開端鋼管ぐいの支持力に関する考察 (その 1)

Abstract

The authers discussed the manner in which the openend steel pipe pile transfers the load to the outer ground and the inner soil column, supposing that the load is carried partly by the skin friction and partly by the reactions at the bottom of the inner soil column and the tip of thin wall of the pipe, as shown in fig.2 (b). Assuming that frictional stress interacting between steel pile and outer or inner soil develops to be perfectly elastic-plastic for the discrepancy of settlement, and that the inner soil column is perfectly elastic, the authers introduced the theoretical solution on the distribution of axial force along the pile axis. From some numerical calculations on steel pipe piles (diameter : 500mm, thickness : 9mm, pile length : 20 m) driven into the grounds as shown in Fig.3, the load-settlement curves, the distributions of axial force, frictional stress and settlement along the pile axis are obtained (Fig.4〜Fig.8). As the result, the following are clarified. In propotional to the increase of load, the frictional stress fo of outer soil grows gradually, and reaches at last to the state being plastic in the full length of pile under the load Rofy. After the load exceeds Rofy, the load-settlement curve breaks down pretty clearly as seen in Fig.4. The distribution of settlement of the inner soil column coincides with that of steel pile in almost full length of pile except a small portion neighbouring the tip of pile. Accordingly, the frictional resistance of the inner soil column will be expected only in such small portion even under the load close to the ultimate capacity. From this result, the tip of pipe pile can not be assumed to be closed with the inner soil under the normal load.