| Summary: | 碩士 === 國立成功大學 === 土木工程學系碩博士班 === 95 === In the past, Simplified Empirical Procedures were adopted for soil liquefaction potential evaluation in Taiwan. One of important problems which the people from the engineering circle are concerned about is, however, whether the procedures are a little too conservative and accordingly increases the cost of project. To work out whether or not liquefaction potential evaluation is exact, the soil specimens that were dug out from the library’s basement of Chang Jung Christlan University located in the southwest of Taiwan is chosen as the object of this study, in which, specimens with relative density at 50%, 60% and 70% are remolded. By means of dynamic triaxial undrained cyclic loading test the definition of soil liquefied is said to be whenever the single-side axial strain reaches 5%. On the basis of the comparison with the results evaluated by using Seed and T & Y SPT Simplified Empirical Procedures, this study probes into the applicability of dynamic triaxial test in the evaluation of soil liquefaction potential.
It is found that, in comparison with the results evaluated by using Seed and T & Y SPT Simplified Empirical Procedures, liquefaction potential of the remolded soil with 60% relative density in this study is close to that under SPT Simplified Empirical Procedures and loose sand whose relative density is 50% shows higher liquefaction potential, whereas dense sand with 70% relative density shows lower liquefaction potential, which means that, when the relative density is higher than 70%, liquefaction impedance strength may be undervalued in Simplified Empirical Procedures, by contrast, it may be overrated on condition that the relative density of loose sand is lower than 50%. Therefore, when evaluating liquefaction potential of some kind of soil, relative density of dense sand should be taken into consideration and the evaluation result of soil liquefaction under dynamic triaxial test should be referred to in order to guarantee the evaluation accurate.
It is also found that in the study, saturation of specimens, disturbance of soil samples and operation errors during the test will have an effect on the exactness of the dynamic triaxial test. In remolding the specimens, not only the operations of membrance, filter paper and cell pressure but errors in sensor system of facilities for the test may result in errors of the test result. This study reveals that, due to the errors arising from these factors, the result of the test will incline to be conservative, yet the liquefaction evaluation under dynamic triaxial test on dense soil layer with higher relative density is less conservative than that under Simplified Empirical Procedures. Hence, in evaluating the liquefaction potential of dense sand, dynamic triaxial test can be adopted as secondary approach so that unnecessary waste in construction cost can be avoided.
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