نوع مقاله : یادداشت فنی
1 پردیس بین المللی ارس، دانشگاه تبریز
2 دانشکده مهندسی عمران - گروه ژئوتکینک، دانشگاه تبریز
عنوان مقاله [English]
Development of Tabriz metropolis on marl layers and increased \ tendency to build high-rise \ buildings have \ resulted in deep \ excavations in these layers. Restrictions of work space have resulted in using soil reinforcement methods in excavations, including grouted anchors. Tabriz Marl is a lacustrine carbonate sedimentary outcrop that surrounds eastern, northern, and southern regions of city in the East Azerbaijan Province of Iran and classified as clayey or silty soil with high plasticity. The objectives of this study were to evaluate the load carrying capacity of tension type grouted anchors implemented in Tabriz marl, their behavior against creep tests and long-term monitoring against lock-off tensile loads. To this purpose, ten full-scale similar anchors were constructed with free length of 4 meters, injected (bonded) length of 3 meters and diameter of 11 cm in marl soil in experimentation site with an area of 800 $m^2$ located in University of Tabriz. Pull-out load tests including creep tests were conducted on four anchors using their results, ultimate load of anchors, maximum friction resistance between anchor grout and marl, load of failure creep rate, and critical creep tension were estimated. Ultimate bond friction was 2.8 $kg/cm^2$ to 3.1 $kg/cm^2$ and empirical reduction factor of marl layer was measured 0.61 to 0.67 and they were compared with the results obtained by different authors. Factor of safety for design load was obtained to be 1.31 against the ultimate load, 1.33 against the failure load, and 1.2 against the critical creep tension. Finally, the amount of creep over one log cycle of time for design load of anchors was estimated to be 0.46 mm on average, assuming to be constant over time, equaling 3.5 mm for 100 years. For long-term relaxation survey of anchors and estimating the load decrease over time, six anchors were locked off and their residual load was read for 6 months. It was tried to model and predict anchor movement and relaxation over time by creep test results, using mathematical relationships along with comparing them with real data on site and finally obtaining long-term behavior of grouted anchors implemented in Tabriz marl. The amount of force reduction in these anchors was 54\% on average that reduces to about 20\%, assuming the removal of settlement of concrete pad as head seating. These values demonstrate time-dependent settlement over seating pad of anchor in marl soil of Tabriz and its high effect on reducing locked force.