A new tunnel inflow classification (TIC) system through sedimentary rock masses

A new classification system with respect to the engineering geological characteristics of rock masses in different geological conditions were presented based on the authors’ experiences and observations. Rock mass composition (RMC), rock type (RT), clay-bearing content (CBC), unconfined compressive strength (UCS) and tunnel depth (TD) were found as the major factors affecting the tunnel inflow. In order to minimize judgmental bias and set up a basic database, data pertaining to these factors were compiled from 33 tunnels project with a total length of about 200 km thoroughly excavated in sedimentary rocks. The classification factors were rated using a combination of the analytic hierarchy process (AHP) and statistical methods. In order to cover all rock mass varieties and lessen the uncertainties, major factors were divided into categories of varying quality. Two statistical criteria were introduced to calculate the weighing of categories. The main advantage of this procedure is its capability of effectively predicting groundwater inflows in a vast variety of geological conditions especially from a single flow pathway such as a brittle fault zone to low permeable rock masses. The proposed classification was applied to the actual rock tunnels. It was revealed that the predicted values were in a good agreement with the actual field measurements and could provide quantitative measures of tunnel inflow. The proposed method could be more feasible for a reliable pre-assessment of groundwater inflows in the future tunnel construction projects under heterogeneous geological conditions. Furthermore, the most important factors as well as their combination are introduced for sedimentary rocks.

► A new Classification system for prediction of water inflow to rock tunnels is introduced.
► It is an efficient method to evaluate tunnel inflow in heterogeneous geological conditions.
► Prediction of High local inflows through singular geological features is considered in the system.
► A new chart to evaluate rock mass composition is proposed.