抄録
This paper is concerned with the theoretical discussions on the extent of elastic recovery and the residual settlement in a loading test on a bearing pile. The loading test is performed under the loading method that the pile is unloaded after every load increase. The relations between skin-friction f and displacement S at the depth z in the loading and unloading processes are assumed as shown in Fig.3, with reference to the experimental results of Fig.2. That is, the f〜S curve in the loading process is expressed approximately as the broken line OAB' under the consideration of the decrease of skin-friction of the disturbed clayey soil surrounding the pile caused by the repetition of loading. If the decease can be neglected, the route O→A→B' will coincide with the route O→A→B. In the unloading process from some loading stage and in the reloading process, the f〜S curves are assumed to be such straight lines parallel to the tangent line OC at the origin, as DE, FG(F'G), HI(H'I) etc. Fig.6〜10 give some numerical examples on the solutions of the differential equation (1). Fig.7 expresses the transitions of the distributions of skin-friction f, settlement S and strain ε along the pile axis corresponding to the unloading processes in Fig.6 and 9. As the result, the following informatinos can be obtained. There exists the negative skin-friction along the pile axis after the unloading. The total negative friction is in equilibrium with the residual point resistance R_<PR> as shown in Fig.8. Accordingly, S_<OR>=S_<PR>+δ_<fR> S_<Oe>=S_<pe>=(δ-δ_<fR> where δ : elastic compression of pile shaft δ_<fR> : residual compression of pile shaft S_<Oe>, S_<OR> : the extent of elastic recovery and the residual settlement of pile top S_<Pe>, S_<PR> : the extent of elastic recovery and the residual settlement of pile point The load〜residual settlement curve is expressed as the curve ε_O〜S_<OR> in Fig.6, 9 and 10, having 3 stages according to the distributions of f in the loading stages before the unloading.
