Experimental Investigation on the Strength Reduction of Soil Surrounding Deepwater Surface Conductor Induced by Vibration

Summary The shallow soil layers in deep water are primarile composed of clay, characterized by weak soil structure, leading to significant safety risks in shallow well construction. Based on this, we refer to the actual dimensions of shallow surface jetting conductor in deep water and the shallow geological parameters of the South China Sea in this paper. We developed an innovative theoretical model of the conductor-soil composite structure under multicycle loading in deepwater shallow layers, considering soil liquefaction. Additionally, by measuring the changes in soil parameters during vibration, we conducted experimental studies to investigate the effects of vibrational loads on the strength and bearing capacity of the soil surrounding the surface conductor. From this study, we found that, upon initiation of vibration, soil pressure and pore water pressure oscillated in opposite directions simultaneously. Soil pressure decreased rapidly from its initial value, while pore water pressure increased rapidly and fluctuated within a certain range. Analyzing the variations in soil pressure and pore water pressure at different depths, it was observed that conductor vibration significantly weakened the effective stress in the soil. The soil above the shallow surface conductor was in a fully liquefied state, with partial liquefaction occurring below the conductor. The strength of the soil in the middle part of the shallow conductor showed minimal weakening and, in some cases, even increased. Under higher-frequency vibrational loads, the degree of soil weakening was more pronounced. Based on the experimental results, theoretical analysis, and numerical simulation verification, it was found that the vertical bearing capacity of the shallow surface conductor decreased significantly after vibration at conventional frequencies, showing a reduction compared with the initial state. With an increase in vibration frequency, the degree of soil weakening exhibited a nonlinear, power-function trend. The study verified that vibration has a notable weakening effect on soil strength, with significant changes in soil strength around the shallow surface conductor under continuous impact and vibration loads, and sensitivity to vibration frequency. These findings provide valuable theoretical and experimental insights for further optimization of deepwater shallow well construction methods and related engineering parameters.