distribution

The structure we describe varies in height along its length and also switches between being an embankment, a viaduct and a cutting. EWR Co. are picking statistics about The Great Wall which may make it seem smaller than it actually is. For example, some of it is at ground level (not much, but some). As it is not one continuous type of structure, the length of each individual section of embankment, viaduct or cutting obviously has a limited length. But one thing is clear: the length of the entire structure from Cambourne North Station to Hauxton junction is 17.4km. As you enter a cutting from an embankment, yes there will be a point where the level difference between the track and the local ground level is zero.

We prefer to present the data in a form that makes it easier to understand.

Figure 2 shows the height above local ground level in metres versus the distance along the track or “chainage” starting at EWRCo.’s proposed Cambourne North Station and ending at their proposed Hauxton Junction. The height is above 4m for 12 km out of the 17.4km from Cambourne north to Hauxton Junction. But the line is particularly high near houses in Highfields Caldecote, Little Eversden, Harlton, the two approaches to Haslingfield and wrapped around the south and east of Harston. 

Figure 3 shows the distribution of heights of the structure above local ground level. Specifically, it shows the length of track above a threshold level. For example, looking at figure 3, there would be just over 6km above a height of 8m.

Leaving out any overhead line equipment, trains are around 4m high. So, with a 4m high embankment or viaduct, it would be possible to see the top of a train above the 8m rooftop of a 2-storey house. 

Embankment Cross Section

CBRR have produced a cross-section of what a 10-metre high embankment would look like (see Figure 4).

The tracks are on a 10m wide platform. To reduce noise impact, we would expect acoustic barriers on either side of the track.  If we are lucky enough to get an electrified line then the Overhead Line Equipment (OLE) would be on top. Remember also that in most of this section the trains will be travelling at up to 100 mph.

Either side there would be slopes, usually at an incline of 1:3, making the width of a 10m high embankment 70m. These slopes would be too steep to be returned to farming. There would be security fences on either side of the embankment and culverts every so often to allow the passage of wildlife and people. 

Consider the school children making their way to Comberton Village College from The Eversdens. Will they divert and cycle down the busy A603? Will they pass through a 70m culvert on dark December afternoons? Will they get through the security fence and cross the tracks? There could be similar issues for young children from Newton to Harston primary school or from Harlton to Haslingfield primary school if there is no safe way to get across the Great Wall.

Much of the route will be on clay and a significant foundation will be necessary with piles beneath it to reduce settlement as shown in Figure 4. Consider the carbon emissions required to make these large structures and carry in the material to do so. The material from the destruction of Chapel and Money hills will not be enough.

Land Take

We have estimated that the total area of land required in this 17.4km section, taking viaducts to be just 10m wide and embankments and cuttings with 1:3 slopes. The width of the embankments can be calculated from their height profile and a 3m width allowance for security fences on either side. The result is an estimated 206.3 acres of land taken by this structure excluding any construction or maintenance roads on either side.

It would be interesting to get an estimate of the weight of material that would need to be transported to make these embankments.

As previously explained the farmland to the south of Cambridge is particularly important for food security when climate change induced sea level rises are considered. The author of that article has estimated that 44.5 acres of his land near Harlton will either be directly lost or become unfarmable – and that is just one farm. The effective land take is likely to be much-much higher than 206 acres. This is farmland that has been cultivated for generation after generation.

Before you reach the conclusion that it would be the same to the north – please consider the trench railway technology proposed by CBRR for the fen-crossing section of their proposal and their proposal is low in the landscape all the way from Cambourne North station into Cambridge.

Viaducts

We can get an idea of what a modern railway viaduct will look like from the recently constructed Hitchin Flyover (See figure 5). But bear in mind this is only 5m high and single track.

Composite Photograph of Highfields Caldecote

An Impression of the Environmental Impact

This post has so far focussed on the facts about the proposed Great Wall. We shared something about how we feel about it here and here.

Local residents Anna and Tom have prepared a video entitled “Muted By Covid” which shows part of the section of the proposed route between Harlton and Haslingfield on the ground.