5TH International Congress on Technology - Engineering & Science - Kuala Lumpur - Malaysia (2018-02-01)

The Analysis Of Skin Friction On Prebored And Precast Piles

The bearing capacity and settlement of a prebored and precast pile are affected not only by the end bearing capacity, but also by the skin friction between the pile and the cement milk poured in the borehole. A number of investigations of the settlement and the interface behavior of various types of pile have been conducted. However, as mentioned above, to date, most of the measurements and experiments were based on driven piles or drilled shafts. The settlement of a steel pile was measured, and based on the results, the maximum skin friction between the steel pile and dry sand was found to depend on the roughness of the steel pile and the sand particle size. Drilled shafts, which have a source of skin friction similar to a prebored and precast pile, showed a relative settlement and high shear stress at the pile-soil interface. Various studies were conducted to investigate the major factors affecting the skin friction of prebored and precast piles. The unit weight of the soil around the pile was found to be the main influence factor for the skin friction. Thorough studies on the cement strength and the skin friction of prebored and precast pile showed that the unit skin friction increased up to 700% as the cement hardened. The proportion of the skin friction to the total bearing capacity also increased up to 400%. Additionally, studies showed that the N-value, the type of soil and the water-cement ratio of the cement milk were the major influence factors affecting the skin friction of prebored and precast piles. Among the major factors, the water-cement ratio of the cement milk was found to have the biggest influence on the skin friction. Skin friction may be one of the most critical factors in designing the prebored and precast pile. Special attention was given to the interface behavior of cement milk-surrounding soil during the installation of prebored and precast pile. Therefore, this study conducted to the case of single pile through small-scale field model pile test. The size and geometry of the small-scale field model piles have been designed pile length 1.3m, boring diameter 0.067m. This study conducted to case of boring diameter 150, 125, 90, 86, 74mm, water-cement ratio 90, 70, 60% using quick maintain-load test. It is shown that the bearing capacity of the pile is increased as the cement-water ratio and cement milk thickness is increase. Considering the scale effect between the small-scale model test and the actual construction site, it was found that, cement milk thickness of 0.1~0.4D(50∼200mm) is reasonable for the stability of the structure. Also, the cement paste water / cement ratio is 90% or less when considering the results of this study and previous studies.
Jongjeon Park, Sangseom Jeong, Dohyun Kim