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.