Strain-Rate Influence on Shear Strength Characteristics of Compacted Asela Clay

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Addis Ababa University


This research work tries to examine the effect of strain rate on shear strength of red clay soil of Asela. It is attempted to identify the effect of strain rate by conducting a series of triaxial compression test and unconfined compression test on remolded soil samples. All the specimens were compacted at optimum moisture content (OMC) with the standard compaction apparatus. Besides basic tests have been done to identify the soil type. Both unconfined compression tests and triaxial tests were done on samples of 38mm in diameter and height twice the diameter. The type of triaxial test employed was consolidated undrained (CU) with pore pressure measurement and with effective consolidation pressure of 200kPa, 300kPa and 400kPa. After saturation and consolidation stage, the specimen were axially loaded at rate of strain varying from 0.001mm/min to 1mm/min. A total of twelve triaxial consolidated undrained tests and sixty unconfined compression test were run. Data presented includes consolidation data, pore pressure observation, stress-strain relationship and modified Mohr failure envelop diagram. The results of triaxial tests were used to examine the stress strain relationship and shear strength parameters. The results showed that strain rate affect both stress-strain relationship and strength of soil. As the strain rate increases the strength of the soil also increase but the strain rate has more pronounced effect on cohesion and little effect on angle of internal friction of the soil. The values of cohesion obtained from modified failure envelop for strain rate 0.001mm/min,0.01mm/min,0.1mm/min and 1mm/min were 40.67kPa, 44.38kPa, 64.6kPa and 93.15kPa for total stress and 39.97kPa, 42.85kPa, 51.92kPa and 79.52kPa for effective stress. The value of angle of internal friction obtained from modified failure envelop for strain rate of 0.001mm/min,0.01mm/min,0.1mm/min and 1mm/min are 14.460,14.530, 14.120 and 14.730 for total stress and 21.870,22.130,21.530 and 21.020 for effective stress. The unconfined compression test were done on the samples of 38mm in diameter and a height of twice the diameter with seven(7) different strain rates(i.e.0.08,0.4,1,1.52,2,5 and 10mm/min) for remolded clay soils. From the test result undrained shear strength in unconfined compression test is directly related to strain rate effects. A higher strain rate results in higher undrained shear strength for Asela red clay soil. The values of undrained shear strength obtained from unconfined compression test for strain rate of 0.08mm/min, 0.4mm/min, 1mm/min,1.52mm/min, 2mm/min, 5mm/min and 10mm/min are 34.02kPa, 36.95kPa, 37.23kPa, 41.77kPa, 42.70kPa, 47.77kPa and 48.46kPa



Geotechnical Engineering stream