CALCULATIONS AND EXPERIMENTAL ANALYSIS OF THE ULTIMATE BEARING CAPACITY OF ROCK-SOCKETED CAST-IN-PLACE PILES

Most of tested piles in domestic construction sites are not loaded to the ultimate loads, and the estimation on the bearing capacity of piles is often underestimated, so that the potential of pile foundations cannot be reasonably brought into play. To correctly calculate the bearing capacity of rock-socketed piles, the classical theory of the limit equilibrium for pile tips was used to calculate the ultimate resistance of pile tips, the friction force on sliding surfaces above the plane of pile tips was taken as the increment of the bearing capacity. By the verification of static load tests for 11 test piles, the ultimate bearing capacity of pile tips embedded in moderately weathered granite was 30% higher than that one calculated by Code for Design of Building Foundation(GB 50007-2011). Further, 10 engineering piles were screened out to be tested. The results showed that: on the same maximum load level, the rock foundation under 5 pile tips damaged to column-block shapes but the bearing capacity of pile tips did not reach the ultimate, and still had greater bearing potential. The rock foundation under 2 pile tips damaged to crushed stones, the bearing capacity of pile tips was close to the ultimate but 22.8% higher than that one calculated by GB 50007-2011. By comparing and analysis of test data from 11 test piles and 10 engineering piles, it showed that If the pile length was more than 25 times of pile diameters, the friction resistance of stratum around piles including the rock-socketed length and the resistance of pile tips all didn't fully bring into play. The optimum rock-socketed depth was 1.0 to 2.0 times the pile diameter. The influence of the sediment thickness under the pile tips on the bearing capacity was not obvious when the thickness of the sediment was more than 50 mm, the influence of structure difference for the rock stratum on the bearing capacity was more than 30%.