ارزيابي رفتار مكانيكي سد مارون با استفاده از تحليل عددي سه بعدي

Numerical Analysis of Earth/Rockfill Dams in Narrow Canyons- Case Study: MARUN Dam

يكي از موارد نامطلوب براي سدهاي خاكي، احداث آن در «دره تنگ» است؛ زيرا در اين شرايط احتمال وقوع پديده انتقال بار يا انتقال تنش (Load Transfer) و به تبعيت از آن، احتمال تفاوت در نتايج تحليل‌هاي دو بعدي و سه‌بعدي سد افزايش مي‌يابد. در واقع رفتار سدهاي خاكي ـ سنگريزه‌اي در دره‌هاي تنگ، متاثر از اثر سه‌بعدي دره است. هندسه سد و به‌طور خاص، نسبت طول تاج به ارتفاع سد بر اثر سه‌بعدي تاثيرگذار است و در مواردي كه فاصله تكيه‌گاه‌هاي سد كم و دره سد تنگ باشد، انجام تحليل سه‌بعدي براي سدهاي بزرگ واقع در دره‌هاي تنگ، ضروري به‌نظر مي‌رسد. تاكنون تحقيقات گسترده‌اي با عناوين و اهدافي شبيه هدف تحقيق حاضر، بر روي دامنه گسترده‌اي از سدهاي خاكي و سنگريزه‌اي انجام گرفته است، اما نظر به اينكه بيشتر تحقيقات به‌صورت مدل‌سازي و تحليل دوبعدي است؛ مطالعه‌اي جامع‌تر و به‌صورت سه‌بعدي ضروري به نظر مي‌رسد تا تفاوت‌هاي اين دو نوع آناليز به‌‌منظور انتخاب روش بهينه به دست آيد. اين مقاله تلاشي براي بررسي اثر سه‌بعدي دره تنگ بر رفتار سد سنگريزه‌اي مارون است كه با 365 متر طول تاج و 165 متر ارتفاع (1/2L/H=) در جنوب غربي ايران واقع شده است. در راستاي اين هدف، تحليل‌هاي دوبعدي و سه‌بعدي سد با استفاده از نرم‌افزار ABAQUS براي بررسي فشار آب حفره‌اي و تغييرشكل‌هاي افقي ناشي از آبگيري انجام گرفته و نتايج به دست آمده از اين دو نوع تحليل به تفصيل با يكديگر و با نتايج ابزار، مورد مقايسه قرار گرفته است.

An earth/rockfill dam is always located in a valley of a river which can have different shapes as a natural structure. Valleys normally appear regularly or irregularly and they can be idealized as the shapes of V, U, rectangular and etc. the shape and type of the valley affect all steps of a dam project, from initial studies up to construction and also dam behavior. Consequently, the shape and size of the valley as an effective factor should be considered in all steps of the project because narrow valleys are the circumstances which are always a barrier to construct the earth dams. So the behavior of earth dams in narrow valleys is affected by 3D effects of valley. The geometry of dam and especially the ratio of crest length to dam height are affecting the 3D behavior. Consequently 3D analysis seems to be necessary for large dams in narrow canyons. Current paper is an attempt on estimation of the 3D effects of narrow valley on the behavior of Marun rockfill dam with crest length of 365m and height of 165m (L/H=2.1), which is located in the south west of Iran. In accordance with this goal, 2D and 3D analyses of dam have been carried out by FEM method and the results are compared with each other. In addition, the arching phenomenon in the clay core of Marun dam is studied.According to the analyses results it’s seemed that in the narrow valley of Marun dam, there are some 3D effects which couldn’t be applied to the model through 2D analysis.Both of analyses showed a same trend for results and the reductions and increases were the same. But the eye taking difference between these two analyses was the overestimation of results of 2D analysis. Both displacements, vertical and horizontal ones, in 2D analysis results were more than 3D values and even more than natural values. An earth dam in a narrow canyon is a structure which should be considered as a 3D volume. In this circumstance, the 3D effects applied with the valley aren’t negligible and a 2D analysis cannot include this 3D behavior and would result in overestimated results which aren’t reasonable. In other words, a mentionable difference between 2D and 3D analyses is the overestimation of results of 2D analysis as both types of displacements, vertical and horizontal one, in such type of analysis results are more than 3D values and even true values. Anyhow it shouldn’t be forgotten that the results of this article belong to a case study which has its special conditions and wouldn’t be applied for all dams in narrow valleys generally because each case has its certain conditions and consequently its different manner.