Journal of the Korean Geo-Environmental Society ISSN:1598-0820(Print) 2714-1233(Online) 한국지반환경공학회 논문집

Success or failure of the bi-directional pile load test for drilled shaft depends on point selection for loading cells, that is balanced location both uplift force and downward force. Methods to evaluate the ultimate unit side resistance in rockmass layer in both domestic and foreign are based on the uniaxial compression strength of rock core, which can hardly be obtained in domestic rockmass layers which are weathered rockmass layer and soft rockmass layer with very low RQD. Therefore, this study suggested the relation charts between the revised SPT N values and developed unit side resistance of each different layers, which were obtained from bi-directional pile load tests in various domestic sites. To evaluate the appropriateness of the relation charts, the developed unit side resistances from the relation charts were used to select the loading cell position and compared with the measured unit side resistances from field pile load test. Results showed that the developed side resistance from relation charts and the measured side resistance of weathered soil layer and weathered rock layer were very close. Average developed side resistance(1,325kN/m2 ), which are average of upper soft rock layer of loading device(1,151kN/m2 ) and lower(1,500kN/m2 ), was similar with the estimated value (1,250kN/m2 ).