بررسی آزمایشگاهی و عددی تاثیر ریز ترک ها بر رفتار مکانیکی نمونه‌های سنگی

درزه ها و ترک ها جزء لاینفک سازه های سنگی بوده که بر اساس نوع کاربری سازه تحت تاثیر مجموعه ای از بارهای استاتیک و دینامیک قرار می گیرند. یکی از مهمترین عامل گسیختگی سازه های سنگی گسترش همین درزه ها و ترک های موجود در سنگ می باشد. ریز ترک ها در سنگ معمولاً به دو شکل طبیعی و القایی مشاهده می شود. در این تحقیق، تاثیر ریز ترک های القایی بر رفتار مکانیکی نمونه های سنگی بررسی شده است. برای این کار از حرارت برای القای ریزترک در داخل نمونه استفاده شده است سپس آزمون های آزمایشگاهی شامل اولتراسونیک، مقاومت فشارشی تک محوره و برزیلی در آزمایشگاه انجام گرفته و الگوی شکست نمونه ها در آزمون مقاومت فشاری تک محوره مورد بررسی قرار گرفته است. نتایج آزمون های آزمایشگاهی نشان میدهد که الگوی شکست نمونه های گرانیتی با افزایش ریز ترک ها از حالت جدایش محوری به حالت شکست برشی تبدیل میشود . به عبارت دیگر افزایش تعداد ریز ترک ها در نمونه های گرانیتی باعث تغییر الگوی شکست نهایی نمونه ها از حالت شکست شکننده به شکست شکل پذیر می شود. همچنین با استفاده از نرم افزار rfpa، ناهمگنی ناشی از ریزترک ها به صورت عددی مدلسازی شده و تاثیر آن بر الگوی شکست نمونه ها مورد بررسی قرار گرفته است. بر اساس نتایج بدست آمده از مدلسازی عددی مشخص گردید که علت تغییر در الگوی شکست نمونه های سنگی با افزایش ریز ترک های القایی، کاهش ترک های کششی و افزایش ترک های برشی در نمونه ها می باشد.

Experimental and numerical investigation of the effect of micro-cracks on the mechanical behavior of rock specimens

It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced microcracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce microcrack in the specimens. In the next, Uniaxial compression test for determination of stressstrain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure. It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced microcracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce microcrack in the specimens. In the next, Uniaxial compression test for determination of stressstrain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure. It is seldom possible that rock engineering structures found without joints, cracks, or discontinuities. On the other hand, the application range of these structures are steadily increasing in recent years and includes bridges, tunnels, slopes, underground gas storage. Thereby, their impact is to be considered in the rock structure design. In the present study, it is intended to evaluate the effect of induced microcracks on the mechanical behavior of rock specimens. For this purpose, 24 cylindrical specimens of Granit were prepared and some of them heated up to 1000 degrees Celsius to induce microcrack in the specimens. In the next, Uniaxial compression test for determination of stressstrain curve of heated and unheated specimens were performed based on International Society for Rock Mechanics (ISRM) suggested methods on a cylindrical specimen with 110 mm and 54 mm in length and diameter, respectively. The tests were conducted using a load controlled testing machine and the loading rate was kept at 0.5 MPa/Sec. Results of experimental tests indicated that mechanical properties of heated specimens decrease with increasing the temperature. In the heated specimens, some fractures induced that influence on the failure pattern of specimens. The failure pattern of unheated specimen is axial splitting mode, while the failure pattern of heated specimen up to 1000 degree Celsius changes to shear mode failure.