Type of building work
This involves construction of a 4-storey flatted factory (with no basement) located
between two existing single-storey terrace houses which were founded on small diameter
bored piles.
What went wrong
Timber planks were used to support a 2m deep excavation to construct a pilecap adjacent
to an existing single-storey house. The ground condition was poor, comprising of soft
marine clay and the timber planks to support the excavation was shoddily done.
Figure 1: Shoddy timber planks to support excavation for
pile cap
The timber planks were not effective in resisting the earth pressure and gave way,
resulting in movement of the marine clay beneath the adjacent house. The ground
movement cracked the small diameter bored pile supporting the adjacent house causing
the entire front section of the adjacent house to collapse.
Figure 2: Cracking and collapse of adjacent single-storey house .
Learning points
a) Every construction project, whether big or small should be given due attention.
b) Properly designed temporary earth-retaining structures should be provided to
protect the sides of the excavation, even for shallow excavation. The design
should take into consideration the effects of inclement weather and presence of
foundation of existing buildings.
c) Extra precautionary measures should be taken when working close to existing
building.
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