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Article Citation - WoS: 5Citation - Scopus: 6Investigation of the Effect of Shearing Rate on Residual Strength of High Plastic Clay(Springer Heidelberg, 2020) Akis, Ebru; Mekael, Ahmad; Yilmaz, Mustafa TolgaThe residual shear strength on failure plane is a crucial parameter to be estimated for analysis of an active landslide. This strength must be determined precisely to build a reliable theoretical model for calculations. The multi-reversal direct-shear test is a practical method to determine this shear strength in laboratory due to wider availability of apparatus. The shearing rate is among the factors that significantly affect the precision of test results for clay specimens. However, limits for this rate are yet to be clarified to shorten the duration of multi-reversal direct-shear tests. In this study, two tests series at different shearing rates were performed to investigate the effect of shearing rate on the residual strength of highly plastic clay sample recovered from a landslide area in Northern Turkey. The shearing rates were set to 0.024 mm/min which was decreased to 0.001 mm/min during the last forward shearing phase for the first test series, whereas the rate was fixed to 0.0007 mm/min for the second test series. The residual friction angle determined by these tests was interpreted by using a theoretical analysis of the landslide, and they were compared with the estimations due to empirical relationships given in the literature. It is concluded that, although the rate of 0.024 mm/min is consistent with the recommendations in literature, this rate can yield overestimation of residual shear strength determined in multi-reversal direct-shear tests.Article The Estimation of the Residual Shear Strength of High Plastic Clays Based on Direct Shear Test Results(Gazi Univ, 2021) Akis, EbruLandslides are the most common incidents with a rate of 45% considering the distribution of natural disaster numbers to disaster types. In order to make remedial measures for the landslides, the residual shear strength parameters formed in the shear plane during the landslide must be estimated as close to the reality as possible. These parameters can be determined by multi-reversal direct shear, ring shear tests, back calculations, correlations in the literature by means of physical properties of the soil. The difficulty of predicting the groundwater conditions during landslide is obvious and it directly affects the residual shear strength values when shear strength parameters are determined using the back analysis method. On the other hand, residual shear strength parameters obtained from the literature can give a wide range. Besides, ring shear tests are not commonly performed in laboratories and depending on the type of soil, multi reveral direct shear tests may need to be performed at very low speeds. Relatively long test time adversely affects the practical use of the multi reversal direct shear tests. In this study, the relationship between peak and residual shear strength in normally consolidated high plastic clays was studied within the framework of the above restrictions. Firstly, the empirical correlation between the residual shear strength and the index porperties and peak shear strength was predicted by evaluating the results of the studies in our country's literature. Then, the results obtained from the multi reversal direct shear tests with remoulded high plastic clay samples and the predicted values were compared.
