A comparative study on the prediction of squeezing behavior: a case study of Gelas tunnel — NW Iran

The particular situation of the Gelas water conveyance tunnel led this study to evaluate squeezing behavior along the second part of the tunnel in northwestern Iran. This section of the tunnel is 20 + 660 m long and has a diameter of around 6.3 m. A variety of sedimentary, metamorphic, volcanic, and plutonic rocks from the Precambrian to the new age are on display in the research field. For more exact investigations, based on some in situ and in lab tests, the study area was divided into 11 engineering geological units. Using GSI, RMi, RMR, and Q-systems, the rock mass classifications were implemented for all units. Considering some geological features including faults and crushed zones and high overburden (up to 600 m) in some parts, 26 sections were selected for the prediction of squeezing behavior using empirical, semi-empirical, and analytical approaches. Based on numerical outcomes and critical strain, an index (SI) was estimated and employed to classify squeezing behavior. A comparison between the squeezing levels, assessed by analytical approaches, and the squeezing levels obtained from the numerical approach shows that both analytical and numerical approaches have approximately the same trend for squeezing level distributions. Also, the same trend of both analytical and numerical approaches reveals that the groundwork utilized for numerical simulation and the estimated squeezing index (SI) technically was faithful and in harmony with the general style obtained from traditional methods.