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Öğe Characterization of liquefaction susceptibility of sands by means of extreme void ratios and/or void ratio range(American Society of Civil Engineers (ASCE), 2010) Yilmaz Y.; Mollamahmutoglu M.The liquefaction susceptibility of various graded fine to medium saturated sands are evaluated by stress controlled cyclic triaxial laboratory tests. Cyclic triaxial tests are performed on reconstituted specimens having global relative density of 60%. In all cyclic triaxial tests, loading pattern is selected as a sinusoidal wave form with 1.0 Hz frequency and effective consolidation pressure is chosen as 100 kPa. Liquefaction resistance is defined as the required cyclic stress ratio causing initial liquefaction in 10 cycles during the cyclic triaxial test. The results are used to draw conclusions on the effect of the extreme void ratios and void ratio range on the liquefaction resistance of various graded sands. © 2009 ASCE.Öğe Engineering properties of medium-to-fine sands injected with microfine cement grout(2011) Mollamahmutoglu M.; Yilmaz Y.This article investigates the penetrability of microfine cement suspensions prepared with Rheocem 900 with and without superplasticizer additive into various graded fine-to-medium sands into which chemical grout permeation is only possible. Initially, the basic rheological properties such as viscosity, setting time, and stability of microfine cement suspensions are studied. In addition, penetration performance of the suspensions into various graded fine to medium sand specimens under different grouting pressures is examined. Finally, the strength and permeability characteristics of various graded fine-to-medium sand specimens permeated with microfine cement suspensions are studied. It is found that a superplasticizer additive greatly increases the grouting performance of microfine cement and reduces the grouting pressure. Moreover, it is seen that the unconfined compressive strengths of sand specimens permeated with a cement grout without additive are slightly less than those of sand specimens permeated with cement grout and superplasticizer additive. Further-more, permeability tests on specimens permeated with cement grouts with or without a superplasticizer reveals that all specimens are impermeable (k<1 10 7 m=s). © Taylor & Francis Group, LLC.Öğe Investigation of the effect of a polypropylene fiber material on the shear strength and CBR characteristics of high plasticity Ankara clay(2009) Mollamahmutoglu M.; Yilmaz Y.Nowadays, many soil improvement methods have evolved with different materials used. In this study, a series of laboratory tests are carried out to investigate the effect of a polypropylene fiber material on the shear strength and California Bearing Capacity (CBR) characteristics of high plasticity Ankara clay. First, geotechnical properties of Ankara clay are presented. Then, results of unconfined compressive strength, triaxial strength (CU type) and CBR tests conducted on the various polypropylene fiber/clay mixtures (0.1%, 0.2%, 0.3% and 0.4% by dry weight) are given. Samples were compacted at optimum moisture contents and maximum dry unit weights obtained from the standard Proctor compaction effort. Standard Proctor compaction tests and CBR tests revealed that percentage of 19 mm length F type polypropylene fiber did not influence much the optimum moisture content, maximum dry unit weight and CBR values. Unconfined compression tests showed that inclusion of fiber content increased the axial strain at failure. Moreover, consolidated-undrained (CU) triaxial test results exhibited that due to inclusion of 19 mm length F type polypropylene fiber, the cohesion intercept decreased slightly but the internal angle of friction increased considerably. © 2009 Taylor & Francis Group, London.Öğe Pre- and post-cyclic loading strength of silica-grouted sand(2010) Mollamahmutoglu M.; Yilmaz Y.The aim of this study is to investigate whether there is a loss in the strength of fine- to medium-grained colloidalsilica-grouted sand after cyclic loading. First, the rheological properties of colloidal silica grouts, such as gel time and viscosity, are studied. Then, appropriate colloidal silica grouts (saline solution/colloidal silica suspension ratios of 10%, 15%, 20% and 25% by weight) are selected. The selected colloidal silica grouts are then injected into fine- to medium-grained sand specimens prepared at an overall relative density of 50%. The strength of the grouted sand specimens is determined by unconfined compression tests. The effect of curing period on the strength of the grouted samples is also investigated. After performing cyclic loading tests on grouted sand specimens at different cyclic stress ratios (0, 0.13, 0.26 0.39 and 0.52), it is observed that none of the samples failed or was damaged, and that the colloidal silica grout provides fine- to medium-grained sand with a significant resistance to cyclic deformation. The samples are then subjected to unconfined compression tests, and the results show that the loss in the strength of colloidal-silica-grouted sand is insignificant.
