Stability analysis of the Haji-Abad tunnel site using experimental and limit equilibrium methods

In this research, engineering geological characteristics of the Haji-Abad tunnel site in Hormozgan province have been assessed and its stability analysis is carried out using experimental and limit equilibrium methods. The tunnel site was divided into ten geotechnical units including T1–T8 and two crushed zones in Units 5 (Tf1) and 9 (Tf2) using the BGD method. The rock discontinuities in the tunnel site have filled by calcite and clay, with dry to wet surface conditions, and low degree of weathering. The internal friction angle of the discontinuities surfaces ranges 15º–45º, their persistence is from about 3 to more than 20m, their spacing is 0.15–4m, and their opening is 0.1–5mm. The compressive strength of the site rocks, except for the two crushed zones that have different conditions, varies 20–120MPa. The moisture content of the samples obtained from the boreholes of the tunnel site were 0.12–2.87%, and their porosity were 7.33–0.32%, respectively. The tunnel site rocks are placed in the very poor to good classes with RQD values from 25 to 90. According to the RMR classification, the rocks in the tunnel site have a score of 18–62 (very poor to good). Also, by using the Q method, the rocks of different unites of the tunnel site were given a score rang of 0.04–2.83 (extremely weak to weak). The GSI method indicated that the site constructing rocks range is 15–61 (very poor to good). By using Unwedge.v.3.0 software, the maximum and minimum weight values of the formed wedges were obtained 5875 and 0.076 tons, with heights of 100.94 and 0.12m, respectively. Also, the safety factor is 0.04–112 and the wedges that had a safety factor less than 1.5 will be reached an acceptable safety factor by installing rockbolt.