Ultimate Limit State Reliability-Based Optimization of MSE Wall Considering External Stability (original) (raw)
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Canadian Geotechnical Journal, 2018
This paper demonstrates reliability-based design for tensile rupture and pullout limit states for mechanically stabilized earth (MSE) walls constructed with geosynthetic (geogrid) reinforcement. The general approach considers the accuracy of the load and resistance models that appear in each limit state equation plus uncertainty due to the confidence (level of understanding) of the designer at the time of design. The reliability index is computed using a closed-form solution that is easily implemented in a spreadsheet. The general approach provides a quantitative link between nominal factor of safety, which is familiar in allowable stress design practice, and reliability index used in modern civil engineering reliability-based design practice. A well-documented MSE wall case study is used to demonstrate the general approach and to compare margins of safety using different load and resistance model combinations. A practical outcome from the case study example is the observation that ...
Geosynthetic Reinforced Soil Structures are widely deployed in variety of applications around the world. And the evaluation of these structures in special loading conditions such as point and linear loads over abutments and also special geometrical conditions such as the nearness to adjacent structures, for example soil nailed wall, may be frequently necessary. There are several guidelines and softwares that are normally being used for design of the above-mentioned structures, However, most of them (if not all) do not make any recommendation for critical conditions and miscellaneous details such as connection of reinforcing element to the wall facade and to the retained zone, while those can jeopardize the whole structure stability. In this article, in order to evaluate the above mentioned topics, results of some parametric studies for an assumed abutment structure are presented. These analysis are based on various guidelines such as FHWA (NHI-10-024., 2009), BS (8006. 2010), Iranian national Code (No. 308, 2005), and guideline of Road Congress India 2014. Also several softwares such as PLAXIS, FLAC2D, MSEW and ReSSA are used. Finally a comparison between results is made and the advantages and limitations of each code and software are addressed.
Reliability Analysis of Anchored Geotechnical Structures for the Design Limit States
Wasit Journal of Engineering Sciences
Reliability has been considered of magnificent importance in engineering design specially in geotechnical engineering due to the unpredictable conditions of soil layers. It is essential to establish well- designed failure modes that could guarantee safety and durability of the proposed structure. This study aims to suggest a reliability analyses procedure for retaining walls by the mean of a reliability index β using the specifications of AASHTO Bridge Design 2002, Eurocode 7, and DIN EN 1993-5 norms. Two failure modes; Tensile failure of tendon (G1) and Failure by bending (G2) were studied and compared by using equation of the Design Limit State (DLS) and by taking some basic geotechnical parameters as Random Variables RV. The analyses demonstrated that the reliability index β and probability of failure Pf are the most important parameter in the reliability analysis. Also, the suitable height (H) for the retaining structure (for all angles ϴ) equals to 6 m and the most critical ang...
Reliability based risk index for the design of reinforced earth structures
Geotechnical and Geological Engineering, 2003
The design methods currently used for earth reinforcement are mostly based on deterministic properties of both the soil and the construction materials used. Nowadays, however, the general trend is designing at a specific degree of reliability. This is even more true where the raw data such as soil properties exhibit significant variation. Deterministic solutions, in this case, may not suffice. Therefore, this paper will attempt to use probabilistic formulations thereby modifying the existing design procedure of reinforced earth retaining walls to account for uncertainties and variabilities. Through a first order Taylor's series expansion about the mean, the mean and variance of the strip reinforcing components, namely width and length, are derived in terms of the variations in the soil properties. Design charts that enable estimation of both mean and variance are developed to avoid extensive partial differentiation involved in the computations. Using appropriate probability distributions along with the mean and variance, the final design outputs are determined for a selected failure probability by introducing what is refered to as 'risk index'. The results indicate that the risk index increases with an increase in the coefficient of variations and a decrease in failure probability. Furthermore, it is shown that in some cases, depending on the variabilities of the soil properties, the classical design technique produced a relatively high failure probability.
Canadian Geotechnical Journal, 2017
Cross correlations between nominal load and resistance terms in limit state functions for geotechnical soil–structure interaction problems can be expected. A closed-form solution for the reliability index for a simple linear limit state function is used to examine the influence of nominal load and resistance correlations on computed margins of safety. The formulation also includes the contribution of the underlying accuracy of the load and resistance equations (method bias) and bias dependencies with the magnitude of nominal load and resistance values assumed in the limit state design function. Sensitivity analyses and example problems for the external sliding limit state for a cantilever wall and the pullout limit state for internal stability of reinforced soil walls with different soil reinforcement types are presented. Ignoring nominal correlations where they exist is shown to underestimate the reliability index in some cases and to overestimate the reliability index in other cas...
Soft ground usually possesses low shear strengths and high compressibility. Reinforced earth (RE) wall is constructed on this soft ground have a tendency to fail. In literature stability of this reinforced earth wall is improved by providing geo-grid reinforcement. In the present paper stability analysis of a highway embankment is presented. The proposed highway embankment is provided along the approach on either side of bridge. The maximum height of embankment is 7m and its stability is a concern. In the preset study modeling and stability analysis of the embankment at typical sections is computed using slope/W using Morgenstern price method. Results of lab tests on subgrade and stability results are presented. It is observed that, the stability is improved using geosynthetics provided near slope face and at base. Parametric study is carried out by varying tensile capacity of geo-grid, number of layers and their influence on stability is quantified and presented.