Volume 15, Issue 3 (2015)                   IQBQ 2015, 15(3): 37-50 | Back to browse issues page

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Abstract:   (2067 Views)
As a disastrous cyclic response of soils, liquefaction commonly takes place in the saturated soils overlaid in seismic regions. Earthquake excitation in loose deposits enforces the soil particles to displace towards a more compacted state. This tendency causes generation of excessive pore water pressure when drainage is prevented or its rate is less than the generation rate. Comprehensive laboratory investigations have been carried out so far in order to capture cyclic behavior of silicate soils. However, cyclic behaviour and liquefaction resistance of calcareous soils has not been fully recognized as well. Calcareous soils evolve from biological resources due to the physiochemical process of marine organisms. Such soils have excessive crushing capability; and thus, their mechanical behaviour is expected to be different than that of terrestrial soil deposits. The current study presents results of several undrained cyclic tests on isotropically and anisotropically consolidated samples of Boushehr calcareous sand. The tests were conducted via a triaxial machine in strain-controlled condition. Bulk samples of the sand were gathered from the coast of Boushehr city located in the southwest of Iran, north bank of Persian Gulf. The sand samples were reconstituted with dry deposition method of sample preparation under various initial relative densities and confining pressures. The consolidation phase of the tests was performed in drained condition for either isotropically or anisotropically consolidated samples. The cyclic loading phase of the tests was conducted by multi-stage procedure in order to recognize soil potential for excess pore water pressure generation. Various levels of controlled cyclic axial strains were applied on the sample in each stage of the cyclic loading phase and the samples were allowed to be drained at the end of each stage. The results are presented in terms of threshold shear strain and dissipated strain energy concept. Comparison is made between the tests results and those reported by the previous studies. The results revealed that liquefaction resistance of the studied sand increases with increasing initial relative density and effective confining pressure whereas the samples with high initial effective stress never liquefied even after one hundred cycles of loading. Relationships between excess pore water pressure and the normalized number of cycles as well as the normalized dissipated strain energy are studied and compared with the relationships presented by the previous researchers for silicate sands. According to the results, such relationships are strongly affected by type of cyclic loading i.e. strain or stress-controlled when excess pore water pressure is correlated to the normalized number of cycles. In fact, evaluation of excess pore pressure is more reasonable to be done with the normalized strain energy in order to minimize the influence of loading type. The threshold shear strain for the studied sand was found to be 0.015% which is comparable with this value for silicate sands.
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Article Type: Original Manuscript | Subject: -------|---------
Received: 2013/09/14 | Accepted: 2015/08/12 | Published: 2015/09/23