BEARING CAPACITY OF DEEP FOUNDATIONS IN SAND

Abstract

LARGE-SCALE MODEL EXPERIMENTS HAVE BEEN MADE TO PROVIDE INFORMATION ON FACTORS WHICH INFLUENCE BEARING CAPACITY OF DEEP FOUNDATIONS IN SAND. CYLINDRICAL AND PRISMATICAL FOUNDATIONS OF VARIOUS SIZES RESTING AT DIFFERENT DEPTHS IN HOMOGENEOUS SAND MASSES OF DIFFERENT RELATIVE DENSITIES WERE LOADED STATICALLY TO FAILURE. SPECIAL LOADING CELLS PERMITTED SEPARATE REGISTRATION OF POINT AND SKIN LOADS THROUGHOUT THE TESTS. ADDITIONAL TESTS WITH MODELS OF SAND COLORED IN LAYERS WERE MADE TO STUDY THE MECHANISM OF SHEAR FAILURE IN THE SOIL MASS. THE MODEL EXPERIMENTS WERE ACCOMPANIED BY STANDARD LABORATORY TESTS FOR DETERMINATION OF PHYSICAL CHARACTERISTICS OF THE SOILS USED. AN ANALYSIS OF SHEAR PATTERNS OBSERVED INDICATES THAT, DEPENDING ON RELATIVE DENSITY OF SAND, ALL THREE TYPES OF FAILURE PREVIOUSLY DESCRIBED IN THE LITERATURE MAY OCCUR AT SHALLOW DEPTHS' GENERAL SHEAR FAILURE, LOCAL SHEAR FAILURE AND PUNCHING SHEAR FAILURE. HOWEVER, AT GREATER DEPTHS ONLY PUNCHING SHEAR FAILURE OCCURS, IRRESPECTIVE OF THE RELATIVE DENSITY OF SAND. THE UNIT POINT AND SKIN RESISTANCES OF THE FOUNDATION INCREASE LINEARLY WITH DEPTH ONLY AT SHALLOW DEPTHS. AT GREATER DEPTHS, BOTH RESISTANCES SHOW A HYPERBOLIC INCREASE AND REACH ASYMPTOTICALLY CONSTANT FINAL VALUES. THESE FINAL VALUES ARE INDEPENDENT OF OVERBURDEN PRESSURE AND APPEAR TO BE FUNCTIONS OF RELATIVE DENSITY OF SAND ONLY. THIS IS EXPLAINED BY THE ARCHING OF SAND ABOVE THE FOUNDATION BASE. ANALYSES OF OBSERVED ULTIMATE LOADS INDICATE THAT A FAIR ESTIMATE OF BEARING CAPACITY CAN BE MADE BY ASSUMING FAILURE SURFACES IN ACCORDANCE WITH OBSERVED SHEAR PATTERNS. /AUTHOR/