SUMMARY Previous field and laboratory studies have shown that the creation of a borehole in a saturated cohesive soil mass induces significant pore water suctions in the vicinity of the hole. The dissipation of these pore water suctions (swelling) leads to local increases in the moisture content and hence a softening of the soil around the hole. This softening may have important consequences for the stability of the hole and also for the ultimate load capacity of any foundation elements (bored piles or drilled shafts) constructed in these holes. This paper presents a semi-analytical solution for the radial dissipation of pore water pressure around a freshly created, vertical hole. It is assumed the soil deforms elastically during the swelling process. The solutions are presented in the form of isochrones of excess pore water pressure and may be used to obtain estimates of the time required for the soil around the hole to swell and therefore to soften. Both permeable and impermeable borehole interfaces have been considered, together with either no support for the hole or partial support provided by hydrostatic pressure within the hole.

A semi-analytical solution for swelling around a borehole

THE STUDY IS MAINLY CONCERNED WITH ANALYSIS OF BEHAVIOR OF FIVE FULL-SCALE INSTRUMENTED DRILLED SHAFTS CAST IN SOIL PROFILES CONTAINING SAND AND TEST LOADED TO FAILURE. TWO SHAFTS WERE CAST BY THE DRY METHOD AND THREE BY THE SLURRY DISPLACEMENT METHOD. FROM FIELD OBSERVATIONS AND MEASUREMENTS TAKEN DURING CONSTRUCTION AND LOAD TESTS, IMPORTANT FINDINGS WERE MADE CONCERNING THE CONSTRUCTION AND THE DESIGN OF DRILLED SHAFTS. WITH RESPECT TO CONSTRUCTION, THE SLURRY DISPLACEMENT METHOD WAS FOUND TO POSSESS A GREAT POTENTIAL FOR FUTURE USE, BUT THIS METHOD MUST BE USED WITH CARE, TO PREVENT THE ENTRAPMENT OF MUD AND SEDIMENTS AT THE TIP AND SIDES OF THE SHAFT AND IN THE CONCRETE. WITH RESPECT TO DESIGN, THE MEASURED LOAD TRANSFER WAS CORRELATED WITH THE PROPERTIES OF THE SAND MEASURED BY DYNAMIC PENETROMETERS. PRESSURE-SETTLEMENT CURVES WERE OBTAINED FOR THE TIPS OF SHAFTS IN VERY DENSE SAND AND SAND OF MEDIUM DENSITY. THE TOTAL SIDE LOAD TRANSFER WAS CORRELATED WITH THE INTEGRAL OVER THE PERIPHERY OF THE SHAFT OF THE PRODUCT OF THE EFFECTIVE OVERBURDEN PRESSURE TIMES THE TANGENT OF THE EFFECTIVE FRICTION ANGLE. THE COEFFICIENT OF CORRELATION WAS FOUND TO BE ABOUT 0.7 FOR SHAFTS WITH PENETRATIONS IN SAND NOT EXCEEDING 25 FT. THERE WERE INDICATIONS THAT THIS COEFFICIENT DECREASES WITH DEPTH AND, THEREFORE, CARE MUST BE EXERICSED WHEN THE RESULTS ARE EXTRAPOLATED TO DEEPER SHAFTS. /CEN. FOR HWY RES/

The behavior of axially loaded drilled shafts in sand

This project involves the design, construction, and testing in the laboratory and field of instrumentation capable of measuring the lateral earth pressure along a drilled shaft. A good deal of work has been done concerning the development of pressure transducers designed to measure stresses in an earth mass. Consequently, these studies have produced theories which set design criteria for soil pressure measuring devices based on soil behavior. This project pulls these theories together, assimilates the present knowledge concerning transducers, and produces a pressure cell designed to measure lateral pressures against a drilled shaft up to 50 psi. Design "maps" based on Timoshenko's theory of a clamped-edge, circular, thin plate are given. These ''maps'' allow the investigator to arrive at the thickness of a pressure-sensitive diaphragm knowing the desired pressure to be measured, the allowable diaphragm deflection to diameter ratio, and the desired sensitivity of the cell. The beryllium copper cell is 2-3/4 inches in diameter and 1/2 inch thick. This cell has been used to measure the pressures exerted against a drilled shaft under curing and loading conditions. Additional work will be necessary in order to evaluate completely the lateral-earth-pressure distribution and load transfer from the shaft to the soil. What is felt to be a satisfactory gage for making the necessary measurements in sands and clays has been developed and is recommended for these studies.

Instrumentation for Measurements of Lateral Earth Pressure in Drilled Shafts

Soil Properties as Related to Load Transfer Characteristics of Drilled Shafts

THIS PROJECT INVOLVES THE DESIGN, CONSTRUCTION, AND TESTING, IN THE LABORATORY AND FIELD, OF INSTRUMENTATION CAPABLE OF MEASURING THE LATERAL EARTH PRESSURES ALONG A DRILLED SHAFT. THIS PROJECT SUMMARIZES AND SYNTHESIZES THE THEORIES WHICH SET THE DESIGN CRITERIA FOR SOIL PRESSURE MEASURING DEVICES BASED ON SOIL BEHAVIOR. THE PROJECT ASSIMILATES THE PRESENT KNOWLEDGE CONCERNING TRANSDUCERS AND PRODUCES A PRESSURE CELL DESIGNED TO MEASURE LATERAL PRESSURES AGAINST A DRILLED SHAFT UP TO 50 PSI. DESIGN 'MAPS' BASED ON TIMOSHENKO'S THEORY OF A CLAMPED EDGE, CIRCULAR, THIN PLATE ARE GIVEN. THESE 'MAPS' ALLOW THE INVESTIGATOR TO ARRIVE AT THE THICKNESS OF A DIAPHRAGM KNOWING THE DESIRED PRESSURE TO BE MEASURED, THE DIAPHRAGM DEFLECTION TO DIAMETER RATIO, AND THE DESIRED SENSITIVITY OF THE CELL. A BERYLLIUM COPPER CELL 2 3/4 INCHES IN DIAMETER AND 1/2 INCH THICK WAS CONSTRUCTED. THE ELECTRONIC PRESSURE SENSING ELEMENT IS A SPECIAL FOUR-ARM BONDED FOIL STRAIN GAGE. THE CELL HAS BEEN USED TO MEASURE THE PRESSURES EXERTED AGAINST A DRILLED SHAFT UNDER CURING AND LOADING CONDITIONS. ADDITIONAL WORK WILL BE NEEDED TO EVALUATE COMPLETELY THE LATERAL-EARTH-PRESSURE DISTRIBUTION AND LOAD TRANSFER FROM SHAFT TO SOIL. IT IS FELT THAT THE DESIGNED GAGE IS SATISFACTORY. /AUTHOR/

Measurements of lateral earth pressure in drilled shafts

AS A PORTION OF A MORE EXTENSIVE STUDY ON DRILLED AND CAST-IN-PLACE CONCRETE PILES, SPECIAL TESTS WERE CONDUCTED ON SMALL-SCALE PILES WHICH HAD BEEN PLACED IN A 30-IN. CUBE OF LABORATORY COMPACTED SOIL. THE USE OF THESE SMALL-SCALE PILES MADE IT POSSIBLE TO CONDUCT THESE TESTS UNDER MORE UNIFORM SOIL CONDITIONS AND TO PERFORM TESTS THAT WERE NOT PRACTICAL FOR THE LARGER FIELD-INSTALLED PILES. ONE SERIES OF SMALL-SCALE PILES WAS USED TO OBSERVE THE INFLUENCE OF SEVERAL FACTORS ON WATER MOVEMENTS FROM UNSET CONCRETE INTO AN ANNULAR ZONE OF SOIL IMMEDIATELY SURROUNDING THE PILES. THESE TESTS INDICATED THAT WATER MOVEMENTS WERE NEGLIGIBLE, EXCEPT WHEN THE INITIAL WATER CONTENT OF THE COMPACTED SOIL (FOR THE TEST CUBES) WAS SEVERAL PERCENT LOWER THAN THE PLASTIC LIMIT OF THE SOIL. BOTH TENSION AND COMPRESSION LOAD TESTS WERE CONDUCTED ON SMALL PILES AND THE TENSION CAPACITY OF THE PILES WAS FOUND TO BE BETWEEN 0.6 AND 0.7 OF THE COMPRESSION PILE LOAD CAPACITY. OTHER SPECIAL TESTS WERE MADE TO OBSERVE THE NATURE OF SOIL DEFORMATION ADJACENT TO THE PILE SURFACE DURING A LOAD TEST AND THE PORTION OF THE PILE LOAD WHICH WAS RESISTED BY END-BEARING STRESSES AT THE BASE OF THE PILE. /AUTHOR/

L A Dubose

Papers

Small-scale load tests on drilled and cast-in-place concrete piles