SUPPORT OF UNSTABLE GROUND

THE PROBLEM OF DEALING WITH UNSTABLE GROUND CONDITIONS ARISES IN TWO ASPECTS OF DESIGN AND CONSTRUCTION: (A) THE SUPPORT OF EXCAVATIONS AND ADJACENT GROUND DURING THE CONSTRUCTION OF THE PERMANENT WORK. SUCH MEASURES INVOLVE THE DESIGN AND PROVISION OF CONSTRUCTION TECHNIQUES TO ENSURE THE SAFETY OF THE WORKS UNTIL THE PERMANENT WORKS HAVE BEEN COMPLETED. (B) THE DESIGN OF THE PERMANENT WORKS TO INCORPORATE THE SUPPORT OF UNSTABLE GROUND CONDITIONS. IN PRACTICE, THE DIVISION DESCRIBED ABOVE IS NOT ALWAYS MUTUALLY EXCLUSIVE IN THAT THE PERMANENT WORKS DESIGN MAY INCORPORATE FEATURES WHICH SERVE TO PROVIDE SUPPORT DURING THE PERIOD OF CONSTRUCTION. AN EXAMPLE OF THIS IS THE USE OF A CONTIGUOUS CONCRETE BORED PILE WALL TO SUPPORT A COFFERDAM EXCAVATION BUT WHICH MAY FORM PART OF THE PERMANENT DESIGN AT THE COMPLETION OF THE WORK. THERE IS A FURTHER DIVISION IN THE TYPE OF GROUND THAT MAY BE ENCOUNTERED AND THIS IS BETWEEN SOILS IN THE CIVIL ENGINEERING SENSE AND THOSE ARISING FROM THE SPECIAL PROBLEMS ASSOCIATED WITH ROCK. INSTABILITY IN GROUND WHICH REQUIRES TO BE EXCAVATED MAY BE THE RESULT OF THE ENGINEERING STRENGTH OF THE SOIL BEING INADEQUATE TO ALLOW IT TO STAND UNSUPPORTED. PROBLEMS FREQUENTLY ARISE FROM THE WATER BEARING STRATA. THERE IS OFTEN A DIFFICULTY IN EXCAVATION WHICH ARISES FROM THE NECESSITY TO SAFEGUARD THE FOUNDATIONS OF ADJACENT BUILDINGS. THE GENERAL METHODS OF PROVIDING SUPPORT FOR EXCAVATIONS ARE TIMBERING, GROUND WATER LOWERING, SHEET PILING, AND OTHER SPECIALIST TECHNIQUES. THESE LAST MAY INCLUDE GROUND FREEZING, DRILLED OR BORED ANCHORS (KNOWN AS GROUND ANCHORS), AND STABILIZING BY THE INJECTION OF CHEMICAL OR OTHER GROUT. THE STABILITY OF PERMANENT OPEN EXCAVATIONS OR EMBANKMENTS MAY BE ACHIEVED BY A NUMBER OF METHODS DEPENDING ON THE MATERIAL ENCOUNTERED: SHEET PILING OR SIMILAR AT THE TOE TO PREVENT A DEEP-SEATED SLIP IN COHESIVE MATERIAL, DRAINAGE OF THE SLOPES BY HERRING-BONE DRAINS TO AVOID WEAKENING OF THE SLOPE BY GROUNDWATER, STABILIZING THE FACE OF THE EMBANKMENT BY TOP SOILING AND SEEDING WITH GRASS, AND WITH UNSTABLE ROCK SLOPES TO PROVIDE AGAINST FALLING MASSES OF ROCK, ROCK BOLTING AND FACING WITH CONCRETE. DURING THE PAST FEW DECADES THERE HAVE BEEN MANY IMPROVEMENTS AND ADDITIONS TO THE TECHNIQUES AVAILABLE FOR OVERCOMING UNSTABLE GROUND CONDITIONS IN TUNNELS AND SHAFTS: GROUNDWATER LOWERING, GROUND TREATMENT, USE OF COMPRESSED AIR, USE OF SPECIAL SHIELDS, FREEZING, AND ROCK BOLTING, COLLIERY ARCHES, OR SPECIAL TIMBERING. /AUTHOR/

  • Supplemental Notes:
    • Vol 66, No 782, P 967
  • Authors:
    • Haswell, C K
  • Publication Date: 1971-9

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Filing Info

  • Accession Number: 00236246
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 8 1972 12:00AM