自升式平台遗留桩坑及周边土体的时空变化特征——以废弃黄河水下三角洲埕岛地区某井场为例

Spatio-Temporal Variation Characteristics of Spudcan-Footprint and Surrounding Soil of Jack-up Platform—Taking a Well Site in Chengdao Area in Abandoned Yellow River Subaqueous Delta as an Example

摘要: 本研究选择废弃黄河水下三角洲埕岛地区的一个典型井场，基于多年水深测量、浅地层剖面探测、工程地质调查资料，详细分析正常固结饱和软黏土为主地层上遗留桩坑及周边土体的时空变化特征。刚形成的桩坑由一个初始泥线以下深度0.33 D (桩靴直径D)、直径2 D的具有双坡结构剖面的凹坑和一个土体强度分布高度异质性的剖面组成。土层破坏以冲剪破坏为主，原始海床以下至稍微延伸到桩靴贯入深度以下的范围被剧烈扰动，在水平方向上强烈扰动出现在距插桩中心线0.5 D范围内，1 D之外的土体影响较小。受扰动的土层可划分为六个性质不同的区域。随后桩坑逐渐趋于夷平，内外土体工程性质也不断发生变化，地层剖面从“软–硬”结构变成了“硬–软–硬”结构，重塑土体强度随时间逐渐恢复，直至超过原状土和重塑区以外土体强度。最后还讨论了桩坑的形成机理及桩坑对二次插桩的影响。

Abstract: In this study, a typical well site in the Chengdao area of the abandoned Yellow River subaqueous delta was selected. Based on years of water depth measurement, shallow profile detection and engineering geological survey data, the spatial and temporal variation characteristics of the spudcan-footprint and surrounding soil on the normally consolidated saturated soft clay were analyzed in detail. The newly formed footprint consists of a concave surface profile with a double-slope structure at a depth of 0.33 D (spudcan diameter D) below the initial mudline, 2 D in diameter and a highly non-uniform shear strength profile. The soil failure was dominated by punching shear failure. The range from the original seabed to a slight extension below the penetration depth of the spudcan was severely disturbed. In the horizontal direction, the strong disturbance appeared in the range of 0.5 D from the center line of the pile, and the soil outside 1 D had less influence. The disturbed soil layer could be divided into six regions with different properties. Subsequently, the pile pit gradually tended to be flattened, and the engineering properties of the soil inside and outside the footprint were constantly changing. The stratum profile changed from “soft-hard” structure to “hard-soft-hard” structure, and the strength of the remolded soil gradually recovered with time until it exceeded the strength of the undisturbed soil and the soil outside the remolded area. Finally, the formation mechanism of pile pits and the influence of old footprints on reinstallation of spudcan were discussed.