LOAD DISTRIBUTION FOR A DRILLED SHAFT IN CLAY SHALE

LARGE DIAMETER DRILLED SHAFTS ARE USED EXTENSIVELY IN MANY AREAS OF THE WORLD TO SUPPORT AXIAL LOADS; HOWEVER, THE BEHAVIOR OF THESE SHAFTS IS NOT WELL UNDERSTOOD. FREQUENTLY THEY ARE DESIGNED AS POINT-BEARING SHAFTS ONLY, WITH NO ACCOUNT BEING TAKEN OF LOAD DISTRIBUTED ALONG THE SIDES OF THE SHAFT. QUESTIONS ARISING WITH REGARD TO THE DESIGN OF SUCH SHAFTS CONCERN THE INTERACTION OF WET CONCRETE WITH SOIL, THE POSSIBLE SHRINKAGE OF CONCRETE ON DRYING, THE EVENTUAL EARTH PRESSURE AT THE INTERFACE OF THE SHAFT AND THE SUPPORTING SOIL, AND THE MECHANICS OF THE INTERACTION OF THE SHAFT WITH THE FOUNDATION. THIS REPORT DESCRIBES A COMPREHENSIVE INVESTIGATION AIMED AT GAINING MORE INFORMATION RELATED TO THE ABOVE QUESTIONS. A 30-INCH BY 28.5-FOOT DRILLED SHAFT WAS INSTRUMENTED WITH ELECTRICAL RESISTANCE STRAIN GAGES, MECHANICAL STRAIN GAGES, EARTH PRESSURE CELLS, AND THERMOCOUPLES AND WAS SUBSEQUENTLY TESTED UNDER AXIAL LOAD. THE INSTRUMENTS WERE READ FOR A SERIES OF LOAD INCREMENTS. THE SHAFT WAS TESTED FIVE TIMES WITH LOADS RANGING UP TO ALMOST 1,000 TONS. THE TEST DATE WERE ANALYZED TO OBTAIN CURVES GIVING DISTRIBUTION OF AXIAL LOAD ALONG THE SHAFT AS A FUNCTION OF DEPTH AND CURVES SHOWING LOAD TRANSFER AT VARIOUS DEPTHS AS A FUNCTION OF DOWNWARD MOVEMENT OF THE SHAFT AT THAT DEPTH. RESULTS OF THESE ANALYSES WERE CORRELATED WITH SOIL PROPERTIES OBTAINED FROM TEXAS HIGHWAY DEPARTMENT CONE PENETROMETER TESTS. A TENTATIVE DESIGN PROCEDURE IS PROPOSED AND THE LOAD-SETTLEMENT CURVES COMPUTED BY THIS DESIGN PROCEDURE ARE COMPARED WITH THE OBSERVED CURVES. /AUTHOR/