تعيين مقادير سختي قايم و برشي درزه هاي سنگي با استفاده از تحليل برگشتي نتايج آزمايش بارگذاري صفحه- مطالعه‌ي موردي: سد بختياري

Determination Of The Normal And Shear Stiffness Of Rock Joints Using Back Analysis Of Plate Load Test Results: Case Study, Bakhtiari Dam

تغييرشكل هاي به‌وجودآمده در يك توده‌ي سنگي را مي توان به دو عامل سنگ بكر و درزه تقسيم كرد. در اين ديدگاه ويژگي هاي درزه، اثرات مهمي مانند كاهش سختي و ناهمساني در رفتار توده‌ي سنگي مي گذارند. در اين بين سختي قايم و برشي درزه، كه در محاسبه‌ي تغييرشكل ها استفاده مي‌شوند، در مدل سازي هاي عددي اهميت زيادي دارند. در اين پژوهش از تلفيق روش عددي و نتايج آزمايش بارگذاري صفحه در سد بختياري براي محاسبه‌ي سختي ها استفاده شده است. با تحليل برگشتي و شبيه‌سازي سه آزمايش بارگذاري صفحه، مقدار عددي سختي قايم و برشي براي سه درزه‌ي مختلف محاسبه شده است. مقدار خطاي تحليل برگشتي براساس مقايسه‌ي مقدار مدول تغييرشكل و نمودارهاي تغييرشكل- بارگذاري ميان آزمايش و مدل سازي بررسي شده است. در نهايت، رابطه‌يي ميان نوع پُركنندگي درزه ها و سختي هاي آنها مشاهده شده است.

It is important to determine the deformation properties of rock masses in many dam engineering projects. Previous studies show the dominant effect of discontinuities on the rock mass deformation modulus. Although the discontinuity properties are very important, determination of their real values, even using in-situ or experimental tests, is not always straightforward. The in-situ experiments are mainly based on calculating the overall properties of rock mass, like the deformation modulus. This paper uses a combined numerical and experimental approach to determine the detailed properties of joints in the Bakhtiari Dam site. Many conventional field and experimental rock investigations were carried out in the Bakhtiari Dam project in order to identify the properties of intact rock, rock mass and joints. The deformation modulus of the rock masses was directly evaluated by field plate load tests. However, due to the lack of experimental equipment, the stiffness properties of the discontinuities were not measured. This paper presents a numerical approach to evaluate the stiffness properties of discontinuities, based on the results of plate load tests. To this end, Udec software was applied for modeling and simulations. Udec software uses DEM, which leads to the ability to define different properties of discontinuity. The various elements considered in the simulation of the plate load tests were: loading pattern, geometry, and mechanical properties of the site material. The geometry and process of calculating the deformation modulus were based on ISRM and ASTM methods, in both numerical and experimental approaches. A direct back analysis technique was utilized to estimate joint shear and normal stiffness and their relevant errors. The calculated stiffness has an optimum error of back analysis that shows the relation between modeling and real experiments. The deformation-loading path, in both numerical and experimental results, has enough similarity in values and slopes, but there are differences in curvature. In addition, the modeling results were compared in front of the geological features for different joint sets. It was observed that the tightness of discontinuities has a strong influence on total stiffness, but infilling material could have different effects.