Analytical solution for evaluating deformation response of existing metro tunnel due to excavation of adjacent foundation pit

The excavation of foundation pit generates soil deformation around existing metro tunnel with shield driving method,which may lead to the deformation of tunnel lining.It is a challenge to evaluate the deformation of shield tunnel accurately and take measures to reduce the tunnel upward displacement as much as possible for geotechnical engineers.A new simplified analytical method is proposed to predict the longitudinal deformation of existing metro tunnel due to excavation unloading of adjacent foundation pit in this paper.Firstly,the additional stress of soils under vertical axisymmetric load in layered soil is obtained by using elastic multi-layer theory.Secondly,the metro tunnel is regarded as a Timoshenko beam supported by Winkler foundation so that the shear effect of tunnels can be taken into account.The additional stress acting on the tunnel due to excavation unloading in layered soil are compared with that in homogeneous soil.Additionally,the effectiveness of the analytical solution is verified via two actual cases.Moreover,parametric analysis is conducted to investigate the responses of the metro tunnel by considering such factors as the variation of subgrade coefficient,offset distance from the excavation center to tunnel longitudinal axis as well as equivalent shear stiffness.The proposed method can be used to provide theoretical basis for similar engineering project.

An analytical method to assess the damage and predict the residual strength of a ship in a shoal grounding accident scenario

In this paper,a simplified analytical method used to predict the residual ultimate strength of a ship hull after a shoal grounding accident is proposed.Shoal grounding accidents always lead to severe denting,though not tearing,of the ship bottom structure,which may threaten the global hull girder resistance and result in even worse consequences,such as hull collapse.Here,the degree of damage of the bottom structure is predicted by a series of analytical methods based on the plastic-elastic deformation mechanism.The energy dissipation of a ship bottom structure is obtained from individual components to determine the sliding distance of the seabed obstruction.Then,a new approach to assess the residual strength of the damaged ship subjected to shoal grounding is proposed based on the improved Smith’s method.This analytical method is verified by comparing the results of the proposed method and those generated by numerical simulation using the software ABAQUS.The proposed analytical method can be used to assess the safety of a ship with a double bottom during its design phase and predict the residual ultimate strength of a ship after a shoal grounding accident occurs.

Rapid Prediction of Structural Responses of Double-Bottom Structures in Shoal Grounding Scenario

This study presents a simplified analytical model for predicting the structural responses of double-bottom ships in a shoal grounding scenario. This solution is based on a series of analytical models developed from elastic-plastic mechanism theories for different structural components, including bottom girders, floors, bottom plating, and attached stiffeners. We verify this simplified analytical model by numerical simulation, and establish finite element models for a typical tanker hold and a rigid indenter representing seabed obstacles. Employing the LS-DYNA finite element solver, we conduct numerical simulations for shoal-grounding cases with a wide range of slope angles and indentation depths. In comparison with numerical simulations, we verify the proposed simplified analytical model with respect to the total energy dissipation and the horizontal grounding resistance. We also investigate the interaction effect of deformation patterns between bottom structure components. Our results show that the total energy dissipation and resistances predicted by the analytical model agree well with those from numerical simulations.