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  Estimation of geotechnical parameters by comparing monitoring data with numerical results (case study of Arash- Esfandiar- Niayesh under passing tunnel, Africa tunnel, Tehran, Iran)

  Under passing tunnels are strongly influenced by the soil around. There are some complexities in specification of real soil behaviour, owning the fact that lots of uncertainties exist in soil properties and additionally inappropriate soil constitutive model. Such mentioned factors may cause incompatible settlements in numerical analysis with the obtained values in actual construction. This paper aims to report a case study on a specific tunnel constructed by New Austrian Tunnelling Method. The tunnel has overburden of about 11.3m, height of 12.2m and, width of 14.4m with 2.5 traffic lanes. The numerical modelling was performed by using a 2D finite element program (PLAXIS Version 8). Soil material behaviour was modelled by hardening soil model. According to the field observations, the numerical estimated settlement at the ground surface was approximately four times more than the field measured one, after the entire installation of the initial lining, which indicates that some unknown factors affect that value. Consequently, the geotechnical parameters were accurately revised by a numerical back-analysis using laboratory and field tests data and based on the obtained monitoring data. The obtained result comparing data confirms that usually, the soil parameters are conservatively low-estimated up to 40 percent by typical engineering experiences, and additionally, the constitutive models cannot be applied properly for all soil conditions. NATM tunnel, Initial lining, Field test data, Laboratory test data, Monitoring data, Numerical back-analysis).

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