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April, 1962

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The sinking of the new 1,600 ft. Crown shaft of the N.C.B.’s Westoe Colliery at South Shields has recently been completed. A high rate of progress was maintained in difficult ground by the contractors, Foraky Ltd. of Nottingham, who were also responsible for excavating the associated skip pockets and ventilation insets.

During all the excavation work loading was carried out by Eimco Model 622 crawler-mounted rocker shovels. The fact that they could be used in the shaft as well as in the skip pockets and ventilation insets was an important consideration in deciding on the loading technique to be adopted.

Sinking of the new shaft was begun in August 1959, and was completed in December 1961. The Crown shaft will become the sole coal-winding shaft of Westoe Colliery, leaving the older Westoe shaft for manriding, materials and stone winding.

Reorganisation of Westoe Colliery will enable vast undersea reserves of coal to be exploited. By 1966 the colliery is expected to produce more than 1,000,000 tons of saleable coal annually. Deep sea boreholes also carried out by Foraky Limited from the N.C.B. Boring Tower have proved the existence of offshore coal seams sufficient to supply the colliery for many years.

The National Coal Board completed more than 7,000 yards of tunnelling in 1960 to link up with the new shaft, which has a finished diameter of 24ft. and is concrete lined throughout. The ultimate depth to the sump is 1,606 ft.

Sinking began 55.5 ft. above Ordnance datum in brown clay and a large fan drift was constructed just below the surface; rock was encountered at about 30 ft. above Ordnance datum. The majority of the strata passed through as sinking proceeded was shale and hard grey sandstone.

In the early stages the rate of progress was curtailed by the presence of water-bearing strata which necessitated pre-cementation, and by old workings which called for special support.

Drilling and mucking out cycle

Six Ingersoll Rand J38 and J50 drills with 6 ft. Uddia steels were used simultaneously to drill shot holes. All compressed-air equipment was fed from a 100 psi service range in the shaft. Each drilling and blasting cycle required on average 96 shot holes, charged with a total of 262 lb. of powder, and parallel mains firing with half-second delay detonators was employed. The drilling and firing stage took between 2½ and 3 hours, producing an average of 200 cu. yd. of spoil in the 26 ft. 6 in. diameter excavation.

Spoil was lifted in 3 cu. yd. hoppits and the rate of progress was limited by the speed of the single winding engine employed, particularly in the final stages of the work. At the 1,400 ft. level the hoppit was filled at the bottom two minutes before the return of the empty hoppit from the surface.

At the surface, hoppits were tipped by lazy chain into 6 cu. yd. dumpers and the spoil used to reclaim a large hollow of waste ground close to the shaft.

Mucking was carried out by a compressed-air operated Eimco model 622 rocker shovel. Two Eimco shovels were available, and were used in rotation. During the construction of skip pockets one shovel was used in the pocket, while the other worked on the shaft floor.

The manoeuvrability and high output of the Eimco rocker shovel and the precision with which the shovel can excavate a particular area of spoil helped considerably to reduce the mucking cycle time. Mucking out process in the 26 ft. 6 in. diameter section of the shaft took approximately eight hours.

The shovels proved most reliable and few mechanical failures occurred, although the machines were in use throughout a full 20 shift week.

Skip pockets

Excavation of skip pockets and ventilation insets was carried out as sinking proceeded. Two double skip pockets and two ventilation insets were completed in reinforced concrete between the surface and 1,400 ft.

The construction of one double skip pocket was completed in a record time of 11 weeks. A total of 3,738 cu. yds. of rock was excavated and 1,721 cu. yds. of concrete, 80 tons of steel beams and reinforcement, and 13,000 sq. ft. of weldmesh were put in place.

Another outstanding achievement was a shaft progress of 62 ft. at the 600 ft. level in four days

Concreting

Concrete for lining the shaft was batched and mixed on the surface. It was carried by conveyor belt to a 6 in diameter pipe running down the shaft. A baffle at the end of the pipe checked the rate of descent. No segregation and no failures were experienced, and an average figure of two inches on slump test was obtained for the lining. Weldmesh was secured to the shaft wall with roof bolts as sinking proceeded and a maximum of 70-80 ft. was excavated before lining.

Minimum wall thickness is 15 in. but this was increased to 3 ft. in water bearing strata, and as much as 6 ft. at certain points in bad ground.

Water bearing strata

Water bearing strata presented difficulties and high rates of water inflow were experienced between 150 and 450 ft., and precementation was adpoted. This was required to halt a water inflow of up to 1,000 g.p.m.

For the first length of advance cementation at 155 ft., a 4 ft. thick mass concrete plug was poured in the base of the shaft. Twenty-six holes of a total length of 1,850 ft. were drilled, and 32 tons of cement injected. The success of the pre-cementation process has been such that at 1,400 ft. the total water inflow was less than 1½ gallons per minute. This may be contrasted with the inflow which caused flooding to such a degree that the Eimco loader was operated with a ‘ snorkel ‘ fitted to the exhaust to prevent flooding of the air motors.

Drawings and Photographs accompanying the article