Abstract: To investigate the influence of crystallization blockages in drainage systems on pore water pressure and structural mechanical responses in semi-enclosed drainage tunnels within salt rock regions and to provide design references for the construction of tunnels prone to crystallization blockages, the authors examine the blockage conditions in three highway tunnels in Yunnan Province, China. Based on crystallization material testing and on-site survey results, a tunnel model with a semi-enclosed drainage system is developed using FLAC3D software. The mechanical effects on the tunnel lining under symmetric and asymmetric blockages in different drainage units are compared and analyzed. The research findings indicate the following: (1) In salt rock regions, calcium carbonate crystallization blockages in tunnel drainage systems primarily occur at the connections between drainage pipe components and then propagate along the pipes. (2) As the number of symmetric and asymmetric blocked drainage units increases, the maximum pore water pressure in the lining follows a Logistic regression model. When the number of blocked units exceeds three, the maximum pore water pressure stabilizes, although the area affected by the blockage continues to expand. (3) The maximum pore water pressure in the lining of semi-enclosed drainage tunnels is consistently located at the crown section. Under symmetric blockage, it is located at the midpoint of the crown directly above the blockage center, whereas under asymmetric blockage, it is located between two drainage units near the side of the blockage. After tunnel blockage, the increase in pore water pressure at the lining′s springline is the most substantial, exceeding 150%. (4) Under symmetric and asymmetric blockage of different drainage units, the maximum principal stress at the crown midpoint remains relatively constant. However, the maximum and minimum principal stresses at other locations show substantial increases. Compared to symmetric blockage, under asymmetric blockage, the location of the maximum increase in the minimum principal stress shifts from the arch shoulder to the arch waist.

Key words: salt rock tunnels, semi-enclosed drainage system, crystallization blockage, lining structure, mechanical response characteristics, pore water pressure