分层土中吸力基础沉贯吸力变化及土体变形规律试验研究

Experimental study on suction variation and soil deformation behavior in layered soil during penetrating of suction caisson

吸力基础近年来在海上风电工程中逐渐得到推广,我国海上风场地基广泛分布分层土,研究吸力基础在分层土中的沉贯特性有助于推动其在我国海上风电工程领域的应用。开展模型试验,探讨了土层分布形式(砂土、黏性土、上层砂土下层黏性土(简称上砂下黏)、上层黏性土下层砂土(简称上黏下砂))对吸力基础沉贯吸力值、沉贯阻力、土塞高度和土体变形的影响。研究发现在上砂下黏土层中,当基础贯入至土层分界处时,基础吸力值陡然增加;当吸力基础贯入至上黏下砂土层分界处时,基础内部吸力值陡然降低,通过有机玻璃吸力基础模型试验阐述了吸力变化的原因。不同土层条件下,基础内部最终土塞高度规律由高到低为:上黏下砂土层、单一砂土层、上砂下黏土层、单一黏性土层,阐明了不同土层分布情况下基础内部土塞形成机理。对于单一砂土层和上砂下黏地基,沉贯结束后,基础周围土体出现环形沉降区域,单一砂土地基中沉降区域范围大于上砂下黏地基情况。对于单一黏性土和上黏下砂土层中,沉贯结束后基础周围黏性土中产生裂缝,且吸力沉贯下土体裂缝数量及裂缝扩展范围大于压贯条件,土体最大裂缝范围约为1.9倍基础直径。

A suction caisson is a top-closed cylindrical steel structure and has been used as foundations for offshore wind turbines.Penetration of the MSC into the desired position under the combined action of the self-weight and applied suction is an issue for design.Model tests were carried out to explore the suction variation and soil deformation behavior in layered soil during penetrating of suction caisson.The influences of soil layer distribution(sand,clay,sand overlying clay and clay overlying sand)were studied.It was found that the soil layer distribution dramatically influences the suction variation behavior during the suction-assisted installation of suction caisson.In the stratum of sand overlying clay,when the suction caisson penetrates the boundary between the sand and clay,a sudden increase of suction was observed.On the contrary,in the stratum of clay overlying sand,when the suction caisson penetrates the boundary between the clay and sand,a dramatically decrease in suction was found.Model tests on perspex-made suction caissons were carried out to visualize the suction variation at the boundary between sand and clay.In addition,the final soil plug heights in different soils are in the sequence of clay overlying sand>sand>sand overlying clay>clay.During suction-assisted installation of suction caisson in sand and sand overlying clay,subsidence regions around the suction caisson were found.The subsidence region around suction caisson in sand is larger than that in sand overlying clay.During suction-assisted installation of suction caisson in clay and clay overlying sand,cracks were observed around suction caissons.It was found that the number of cracks and the crack length for the suction caisson installed by applied suction are larger than thoseinstalled by jacked force.The maximum crack range of clay surface is approximately equal to 1.9 times the diameter of suction caisson.Results can guide the suction caisson investigation in layered soil.