Mechanically stabilized earth (MSE) reinforcement tensile strength from tests of geotextile reinforced soil

Bridge abutments made of geotextile reinforced soil have been shown to support the bridge load without the use of piles. The use of mechanically stabilized earth as bridge abutments eliminates the "bump at the end of the bridge". The use of this technology is attractive because it is fast and fairly easy and inexpensive to construct. However, current design procedures are considered to be conservative. To determine the strength, and to better understand the behavior of reinforced soil, large unconfined cylindrical soil samples reinforced with geosynthetics were axisymmetrically loaded. Samples were 2.5 ft in diameter and 5 ft in height. Peak strengths of 4.8 ksf to 9.6 ksf at 3% to 8.5% strain were obtained from cylinders reinforced with geotextiles at 6-inch vertical spacing. A strength reduction occurred after the peak strength but most of the loads were sustained up to at least 10% strain before yielding. Tension in the reinforcement appears to be mobilized first in the middle layers, as determined from the location of tears in the geotextile. The strain in each layer was normalized by the maximum strain among all the layers in the sample. The normalized strains led to the development of the strain distribution factor (SDF). An equation to calculate for the required tensile strength in the reinforcement, Tmax AU, in a reinforced bridge abutment is proposed. The proposed equation is calculated as a factor of the vertical stress, the lateral earth coefficient, the vertical spacing, and the SDF. The tensile stresses in the reinforcement during loading were used to empirically derive the value of the lateral earth coefficient. The lateral earth coefficient value used in the equation is taken as the difference of Ko and Ka. The proposed equation values are larger or almost equal, depending on the type of facing, when compared to the K Stiffness method values but gave values that are about one-half of those obtained using the NCMA and Demo 82 methods.