AASHTO results for case 1 (s=0.4 m) confirmed that at height h=6.0 m, the wall was at the verge of failure, which coincided with the definition of a critical state in FLAC analysis. The ultimate strength of geotextile exceeded the maximum reinforcement force from internal stability analysis (Tmax), except for the fifth layer, which indicated that, internally, the wall was stable. The factors of safety against sliding and bearing capacity showed that the wall was stable with respect to direct sliding (F s=2.914) and bearing capacity failure (F s=86.4). The results for case 1 show that, according to analysis, the wall was at the verge of failure due to toppling (F s=1.09). The excessive factors of safety against bearing capacity for cases 1, 2, and 8–1 were a result of the artificially high cohesion used in FLAC models to represent very stiff foundation soil. The factors of safety for sliding and overturning are calculated for the wall-foundation interface and represent their minimum values. Major results from the MSEW 1.1 analysis are given in table 5.2.
All reduction and correction factors in the MSEW 1.1 analysis were specified to be equal to 1.0. Since up to five different reinforcement types can be specified in MSEW 1.1, only the maximum axial forces of the bottom five layers were used. The ultimate strength of reinforcement was specified to correspond to the maximum axial force in reinforcement calculated by FLAC. The wall geometry and reinforcement layout were the same as those used in the FLAC models (figure 3.1). No water table, surcharge loads, or seismicity were introduced in the analysis. The analysis mode of the program was used for simple wall geometry, modular block facing, and geotextile reinforcement. The input data used in the AASHTO 98 analysis with the MSEW 1.1 program are given in table 5.1. Case 1 (s=0.4 m)-external mode (direct sliding/overturning).The following four cases were selected to represent different failure modes identified with FLAC: The purpose was to compare FLAC predictions with an existing design method. 5.1 Analysis of Baseline Cases using AASHTOįour model walls at the critical state were analyzed according to AASHTO design method using the program MSEW 1.1 (ADAMA Engineering 1998). Third, stress distributions from FLAC analysis were compared with the AASHTO values. Second, the slopes' slip planes of all cases at the critical and failure states were measured from FLAC plots, and are presented together with the values resulting from the Rankine's and Coulomb's earth pressure theories.
82: Mechanically Stabilized Earth Walls and Reinforced Soil Slopes, Design and Construction Guidelines," (FHWA, 1997).įirst, the program MSEW 1.1 (ADAMA Engineering 1998) was used to analyze four baseline cases that represent all four failure mechanisms identified by FLAC. The details of AASHTO design are given in "Demonstration Project No. This chapter compares FLAC predictions with calculations done in accordance with AASHTO, Section 5.8, 1998 (AASHTO 1998). Effects of Geosynthetic Reinforcement Spacing on the Behavior of Mechanically Stabilized Earth Walls CHAPTER 5.
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