THE DESIGN OF DRILLED FOUNDATIONS

A BRIEF OUTLINE IS PRESENTED OF TECHNIQUES FOR DETERMINING THE SAFE BEARING CAPACITY OF DRILLED CAST-IN-PLACE CONCRETE PILES WITH SPECIAL REFERENCE TO THE SOIL CONDITIONS OF THE ARID SOUTHWEST. IN APPLYING SOIL MECHANICS TO THE DETERMINATION OF SAFE BEARING CAPACITY, ULTIMATE CAPACITY IS OBTAINED BY SUMMATING SIDE SHEAR CALCULATED BY THE COULOMB- MOHR EQUATION AND END BEARING COMPUTED BY THE SEMI-EMPIRICAL TERZAGHI EQUATION MODIFIED FOR THE CASE OF DEEP FOUNDATIONS. AN APPROPRIATE FACTOR OF SAFETY IS APPLIED AND SETTLEMENT ANALYSIS IS MADE TO ENSURE THAT TOLERABLE FOUNDATION MOVEMENTS ARE NOT EXCEEDED. TRIAXIAL SHEAR AND UNCONFINED COMPRESSION TESTS ARE USED AS ROUTINE METHODS OF SHEAR STRENGTH DETERMINATION. THE USE OF THICK WALLED OPEN END DRIVE SAMPLERS LINED WITH METAL OR PLASTIC RINGS IS NECESSARY FOR EFFICIENT SAMPLING OF THE COHESIVE SOILS IN THE SOUTHWEST WHICH ARE PARTIALLY SATURATED WITH RELATIVELY FIRM, AND ARE CEMENTED OR FISSURED TO VARYING DEGREES. THE SAMPLES CAN USUALLY NOT BE EXTRUDED FOR TRIAXIAL OR UNCONFINED COMPRESSION TESTING. THE DIRECT SHEAR TEST WAS WIDELY ADOPTED FOR DESERT SOIL CONDITIONS BECAUSE THE TESTING APPARATUS CAN BE DESIGNED TO RECEIVE THE LINEAR RINGS WITH SOIL SPECIMENS AS SECURED IN THE FIELD. SIDE SHEAR AND END BEARING COMPUTATIONS ARE PRESENTED. BOTH STRAIGHT PILES AND THOSE WITHIN LARGE BASES (BELLS) ARE DISCUSSED. PILES CONSTRUCTED WITHOUT THE USE OF CASING AND THOSE IN WHICH CASING IS EMPLOYED, IN ADVANCING EXCAVATIONS AND WITHDRAWN AS CONCRETE IS PLACED, ARE DESCRIBED. THE ULTIMATE BEARING CAPACITY OF PILES BEARING ON SANDS, SATURATED CLAYS AND SOFT TO MODERATELY FIRM PARTIALLY SATURATED COHESIVE SOILS PROBABLY CAN BE PREDICTED WITHIN PLUS OR MINUS THIRTY PERCENT BY CAREFUL ANALYSIS USING THE PROCEDURES OUTLINED. ULTIMATE BEARING CAPACITY COMPUTATIONS IN CONJUNCTION WITH CONVENTIONAL SETTLEMENT ANALYSIS PROVIDE A SOUND BASIS FOR DESIGN. ADDITIONAL LOAD TESTS ARE NEEDED TO VERIFY THE CAPACITY OF PILING IN PARTIALLY SATURATED COHESIVE SOILS, PARTICULARLY STRONGLY CEMENTED SOILS WHERE SATISFACTORY SAMPLES ARE DIFFICULT OR IMPOSSIBLE TO OBTAIN.

Subject/Index Terms

Filing Info

  • Accession Number: 00209303
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 28 1970 12:00AM