Papers by Keyword: Soil Plug

Abstract: The vertical bearing capacity of a special pile group of platform in an offshore gas field has been studied. Large diameter d (2.134 m), deep penetration l (96 m), small spacing sa (3.507 m), and only one row piles are the usual characteristics of the pile group foundation in offshore engineering. According to the requirements of the related design code, the super pile group effect has to be considered. However, with the usual design code, when sa/d, the ratio of spacing to diameter, is less than 2.0, there is no way to consider the pile group effect. In this paper, considering the occlusion effect of soil plug of pipe pile, several methods have been introduced to study the super pile group effect of the vertical bearing capacity. These methods include linear elastic theory method, the method recommended by the Code of Pile Foundation in Port Engineering (JTJ254-98), and the method with virtue of the existing pile group model test results. Meanwhile, the plugged and unplugged conditions have been considered, respectively. Through the analysis, the factors of safety in extreme and normal operation states are obtained, and the results satisfy the design specifications.

Abstract: The main mode of pile-soil interaction and the influence factors of pile sinking in offshore platform construction were analyzed and discusses the reasons that penetration resistance increases after stop driving and then continue. To study the drivability of piles of specified driving hammer, taking a jacket platform of Bohai Sea for instance, the results showed that continuous driving will make the open-end steel piles be driven to the designed depth, and driven-on will cause soil plug and pile driving refusal. Based on the results, the paper gives some suggestions about pile driving.

Abstract: A physical model test is conducted to study the hydraulic gradient and soil plug development during the suction penetration of bucket foundation in the silts. Furthermore, a FEM simulation is carried out by changing the geotechnical parameters and constitutive model to deeply study the suction penetration mechanism. Through the comprehensive analysis, the results indicate that the seepages inside and outside the bucket foundation are the direct reasons for the formation of soil plugs, and that there are the high hydraulic gradient and the safety mechanism preventing soil flow failure for the silts in the bucket foundation. The seepage changes not only the permeability of soil body but also the physical and mechanical properties, and enhances the rheological property and time effect. Thus, the soil plug failure is not seepage failure, not unloading expansion yet, is a complex deformation failure mode under the protection of safety mechanism of bucket foundation.