تأثیر بار ترافیکی بر گودبرداری نگهداری شده توسط انجماد مصنوعی زمین؛ مطالعه موردی: قطار شهری تبریز

نوع مقاله : Articles

نویسندگان

گروه ژئوتکنیک، دانشکده مهندسی عمران، دانشگاه تبریز، تبریز، ایران

چکیده

روش انجماد مصنوعی زمین به عنوان یک روش بدیع مطرح می­گردد که نه تنها از لحاظ فنی و اقتصادی قابل قبول است بلکه دوست­دار محیط زیست بوده و در تمامی انواع خاک­ها و شرایط آب زیرزمینی قابل استفاده است. هدف از این مطالعه، تحلیل و طراحی مکانیکی دیوار خاک منجمد تحت تاثیر کاهش دما و عبور بار ترافیکی می­باشد. در این مطالعه با استفاده از مدل رفتاری موهر- کولمب اصلاح شده که با بهره­گیری از نتایج آزمون­های آزمایشگاهی بر روی خاک منجمد، صحت­سنجی شده است، به شبیه­سازی سه­بعدی اجزای محدود دیوار خاکی منجمد و بررسی پارامتری آن توسط نرم­افزار آباکوس پرداخته شده است. لازم به ذکر است که این پژوهش در قالب یک مطالعه موردی صورت گرفته و تمامی نمونه­های آزمایشگاهی از گمانه­های مطالعاتی خط 2 قطار شهری تبریز به دست آمده­اند. مطابق نتایج آزمایش­ها، رفتار نرم شونده در تمامی نمونه­های خاک منجمد به وضوح مشاهده می­شود و نمودارهای تنش-کرنش یک قله (Peak) و یک حالت پس­ماند (Residual) از خود نشان می­دهند. نتایج آزمایش سه­محوری بر روی خاک منجمد نشان می­دهند که با کاهش دما مقاومت برشی خاک ماسه­ای بددانه­بندی شده منجمد به طور قابل ملاحظه­ای افزایش می­یابد.  نتایج تحلیل­های عددی نشان می­دهند که تغییرمکان جانبی دیوار خاک منجمد تحت تاثیر گودبرداری به سمت داخل گود در مقطع وسط دیوار بیشتر از مقطع تکیه­گاه دیوار بوده و تاثیر عبور بار ترافیکی بر روی مقطع وسط دیوار و افزایش تغییرمکان جانبی آن بیشتر از مقطع تکیه­گاه دیوار می­باشد. همچنین قابل ملاحظه است که کاهش دما از  تا  تاثیر قابل ملاحظه­ای بر کاهش تغییرمکان جانبی دیوار خاک منجمد در مقطع تکیه­گاه ندارد (حدود 2 تا 3 %)، در حالی که در مقطع وسط دیوار کاهش دما در محدود مذکور تا حدود 13% منجر به کاهش تغییرمکان جانبی دیوار خاک منجمد به سمت گود می­گردد.

کلیدواژه‌ها


عنوان مقاله [English]

The Effect of Traffic Load Excavation Supported by Artificial Ground Freezing: A Case Study of Tabriz Subway

نویسندگان [English]

  • Mahzad Esmaeili-Falak
  • Hooshang Katebi
Geotechnical Eng. Dept., Faculty of Civil Eng., University of Tabriz, Tabriz, Iran
چکیده [English]

In this study, the impact of passing traffic and temperature reduction on the stability of the frozen soil wall is studied. Design geometry and mechanical properties of the frozen and unfrozen soil have been simulated according to the line 2 of Tabriz Subway. In order to numerical modeling, in all stages of the present study, the ABAQUS finite element software has been used. For modeling of unfrozen soil, mechanical properties resulted from experimental tests on the samples obtained from boreholes, then the Mohr-Coulomb constitutive model has been used. Since the frozen soil is an unconventional material, there is no reasonable constitutive model for that. Taking into account the actual site conditions (including unit weight, water content, void ratio and lateral earth pressure), more than 60 triaxial compressive tests were conducted on the frozensoil samples. Results from triaxial tests on the frozen soils showed that shear strength of frozen poorly graded sand increases with temperature reduction. Thus, by modeling the triaxial test on frozen soil in ABAQUS software, Mohr-Coulomb constitutive model was verified according to the experimental results of triaxial tests,so that it can model the strain-softening elasto-plastic behavior of frozen sand. The geometry of metro station excavation with the length of 104 m and the depth of 10 m was simulated according to the cut and cover method, consequently. Analysis results showed that lateral displacement of the frozen soil wall into the excavation due to the cut at middle section of the wall is greater than the supports section. Besides, the effect of passing traffic load on the middle section of the frozen soil wall is greater and it leads to larger lateral displacement into the excavation in thissection. The reason of this fact is the friction between unfrozen and frozen soil at the place of abutments. Therefore, in close section to abutments of frozen soil wall, thin and warmer (subzero) temperatures can be used. It is worth mentioning that the decrease in temperature has no significant effects on lateral displacement reduction of the frozen soil wallat abutments (about 2-3%), while, this value is up to 13% at the middle of the frozen soil wall. Eventually, the method of artificial ground freezing for supporting the excavations in this study (subway station of line 2, Tabriz subway) is recommended, which is adjacent to the main road and heavy vehicles traffic is possible.

کلیدواژه‌ها [English]

  • Artificial Ground Freezing (AGF)
  • Finite Element Method (FEM)
  • Triaxial Compressive Test
  • Traffic Load
  • Tabriz Subway
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