In many cases of foundation structures on soft soils, pile foundation proves to be the logical and economical choice. However, the use of pile foundation is not limited to soft ground. Current method of predicting downdrag forces along the pile shaft in clay could overpredict the estimated capacity. Therefore, understanding the nature and the behavior of downdrag forces along the pile shaft is essential. This paper describes the measurement of negative skin friction forces on the model piles driven in the cylindrical chamber filled with remolded marine clay. Three instrumented systems, load cells were installed on the model piles consisted of three parts to measure the negative skin friction forces independently. Pore pressures and ground movements in the ground were monitored throughout the period of investigation. The results were analyzed and discussed in this paper.
Pile foundation has been used for a foundation method to solve a design and construction problem to be faced up to foundation construction on soft clays for a long time. In case of constructing pile on soft clays, negative skin friction is developed along the pile due to the relative displacement of soil and Pile, and this acts as force to the pile. Especially, when negative skin friction exceeds the design load of pile, it has an influence on the compatability of structure because differential settlement of foundation is occurred. Downdrag or negative skin friction arises when the soil surrounding a pile settles more than the pile. Such negative skin friction decreases the carrying capacity of a pile and increases the compressive stress in the pile. Poulos(1989) has interpreted in detail the influence of soil move on load-settlement characteristics of piles, and has proposed that the pile settlement should be considered as a relevant design aspect for piles subjected to negative skin friction.
