Abstract: In order to deeply understand the expansion deformation mechanism during the use of ar ⁃ gillaceous soft rock tunnels in skarn，and to evaluate the influence of clay minerals on the expansion char ⁃ acteristics of skarn.Firstly，sample rock point load tests and mineral composition analysis were conducted to clarify the composition and content of expansive minerals in skarn.Secondly，skarn with different clay mineral contents were selected，and the side-limit expansion rate method was used for measurement，and the relationship between the expansion characteristics of skarn and the type and content of clay minerals was analyzed.The test results showed that the maximum expansion rate of skarn with different clay mineral compositions within 100 h was 99.32%，and the minimum was 19.26%.The test results indicated that the influence degree of clay mineral composition on the expansion rate of skarn ranged from strong to weak: chlorite >kaolinite >limonite.The expansion modification test research using clay stabilizers was carried out，and it was shown that the free surface pressure of the clay stabilizer had a significant inhibitory effect on the expansibility of chlorite.For the skarn waterlogged tunnel，a new technology of surrounding rock modification +anchor-net-spray combined support was proposed.Engineering tests showed that the modi⁃ fied anti-expansion combined support technology could effectively extend the service life of skarn soft rock tunnels，and could be further promoted and applied.

Key words: skarn, clay mineral content, confined expansion rate, swelling modification