[Railway reconstruction Italy 1943-1946 published by Royal Engineers, 1946]
DESCRIPTIVE ACCOUNT OF RAILWAY CONSTRUCTION ACTIVITIES
Railway Construction considered in relation to the ultimate Railway system
9. - Line 217/8 - Pisa-Pistoia-Prato..
A drawing illustrating the bridge repairs carried out on this line is included at Plate Nº. 31.
This line formed a second class connection between the West Coast Route, Line 50 at Pisa and the Main Inland Route, Line 65. Leaving Pisa, it shares Line 50 for two kilometres to cross the River Arno by a five span steel bridge before turning North-East. Travelling North-East, North and East, the line pursues a tortuous course along the Northern fringe of the Arno plain. At one place it passes through a gap in a spur projecting from the hills to the North, and at another place just before reaching Pistoia it passes under another spur by means of the Serravalle Tunnel. At Pistoia, it joins the line Florence-Pistoia-Bologna, known as the « Porrettana ». At Prato it joins Line 65. The greater part of the line runs across flat low lying country. Bridges tend to be small but very numerous. In Winter, the countryside becomes waterlogged and in many cases flooded and access to bridge sites is very difficult. The line is single track, steam operated from Pisa to Pistoia and from Pistoia to Prato it is double track, electrically operated.
Demolitions on the line were heavy. 38 bridges out of a total of 49 bridges of span of 5 metres or greater were demolished, including all large bridges. 2 tunnels out of a total of 3 tunnels on the line were demolished. Out of the whole 84 kilometres length of route of this line, every rail had been demolished by cutting at the centre with an explosive charge.
Reconstruction of the line was carried out by R.C.E. 1212 with the following units under command:
|10||Railway Construction Company, R.E.|
|159||Railway Construction Company, R.E.|
|160||Railway Construction Company, R.E.|
|45||Mech. Equip. (Tn.) Platoon, R.E.|
|2||Railway Bridging Section, R.E.|
|29||Railway Survey Company, R.E.|
|(H.Q. and two Sections only).|
Concluding stages of the work on the Serravalle Tunnel were carried out by 61 Tunnelling Company, S.A.E.C., under command of R.C.E., S.A.E.C.
Signal and Telegraph work on the line was carried out by 104 Construction Section, R.Sigs., under command of 3 Railway Telegraph Company, R.Sigs.
The reconstruction of the line commenced on 14 October 1944. The section from Pisa to railhead at Montecatini was opened out on 7 January 1945. The Section from Prato to Pistoia was opened on 28 February 1945 and the final obstacle to through running, the Serravalle Tunnel, was cleared for traffic on 10 May 1945.
Two reconstruction works on this line merit special attention:
a) Bridge over River Arno at Pisa.
The reconstruction of this bridge was carried out by 10 Railway Construction Company, R.E. Work commenced on 17 October 1944 and the bridge was opened for traffic on 31 December 1944.
The original construction of this bridge had consisted of a five span steel through girder bridge. All the spans were of equal size and were 71 ft. 11 ins. centre to centre of piers. The steel span had all been demolished by the enemy beyond all hope of salvage and the piers and abutments had been demolished down to about 25 feet below rail level. The stumps of the piers and abutments were sound.
The level to which the piers and abutments had been demolished was approximately the mean Winter water level of the river and some interruption to the initial stages of the work was caused by the river rising in flood. The piers were brought up in concrete, clear of normal flood level, and were then completed in two bay by one bay light steel trestling. The superstructure was composed of three 75 ft. and two 70 ft. U.C.R.B. Deck spans.
b) Serravalle Tunnel.
This tunnel proved to be one of the most difficult to repair of those which have been encountered in the Italian campaign. Preliminary reconnaissance revealed demolitions at each portal completely closing the tunnel. The overburden at the West end appeared to consist principally of solid rock of considerable depth. At the Eastern end the overburden was shallow and consisted of waterlogged earth. The total length of the tunnel was 4,328 feet.
There thus appeared every hope that entry into the tunnel would be rapidly made by the use of normal earthwork plant, operating from outside the demolitions. The waterlogged nature of the earth at the East portal favoured the use of draglines and these were put to work. At the West portal, the overburden rose sharply from the portal and the only possible method of clearance was by Face Shovel Excavator working on the track formation and discharging to dumpers.
Excavation of the East portal demolitions was carried out as planned. On entry to the tunnel being made, it was found that there was a considerable quantity of water in the tunnel and that furthermore there was an internal demolition about halfway through the tunnel which was causing complete blockage.
Figure 81. - Line 218. Serravalle Tunnel, East portal during clearance of demolition. Mechanical Equipment work was by 45 Mech. Equip. (Tn.) Platoon, R.E. Other works were commenced on 24 November 1944 by 160 Rly Constr. Coy., R.E. and completed by 61 Tunnelling Coy., S.A.E.C., under job Nº. 218/47 On 15 June 1945.
Meanwhile, clearance operations had been proceeding at the West portal with somewhat disappointing results. The rock overburden at this point, which had appeared to be sound and stable, was found to be intersected with numerous clay lined fissures. This rock, shaken by the shock of the demolition and continually soaked by the Winter rains, absorbed water into these fissures resulting in softening of the clay lining and consequent instability. As excavation of the foot of the slope proceeded, so did sections of the face above, being undercut, flake off and fall to the bottom. As the rock face was a very high one, this process severely retarded progress.
Figure 82. - Line 218. Serravalle Tunnel, West portal showing laminated nature of the rock and the complete submersion of the portal. This work also, came under Job. Nº. 218/47.
At a meeting on the ground on 31 January 1945, the whole position was reconsidered in the light of the information available. Two main factors influenced this consideration. First. The newly discovered demolition in the middle of the tunnel. Second. The lack of progress in clearing the demolitions at the West portal by ordinary excavating methods. It was decided that, if the tunnel were to be opened in time to give support to the impending Army operations in the Spring, the method of attack would have to be changed. The only method which promised to be effective was that of driving through both demolitions by pure tunnelling methods. As the only tunnelling personnel available to Tn. were in the South African Group, the whole of the work was taken over by R.C.E., S.A.E.C. Accordingly, 61 Tunnelling Company, S.A.E.C., moved to the tunnel on 10 February.
Owing to the wet nature of the ground at the East portal, the open cut at that point, which had been made in clearance of the demolition, gave signs of collapsing. A buttress support similar to that used at the South portal of the Appennine Tunnel, but formed of single members of Light Steel Trestling, was therefore built across the cutting, sufficiently wide to clear the outside width of tunnel lining to be rebuilt. By excavating below this framing and driving austerity sleepers down in the form of vertical spiling the original invert and foundations were exposed and the new lining rebuilt. The original cross-section for the side walls was retained, but the new arch was made semicircular and with a flatter curve in view of the side pressures which were being exerted. As side walls were carried to springing height, inside thrust members of L.S.U.S. Trestling were placed between the walls to prevent movement. These were left in position until the full section of the tunnel had been built and back-loaded, by filling in the cutting. 333 feet of new tunnel and a new portal were built in this way, using 550,000 bricks. By 24 April, the whole of this section, with new tracks and drain, was completed.
In order to work on all available faces, a vertical vent shaft which pierced the tunnel midway between the central and West portal demolitions was brought into operation. A heavy diesel driven winch and headgear, assembled from Light Steel Trestling, was installed at the top of the shaft. A cage running on wire rope guides was installed in this shaft and regular mine system of working started inside the tunnel. The shaft was elliptical in cross section with diameter 10 feet by 6 feet. The cage was large enough to carry one Hudson mine car of four persons.
Work on both faces of the blockage in the centre of the tunnel indicated immediately that any hope of a domed roof inside the demolition could not be entertained. The tunnelling method of timbered sets with spiling and face boarding was instituted and carried through running mud and boulders as a heading which holed on 4 April. Concrete lining of the arch with concrete haunch beams and precast ribs followed face advance. Removal of the bench and rebuilding of walls followed and was expedited by sinking intermediate excavations below the beam and pouring 8 foot lengths of wall at 8 ft intervals along the whole of the length of bench to be removed. Disposal of muck from both faces presented difficulties in the fact that access was bottle-necked respectively by the East portal reconstruction and the limited capacity of the shaft which also handled spoil from the West inside face. 170 feet of tunnel opened up and rebuilt at this point entailed the placing of 660 cubic yards of concrete and the tramming of 7,500 tons of muck. This work was completed with new drain in the invert and tracks on 7 May 1945.
Up to the time when it was decided to start tunnelling operations, clearance at the West portal had been carried out by working a 5/8 yard face shovel in the cutting, loading into 10 yard Athey wagons. By this means, approximately 50 feet of cutting had been opened up, one side of which consisted of a smooth face of Argillite strata dipping at an angle of 60º into the tunnel. This face reached a height of about l00 feet above track level, and as work progressed the lower portion started to bulge dangerously as the outer 4 feet thick slab started to slide down into the cutting. It was obvious that if this movement was not arrested, the amount of muck to be cleared would ultimately reach a figure of at least 60,000 cubic yards and the delay would probably run into months. A steel flying buttress was therefore built across the cutting at tunnel roof height, consisting of 4 storeys of L.S.U.S. Trestle members, over a distance of some 40 feet. Tunnelling methods were then started under this cover through the «slabby» rock formation, loosened up by demolition and subsidence.
Shortly after this work had started and sections of concrete lining had been advanced into the tunnel it was found that creep of the hillside was exerting pressure on the new concrete before if had set and at least 30 feet of arch was seriously fragmented. The remedy in this occasion was achieved by drilling several hundred holes into the rock face above the buttress structure and blasting this down as a loose mass on top of the buttress. This effectively relieved the pressure and allowed the normal timbered heading method to be followed and the factured lining to be removed and rebuilt.
Simultaneously with the above works, a 100 ft winze at 23° down, was sunk from the side of the hill to intersect the tunnel at the centre of the break. This holed into a short domed cavity from which two additional heading faces were worked. The fourth face was worked from inside the tunnel by access through the elliptical shaft. These four faces presented the utmost difficulty, as tunnelling had to be carried through a zone of caved slabs of argillite, striking almost parallel to the tunnel and dipping at 60° into it.
After completion of the heading, work on removal of the bench and rebuilding the walls was again carried out from the four faces and intermediate excavations. This was made more difficult due to the presence of tangled steel wreckage of rolling stock which had been blown up in the demolition zones: 346 feet of tunnel, (involving the placing of 1,450 cubic yards of concrete and tramming of 11,000 tons of muck), was rebuilt at this point.
On several occasions during the opening of this tunnel, men were trapped inside cavities by caving of roof structures and although injuries were high, no fatal accidents occured. The Italian Military Labour, under the leadership of the mining personnel, worked extremely well under what were appallingly dangerous conditions. Over 160 cases of injury, involving absence from work, were recorded in the drive to put this tunnel through.
The tunnel was opened on 10 May 1945.
[Railway reconstruction Italy 1943-1946 published by Royal Engineers, 1946]