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Measurement of Amorphous Peat Shear Strength in the Direct Shear Box at High Displacement Rates


The ASTM standard provides guidelines for the drained direct shear test (DST) and requires the samples to be sheared at rates estimated from time to failure, \(t_{f} \ge 50t_{50}\) (where \(t_{50}\) is the time required to achieve 50% consolidation). This paper investigates the potential of estimating the undrained strength of peat in the DST owing to its ease of accessibility and simplicity over other laboratory tests. In this experimental study, peat samples were sheared at various displacement rates at \(t_{f} /t_{50}\) values of 0.065–70. The samples tested at the ASTM specified rate of \(t_{f} \ge 50t_{50}\) exhibit continuous increase and decrease in shear stress and volume respectively with increasing shear strain. Hence, determining the drained strength properties of peat in the DST apparatus is complicated. However, it is concluded that the shear stress ratio, \(\tau /\sigma {^\prime }_{v}\) of the DST test samples sheared at rates corresponding to \(t_{f} \le 0.2t_{50}\), reasonably corresponds to that measured in undrained direct simple shear (DSS) tests on peat, found in the literature. Therefore, DST conducted at high displacement rates will be adequate for preliminary evaluation of the shear strength of peat at close to undrained conditions, when constant volume DSS apparatus is not available.

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The work presented in this paper is supported by the UNIMAS small Grant Scheme (Grant No. FO2(S165)/1198/2015(02)) and the Fundamental Research Grant Scheme (Grant No. FRGS/TK01(02)/1302/2015(19)). The authors are very grateful to Mohd Nazri Zaidan, an intern student at the Universiti Malaysia Sarawak for his helping hand during the experiment. Also, Haji Affandi and all other geotechnical laboratory technicians are gratefully acknowledged for their support and time. The second author is grateful for the postdoctoral fellowship financial support in COFS, UWA, provided by the ARC Industrial Transformation Research Hub for Offshore Floating Facilities (funded by Australian Research Council).

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Correspondence to Akeem Gbenga Amuda.

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Amuda, A.G., Sahdi, F., Hasan, A. et al. Measurement of Amorphous Peat Shear Strength in the Direct Shear Box at High Displacement Rates. Geotech Geol Eng 37, 1059–1072 (2019).

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  • Peat
  • Undrained strength
  • Direct shear test
  • Displacement rates
  • Consolidation