9
ON
WEDNESDAY, OCTOBER 12, 1977
SLIPPAGE OF DECOMPOSED GRANITE CAUSED
EARTH SUBSIDENCE IN NATHAN ROAD *****
THE EARTH SUBSIDENCE, WHICH OCCURRED LAST MONTH UNDER NATHAN ROAD NEAR ITS JUNCTION WITH ARRAN STREET, WAS CAUSED BY THE SLIPPAGE OF A COMPLETELY DECOMPOSED GRANITE SEAM EXPOSED DURING ROCK TUNNELLING OPERATIONS FOR THE MASS TRANS IT RAILWAY, THE DIRECTOR OF PUBLIC WORKS, THE HON. DAVID MCDONALD, SAID TODAY.
IN ANSWER TO A QUESTION BY DR. THE HON. HENRY HU IN THE LEGISLATIVE COUNCIL, HE SAID THE SEAM WAS FIRST EXPOSED IN THE TUNNEL ON SEPTEMBER 1.
AS A RESULT, MR. MCDONALD SAID, PROBES WERE CARRIED OUT TO TRY TO ASSESS THE EXTENT OF THE SEAM AND THE EXPOSED FACE WAS SAND-BAGGED AND SHORED TO SECURE IT UNTIL THE PERMANENT LINING WORKS COULD BE CARRIED OUT.
+THE FORM OF PROTECTIVE MEASURES ADOPTED WAS CONSIDERED TO GIVE ADEQUATE SECURITY BY BOTH THE CONTRACTOR AND THE MASS TRANS IT RAILWAY CORPORATION'S SUPERVISORY STAFF, HE ADDED.
+CONTRARY TO THE CONCLUSIONS DRAWN FROM THE INVESTIGATIONS EVENTS PROVED THAT THE EXTENT OF THE COMPLETELY DECOMPOSED GRANITE SEAM WAS GREATER THAN ESTIMATED AND IN CONSEQUENCE THE PROTECTIVE MEASURES FAILED TO GIVE ADEQUATE SUPPORT.+
MR. MCDONALD SAID THAT AFTER THE COLLAPSE THE AREA IN NATHAN ROAD WAS CORDONED OFF AND THE BUILDINGS ON THE CORNERS OF THE ROAD JUNCTION WERE EVACUATED AS A PRECAUTIONARY MEASURE.
GROUTING WAS CARRIED OUT TO PREVENT FURTHER MOVEMENT OF THE COMPLETELY DECOMPOSED GRANITE. THE TENANTS OF THE EVACUATED BUILDINGS WERE THEN ALLOWED TO RETURN TO THEIR PROPERTIES.
+AS A RESULT OF THIS EXPERIENCE THE CORPORATION HAVE ESTABLISHED REVISED METHODS OF WORKING WHICH WILL ENSURE A GREATER DEGREE OF INVESTIGATIVE PROBING AND HAVE ADOPTED MORE CAUTIOUS METHODS OF DEALING WITH COMPLETELY DECOMPOSED GRANITE SEAMS NO MATTER HOW SMALL OR INSIGNIFICANT THEY APPEAR TO BE, HE SAID.
/10
Page 10Page 11