- Volume:13 Issue:3, 2019
- تاریخ انتشار: 1398/08/10
- تعداد عناوین: 8
انفجار و لرزش های حاصل از آن در مقایسه با ساختارهای زمین شناسی و آب زیرزمینی، به دلیل قابلیت کنترل بهتر آن، تاثیر کم تری در ناپایداری حفریات زیرزمینی دارند. عدم اجرای اصولی فرآیند انفجار، ممکن است منجر به آسیب های جدی شود. در این تحقیق مدل سازی روی رمپ قره چنگول معدن سرب و روی زه آباد در برابر بارهای انفجاری انجام شده است. این معدن در جنوب روستای زه آباد واقع در70 کیلومتری شمال شهرستان قزوین در بخش طارم سفلی واقع است. به منظور به دست آوردن خواص فیزیکی و مکانیکی سنگ های در برگیرنده رمپ و پارامترهای مقاومت برشی ناپیوستگی ها، آزمایش هایی شامل آزمایش های تک محوری، سه محوری، برزیلی، برش مستقیم، تعیین وزن مخصوص و سرعت امواج طولی انجام شد. هم چنین برای شبیه سازی شرایط پیچیده حاکم بر فرایند انفجار، با توجه ناپیوسته بودن محیط، برای مدل سازی عددی از نرم افزار المان مجزای UDEC استفاده شد. در انجام یک تحلیل دینامیکی ابتدا باید مدل در حالت استاتیکی به تعادل برسد. بعد از تعریف شرایط مرزی جاذب، بارهای دینامیکی بر اساس مدت زمان تعریف شده به مدل وارد می شود. در بحث پایداری معادن و فرآیند انفجار، بار دینامیکی حاصل از آن اغلب به صورت یک پالس به مدل اعمال می شود. با وارد کردن بار دینامیکی و در نظر گرفتن سایر تغییرات یاد شده نسبت به تحلیل استاتیکی، می توان پاسخ دینامیکی فضای زیرزمینی را تحت بار لرزشی انفجار و یا زلزله پیش بینی کرد. برای این منظور موج ضربه ناشی از انفجار به صورت پالس نمایی با فشار بیشینه 41/4 مگاپاسکال و پهنای زمانی 7/0 تا 7 میلی ثانیه به مرز سمت چپ مدل اعمال شد. نتایج حاصل از تحلیل عددی نشان می دهد که در حالت استاتیکی فضای زیرزمینی مورد نظر پایدار است و بلوکی ریزش نمی کند. بعد از اعمال بار حاصل از انفجار نتایج نشان می دهد، رمپ پایدار می ماند و نیازی به نصب سیستم نگه داری نیست و در اطراف رمپ موردنظر ریزشی صورت نمی گیرد.کلیدواژگان: معدن سرب و روی زه آباد، رمپ قره چنگول، بارگذاری انفجار، پایداری، تحلیل دینامیکی، مدل سازی عددی
ستون سنگی یکی از روش های متداول بهینه سازی زمین است. در باره رفتار ستون های سنگی تحت بارهای قائم تحقیقات متعددی انجام شده است لیکن بررسی های محدودی در باره مقاومت برشی خاک های مسلح شده با ستون سنگی انجام شده است که اغلب پژوهش های انجام شده به صورت تحلیلی یا عددی است. در این مقاله به بحث و بررسی آزمایش های انجام شده در خصوص مقاومت برشی ستون های سنگی در بستر ماسه ای سست مسلح شده با ستون سنگی پرداختیم. آزمایش ها در دستگاه برش مستقیم با جعبهبرش به ابعاد 305×305 و عمق 4/152 میلی متر در سه تنش قائم شامل 55 و 75 و 100 کیلو پاسکال و چهار نسبت ناحیه اصلاح شده برابر با 4/8 و 12 و 4/16 و 25 درصد و سه نوع آرایش قرارگیری ستون سنگی (آرایش منفرد مربعی، مثلثی) بررسی شده است. نتایج بیان گر بهبود رفتار و سختی ترکیب خاک-ستون سنگی و افزایش مقاومت برشی بستر ماسه ای در حضور ستون سنگی می باشد. نتایج حاصل بیان گر تاثیر آرایش قرارگیری ستون های سنگی در افزایش مقاومت برشی است. بیش ترین افزایش مقاومت برشی و افزایش سختی مربوط به آرایش مربع و کم ترین آن مربوط به آرایش منفرد است. در ادامه مقاله به بررسی و مقایسه مقاومت برشی معادل و پارامترهای مقاومت برشی معادل به دست آمده از نتایج آزمایش و روابط تحلیلی پرداخته شده است. نتایج بیان گر آن است که مقاومت برشی و پارامترهای مقاومت برشی معادل حاصل از نتایج آزمایش ها بیش تر از مقادیر حاصل از روابط تحلیلی است. بدین منظور یک ضریب اصلاحی به منظور ارتباط بین نتایج حاصل از آزمایش ها و روابط تحلیلی ارائه شده است.کلیدواژگان: ستون سنگی، مقاومت برشی معادل، ماسه سست، برش مستقیم
در این تحقیق، ارتباط وواکنش کمی وکیفی آب چشمه کارستی شهر ری (چشمه علی) در جنوب شهر تهران با آب زیرزمینی آبرفت های آبخوان های محیط کارستی و محیط آبرفتی از یک دیگر جدا است و دو محیط زمین شناسی وآب زیرزمینی کاملا متفاوت را نشان می دهد. آبخوان آبرفتی، محیط متخلل پیوسته آب زیرزمینی است، در صورتیکه آبخوان کارستی محیط درز وشکافدار آب زیرزمینی می باشد. در این تحقیق، ارتباط وواکنش کمی و کیفی آب چشمه کارستی شهر ری (چشمه علی) با آبخوان آبرفتی اطراف آن بررسی شده است. در این بررسی پژوهش های زمین شناسی، کمیت و کیفیت آب زیرزمینی چشمه علی و آبرفت های مجاور آن، خصوصیات هیدرودینامیکی چشمه و آبخوان آبرفتی مجاور چشمه مطالعه و بررسی شد. نتایج حاصل از بررسی ها گویای شرایط زمین شناسی، هیدروژئولوژی و شرائط هیدرولیکی متفاوت بین چشمه کارستی شهرری و آبخوان آبرفتی اطراف آن است و نبود ارتباط هیدرولیکی بین دو محیط آب زیرزمینی آبرفت و کارست در مجاور هم و متفاوت را نشان می دهد، که در اثر عملکرد گسل شمال شهر ری شکل گرفته اند.کلیدواژگان: کارست، آبرفت، چشمه علی شهر ری، ارتباط کارست وآبرفت
از خاک های لسی در سه منطقه شرق و شمال شرق استان گلستان نمونه برداری شد و آزمایش پین هول روی نمونه های با وزن واحد حجم طبیعی (gn) و حداکثر (gdmax) انجام شد و میزان واگرایی آن تعیین شد. پیشنیه تحقیق، شواهد صحرایی و نتایج آزمایش های آزمایشگاهی حکایت از واگرا بودن خاک مناطق نمونه برداری دارد. نتایج نشان می دهد، تراکم خاک باعث کاهش شدت واگرایی می شود و نرخ جریان را کم می کند، به طوری که نرخ جریان در نمونه مراوه تپه به میزان 38 درصد، در نمونه چشمه لی به میزان 13 درصد و در نمونه بق قجه بالا به میزان 43 درصد کاهش یافته است. تراکم نمی تواند واگرایی خاک را از بین ببرد. افزودن نانورس باعث کاهش شدت واگرایی خاک شده و در غالب موارد خاصیت واگرایی آن را از بین می برد. به منظور بررسی اثر نانورس روی شدت و کاهش خاصیت واگرایی خاک با نسبت های 5/0، 1، 2، 3، 4 و 5 درصد وزنی نانورس مونت موریونیت افزوده شد. میزان واگرایی نمونه های دارای نانورس در دستگاه آزمون پین هول اندازه گیری شد. هم چنین روش اختلاط نانورس با خاک واگرا رفتارهای گوناگونی را در شدت واگرایی و کاهش آن نشان می دهد. نانورس به چهار روش با خاک های مناطق نمونه برداری مخلوط شدند. در روش A ، با تهیه گل همگن از خاک و نانورس با هم زن برقی کاملا مخلوط شدند. در روش B، اختلاط خاک لس با نانورس در رطوبت بهینه انجام شد. در روش C. اختلاط خاک لس با نانورس به صورت خمیر به وسیله هم زن دستی انجام شد. در روش D. اختلاط خاک لس با نانورس به صورت خشک ارتعاشی به وسیله لرزاننده الک دانه بندی انجام شد. نتایج بررسی نشان داد که، نسبت وزنی یک درصد نانورس از نظر فنی و اقتصادی مناسب ترین نسبت اختلاط است. با این نسبت وزنی، روش تهیه گل همگن با هم زن برقی (روش A) کم ترین نرخ جریان را به وجود می آورد؛ به طوری که نرخ جریان از 3/1 میلی لیتر در ثانیه در خاک خالص به 3/0 میلی لیتر در ثانیه در خاک حاوی نانورس در هد 50 میلی متر کاهش می یابد. از این رو، می توان گفت این روش مناسب تر است ولی از لحاظ اجرایی کارایی ندارد و روش B مناسب تر است. در روش B نرخ جریان از 3/1 به 55/0 میلی لیتر در ثانیه در همین حد می رسد.کلیدواژگان: نانورس، خاک واگرا، لس، استان گلستان، مواد افزودنی
ارزیابی فرونشست زمین به کمک تلفیق روش تداخل سنجی راداری و اندازه گیری های میدانی و بررسی دلایل و اثرات آن بر شهر مشهدصفحات 435-462
مشهد دومین کلان شهر ایران است. به دلیل برداشت بیش از حد از منابع آ ب های زیرزمینی، عوارض فرونشست به صورت شکاف زمین و ترک در دیوار سازه های مسکونی در حریم شمالی شهر مشهد مشاهده شده است. هدف از این پژوهش پایش دقیق نرخ فرونشست سالانه به کمک تمامی داده های موجود و علت یابی این پدیده با توجه به ویژگی های زمین شناختی و هیدروژئولوژیکی منطقه است. ابتدا به کمک روش ترازیابی دقیق که قدیمی ترین داده ها را از فرونشست زمین در اختیار قرار می دهد، سابقه فرونشست بررسی شده است. سپس پردازش تداخل سنجی راداری برای کل دشت مشهد به کمک 23 تصویر ماهواره ENVISAT انجام گرفته است. نتایج نشان می دهد که دو کاسه فرونشستی یکی از شمال غرب و دیگری از جنوب شرق وارد حریم شهر مشهد شده است و در دشت مشهد در سال 2010 محدوده ای به وسعت km2 7/13 با میزان بیش از cm/year20 در حال فرونشست بوده است. بررسی مقاطع زمین شناسی که به صورت طولی و عرضی دشت را قطع کرده اند، نشان می دهد، بیش ترین میزان فرونشست در مناطق با افت شدید سطح آب زیرزمینی، بافت خاک تناوب ریزدانه و درشت دانه و ضخامت زیاد آبرفت ایجاد شده است. هسته مرکزی شهر مشهد نیز از نظر زمین شناسی بسیار مستعد فرونشست است و پیش بینی می شود در صورت کاهش ورودی پساب به آبخوان شهری در آینده فرونشست چشم گیری در این مناطق ایجاد شود.کلیدواژگان: فرونشست زمین، تداخل سنجی راداری، ترازیابی دقیق، آب زیرزمینی، شهر مشهد
نتایج حاصل از پژوهش های متعددی نشان داده است که در خلال وقوع یک زلزله مشخصات لرزه ای حرکت زمین در فواصل نزدیک به ابعاد سازه های مهندسی طویل به طور چشم گیری تغییر می باید. تعیین دقیق مشخصات حرکت زمین در نقاط واقع بر یال دره ها به دلیل قرارگیری تکیه گاه های سازه های طویلی مانند سدها و پل ها روی آن ها اهمیت خاصی در مهندسی زلزله دارد. هدف این مقاله تولید زلزله های مصنوعی غیریک نواخت در یال دره های مثلثی با درنظرگیری اثرات توپوگرافی دره است. به منظور تولید زلزله های مصنوعی غیریک نواخت از روش بازنمایش طیفی که یکی از پرکاربردترین روش های موجود در زمینه تولید تاریخچه های زمانی غیریک نواخت است، استفاده می شود. در اکثر پژوهش های موجود در ادبیات فنی توابع نبود انسجام لرزه ای برای ساختگاه های مسطح ارائه شده اند،از این رو، نمی توانند الگوی مناسبی برای تولید زلزله های مصنوعی در سازه های طویلی مانند پل ها و سدها که تکیه گاه های آن ها درون عوارض توپوگرافی دره قرار دارند باشند. به منظور درنظرگیری اثرات توپوگرافی ابتدا الگوی تقویت طیفی امواج لرزه ای در عارضه دره از طریق انجام تحلیل دینامیکی تاریخچه زمانی به وسیله برنامه Flac2D به دست آمده و سپس از توابع تقویت به دست آمده در تولید رکوردهای متغیر در یال دره استفاده می شود. مقایسه مشخصات رکوردهای تولید شده با توابع تقویت دره نشان می دهد روش پیشنهادی این مقاله به طور موفقیت آمیزی قادر به تولید تحریکات غیریک نواخت تکیه گاهی در یال دره است.کلیدواژگان: اثر توپوگرافی، دره مثلثی، تقویت طیفی، زلزله مصنوعی، تحریکات چند تکیه گاهی
آزمون نفوذ استاندارد (SPT) یکی از متداول ترین ترین آزمایش ها در تحقیقات ژئوتکنیک است. در این تحقیق با استفاده از نتایج آزمایش نفوذ استاندارد، برآورد خصوصیات خمیری و فیزیکی خاک های رسی باروش های آماری بررسی شده است. محدوده بررسی شده مربوط به انواع لایه های رسی و مارنی در شهر تبریز واقع در شمال غرب ایران است. دو گمانه ماشینی حفاری شده و آزمایش نفوذ استاندارد به همراه سایر آزمون های آزماشگاهی برای تعیین همه خصوصیات خمیری و فیزیکی روی نمونه های تهیه شده انجام شد. با استفاده از نتایج پژوهش های پروژه های مهم موجود در منطقه، بانک اطلاعاتی مشتمل بر 107 سری از خصوصیات لایه های منطقه تهیه شد. ضریب هم بستگی اسپیرمن بین خصوصیات فیزیکی و خمیری خاک شامل درصد رطوبت طبیعی، درصد ریزدانه و درصد ذرات رسی، حد روانی، حد خمیری، دامنه خمیری، شاخص استحکام، فعالیت، تخلخل اولیه، وزن مخصوص خشک و تنش موثر قائم با عدد نفوذ استاندارد تصحیح شده تعیین شد. 8 رابطه تجربی موجود برای برآورد نفوذ استاندارد تصحیح شده با داده های این تحقیق صحت سنجی شد. برای این روابط عموما نتیجه ضعیف از نظر ضرایب آماری شامل ضریب تبیین (R2)، خطای ریشه میانگین مربعات (RMSE) و شیب خط رگرسیون(CR) به دست می آید. با استفاده از رگرسیون غیرخطی و بر اساس داده های تحقیق حاضر، هشت رابطه تجربی جدید بررسی و پیشنهاد شد. ضریب تبیین، خطای ریشه میانگین مربعات و شیب خط رگرسیون برای روابط پیشنهادی نسبت به روابط موجود بهبود یافته است. ضرایب آماری برای مناسب ترین رابطه به منظور برآورد شاخص استحکام خاک با استفاده از نفوذ استاندارد تصحیح شده حدود 0.7 با خطای 129/0 به دست آمد. هم چنین دو رابطه برای هم بستگی تنش موثر قائم و عمق نمونه با نفوذ استاندارد تصحیح شده پیشنهاد شد.کلیدواژگان: عدد نفوذ استاندارد، خصوصیات خمیری، خاک های مارنی رسی تبریز، روابط تجربی
سنگ نمک در مقایسه با سنگ های سیلیکاته رفتار شکل پذیر زیادی را حتی در شرایط پایینی از دما و فشار نشان می دهد. بنابراین بررسی ریزساختارهای سنگ نمک در درک مکانیزم های دگرشکلی که تغییرشکل سنگ ها را کنترل می کنند کمک کننده است. در این پژوهش ریزساختارهای موجود در سنگ نمک طبیعی متعلق به گنبدنمکی دهکویه با استفاده از روش پراش الکترون های برگشتی (EBSD) به منظور یافتن علت پدیده لهیدگی در مقیاس میکروسکوپی بررسی شد. بررسی ریزساختاری نشان داد که جریان شکل پذیر نمک نتیجه عملکرد خزش نابه جایی و تبلور مجدد است. برخی از دانه ها تغییرشکل درون بلوری مهمی را نشان دادند. تحلیل دگرشکلی دانه های تغییر شکل یافته نشان داد که تغییر شکل درون دانه ای نتیجه لغزش بر روی سیستم لغزشی <110> (110) و <110> (111) است. لغزش روی چنین سطوحی می تواند در همگرایی دیواره تونل نیز موثر باشد. ریزساختارهای مشاهده شده در این پژوهش با ریزساختارهای ارائه شده برای نمونه های شیستی در منطقه هیمالیا قابل قیاس است. از این رو، این پژوهش پیشنهاد می کند که وقتی سنگ های اطراف تونل دربردارنده برخی از ریزساختارهای خاص باشند لهیدگی بوقوع می پیوندد. به نظر می رسد نوع سنگ و تاریخچه تکتونیکی مهم ترین عوامل در وقوع این پدیده هستند.کلیدواژگان: لهیدگی، ریزساختارهای موجود در سنگ، خزش نابه جایی، روش پراش الکترون های برگشتی
Unsystematic execution of blasting process may result in serious damages. Blasting is a very complex process and almost all of blast designs are made based on empirical relations resulting from trial and error. In recent decades, considerable development of numerical methods has been made possible to achieve high accuracy study of blast effects on surface and subsurface structures. Among these methods are boundary element method, finite difference method and finite element method. It should be mentioned that there is currently no software which might be able to completely simulate blast process. But the UDEC software is able to simulate different aspects of this phenomenon through simplification and focusing on each aspect. Therefore, the UDEC software was selected. In the present study, the modeling has been performed for Ghareh Changool ramp of Zehabad Zinc and Lead Mine against blast loads.Material and methods
Zehabad Ore deposit is located around 2 km south of Zehabad Village of Tarom Sofla County, 56 km to northwest of Qazvin at 49˚ 25' east longitude and 36˚ 28' north latitude.
The formation surrounding the ore deposit is generally made up of pyroclastics, lavas and sedimentary rocks of Eocene age (Karaj Formation) which have been divided into 22 stratigraphic units. Lithological composition of the tuff units are often rhyolithic to dacitic and the lava units are consisted of rhyolite, dacite and andesite.
To accomplish this study, we took rock blocks from Ghareh Changool ramp. Then, the blocks were cored in the laboratory to provide cylindrical samples for doing uniaxial compressive, triaxial, Brazilian and direct shear tests. Physical and mechanical properties of the tuff samples were determined according to ISRM standards.
In the present study, field studies were done to calculate strength parameters and properties of the joints. Based on these studies, three major joint sets were determined. In order to obtain the shear strength parameters of the joints, the cylindrical samples of andesitic tuff were molded by concrete and direct shear test was done on all of the joints according to ASTM D 4554.Results and discussion
To simulate the complex conditions of blast process, we used the discrete element software of UDEC for numerical modeling considering the discontinuity of the medium. To do a dynamic analysis, first the model should come to equilibrium in the static state. The space considered to be modeled in the study was a horse-shoe-shaped ramp with 4 m base, 4 m height and 1.5 m arc radius which was located in rocky medium consisting of tuff. The height of overburden above the roof of the ramp was about 190 m. The dimensions of the model in UDEC was 20*20 m2. The behavioral model considered for the rock blocks and discontinuities were the elastic isotropic and surface contact of the joint (elasto-plastic) associated with Coulomb sliding failure, respectively. After defining the absorbing boundary conditions, the dynamic loads were applied to the model based on the defined time period. In mines stability and blasting process, the dynamic load resulting from the blast is often applied to a model as a pulse. By application of dynamic load and considering the other mentioned variations with respect of static analysis, the dynamic response of underground space could be estimated under vibration load of blast or earthquake. To do this, the blast impact wave was applied to the left side of the model as exponential pulse with maximum pressure of 4.41 MPa and time width of 0.7 to 7 msec. The results of the numerical modeling in static analysis indicated that no block would fall (Fig. 1). After application of the blast load, the results showed that there was no falling around the ramp (Fig. 2).Conclusion
1. In static condition, after initial equilibrium no block was fallen into the ramp, regarding the blocks’ magnification plots, as a result the ramp was stable in the static loading.
2. In dynamic loading case, considering the displacement plots around the ramp and the low values of these displacements, as well as, magnification plot of the blocks 40 msec after the blast it can be said that no block was fallen into the ramp. Therefore the ramp was stable in the dynamic loading case and there was no need to install support system. .Keywords: Zehabad lead, zinc mine, Ghareh Changool ramp, blast loading, stability, dynamic analysis, numerical modeling
Stone column installation method is one of the popular methods of ground improvement. One of the common uses of stone columns is to increase slope stability. Several studies have been performed to examine the behavior of stone columns under vertical loads. However, limited research, mostly focused on numerical investigations, has been performed to evaluate the shear strength of soil reinforced with stone column. The study presented herein is an experimental program, aimed to explore the shear strength of loose sand bed reinforced with stone column. Direct shear tests were carried out on specimens of sand bed material, stone column material and sand bed reinforced with stone column, using a direct shear device with in-plane dimensions of 305*305 mm2 and height of 152.4 mm. Experiments were performed under normal stresses of 35, 55 and 75 kPa . In this study, 4 different area replacement ratios (8.4, 12, 16.4 and 25%), and 3 different stone column arrangements (single, square and triangular) were considered for investigation. The obtained results from this study showed that stone column arrangement had an impact on improving the shear strength of stone columns. The most increase in shear strength and stiffness values was observed for square arrangement of stone columns and the least increase was for single stone columns. This study also compares the equivalent shear strength values and equivalent shear strength parameters (internal friction angle and cohesion) measured during experiments with those predicted by analytical relationships. Results show that shear strength values and shear strength parameters measured from experiments are higher than those obtained from analytical relationships. Accordingly, a corrective coefficient was calculated for each column arrangement to represent the correlation between experimental and analytical results.Material Properties of Loose Bed and Stone Column
Fine-grained sand with particle size ranging from 0.425 to 1.18 mm was used to prepare loose sand bed, and crushed gravel with particle size ranging from 2 to 8 mm was used as stone column material. The sand material used as bed material had a unit weight of 16 kN/m3 and a relative density of 32.5%, and the stone material used in stone columns had a unit weight of 16.5 kN/m3 and a relative density of 80%. The required standard tests were performed to obtain the mechanical parameters of bed material and stone column material. As the diameters of model scale stone columns were smaller than the diameters of stone columns installed in the field, the particle dimensions of stone column material were reduced by an appropriate scale factor to allow an accurate simulation of stone columns behavior.Testing Procedure In this study, large direct shear device with in-plane dimensions of 305*305 mm2 and height of 152.4 mm was used to evaluate the shear strength and equivalent shear strength parameters of loose sand bed reinforced with stone column. Experiments were performed under normal stresses of 35, 55 and 75 kPa.Two class C load cells with capacity of 2 ton were used to measure and record vertical forces and the developed shear forces during the experiments, and a Linear Variable Differential Transformer (LVDT) was used to measure horizontal displacement. All achieved data from the experiments including data on vertical forces, shear forces and horizontal displacements were collected and recorded using a data logger, and an especial software was used to transfer data between the computer and the direct shear device. All specimens were sheared under a horizontal displacement rate of 1 mm/min.Testing Program
Experiments were performed on single stone columns and group stone columns arranged in square and triangular patterns. The selected area replacement ratios were 8.4, 12, 16.4, and 25% for single stone columns, and 8.4, 12 and 16.4% for square and triangular stone column arrangements. To eliminate boundary effects, the distance between stone columns and the inner walls of the shear box was kept as high as 42.5 mm. In total, 12 direct shear tests were carried out, including 2 tests on loose sand bed material and stone column material, and 10 tests on stone columns with different arrangements. From the tests performed on group stone columns, 4 tests were performed on single stone columns, 3 tests on stone columns with square arrangement and 3 tests on stone columns with triangular arrangement. Hollow pipes with wall thickness of 2 mm and inner diameters equal to stone column diameters were used to construct stone columns. To prepare the specimens, first, the hollow pipes were installed in the shear box according to the desired arrangement. Then, bed material with unit weight of 16.5 kN/m3 was placed and compacted in the box in 5 layers, each 3 cm thick. Stone material was uniformly compacted to construct stone columns with uniform unit weight. The compaction energy was 67 kJ/m3 in all tests.Results and discussion
In this paper, the behavior of stone columns under shear loading was experimentally investigated in large direct shear device by performing tests with different area replacement ratios (8.4, 12, 16.4, and 25%), different stone column installation arrangements (single, square and triangular), and different normal stresses (55, 75 and 100 kPa). The key findings of this study are as follows:1. Shear strength increases with increase of area replacement ratio due to the higher strength of combined soil-stone column system, and due to the increase of stone column area effective in shear plane. The amount of shear strength increase with area replacement ratio is low for ratios lower than 15%. However, this amount is higher for area replacement ratios higher than 15%.2. For stone columns with equal area replacement ratios, higher shear strength was mobilized in stone columns with square and triangular installation arrangements compared to single stone columns. Among the installation patterns investigated in this study, stone columns with square arrangement experienced the highest increase in shear strength value, while single stone columns experienced the lowest. One of the reasons of shear strength increase in square and triangular patterns is the increase of confining pressure applied by stone columns to the soil between them. Another reason is the increase the total lateral surface by changing the column arrangement from single column to square and triangular patterns. This increased lateral surface increases the lateral force imposed on the stone columns, resulting in higher shear strength mobilization of stone material.3. The slope increase of shear strength-horizontal displacement curves shows that soil-stone column system has higher stiffness than loose sand bed, and this stiffness varies with area replacement ratio and installation pattern. The maximum stiffness values refer to stone columns installed in square pattern and the minimum values refer to single stone columns. In general, stone column installation pattern has an effective role in increasing stiffness.4. Results show that shear strength parameters increase in soil reinforced with stone column. The maximum increase in internal friction angle refers to stone columns with square pattern and the minimum increase refers to single stone columns.
5. The equivalent shear strength values measured from experiments are higher than those obtained from analytical relationships. Accordingly, it is conservative to use analytical relationships to calculate shear strength parameters. It is worthy to mention that these relationships assume that the value of stress concentration ratio is equal to 1. Results from this study indicate that the value of stress concentration ratio should be accurately calculated and used in the relationships.6. As discrepancy was observed between values measured from experiments and those obtained from analytical relationships, corrective coefficients were calculated to modify analytical relationships. These coefficients were computed and presented based on stone column installation pattern, area replacement ratio and the applied normal stressKeywords: Stone Column, Equivalent Shear Strength, Loose Sand, Direct Shear Test
Study of the Shahre Rye’s Karstic Spring and its Surrounding Alluvial Aquifers Relationship, Northern IranPages 395-410
In this research, the relationship and reaction between quantitative and qualitative Shahre Rye spring’s karstic water (Cheshme Ali) and spring’s adjacent alluvium aquifer have been considered to determine the relationship between alluvial and karstic aquifers and to study the connections between the two different groundwater environments. The results of the present research suggest geological conditions, hydrogeology and different hydraulic condition between Cheshme Ali karstic water with its surrounding alluvium’s aquifer. However the study results show the lack of a hydraulic connection between the two different groundwater environments (karst and alluvium) that are formed by north Rye fault.Introduction
There have been many studies in the field of the present research, some of which are mentioned below.(Tobarov, 1966). The N. Massei et al. (2002). (Robert E. 2005). (Ezatollah Raeisi 2008). (Cholami et al. 2008). (N. Goldscheider and C. Neukum 2010). (Dusan Polomcic et al. 2013).
The aim of this research is to identify the hydraulic relation between the alluvial aquifer and the karstic aquifer of the Cheshme Ali, during which the geographic, topographic and geologic situations and the changes in water discharge of Cheshme Ali and the changes in water table of the observation wells of the aquifer to the north of the spring have been reviewed simultaneously.The results indicate a lack of relation between the alluvial aquifer and the karstic aquifer of the Cheshme Ali in Shahre Rye.The general specification of the study area
The surface area of Shahre Rye equals to 2,293 km2 and the city is limited to the north by Tehran, to the south by Qom, to the east by Varamin and Pakdasht and to the west by Islamshahr, Robat Karim and Zarandieh (Fig. 1). The Cheshme Ali is located in the eastern parts of the city and southeast of Tehran. From a geographic point of view, the Cheshme Ali spring is situated in the southern part of the Cheshme Ali hill, and after leaving the ground, the spring's water flows to the south of Shahre Rye.Methodology
The topographic specifications of the Cheshme Ali and its surrounding are as follows:The highest points of the Cheshme Ali's surroundings are the Sepaye Hills with an altitude of 2,085 m above the sea, which are located to the east of Cheshme Ali. The height of Bibi Shahbanoo hill to the southeast of Cheshme Ali is about 1,498 m. The altitude of the northern hill of Cheshme Ali, where the spring is located is about 1,077 m and the lower sloped land surrounding it have an altitude of 1,072 m above the sea. This means that the opening of the Cheshme Ali spring is located at 1,072 m above the sea.2. Geology From the geological point of view, the existing units around Cheshme Ali of Shahre Rye consist of Precambrian, Mesozoic and Cenozoic sediments and rocks as geological specifications of Cheshme Ali and its surroundings are shown in Fig. 2.From the structural geology, and geological specifications two geological sections AB, CD Were prepared and presented in Figure 3. The Figure 3 shows, Cheshme Ali spring appears from Cretaceous thick layered limestone (Tizkooh formation Kt1) and the shahre Rye fault mechanism on either side of layering. However the water flow of cheshme Ali is nearly east – westerly after spring’s openings (A) and then spring water flow direction is to the south (Fig. 4). The hydrogeology of the spring and the wells 1. The Cheshme Ali in Shahre Rye is a karstic spring, with few hydrogeological specifications that are concluded from the result of geological and hydrogeological review and analysis of the spring’s water quality. Therefore, the karstic Cheshme Ali spring has a varied range of discharge which is from medium (25 to 100%) to high (>100%). Moreover in the curves of the spring’s discharge and simultaneous rainfall, shown in figure 5, the peak volume of water discharge of the spring corresponds fully with the peak rainfall, underlining the influence of simultaneous rainfall on the spring.The study of the hydrographic makeup of the spring (curve 2) shows the difference in the period between the upward curve (seven and a half months) and the downward curve (four and a half months) underlining the lower permeability of the spring’s intake area versus the grounds conducting spring water to the openings.2. The hydrogeology of the surrounding wells:For the purpose of studying the fluctuation of water tables of the observation wells around the spring and in its adjacent alluvial aquifer, the isobaths maps of groundwater level and groundwater table of the spring’s surrounding areas were drawn ( Fig.6). The level of groundwater table to the north of spring is 5.9 m and 6.6 m to the south of it, while the spring water is at ground level. In order to have a better understanding of the potentials of groundwater table in Shahre Rye’s Cheshme Ali and its surrounding environments from south to north, the potential profile is provided in figure 7 using the potential figures of witness wells and the Cheshme Ali spring. In the potential profile, the groundwater level of the Cheshme Ali is higher than the groundwater potential level of the witness wells, which seems to suggest the recharge of the plain by the spring.The review of the groundwater quality in wells and the Cheshme Ali spring The groundwater quality characters of the Cheshme Ali and the wells to the north and south of the spring are presented in table 2,that shows three differences and similarities in the results of the chemical analysis of water from Cheshme Ali and from wells located to the north and the south of the spring. The difference between the chemical composition of water from the spring and the chemical composition of the well located to the north is considerably more than the difference between the chemical compositions of the spring and the well located to the south.
Based on the geological studies of this research, the Cheshme Ali spring in Shahre Rye appears from the Karstic Tizkooh formation (Fig. 2) and the geological structure shows a northerly direction for the slopes of the layers in Tizkooh formation, and an east-westerly direction for the appearance of the spring water (Fig. 3 and Fig. 9). The spring’s flow is disseminated and the spring is of Karstic - fault type (table 1). The discharge of Cheshme Ali corresponds entirely to rainfall and is influenced a lot by it (Fig. 5). The condition of groundwater table of the well and the spring (Fig. 6, A) and the water level potential of the spring and its surrounding wells underlines the existence of two different hydraulic environments (Fig. 6, B). Moreover, from the aspect of potential groundwater column, there is a large difference between the groundwater table potential of the spring and the potentials of the two wells to the north and south of the spring (Fig. 7and8). From a qualitative aspect, the quality of spring water differs greatly from the quality of water from the wells located to the north and south (table 2).The results of this research are as follows:1. The study of geologic, structural geology and the geological section shows the water in the Cheshme Ali of Shahre Rye is originating from the Karstic formation of Tizkooh that layers sloping are to the north, the spring water appears from the site of the Rye fault and then flows to the west.2. The studies have proven that Cheshme Ali to be a Karstic – fault spring with disseminated flow, whose discharge is influenced by rainfall and condition of groundwater level and the table which underlines the alluvial aquifer shows lack of relation between two alluvial and karstic aquifers.3. The water quality analyses show a great difference between the specifications of the spring water and its surrounding wells groundwater.4- The north Rye fault mechanism are formed two different groundwater environment ( Karstic and alluvium) and however different groundwater conditions between north and south of alluvium.Keywords: Karst, alluvium, Cheshme Ali, Relation between Karst
Investigation of the Effect and Mixing of Nano-clay on the Severity of Dispersion on Samples of Loess Soils in Golestan ProvincePages 411-434Introduction
The dispersivity phenomenon occurs due to the dissolution of some of the ions in clay soils or against the shear stress of normal water flow in cohesion-less soils. Water surface flows in low slopes cause surface erosion of dispersive soils. Dispersivity in the soil starts from a point and gradually expands; the starting point can be the holes from the activity of the animals, the existing cracks or the growth path of the roots of the plants. There is a lot of field evidence to recognize the dispersivity of the loess soils. In field investigations, soil dispersivity can be detected according to the following parameters: geological origin of the loess soil, mineralogical composition, gradation, drainage pattern, slaking of agglomerates, specific morphology, high permeability, geographical area (length and width relative to origin), soil color, relationship between slope and soil erosion, precipitation, erosion of column cracks, heeling, mud flowing runoff and the presence of salt crystals in loess soils. In terms of sedimentological characteristics and engineering geological properties, Golestan loesses have been dispersed in three areas 1, 2 and 3, which are consistent with the loesses of clay, silt, and sand types, respectively.Material and methods
Loess soils in three regions of east and northeast of Golestan province were sampled. Sampling was conducted in two forms of wax-coated agglomerates and metallic cylindrical tubes. Depth of sampling follows the foundation of the buildings located on the Mehr Housing site and the Cheshme Lee village, varying from 0.5 to 2 meters. On the path of the Beqqeje Bala village, sampling was carried out from the path trench. After transferring to the laboratory, samples were subjected to gradation testing, Atterberg limits test to determine the unit weight of the volume and density.
The pinhole test was done on samples with the unit weight of normal volume (gn) and maximum volume (gdmax) and its rate of dispersion was determined. The research background, field evidence and the results of laboratory experiments indicate the dispersion of soil sampling areas. The results show that soil compaction reduces the severity of dispersion and decreases the flow rate, so that the flow rate has decreased in the Maravehtapeh sample by 38%, in the Cheshmeli sample by 13% and in the Beqqeje Bala sample by 43%. Compaction cannot eliminate the dispersion of soil. Adding nanoclay decreases the severity of soil dispersion and eliminates its dispersion properties in most cases.In order to evaluate the effect of nanoclay on severity and to decrease the dispersion property of soil with ratios of 0.5, 1, 2, 3, 4 and 5 wt%, of Montmorillonite Nanoclay was added.
The nanoclay used in the present research was selected from the Sigma-Aldrich America Company called montmorillonite nanoclay and was purchased from its domestic representative, i.e. Iranian Nanomaterials Pioneers Company. The product has a density of 300 to 370 kilograms per cubic meter and a particle size of between 1 and 2 nm. The specific surface area of the nanoparticle is about 250 square meters per gram. Its color in normal light and in 1 to 2% moisture is yellow to yellowish buff.Results and discussion
The rate of dispersion of samples with nanoclay was measured in Pinhole Test Apparatus. Also, the method of mixing nanoclay with dispersive soil shows different behaviors in severity of dispersion and its reduction. Given that the specific surface of nanoclay is high and this property can include the whole surface of soil grains as a sticky coating and increase soil cohesion, the mixing method is practically one of the most important steps in examining the effect of nanoclay on soil stabilization. At ratios of 0.5, 1, 2, 3, 4 and 5 wt% of nanoclay, nanoclay was mixed with soils of sampling regions by fourmethods
In the method A, they were completely mixed with the preparation of a homogeneous mud from soil and nanoclay via an electric mixer.In the method B, mixing of loess soil with nanoclay was performed in optimum water content.In the method C, mixing of loess soil with nanoclay was conducted in the form of dough by hand mixer. In the method D, mixing of loess soil with nanoclay was carried out in the form of vibration dry by grading sieve shaker.After mixing with nanoclay in the desired method (four methods A, B, C, D), the samples were first stored in sealed plastic containers for 24 hours. Then, the samples containing nanoclay were reconstructed in cylindrical mold of the pinhole device with the unit weight of maximum dry volume and moisture of two percent higher than the optimum moisture content and a hole was created in the middle of it. The samples remained in this position for 24 hours, and then the test was performed. Testing was carried out on each sample according to the standard D4647-93, and flow rate reading was done over a period of two minutes to 18 minutes.Conclusion
The conclusion of this study shows that the three loess samples taken have a dispersivity potential and the flow rate is low in the unit weight of maximum volume, but the dispersivity potential does not eliminate. Adding nanoclay with any weight ratio reduces the flow rate and eliminates the soil dispersivity potential.The results of this survey showed that 1% nanoclay weight ratio is technically and economically the most appropriate mixing ratio. With this weight ratio, the method of preparing homogeneous mud with an electric mixer (method A) produces the lowest flow rate, so that the flow rate from 1.3 ml per second in pure soil to 0.3 ml per second in the soil containing nanoclay is reduced by 50 mm. Therefore, it can be said that this method is more suitable, but it is not operationally efficient and the method B is more appropriate. In the method B, the flow rate reaches from 1.3 to 0.55 ml per second.Keywords: Nanoclay, Dispersive Soil, Loesse, Golestan Province, Additives materials
Land Subsidence and its Consequences in Mashhad City by Integrating Radar Interferometry and Field MeasurementsPages 435-462Introduction
Mashhad city, the second largest metropolis of Iran, is located in an arid and semi-arid region. Overexploitation of groundwater in Mashhad plain has caused up to 22.5-meter drop in the groundwater level from 1984 to 2013. The groundwater depletion in the unconsolidated aquifer has resulted in subsidence and cracks on the land surface. To determine the land subsidence rate map and the reasons for hot spot subsidence, the latest Envisat images of the ESA Space Agency's Archive for Mashhad plain were used. leveling and GPS data were combined with the radar interferometry results and the annual subsidence rate maps with high precision were obtained. Finally, the geology and soil texture maps of study area are compared to the land subsidence map.
To assess the land subsidence in Mashhad plain three methods of leveling, GPS and Insar are used. Leveling data are available in three profile of of Mashhad-Quchan (BCBD), Mashhad-Kalat (BDBE) and Mashhad-Sarakhs (BEBN) in two time interval of 1994-2003. The highest rates of subsidence in the BCBD, BDBE and BEBN lines are 7, 3.5 and 8.1 cm/year, respectively. Six permanent GPS stations have been installed in Mashhad plain, among them, NFRD, GOLM and TOUS have recorded the land subsidence, with the highest annual rate of 21.2 cm/year at TOUS Station. The third method applied to assess the history of land subsidence was InSAR radar interferometry which provided the extent and pattern of subsidence in all of the study area. For this, 23 images of the Envisat ASAR are processed during the 05/24/2010 to 06/30/2003 time period. The highest subsidence rate estimated by this method was 32 cm/year in the northwest of Mashhad. In general, two subsidence bowls, in the northwest and south east of Mashhad city are identified. Fig. 1 shows the annual subsidence rate map in Mashhad plain. Using the root-mean-square error (RMSE), the accuracy of the InSAR method was verified with GPS and leveling data.Discussion
The rate and distribution of land subsidence in Mashhad plain are affected by geological factors such as soil texture, deposit thickness, geological structures and groundwater drawdown. The geological and geophysical studies and exploratory drilling results in the Mashhad Plain indicate that the bedrock morphology is very rough. The bedrock outcrops in some places while in some other places covered by more than 300 meters alluvial deposits. Generally, by distance from the mountain, alluvium thickness and as a result the likelihood of subsidence would be increased. Mashhad plain is surrounded by the active and quaternary faults in the north and south edges. In the north of Mashhad plain Marly bedrock is uplifted by Tous fault and outcropped in the north of fault. In the south of Mashhad two normal faults have resulted to the increase of alluvium thickness in south and central of Mashhad plain. The change of river pathway also let to deposition of a sequence of the fine-grained and coarse-grained soils in central of plain between Toos and southern branch of South Mashhad fault (F2).used to draw the cross sectionIn order to evaluate the subsurface conditions and its effect on the land subsidence, the soil texture are studied using the deep water wells and piezometers log (Figure 2). Fig. 3 shows the longitudinal section (northwest to southeast) of the area. As it can be observed, the soil texture includes of alternation of fine and coarse grains layers (Figs. 4). In this condition, sandy soils help to shortening the drain path of clayey layers and leads to acceleration of the consolidation. The average rate of annual subsidence in the area is 14 cm for one meter of drop in the groundwater level.Nowadays, in the urban area, due to the urban sewage waters, there is a rising of groundwater level. Therefore, no land subsidence has occurred in the central parts of the city. It is expected by completion of urban sewage network about 62 million cubic meters of sewage water will be eliminated from the aquifer recharge, which will cause a notable drop in the groundwater level and prominent land subsidence in specific area of the city. Considering the geological conditions and the operation of the existing faults, it is expected that in the case of groundwater drop, no significant subsidence will occur in south of the F2 fault, due to the decrease in the alluvium thickness and to the coarse texture of the soil. But in the northern and northeastern parts of the city, which are located between F2 and the Tous faults, high rate of land subsidence is expected.
Figure 4: The cross section of soil texture and the annual average rate of land subsidence and groundwater level dropConclusions
Using the radar interferometry processing, the highest annual rate of subsidence in Mashhad plain is about 32 cm/year. Land subsidence in Mashhad plain has an increasing trend and the geological conditions have a critical role in the subsidence rate and its pattern. Generally, soil texture near the mountain area in South is coarse and grain size decreases toward the center of the plain. But because the outcrop of Marly formation in the north slopes, soil texture is mainly fine grains. In the center of Mashhad plain soil texture constituted of fine and coarse grains which are converted together as inter fingering facieses, which have a critical role in decreasing of the consolidation time and increasing the land subsidence rate. It is predicted by complimenting of the urban wastewater network, the groundwater level will be dropped in the city area and the northwest and southeast subsidence ellipsoids which already can be seen will be connected together. Therefore, the area between F2 and Toos faults, will be shown the highest rate of subsidence, due to high thickness and fine-grained soil texture.Keywords: Land subsidence, Interferometric Synthetic Aperture Radar (InSAR), Groundwater decline, Leveling, Mashhad City
Generation of Non-Uniform Artificial Earthquakes on the Slope of Two Dimensional Triangle Valleys Considering Topography EffectPages 463-484Introduction
Past research studies have demonstrated that seismic ground motion can vary significantly over distances comparable to the dimensions of long span engineering structures. The accurate determination of earthquake ground motion at the base of long span structures such as dams and bridges whose piers are located on the valleys surface is one of the most important issues in earthquake engineering. In this paper, the spatially variable earthquake ground motions are generated at stations located on the valley slopes, considering the topography effect of a triangular valley. To this end, the simplified geometry of the valley of Masjed Soleyman embankment dam has been used for numerical modeling. The spatially varying ground motions are simulated by using spectral representation method. According to this methodology, the generated time histories are compatible with prescribed response spectra reflecting the wave passage and loss of coherence effects. This method assumes that the response spectrum is identical for all stations i.e., they have the same amplitudes and frequency content. This assumption is not valid for stations located on valley surface in which the amplitude and frequency content of the seismic waves are changed considerably by topography features. It is concluded that the proposed method in this study can lead to artificial spatially variable earthquake ground motions which can be readily reflect the amplification pattern of 2D triangular valleys.Material and methods
In the first part of this paper, seismic response of a triangular valley is investigated through time history analysis conducted by using FLAC2D computer program. The geometry of the valley analyzed in this paper is chosen close to the valley of the Masjed Soleyman embankment dam. Dynamic analysis is conducted using an artificial earthquake generated by spectral representation method. The material properties are obtained based on the results of a comprehensive study carried out to identify the dynamic characteristics of two large embankment dams in Iran. Spectral amplification functions of seismic waves are calculated by dividing the response spectra of stations located on the slope of the valley to that in base of the valley. These functions are then used as target quantity for generation of spatially variable ground motions at points located on the valley. In this study, spectral representation method, the most widely accepted method for generation of spatially variable ground motions, is developed to take into account the topography effect. According to this methodology, the generated time histories are compatible with prescribed spectral amplification functions reflecting the wave passage and loss of coherence effects. The Harichandran-Vanmarcke coherency model is used to simulate spatially variable seismic ground motions.Results and discussion
Based on the obtained results the maximum and minimum values of peak acceleration are yielded at the base and at the edge of the valley, respectively. The results indicate considerable increase of the acceleration RMS at points near the edge of the valley. Maximum spectral amplification is also observed at the edge of the valley. For all points located on the valley, the first peak spectral amplification occurred at frequency of 1.15Hz, which can be readily interpreted as the natural frequency of the valley. In order to evaluate the accuracy of the proposed method, the RMS and spectral amplification functions of artificial earthquakes are compared to target quantities. A very good consistency between the spectral amplification of artificial earthquakes and target spectral amplifications was observed in terms of both amplitude and frequency content.Conclusion
The following conclusions were drawn from this paper.
- Artificial earthquakes generated using proposed method of this paper are in a very good agreement with the amplification pattern of the valley.
- The results of this study can be readily used to investigate the influence of spatial variability of earthquake ground motion on structures like bridges and dams whose supports are located inside the valley and are subjected to multi-support earthquake excitation.
- The proposed method of this paper is not limited only to the valley topography, but it can be effectively used in the generation process of non - uniform artificial earthquakes for stations located on other topography features. The latter can be carried out by establishing the spectral amplification functions of other topography features such as slopes and hills resulted from field or numerical studies.Keywords: Topography Effect, Triangular Valley, Spectral Amplification, Artificial Earthquake, Multi-Support Excitation
Estimation of Physical and Engineering Properties of Clayey Soils According to Standard Penetration Test: A Case Study of Tabriz Clayey MarlPages 485-510Introduction
The standard penetration test (SPT) is one of the most common tests in geotechnical investigations. The results of this test are known as a simple, inexpensive, and tangible criterion in geological and geotechnical engineering. Many computational methods and engineering judgments depend on the results of this test. In this research, estimation of physical and engineering properties of clay soils was carried out using statistical methods based on standard penetration test results. The scope of this case study is related to a variety of clayey soils in Tabriz (the northwest of Iran). The existing relationships were confirmed based on database of this study. After statistical analysis of the database, eight relationships including single and two-variable associations have been proposed to estimate the physical and engineering properties with better performance using nonlinear regression.Material and Methods
Different types of clayey silt and marl layers spread in Tabriz were included for the purpose of this study. The geological age of these layers dates back to the Miocene and Pliocene era. This research was conducted in two sections of the field and analysis. Two machine boreholes were drilled, and, based on ASTM, a standard penetration test with other laboratory tests were performed on the soil specimens in order to determine the physical and plasticity properties. According to the results of this study and the existing data, a total of 107 series were prepared. Based on the soil properties, 11 variables were selected including the fine grain percentage (FGP), liquid limit (LL), plastic limit (PL), percentage of clay particles (C), plastic index (PI), consistency index (CI), activity (A), dry unit weight (γd), natural moisture content (wn), initial void ratio (eo), and effective vertical stress (σ'v). The standard penetration tests were run for each meter in drilled boreholes. The results of this test were corrected according to NCEER method. The correlation between the variables and corrected standardized penetration test results (N60) were studied by Spearman ranking coefficient. Verifications of the existing eight experimental relationships between standard penetration and other soil properties, proposed by Kayabasi (2015) and Hoshmand et al., (2012), were checked out using the findings and data of the present study. The linear, exponential, logarithmic, and exponential regressions between each variable and N60 were investigated using SPSS software, version 16. The best regression with the highest R2 for each variable was selected. Eight new relationships were proposed. Performance of the suggested relationships was compared with the existing relationships.Results and Discussion
The findings of the current study could be summarized as:1. The clay soils of the studied area in Tabriz were classified into four categories including CH, MH, CL, and ML according to USCS classification. The range of changes in plastic index and liquid limits of the samples were 9.19 ~ 45% and 29 ~ 77%, respectively. The corrected standard penetration test results (N60) changed from 9 to 28 showing that soil compression was low to high.2. The highest positive and negative Spearman correlation coefficients were related to the consistency index (+0.772) and moisture content (-0.759), respectively.3. The existing empirical relationships, based on the database of this study, were found to have better statistical coefficients in terms of consistency index, activity, moisture percentage, and fine grained percentage. In term of sample depth, the experimental relationship, showed the lowest statistical coefficient.4. Four single-variable and two-variable relationships were proposed by nonlinear regression analysis. Using these relationships, clay soil properties including activity, moisture content, fine grain percentage, and consistency index were estimated based on N60. In addition, two relations were proposed between sample depth (D) and vertical effective stress (σ'v) with N60. The statistical coefficients of the suggested relationships were better than the existing empirical relationships. The proposed relationship of estimating the consistency index with coefficient (R2) of 0.673 and regression line slope of about 1 had the best performance.Conclusion
In general, the main objective of this study was to investigate the correlation between physical and plasticity properties of clay soils and N60 on Tabriz clayey soils. Clay soils of the present study included various silty and marl layers. Sufficient correlation was observed between the physical and engineering properties of clay soils and N60. The validation of the existing experimental relationships based on A, wn, FGP, and D resulted in weak statistical coefficients (R2 <5) employing the database of the current study. Six new experimental relationships were proposed to estimate A, FGP, wn, and CI as well as two correlations of N60 with effective stress and sample depth. Generally, the results have been revealed that the statistical coefficients of the proposed relationships were improved compared with the existing relationships. The most suitable relationship was the estimation of soil consistency index (R2~70) and root mean square error (RMSE=129). Finally, due to the novelty of this research topic, verification and development of the proposed relationships for the soils has been recommended in other areas.Keywords: Empirical equation, Plasticity properties, Standard penetration test, Tabriz clayey marl
Evaluation of the Cause of Squeezing Phenomenon in Tunnels on the Basis of Observed Microstructure in Salt RockPages 511-540Introduction
Generally, in engineering geology physical and mechanical properties of rocks are investigated in macroscopic scale, and less attention is paid to investigate the texture and microstructure developing in rock during deformation. Salt rock, as a best example of ductile rocks, has attracted the attention of many researchers. Compared to silicate rocks, salt rock exhibits extensively ductile behavior at even low temperature and pressure. In micro-tectonics, salt is important, because of it is useful as an analogue material for understanding the microstructural processes and textural development in silicate rocks. Deformed salt rock can display microstructures developed in silicate rocks at high pressures and temperatures. Regarding the similarity between microstructures of salt rock and silicate rocks, investigation of microstructure and deformation mechanism in salt rock can be helpful in understanding the main cause of the squeezing phenomenon in tunnels.One of the effective factors on squeezing phenomenon is the structures and microstructures of rock. Rock mass classifications that contain rock mass structures are used in the predicting methods. But, so far, no attention has been paid to the role of rock microstructure in predicting the squeezing phenomenon.This study is aimed to identify deformation mechanisms occurring in microscopic scale in rocks and lead to tunnel convergent in large scale. To achieve this goal, the microstructures in a naturally deformed Late Pre-Cambrian to Early Cambrian Hormuz salt rock from the active Deh Kuyeh salt fountain in Fars province were investigated using Electron Backscatter Diffraction (EBSD).Materials and Methods
Deh Kuyeh salt diapir was located at about 27 km NE of Lar city. Salt samples were taken from top of the east and west glaciers (S1 and S2) and from the middle part of diapiric stem (sample S3). Raw samples were first cut dry into slabs (approximately 3´2 ´1 cm). Thin sections were prepared following the procedure of Schleder and Urai (2005) and Urai et al. (1987).Halite crystallographic orientation data were collected using a Zeiss SIGMAVP FEGSEM. EBSD patterns were collected using an accelerating voltage of 30 kV, beam current of ~ 100 nA and a working distance of about 30 mm. Oxford instruments AZTEC software was used for data acquisition. EBSD large step size (50 mm) mapping was used to examine the overall microstructure in each sample. EBSD data were processed using HKL Channel 5 software.Results and Discussion
All samples showed relatively similar microstructures. Samples comprise a small number of large grains in a matrix of smaller grains. Most grains were irregular in shape with lobate boundaries and internal distortion. Microstructural study revealed that the ductile flow of the salt was accommodated by dislocation creep and dynamic recrystallization. Salt grains show lattice distortion and a prevalence of low-angle boundaries that are evidence for dislocation creep and recovery processes. Misorientation analysis suggests that (110) <110> and (111) <110> slip systems are responsible for crystal plastic deformation of salt grains. Schmid factor analysis showed that stresses acting on inclined directions lead to the maximum activity of these slip systems.The observed microstructures in the salt are comparable with the microstructures presented for schist samples from Himalaya region. The rock along Himalaya main trusts also showed evidence of dislocation creep and development of crystallographic preferred orientation. Hence, this article suggests that the rock type and its microstructures are the most important factors in occurrence of tunnel convergent.Conclusions
This article proposes that deformation mechanisms occurring in micro-scale control the rock behavior in large scale. All rocks can behave as a ductile material depending on the temperature and pressure. In intrinsically ductile rocks like salt rock, presence of many active slip systems facilitates rock deformation under lower pressures and temperatures than silicate rocks. High tectonic stresses in shear zones lead to development of a strong shape preferred orientation and crystal preferred orientation in rocks. These microstructures facilitate rock deformation under stresses exiting in tunnels. It can be said that rock type and tectonic history of the area play the most important role in occurrence of squeezing phenomenon. Other factors such as current stress system in the area control deformation speed in tunnel. It seems investigating microstructures of rocks from tunnel route before and after excavation can be effective in identifying places with high possibility of squeezing.Keywords: Squeezing, microstructures in rock, dislocation creep, Electron backscatter diffraction method