Periphery Mapping in NATM Tunnels

In this study; to get different approach to periphery mapping technique the application of tunnels opened by NATM (New Austrian Tunneling Method) method is aimed. Surface settlements due to excavation are important to keep under control in every stage of tunnels are opening by NATM method. During the progress of the tunnel, weak zones must be identified and spreading of weak zones should be estimated. As a result of detection of weak zones and other geological structures, stability can be achieved by applying additional support systems (additional rock bolt, cement and/or chemical injection, temporary invert concrete with strut etc.) before geological structure cause of the surface settlement. All geological structures encountered along the route are saved on the periphery map. Periphery map allows for three dimensional observation and estimation. Because of NATM is a gradual excavation method, periphery map allows to estimate of the geological structure of other stages. Dimensions and orientations of discontinuities (faults, beddings etc.) encountered along the tunnel progress is saved on the periphery map. Existing faults in progress of the tunnel can be estimated with the help of periphery map. Also, bedding orientation is an important parameter in tunneling works can be estimated with the help of periphery map. According to estimated fault and bedding orientation, additional precautions (AGF umbrella arc, fore pilling, face bolt, additional steel support, gradual excavation etc.) are taken to the stability of the excavation surface. It is important to hold to existing water level to keep under control of surface settlement in NATM tunnels. During the progress of the tunnel, periphery map is prepared to showing to status of water on tunnel surface. While excavations continuing, geotechnical values such as RMR, Q, GSI, are calculated with geotechnical data which was collected according to observational standards published by ISRM (International Society for Rock Mechanics) in 1981, are processed on periphery maps. So the areas, additional support measures to be taken, will be selected. NATM is a method of gradual excavation. The NATM tunnels which is designed to initially opening of the pilot tunnel, geological and geotechnical properties of the tunnel on the main section are determined with the help of periphery map prepared with pilot tunnel data. Also, after the excavation of the top heading, estimating the other stage's (such as Upper Medium Heading UMH, Lower Medium Heading LMH, bench and invert) geological and geotechnical properties, collectively showing the concerned data to be provided.