374 REPORT—1883. 
forward ready to recommence operations. The radial arms of the bore- 
head are fitted with cutters, or discs of chilled cast iron, which are trun- 
cated cones, and which, as they wear, can be slightly turned round, thus 
exposing a fresh cutting edge without so frequently incurring the delay 
of replacing the cutters. The bore-head is driven by a pair of compressed 
air engines, having cylinders 12 inches in diameter and 18 inches stroke, 
and running at from 80 to 100 revolutions per minute. The compressed 
air is supplied at a pressure of 35 to 40 lbs. per square inch by compressors 
at the surface, driven by. portable engines. This machinery cuts the 
sandstone rock cleanly and accurately to a diameter of 7 feet, delivering 
in small pieces. The greatest progress hitherto made has been about five 
yards in twenty-four hours, and twenty-four lineal yards in a week of six 
working days, and the machine has now driven a total of 260 yards of 
heading. The rock thus cut is found to yield much less water than when 
explosives are used, so that it has not been necessary to line this portion 
of the heading. Only seven men are required to work and tend the 
machine, which is fitted with an endless strap and buckets to deliver the 
débris into tubs at the tail. The chief difficulties encountered have been 
the keeping of the machine in true line and level, the dust caused in the 
drier parts of the rock, and the foggy atmosphere resulting from the use 
of compressed air, together with certain defects in detail, which are 
gradually being remedied. Simultaneously with the drainage headings 
the main tunnel has been driven forward. The excavation has been 
throughout in sandstone rock, the roof being generally excellent, and 
requiring but little support. The rock is very solid and homogeneous, 
but varies considerably in the quantity of water it yields, thin layers of a 
white colour being more porous than the rest. The rock under the river 
on the Liverpool side is remarkably dry. The faces under the river are 
carried forward by means of a bottom heading, which is first driven by 
hand in the usual manner, and from this ‘break-ups’ are made to the 
full size of the tunnel—not more than 12 feet lineal of excavation are 
allowed to be exposed at one time, the brickwork following on as closely 
as possible. The excavation under the river is 304 feet wide by 274 feet 
high, and is lined with brickwork in cement 2 feet 3 inches thick; the 
internal finished dimensions of the tunnel are 26 feet wide and 23 feet 
high, recesses for platelayers being placed at intervals. The two inner 
rings of brick are of Staffordshire blue, the remaining rings of Burnley 
or other approved red brick, the filling of broken stone or bricks, the 
whole set in cement, mixed in the proportion of one of cement to two of 
sharp sand or gravel. Landwards the lining of the tunnel is reduced in 
thickness to 1 foot 6 inches, and then to 1 foot 2 inches. In order to 
leave the main shafts clear for pumping purposes the drainage heading 
is now connected with the main tunnel on the Liverpool side by a staple 
shaft 9 feet in diameter and 25 feet deep, and a similar connection is 
being made on the Birkenhead side. The underground stations at 
James Street, Liverpool, and Hamilton Square, Birkenhead, are excavated 
in the solid rock, which is then lined with brickwork, and are 400 feet 
long and 50 feet wide by 30 feet high from the rails. These will be 
lighted by electricity and approached by hydraulic lifts. For the purpose 
of keeping the works clear of water, extensive pumping plant has been 
erected at Woodside, Birkenhead, and St. George’s Dock, Liverpool, and 
this has proved most efficient. Owing to the depth of water (90 feet) 
in the river Mersey, and the high levels of the towns on either side, 
