Abstract
On the vertical loading tests of SL piles, the behavier of shear stress of bitumen τ_<SL> are observed as follows. τ_<SL> is increasing when the top load is added and is decreasing while the top load is holding constant. The measurement values of the stiffness modulus of bitumen S_<LT> on the loading test are different from the general stiffness modulus S in Fig. 1 which is the values under the condition of constant stress or constant speed of deformation. The results of the experimentation which shear stress is moving step by step increasingly of decreasingly are indicated in Fig. 8 to Fig. 12. The measurement values are nearly equal to the calcurated values in the range of τ_<SL><_yτ_<SL>. The stiffness modulus of the vertical loading test are explained by the modulus S_c on the composition of increasing and decreasing step loads which are indicated in (7) and (9) equations.
