Experimental study on the effect of large scale cavities on mechanical behavior of rock mass

Due to the presence of large civil projects in the Zagros region, the engineering parameters of Asemari formation rock mass have attracted wide attention. One of the characteristics of this formation is the existence of cavities which based on their that related to the shape and position which can reduce strength and deformation parameters of rock mass. In first part of this research, laboratory modeling is used for evaluation of macro porosity effect on deformation modulus and strength of rock. Porous samples were created by plaster and spherical polystyrene granules with have 4 and 6 mm diameter. The range of porosity investigated was approximately 0-45% for uniaxial stengthstrength and 0-30% for elastic modulus. According to the results, uniaxial compression strength and deformation modulus decrease exponentially and by increasing the size of pores from 4 mm to 6 mm. This , decrease ing in the amount of uniaxial strength and elastic modulus is lower less than 7 percent.
In the second part, with regard to thatsince the porous material can be considered as a special case of composite materials, effect of the amount of spherical pores on the elastic modulus was studied by micromechanics method and different homogenizing models. By curve fitting in range of 0-30% porosity, reduction of elastic modulus can be determined by exponential relation. The experimental results match well with models which considered the shape. In porosity of less than 15%, with regard to small differences in Eshelby, Self consistent, Mori-Tanaka and Lielens models, experimental results have good accordance with them. With increased porosity, experimental results tend to Selfself consistent and Eshelby model.