نوع مقاله : مقاله پژوهشی

نویسندگان

• سمیه رستمی ¹
• حجت احمدی ²
• ناصر آق ³

¹ دانش آموخته کارشناسی ارشد سازه های آبی؛ گروه مهندسی آب پژوهشکده آرتمیا و آبزی پروری دانشگاه ارومیه، ارومیه، ایران

² دانشیار گروه مهندسی آب پژوهشکده آرتمیا و آبزی پروری دانشگاه ارومیه، ارومیه، ایران

³ استاد پژوهشکده آرتمیا و آبزی پروری دانشگاه ارومیه، ارومیه، ایران

چکیده

بحران اخیر و خشک شدن بخش اعظم دریاچه ارومیه هم اکنون یکی از بزرگترین مخاطرات زیست محیطی در ایران محسوب می‌شود. با وجود تلاشهای گسترده صورت گرفته برای احیای دریاچه ارومیه، به دلیل محدودیت روانابهای ورودی به دریاچه، موفقیت قابل توجهی در این خصوص حاصل نشده است. یکی از روشهای که می‌تواند برای احیای دریاچه مورد استفاده قرار بگیرد احیای فازبندی دریاچه ارومیه است بر این اساس بر روی دو مسیر مشخص پیشنهادی بر اساس حجم آورد رودخانه ها برای شکل گیری عمق مناسبی از آب دریاچه، نمونه های دست نخورده انتخاب گردید و آزمایشهای متداول شناسایی مواد بستری، مقاومت برشی و تحکیم پذیری انجام شد. نتایج بررسی نشان داد که مواد بستری در هر دو مسیر انتخابی مشابه هم و بسیار سست با درصد بالای مواد آلی فعال می‌باشد. پارامترهای مقاومت برشی حاصل از آزمایشها نشان دهنده مقاومت برشی بسیار پایین مواد در دامنه 6 تا kg/cm2 12 می‌باشد. همچنین ضرایب فشردگی و تورمی برای نمونه های اخذ شده برای مسیر شمالی تر بیشتر از مسیر جنوب دریاچه حاصل شد. میزان ماده آلی در دامنه 54/3 تا 67/4 درصد قرار دارد و لذا نوع خاک بستر دریاچه نرم آلی ارزیابی شد. نتایج بررسی نشان می‌دهد به منظور اجرای فازبندی و جدا سازی موقت بستر دریاچه به بخشهای کوچکتر می بایستی از سازه‌های سبک با سطح پی وسیع استفاده کرد.

کلیدواژه‌ها

• فازیندی
• مقاومت برشی
• مواد بستری
• تحکیم پذیری

موضوعات

• ژئوتکنیک

عنوان مقاله [English]

Investigation on the geotechnical properties of Lake Urmia bed materials: with the Stepped Restoration perspective

نویسندگان [English]

• Somayeh Rostami ¹
• Hojjat Ahmadi ²
• Nasser Agh ³

¹ Department of Agriculture, Urmia University

² Associated professor, Department of water engineering, Urmia University, Urmia

³ Artemia research institute, Urmia University

چکیده [English]

Introduction

Drying almost the whole of Lake Urmia is one of the main environmental crises of Iran nowadays. Despite great efforts to restoration of the lake since 2014, owing to the limitation of inlet flow to the lake, insignificant success has been reached. Actually, in the basin of Lake Urmia, the evaporation rate is very high and based on the reported data it is over 1000 mm annually, while the precipitation is about 330 mm. Hence, the pure evaporation height from the surface of the lake is higher than the lake water level rising during recent years. Therefore, in order to overcome the shortage of inlet flow to Lake Urmia, the evaporation area as well the surface of the water body must be equivalent to the evaporation rate. Samadzadeh et al. (2018), reported that by the construction of new dikes inside the lake, consequently by dividing the lake into some smaller parts and restore each part separately one by one, the lake could be restored with the available inflow of feeder rivers of the lake. However, difficulties of construction of causeway through lake Urmia confirmed that the sedimentary bed materials of the lake are classified as problematic material from a point of geotechnical view (Eslami et al., 2020). Henceforward, dividing the lake into smaller phases is not possible by using ordinary methods like earthen dikes which have been used in the restoration of the Aral Sea. In this regard, we explored the geotechnical properties of bed materials of Lake Urmia to choose a compatible method with the environment of the lake as well as the proper hydraulic structures to divide Lake Urmia into smaller regions proportional to annual discharges of its basin rivers.



Materials and Method

Lake Urmia is one of the largest hypersaline lakes located northwest of Iran. The area of the lake and its basin are about 5000 and 52000 km2. During las past two decades the lake has been faced with an intense drawing of water level, and almost the lake has vanished. Based on the published investigation regarding phases restoration of Lake Urmia, two different routes have been suggested by Samadzadeh et al., (2018) based on water balances of the lake. Therefore, we also followed the proposed routes to investigate the geotechnical properties of the bed materials. The first route complies with the constructed causeway. In this route, almost the total of the distance from the west to the east shore has been blocked by road dike, except the bridge with a span of around 1200m. The second route is located in the southern region of the lake and it started from Rashakan on the west coast to the east direction which intersects Espir and kaboodan islands. The length of the current route is about 19 km. For each route, three points with a distance of 200 m from each other (from the west coast) in the form of disturbed and undisturbed specimens have been prepared. Identification tests, shear strength tests include vane shear test, uniaxial shear test, and consolidation test have been carried out. In order to study the effect of salt and fresh water on the mechanical and physical properties of the bed and sedimentary material, some tests such as Aterberg limits have been conducted by using fresh and saltwater separately.

Results and Discussion

Based on the achieved results of laboratory tests, the bed materials of Lake Urmia in both routes were classified as OH and OL while treated with fresh and saltwater based on the Unified soil classification system, respectively. Also, shear strength tests showed a low strength of about 12 kg/cm2 for the bed materials of route 2 while the half is for the first route in direction of the causeway at the northern part of the lake. The content of organic materials was detected 3.54 and 4.67 for the first and second studied routs respectively. Odometer tests results revealed that the bed materials of the studied routs could be classified as soft or very soft soils. Therefore, construction of any heavy structure such as a levee to divide or isolate the lake is almost impossible with the ordinary techniques, however, light and thin structures like sheet piles could be a good alternative to the aim.

کلیدواژه‌ها [English]

• Phasing
• Shear strength
• Bed material
• compressibility