WEDNESDAY, JULY 22, 1987
MARBLE IN THE YUEN LONG AREA
THE GEOTECHNICAL CONTROL OFFICE HAS RECENTLY CONFIRMED THE EXISTENCE OF MARBLE BEDROCK IN THE NORTHWEST NEW TERRITORIES AS
PART OF ITS NEW GEOLOGICAL MAPPING PROGRAMME OF THE TERRITORY.
THE MARBLE OCCURS IN ISOLATED PATCHES BENEATH AN APPROXIMATELY TWO KILOMETRE WIDE STRIP OF LAND FROM NORTH OF SHENZHEN TO JUST NORTH OF TUEN MUN. IT IS PARTICULARLY PREVALENT IN THE YUEN LONG AREA AND FORMS PART OF WHAT GEOLOGISTS CALL THE YUEN LONG FORMATION, WHICH IS OF CARBONIFEROU AGE (ABOUT 250 MILLION YEARS OLD).
NO MARBLE CAN BE SEEN AT THE GROUND SURFACE BECAUSE IT IS COMPLETELY COVERED BY A THICK LAYER OF ALLUVIAL SOIL. ITS EXACT LOCATIONS ARE THEREFORE UNKNOWN, AND INFORMATION AS ΤΟ WHERE IT EXISTS HAS ONLY BEEN FORTHCOMING FROM BOREHOLES DRILLED THROUGH THE ALLUVIUM INTO THE ROCK FOR THE DESIGN OF BUILDING FOUNDATIONS AND GROUNDWATER EXTRACTION WELLS.
PRINCIPAL GOVERNMENT GEOTECHNICAL ENGINEER, DR E.W. BRAND, SAID THE MARBLE HAD POSED PROBLEMS FOR SOME BUILDING WORKS IN THE YUEN LONG AREA BECAUSE IT HAD BEEN FOUND ΤΟ CONTAIN CAVITIES IN A FEW PLACES.
IN FACT, THE EXISTENCE OF CAVITIES IN THE MARBLE WAS FIRST DISCOVERED MORE THAN FIVE YEARS AGO, AND A TECHNICAL PAPER DESCRIBING PROBLEMS ENCOUNTERED WITH THE CONSTRUCTION OF BUILDING FOUNDATIONS IN YUEN LONG WAS PUBLISHED BY K.L. SIU AND S.H. KWAN OF FREEMAN FOX AND PARTNERS AS EARLY AS 1982, HE SAID.
MARBLE IS MADE OF CALCIUM CARBONATE. OVER MILLIONS OF YEARS, THIS IS DISSOLVED BY THE WEAKLY ACID GROUNDWATER TO FORM CAVITIES.
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"THE CAVITIES CAN BE VERY LARGE, AND THERE 13 NO WAY OF KNOWING WHERE THEY WILL OCCUR ON THE YUEN LONG PLAIN, DR BRAND SAID. "THEY CAN ONLY BE FOUND BY DRILLING DEEPLY INTO THE MARBLE BENEATH THE ALLUVIUM.
DR BRAND EMPHASISED THAT MARBLE DOES NOT OCCUR EVERYWHERE UNDER THE YUEN LONG PLAIN, AND EVEN WHERE IT DOES OCCUR IT MAY NOT CONTAIN CAVITIES. HOWEVER, THOSE RESPONSIBLE FOR DESIGNING BUILDINGS JIN THE AREA SHOULD BE AWARE THAT THERE COULD BE PROBLEMS WITH THE CONSTRUCTION OF FOUNDATIONS IF MARBLE EXISTS UNDER THEIR SITES.
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"ALL THE PROBLEMS CAN BE OVERCOME BY A GOOD GEOTECHNICAL ENGINEER, STRESSED DR BRAND, BUT MORE THOROUGH INVESTIGATIONS ARE REQUIRED ON SUCH SITES, AND THE FOUNDATION COSTS MIGHT BE HIGHER USUAL.
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THAN
/DR BRAND