湿陷性黄土砂井浸水试验的应用研究

随着中国西部大开发战略的进一步实施,湿陷性黄土地区的工程建设项目越来越多。黄土具有分布广、厚度大、湿陷性强、不均匀等特点,这就需要对黄土工程场地的湿陷性做出合理评价。测试和评价黄土湿陷性及地基湿陷变形的方法主要有两种:一是依据室内单轴压缩侧限变形应力条件浸水试验测试湿陷系数,评价黄土的湿陷性强弱,计算各土层的湿陷变形评价地基的湿陷等级,但其评价结果往往与实际情况有较大差异,甚至得到错误的结论;二是现场浸水试坑试验,这种试验在工程场地原位进行,在黄土工程中被广泛应用并得到认可,但受工程场地条和干旱半干旱气候环境件制约,试验费用高,周期长、难度大。鉴于目前黄土湿陷性评价方法的不足以及深厚黄土层湿陷性评价分析的需要,从黄土湿陷变形的特性和浸水入渗特征出发,业已提出了原位砂井浸水试验方法。分别在兰州榆中和西安选取了3个具有代表性的试验场地进行了试验,并与其它两种湿陷性评价方法进行了对比,进一步验证了该新方法对湿陷性评价的合理性、准确性以及实用性。

Application of sand drain immersion tests on collapsible loess

With the further development of China's western development strategy, more and more projects are constructed in collapsible loess area. The loess area is characterized by wide distribution, large thickness and different strong collapsibilities and nonuniformity. Therefore, it is necessary to evaluate the collapsibility of loess reasonably. There are two main types of testing and evaluation methods for collapsibility of loess and collapsibility deformation of foundation. One is to test the collapsibility coefficient based on the immersion tests on stress condition of indoor uniaxial confined compression tests and to evaluate collapsibility strength of loess the. Then the collapsibility grading of foundation is evaluated according to the calculated results of collapsible deformation. But the evaluation results are often different from the actual situation facts and even wrong conclusions are obtained. The other is the field immersion test which has been widely used and accepted in loess engineering. But it is influenced by the condition of engineering site and arid-subarid palaeoclimate. The experiments have the following characteristics: high cost, long cycle and high difficulty. Due to the deficiency of evaluation methods for loess collapsibility and the necessity of collapsibility evaluation and analysis of thick loess and based on the characteristics of collapsible deformation and water infiltration of loess, the in-situ sand drain immersion test method is proposed. 3 representative sites for trial in Lanzhou and Xi'an are selected. The results are compared with those obtained by other two collapsibility evaluation methods, and the rationality, accuracy and practicability of the new method for collapsibility evaluation are validated.