فهرست مطالب

Engineering Geology - Volume:13 Issue:2, 2019
  • Volume:13 Issue:2, 2019
  • تاریخ انتشار: 1398/05/10
  • تعداد عناوین: 8
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  • کاظم بهرامی، محمود فاطمی عقدا*، علی نورزاد، مهدی تلخابلو صفحات 185-212

    شناخت عوامل موثر بر مقاومت سایشی سنگ دانه ها  تاثیر زیادی در پی جویی سنگ دانه هایی با مقاومت سایشی مناسب دارد. در این پژوهش ارتباط محیط های زمین شناسی با مقاومت سایشی سنگ دانه ها، بررسی شده است. نمونه برداری از سه محیط واریزه ای، مخروط افکنه ای و رودخانه ای در دو منطقه دشت دیره با سنگ های آهکی و منطقه دماوند با سنگ های آتشفشانی انجام شده است. آزمایش های سایش لس آنجلس، تخلخل و درصد سنگ دانه های دارای ریز ترک روی نمونه های برداشت شده از محیط های مختلف انجام شد. نتایج نشان می دهد که کم ترین میزان افت وزنی در محیط های رودخانه ای به میزان 7/23 و 42 و بیش ترین میزان افت وزنی در محیط های واریزه ای به میزان 3/49 و 48 به ترتیب در منطقه دیره و دماوند دیده می شود. محیط های مخروط افکنه ای نیز حالتی حدواسط این دو را دارند. با افزایش مساحت و طول مسیر جریان در حوزه بالادست مخروط افکنه ها میزان افت وزنی کاهش می یابد. تفاوت میزان افت وزنی در محیط های مختلف به علت تفاوت در میزان ریزترک، تخلخل و قشر هوازده ایجاد شده بر سنگ دانه ها است. شدت اختلاف میزان افت وزنی در دو منطقه دماوند و دشت دیره با هم متفاوت است به گونه ای که میزان افت وزنی سنگ دانه های واریزه ای دشت دیره دو برابر سنگ دانه های رودخانه ای در همان منطقه است در حالی که در منطقه دماوند این اختلاف حدود 11 درصد است. این تفاوت می تواند ناشی شدت درزه داری کم تر و در نتیجه تفاوت کم تر درزه داری سنگ دانه های موجود در محیط های مختلف در منطقه دماوند باشد.

    کلیدواژگان: رودخانه، مخروط افکنه، واریزه، سنگ دانه، مقاومت سایشی
  • متین جلالی مقدم*، امیرعلی زاد، نیما مهران نیا، نادر دستاران صفحات 213-236

    مهارهای صفحه ای یکی از انواع مسلح کننده های مکانیکی هستند که کاربردهای گسترده ای در فعالیت های ژئوتکنیکی ساحلی و فراساحلی مانند ساخت دیوارهای حائل مکانیکی، مقابله با بالازدگی فونداسیون ها، تثبیت توربین های باد و سکوهای شناور دریایی در برابر تلاطم آب دریا، و مهار خطوط لوله مدفون و مستغرق دارند. در این مقاله نتایج مدل سازی آزمایشگاهی دیوارهای حائل مهار صفحه ای با هدف بررسی عملکرد آن ها ارائه شده است. موارد بررسی شده بر قابلیت باربری پاشنه بارگذاری و تغییرمکان های افقی دیواره شامل ارزیابی تاثیر شکل مربعی و دایره ای صفحات مهاری، ابعاد آن ها در دو اندازه مختلف، تحت سه چیدمان لوزی، مربعی و 5 مهاره بوده است. به منظور مشاهده سطح لغزش بحرانی و میزان تاثیر موارد مذکور روی گوه گسیختگی از روش سرعت سنجی تصویری ذات (PIV) استفاده شده است. بر این اساس، بیش ترین قابلیت باربری دیواره و کم ترین جابه جایی افقی آن به ترتیب مربوط به چیدمان 5 مهاره، لوزی و مربعی بوده است. چیدمان لوزی با وجود یک مسلح کننده کم تر اختلاف نسبتا کمی با نتایج چیدمان 5 مهاره داشته است. شکل دایره ای صفحات پایداری بیش تری را در دیواره فراهم آورده اند. بر طبق نتایج تحلیل PIV، کرنش ذرات در سطح لغزش بحرانی، در چیدمان های 5 مهاره و لوزی کوچک تر از چیدمان مربعی و در صفحات دایره ای کوچک تر از صفحات مربعی به دست آمده است. چیدمان مسلح کننده ها و ابعاد صفحات تاثیر چشم گیری بر عمق گوه گسیختگی در خاکریز دیواره داشته اند.

    کلیدواژگان: مهار صفحه ای، دیوار حائل، سرعت سنجی تصویری ذات (PIV)، ژئوتکنیک ساحلی و فراساحلی، مدل سازی آزمایشگاهی
  • سید طاها طباطبایی عقدا، علی قنبری*، غلامحسین توکلی مهرجردی صفحات 237-260

    در شهرهای بندری، برداشت و انباشت رسوبات حاصل از عملیات لایروبی به عنوان چالشی جدی به دلیل ایجاد مشکلات زیست محیطی و اقتصادی مطرح است. حجم زیاد این رسوبات ضرورت استفاده دوباره از این مصالح را روشن می سازد. اغلب به دلیل مشخصات مکانیکی ضعیف، این مصالح به صورت مستقیم برای استفاده در پروژه‏های عمرانی مناسب نیستند و بهبود خواص مکانیکی آن ها ضروری است. یکی از روش های به سازی خاک، استفاده از ژئوسنتتیک ها است. در این بین، ژئوسل به واسطه ساختار سه بعدی آن و خاصیت محصورکنندگی خاک درون سلول ها، موجب بهبود چشم گیری در ویژگی های مکانیکی خاک می‏شود. این موضوع در کنار سرعت و سهولت اجرا، ژئوسل را به گزینه ای مطلوب برای تسلیح خاک های دانه ای تبدیل کرده است. به واسطه عملیات لایروبی سواحل شمالی خلیج فارس برای ساخت فازهای دوم و سوم توسعه بندر شهید رجایی، حجم زیادی از ماسه کربناته در مجاورت حوضچه آرامش این بندر در حال انباشت است. برای ارائه راهکار برای استفاده مجدد از این مصالح، در این پژوهش تاثیر مسلح سازی ماسه با ژئوسل بر رفتار بار-نشست آن، از طریق آزمون بارگذاری صفحه بررسی می شود. برای این منظور، از یک مدل فیزیکی شامل صفحه بارگذاری دایره‏ای شکل واقع بر مدل خاکی، تحت بارگذاری تکراری استفاده شده است. مدل های خاکی استفاده شده، از ماسه کربناتی مسلح با ژئوسل و غیرمسلح با دو نوع رویه از جنس شن خوب‏ دانه‏بندی شده و ماسه لایروبی شده، تشکیل شده اند. نتایج این تحقیق نشان می دهد که استفاده از ژئوسل به عنوان مسلح‏کننده و هم چنین شن خوب دانه بندی شده به عنوان رویه در لایه سطحی مدل خاکی، می تواند موجب بهبود چشم گیر در رفتار بار- نشست ماسه لایروبی شود.

    کلیدواژگان: ژئوسل، آزمون بارگذاری صفحه، ماسه لایروبی کربناته، رفتار بار- نشست
  • واحد قیاسی*، مبین مرادی صفحات 261-288

    در طراحی فونداسیون ها، ایده تلفیق رادیه و پی های عمیق به منزله گزینه ای جدید در مبحث پی سازی مطرح شده است. به کارگیری پی های عمیق در زیر پی های گسترده (سیستم پی گسترده مرکب) می تواند سبب کاهش نشست و اثر توام افزایش ظرفیت باربری شود. در این پژوهش، تغییرشکل پی، گشتاور وارد بر پی و هم چنین سهم بار شمع ها در باربری سیستم مرکب پی- شمع تحت بارگذاری استاتیکی در خاک ماسه ای با استفاده از مدل سازی اجزای محدود برای چیدمان های گوناگون شمع ها و سیستم های مختلف پی- شمع از نظر اتصال پی و شمع ها، بررسی شده و مورد تجزیه و تحلیل قرار گرفته است. در ادامه، اثر طول شمع و ضخامت پی گسترده در عملکرد سیستم مرکب نیز بررسی و بیان شده است. نتایج به دست آمده نشان می دهند که استفاده از شمع های طویل در مرکز و شمع های کوتاه تر در پیرامون پی سبب کاهش نشست حداکثر و نشست های غیریکنواخت پی شده و کاهش چشم گیر لنگر وارد بر پی را به موجب شده است. و در کنار این ها سبب افزایش باربری شمع ها در سیستم مرکب شده است. همین طور افزایش ضخامت پی باعث ازدیاد نشست حداکثر پی، نشست متوسط پی، لنگر خمشی وارد بر پی شده است. و اثرات مثبت افزایش ضخامت پی، کاهش نشست های غیریکنواخت پی و افزایش مشارکت شمع ها در باربری هستند.

    کلیدواژگان: تجزیه عددی، تغییر ضخامت پی گسترده، تغییر طول شمع ها، پی های رادیه مرکب
  • سید داود محمدی*، الهه حسین آبادی صفحات 289-316

    آلودگی خاک‌ها با هر کدام از فرآورده‌های نفتی باعث تغییر در ویژگی‌های زمین‌شناسی مهندسی خاک‌ها شده و رفتار خاک‌ها را تغییر می‌دهد. در این پژوهش به‌منظور بررسی تاثیر آلودگی ناشی از گازوییل بر فرسایش‌پذیری خاک‌ها، محدوده انبار نفت همدان انتخاب گردید و به این منظور از دستگاه شبیه‌ساز باران استفاده شد. براساس نتایج حاصل از بررسی‌های صحرایی و آزمایشگاهی، سه لایه خاک در محدوده بررسی شده وجود دارد که مطابق رده‌بندی یونیفاید در رده SM قرار دارند و دارای مقادیر بسیار بالای آهک، یعنی 15/85%  در لایه بالایی، 16/62% در لایه میانی و 72/88% در لایه پایینی هستند. تعیین ویژگی‌های زمین‌شناسی مهندسی نمونه‌ها با انجام آزمایش‌های تعیین درصد رطوبت، دانه‌بندی و هیدرومتری، کلسی‌متری، تعیین GS، حدود آتربرگ، تراکم استاندارد، برش مستقیم و مقاومت فشاری تک‌محوری روی نمونه‌های غیرآلوده و آلوده به گازوییل انجام شد. برای بررسی اثر ویژگی‌های زمین‌شناسی مهندسی نمونه‌های غیرآلوده و آلوده به گازوییل بر فرسایش‌پذیری با استفاده از دستگاه شبیه‌ساز باران، از شیب‌های 10، 20، 30 و 40 درجه، شدت بارش مشابه با میانگین شدت بارش منطقه و تراکم خاک با رطوبت بهینه استفاده شد. نتایج به‌دست آمده نشان می‌دهد که آلودگی ناشی از گازوییل باعث کاهش مقادیر پارامترهای مقاومتی خاک‌های منطقه بررسی شده و این کاهش مقادیر پارامترهای مقاومتی، خود باعث افزایش فرسایش‌پذیری خاک‌های آلوده نسبت به خاک‌های غیرآلوده شده است. بدین صورت که حداکثر مقدار فرسایش در سه لایه خاک در 19 و 15 درصد گازوییل تقریبا 3 برابر مقدار فرسایش در حالت غیرآلوده است.

    کلیدواژگان: آلودگی خاک، ویژگی های زمین شناسی مهندسی خاک، دستگاه شبیه ساز باران، فرسایش پذیری، انبار نفت، همدان
  • سعید مجدی فر*، نسترن استاد مهدی عراق صفحات 317-338

    در این پژوهش با استفاده از سنجنده آستر تلاش شده است کاربرد الگوریتم ماشین بردار پشتیبان در تفکیک دگرسانی های هیدروترمال ذخایر مس پورفیری بررسی شود. برای آموزش این الگوریتم در مجموع 2204 پیکسل از مناطق کانی سازی شده انتخاب شد. باندهای 4، 6، 7 و 8 سنجنده آستر برای شناسایی دگرسانی های فیلیک و آرژیلیک و 9 باند محدوده مرئی و مادون قرمز نزدیک برای شناسایی دگرسانی پروپیلیتیک به عنوان ورودی این الگوریتم انتخاب شدند. به منظور ارزیابی خطای طبقه بندی، ماتریس درهم آمیختگی بررسی شد. نتایج ماتریس در هم آمیختگی بیان گر آن است که خطای طبقه بندی برای زون فیلیک و آرژیلیک نسبتا بالاست و امکان تفکیک این دو زون به سادگی امکان پذیر نیست در حالی که دگرسانی پروپیلیتیک به خوبی طبقه بندی شده است. هم چنین این تحقیق تابع خطای جدیدی به نام خطای کور را تعریف کرد که با استفاده از ماتریس درهم آمیختگی نسبت پیکسل های دگرسان طبقه بندی نشده را محاسبه می کند. بر اساس مقدار این خطا، ماشین بردار پشتیبان 6/73 درصد از پیکسل های دگرسان را طبقه بندی نمی کند. هم چنین صحت کل طبقه بندی الگوریتم ماشین بردار پشتیبان برابر06/66 درصد و ضریب کاپا برابر6522/0 است.

    کلیدواژگان: دگرسانی آرژیلیک، دگرسانی فیلیک، دگرسانی پروپیلیتیک، مس پورفیری، ماشین بردار پشتیبان
  • عرفان نادری، عادل عساکره*، مسعود دهقانی صفحات 339-370

    ساختن پی ها روی خاک نرم به دلیل کم بودن ظرفیت باربری و افزایش مقادیر نشست در این خاک ها همواره از  مشکلات پیش روی مهندسان ژئوتکنیک بوده است. یکی از راهکارهای موجود برای برطرف کردن این مشکل، اضافه کردن المانی تقویتی به خاک است و یکی از المان هایی که می توان به خاک اضافه کرد ستون سنگی است. در این روش، 15 الی 35 درصد از حجم خاک نامرغوب با خاک مناسب جای گزین می شود. در این تحقیق به بررسی آزمایشگاهی تاثیر وجود ستون سنگی تکی و گروهی و هم چنین تاثیر موقعیت مکانی و طول ستون سنگی بر ظرفیت باربری پی نواری قرار گرفته در مجاورت شیروانی از جنس خاک رس نرم می پردازیم. هم چنین ستون های سنگی با استفاده از دورگیر قائم، مسلح شده و تاثیر مسلح کردن ستون سنگی در حالت های مختلف نیز بر رفتار پی نواری مجاور شیب بررسی شد. نتایج نشان داد که تقویت کردن شیب رسی با ستون سنگی، در همه حالت ها موجب افزایش ظرفیت باربری پی نواری قرار گرفته در مجاورت شیب می شود. هم چنین مسلح کردن ستون سنگی با دورگیر، سبب بهبود عملکرد ستون سنگی و افزایش ظرفیت باربری پی نسبت به حالت مشابه ستون سنگی غیرمسلح می شود. طول بهینه ستون سنگی غیرمسلح قرار گرفته در زیر پی 4 برابر قطر ستون است. بیش ترین تاثیر ستون سنگی روی ظرفیت باربری پی نواری زمانی اتفاق افتاد که ستون سنگی در زیر پی قرار گرفت و با افزایش فاصله بین مرکز ستون و مرکز پی، ظرفیت باربری پی کاهش یافت. هم چنین با بررسی راندمان گروه ستون های سنگی مشخص شد در هر دو حالت مسلح و غیرمسلح، عملکرد گروه دوتایی ستون های سنگی در مقایسه با گروه سه تایی بهتر است.

    کلیدواژگان: ستون سنگی، ظرفیت باربری، پی نواری، شیروانی، خاک رس
  • رضا نصیرزاده قورچی، مهدی امینی*، حسین معماریان صفحات 371-398

    طراحی و اجرای شیروانی ها یکی از حساس ترین و مهم ترین مسائل در پروژه های عمرانی و معدنی محسوب می شود. در علم ژئوتکنیک، به دلیل دسترسی نداشتن به اطلاعات کافی و مطمئن پیرامون کمیت های طراحی، ارائه یک مدل کاملا قطعی غیرممکن است. از این رو، در سال های اخیر، برای تحلیل پایداری شیروانی ها بیش تر به روش احتمالاتی مراجعه شده است. در این تحلیل ها، کمیت های تاثیرگذار در پایداری شیروانی به صورت توزیع های آماری در نظر گرفته می شوند و در نتیجه ضریب اطمینان نیز یک توزیع آماری خواهد شد. از این رو، ابتدا خلاصه ای از تحقیقات انجام شده روی تحلیل احتمالاتی شیروانی ها ارائه شده و برتری تحلیل احتمالاتی نسبت به تحلیل قطعی در طراحی شیروانی ها بررسی می شود. در ادامه، برای شفاف شدن توصیف های مذکور، شیروانی مشرف به سرریز آزاد سد کوار شیراز با روش شبیه سازی مونت کارلو به صورت احتمالاتی با استفاده از نرم افزار SLIDE تحلیل می شود. این تحلیل ها نشان می دهند ضریب اطمینان محاسبه شده به وسیله تحلیل احتمالاتی به صورت یک تابع توزیع ارائه می شود که نسبت به تحلیل قطعی که نتیجه آن صرفا یک مقدار مشخص است، تصویر روشن تری از شکست ارائه می کند. هم چنین نتایج تحلیل احتمالاتی نشان می دهد که می توان شیب شیروانی را بهینه کرد به نحوی که کاملا پایدار بماند و حجم عملیات سنگ برداری نیز بهینه شود. از این رو به کمک تحلیل احتمالاتی شیب بهینه این شیروانی تعیین شد که در این حالت میزان سنگ برداری حدود 28000 متر مکعب کم تر می شود.

    کلیدواژگان: تحلیل احتمالاتی، تحلیل قطعی، سرریز آزاد سد کوار شیراز، مونت کارلو، نرم افزار SLIDE
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  • Kazem Bahrami, Seyed Mahmoud Fatemi Aghda*, Ali Noorzad, Mehdi Talkhablou Pages 185-212
    Background

    Aggregates are one of the high demand building materials in construction of structures and their characteristics have important effects on durability and permanence of projects. Abrasion resistance is one of the important features of aggregates that their utilization in concrete and asphalt are affected by texture and lithology of them. As rock consisted of harder minerals have higher abrasion resistance like igneous rocks, due to more siliceous minerals. More varieties in mineralogy compound usually lead to increase in aggregate abrasion. Aggregates that are contained of different minerals usually have less abrasion resistance. Porosity usually decreases the resistance abrasion. In addition to lithological properties, the environment where aggregates are deposited is important in determining resistance-related parameters of aggregates. Rivers, alluvial fans, and taluses are the main environments where aggregates are deposited. Geological processes, such as weathering and particle movement may cause changes in natural aggregates, hence affecting their abrasion and impact resistance. Rock weathering can results in increasing porosity, producing minerals that are weaker in comparison to their original rock. In the process of particles transport by stream water, weak parts of aggregates will be omitted. The present study is focused on the relationship between geology medium and the weight loss of aggregate in Los Angeles test. 

    Methodology

    Considering that lithology features in aggregates resistance against abrasion have an important role, in order to examine the effect of various geology environments in abrasion resistance of aggregates, the medium should be chosen having similar lithology. Therefore, the north of Damavand and the south of Daneh Khoshk anticline (north of Dire plain) were firstly chosen by using geology map, satellites images and field study. Damavand zone consists of trachyte and trachy-andesite volcanic rocks. These rocks cover the whole area around the Damavand peak. Also, Daneh Khoshk anticline is covered by thick Asmari formation. The selected environment are in the length of each other. Such that taluses feed alluvial fan and alluvial fans feed rivers. Samples were collected from different area of southern part of anticline. 10 river area, 12 alluvial fan and 6 taluses in the south-west area of Daneh Khoshk anticline (north of Dire plain) were chosen. Los Angeles test has been done according to standard A method ASTM D2216-10, 1990 on samples and the results were analyzed by analogous analyzer.

    Results and discussion

    Results show that porosity and micro-crack percentage increase, respectively in accumulated aggregate in river, alluvial fans and taluses areas. Also, porosity and micro-crack in various alluvial fans is different and is influenced by the area and length of main channel of alluvial fans’ catchment. The porosity decreases by the increase in the length of channel and area of alluvial fans’ catchment.The percentages of aggregate weight loss in talus, alluvial fan and river areas decreases, respectively. Based on the obtained results, the lowest rates of weight loss belong to river environments (23.7 % in Daneh Khoshk and 42% in Damavand) whereas the highest rates of weight loss belong to taluses (49.3% in Daneh Khoshk and 48% in Damavand). The alluvial fans have an average state. Another noticeable point is the high weight loss in Los Angeles test in Damavand aggregate. Due to having harder mineral, igneous aggregate have more abrasion resistance, but this research illustrates that the weight loss resulting from Los Angeles test in these aggregates is high. This is because of virtues texture that weakness against the impact as well as their high porosity.

    Conclusion

    The result of this research indicates that the volume of aggregate weight loss in Los Angeles test is related to aggregate accumulation environment. The extent of aggregate abrasion resistance is lowest in talus medium and increases in alluvial fan and river environment, respectively. The difference in aggregate abrasion resistance in various areas result from geology process differences that applies to aggregates in various environment. The extent of caring particles in talus environment is very low and the type of movement is mass or sliding type in these media, micro-crack and weak parts remains within aggregates. The surface of micro crack is weak such that breaks easily in Los Angeles test due to the pressure results from the impact of aggregate, as well as the impact of steel ball on aggregate leading to aggregate breakages. Aggregates move more distances in alluvial fan and river. Aggregate strike together in riverbed and alluvial fan yielding to aggregates breakages from micro-cracks. As the movement distance increases, aggregates approach more to intact rock. During the particles move, the weathered and weak parts are damaged by aggregate abrasion to riverbeds and alluvial fan, and more resistant and harder aggregates remain. As the water current increases, the aggregates impact each other harder, more resistant micro-crack breakages and this change leads to decrease the weight loss in Los Angeles test.

    Keywords: river, alluvial fan, talus, aggregate, abrasion resistance, Damavand, Daneh Khoshk anticline
  • matin jalali moghadam* Pages 213-236
    Introduction

    Retaining walls are geotechnical structures built to resist the driving and resistant lateral pressure. In terms of serviceability life, these walls are divided into two groups including short-term structures (temporary), such as urban excavation project, and long-term (permanent) structures, such as Mechanically Stabilized Earth Walls (MSE Walls). Retaining walls are implemented by two main methods including Top-down and Bottom-up. Among the reinforcements applied in the Bottom-up walls, one can name geocells, geogrids, metal strips, and plate anchors. On the other hand, the common reinforcements applied in the Top-down walls are grouted soil nails and anchors and helical (screw) soil nails and anchors.Plate anchors are burial mechanical reinforcements that have one or multiple bearing plates with a bar or cable to transfer the load to an area with stable soil. Among different types of plate anchor applied in onshore and offshore projects, one can name simple horizontal, inclined, and vertical plate anchors, deadman anchors, multi-plate anchors, cross-plate anchors, expanding pole key anchors, helical anchors, drag embedment anchors, vertically loaded anchors (VLAs), suction-embedded plate anchors (SEPLAs), dynamically-embedded plate anchors (DEPLAs) like Omni-max and torpedo anchors, and duckbill, manta ray and stingray anchors.The present research reports the results from physical modeling of plate anchor retaining walls under static loading. The evaluation parameters in this work include the geometry, dimension, and reinforcement configuration of plate anchors on wall stability. PIV technique was employed to observe critical slip surface. It is worth mentioning that PIV is an image processing technique firstly used in the field of fluid mechanics to observe the flow path of gas and fluid particles. This method was used in geotechnical modeling by White et al. (2003) and few reports are already available about its application to observe wedge failure of mechanically stabilized retaining walls.

    Material and methods

    To carry out tests at a laboratory scale, a dimensionality reduction ratio of 1/10 was applied. Thus, all dimensions of the designed retaining wall were divided by 10. As a result, a retaining wall with a height and length of 3000 mm was reduced to a wall with 300×300 mm2 dimensions. To build a retaining wall, a chamber was designed with a length, width, and depth of 1000 mm, 300 mm, and 600 mm, respectively.The soil used in all tests was the sandy soil supplied from Sufian (in Eastern Azerbaijan, Iran). According to the Unified Soil Classification System (USCS), the soil is classified as poorly graded sand with letter symbol ‘SP’.To create a perfect planar strain condition and prevent any friction between the footing and the lateral sides of the test box, the footing length was selected 1 mm smaller than the 300 mm width of the test chamber. Therefore, the length, width, and thickness of footing were selected as 299, 70, and 30 mm, respectively.The length and diameter of applied tie rods were respectively 300 mm and 4 mm, which are the smaller scales of 3000 mm length and 40 mm diameter tie rod. The two sides of the tie rods were threaded to plate anchors and wall facing. Four polished square and circular anchor plates with two different areas were used. The area of small and medium circulars are respectively equivalent to the area of small and medium square plates.Because no post-tensioning occurs in these plate anchors, the horizontal and vertical distances were both selected as 1500 mm. By applying a dimensionality reduction coefficient of 1/10, a 150 mm center-to-center distance was obtained for reinforcements in the wall. Accordingly, three applied reinforcement configurations including 5-anchor, diamond, and square configurations were used. To construct permanent retaining wall facing, prefabricated or precast concrete blocks with a thickness of 300 mm were used. Wood (2003) conducted a dimensional analysis and introduced four types of material with different thicknesses for a 300 mm concrete facing in laboratory modeling. Accordingly, a 0.9 mm thick aluminum plate was used in the experiments performed in the present work.

    Results and discussion

    With an increase in dimensions of anchor plates, an increase in bearing capacity of footing and a decrease in horizontal displacement of the wall are noticed. By comparing the 24 mm footing settlement in three configurations, with changing dimension of the plates from C1 to C2 and S1 to S2 respectively, 63% increases are observed in bearing capacity of the wall.An increase in anchor plate dimensions results in a significant decrease in wall displacement. Therefore, changing the plates from C1 to C2, S1 to S2 leads to 24% and 28% declination in wall displacement.By changing reinforcement configuration from square to diamond, diamond to 5-anchore, and square to 5-anchor, respectively, 27%, 31%, and 67.5% increases in bearing capacity for small plates, 9.2%, 27%, and 38% for medium plates are achieved using a comparison of the final loading steps in experiments. An analogy of percentages shows that a decrease in the effect of changing the reinforcement configurations on the bearing capacity of the wall with an increase in plate anchors dimensions is reached. 

    Conclusion

    In the present research, a set of laboratory experiments were carried out to evaluate the stability of mechanical retaining walls reinforced with plate anchors with different geometries (square and circular), sizes (small and medium), and configurations (diamond, square, and 5-anchor). The main results of the present work can be outlined as follows:• The maximum bearing capacity is for the 5-anchor configuration since it has one more reinforcement. After 5-anchor configuration, the diamond configuration results in a higher bearing capacity compared to the square configuration.• Circular anchor plates compared to square anchor plates provide a higher wall stability and in the most of the experiments lead to higher bearing and lower displacement in the wall.• Wall displacement in a diamond configuration with one less reinforcement shows a little difference with 5-anchor configuration. The maximum wall displacement occurs in a square configuration and more wall swelling is observed in the wall middle height due to inefficient anchors configuration in the wall.

    Keywords: mechanical retaining walls, plate anchors, bearing capacity, wall displacement
  • Seyed Taha Tabatabaei Aghda, Ali Ghanbari*, Gholamhosein Tavakoli Mehrjardi Pages 237-260
    Introduction

    In some ports, the dredging and accumulation of a large amount of sedimentary material turned to a serious challenge, because of their sequent environmental and economic effects. These problems clarify the necessity of reusing dredged materials. Often, owing to their poor mechanical properties, they are not applied directly in technically engineering uses, so they require to be improved. Geocell application is one of the methods used for the improvement of soil behavior, which confines the sand mass through itself in the three-dimensional structure. These methods ease the speed of applying emerged it into a perfect option for stabilizing of the granular soil.
     In Shahid Rajaee port, by the dredging process for developing new phases, a large amount of calcareous sand is being accumulated near the Persian Gulf coastline. Therefore, in order to provide a solution to reuse these materials, this study attempts to investigate the beneficial influence of reinforcing sand by geocell on its load-beneficial behavior experimented by the plat loading test. For this purpose, a large scale model including circular foundation on reinforced and unreinforced sand has been employed under cyclic loading process.

    Material and Methods

    SoilsTwo types of soils were used in this study. The first type was the sand derived from the dredging process of Shahid Rajaee port which has been used in different layers of the models. The second type of soil was well-graded gravel which has been used only in the cover layer. Geocell The geocell in this study were made of heat-bonded non-woven polypropylene geotextiles. Single cells were 110 mm long, 100 mm wide and 100 mm height.
    Plate load test In order to determine the bearing capacity of backfills, repeating plate load test was used with 150 mm diameter. Loading process included four stress levels (250, 500, 750 and 1000 kPa) consisting of 10 cycles each. Test backfills Four backfills was made by manually compacting the dredged sand, with tamper up to 350 mm in reinforced cases and 450 mm in unreinforced cases. Then geocells placed and dredged sand filled with accuracy in cells. Finally, a 50 mm thick sand or gravel cover layer, was placed. All lifts were compacted to 70% of relative density with 4% moisture content.

    Results and Discussion

    PLT results are summarized in Table 1. According to the results, only geocell reinforcement backfills can carry standard truck wheel load (550 kPa). Geocell can increase the ultimate strength of backfills with a sand cover layer by 70% (from 416 kPa to 725 kPa) while in backfill with a gravel cover layer showed 80% increase (from 520 kPa to 960 kPa) in ultimate strength. The gravel cover layer in unreinforced backfills increases the ultimate strength by 25 percent (from 416 kPa to 520 kPa). Table 1. Results of PLT and performance ratings Base on Table 1, bearing capacity ratio (BCR) has been increased up to 2.3 and has best when geocell reinforcement and gravel cover layer were used together. Geocell utilization as reinforcement for sand backfills, improves the stress-settlement behavior. Dredged sand can be used as backfill material for yards and access roads when reinforced with geocell and covered with a layer of well-graded gravel.

    Keywords: Geocell, Plate loading test, dredged sand, load-settlement behavior
  • Vahed Ghiasi*, Mobin Moradi Pages 261-288
    Introduction

    Raft foundations are generally used to support buildings and structures, with or without basements, in dry or high ground water table conditions. When the shallow subsoil conditions are unfavorable (unsafe bearing capacity or excessive settlements) then load bearing piles can be used for transferring the total loads to more competent soil layers. In many cases, the maximum and differential settlements are the controlling factors to the selection of composite foundations systems including piles and raft. The piled raft foundation contains three elements of load-bearing; namely piles, raft and the underlying soil mass. Matching their relative stiffness, raft foundation distributes the whole load is transferred from the superstructure to the top soil and the connected piles. In foundation design, the idea of combining mat foundation and deep foundations as a new option in the topic of foundation engineering has been raised in recent years. The use of deep foundations under mat foundations (Piled-raft Foundation) can leads to reduce the settlement and the effect of bearing capacity. In conventional design of piled foundations, it was usually postulated that the overall load is supported by the piles. In composite foundation systems, raft contribution is taken to confirm the bearing capacity in ultimate moment and the serviceability of all over system.

    Material and methods

    Composite piled-raft foundations including pile and raft have been considered in this research. Knowing the performance of composite piled raft systems is important because of the fact that the decreasing role of differential settlement and piles plays the role of supporting the underlying soil and increasing the load bearing capacity of the soil. A case study has been used to analyzing the performance of piles and shallow foundation systems in this study. For this purpose, the finite element PLAXIS 3D foundation software is used to analyze the foundation deformation. Raft foundation with a thickness of 0.3m and dimensions of 6 × 6m, which is located on a uniform sandy soil mass, and depth of raft from the soil surface is 2 m. Piles with a circular section of length 10 m, a thickness of 0.5 m and with 9 numbers below and within soil are located. Groundwater level is not considered, which actually indicates that the water level is outside of the 25m thick layer of the sand. In this research, deformation of foundation, moment applied on foundation and also the contribution of piles in the bearing of combined system under static loading in sandy soil for the various of pile lengths 7m to 13m and different thickness of raft 0.3m to 1m in the piled-raft foundations regarding connection of raft and piles, has been analyzed.

    Results and discussion

    The obtained results indicate that the first to third layouts in the optimal system where the central piles are longer, the settlement has had a maximum decline. A comparison of the default composite system with a 10 meter pile length and an optimal proposed system illustrates that the optimal system in the first and fourth layouts reduces differential settlement of raft in relation to the default system. Applying variations in pile lengths the optimal system has led to a reduction in the amount of bending moment applied to the raft in all layouts. Composite systems with the first, second and third layout, optimize system utilization effect on increasing the share of piles bearing. But in the fourth, with the optimum layout of the composite piled-raft system share of piles bearing to the total load on the same analogy in the basic system, the less value has been raised this argument that the position of the scattered placement of piles are the reason for this issue. The raft thickness of the composite system is another parameter whose performance has been measured against the raft settlement. With the increase in the maximum amount of raft thickness increases the settlement which of course this increasing is small and very different thickness is not notable. By increasing the raft thickness, reducing the differential settlement is sensible but the major settlement reduction in the thickness of 0.3m to 0.5m has been occurred. With increasing the raft thickness the value of the moment has been increased. This moment increasing in the piled-raft system with disconnected piles over other systems in the primary thickness, moment is created about 60 kN and the raft thickness 1m, this moment value has reached more than 100 kN, as well as, by increasing the raft thicknesses, the amount of load share of the piles to the total load increased, significantly.

    Conclusion

    The following conclusions were drawn from this research.-Use a long piles in the center and the shorter piles about the raft reduce the maximum settlement, differential settlement and significant reduction of the raft foundation moment, and beside these, piles bearing the composite piled-raft system is increased. By increasing the raft thickness increases the maximum settlement, mean settlement, bending moment of raft has been increased. The positive effects of increasing the thickness of raft foundation is reducing the differential settlements and increasing the pile contributions in the bearing. This result has been expected due to increasing the raft mass and rigidity.
    -The combined piled-raft system utilizes connected and disconnected piles to the raft and detached from it simultaneously to improve the expected indices.

    Keywords: Numerical analysis, Raft thickness changes, Pile length changes, Piled raft foundations
  • Seyed Davoud Mohammadi*, Elahe Hosseinabadi Pages 289-316
    Introduction

    In regard to consumptions of oil materials by human, soil contamination causes worriness in environment and geotechnics areas in previous years, such that studying of soils lead to soil refine, soil bearing capacity and soil changing by infiltration of contamination. The rates of problems on environment are different and it depends on soil types and its structure, organic materials values, soil permeability, climate and type of contamination. In viewpoint of geotechnics, many investigations have been done on various contaminated soils that their result leads to optimum application of those as road construction and decrease of costs. In this research, with adding of different percentages of gasoil into the soil, engineering properties of contaminated soils were investigated and its effect on the erodibility of soils was studied. Regarding to the Hamedan oil storages complex extension and lateral installations, the study of contaminated soils are essential. Also, because the location of that complex is at urban area, the environmental risk of leaking of oil materials is available. Thus, the goal of this research is to investigate the erodibility of contaminated soils at the studied area.     

    Material and methods

    Hamedan oil storages complex is located about 17.7 km far from Hamedan city. In order to study engineering geological properties and erodibility of three layers of soils in studied area, the soil samplings were done from three soil layers. Based on the field and laboratory results, all of three soil layers were classified into SM class and had too much lime (Table 1). Testing program is divided into engineering geological tests and erodibility tests. All of the engineering geological tests on the uncontaminated and contaminated soils were undertaken according to ASTM (2000) (Table 2). In order to prepare the contaminated soils and to determine the maximum absorbable gasoil, the soil samples were contaminated by gasoil and some standard compaction tests were undertaken on the soils. According to the test results, upper and lower layers were saturated by 19% of gasoil and middle layer was saturated by 15% of gasoil. After determination of gasoil saturations percentages for studied soil layers, the 7, 13 and 19 percentages of gasoil were added into the upper and lower layers and the 5, 10 and 15 percentages of gasoil were added into the middle layer. Thus, for engineering geological tests, 9 samples of contaminated soils were prepared.Table 1. Soil properties of studied area Lime percentage To prepare the sample for direct shear test, a mould with dimension of 10 cm *10 cm *2 cm was used. Then, the prepared sample was set inside the shear box and vertical stress was applied. All of direct shear tests were done in unconsolidated-undrained condition (UU), in maximum dry unit weight dmax) and in optimum water content ( opt)of soil samples.All of the soil samples for uniaxial compressive strength tests were prepared in maximum dry unit weight and optimum water content. To prepare the soil samples, a split tube mould with 5*10 cm of dimensions was used. Based on that test, the soil samples are set under axial load and failure occurred at the end of the test.To investigate the effect of gasoil on soil erodibility, first the erodibility tests by using rainfall simulator were done on uncontaminated soils and then, on contaminated soil with different percentages of gasoil. All of soil samples for erodibility test were prepared into the pans with 30*30*15 cm of dimensions and in maximum dry unit weight and optimum water content. The thickness of soil samples were 5 cm and the gravelly drainage layers were 10 cm. The rainfall intensity was equal to rainfall intensity of sampling area (29 mm/hours) and the steepness of soil samples were equals to sampling area steepness (10 to 40 degrees). After catching of runoff and drained water, the eroded soils were weighted and the weight loss of soil samples was calculated.   

    Results and discussion

    All of the engineering geological tests results are shown in Table 3. With increasing of the gasoil percentages, dry maximum unit weights of all three layers have decrease trends while the optimum water contents have increase trends. Surrounding of the soil grains by gasoil and water causes the easy sliding of grains and more compaction. The Atterberg test results shows that liquid and plasticity limits of soil had increase trend with increasing the gasoil. In the middle layer its trend is more than the others. Because the viscosity of gasoil is more than the water viscosity, the adhesion of contaminated soil would be more than the uncontaminated soil and then, the liquid and plasticity limits of contaminated soils are more than the others. The uniaxial compressive strength results show that the undrained strength of contaminated soils would be decrease with increasing the gasoil content. This behavior is the result of sliding of the contaminated soil grains on each other.The results of erodibility tests results are shown in Table 4. The erodibility would be increase with increasing the gasoil percentages. Also, it would be increase with steepness dips degrees. In compare to the uncontaminated soils, the maximum weight loss of the contaminated soil is 608.3 kg/m2.hr in 15% of gasoil and 40 degrees of steepness in L2 layer. The minimum weight loss of the contaminated soil is 13.33 kg/m2.hr in 0% of gasoil and 10 degrees of steepness in L3 layer. Thus, the assessment of gasoil effect on erodibility of soils is very important.Table 3. Results of the engineering geological tests on the uncontaminated and contaminated soil samples
    Layers

    Conclusion

    1. According to the grain size analysis test results, all of three layers of soils around the Hamedan oil storage are SM with too much lime.
    2. With increasing the gasoil, liquid and plasticity limits of three soil layers had increase trend. its trend in the middle layer is more than the others.
    3. According to the erodibility results of contaminated soils, the weight loss of middle layer was more than the other layers because of the middle soil layer had lower percentages of lime.   
    4. The gasoil causes decrease of soil strength and increase of weight losing. Thus, the uniaxial compressive strength and weight losing have reverse correlation.  
    5. With increasing of the contamination, the cohesion and internal friction angle of soils would be decrease and then, the erodibility would be increase.
    6. Maximum of erosion of contaminated soils was in 15 and 19 percentages of gasoil and it was three times more than that of uncontaminated soils.
    7. The critical steepness of uncontaminated soil layers was 40 degrees for all three layers, but it was different for contaminated soils, 
    8. Regarding to the location of Hamedan oil storages, the environmental risk of oil leakages and erodibility of contaminated soils are certain.  

    Keywords: Soil contamination, Engineering geological properties of soil, Rainfall simulator, Erodibility, Oil storage, Hamedan
  • Saeed Mojeddifar*, Nastaran Ostadmahdi Eragh Pages 317-338
    Introduction

    This work intends to apply ASTER images to discriminate hydrothermal alteration zones in Kerman Cenozoiic Magmatic Belt (KCMB). Band ratio, principal component analysis, Crosta and color composite images are important methods to analyze satellite images. Previous researches showed that these techniques are not able to discriminate hydrothermal alteration zones and they usually detect vegetation covering as alteration zones. The reason is found in the spectral signature of vegetation and alteration minerals. It means that they present the same interaction when face with electromagnetic energy in different wavelengths. Hydroxyl-bearing minerals are the important products of hydrothermal alteration. Clays, which contain Al-OH- and Mg-OH-bearing minerals and hydroxides in alteration zones, are distinguished by absorption bands in the 2.1–2.4 µm range of ASTER data. Solving these problems is difficult when using standard image-processing techniques such as band rationing, principal component analysis, or spectral angle mapper. In recent years, several attempts were made to extract altered regions in the areas covered with vegetation. To overcome this problem, this research uses ASTER data by applying support vector machine (SVM) algorithmn. SVM is a new technique for data classification in remote sensing application. This paper aims to investigate the potential of SVM algorithm in mapping of hydrothermally altered areas. In many applications, SVM has been shown to provide higher performance than traditional learning machines and has been introduced as powerful tools for solving classification problems. The adopted dataset contains three ASTER scenes using SWIR and VNIR bands, covering the Meiduk porphyry copper deposit, Kader, Abdar and Iju occurrences located in Kerman Province, southeast Iran.

    Material and methods

    This work has been prepared on three ASTER level 1B scenes. Two scenes were acquired on 18th April 2000 and another scenes on 15th June 2007. These scenes were georeferenced by using an orthorectified ETM +  image,  in  UTM projection and WGS-84 ellipsoid as a datum.  The first two data sets were corrected for Crosstalk. Atmospheric corrections were also performed by using Fast Line of Sight Atmospheric Analysis of Spectral Hypercubes (FLAASH). The data sets were then mosaicked. Internal Average Relative Reflectance (IARR) correction was also applied. In this part, the training and test samples of the ASTER data are presented. The adopted image is a multispectral satellite image that contains 2204 training pixels which 516 pixels are related to arjillic zone, 1278 pixels are related to phyllic zone and 500 pixels are pertinent to propylitic zone (Fig. 1).

    Fig. 1. Training pixels for learning SVM algorithm; Red pixels: arjillic; Green pixels: phyllic; Blue pixels: propylitic

    Results and discussion

    ASTER bands 4, 6, 7 and 8 were applied for determination of phyllic and arjilic zones and 9 bands of ASTER for propylitic alteration. In order to evaluate the developed algorirhm, confusion matrix was used and validation showed that discrimination of phylic and arjilic is not possible but propylitic zone could be identified by SVM. Also, the present research introduced a new error function, so called blind error, which is calculated using confusion matrix. Based on blind error, SVM did not classify 73.6 percent of the alteration pixels. But the remained pixels were classified with accuracy of 66.06%. Honarmand et al. (2011) and Mojedifar et al. (2013) studied the field samples of the present study area. Their studies showed that sericitization is the most widespread form of hydrothermal alteration at the Iju, Serenu, Chahfiroozeh, Meiduk, Parkam, Kader and Abdar porphyry copper deposits. Two types of phyllic alteration could be found in the study area including ferric-iron-rich and iron-oxide poor phyllic alteration. ASTER images were also analyzed by band rationing and principal component analysis (PCA) in order to compare their results with the SVM classified image. A comparison of the field data with altered areas mapped by PCA reveals errors in the classified map. Vegetation cover and sedimentary rocks are enhanced, which are erroneously identified as areas of alteration. The band ratio approach yields similar errors to those produced by the PCA method. These problems are less evident in the classified image obtained by SVM. The qualitative assessment of the accuracy of these methods indicates that SVM algorithm could be a reliable technique for alteration mapping, provided that the nature of the training areas is well known.

    Conclusion

    A comparison of the results obtained from traditional classification methods and support vector machine algorithm was performed in order to map hydrothermal alteration. Since the known occurrence of mineralization in the study area is consistent with the mapped distribution of hydrothermal alteration using SVM, this method is suggested to apply in exploring for hydrothermal alteration in other parts of the Iranian Cenozoic magmatic belt.

    Keywords: Phyllic, Arjilic, Prophylitic, Porphyry Copper, Support vector machine
  • Erfan Naderi, Adel Asakereh*, Masoud Dehghani Pages 339-370
    Introduction

    Bearing capacity is very important in geotechnical engineering, which depends on factors such as footing shape, stress distribution under footing and failure mechanism of soil. Construction of the footing near a slope affects the behavior of footing and reduces the bearing capacity. Also, construction of structures on soft soil usually involves problems such as excessive settlement, deformation and stability problems. In order to increase the bearing capacity, especially in soft soils, one method is adding stone columns to soils. In this method 15 to 35 percent of unsuitable soil volume is replaced with appropriate material. In this research, the bearing capacity and settlement of a strip footing on a clayey slope reinforced with stone columns is investigated. For this purpose, a series of small-scale model tests was performed on the slope reinforced with both types of ordinary and vertical encased stone columns. The effects of length of stone column and location of stone column on the behavior of footing was studied and the optimum length of column and best location for column were determined. Also, some tests were performed on the effect of group stone columns on the footing and the efficiency of columns was investigated.

    Material and methods

    In order to determine properties of clay soil, stone column and encasement material, some preliminary standard tests were performed. The stone column material was selected with aggregate size ranging from 2-10 mm considering the scale effect. The performance of stone column depends on the lateral confinement provided from the surrounding soil and this lateral confinement represents undrained shear strength of the soil. In very soft soils (cu<15 kPa), the lateral confinement is not adequate and the stone column cannot perform well in carrying the required bearing capacity. For this reason, a series of undrained shear strength standard tests were carried out on clay samples with different water contents. According to these tests, the amount of water content of clay related to cu-15kPa was equal to 25%; while the natural water content of the clay was 4%. Therefore, the additional amount of water was weighted and added to clay. The apparatus of this research was consisted of two main parts including a test box and a hydraulic loading system. The test box dimensions should be such that for all states of the tests, the stress in the soil applied from the loading would be almost zero at all boundaries of the box. Thus, a box was built to accommodate the clay slope with 150 cm×120 cm×30 cm dimensions. The test box was built using steel material and steel belts were welded around it to prevent the deformation at high loads. The front side of the box was made from two pieces of tempered glass and a 10 cm×10 cm grid was drawn on them, for making the slope during construction and observation of deformations during the loading easier. The model strip footing dimensions were 29 cm length, 10cm width and 4cm height and it was made from steel to have no deformation during the loading. The displacement of the footing was measured using two dial gauges with accuracy of 0.01 mm. The clay was filled in the test box in 5 cm thick layers and compacted with a special 6.8 kg weight tamper. All model stone columns were constructed using the replacement method. In this method, a 10 cm diameter open ended steel pipe was inserted into the soil and the clay within the pipe was excavated. Then the stone column material charged into the hole in 5 cm layers and each layer was compacted using a 2.7 kg special circular steel tamper with 10 blows. The 5cm compactions were repeated until the construction of ordinary stone column was completed. For construction of vertical encased stone columns, the cylindrical encasement mesh should be constructed first. Then, after excavating the hole, the prepared encasement mesh was placed inside the hole and the aggregates were charged into the hole in 5 cm layers and compacted.

    Results and discussion

    The loading method used in all tests was a stress control method. Bearing capacity values were determined from pressure-displacement diagrams using tangent method. All test results show that when any type of stone columns was added to slope, the bearing capacity of adjacent footing was increased. Vertical encasing of stone columns leads to a further improvement in the behavior of the footing. Influence of length of ordinary stone columns on the behavior of strip footing near clayey slope, was studied for four different lengths. Results show that, the optimum length of stone columns giving the maximum performance is about 4 times their diameter. Also, the location of column for both ordinary and vertical encased stone columns was studied using a series of laboratory tests and results show that the best location for the stone column is right beneath the footing. Also, group stone column tests resulted that for both ordinary and vertical encased types of stone columns, the group of two columns had a better efficiency than the group of three columns.

    Conclusion

    In this investigation, some model tests with 1/10 model scale on a strip footing near a clayey slope reinforced with stone columns were performed and the effects of different parameters such as stone column length and location were studied. Based on results from experiments on different states of stone columns, the following concluding remarks may be mentioned:- The maximum encasement influence was observed when the encased stone column is placed under the footing.
    - The optimum length of ordinary stone columns which are placed beneath the strip footing gives the maximum performance more than 4 times to their diameter.
    -Bulging failure mode governs when the stone column is placed under the footing. When stone column is not beneath the footing, the failure mode was lateral deformation.
    - Comparing the different locations of stone columns in the slope shows that for both ordinary and vertical encased stone columns, the best location having the most influence on the strip footing is under the footing and with increasing the spacing between column and footing, the bearing capacity is reduced.

    Keywords: Encased stone column, Bearing capacity, Strip footing, slope, Clay
  • Reza Nassirzadeh Goorchi, Mehdi Amini*, Hossein Memarian Pages 371-398
    Introduction

    One of the most sensitive and important issues in some civil engineering projects is slope design and application. The process of slope design always involve many uncertainties. Hence, it is impossible to accurately comment on its stability or instability. Most of the uncertainties in the slope stability analysis are related to the nature of materials, geometry, environmental conditions, model errors, and measuring errors as well. Therefore, the slope stability analysis with a deterministic approach which uses the concept of safety factor would often not result satisfactory. Consequently, the use of probabilistic methods is more advised. Accordingly, in recent years, the probability analysis has been used to slope stability analysis. In these analyses, the effective quantities of slope stability are considered as statistical distributions, and the reliability coefficient would then be a statistical distribution. Likewise, one of the approaches to simulate uncertainties in the probabilistic analysis is to use the variation coefficient. If the variation coefficient changes, the probability of failure will change accordingly. When the variation coefficient becomes a larger number, costly solutions are required to reduce the probability of failure. If the variation coefficient becomes low, the reliability will be increased and the required costs to reduce the probability of failure will be decreased. Therefore, determining the amount of variation coefficient in these analyses is very important. Furthermore, the correlation coefficient between the quantities is another effective parameter in computing the probability of failure.

    Material and methods

    In this research, the stability analysis of the slope facing the spillway of the Shiraz Kavar dam has been done in two probabilistic and deterministic methods. Since circular slip probability is more likely than other types of failure, in the analysis of the stability of this slope, the problem of circular failure is very important, and an appropriate equilibrium program should be used for circular failure analysis. Therefore, SLIDE software was used to slope stability analysis. For material behavior, the Hook-Brown failure criterion was applied. In order to determine the strength parameters of the criterion, Geological Strength Index (GSI), uniaxial compressive strength (UCS) and rock constant parameter mi were used. For crushed rock with a moderate quality of crushing, the GSI quality of the rock mass was about 23 to 38, which the average value of that for the rock mass of the overflow was assumed 35. Also, the uniaxial compressive strength of the rock was evaluated about 50 to 100 MPa with an average value of 75 MPa. In addition, the value of mi was 10, and due to mechanized drilling, the disturbance factor was considered to be 1. The amount of unit weight was assumed to be 22 kN/m3. The initial model used for deterministic and probabilistic analyses, is the Morgenstern-Price model. To conduct probabilistic analyses, Monte Carlo simulation was performed using random sampling method (RS-MC) and 200,000 sampling were used to converge the simulation results. To determine the coefficient of variation and the probability distribution of UCS, GSI and mi, the proposed values ​​of Hook (1998) were applied and for unit weight (γ) James Rodriguez and Sitar (2007) studies were used. Also, the minimum and maximum values ​​of UCS and GSI are determined based on the results of experiments, and Third Sigma rule was utilized for mi and γ quantities. Since the earthquake phenomenon is rarely of great intensity and the number of small earthquakes is higher, therefore the truncated exponential distribution function can be in good agreement with the results of the earthquake. Usually, the maximum magnitude of the earthquake acceleration coefficient is twice that of the average.

    Results and discussion

    In the presented paper evaluation denotes that the safety factor computed by probabilistic analysis is given as a distribution function. The function provides a clearer view of failure condition. However, a deterministic analysis only illustrates a certain value for the failure. In addition, the results of the probabilistic analysis show that it is possible to optimize the dip of the slope; such that it remains completely stable and the volume of earthwork is also minimized. Therefore, by using probabilistic analysis, the optimal dip of the slope was determined. In these circumstances, the amount of earthwork was decreased by 28,000 cubic meters. Also, the sensitivity analysis of the variation coefficient and correlation coefficient between parameters are analyzed. The results of the sensitivity analysis of the failure probability versus the variation coefficient of the quantities showed that the quantities of sensitivity factor for static conditions is greater than the corresponding pseudo-static, and the GSI amount is the highest, while the specific gravity has the least effect on the probability value. In addition, the analysis indicated that if the GSI coefficient of over 21% is selected, the probability of a static failure is higher than the permissible limit. Also, increasing the variation coefficient of quantities by as much as 50% exhibits that the probability of static failure is still below the permissible limit. Also, the correlation coefficient between UCS and GSI shows that the higher variation coefficient of the quantities is chosen, the more variations of failure probability compared to . In the case of pseudo-static conditions, variations in the failure probability are linear in relation to , while in static conditions, these changes are exponential for an increase of 50% in the variation coefficient. Also, to reduce the coefficient of variation by 50%, the probability of static failure for different values of  is approximately zero.

    Keywords: Probabilistic analysis, Deterministic analysis, Spillway, Shiraz Kavar dam, Sensitivity analysis, Variation coefficient