Abstract: 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.