CO129-572-3 Jubilee Reservoir- Shing Mun- defect in Pineapple Pass Dam. For extracted photographs see CN 3-48.... 1-12-1937 - 15-6-1938 — Page 23

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draw-off pipe passing through the concrete diaphragm at level 529 or about 15 ft. below the ground level at that

point.

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(8) This draw-off was abandoned, the pipe being cut off on the upstream side of the corewall and plugged with

concrete. The corewall was built solid and the pipe on

the downstream side removed for a distance of about 12 ft.

from the corewall, the mouth of the pipe being provided

with 1" mesh screen, this portion of the trench being

refilled with broken stone.

bulk of the leakage water.

(9)

This pipe now conveys the

The surface of the sand wedge which has been

exposed at a pit near the draw off pipe has sunk 1.3 ft.

and the sand contains fine particles which might pass through

the screen having 1" me sh.

POSSIBLE CAUSE OF MOVEMENT

The movement of rockfill referred to under

paragraph (4), and the sinking of the sand in the wedge

referred to in paragraph (9), could be explained by assuming that the following events had taken place:

(a)

(b)

(c)

The formation of a horizontal crack in the corewall

allowing water to escape over considerable length

of the wall.

The escape of fine particles of sand through the

old draw-off pipe referred to under paragraph (8),

forming a longitudinal cavity by the arching of

the sand above the plane of leakage.

This would have the effect of altering the equal

distribution of load, throwing an extra stress on

the upper portion of the rockfill thus accounting

for the movement which had taken place.

The only fact which can be adduced against hypothesis (b) is that the water appears to be flowing