Improvement For Active Earth Pressure Calculation Methods And Research On Retaining Wall Design Standards

Since retaining walls are widely used in practical engineering, earth pressure has been a hot issue for scientists and engineers. In the design of retaining walls, engineers often encounter complex soil conditions, such as layered soil. Previous theoretical researches are mainly for homogeneous soil and less are carried on layered soil especially for cohesive case behind the wall. For methods commonly used in practice like equivalent and layering calculation have also significant limitations in the application. In fact, it has already a mature solution for the presence of layered soil in slope stability analysis, which can be introduced into active earth pressure calculation. By using the vertical slice method, it can not only get an accurate expression for active earth pressure, but also get the precious experience in the treatment of complex soil and slope surface shape and critical slip surface searching methods from slope stability analysis. Therefore, a simplified formula of Coulomb active earth pressure calculation is derived separately based on the force balance equation of earth pressure calculation proposed by Chen & Li (1998) [15] using the method of vertical slice, which would solve earth pressure calculation problems of layered soil include cohesive soil. In addition, critical slip surface searching is needed during Coulomb earth pressure calculation. To facilitate engineering applications, an easy operation and transparent calculation program of Coulomb active earth pressure calculation on retaining wall is developed based on the Excel interface according to the simplified formula proposed in this paper, with which engineers can easily carry out the active earth pressure and search the critical slip surface.In addition, fixed value method measured with safety factor is often used in traditional retaining wall stability analysis. As the randomness of each design variables cannot be considered by a single factor, which results in the safety factor specified met while damage still occurring for some retaining walls, the reliability and partial coefficients limit state design methods which considering parameter variability need to be introduced into retaining wall’s design. This paper conducts a preliminary exploration on it and the main work is as follows:(1)The reasonableness for the allowing security factors of stability against sliding provided by SL 379-2007 "Hydraulic Retaining Wall Design Specifications" is analyzed by comparing the relevant specifications of retaining wall. It’s obtained that the allowing safety factors specified in the code is lower than other retaining wall design specifications.(2)The reliability criteria provided by GB 50199-94 "Unified Standard for Reliability Design of Hydraulic Engineering Structures" is introduced into the design of hydraulic retaining wall to measure the rationality of the single factor of safety standards and improve it quantitatively, by putting the two in the same platform comparing, using the’relative safe rate method’proposed by Chen Zuyu et al. [72] According to the analysis, for hydraulic retaining wall in grade 1,2 and 3, the allowing safety factors are 1.6,1.45 and 1.3. The universality study of the allowing safety factors proposed is carried out and the rationality of it is verified.(3)Considering the parameters variability in hydraulic retaining wall design, partial coefficients of material parameters are calibrated as γf=1.311, γc=1.570. And the reasonableness of them is verified by establishing the contact between partial coefficients and reliability with the ’relative safe rate method’.