Improved Gauss-Newton-Marquardt algorithms for displacement back analysis of casing external loads in salt stratum

An improved Gauss-Newton-Marquardt (GNM) algorithm is proposed in the paper for displacement back analysis of casing external loads in salt stratum to optimize the solution based on traditional GNM algorithm. In the improved GNM algorithm, the direct solution method of partial derivative used in stochastic finite element method is adopted to substitute the difference method employed in traditional GNM algorithm. The calculation results show that the improved GNM algorithm is more efficient and precise in solving the displacement back analysis of casing external loads in salt stratum than traditional GNM algorithm. And the improved GNM algorithm is worthy to be applied greatly in the engineering practice. The calculating results of displacement back analysis are agreeable with the measured values indicating it´s suitable and valuable in practice. The improved GNM algorithm is versatile and suitable to solve the displacement back analysis problems in other engineering fields.