No_2_August_1963 — Page 93

MANDARIN HOTEL

This meant that a decision as to the method of piling to be used had to be made based on a very

limited preliminary site investigation of the sub-strata as only five test bores could be made before demolition of the old building.

Geographically this area of Hong Kong consists almost entirely of granite in various stages of decom- position. The test bores indicated that below the original sea bed there was a stratum of decomposed granite of a fairly uniform nature and that the top of the un-decomposed bed rock was approximately 90 to 100 feet below ground level.

At this stage the approximate final load of the building had to be estimated, for the purpose of a decision on methods of piling, on the sketch plans of the building. On the basis of information then avail- able the clients were faced with a choice between having a building of 27 storeys (the maximum permis- sible under the local ordinances con. trolling the volume/site ratio) with a piling system which transferred the load of the building direct to the strata of bedrock or, alternatively, a building of perhaps two storeys less (64 bedrooms in the terms of a hotel) on conventional piling found- ed in the layer of hard decomposed granite.

CHATER

ROAD

The decision reached was to build to the full permissible height, using the "Hochstrasser" system of 4-foot diameter piles carried down to bed- rock.

cut-

Basically this system consists of driving a 4-foot diameter steel tube with a carborundum-toothed ting edge down to and into the bed. rock strata. When this point was reached a diamond-drill test bore was made to ensure that the next 20 feet was bed rock and not merely a a further layer of rock overlying layer of softer material.

This, with the first few piles. proved completely satisfactory. Un- fortunately subsequent piles encoun-

SERVICE LIFTS

RUBBLE MOUND

EXCAVATED

PASSENGER LIFTS

MEZZANINE FLOOR

SHEET PILING:

OLD SEA WALL

PLAN *

20

SCALE IN FEET

RUBBLE

MOUND

STREET

HOUSE

ICE