Abstract
Ground Reaction Curve (GRC) is one of the most important elements of convergence-confinement method generally used to design tunnels. Realistic presentation of GRC is usually assessed based on the advanced rock strength criteria, also, rock mass behavior (including plasticity and softening treatments). Since taking these parameters into account is not simply possible for practitioners and needs complicated coupled theoretical-numerical solutions, this paper presents a simple novel approach based on Evolutionary Polynomial Regression to determine GRC of rock masses obeying both Mohr-Coulomb and Hoek-Brown criteria and strain softening behaviors. The proposed models accurately present support pressures based on radial displacement, rock mass strength and softening parameter (determination coefficient of 97.98% and 94.2% respectively for Mohr-Coulomb and Hoek-Brown strain softening materials). The accuracy of the proposed equations are approved through comparing the EPR developed GRCs with the ground reaction curves available in the literature. Besides, the sensitivity analysis is carried out and in-situ stress, residual Hoek-Brown’s m constant and residual dilation angle are introduced as parameters with the most influence on the support pressure in Hoek-Brown and peak and residual geological strength index are the most affective parameters on the support pressure of tunnels in the strain softening Mohr-Coulomb rock mass.
Highlights
Tunneling projects consist of different phases including pre-construction studies, risk assessment, cost evaluation, design phase, construction, monitoring (Sayadi et al 2012; Hasanzadehshooiili et al 2012a, 2012b; Ghorbani et al 2013; Zavadskas et al 2015; Zhang et al 2016)
In development of ground reaction curve, changes in the support pressures due to the tunneling is tracked near the tunnel face and the concerning radial tunnel displacement-support pressure curve is reported as the GRC, which is conjunctly used with support characteristic curve (SCC) to gain the optimum time of installation of the support system
EPR models based on Mohr-Coulomb strength criterion and strain softening
Summary
Tunneling projects consist of different phases including pre-construction studies, risk assessment, cost evaluation, design phase, construction, monitoring (sometimes some of the mentioned phases will be merged when performance based design is the selected design method) (Sayadi et al 2012; Hasanzadehshooiili et al 2012a, 2012b; Ghorbani et al 2013; Zavadskas et al 2015; Zhang et al 2016). There are some main problems such as uncertainties in rock nature, variation of ground condition, ground deformation induced by redistribution of in-situ stresses and difficult computational procedure, which makes it difficult to accurately and obtain the pressure on and sustained by internal support of rock circular tunnels (Hasanzadehshooiili et al 2012b) In this regard, it is common among practitioners to design tunnel structures more conservatively. Convergenceconfinement method is one of the most in demanding design methods widely used by tunnel and rock mechanics engineers This method is founded based on three fundamental elements consisting longitudinal deformation profile (LDP), support characteristic curve (SCC) and ground reaction curve (GRC) (Brown et al 1983). In development of ground reaction (response) curve, changes in the support pressures due to the tunneling is tracked near the tunnel face and the concerning radial tunnel displacement-support pressure curve is reported as the GRC, which is conjunctly used with SCC to gain the optimum time of installation of the support system
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