A Study On Reliability Of Structural Systems Of Gravity Retaining Walls

Gravity retaining walls are among the most frequently used structures in civil engineering in China, because of its low cost, materials availability and could easy workmanship. At present, safety factor method is adopted in retaining walls' design and analysis. Because of the randomicity of physical mechanical property of soil is not considered, some earth retaining walls which are safe enough according to safety factors damage soon when they are put into use. If reliability analysis method were introduced into retaining walls' design and analysis, a lot of damage could be decreased. Some scholars in China and overseas have done some work in introducing reliability method into retaining walls' design and analysis. The main research aspects of this paper on base of predecessors' research achievement are as follows:(1) The random variables which affect gravity retaining walls' reliability are analysed. It is assumed that the inner friction angle of backfills, the friction angle between wall back and backfills, the unit weight of backfills, the coefficient of base friction, the foundation limit load, the saturated unit weight of backfills, hydraulic gradient, etc., are random variables which obey normal distribution. According to reliability theory, the structural performance functions of earth retaining wall anti-overturning, anti-sliding, foundation bearing capacity, material tensile strength, material compressive strength, material shear strength are established. Taking a practical gravity retaining wall in Gansu province for an example, the reliability index of every failure mode is computued by design point method in the first order second moment theory in structural reliability analysis.(2) In order to reflect the real reliability of gravity retaining walls' stability, system reliability calculation theory is introduced. It is assumed that the three failure modes, i.e., earth retaining wall overturn, slide or exceed foundation bearing capacity form a serial system. On the base of reliability index of single failure mode, the reliability index of structural systems can be computed by step-by-step equivalent plane method, and the failure probability of structural systems of earth retaining walls' stability can be computed too.(3) Reliability calculation process of a practical gravity retaining wall in Gansu province is simulated by Monte-Carlo simulation. From the simulation results, the reliability index of single failure mode which is computed by design point method in the first order second moment theory and the reliability index of structural systems which is computed by step-by-step equivalent plane method are comparatively precise. So the two reliability calculation methods can be generalized in reliability analysis on earth retaining walls.(4) The difference of the reliability index of structural systems between former and after rebuild of a practical gravity retaining wall is analysed. The reliability index of structural systems of the new earth retaining wall is greater than the intrinsic one. When the influence of hydrodynamic pressure is considered, the reliability indexes of structural systems of the intrinsic earth retaining wall and the new earth retaining wall are both diminished, and the corresponding failure probabilities of structural systems become greater. Based on the global position system(GPS) and the total station technic, a monitoring method is adopted to monitor the distortion of the new earth retaining wall. From the results, the whole earth retaining wall did not settlement and incline obviously in observation period, and it is safe at present.(5) The relationship between safety factors and reliability indexes of gravity retaining walls' stability resistance overturning and silding is researched. 36 earth retaining walls which have different section dimensions are designed for a cohesive soil slope in Gansu province. The safety factors and reliability indexes of every retaining wall are computed. Arrange the results and plot curves to represent the relationships between safety factors resistance overturn and slide and reliability indexes respectively. From the figures, the reliability index increases with increasing the corresponding safety factor.