Perhaps the most remarkable of all the mines where the twin mines at Petit Bois or S.P.13, each with 30,000 lbs of ammonal with blastine chambered at the end of an 1,800-foot-long gallery, the second longest. The shaft was sunk 500 yards behind the British lines in the shelter of the ruins of Vandamme Farm in late 1915 by 250 Tunnelling Company. The shaft went down 58 feet with a gallery driven to 55 feet before it was decided to go deeper still and by the end of January 1916 the shaft was sunk to a depth of 97 feet with 25 feet of gallery driven towards the objective of the Petit Bois salient in the German lines.
The original 55-foot gallery was converted into a pump chamber. By the end of February 1916, a second shaft had been sunk to a depth of 88 feet. An air compressor and electric light plant were installed on the surface, while underground a chamber was created for the installation of a mechanical excavator.
Stanley Heading Machine
Norton-Griffiths paid a visit to then Captain Cecil Cropper who remembers that Norton-Griffiths showed great interest in the work going on at S.P.13. He [Norton-Griffiths] arranged for experts to come over from London to inspect the blue clay and for a tunnelling machine, similar to those used in the cutting of the London underground tube tunnels, to be designed and sent over.
Cropper recalled that: ‘Our great worry was that the enemy would hear the exhaust from the compressor on still clear nights and begin to shell us out of our position. We drove the tunnel out with a ‘head shield’ before the breakdown ocurred. We couldn’t go on because the clay swelled so fast it seized the machine. This condition put an end to all our hopes of ever reaching our objective within a reasonable time and the scheme had to be abandoned.’
The machine was a Stanley Heading machine weighing seven tonnes and designed for use in coal mines to drive the roads and headings underground. It ran on rails and had flanged wheels not unlike a locomotive and was powered by compressed air which was fed via pipes from a two-cylinder engine which was located in a dugout near the shaft. It began work on March 4, 1916, at 11pm, cutting the clay with two rotating blades which cut a circular tunnel 2.4 metres in diameter with the machine held in place by jacks which were tightened against the roof. The jacks were slackened to allow the machine to move forward each time a ring was cut. A team of tunnellers followed up behind and installed an interlocking oak lining.
The ‘bugger’ element was that the machine did not like the Flanders clay and it also had the habit of digging in a downward motion ‘diving’ rather than going straight ahead.
Each time they stopped the machine to move it forward or for maintenance the blue clay, which was constantly swelling, gripped the colossus and held it in place with a vice like grip. Despite this the tunnellers persevered until after driving the gallery some thirty six metres their patience gave out and they abandoned the machine. Today, it is still where it was left, some 36 metres down, and directly beneath the road that runs past Vandamme Farm.
The main gallery from shaft No.1 was making good progress with the clay kickers moving this forward advancing at a rate of 30 to 35metres (100 to 150 feet) per week. They encountered pressure from the blue clay swelling which caused the props to splinter. This was overcome by spacing the props at 1 metre (2 feet) centres and allowing the clay to easy between to relieve the strain. The enemy also caused a delay when their shelling hit the compressor house.
Disaster strikes
The drive continued and at 457 metres (1,500 feet) it passed under the German front line and 10 metres (30 feet) further on the tunnellers created a ‘Y’ with a further delay caused by a breakdown in the electric light system and by the amount of spoil coming back from the two tunnels. Worse was to come at 6.30am on the morning of 10 June 1916 when the Germans fired two heavy mines at the shoulder of their salient. The northern most crater from these explosions was directly above the gallery for S.P. 13 and was completely destroyed for a distance of 365 metres (1,200 feet) worse, the collapse had trapped twelve men working at the face in the undamaged area of gallery.
A rescue was immediately started to dig around the collapse and reach the trapped men. They worked day and night in continuous shifts digging at the rate of 12 metres (40 feet) per day however, the tunnel collapse was 76 metres (250 feet) and it took them six and a half days to reach the face. They expected to find all the men dead and had already dug graves for them. They did indeed find eleven men dead and the twelfth was assumed to be buried under the debris. The eleven dead men are buried at Kemmel Chateau Cemetery. They are: Sergeant H. B. Lambert, Corporal A. Graham and 9 sappers : Kelly R, William Henry, W Vowies, James Henry, G. Quayle, W. Thomas, G. Grant, Adam Wright and Joseph Wood.
They left the gallery to allow the air to clear and to their utter amazement when they returned to the gallery, they noticed movement in the dim light and a voice saying ‘For God’s sake give me a drink! It’s been a damned long shift!’
This was Sapper William Bedson. He explained that after the explosion the other eleven men had gone to the broken end of the gallery were a tiny amount of air was coming through an air pipe and they had attempted to dig themselves out. The next day they gave had given up and spaced themselves out along the gallery and by 8pm on the third day all eleven were dead. Bedson, an experienced coal miner had survived by lying down by the face, which was a little higher. He knew that a party of coal miners had been rescued after thirteen days trapped underground. He had two Army biscuits and a water bottle. From time to time he took a drink from the bottle and then rinsed round his mouth and returned it to the bottle. He did not eat the biscuits. To keep himself warm he made a suit from sandbags and every night he slept on a bed bogie truck with sandbags placed onto top and he remembered to wind up his watch before going to sleep.
After his rescue Bedson was taken by stretcher down a communication trench and he and the bearer party had a narrow escape from shell fire. He had already been wounded in 1914 on the same front, then wounded again at Gallipoli. On recovering from this latest experience he had volunteered to return to his unit however, he was posted to a Base Depot.
The Mines are completed
After a great deal of repairs the right branch of the ‘Y’ was advanced to 570 metres (1,874 feet) and a chambered with a charge of 41,150 lbs of ammonal made ready. At 540 metres (1,800 feet) the left branch was chambered and charged with 32,850 lbs of ammonal and tamped back to the ‘Y’ branch. For a few days in August 1916 the Germans fired three mines in the area of S.P.13 and the charges were heavy enough to break the leads to the mines outside of the tamping, and the main gallery was damaged necessitating repairs to be carried out. No further enemy activity took place in the area.
Crownholes
The physical evidence of collapse are crownholes, these are a subcircular depression caused by the failure of the supporting timbers beneath. The collapse forms a bell shaped chamber above the point of failure and the roof gradually collapses until the final crownhole appears on the surface.
Crownholes are very common in the Salient and we all drive, walk or cycle past them on our battlefield tours. Those most at risk are the farmers. You may notice many fields that could be growing crops have been left as pastureland this is because to drive over them too often with a tractor is to invite disaster.
