Estimation of Elastic Modulus of Intact Rock using Artificial Neural Network and Nonlinear Regression

Authors

1 Department of Civil Engineering, University of Isfahan

2 Department of geology, University of Isfahan

Abstract

Elastic modulus of intact rock is an essential requirement of many geo-mechanical analyses, especially rock excavation projects. Core samples with high quality and proper geometry are required to directly determine elastic modulus, but providing appropriate core samples from fractured and weathered rocks is not possible. Therefore, models are developed to estimate elastic modulus based on the index intact rock properties. In this study, the optimum estimation of elastic modulus of intact rock is obtained using multi-layer perceptron neural network with back propagation algorithm and data of rock mechanic experiments. The results are compared with the nonlinear regression method. For this purpose, 121 data sets obtained from rock tests of three tunnel projects (Beheshtabad, Rudbar and Sabzkuh) are analyzed. Various parameters are considered to estimate elastic modulus such as porosity, uniaxial compressive strength, compressive wave velocity, tensile strength and density. Based on the optimization of the neural network components, the network with two layer and four neuron in hidden layer, one neuron in the output layer, one data series in the input layer and tansig activation function was chosen as the optimum structure of the neural network. Finally, the neural network model was built using various parameters combinations. The results of the estimation methods are evaluated using their coefficient of determination and root mean square error as performance criteria. The comparison shows better performance of the neural network model relative to the nonlinear regression method. Uniaxial compressive strength, compressive wave velocity and tensile strength are the effective parameters in performance of the neural network model, respectively.
 

Keywords


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