大厚度湿陷性黄土地层的现场砂井浸水试验研究

针对大厚度黄土湿陷变形室内试验评价不准确,现场原位浸水试坑试验评价方法周期长、费用高且难以适应线性工程技术要求等不足,提出了一种新的现场试验评价方法:砂井浸水试验方法。其核心是利用湿陷变形土体与未湿陷变形土体之间产生相对沉降差及地裂缝,通过湿陷性黄土场地设置砂井,将水直接导入某一深层湿陷性黄土地层及砂井圆周边土体,以此来测定砂井井底下地层和砂井孔深范围内黄土的湿陷变形量。该方法具有操作简便、花费小、周期短和灵活性高等特点。依托宝兰客专建设项目,在具有代表性的大埋深自重湿陷性黄土场地开展了4个不同深度的砂井浸水试验,测试了砂井场地的沉降变形及井底湿陷性土层的沉降变形,同时配合井底土层含水量的量测,分析了井底黄土的湿陷性变形特征。参考现有规范中建议的该地区自重湿陷量修正系数,对比砂井浸水试验结果与室内试验结果,初步论证了砂井浸水试验的合理性,及其在大厚度湿陷性黄土线性工程上运用的优势。

In-situ sand well immersion tests on self-weight collapsible loess site with large depth

The evaluation of collapse deformation laboratory tests on the loess with heavy section is not accurate ingeneral. The in-situ comprehensive soaking tests are time-consuming and costly, and they cannot meet the requirements for linear engineering. Therefore, a new in-situ test method, namely sand well immersion test, is proposed to overcome the shortcomings mentioned above. Its core is the utilization of the relative differential settlement and ground fissures generated between collapsible soil and non-collapsible soil. The water can directly flow into the loess with a certain depth and the soil mass surrounding the sand well by setting up sand well on collapsible loess ground, so that the collapsibility deformations of loess under the bottom of sand well and in the range within the depth of sand well are determined. The method is characterized by easy operation, low cost, short cycle and high flexibility. Based on Baoji-Lanzhou passenger lines, four sand well immersion tests with different depths are performed on a representative self-weight collapsible loess site with large depth. The settlement deformations of sand well site and collapsible soil layers under the bottom of sand wells are measured, through the measurement results of moisture content measurement of soil layers under the bottom of sand drain to analyze the collapsible deformation characteristics of loess layers under the bottom of sand wells are analyzed. With reference to the correction factor of collapse settlement under overburden pressure in this region suggested by the existing specifications, the sand well immersion and the corresponding laboratory compression test results are comparatively analyzed so as to preliminarily demonstrate the rationalitily of the proposed sand drain immersion test method and its advantages in linear engineering on self-weight collapsible loess site with large depth.