فهرست مطالب

مجله زمین شناسی مهندسی
سال چهاردهم شماره 4 (زمستان 1399)

  • تاریخ انتشار: 1399/12/04
  • تعداد عناوین: 7
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  • مازیار حسینی*، مجید طارمی، مهدی سعیدی، وحید سلیمانی، مهدی سلطانی صفحات 581-608

    توسعه شهری در کلان شهر تهران باعث شده که برای ساخت سازه های بلند، بزرگ راه ها، تونل ها و سایر تاسیسات شهری، حفاری هایی با عمق و حجم زیاد انجام گیرد. آبرفت های شرق تهران (سری A)، نهشته های درشت دانه، همگن و سیمانته هستند. در این پژوهش تاثیر درجه سیمانتاسیون بر پارامترهای مقاومتی و سرعت موج برشی خاک بر اساس پژوهش‌های انجام شده در بزرگراه شرق تهران انجام شده است. به‌منظور تعیین خصوصیات ژیوتکنیکی و سرعت موج برشی خاک، از آزمون های برجا همانند بارگذاری صفحه، برش برجا، پرسیومتری و لرزه ای درون‌گمانه ای، برداشت های صحرایی و آزمون های آزمایشگاهی استفاده شده است. هم‌چنین تجزیه شیمیایی برای شناسایی نوع کانی ها و جنس مواد سیمانته انجام شده است. نتایج آزمایش ها نشان داد که سیمانتاسیون این آبرفت ها متوسط تا زیاد است و جنس مواد سیمانی در این خاک ها عموما کربناتی و به‌ویژه کلسیتی است. جمع بندی نتایج نشان داد که با افزایش درجه سیمانتاسیون، مدول تغییر شکل حدود 25 درصد، چسبندگی حدود 55 درصد و سرعت موج برشی حدود 30 درصد افزایش می یابد. افزایش ها این پارامترها با عمق رابطه مستقیم دارد. این در حالی است که درجه سیمانتاسیون تاثیری قابل توجهی روی زاویه اصطکاک داخلی خاک ندارد.

    کلیدواژگان: آبرفت های شرق تهران، آزمون های برجا، تجزیه شیمیایی، سیمانتاسیون، مقاومت
  • علی محمد رجبی*، شیما بخشی اردکانی صفحات 609-634

    تثبیت و به سازی خاک یکی از روش های موثر در بهبود رفتار خاک در مهندسی ژیوتکنیک است. امروزه علاوه بر تثبیت کننده های متعارف سیمانی و آهکی، از مواد شیمیایی طبیعی معدنی نیز برای اصلاح خواص نامطلوب خاک استفاده می شود. در این پژوهش از زیولیت و سپیولیت به عنوان دو ماده افزودنی برای تثبیت خاک های ماسه رسی و رس ماسه دار و تاثیر آن بر مدول الاستیسیته و هدایت هیدرولیکی خاک استفاده شده است. به این منظور آزمایش مقاومت فشاری تک محوری روی خاک های تثبیت نشده و تثبیت شده با افزودنی های مذکور در درصدهای 5، 10، 15، 20 و 25 و زمان های آنی (بلافاصله پس از اختلاط)، 7، 14 و 28 روز انجام شده و مدول الاستیسیته در شرایط مختلف آزمایش تعیین شده است. آزمایش نفوذپذیری نیز به دلیل بررسی اثر این دو افزودنی در درصدهای مختلف و زمان آنی انجام شده است. هم چنین به دلیل بررسی نحوه تاثیر مواد افزودنی بر ریزساختار خاک، عکس برداری SEM برای خاک تثبیت نشده و تثبیت شده با هر دو افزودنی در زمان عمل آوری 28 روز انجام شده است. نتایج نشان می دهد میزان افزایش مدول الاستیسیته در تثبیت با سپیولیت نسبت به زیولیت بیش تر است. به علاوه در هر دو افزودنی بیش ترین میزان افزایش مدول الاستیسیته مربوط به 25 درصد افزودنی و زمان 28 روز است. هم چنین میزان نفوذپذیری با افزایش هر دو افزونی کاهش می یابد به طوری که این میزان کاهش در سپیولیت بیش تر از زیولیت است. بررسی تصاویر SEM معرف تغییر در ریزساختار خاک در نتیجه افزودنی های مذکور است. نتیجه این که  تغییرات مدول الاستیسیته و هدایت هیدرولیکی خاک را می توان به وقوع واکنش های شیمیایی در کنار تغییرات فیزیکی نسبت داد.

    کلیدواژگان: مدول الاستیسیته، SEM، زئولیت، سپیولیت، هدایت هیدرولیکی، بهسازی خاک
  • علی ساکت، سید محمود فاطمی عقدا*، احمد فهیمی فر، حسین صادقی صفحات 635-668

    تحلیل زمان، مکان و بزرگی پیش لرزه ها و پس لرزه ها از جمله مواردی است که در دهه های اخیر مورد توجه متخصصان رشته های مرتبط از جمله زمین لرزه شناسان، مهندسان سازه، مدیران بحران و دیگر علوم مرتبط قرار گرفته است. زیرا این تحلیل ها در کنار شناسایی شرایط لرزه زمین ساختی منطقه و رفتار گسل مسبب زمین لرزه، کمک زیادی به روندیابی پیش لرزه ها و پس لرزه ها با هدف کاهش تلفات و حتی کاستن تنش های روانی جامعه آسیب دیده و بازمانده در منطقه زلزله زده و مدیریت کارآمد بحران در آن شرایط می کند. در این مقاله به بررسی و ارزیابی داده های مربوط به یک زمین لرزه واقعی و تجربه مشابه به دست آمده از دیگر زمین لرزه ها و ارایه الگویی کاربردی در زمینه پیش بینی پارامترهای زمین لرزه اصلی و هم چنین مکان یابی و تعیین بزرگی و زمان پس لرزه ها با هدف کاهش اثرات ناشی از آنها در مناطق زلزله زده می پردازیم. بر این اساس، در پژوهش حاضر، نتایج بررسی های مربوط به تحلیل مبنایی پارامترهای پیش لرزه ها و پس لرزه های زمین لرزه آذرماه 1391 زهان در استان خراسان جنوبی بررسی شد. اهمیت بررسی و پژوهش های کاربردی در این بخش از ایران به دلیل این است که این بخش از ایران با این که در دهه های گذشته شاهد زمین لرزه های مخرب و بزرگی بوده است، در بیش از دو دهه اخیر، با یک نبود لرزه ای مشخص مواجه شده است. چنین شرایطی، بررسی متمرکزتر در باره تغییرات لرزه خیزی در این محدوده، به دلیل قریب الوقوع بودن یک زمین لرزه بزرگ را ضرورت می بخشد. نتایج به دست آمده از این پژوهش روی تحلیل روند تغییرات پیش لرزه ها نشان داد که با بررسی تغییرات مکانی، بزرگی و عمق پیش لرزه ها می توان تا حدود زیادی به روند یابی پارامترهای زمین لرزه اصلی رسید. ضمن این که فراوانی پس لرزه ها و فواصل زمانی(سکون لرزه ای) مشخص بین آنها می تواند به عنوان نشان گرهایی برای شناسایی زمان پس لرزه های بزرگ تر استفاده شود و تحلیل های انجام شده در این پژوهش نشان داد روش هایی از جمله مدل های ارایه شده در باره سری زمانی در کنار تحلیل سکون لرزه ای به تدقیق زمان پیش بینی پس لرزه های بزرگ می انجامد.

    کلیدواژگان: زمین لرزه زهان، روندیابی پس لرزه، پیش لرزه، سکون لرزه ای، گسل مسبب، تنش اصلی حداکثر، مدیریت ریسک
  • وحید شیرغلامی، مهدی خداپرست*، ابولقاسم معزی صفحات 669-702

    جابه جایی زمین ناشی از حفاری در محدوده شهری، همواره با چالش های جدی از دیدگاه ژیوتکنیکی و سازه ای مواجه بوده است. در این زمینه آسیب دیدگی ساختمان ها و تاسیسات مجاور گود به دلیل تجاوز مقادیر تغییر شکل زمین از محدوده مجاز، خسارات جبران ناپذیری را به همراه دارد. بنابراین پیش بینی حرکت زمین مجاور گود در طراحی ها اهمیت ویژه ای دارد و طراحی سیستم مهاری گود، کنترل تغییرشکل جانبی دیواره گود و نشست سطح زمین  امری اجتناب ناپذیر است. این پژوهش، به بررسی پایدارسازی گود از دیدگاه تغییرشکل با استفاده از سازه اصلی به روش ساخت از بالا و بر اساس پروژه ای واقعی می پردازد. برای این منظور، مراحل اجرا در روش ساخت از بالا به صورت مقطعی و با استفاده از دوربین توتال استیشن مورد پایش قرار گرفته و داده های حاصل از ابزارسنجی گود، بر اساس روش های آماری تحلیل شده است. در این رابطه مدل سازی مراحل مختلف پایدارسازی گود با استفاده از نرم افزار المان محدود آباکوس [1] انجام شده و به منظور صحت سنجی و پیش بینی روند تغییرشکل ها، کالیبراسیون مدل عددی بر اساس نتایج حاصل از پایش های میدانی صورت پذیرفته است. در ادامه پارامترهای مختلف سیستم مهاری به منظور بررسی عملکردی، متغیر در نظر گرفته شده و در نهایت با استفاده از 160 مدل عددی، امکان تخمین سختی مورد نیاز سیستم مهاری با توجه به تغییرشکل مجاز، در 4 ساختگاه مختلف و در قالب روابط نمایی ارایه می شود.

    کلیدواژگان: ارزیابی تغییر شکل، روش ساخت از بالا، ابزارسنجی، روش المان محدود، طراحی مبتنی بر تغییرشکل
  • سهیل قره*، کیمیا یزدانی، فاطمه اخلاقی صفحات 703-728

    به سازی خاک های مسئله دار در محیط های شهری و به ویژه کلان شهرها از مهم ترین چالش های مهندسان عمران است. در این پژوهش با توجه به قابلیت افزایش سطح ویژه ذرات خاک به وسیله نانوذرات، به منظور به سازی خاک اطراف حرم مطهر رضوی در مشهد، بررسی های آزمایشگاهی روی ترکیبات جدیدی از نانوذرات رس و سیلیکا انجام شد که بر اساس نتایج، نسبت های بهینه نانورس 5/2% و 5% و نسبت های بهینه نانوسیلیکا 25/0% و 1% به دست آمدند، به طوری که هیبرید ساخته شده از 5% نانورس و 1% نانوسیلیکا به عنوان بهترین ترکیب موجب افزایش 785% ظرفیت باربری و کاهش 60% نشست خاک بررسی شد. در راستای این پژوهش، روش به سازی پیشنهادی جای گزینی مناسب برای روش های سنتی نظیر اجرای شمع بتنی مسلح، سیستم میکروپایل، جت گروتینگ و غیره در بناهای فرسوده است که علاوه بر افزایش سهولت اجرا و سرعت عملیات اجرایی، به میزان چشم گیریر با کاهش هزینه های اجرا همراه است.

    کلیدواژگان: به سازی خاک، هیبرید نانوذرات، ظرفیت باربری، نانورس، نانوسیلیکا
  • علی اکبر مومنی*، مینگ تااو، علیرضا طالب بیدختی صفحات 729-748

    تونل های کم عمق نقش حیاتی در برنامه ریزی شهری و خطوط حمل و نقل ریلی و جاده ای دارند. وجود این حفرات زیرسطحی می تواند باعث تمرکز تنش شده و ناپایداری این فضاها را در برابر بارهای استاتیکی به ویژه دینامیکی در پی داشته باشد. از این رو، هدف از این پژوهش ارزیابی تاثیر وجود حفره بیضوی و جهت یابی آن بر رفتار ماسه سنگ تحت بارهای استاتیکی فشاری و دینامیکی کششی است. به منظور ارزیابی تاثیر حفره در برابر شرایط تنش استاتیکی دو گروه از مغزه های ماسه سنگی بدون حفره و حفره دار با جهت یابی 0و 30و 60 و 90 درجه فراهم شده و تحت آزمون بارگذاری فشاری تک محوری قرار گرفتند. حین آزمون علاوه بر ثبت تنش، با به کار بردن کرنش سنج، سنسور ثبت انتشار امواج صوتی و دوربین، آسیب و تغییر شکل پذیری نمونه ها ثبت شد. برای انجام آزمون بارگذاری دینامیکی از دستگاه میله فشار هاپکینسون استفاده شد. به علاوه روند گسترش آسیب با استفاده از دوربین با سرعت زیاد با نرخ یک عکس در 10 میکروثانیه، ثبت شد. نتایج به دست آمده نشان داد که وجود حفره باعث کاهش مقاومت سنگ در بیش ترین حالت (0=θ) تا 55 درصد و در کم ترین حالت (90=θ) تا 77 درصد مقاومت فشاری تک محوری می شود. آزمون بارگذاری دینامیکی کششی نشان می دهد که حفره بیضوی نزدیک تر به مرز انعکاس موج فشاری به کششی به علت قرارگیری در منطقه سوپر پوزیشن سالم مانده در حالی که حفره موجود در خارج از این منطقه با هر جهت یابی دچار گسیختگی ورقه ای شده است. بررسی سطح شکست با استفاده از تجزیه میکرسکوپ الکترونی و بررسی مقطع نازک نشان داد که شکستگی غالب از نوع مرز بلوری بوده است و سیمان اکسید آهن نقش کلیدی در توسعه این نوع شکستگی دارد.

    کلیدواژگان: ماسه سنگ، حفره بیضوی، تمرکز تنش، بارگذاری دینامیکی، گسیختگی ورقه ای
  • طیبه میرجلیلی، ماشالله خامه چیان*، محمدرضا نیکودل صفحات 749-776

    هدف این تحقیق بررسی تاثیر ویژگی های زمین شناسی مهندسی سنگ دانه های کربناته روی ویژگی های سنگ های مصنوعی با سیمان غیررزینی و سپس مقایسه ویژگی های مهندسی سنگ های مصنوعی ساخته شده با سنگ های طبیعی است. در این تحقیق به منظور بررسی تاثیر ویژگی های سنگ دانه های کربناته بر سنگ مصنوعی از 7 نمونه سنگ ساختمانی شامل سنگ چینی (مرمریت ریزبلور)، مرمر کریستال (مرمریت درشت بلور)، مرمریت (نهان بلور)، سنگ آهک سیاه، 2 نمونه تراوراتن و انیکس استفاده شده است. از این نمونه های سنگی، ویژگی های زمین شناسی مهندسی نمونه ها تعیین شد. پس از طراحی قالب برای ساخت سنگ مصنوعی، سنگ دانه هایی با دانه بندی و طرح اختلاط یک سان تهیه و برای تمامی سنگ دانه ها با شرایط ویبره، فشار و خلا یکسان، دو نمونه سنگ مصنوعی درشت دانه و ریزدانه ساخته شده است. بعد از ساخت، اقدام به انجام آزمایش های فیزیکی، مقاومتی و دوام شد و سپس نتایج حاصل مقایسه شد. بررسی نتایج پارامترهای مهندسی نشان داد سنگ های مصنوعی تراورتن حجت آباد دارای کیفیت مهندسی مشابه نسبت به سنگ طبیعی خود دارند. سنگ های مصنوعی مرمر و تراورتن توران پشت حدود 11 تا 32 % افزایش کیفیت و ولی سنگ های مصنوعی سنگ چینی، آهک سیاه، انیکس و مرمریت حدود 6 تا 33 % کاهش کیفیت نسبت به سنگ طبیعی خود دارند نمونه های تولید شده از این سنگ ها نیز اگر چه از نظر پارامترهای مقایسه ای سنگ مصنوعی کم تر از سنگ طبیعی است اما در محدوده قابل قبول به عنوان مصالح ساختمانی قرار می گیرند.

    کلیدواژگان: ویژگی های زمین شناسی مهندسی، سنگ ساختمانی، سنگ مصنوعی، سنگ دانه، کربناته.
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  • Maziar Hosseini*, Majid Taromi, Mahdi Saeidi, Vahid Soleimani, Mehdi Soltani Negar Pages 581-608
    Introduction

    Series A of coarse-grained alluvial deposits of Tehran are extended in eastern and north-eastern areas of Tehran. Analyzing and studying of these alluvial deposits from a geological point of view as well as their creation time and general characteristics such as the deposits’ mineral types, their source, and formation conditions, gives a better point of view to geotechnical engineers about exploring their characteristics as well as geotechnical aspects in underground structure design, excavations, and foundation design processes. On the other hand, in order to analyze stability, estimating the factor of safety and the seismic design of these structures, considering their location, which is in Tehran with a high seismic hazard area, the necessity of knowing the exact mechanical and dynamic properties of Tehranchr('39')s alluvium is felt more than ever.

    Material and methods

    Due to the grain size of Tehran’s coarse-grained alluviums (series A) as well as high level of cementation of them, it is impossible (or maybe so difficult) to make undisturbed samples in order to do experiments. Such that it is excavated 23 boreholes with 30 to 140 meters depth as well as 17 test wells with 20 meters depth in an area which was extended in 10 kilometers in long which were located in Tehran’s No. 13 and No. 14 districts (as it can be seen in Figure 1). During the excavation of the entrance ramp and tunnel of eastern highway of Tehran, in-situ tests have been done in different sequences. Since it was important to investigate real behavior of these alluviums, different in-situ tests such as plate load test, in-situ shear test, pressuremeter test, and downhole test have been done as well as many laboratory and field tests. Furthermore, (1) X-Ray Diffraction (XRD) and (2) X-ray Fluorescence (XRF) as well as (3) Scanning Electron Microscopy (SEM) methods, have been used to explore the type of minerals and those used in cementation.Figure 1. a) Geological plan and the location of boreholes and test wells in the alignment of East Tehran Freeway

    Results and discussion

    Based on the results of XRD tests, it is quite clear that the largest weight percentages of tested samples are lime and silica.Calcium and magnesium levels-as the high-power cations in flocculation process-in soil sample No. 1 (soil with high cementation level) are much more than soil sample No. 2 (soil with moderate cementation level).This is the cause of high cementation level of soil sample No. 1 comparing with soils sample No. 2. A rapid increase in stress level can be seen in in-situ shear test results, in low shear displacements, up to reaching a maximum of τp (peak point) and afterwards reduction in shear stress with softening behavior.  Cohesion and shear strength levels also increase by increasing the depth. According to the plate load tests results, an increase in soil modules changes can be seen in different depths by depth increasing.Large tendencies to increase in volume and dilation can be seen in under shear load cemented soils, after applying a primary compression on them. A brittle behavior with the occurrence of a certain peak can be seen in cemented samples. The significant increase in strength is directly related to the severe dilation rate, which can be seen in cemented samples results.  The shear strength would be decreased, if this cement is broken during the particles’ displacements.The results of downhole tests are shown in Figure 2. According to this figure, it has been explored that Vs,30 is about 600 m/s in moderate cemented soils while it is about 850 m/s in highly cemented soils.  Because of the homogeneity and uniformity of sedimentary deposits, shear wave velocity is increasing due to the higher density of the layers and high level of cementation in both of the soil types. However, this increase is not significant at depths above 25 meters.

    Conclusion

    Based on the results, cementation level of the eastern coarse-grain-alluvium of Tehran is moderate to high and minerals used in cementation of this type of soil are generally carbonated and especially calcite.Investigating the level of cementation of soil as well as the results of chemical analysis and in-situ tests, it can be found that the strength and deformation parameters of the soil are directly related to the degree of its cementation.Based on the obtained results, the deformation modulus increases by about 25%, the cohesion by about 55% and the shear wave velocity by about 30% with increasing the degree of cementation (Table 1).Increases of these parameters are directly related to depth. However, the cementation level does not significantly affect the internal friction angle of the soil.

    Keywords: Tehran eastern alluviums, In-situ tests, Chemical analysis, Cementation, Shear wave velocity
  • Ali M. Rajabi*, Shima Bakhshi Ardakani Pages 609-634
    Introduction

    Improving the geotechnical characteristics of soils including superficial or deep soils has always been a challenge to geotechnical engineers. Therefore, various physical and chemical methods are used to improve different types of soils. In general, any physical, chemical, biological or combination of methods are used to change the characteristics of natural soil mass in order to achieve engineering goals which is defined in the "soil stabilization." Among different types of additives for soil stabilization, the use of pozzolans has been investigated by researchers because of their chemical compatibility with the environment and the cementation products due to chemical reactions. Todays, a lot of researches has been done on the use of natural or artificial zeolites as pozzolanic materials for the production of cement mixtures. This material, as a pozzolan, increases the speed of the pozzolanic reactions and reduces the density of cement products. However, many studies have been done to investigate the effect of zeolite and sepiolite on the resistance of cement products such as concrete, but so far, the use of these additives has been less considered for soil improvement. On the other hand, because of the compatibility of zeolite and sepiolite with the environment and their unique physiochemical properties, it is necessary to pay attention to these additives in order to improve the soil. Therefore, in this research, the effect of zeolite and sepillot additives with different percentages at different treatment times have been investigated to determine the elasticity modulus and hydraulic conductivity with focus on soil microstructure behavior.

    Materials and methods

    1. The properties of the soils In this research, two types of soil including clayey sand (with 20% clay) and sandy clay (with 51% of clay) were used. The studied soils were a mixture of clay and sand of Firoozkouh (a typical type of sand located in north of Iran). Some physiochemical properties of zeolite and sepiolite are presented in Table 1.Table 1. Physiochemical properties of zeolite and sepiolite used in this study 2. ExperimentsThe uniaxial compressive strength tests were performed at 0.1 mm/min according to ASTM D2166 standard. The stabilized soil samples were compacted at percentages of 0, 5, 10, 15, 20 and 25 in cylindrical molds (38mm × 76mm) in five layers to achieve the desired density. In order to investigate the effect of curing time, the samples were placed inside sealed containers and underwent the test at instantaneous, 7, 14, and 28 days and at the desired additive percentages. To investigate the effect of additives on the soil hydraulic conductivity, clayey sand soil with additives 5, 10, 15, 20, and 25% was prepared using dry mixing method. Then, the prepared mixture was poured from a specific height into the permeability mold with a height of 8.65 cm and diameter of 5 cm. In this way, the specific dry unit weight of all samples was obtained as 1.47 g/cm3, close to the minimum specific dry unit weight. In this research, concerning the considerable effect of fine-grained soils on hydraulic conductivity, falling head test was used to determine the permeability coefficient.In order to the morphology of the clayey sand soil without additives and stabilized with additives 15% was examined through SEM test.

    Discussion and results

    1. Modulus of elasticity In this study, after uniaxial tests in different percentages and ages, the stress-strain graphs were plotted and then the elasticity modulus was calculated. The results showed that, with increasing zeolite content, the modulus of elasticity has been increased and, with increasing curing time, except for a slight decrease, after 7 days, the modulus of elasticity increased. During the initial treatment (7 days), the hardness of the sandy clay soil decreased and then increased with increasing time. In general, hardness in both soils in the high percentages of zeolite is significantly is increased. Also, the effect of sepiolite on the modulus of elasticity has been studied. The results indicate that with the increase in the percentage of additive and lengthening the curing time, the modulus of elasticity is increased. This increase in the stabilization of both sandy clay and clayey sand soil is almost the same. In addition, in the case of sepiolite modification, the elasticity of sandy clay and clayey sand is approximately equal to 5 times in comparison to the initial value of unstabilized soil. However, in zeolite, the modulus of elasticity in clayey sand soils is almost 2 times, and sandy clay is nearly 5 times higher. 2. Permeability To investigate the effect of additives on the soil hydraulic conductivity, clayey sand soil with additives 5, 10, 15, 20, and 25% was prepared using dry mixing method. The samples were saturated in a short period and permeability test was carried out immediately. Permeability coefficient changes were mostly influenced by physical factors. Therefore, due to the fineness of both types of additives, the hydraulic conductivity decreases with increasing additive content. The amount of reduced hydraulic conductivity in sepiolite stabilization is greater than zeolite due to the structure of the sepiolite (fiber-shaped) compared to zeolite.3. SEM imaging In this study, attempts were made to examine the reasons behind the obtained results more carefully through SEM imaging.Figure 1. SEM image of non-stabilized clayey sand soil (a) soil stabilized with zeolite 15% (b) soil stabilized with sepiolite 15% (c) during the curing time of 28 days at magnifications 10000XFigure 1a displays the SEM image of non-stabilized clayey sand soil. As can be seen in the figure, the soil structure is clear as layered and clay scales can be seen as laminated. Figure 1b demonstrates the SEM images of clayey sand soil stabilized with zeolite 15% during the curing time of 28 days. The sample has lost its layered structure in response to stabilization with zeolite during the curing time and changed into an integrated structure. This can be due to incidence of chemical reactions such as ion exchange and pozzolanic reactions in response to adding zeolite. Figure 1c demonstrates the SEM images of clayey sand soil stabilized with sepiolite 15% during the curing time of 28 days. As shown in the figure, the sepiolite has a fibrous-shaped structure that is longitudinally twisted. Also, with  curing time increase, complex structures have emerged that could be due to the occurrence of chemical reactions.

    Conclusion

    This study examined the effect of zeolite and sepiolite additives on strength parameter of clayey soils. Accordingly, uniaxial compressive strength test was performed on clayey sand and sandy clay soil at percentages of 0, 5, 10, 15, 20 and 25% of zeolite and sepiolite with instantaneous curing times of 7, 14 and 28 days. Further, permeability test was conducted at different percentages on stabilized clayey sand soil. Also, to investigate the effect of these materials on soil microstructure, SEM imaging was performed at 28 days. The results show that both additives increase the elastic modulus of clayey sand and sandy clay soils. Also, the results indicate a steady increase in the stiffness of the cured soil with sepiolite during processing time. However, reducing soil hardness can be seen in stabilizing with zeolite at lower rates and lower percentages. In permeability test, hydraulic conductivity decreases with increasing additive content. The rate of permeability reduction in sepiolite is higher than zeolite. SEM images show that chemical reactions create an integrated structure that ultimately increases uniaxial compressive strength and modulus of elasticity. Also, SEM imaging depicts physical changes along chemical reaction in soil stabilized with sepiolite. Ultimately, increasing soil strength resulting from additive alongside environmentally friendliness is recommended in superficial and deep improvement of soil../files/site1/files/144/Rajabi.pdf

    Keywords: Elastic Modulus, SEM, Zeolite, Sepiolite, Hydraulic Conductivity, Soil Improvement
  • Ali Saket, Seyed Mahmud Fatemi Aghda*, Ahmad Fahimifar, Hossein Sadeghi Pages 635-668
  • Vahid Shirgholami, Mahdi Khodaparat*, Abolghasem Moezi Pages 669-702
    Introduction

    Excavation in urban areas occasionally is accompanied by the improper performance of the support system for even small deformations. In this regard, deformation control design based on force-based approaches provides a more realistic reprehensive of excavation performance. Top-down deep excavation techniques are among the modern excavation stabilization methods in urban areas. In this method, unlike the conventional methods, it is possible to perform the excavation and construction operations simultaneously. The present study aims to investigate excavation stabilization using the main structure through the top-down approach. For this purpose, field and numerical evaluations of the stabilized project were conducted based on the top-down approach in the downtown of Qom city, Iran. This research reports the information obtained through monitoring and modeling using the finite element ABAQUS software, predicting the occurred deformations until the end of excavation operations using the calibrated model, and offering an initial estimation of the required stiffness for the support system with respect to the lateral deformations in four sites proposed, according to the studies of Line A Qom Subway. Project specifications Based on the geological studies of Line A Qom Subway Tunnel, the geological layers are classified into four soil classes. Qc-1 consists of gravely sand with fine content of 5 to 20%; Qc-2 is silty and clayey sand with fine content of 35 to 60%; Qf-1 is clayey silt with fine content of 60%; and Qf-2 is a silty clay layer with fine content above 60%. Line A of Qom subway passes the study area of the present study, which is located in Ammar e Yaser Street (Station A6). Based on the geotechnical studies of the project site, the site in the levels near the ground consists of Qc-2 but in the lower elevations, it is composed of Qc-1 and Qf-2. Salam Trade Complex, located in the downtown of Qom city, has 6 underground stories and 6 above-ground stories. It is limited to the main street in the south and to urban decay in the three other directions. The final excavation depth, length, and width is -21, 36, and 32-52 m, respectively. The project structure consists of a steel moment frame with a retaining wall in the negative elevations and metal deck frame for ceiling construction. In this project, excavation wall deformation was monitored in three important sections (A, B, and C). Due to the vicinity to urban decay, a total station TS02 was used for monitoring these sections. According to the field surveys, the maximum horizontal deformation of the walls in sections A, B, and C is 24.10, 42.16, and 47.21 mm, respectively, which were measured in the 0, -1.5, and 0 m elevations. Monitoring process and numerical simulation To calibrate the prepared model, a sensitivity analysis was performed on geotechnical parameters including modulus of elasticity (E), internal friction angle (φ), and cohesion (C) of the layers by simulating 60 numerical models. Based on the sensitivity analysis results, an increase in internal friction angle and elasticity modulus for layer 1 (i.e., φ1 and E1) and elasticity modulus of layer 3 (E3) results in a decrease in lateral deformation. Finally, using the sensitivity analysis results and after several trials and errors, the numerical models for sections B and C were calibrated when reaching the depths of -8 and -11 m, respectively. Using these models, then, it is possible to predict deformations up to the end of the project.To determine the required stiffness for the excavation support system, regarding the acceptable deformation of the adjacent soil mass, 160 numerical models were built and their results were analyzed. Based on the results of Brason and Zapata (2012), relative stiffens (R) were used to develop a relationship between the maximum lateral deformation of the wall and the required stiffness of the support system. R is a dimensionless parameter that represents the stiffness of a solid support system; the greater this value is, the more flexible the system would be. In this study, caisson pile length, excavation width, and buried depth of the wall were used for determining the R.R =  (1) Figure 2 presents the maximum occurred deformation in terms of depth versus the relative stiffness for sites QC and QF. Figure 2. Maximum deformation in terms of depth versus the relative stiffness for sites QC and QF

    Conclusion

    According to the monitory data, the maximum lateral deformation in sections B and C until the end of the project was 42.16 and 47.2 mm, respectively. Moreover, the deformation of the other points inside the excavation was 30 mm.Considering the occurrence of maximum lateral deformations in the higher elevations in the monitored sections, it is inferred that excavation support at the ground level plays a key role in this approach. Hence, the lack of completing the structural frames and slabs for facilitating the excavation operation can lead to an increase in deformation levels. Based on the prepared graphs, the top-down approach in sites QC-2 and QF-2, compared to sites QF-1 and QC-1, provides a more desirable performance for deformation control.

    Keywords: Top-down excavation, Deformation assessment, Total Station TS02, FEM, Line A Qom Subway Tunnel
  • Soheil Ghareh*, Kimiya Yazdani, Fatemeh Akhlaghi Pages 703-728
    Introduction

    The existence of problematic soils due to their geotechnical properties, such as low strength and stability, high compressibility, and swelling, is one of the most important issues and challenges that geotechnical and civil engineers are faced in urban environments, especially in metropolises. Various methods are used to stabilize and to improve the behavior of problematical soils such as compaction, consolidation, stone columns, jet grouting, biological procedures, and additive materials including nanomaterials. Because of their high specific surface, the use of nanoparticles is very effective to increase the shear and mechanical strength parameters of soil. Mashhad city is located on alluvial deposits of Mashhad Plain. A wide area of this city, especially the central and eastern areas where the Imam Reza holy shrine is located, has been built on weak and fine-grained deposits. Considering constructing high-rise buildings such as hotels and commercial complexes in these areas, as well as the need for restructuring the urban decay, the soil improvement will be inevitable. Given the significant application of these nanoparticles, the purpose of this study is to investigate the effects of nanoclay and nanosilica on each other and to find their optimal composition as a suitable alternative for traditional materials to improve the weak and problematic soils. This not only increases the bearing capacity and strength properties but also reduces the cost and time of project implementation.

    Method and Materials

    To achieve a hybrid with maximum strength and bearing capacity in executable projects, laboratory tests were performed on the soil picked up from the vicinity around Razavi holy shrine in Mashhad mixed with nanoclay and nanosilica. The type of soil is classified as CL-ML based on sieve and hydrometer tests. The nanoclay used in this research is the type of montmorillonite- K10, and the nanosilica is as a powdered shape with 99% purity.At first, nanoclay and nanosilica were mixed independently with soil in six different weight ratios (0%, 0.1%, 0.5%, 1%, 2.5%, & 5%) and (0%, 0.1%, 0.25%, 0.5%, 0.75%, & 1%). Soil mechanical and strength properties, including compressive and shear strength, settlement, plasticity index, and swelling, were studied by standard laboratory tests on all specimens. After determining the optimum ratio of each nanoparticle, four hybrids consisting of nanosilica and nanoclay were made in four different combinations and then the effects of these four hybrids were investigated on the soil in the laboratory scale (Table 1). Table 1. Composition of hybrids made with different percentages of nanomaterials

    Conclusion

    The results of the Atterberg limit test on improved and pure soil indicate that the addition of nanoclay and nanosilica and the optimized ratios of these nanoparticles hybrid to increase the soil resistance parameters did not change the soil swelling index.Evaluation of shear strength test results showed a significant synergistic effect of these nanoparticles on increasing the shear strength parameters. The nanoparticles hybrid of 2.5% nanosilica and 1% nanosilica increased the cohesion up to 106% and also hybrids of 5% nanosilica and 1% nanosilica increased the internal friction angle of soil up to 32%. Examination of unconfined compressive strength tests presented a 134% increase in the compressive strength of the specimen improved with 2.5% nanoclay and a 620% increase in soil improved with 1% nanosilica. The optimum hybrid compositions of 5% nanoclay and 1% nanosilica increased significantly the compressive strength of the studied soil up to 785% and reduced the settlement of the soil by 60% compared to pure soil Laboratory studies of electron microscopy examination on ​​pure and improved soil samples with nanoparticle hybrid revealed the presence of these particles in pores of the improved soil. On the other hand, the high specific surface area of ​​the nanoparticles increased the interaction of the soil particles, and the effect of adding these nanoparticles on the refining process is observed in compressive strength increase. As the nanoclay, nanosilica, and hybrid of nanoparticles are the results of soil processing, these particles are very effective to solve the environmental problems because of good compatibility with soil environments. In addition, low volumes of nanoclay, nanosilica, and hybrid in these nanoparticles are necessary to increase the compressive strength and decrease the settlement of soil. Therefore, using these nanoparticles at the project site reduces significantly the cost and execution time of the project.

    Keywords: Soil improvement, Hybrid, Nanoclay, Nanosilica, Bearing Capacity
  • AliAkbar Moomeni*, Ming Tao, Alireza Taleb Beydokhti Pages 729-748
    Introduction

    Shallow tunnels have a vital role in urban planning, railway and highway transportation lines. The presence of underground cavities can leads to stress concentration and consequently, instability of the spaces against static and especially dynamic loads. Therefore, the aim of this study was to evaluate the effect of elliptical cavity and its inclination on sandstone rock behavior under compressive static and tensile dynamic loads. In order to evaluate the effect of the cavity under static stress conditions, two groups of intact and hole-bearing sandstone cores with 0, 30, 60, and 90 degrees of hole inclination were prepared and tested under uniaxial compressive loading test. During the test, in addition to the stress recording, damage and deformability of the samples were recorded by using the strain gauge, acoustic emission sensor and camera. Split Hopkinson pressure bar (SHPB) test apparatus was used for doing dynamic loading test. Furthermore, the damage process was recorded using a high-speed camera with 10 micro-seconds interval of frame capability. The obtained results showed that presence of the cavity reduced the rock strength in maximum state (θ=0) up to 55% and in minimum state (θ=90) up to 77% of its initial uniaxial compressive strength. Dynamic tensile loading tests illustrate that the elliptical hole near the free end of sample (reflection boundary of compressive wave to tensile wave) is stable due to locating in superposition area, while the other cavity out of the area with each inclination was undergone to spalling failure. Assessment of failure surface using scanning electron microscope and thin section study indicates that the dominant fracture is grain-boundary type and iron oxide cement has a vital role in developing of this type of fracture.

    Keywords: Sandstone, Elliptical hole, Stress concentration, Dynamic loading, Spalling failure
  • Tayebeh Mirjalili, Mashala Khamechian*, Mohammadreza Nikudel Pages 749-776

    This study aimed at evaluating the effect of calcic aggregates of engineering geological properties on the artificial stones properties, non-resin cemented and then, to make a comparison between the engineering properties of artificial and natural stones. To investigate the effect of calcic aggregates properties on artificial stones, seven samples of building stones including black limestone, three samples of marble (Chinese stone, marble and crystalline marble) and two samples of travertine and onix were used. Engineering geological properties of the samples were then determined. In the next stage, after designing mould for constructing artificial stones, aggregates with the same grading and mixture design were provided. Then two samples including coarse and fine grained artificial stones were made for all of the mentioned aggregates under the same vibration, pressure and vacuum conditions. Next physical, strength and durability tests were conducted, and the obtained results were compared. The results of engineering parameters showed that Hojjat Abad travertine artificial stones have similar engineering quality to own natural stone and Crystaline Marble and Turan Posht travertine artificial rocks have about 11 to 32% increase in quality but Chinese stone, Black limestone, onix and marble have a 6 to 33% lower quality than own natural stone. However, the samples made of other stones in view of the compared parameters related to artificial stones have lower quality than natural stones; however, they are placed in the acceptable range as building materials.

    Keywords: Building stone, Artificial stone, Aggregate, Calcic, Engineering Geological properties