Site Name: Monkton Farleigh Ammunition Depot - Farleigh Down Tunnel
Sub Brit site October 1985, March 1988 & February 2005
Monkton Farleigh ammunition depot utilised an old stone quarry below a plateau some 450 feet above the valley floor in which ran the main line railway that was its principal source of supply. Before the depot could be commissioned, an efficient means was need to bring in ammunition from the railway at Farleigh Down Sidings. The sidings were just over a mile from the depot as the crow flies but more than four miles by road along steep and tortuous country lanes.
In November 1937 the Great Western Railway were contracted to lay the sidings and build a 1000 foot long raised loading platform complete with a narrow gauge track to carry the ammunition wagons. Outline plans had already been prepared to drive a mile long tunnel from the heart of the workings terminating in an underground sorting yard built beneath the sidings in the valley below.
The tunnel to the railway sidings at Shockerwick was a key feature of Monkton Farleigh mine, offering a secure route, invisible to aerial reconnaissance. The tunnel terminated at a loading platform thirty feet below ground level at a right angle to the main-line platform. The design was finalized in December, 1938, and by the end of the following year the upper terminus was completed. Boring the one-and-a-quarter-mile-long tunnel was a specialist task completed under contract by the Cementation Company. The tunnel runs from quarry floor level near Main West to the underground loading platform near the main line railway at a constant gradient of 1:81/2. Deep tunneling was required for the top half of the route whilst the lower half is at or just below ground level and was constructed by the `cut and cover' method. A depth of 180 feet was reached near the edge of the Farleigh Down escarpment.
The loading platform and transit shed at the top of the slope shaft up from the tunnel in March 1988
Photo by Nick Catford
Work on the entire length of the tunnel started simultaneously and to facilitate this, two deep shafts were sunk at 800 foot intervals. A further shallow opening was made just below the Kingsdown Road from which point a broad trench was opened out across the fields in preparation for construction of the `cut and cover' section.
Drilling equipment and headgear was erected at the site of the two deep shafts from where tunneling continued until the summer of 1940. Waste from the top shaft was carried by rail across the village road and dumped in the old quarries. Waste from the other shaft in Ashley Woods was distributed among the trees where the dense overgrowth provided adequate camouflage.
At some points, depending upon the undulation of the land, the box
was completely buried, but for much of its length it was hardly below
ground at all and had to be disguised by forming a gently sloping earth
bank over it.
Photo:The underground sorting yard in October 1985
Photo by Nick Catford
By May, 1941, almost half of the length was completed and the floor and side walls of the remainder were in place, as were the main walls of the underground sorting yard.
In November, 1941, engineers from Richard Sutcliffe Ltd started assembling
the tunnel conveyors, completing the task by the following April. Because
of the heavy load carried against the gradient when, on receipt, it
was necessary to use two separate units running in tandem and linked
by gravity rollers.
Unloading 155mm propellant charges at Farleigh Down in the autumn of 1943
The upper conveyor was 2,171 feet long and the lower one 2,372 feet. Although the majority of the belts in the depot were twenty-six inches wide running at seventy-five feet per minute, those specified for the tunnel were heavy-duty type, using thirty-inch belts running at 350 feet per minute. Initially Sutcliffe's suggested the best results would be obtained by spacing the belt support rollers at eighteen inch intervals throughout the length of the conveyor, but in practice this spacing caused certain types of ammunition boxes to bounce uncontrollably and fall off. Eventually it was found that the most satisfactory results were obtained by using a regular progression of roller spacing, from nine inches to three feet and back again, along the whole length of the belt. The tendency to bounce was further reduced by increasing the tension on the belt to three and a half times that for which the machine was designed, and by reducing the speed from 350 feet to 250 feet per minute. It was expected that these alterations would put an excessive load on the existing gearboxes and this proved to be the case. Within nine months the teeth of the large spur gears were worn wafer thin and the main drive shafts had collapsed twice in quick succession, putting the tunnel out of action for several days.
For further information and pictures of Farleigh Down Tunnel click here