Back Analysis of Settlement Data during Tunnel Excavation on Urban Areas (Case Study: Tehran Subway- Line 6)

Prediction and control of settlement have great importance both in terms of safety and economic point of view on urban area. Tehran subway- line 6 starts from Kouhsar square in the end of north Kouhsar Boulevard placed in north-west of Tehran and ends in Dolat-abad terminal at south of Tehran. North part of line 6 excavated using NATM method. Monitoring and instrumentation system are well equipped and their data have been processed during excavation. Although geotechnical parameter obtained from laboratory and in-situ tests and on the other hand there are distances from sample location to tunnel route, it is possible that different factors such as local heterogeneities in layers or variation of soil between two positions affect the geotechnical parameters. One of the best methods to evaluate these parameters in large scale is back analysis based on instrumentation results. In this paper numerical modeling are done with Plaxis2D software and using back analysis, geotechnical parameters estimated. Different parameters such as cohesion, angle of friction, elastic modules investigated. Also, stresses relaxation were examined before support installation. Based on sensitivity analysis, elastic modules and friction angle have the most influence on ground surface settlement. For example, changes of the friction angle from 24 to 40 will change settlement from 51.3 to 14.7. Also, changes of elastic modules from 75 to 215 will change settlement from 23.2 to 8. Based on these finding, changes of these two parameters in 9 different sections on tunnel route were verified settlement in numerical method with instrumentation settlement. Result shows that increase elastic modulus in numerical models about two times provide good result. Friction angle changes between 37 to 40.