SOME PLAINS IN SPAIN-LANDSLIDES THREATEN ROTA LIVING AREAS

THE ATTRACTIVE AND HISTORIC NAVAL STATION AT ROTA IN APRIL OF 1963, HAD SERIOUS CRACKS SUDDENLY APPEAR IN THE FLOOR AND CENTER BEARING WALL OF THE OFFICER'S QUARTERS. THESE COULD BE TRACED IN THE LAWN AND GARDEN OUTSIDE THE HOUSE, INDICATING A MASSIVE BLOCK EARTH MOVEMENT. FOUR OTHER STRUCTURES FARTHER TO THE WEST WERE EVACUATED SHORTLY THEREAFTER BECAUSE OF THEIR PROXIMITY TO THE CLIFF EDGE. THE BASIC SUBSTRATUM OF THIS PORTION OF THE COASTLINE IS A STIFF GREY PRECOMPRESSED CLAY OF THE EOCENE PERIOD WHICH LIES CLOSE TO THE PRESENT WATER LEVEL AT THE WESTERN AND EASTERN EXTREMITIES BUT RISES TO THE SURFACE IN THE WEST CENTRAL AREA. MINERALOGICALLY THIS CLAY IS A MIXTURE OF ILLITE AND MONTMORILLONITE, AND IT HAS A LIQUID LIMIT VARYING FROM 60 TO 120. THE OVERLYING DEPOSITS AT BOTH EASTERN AND WESTERN ENDS ARE OF A LATER PERIOD AND ARE COMPRISED OF STRATIFIED SILTS, CLAYS AND CEMENTED SANDS. THESE ARE MORE PERVIOUS MATERIALS, WHICH WERE LAID DOWN OVER THE EARLIER EOCENE CLAY SURFACE DURING PERIODS OF HIGHER WATER LEVELS AND WERE LATER SUBJECTED TO PROGRESSIVE EROSION. THE CLAY PORTIONS OF THE CLIFF IN THE CENTRAL AREA ARE CHARACTERIZED BY SLOPING FACES, AND THE MORE PERVIOUS CEMENTED MATERIALS AT THE ENDS ARE CHARACTERIZED BY VERTICAL FACES. TWO MAJOR TYPES OF FAILURES ARE RECOGNIZED: THE FIRST OF THESE OCCURS IN THE CLAY WHICH WHEN EXPOSED TENDS TO EXPAND GRADUALLY FROM ITS PREVIOUSLY HIGHLY COMPRESSED CONDITION, THE SECOND IS A BLOCK SLIDE IN WHICH A MASS OF THE UPPER CEMENTED SOIL SLIDES ON THE UNDERLYING CLAY SURFACE. THE FOLLOWING CONSTRUCTIVE ADVICE IS OFFERED OVER AND ABOVE EXPLORATORY STUDIES OF THE GEOLOGY AND CONFORMATION OF THE CLIFF: (1) EARLY IN THE CONSTRUCTION STAGE, OR PREFERABLY DURING THE PLANNING OR DESIGNING STAGE, SURVEY MOVEMENTS SHOULD BE ESTABLISHED FOR HORIZONTAL AND VERTICAL CONTROL CLOSE TO THE CLIFF LINE, (2) THE POTENTIAL HAZARDS OF GROUND MOVEMENT NEAR CLIFFS SHOULD BE CONSERVATIVELY VIEWED, AND (3) IT IS WISE TO REMEMBER THAT NEARLY ALL SERIOUS SLIDE PROBLEMS ARE GENERATED BY WATER, I.E., WEAKENING OF NATIVE SOILS OR ROCK, LUBRICATION OF SURFACES AND INCREASE OF OUTWARD SEEPAGE FORCES.

  • Supplemental Notes:
    • Vol 8, No 7, PP 4-10, 10 FIG, 1 TAB
  • Authors:
    • Brown, P P
  • Publication Date: 1967-10

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  • Accession Number: 00234301
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 6 1994 12:00AM