NUMERICAL ANALYSIS OF EMBANKMENT AND REINFORCED MSE WALL WITH CRUSHED SLAG AS BACKFILL MATERIAL

Abstract

Mechanically stabilized earth are the structures that are widely used to retain the earth mass. These are made with the help of reinforced soil that increases the shear strength of soil, known as RE (reinforced earth). Validation and numerical analysis of MSE wall with concrete panel facing located at A4 Portuguese highway between Amarante and Vila Real was done as per data obtained from Cristelo et al. (2016). The wall was built in 2010 to provide support to a section of Portuguese highway. The wall has a length of approximately 335 m, with a height ranging between 7 and 12 m (unpublished Infratunel internal document from 2009, “Marao Highway, Amarante/ Vila Real, Subsector Geraldes/ Padronelo –Design of Complementary Projects: Walls” (in Portuguese)). After validating results, the material used in the MSE wall was replaced by Crushed slag. Analysis of MSE wall having slag as backfill was done using FEM software PLAXIS 2D. Axial tensile forces in different reinforcements and locations were obtained. This report presents modelling of a 6 m high MSE wall using PLAXIS 2D. Concrete panels, bearing pad and geogrid elements are used to model. Different type of soil was considered in analysis namely retained soil, reinforced soil and foundation soil. The geogrids are provided at five different spacing for analysis viz. 0.3, 0.4, 0.5, 0.75 and 1 m. On top of backfill, base course and asphalt concrete layer was used for applying the traffic loads in analysis according to IRC 06-2014. For 12 m width of pavement three class-A type loading was applied in simulation. Variations are plotted for maximum total, vertical and horizontal displacements for different spacing of geogrids. Graph for maximum shear force on concrete panel and maximum axial force in geogrid was also plotted with different spacing of geogrid. The results show that the shear force was minimum for 0.4 m spacing of geogrid. Maximum horizontal displacement and axial force in geogrid vary linearly with spacing of reinforcement. An embankment model of slope 1V:2H having top width 1.4 m and 1 m height was made in laboratory with crushed slag sand. The embankment was then loaded with dead weight on wooden footing of 23 cm width at different setback distance. The loading was done at setback ratio (x/B) of 0, 1, 2 and 2.5. Load displacement curves were plotted based on the observations obtained from laboratory model. From the load displacement plot at setback ratio of 2.5, elastic modulus of material was found using the equation given by Vesic (1961). Further, Numerical analysis was done in PLAXIS 2D. Mesh convergence study was performed in PLAXIS 2D to obtain optimum element size mesh to generate accurate results. Validation was iii done for the model embankment of slope 1V:2H that was made in laboratory. Load displacement curve was produced in each case. The pattern of failure was also analyzed with the help of incremental displacements color pattern obtained from PLAXIS output program. Bearing capacity for slopes with increasing steepness of 1V:2H, 2V:3H, 1V:1H, 2V:1H respectively was determined by loading the embankment at different setback distances. Parametric study was performed for variation of bearing capacity with four different angles of slope, at four different setback ratio and for three different relative density of crushed slag used in embankment. Total 48 cases were analyzed with the help of PLAXIS 2D and bearing capacity was compared by varying different parameters in the embankment. It was found that bearing capacity decreases with increase of the steepness of slope and increase with the increase of setback ratio and relative density of crushed slag. To improve the bearing capacity of embankment, geotextile was used to make reinforced soil wall (RSW) with wrap around facing in PLAXIS 2D for 4 m high wall and 7.5 m width. On top, layer of base course and asphalt concrete was made and traffic loads were applied for analysis according to IRC 06-2014. Maximum horizontal and vertical displacements with axial tension force in reinforcement was analyzed through FEM.