A novel solution for ground reaction curve of tunnels in elastoplastic strain softening rock masses

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.

Evaluation of Induced Settlements of Piled Rafts in the Coupled Static-Dynamic Loads Using Neural Networks and Evolutionary Polynomial Regression

“…Hence, the application of neural network modeling and evolutionary polynomial regressions (EPRs), which are believed to be common ways to accurately and timely predict engineering complicated functions, can be examined. Different attempts to apply neural networks and EPRs to model different civil and geotechnical problems are presented in the literature [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. They are well-applied in a wide range of problems from deep soil stabilizations, concrete, and their related structures, compressive strength of soils, rocks, and stabilized samples, bearing capacity of shallow and deep foundations, lateral spreading, rock mechanics, rock engineering, and soil mechanics [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33].…”

Neural Prediction of Tunnels’ Support Pressure in Elasto-Plastic, Strain-Softening Rock Mass

“…In this method, a ground reaction curve (GRC) is applied to evaluate the interaction between the rock mass and the support system near the tunnel's face at the time of construction [1][2][3]. The classical problem of a circular tunnel constructed in the rock mass medium is illustrated in Figure 1b (according to [4]). This problem uses two well-known rock mass strength criteria: Mohr-Coulomb and Hoek-Brown.…”

“…These criteria are usually adopted to investigate the behavior of materials. As described in references [4][5][6], the governing equilibrium equation of this problem is as presented in Figure 1d. In Figure 1, is the radial stress, and represents the tangential (hoop) stress, while the distance from the center of tunnel is shown using the parameter.…”

“…In this regard, a plastic potential function and associated/non-associated flow rules are applied to find the governing relationship between the radial and tangential plastic strains [1,4,5,[7][8][9][10][11][12][13]. The stress-strain around the tunnel is also calculated, considering the strength parameters in different zones (the peak, residual, and softening parameters), as presented in Figure 1a,c, according to reference [4]. As explained in reference [4], using different yield and potential functions, the non-associated flow rule is the modeled and adopted as the flow rule in all the cases.…”

“…The stress-strain around the tunnel is also calculated, considering the strength parameters in different zones (the peak, residual, and softening parameters), as presented in Figure 1a,c, according to reference [4]. As explained in reference [4], using different yield and potential functions, the non-associated flow rule is the modeled and adopted as the flow rule in all the cases. Also, starting from the peak strength parameters, the deterioration of the strength parameters of the material (referred to as the softening behavior of the rock mass around the tunnel) begins and continues.…”