黄土地基次生病害的夯挤桩处治技术试验研究

Experimental Study on Rammed Compaction Pile Treatment Technology for Secondary Diseases of Loess Foundation

摘要: 针对既有交通工程场景下受限高限宽条件约束的区域，黄土地基深层土体因浸水饱和引发次生病害的问题，本研究采用水泥级配碎石夯挤桩技术开展治理效能研究，并依托室内模型试验展开系统分析。试验过程中，分别对天然状态未浸水地基、下部土体浸水饱和厚度达1 m及2 m的地基开展荷载测试，随后进一步完成水泥级配碎石夯挤桩单桩、群桩复合地基的分级加载试验。试验结果表明：当饱和土层厚度为1 m时，地基沉降量较未浸水工况提升16.23%；饱和土层厚度增至2 m时，沉降量较未浸水工况增幅达27.64%。群桩复合地基累计平均沉降量相较于单桩复合地基提升54%，群桩效应特征显著。单桩与群桩复合地基的承载特性存在共性规律：随着上部荷载的逐步增大，桩身应力沿深度方向均呈现出先增大后减小的变化特征，应力峰值位置出现在桩顶以下0.2~0.3倍桩长区间。同时，群桩复合地基内部不同位置桩体的应力分布存在差异，中桩桩身应力峰值最高，边桩次之，角桩最小；相较于单桩复合地基，群桩复合地基中桩间土的承载作用发挥更为充分，桩土协同工作效应表现得更为突出。

Abstract: To address the issue of secondary distresses induced by water immersion and saturation of deep loess foundation soils in restricted height and width zones of existing traffic engineering projects, this study investigates the treatment effectiveness of cement-graded gravel tamped compaction piles, and conducts a systematic analysis via laboratory model tests. In the experimental program, load tests were performed on foundations under three conditions: natural unsaturated state, foundations with 1 m and 2 m thick saturated underlying soil layers, respectively. Graded loading tests were then carried out on single-pile and pile-group composite foundations reinforced with cement-graded gravel tamped compaction piles. The test results indicate that when the saturated soil thickness is 1 m, the foundation settlement increases by 16.23% compared with the unsaturated condition; when the saturated soil thickness increases to 2 m, the settlement increases by 27.64% relative to the unsaturated case. The cumulative average settlement of the pile-group composite foundation is 54% higher than that of the single-pile composite foundation, demonstrating a significant pile-group effect. The bearing characteristics of single-pile and pile-group composite foundations follow a similar trend: with the gradual increase of the upper load, the axial stress along the pile shaft first increases and then decreases with depth, and the stress peak occurs at a depth of 0.2~0.3 times the pile length below the pile head. Furthermore, the stress distribution of piles at different positions within the pile-group composite foundation is distinct: the peak shaft stress of the central pile is the largest, followed by the side piles, and the corner piles show the smallest value. Compared with the single-pile composite foundation, the bearing contribution of the inter-pile soil in the pile-group composite foundation is more fully mobilized, and the pile-soil synergistic interaction is more pronounced.