July_1965 — Page 39

CIVIL ENGINEERING & PUBLIC WORKS

decomposed rock for the dam); an eight-cylinder Paxman diesel engine developing 1,150 h.p. at 1,000 r.p.m.; a 280 p.s.i. air compressor for starting the diesel engine; two 410 kW DC generators; and one 535 kW AC al- ternator,

The trolley travels at a constant speed of 10 ft. per second, so a con- stant speed 250 kW AC motor is used for driving the cable drum. Dia- meter of the cable is 2 in.

The opening and closing cables for the grab are also used in the lower- ing and lifting operation. Diameter of these cables is 1 in. The opening and lifting operations are each pow- ered by a 290 kW variable speed DC motor.

When lowering, the kinetic energy is dissipated by reversing the motor and using it as a generator, the power thus generated being converted into heat by a 400 kW resistance which is fan cooled.

Automatic Operation

The control cabin is placed above the hull, between the two trolley booms, which are 30 ft. apart. Two operators sit side by side before iden- tical three-lever control panels.

For automatic control there are two built-in operations dredging and placing. The operator can pre- select: (a) the distance at which the trolley is to be stopped: (b) the depth at which the bucket is to be stopped. In addition to the preselection pos- sible with automatic control, trolley movement is also controlled automa- tically.

Auxiliary equipment on the pon- toon includes: a fresh water circuit: sea water for cooling: 100 p.s.i. air compressor; four fans for the engine room: two hydraulic winches for moving the barge; one winch for gen- eral use; two hoists; lighting: and ac- commodation and services for 32 people.

The Biarritz cost about HK$10 mil- lion to construct and equip. Her es- timated output is 500,000 cu.yd. a month.

It is most unlikely that the Biarritz

Far East Architect & Builder July, 1965

will be put to work on other dredging jobs when she has completed her task in Hong Kong.

This is due to the fact that the in- stallation was designed specially for the work at the Plover Cove where suction methods could not be employ- ed.

However, this does not mean that

The Biarritz

the Biarritz will be thrown on the scrap-heap as soon as the job is fin- ished. For the craft has been so con- structed that the forward part of the trolley tracks can be removed, an operation which converts the Biarritz into a sheerlegs with a double hoist- ing device. Such a craft is always in demand in every part of the globe.

FIRST PLOVER COVE TUNNEL DRIVEN

BREAKTHROUGH on the first of eight tunnelling operations on the Plover Cove scheme took place at an official ceremony last month. The ceremony was conducted from the Chung Mei portal of the two-and-a-half mile long tunnel leading to Nam Chung, which will carry water from the Nam Chung area into Plover Cove.

'The tunnel is part of Stage II of the scheme, and has been built by the Sentab Gammon consortium. The firm is a joint enterprise between Hongkong's Gammon (H.K.) Ltd. and the Swedish firm Sentab.

Work began a year ago. It proceeded at a record rate and was never halted for more than a few hours. The tunnel is 4.200 yd. long and 12 ft. high.

re-

An interesting aspect of the work was the use of cement spraying equipment, which placed the usual steel The ribbing support. spraying proved much faster, and highly effi cient, allowing rapid resumption of work after blasting even when the tunnel roof was unstable.

The tunnel drops 30 ft. from the Nam

Chung end, and will be further lined with

concrete before water flows through. Intake structures and a 280 ft. shaft at the Nam Chung end of the tunnel have also to be con- structed.

Mr. N. Ellstrom, contract manager for Sentab Gammon, said at the ceremony that the maximum rate of

reached 78 tunnelling

yards per week, a record for Hong Kong. The greatest distance covered in a month was 900 ft. and this rate was nearly reached on several other occasions.

Guests inspect scene of breakthrough