MANDARIN HOTEL
tered large boulders of undecompos- ed rock at levels 40 to 60 feet below ground. Test hores indicated strata of relatively soft decomposed rock below these boulders.
This meant that these areas of un- décomposed rock would either have to be broken up by heavy chisel or drilled through in order to found the piles on satisfactory material. This was. in fact, done with one or two piles. but it became obvious that the delay thus involved might result in a serious loss in revenue in terms of the opening date of the hotel.
By this time, however, the detail. ed design of the superstructure of the building had advanced to a stage where the total weight was known. and by various methods (described later in this article) it had been found possible to reduce the weight of the building, without reducing its height, to a point where it would just be possible to carry the load of the building on a more convention- al system of piling carried down to the hard decomposed granite strata.
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SERVICE
with the maximum density of piling permissible under the local engineer- ing code (i.e. minimum spacing of piles at 3.14 times the diameter of the piles).
was
The alternative system proposed 20-inch diameter "Colcrete" piles, driven to an average depth of 60 feet.
This system was adopted, pile tests were entirely satisfactory and in spite of the bold decision to change horses in midstream the piling con-
tract was
completed within a few weeks of the original contractual date. A total of 1,085 of these piles was driven on the site, which is 178-feet by 160 feet. Over these has been cast a raft of reinforced concrete 7 feet 6 inches thick which forms a combined mass pile capping and basement floor slab.
In addition to these piling pro- blems, common to every
architect and site engineer who has to work on the Hong Kong water front, one particular and unusual problem was encountered. This was due to the fact that one side of the site coincid- ed with a rubble mound which had
PASSENGER LIFTS
OPEN ARE A
PODIUM
TYPICAL FLOOR PLAN
SCALE IN *ELT
been the foundation of an old sea- wall along one edge of an early re- clamation.
This rubble mound had sea water running in and out of it with the rise and fall of the tide, acting as a "French drain." This mound had to be removed so that the piling could penetrate. This required the use of temporary coffer dams and the obstructions had to be removed by divers using water jets to loosen the boulders.
Bottom of the basement slab ex- cavation was 10 feet below high tide, but fortunately site investigation re- vealed an impervious layer of clay some 35 feet below ground level, so that by driving steel sheet piling 40 feet long around the perimeter of the site the excavation could be done in fairly favourable conditions and only a small amount of pumping was required.
In a building of this sort, where the upper
floors consist of several small units (the bedrooms) and the lower floors contain large public rooms. the conventional beam and column construction requires exceed. ingly large columns and beams in the lower floors in order to take the wind stress.
It was decided to take this wind stress in the upper floors by means of cross walls. which would also serve as partitions between bed- rooms. This particular feature made the superstructure both light and economical.
The cross walls, coupled with flat slabs. eliminated all beams and the maximum thickness of cross
wall was 7 inches at the lowest bedroom floor (ie. at the 5th floor).
At the fourth floor level (i.e. be- low the bedrooms) all wind stresses from the upper section are trans- ferred by means of a floor 3-feet 6- inches thick and girders 14-feet deep and 4-feet wide to a heavy central core running down to the basement.
By this means the wind load was separated from the other loads and the columns in the lower floors had to take only the vertical loads of the building and could therefore be reduced to a minimum size.
Introduction of this 3-feet 6-inch floor also permitted a much wider spacing of the columns for the low- er floors containing the public rooms and, since there were no wind mo
THE HONG KONG & FAR EAST BUILDER-VOLUME 18, NUMBER 2