Abstract: When the tunnel passes through the hourglassshaped karst in Wuhan area, the karst treatment range will directly affect the project safety and investment. The analysis and research of karst collapse angle are carried out to quantify the karst treatment area. Firstly, the model test is adopted to simulate the process of karst collapse to verify the mechanism of seepage liquefaction collapse of saturated sandy soil; the sand loss and collapse angle are researched quantitatively; and the collapse angle is calculated to be 35.8°. And then, the deformation morphology of the tunnel is analyzed by numerical simulation of karst collapse process under 5 working conditions; the minimum safety distance between tunnel and karst cave is determined based on the tunnel deformation control standards, and the karst collapse angle is calculated to be 33.9 °. Finally, comparison is made on karst collapse angle between model test and numerical calculation, and the conclusion that the collapse angle of hourglassshaped karst is similar to the friction angle of sand soil and the collapse angle is 1 ~ 3 ° larger than internal friction angle is obtained. The research results are applied to the hourglassshaped karst treatment of Wuhan Metro Line 6, and the collapse angle is taken as 35° to calculate the karst treatment range. According to this scheme, the shield passed through the karst area smoothly.

Key words: tunnel, hourglassshaped karst collapse, collapse angle, numerical analysis, model test