كليدواژه :
لوله مدفون , گسل معكوس , مدل عددي , نرم‌افزار abaqus , اندركنش خاك و لوله
چكيده فارسي :
خطوط لوله مدفون به واسطه طول زياد خود ناگزير از عبور از گسل هايي هستند كه حركات بزرگ آن ها مي تواند باعث بروز شكست و گسيختگي در لوله هاي مدفون شود. اين حركات بزرگ ممكن است در يك زمين لرزه رخ دهد و يا اينكه بر اثر حركت خزنده گسل كه در طول عمر بهره برداري خط لوله اتفاق مي افتد، بوجود آيد. بنابراين ضروري است رفتار لوله هاي مدفون در برابر حركات گسل مورد مطالعه قرار گيرد. در ادبيات فني موجود، تمركز بيشتر بر مطالعه رفتار خطوط لوله در گذر از گسل هاي نرمال و امتداد لغز بوده است. در مطالعه حاضر، رفتار لوله هاي مدفون گذرنده از گسل معكوس با كمك نرم افزار آباكوس مطالعه شده است. ابتدا نحوه و روند شبيه سازي هاي انجام شده با نتايج آزمايشگاهي و عددي ديگر مقايسه شده است كه نشان از صحت نتايج دارد. سپس مطالعه حساسيت بر روي تاثير نوع خاك و پارامتر هاي ژئوتكنيكي آن و همچنين اثر نسبت عمق دفن به قطر لوله انجام گرفته است. مطالعات عددي انجام شده نشان مي دهد كه كرنش هاي فشاري علت اصلي وقوع گسيختگي لوله ها در گسلش معكوس هستند و استفاده از خاك هاي نرم و با تراكم كم و هم چنين كاهش عمق دفن لوله سبب كاهش مقادير كرنش هاي فشاري و كششي ايجاد شده در لوله مي شوند. اين در حالي است كه تغيير مدول الاستيسيته خاك تاثير چنداني بر مقادير كرنش هاي ايجاد شده در لوله ندارد. همچنين، افزايش زاويه اتساع خاك در جابه جايي هاي بزرگ گسل سبب افزايش مقادير كرنش هاي ايجاد شده در لوله مي شود.
چكيده لاتين :
Pipelines are considered as lifelines, because they are used for transportation of different fluids such as natural gas, oil and water, which the human life depends on their existence. The damages to the pipelines are usually associated with human fatalities, financial losses and also environmental pollution. Earthquake wave propagation and permanent ground displacement (PGD) caused by surface faulting are potentially devastating natural events which threaten buried pipelines. Although small regions within the pipeline network are affected by faulting hazards, the rate of the damage is very high since fault movement imposes large deformation on pipelines. On the contrary, the whole of pipeline network is influenced by the wave propagation hazards, but the damage rates is lower which leads to lower pipe breaks and leaks per unit length of the pipe. On the other hand, buried pipelines due to their long length, have to pass through active faults which their large movements may lead to failure and rupture of the buried pipes. It is, therefore, essential to investigate the behavior of buried pipelines against fault displacements in order to mitigate the losses caused by these natural events and to try to keep them in service under various situations. Over the years, many researchers have attempted to analyze pipeline behavior via numerical, analytical an experimental modeling, but most of these works were designed to assess pipe response to strike-slip faulting and some were implemented to recognize the behavior of pipelines under normal faulting with right deformation angles. In the present study, In order to understand the behavior of the pipelines under reverse fault movements, the effects of different geotechnical and geometric conditions on the response of the pipes is examined. Numerical simulations have been conducted using the software ABAQUS based on finite element method. In most of the previous studies, a simplified beam-spring model was used to simulate the behavior of the pipes, but in this study a 3-D continuum model is employed to simulate the behavior of the buried pipes against reverse fault movements. In order to increase the accuracy of the analysis, it is tried to use the elements that best match with reality of the nature of soil and pipe behavior and the interaction between them. The results of the numerical study confirmed that the compressive strains in pipe caused by reverse faulting are larger than the tensile strains, thus compressive strains are considered as the main cause of the failure of the buried pipes in the reverse fault motions. Investigating the pipes behavior in different soil types demonstrated that the buried pipelines in loose and soft soils experience less amount of strain in comparison with those which are bureid in other types of the soils. This is due to the fact that the displacement of the pipeline in loose and soft soils is easier and there are less soil resistance forces against pipe displacement. The assessment of effect of soil dilatation angle illustrated that in large fault displacements, the amounts of pipe strain decline with the reduction of the dilation angle, while changing the modulus of elasticity of the soil has no impact on the response of the pipes. The results also showed that by reducing the burial depth, the level of strain induced in the buried pipes decreases.
