<p>The reliability of carrying borehole data as a basis for designing tunnels and developing geotechnical design baselines in the Himalayan geology is questionable. In the young and rapidly changing Himalayas, geological features such as lithology, joint orientations, folds, faults, foliations, bedding planes, and shear zones frequently change in all directions, whether the ground is being investigated vertically or inclined. This study highlights these geological variations in the alignment of Tunnel-1, which is part of the 125 km Rishikesh-Karanprayag new single broad gauge rail line project being undertaken in the state of Uttarakhand, India. This study presents the lengths of predicted geological rock classes, discusses and describes the procedure for determining these rock classes. However, it is important to note that the actual geological data and percentages of encountered rock class sections in the tunnel are often different from those derived from borehole data. In this study, a detailed comparison of the predicted and actual rock classes encountered during tunnel construction is presented. Furthermore, these uncertainties can lead to changes in tunnel design for stability. This study presents a case study of two boreholes (BH-16 and BH-17) encountered inside the main and escape tunnel drives (MT-3 and ET-4) to reflect the uncertainties involved in predicting rock classes and those found on the ground. During the design phase of the tunnel, a geotechnical baseline report is prepared based on interpretations framed from in-situ geotechnical investigations, including borehole drilling, sampling, and testing results. The percentage of rock classes is predicted during ground analysis based on the determination of geological-geotechnical parameters along the tunnel.</p>