تأثیر میزان تنش و ابعاد صفحه بر مدول تغییر شکل توده سنگ در آزمایش بارگذاری صفحه‌ای

نوع مقاله: گزارش فنی

نویسندگان

1 گروه زمین شناسی، دانشکده علوم، دانشگاه فردوسی مشهد

2 گروه زمین شناسی، دانشکده علوم، دانشگاه اصفهان

10.29252/anm.8.16.95

چکیده

مدول تغییر شکل توده‌سنگ که از مهم‌ترین پارامترهای توده‌سنگ در طراحی‌های مهندسی سنگ است، به دو روش مستقیم(با استفاده از روابط تجربی) و غیر مستقیم(با استفاده از آزمایش‌های برجا) به دست می‌آید. آزمایش بارگذاری صفحه‌ای با توجه به حجم نسبتاً بزرگی از سنگ، که تحت تأثیر قرار می‌دهد و نیز روش انجام ساده‌تر آن، از معمول‌ترین آزمایش‌ها برای اندازه‌گیری مدول تغییرشکل‌پذیری برجای توده‌سنگ است. این آزمایش‌ها بسته به هدف آزمایش و کاربرد نتایج آن، با تنش‌های متفاوت و اندازه صفحات بارگذاری متفاوت انجام می‌شوند. در این پژوهش، مقایسه‌ای بین نتایج آزمایش‌های انجام شده با دو تنش مختلف و همچنین صفحات با قطر متفاوت صورت گرفته است. در این مقایسه از روش‌های آماری تحلیل همبستگی و آزمون t با زوج داده‌ها استفاده گردید. نتایج تحلیل‌های انجام شده بر روی آزمایش‌های با حداکثر تنش‌های 20 و 40 مگاپاسکال، نشان می‌دهد که بین نتایج آزمایش با بارهای مختلف، اختلاف معنی‌داری وجود ندارد و میزان بیشینه تنش وارده بر سنگ، بر مدول تغییرشکل‌پذیری به دست آمده از آزمایش، تأثیری نداشته است ولی نتایج حاصل از آزمایش‌هایی که با دو صفحه با قطرهای متفاوت در یک موقعیت انجام شده‌اند، نشان می‌دهد که، اختلاف معنی‌داری بین آنها وجود دارد و مدول‌ تغییر شکل‌پذیری به دست آمده از آزمایش با صفحات با قطر بزرگ‌تر، در توده‌سنگ‌های با کیفیت بالا، بزرگ‌تر از صفحات با قطر کم‌تر بوده و در توده‌سنگ‌های ضعیف، برعکس است. به نظر می‌رسد، این اختلاف ناشی از تأثیر نسبت ابعاد صفحه بارگذاری به ابعاد گالری آزمایش باشد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Effects of Stress Value and Loading Plate Dimensions on In-situ Deformation Modulus of Rock Mass in Plate Loading Test

نویسندگان [English]

  • Mohsen Rezaei 1
  • Mohammad Ghafoori 1
  • Rasoul Ajalloeian 2
1 Geology Group, Dept. of Sciences, Ferdowsi University of Mashhad
2 Geology Group, Dept. of Sciences, University of Isfahan
چکیده [English]

Summary
The plate loading test is one of the most common in-situ tests used for evaluation of rock mass deformation modulus. In this test, during several cycles of loading and unloading, corresponding displacements are measured. These tests are carried out under different values of stress and by different plate dimensions. In this study, a comparison has been made between the results of this test considering two different stress values and two different plate sizes.
 
Introduction
Rock mass deformation modulus (Erm) is a basic input parameter for most rock engineering projects. For these purposes, it is necessary to obtain this parameter before starting numerical modeling. The plate loading test is a common test for determination of rock mass deformation modulus. This test has been used in several projects around the world. Erm of rock masses in Bakhtiari dam site is determined by Plate loading tests using different loading plate sizes and different stress values. Bakhtiari dam site is located in southwest part of Iran, almost 70 km northeast of Andimeshk city (Khuzestan province), and 65 km southwest of Doroud city (Lorestan province). In this paper, the obtained Erm from plate loading tests with different stress values and different plate sizes has been compared.
 
Methodology and Approaches
Plate loading tests at Bakhtiari Dam site are carried out using rigid loading plates with diameters of 650 and 915 mm and under maximum stresses equal to 20 and 40 MPa. In this test, two opposite areas in test galleries are loaded using rigid loading plates by means of hydraulic pump system. During the tests, the rock displacements are measured using borehole extensometers that fixed in several positions inside the drilled boreholes in the center of each loading area. The deeper extensometer in each borehole (used as a fixed point) is positioned at the end of borehole at depths more than 6 m. Erm is calculated according to ASTM D 4394 – 08.
 
Results and Conclusions
In the Bakhtiari dam site, plate loading tests carried out to determine deformation modulus of rock mass with different loading plate size and different stresses. In case of two maximum stress values of 20 and 40 MPa, no significant difference is evaluated. Conversely, using two different diameter plates in same position resulted in significant different results. For high quality rock masses, the larger the plate diameter is, the greater the evaluated Erm is. This difference is recognized to be related to the ratio of gallery dimension to loading plate size.

کلیدواژه‌ها [English]

  • Rock Mass
  • Plate Loading Test
  • Stress
  • In Situ Test
  • Deformation Modulus
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