April_1966 — Page 69

CIVIL ENGINEERING AND PUBLIC WORKS

TANKER TERMINAL FACILITIES

for Esso Hong Kong

LATE in 1964 Esso Standard Oil

(Hong Kong)

Ltd. announced that they were embarking on a re- entry programme into Hong Kong and at the same time stated that they had entered into a contract with

China Light & Power Co. Ltd. for the provision of fuel oil as from January 1, 1966.

The re-entry programme consists of establishing a tanker terminal at Nga Ying Chau, which lies off the north east coast of Tsing Yi Island, and the provision of bulk depots both on the mainland at Tsuen Wan and Hong Kong Island at North Point, quite apart from initiating marketing opera- tions. Products will be first received at Nga Ying Chau and then either barged across to Tsuen Wan and North Point for marketing or trans- ferred direct to the Hok Un power station.

From a tanker handling point of view the site is advantageous Tsuen Wan is generally accepted to be a well sheltered anchorage and, ex- cept for areas of the channel north of Tsing Yi Island, there is deep water all the way up through the East Lam- ma Channel and to the west of Tsing Yi Island.

One of the principal features of this project has been the speed with which it has had to be carried out. Key dates were as follows: Consultants first briefed

October, 1964. Reclamation contract commenced

on site

January, 1965. First tank foundation completed

May, 1965. Reclamation and tank foundations

substantially complete

September, 1965. Work begun on marine facilities

August, 1965. Pier and dolphins substantially

complete (except for stressing and catwalks) December, 1965.

Ground Investigation

Nga Ying Chau is a small island which rises to about ninety feet above sea level at its highest point. A visual

Far East Architect & Builder April, 1966

by K.A. Phillips and W. T. Yuen

of Scott & Wilson, Kirkpatrick and Partners

This article is based on a En- paper presented to the gineering Society of Hong Kong by Mr. K. A. Phillips, DIC, AMICE, MASCE, and Mr. W. T. Yuen, BSc(Eng.), AMICE, AMIStructE, of Scott & Wilson, Kirkpatrick and Partners. It describes the de- sign and construction of the principal civil engineering works carried out at Nga Ying Chau, a small island opposite Tsuen Wan, to provide a tanker ter- minal for Esso Standard Oil (Hong Kong) Ltd. This terminal will accommodate tankers of up to 65,000 d.w.t.

examination of the site suggested that it is rocky and granitic and has little overlying decomposed rock, particu- larly at the north end.

South of the site, it was apparent that the rock type changes and that there is relatively deep decomposition giving rise to a red soil which is plas- tic and, in fact, supports a small brick- making industry.

A ground investigation was carried out by Gammon (Hong Kong) Ltd. under direction of the consultants during November, 1964. A total of 23 marine borings were put down and three holes were drilled on land.

Off shore, where the pier is sited. sandy mud overlies rock which is gen- erally only covered with a thin man- tle of fully decomposed rock.

Within the area reclaimed around the island conditions vary. Along the line of the northern sea wall the sub- soil is generally decomposed granite. overlain by a thin deposit of sand or silty sand whereas the northern length of the eastern sea wall is in shallow water and crosses a reef of rock or partially decomposed rock whilst along the southern length of this wall the subsoil generally consists of de- composed granite overlain by grey mud to a depth of 20 to 25 ft.

Reclamation

The aim was to balance, cut and fill. The drill holes suggested that the excavation would be mostly rock but in our experience the soil profile of the local decomposed rocks is some-

what unpredictable, particularly in an area such as this where it is known that the geology is complex. There- fore we made what we thought would be a slight overestimate of bulking and allowed in the contract for extra fill to be brought in from an area outside the site, if necessary, under an earth permit.

Fortunately the balance was re- markably good. Very little spoil had to be brought in and most of this was for the surface of the reclamation which was specified to be free of rock.

The reclamation and sea wall cons- truction were carried out as follows: (i) All mud was dredged from under the sea wall and reclamation in the south east corner of the site. (ii) Reclamation was formed by end tipping from the shore whilst selecting materials to ensure that rock, both graded and quarry run, was used for the seaward protection. In the south east corner it was originally planned that the sea wall construction should be independent of the re- clamation to ensure that mud was excluded. As it happened the rate of reclamation was very fast and at this stage excavated ma- terial was almost entirely rock and therefore the same proce- dure was used as for the rest of the site.

(iii) The sea wall proper (Fig. 1) con-

sisted of a filter to retain the soil followed by a substantial core of quarry run rock which could be varied, above a minimum width. to suit the quantity of rock ob- tained in the excavation and faced with a graded rock which might or might not be obtainable from the site.

The grading for the facing rock was as follows: "sizes of individual pieces of rock are to be evenly grad- ed from a minimum of 5 cwt, to a maximum of 1 ton with at least 50 per cent, larger than 10 cwt.”

The size of facing rock was based on Hudson's modification of Iribar- ren's formula for which an effective

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