Analysis of collapsible deformation and vertical soil pressure action of thick loess foundation
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摘要:
黄土地基浸水后的湿陷变形对黄土地区的工程建设具有重大影响，但以往研究对深厚黄土地基土浸水过程的湿陷特性及其土压力变化规律研究不够充分。以中兰铁路兰州新区南站某场地为例，开展现场浸水试验，对深厚湿陷性黄土场地的地表位移及地基深层湿陷变形进行监测，同时埋设土压力盒，对浸水湿陷过程中地基土的竖向土压力的变化规律进行分析。研究结果表明：（1）该深厚黄土场地最大湿陷下沉量在150 cm左右，浸水范围10 m以外的地表基本不发生湿陷下沉；（2）根据深层沉降测试结果可知，0~15 m深度范围内该黄土地基为强湿陷土层，湿陷量达到120 cm左右，占整个场地湿陷量的80%以上，24 m深度以下地基土不发生湿陷，为非自重湿陷土层；（3）根据土压力监测分析，15 m深度以上的地基土浸水后土体结构完全溃散，测试得到的土压力即为上覆土体的自重压力，15 m深度以下的土体浸水后虽产生一定的湿陷下沉，但土体结构未发生完全破坏，对上覆自重荷载仍具有一定的支撑作用。研究结论可为中兰铁路后期工程及兰州新区的建设提供一定的技术参考。
Abstract:The collapsible deformation characteristics of loess foundation after flooding are of great significance in the engineering construction in loess regions. However, previous studies of the collapsible characteristics of deep loess foundation soil during the process of flooding and the variation law of soil pressure are not perfect. In this paper, a site in the South Station of Lanzhou New District of the Zhongwei-Lanzhou Railway is taken as an example and a field immersion test is carried out at the site to monitor the surface displacement and deep wet sink deformation of the foundation of the deep wet sink loess site. At the same time, soil pressure boxes are buried to analyze the change law of vertical soil pressure of the foundation soil during the immersion wet sink process. The research results show that (1) the maximum wet sink of the deep loess site is around 150 cm, and wet sink basically does not occur at the ground surface outside 10 m of the water immersion range. (2) According to the deep settlement test results, it can be seen that the loess foundation 0−15 m deep is the range of the strong wet sink soil layer, and the wet sink amount reaches about 120 cm, accounting for more than 80% of the wet sink amount of the whole site. Wet sink does not occur in the foundation soil 24 m deep and it is a non-self-weight wet sink soil layer. (3) According to the soil pressure monitoring analysis, it is obtained that the soil structure within 15 m in depth is completely collapsed after water immersion, and the soil pressure obtained from the test is the self-weight pressure of the overlying soil. A certain amount of wet subsidence after water immersion occurs at a depth of 15 m or less, but the soil structure is not completely destroyed, and it still has a certain support effect on the overlying self-weight load. The results of this study can provide some technical references for the later construction of the Zhongwei-Lanzhou Railway and the Lanzhou New District.
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表 1 试验场地地层岩性表
Table 1. Lithology of the test site
地层名称 分布深度/m 地层岩性 岩性特征 砂质黄土
（
）0~3.5 第四系全新统
（Q4）浅黄色，稍湿，稍密，
以砂质黄土为主砂质黄土
（
）1.5~45 第四系上更新统
（Q3）浅黄色，稍湿，稍密，土质
均匀，可见针孔状大孔隙和
虫孔，具湿陷性
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表 2 土体基本物理指标
Table 2. Basic physical properties of soil
土样 最优含水率/% 最大干密度/（g·cm−3） 液限/% 塑限/% 土粒比重 粉质黏土 13.2 1.89 29.27 16.68 2.71
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