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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

STRUCTURES ON COASTAL ALLUVIUM

ISOSTATIC MOVEMENTS IN THE EARTH'S CRUST AND EUSTATIC CHANGES IN THE VOLUME OF WATER IN THE SEA SINCE THE FINAL NORTHERLY WITHDRAWAL OF THE ICE COVER SOME 10,000 YEARS AGO HAVE PRODUCED A NET EUSTATIC RISE IN SEA-LEVEL AROUND THE COASTS OF BRITAIN OF ABOUT 180 FT. THE CHARACTERISTICS OF COASTAL ALLUVIUM ARE ALTERNATING DEPOSITS OF PEAT AND OF "ORGANIC CLAYS", USUALLY OF SILTS IN GRADING, THAT ARE NORMALLY CONSOLIDATED IN THE SENSE THAT THEY HAVE NEVER BEEN SUBJECTED TO CONSOLIDATION PRESSURES GREATER THAN THEIR OWN WEIGHT. DEPTHS OF 100 FT. ARE FOUND, AND THEY REST UPON POST-GLACIAL GRAVELS, BOULDER CLAYS, OR BEDROCK. THE PHYSICAL PROPERTIES ARE REMARKABLY CONSISTENT. BENEATH A DESICCATED CRUST OF ABOUT 4 FT. IN THICKNESS, HAVING SHEAR STRENGTHS OF ABOUT 1500 LB/SQ. FT., THE STRENGTH DROPS IMMEDIATELY AT THE WATER-TABLE TO ABOUT 200 LB/SQ. FT. AND THEN INCREASES LINEARLY WITH DEPTH AT APPROXIMATELY 0.3 TIMES THE EFFETIVE OVERBURDEN PRESSURE. FOUNDATIONS FOR MAJOR ENGINEERING STRUCTURES ON COASTAL ALLUVIUM OBVIOUSLY LEAVE LITTLE CHOICE BUT TO USE PILES OR CYLINDERS, OPEN OR COMPRESSED AIR CAISSONS, OR 'BUOYANT' FOUNDATIONS. IT IS IN THE INTERMEDIATE CLASS OF STRUCTURE, SUCH AS FOR MORE EXTENSIVE INDUSTRIAL BUILDINGS OF WIDER ROOF SPANS, THAT PROBLEMS ARISE. THEN IT IS MORE DIFFICULT TO JUSTIFY THE COST OF FULLY SUSPENDED FLOORS RESTING ON PILES. IN A TYPICAL EXAMPLE OF AN INDUSTRIAL BUILDING OF THIS TYPE BUILT IN 1958, THE PRODUCTION FLOOR WAS DELIBERATELY CAMBERED BY 6 IN. IN ORDER TO ALLOW FOR THE SETTLEMENT. UNUSUALLY WIDE JOINTS (3/4 IN.) WERE LEFT BETWEEN THE SMALL PANELS (12 FT. 6 IN.) IN WHICH THE CONCRETE FLOORS WERE CAST, IN ORDER TO ALLOW FOR THE HORIZONTAL COMPRESSION THAT WOULD OCCUR WITH SETTLEMENT, NO REINFORCEMENT OR DOWELS BEING LAID ACROSS THESE JOINTS. SIMILAR JOINTS WERE PROVIDED AT PILED COLUMN BASES AND WALL BEAMS; OVER INTERNAL COLUMN BASES IT WAS RECOGNIZED THAT THE GRANOLITHIC FLOOR SURFACE WOULD HAVE TO BE BROKEN OUT OCCASIONALLY AND LOWERED. AFTER SEVEN YEARS IN SERVICE (1965) LEVELS TAKEN IN THE FACTORY SHOWED ABOUT 4 INCHES OF CONSOLIDATION AT FLOOR LOADINGS, OF 0.38--075 CWT/SQ. FT. IN 1965 IT WAS ESTIMATED THAT LESS THAN ANOTHER INCH OF MOVEMENT WOULD OCCUR N THIS FLOOR DURING THE ENSUING 10 YEARS.

  • Supplemental Notes:
    • Vol 66, No 782, PP 973, 975, 4REF
  • Authors:
    • Haigh, I P
  • Publication Date: 1971-9

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  • Accession Number: 00236248
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 8 1972 12:00AM