Time：5月16日 10:25 -10:50
Title: RATIONAL AND SIMPLIFIED APPROACH FOR DETERMINATION OF SEISMIC INDUCED EARTH PRESSURE ON NON-YIELDING WALLS /刚性墙地震土压计算的合理简化方法
Abstract: Based on Coulomb earth pressure theory, Bo Liang’s calculation method, and Yuliang Lin’s graphical method, a more rational and efficient method for determining the seismic-induced earth pressures of non-yielding walls such as abutments and massive walls is proposed. This approach is a significant improvement to the traditional pseudo-static Mononobe-Okabe (M-O) method that has been widely adopted in practice since 1930s, in which effect of wall rigidity, wall inertia, critical rupture angle behind the wall, and effect of superstructure stiffness are considered in addition to the usual wall inclination, backfill slope, soil-wall friction, and soil cohesion. The equation for determining the active earth pressure is derived first, followed by the parametric studies and numerical analyses, and the comparisons with the conventional Coulomb’s earth pressure theory, M-O method, and the more recent computation method proposed by Yuliang Lin. Then, the effects of various system parameters on seismic-induced earth pressures are studied. The primary findings include:
(1) The traditionally-used methods including the Coulomb pressure method, M-O method, and Yuliang Lin’s more recent method seem to yield lower active earth pressures by 10-40% compared to the proposed method (Fig. 1). This is because the conventional methods are intended for retaining walls rather than for abutments which have apparently different geometry. The higher pressure difference occurs when the inclination of the rear face of walls is more significant and in this case using any of the traditional methods to compute earth pressures would be unconservative or unsafe.
Fig. 1 Comparison between the various methods
(Note: For noncohesive soils, Lin’s method yields the same earth pressure as M-O method.)
(2) The larger the internal friction angle of backfill () is, the smaller the abutment active earth pressure (Fig. 2). The active earth pressure decreases with the increase of the external friction angle between the rear face of abutment wall and the backfill. It also decreases with the increasing inclination angle () of the rear face (Fig. 2).
Fig. 2 Effect of external friction angle on the active earth pressure coefficient
(3) The effects of various system parameters on active earth pressures are similar whether a conventional method or the proposed method is used.
(4) In terms of the passive earth pressure, the pressure deference between the proposed method and any of the traditional methods becomes more apparent with the increasing internal friction angle of backfill. While this difference is diminishing with an increasing external friction angle. The effects from the system parameters are similar to active pressures, however.
Contrary to retaining walls, abutments are more susceptible to the effects from the superstructure under the earthquake action. As such, the induced earth pressure is significantly greater. A rational determination of seismic-induced earth pressures must consider the effects of the mass and stiffness from the superstructure on the abutment. The larger the structural mass and stiffness are, the greater the earthquake force. Note that the axial stiffness of the superstructure is far greater than the abutment stiffness. Finite element analyses using ABAQUS are performed by considering the ratios of superstructure axial stiffness to abutment stiffness of five actual bridges in Shanxi Province. The accuracy and effectiveness of the proposed method for determining seismic-induced earth pressures are hence further validated.
Lastly, pertinent conclusions and useful design recommendations are made, which are expected to benefit the engineering community.
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