Recep Temiz, Ebu Bekir Aygar, Candan Gokceoglu

A comprehensive assessment of differences in rock mass classes estimated during investigation and encountered during tunnel excavation

Abstract The present study aims to perform statistical analyses on rock mass class differences estimated during the investigation and encountered during excavation phases of various tunnel projects and to quantitatively evaluate these differences. Using data obtained from 14 different highway tunnels constructed in Türkiye, the differences between the rock mass classes predicted during the investigation phase and the actual values encountered during excavation were analyzed with the parameter of Mean Percentage Absolute Difference (MPAD). The effects of the parameters introduced in the study, such as the drilling length ratio to tunnel length (LDn), total core recovery ratio (TCRn), rock quality designation ratio (RQDn) and uniaxial compressive strength test number ratio (UCSn), on these differences were investigated with regression and Random Forest algorithms. The results showed that TCRn and RQDn have a strong inverse relationship on MPAD, in other words, the rock mass class differences decrease with the increase of these parameters. In addition, it was determined that the drilling length and total core recovery values are of critical importance in reducing the uncertainties in the tunnel route. This study is expected to contribute to more accurate predictions and to reduce cost and time losses by providing a quantitative approach to minimize uncertainties in tunnel constructions during the excavation phase.

Doi https://doi.org/10.5200/baltica.2026.1.8

Keywords geotechnical investigation; drilling, tunnel; RQD; RMR; uncertainty

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