Finite Element Analysis of Damage to Highway Embankments due to Dynamic Subsidence Resulting from Longwall Mining

A coal panel of a longwall mining site was extracted below highway I-70. A 70 ft embankment is located in the center of the panel. This study analyzed the influence of subsidence due to longwall mining on the behavior of this embankment and others along this highway. A Finite Element Method (FEM) that uses ABAQUS, and a field study that employs slope stakes, inclinometers and piezometers were used to analyze its deformation and stability. A user-defined displacement model was applied to the embankment’s bottom to simulate the dynamic subsidence. This model was obtained from a regression analysis of the vertical subsidence profile obtained from the Surface Deformation Prediction System (SDPS) software. In the field study, the ARCGIS (Lidar method) was utilized to construct the vertical subsidence contour employing data from the slope stake survey conducted by PennDOT. The embankment deformations from the simulation were compared to those obtained from the field measurements. Both indicated that the location of the maximum subsidence on the embankment was the same. Using the FEM, a slope stability analysis of the embankment was conducted at each step of the dynamic subsidence. Sections experiencing large deformations were determined. These sections were used for a slope stability analysis employing the shear strength reduction method (SRM). Factors of safety (FS) and their equivalent shear strength reduction factors (SRF) were calculated at these critical cross sections. An FS range was proposed to describe the slope stability of the embankment. The lower bound of the FS range identifies an embankment experiencing small deformations. The upper bound of the FS range identifies an embankment that experienced large deformations. This upper bound FS developed in response to the strain hardening behavior of the soils. This behavior was obtained from triaxial compression tests. Thus, as a result of the deformations induced by the longwall mining, the embankment became stronger and safer. Also, a parametric study was conducted to explore the influence that the orientation of the longwall mining and the overburden level have on the deformations and stability of the embankments. It was found that these parameters have a significant influence