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Study on Effect of Regular Roughness and Filling of Discontinuity in Shear Strength of Rock Mass with Laboratory Tests

Jahanian, Homayoun | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 46944 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Sedghiani, Mohammad Hossein
  7. Abstract:
  8. Effect of discontinuities on shear behavior and shear strength of rock masses are very important. Infill materials found in natural rock discontinuities may cause a reduction in joint shear strength, influencing rock mass stability. Many researches have been done in the field of behavior of infilled and unfilled discontinuities. The models and relationships developed through such studies will be of immense help to mining and civil engineering projects in rock masses. Rough surfaces in rock masses are found in rock joints. In general this research includes studies on the effect of joint surface mechanical and geometrical characteristics, asperity orientation and infill materials mechanical and geometrical characteristics. For the first time this research has studied the effect of asperity orientation on shear strength of infilled joints. A new shear strength model was developed for predicting effect of asperity orientation on infilled joint shear strength based on laboratory testing. The shear behavior of infilled joints under forward and reverse loading has been studied in this research. In this research, the shear behavior of joints was studied under CNL condition. Many civil engineering projects are constructed in Shemshak formation (North, west and center of Iran). Since sandy clay is similar to infill material found in Shemshak formation infilled joints, it was used as infill material in this research. A new model for predicting the effect of asperity orientation on shear strength of infilled joints based on a series of tests carried out on two types of model joint surfaces with asperity angles of 30o and 45o is presented. Sandy clay was used as infill material in all tests. All tests were carried out in a large-scale shear apparatus under constant normal stress (CNL) conditions. The results indicate that at low infill thickness to asperity height ratio (t/a), the combined effect of the basic friction angle (b) and the joint asperity angle (i) is pronounced, but diminishes with increasing t/a ratio so that the shear strength converges towards the infill alone. The results indicate that shear strength of infilled joints diminishes with increasing asperity orientation angle. The relationship between shear strength and asperity orientation angle is linear. The new model successfully describes the effect of asperity orientation on shear strength of the sandy clay filled model joints. The joints with low asperity angle exhibit higher shear strength during forward shearing cycle than the reverse cycle because the infill become aligned in the shearing direction during the forward cycle. This effect reduces the angle of shearing resistance in the reverse cycle. But in joints with steeper asperity angle, the reverse cycle exhibits greater shear strength. This is caused by the increased asperity interaction of the steeper joint surface profile due to infill disturbance
  9. Keywords:
  10. Shear Strength ; Infilling ; Direct Shear ; Discontinuity Planes ; Regular Roughness ; Asperity Orientation ; Shemshak Formation

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