Study On Damage Mechanism Of Typical Side-Hill Gravity Retaining Walls In The 5.12 Wenchuan Earthquake Regions

On May 12,2008, an earthquake measuring eight on the Richter scale happened in Wenchuan County, mountainous area of western Sichuan Province of China. The earthquake greatly damaged cut slope retaining walls, and especially gravity retaining walls. From a comprehensive investigation and summary of gravity retaining walls damage conditions on the 18 roads (about 3500km in length) from the disaster area after the earthquake, this paper summarizes five characteristic failure types, namely, wall cracking, wall failure, wall extraversion, wall slip and retaining wall failure by rock fall according to statistical and analytical data.Analytical data of damage finds that the amplification effect of displacement of cut slope increases with elevation bigger, and especially the gravel soils at top of slope is more obvious than lower rock, the amplification effect of acceleration largens with the height of slope. In Wenchuan earthquake, increasing of earth pressure on wall back is one of the main reasons of wall failure. Using the FLAC3D to calculate the time history curve and the distribution form of dynamic earth pressure, then comparing the peak value of dynamic earth pressure with the calculated value by Pseudo-static method, the time history curve shows that dynamic earth pressure has time-varying feature and pressure distribution is the combination of several distributions including inverted triangle and parabola.On the basis of distribution form of dynamic earth pressure, owning to the effect of dynamic earth pressure, increasing obviously of earth pressure turns up the overturning moment, slipping force and load on the wall, reduces the factor of wall overturning stability and wall slipping stability leads to wall extraversion or lower stability of wall slipping, and tension crack or shear crack when the bending moment and shear stress of the wall exceeds the bending strength and shear strength.On the basis of damage investigation, the paper analyses the influence of dynamic earth pressure as additional pressure on the wall stability, foundation bearing capacity and wall crack to reveal the damage mechanism of cut slope gravity retaining walls damaged by high intensity of Wenchuan earthquake serves as theoretical reference for practical engineering.