طراحی و ساخت جعبه برش دو بخشی جهت مدل‌سازی گسلش عادی و معکوس در دستگاه سانتریفیوژ ژئوتکنیکی

نوع مقاله : Articles

نویسندگان

1 گروه زمین‌شناسی، دانشکده علوم، دانشگاه فردوسی مشهد

2 دانشکده مهندسی عمران، پردیس دانشکده‌های فنی، دانشگاه تهران

چکیده

در اثر جابه‌جایی ریز صفحات نسبت به همدیگر امواج لرزه‌ای و شکست گسل شکل می‌گیرد که با توجه به عمق، میزان جابه‌جایی، نوع جابه‌جایی، شرایط زیرسطحی پیامدهای متنوعی را بر روی سطح زمین از خود نشان می‌دهد. تاکنون مطالعات محدودی بر روی گسلش سطحی صورت گرفته است اما به دنبال وقوع سه زمین‌لرزه چی‌چی تایوان، دوزجی وکوجاعلی ترکیه انجام چنین مطالعاتی شتاب گرفته است. با توجه به از بین رفتن سریع شواهد سطحی گسلش و کم بودن زمان بررسی‌ها از یک طرف و زمان‌بر بودن و بالا بودن هزینه ساخت نمونه‌های بزرگ‌مقیاس (شرایط 1g) از طرف دیگر، اهمیت مطالعات گسلش در شرایط گرانش تشدید شده (Ng) به کمک دستگاه سانتریفیوژ را آشکار می‌کند. در این تحقیق ابتدا جزئیات جعبه دو بخشی گسلش مورد استفاده تشریح شده است. سپس نتایج هفت آزمایش شبیه‌سازی گسلش انجام شده به کمک این جعبه ارائه شده است. پنج آزمایش اولیه به‌منظور کالیبراسیون جعبه و کاهش شرایط مرزی بوده است و دو آزمایش نیز به شبیه‌سازی گسلش عادی و معکوس-  بعد از کسب شرایط مطلوب – بر روی خاک‌های دانه‌ای پرداخته است سپس نتایج مقدار جابه‌جایی منتقل شده به سطح زمین، میزان جابه‌جایی مورد نیاز سنگ کف جهت ظهور گسل در سطح، تغییر زاویه گسل از سنگ کف تا سطح زمین، وسعت منطقه تغییر شکل در گسلش معکوس و عادی با همدیگر مقایسه شده است.

کلیدواژه‌ها


عنوان مقاله [English]

Centrifuge Modeling of Reverse and Normal Faulting with a Designed and Manufactured Split Box

نویسندگان [English]

  • Naser Tali 1
  • Gholam Reza Lashkaripour 1
  • Naser Hafezi Moghadas 1
  • Abbas Ghalandarzadeh 2
1 Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
2 School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran
چکیده [English]

Due to the relative displacement of the earth crust micro plates, seismic waves and fault ruptures are formed, which shows different consequences on the ground surface. These effects vary according to fault depth, displacement value, type and sub-surface conditions. Although limited studies have been conducted on fault rupture propagation so far, studies have been accelerated following the occurrence of three earthquakes in Taiwan (Chi-Chi), and Turkey (Duzce and Kocaeli). Because of limited time to study the fault ground rupture after an earthquake, and the huge cost of performing large-scale tests (1 g conditions), it is important to perform studies on centrifugal model of fault rupture phenomena adopting accelerated gravity condition (Ng). In this study, a split box was designed and manufactured to simulate reverse and normal faulting. It was composed of a fixed and movable part designed to simulate footwall and hanging wall, respectively. The Firoozkuh sand No. 161 with a relative density of Dr=70% that is uniformly-graded fine clean sand with a mean grain size (D50) of 0.3 mm, maximum void ratio (emax) of 0.943 and a minimum void ratio (emin) of 0.548 was used in these tests. The tests were performed at the centrifuge facility of the University of Tehran, using Actidyn Systems C67-2 equipment and at a centrifugal acceleration of 60 g. Five initial tests were conducted to improve the boundary conditions of the models. The sidewalls of the model could create undesirable friction that could affect the test results; thus, different solutions were examined for reducing friction. Polyurethane sheets, double polyurethane sheets and silicon oil were used on both sides of the split box to reduce the frictional resistance. These tests were conducted using polyurethane sheets along with silicon oil-covered surfaces, which were determined to be the best solution. The other two experiments were designed to simulate normal and reverse faulting after obtaining desirable and appropriate conditions. The results of simulation showed that the vertical movement of bedrock in reverse faulting dissipated throughout the soil layer, and amplificated throughout the soil thickness in normal faulting that the value of DDR (Dissipated Displacement Ratio) was 91% and ADR (Amplificated Displacement Ratio) was 124%, respectively. The required h/H ratios for complete development of a failure surface were 5.57% and 1.85% in reverse and normal faulting, respectively. The failure surface approached the ground surface at a smaller dip angle (50 ̊) than the fault dip angle at bedrock (60 ̊) in reverse faulting and it became increased (84 ̊) in normal faulting. The scarp fault in normal condition is sharper and higher than reverse faulting; therefore, the buildings located in this area suffer damages that are more drastic than reverse faulting. According to the conditions of this study, the width of deformation zone is almost equal in reverse and normal faulting, but its location with respect to bedrock fault tip is different in either types. The width of deformation zone is equal to the soil layer thickness, and its border moved toward hanging wall side almost one third of the soil layer thickness in normal faulting. Increases in the price of urban land and a shortage of land for construction make optimal determination of this zone of special importance. Therefore, for effective usage of land, it is suggested that complementary studies (field investigation or laboratory model testing) be performed.

کلیدواژه‌ها [English]

  • centrifuge
  • Faulting
  • Split Box
  • Rupture Propagation
  • Reverse Faulting
  • Normal Faulting
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