BUCKLING CAPACITY OF PILES IN SOFT CLAY

An experimental verification is presented of the theory for the buckling of piles that are partially embedded in soft clay, under axial and eccentric loading. The experimental work was done on brass tube piles embedded in a drum of soil; the soil was made by mixing water with powdered bentonite. The results show that the predicted values of the buckling load from elastic theory are in close agreement with the experimental results, the maximum deviation being 4 percent. Tests on eccentrically loaded piles partially embedded in soil (using the same soils as those in the axial buckling load tests) showed that the agreement between the failure loads calculated from elastic theory and the experimentally observed failure loads is fair. However, the observed failure loads were higher than the calculated loads, for both embedded piles and loads in air. This was probably because the actual failures were due to stress in the plastic range and not in the elastic range as assumed in the theory. The test results when failure loads deviated from the general trend of the other test results, may indicate that the secant modulus should be used instead of the initial tangent modulus for determing the soil stiffness. Conclusions are listed which refer to piles that are sufficiently embedded in soil to be considered infinitely long. These conclusions relate to the coefficient of lateral stiffness, the value of the modulus of subgrade reaction, the prediction of the ultimate load of eccentrically loaded columns, the prediction of buckling load of a pile, and the effect of eccentricity and initial curvature on the bearing capacity of a buckling pile.