Narrow Results

Presented herein is a computationally efficient 2D theoretical model for simulating the steady response of a floating slab track-tunnel-soil system. The track-tunnel coupled system is simplified as a beam-spring system and embedded in soil layers. The tunnel is modeled by a Timoshenko beam with its interaction with the soil layers accounted for by two transfer matrices, with each derived for the soil layer above and beneath the tunnel. The approach as proposed herein has been referred to as the Timoshenko beam-transfer matrix method (TTMM), that allows one to analyze the response of the coupled system, including the tunnel motion and soil stresses. The results obtained were compared with those furnished by the pipe-in-pipe (PIP) approach, and were found to be consistent for exciting frequencies smaller than the tunnel second-mode cut-on frequency. The origin of discrepancies was investigated by the dispersion characteristic analysis, which is attributed to the absence of several in-plane modes when the tunnel is simplified as a Timoshenko beam.

The interaction between underground pipelines and soils is crucial to the design and maintenance of underground pipeline network systems. In this paper, the dynamic stiffness matrix in the frequency-domain of the buried pipeline is obtained by the improved scaled boundary finite element method (SBFEM) coupled with the finite element method (FEM) at the interface between the far and near fields. A new coordinate transformation together with a scaled line is introduced in the improved SBFEM. Combined with the mixed variable algorithm, the time-domain solution of the buried pipeline under dynamic loads is then obtained. The accuracy of the proposed algorithm was verified by numerical examples. A parametric study is performed to assess the influence of the anisotropic characteristics of the layered soils on the dynamic response of the pipeline, the result of which provides a reliable basis for engineering practice. The results show that these parameters have a significant impact on the pipeline. The understanding of this impact can contribute to the design, construction, and maintenance of the corresponding engineering projects.

The transfer matrix method is applied to the buckling of end-bearing piles partially or fully embedded in a layered elastic medium with a constant coefficient of subgrade reaction for each layer. The solution of the governing differential equation for each pile segment can be expressed as the product of a fourth-order matrix and a coefficient determinant. Using the transfer matrix method and combining the boundary conditions at both ends of the pile, the buckling load is obtained by solving the eigenvalue equation. A parametric study is performed to investigate the effects of the properties of the soil–pile system on the stability capacity of the pile. It is shown that the effects of the embedment ratio, soil layer thickness, and soil stiffness on the buckling of piles are quite significant. Several calculation examples are presented to verify the present method.