مطالعه عددي افزايش ظرفيت باربري پي هاي حلقوي و دايره‌اي مستقر بر خاك‌هاي دانه‌اي مسلح شده به وسيله‌ي سامانه مهارشبكه

A Numerical Study on Bearing Capacity of Ring and Circular Foundations on Granular Soils Reinforced by Grid-Anchor System

تسليح خاك يكي از روش‌هاي بهبود خواص مكانيكي خاك است. پژوهش‌هاي زيادي طي چهار دهه اخير به منظور تعيين نوع مسلح كننده و همچنين ميزان افزايش ظرفيت باربري خاك مسلح شده با مسلح كننده‌ها انجام شده است. به تازه‌گي نوع جديدي از مسلح كننده‌هاي پليمري براي افزايش ظرفيت باربري خاك‌هاي دانه‌اي ابداع شده است. اين سامانه جديد كه مهارشبكه (G-A)نام‌گذاري شده است]1[، با تغيير ساختار ژيوگريد معمولي و اضافه كردن قلاب هاي پليمري به آن، ساخته مي شود. در اين مقاله سعي شده است كه با كمك تحليل هاي عددي، توان اين نوع مسلح كننده در افزايش ظرفيت باربري پي هاي حلقوي و دايره اي بررسي شد. عمق اولين لايه مسلح كننده، فاصله بين لايه‌ها، تعداد لايه‌ها، پهناي مسلح كننده و پهناي موثر قلاب‌گذاري در دو حالت پي حلقوي و دايره‌اي به گونه‌اي تعيين شده‌اند كه شاهد بيشترين ظرفيت باربري باشيم. تاثير سختي مسلح كننده در افزايش ظرفيت باربري در پي‌ها نيز مورد بررسي قرار گرفته‌اند. در پايان نتايج بدست آمده، با نتايج ظرفيت باربري پي واقع بر خاك ماسه اي غيرمسلح و ماسه مسلح شده با ژيوگريد معمولي مقايسه مي شوند.

The use of geosynthetics in civil engineering projects is growing rapidly. One of these applications is the construction of a reinforced soil foundation to increase bearing capacity of shallow spread footings. More recently, results of several numerical studies, laboratory and large scale tests to determine the ultimate bearing capacity of square shallow foundations supported by sand reinforced with layers of geogrid have been published in the literature. The Maximum allowable pressure that can be apply to the soil is known bearing capacity (B.C). B.C is depending to the shape footings, distribution of installation stress and modeling of occurring failed in soils. Ring foundations are one of the different kinds of convention foundations that it can be able to transforming of applied loading to the surface. Ring foundation for axisymmetric loading and geometry is useful and used. Because of its dimensions and saving in consuming materials and costs in stage of footing construction, this foundation it is more beneficial than circular footing in similar conditions. Soil reinforcement is one of the soil improvement techniques. Over the last four decades, a large number of researches have been carried out in order to obtain the reinforcement type and the bearing capacity improvement of the reinforced soil. One of the most important of characterization of polymeric reinforcements are ability of deformation in compared of the other current reinforcements such as aluminum and steel strips A new reinforcement type called Grid-Anchor (G-A) has been recently invented which is made of geogrids by adding polymer anchors to it. In this study the bearing capacity of ring and circular footings located on granular soils reinforced with the G-A is investigated using numerical analyses. Commercial finite-element software PLAXIS is employed to perform the simulations. . In this software, users by defining stage construction, can able to modeling of reality boundary conditions and loads and phases of construct. The effect of depth of the first reinforcement layer, the vertical spacing, the number and width of reinforcement layers, the distance that anchors are effective, for each foundation were investigated. The effect of reinforcement stiffness for two types of footing has been investigated. A comparison between the results obtained for the G-A and geogrid reinforcement systems and unreinforced soils is demonstrated as well. In soil reinforced with geogrid and G-A reinforcements, when the layer of geogrid and G-A are lower than 3, in circular footing, increasing of B.C for both of them reinforcement s are similar but after 3 more layers, B.C in G-A has huge difference than geogrid. This difference is result in anchors effect.