Prototype reinforced soil embankment for reconstruction of US 62 slope failure in Chickasha, OK
Miller, Gerald A.
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One of the main concerns in internal stability of reinforced soil structures constructed with fine-grained or marginal quality soils is the change in shear strength of the soil-reinforcement interface when the soil gravimetric water content (GWC) increases. This increase can occur during construction or service life of the structure, e.g. due to prolonged precipitation. The resulting loss in the soil matric suction could reduce the interface shear strength leading to serviceability problems or even failure of the reinforced soil structure. In this study, three (3) 1 m-high and two (2) 1.7 m-high model embankments were constructed, which were all subjected to strip footing loading in plane-strain condition. The model embankments were constructed using a mixture of lean clay (CL), sand and a small percentage of commercially available sodium bentonite at the GWC values ranging between OMC-2% and OMC+2% (OMC: Optimum Moisture Content). The purpose for building smaller embankment models was to study the behavior of a single soil-geotextile interface in an embankment configuration. Therefore, the smaller models included only a single reinforcement layer which was placed 180 mm below the embankment surface. In contrast, the larger models were intended to simulate field reinforced embankments. Hence, those models were reinforced with four (4) layers of reinforcement with a uniform vertical spacing of 300 mm. The location of single reinforcement layer in smaller models was selected based on preliminary embankment tests and numerical simulations to ensure that it would intercept the failure surface that developed underneath the strip footing near the embankment slope. The embankments were instrumented to measure the footing load, earth pressure, reinforcement strains and the soil GWC and matric suction values during the tests. A primary objective of the embankment tests was to investigate the influence of the as-compacted GWC value of the soil on the performance of the model embankments and thereby, validate or make necessary adjustments in the values of the moisture reduction factors (MRF) for reinforced embankment design that the authors had developed based on their prior pullout and interface shear tests.