بررسي اثر افزودن الياف موكت در افزايش فشار آب حفره ‌يي در ماسه‌ي انزلي به كمك دستگاه تانك شفاف

Investigation into the Effect of Carpet Fiber Inclusion on the Pore Water Pressure Generation Potential of Sand in a Quick Tank

در اين نوشتار، به بررسي تاثير الياف موكت در شكل گيري و افزايش فشار آب حفره‌يي در ماسه در اثر اعمال بارهاي هارمونيك پرداخته شده است. در اين راستا، از مدل‌سازي فيزيكي در دستگاه تانك شفاف استفاده شده است. بدين منظور، الياف موكت در درصدهاي وزني و نسبت ابعاد مختلف با حفظ درصد تراكم بخش ماسه‌يي با ماسه مخلوط و به روش كوبش خشك متراكم شده است. نتايج بيان‌گر كاهش پتانسيل شكل گيري فشار آب حفره‌يي با افزايش درصد وزني الياف موكت است. علاوه بر توزيع تصادفي الياف، توزيع منظم (سيستماتيك) يا لايه‌يي موكت در خاك ماسه‌يي ريزدانه نيز مورد مطالعه قرار گرفته است. نتايج آزمايش‌هاي مدل‌سازي حاكي از تاثير اندك اين نوع تسليح در خواص هيدروليكي خاك و پتانسيل شكل گيري فشار آب حفره‌يي در اثر ارتعاش ديناميكي است. در مجموع نتايج آزمايش‌هاي انجام‌شده حاكي از تاثير مثبت افزودن تصادفي الياف موكت به ماسه در كاهش پتانسيل شكل گيري و توسعه‌ي فشار آب حفره‌يي است.

In this study, the effects of carpet fiber inclusion on pore water pressure development in fine sand are investigated, while dynamic loads are applied. In this regard, quick tank model tests are used. A quick tank comprised of a transparent plastic storage container of sand, a shaker and a water drainage system was employed. Different reinforcement parameters, namely, fiber weight content and fiber aspect ratio varied through physical modeling, in order to study the reinforcement effects. Two different fiber weight contents (0.5 and 1%) and a wide range of aspect ratios for the slender fiber elements (1, 3, 5, 9) were utilized in order to scrutinize the effect of each factor on the pore water pressure development regime. Dry tamping was employed to mix and prepare the models in a layered structure. Samples were then saturated gradually from the bottom. Harmonic shaking was applied afterwards. Shaking frequency was maintained constant at 2.66 Hz through different models. Furthermore, constant shaking amplitude of 0.34g was chosen in order to guarantee a shaking assumed strong enough to induce excess pore water pressure inside the constructed models. Pore water pressure was recorded at three different levels, at the bottom, middle and top of the models, utilizing three pore pressure transducers connected to a data logger. Records of pore water pressure are then prepared for different models with variable reinforcement parameters, to draw conclusions about their effect on the potential of pore water pressure development in the reinforced models in comparison to the plain sand model. It was noticed that carpet fiber inclusion in fine-grained sand reduces the potential of excess pore water pressure development due to its porous structure. However, this effect is hindered when the level of effective stress rises. It is, therefore, evaluated to be suitable for reinforcement of granular soil in shallow depths. Utilization of such fibers in the reinforcement of backfill material in retaining structures, quay walls and road embankments are also potential applications. Aspect ratio, on the other hand, shows a dual effect on the hydraulic behavior of reinforced sand. On the one hand, increasing the aspect ratio will lead to the formation of larger clusters of porous elements, which, itself, induces a reduction in pore water pressure development potential. On the other hand, larger aspect ratio, while maintaining constant fiber weight fractions, will lead to a decrease in the number of porous elements within the whole mass of the model. This implies that an optimum aspect ratio is to be expected. Systematic reinforcement was also studied in comparison to the plain model. It did not show any significant improvement in pore water pressure reduction potential. Comparison of pore water pressure developed in different random and systematic reinforced models led to the conclusion that laying of the carpet layers horizontally does not allow efficient pore water drainage, as the drainage direction is vertical. A totally different pattern of drainage condition is expected when the distribution is random.