Compression jointed rock mass

Practically, r(xk masses are in compression and shear state because of the in situ stresses. The unloading of the rock nnasses near excavated slopes causes tension-shear stress state in part of the slopes. Consequently, it is necessary to set up constitutive model of jointed rock masses considering both compression-shear and tension-shear mechanisms. 

A A constitutive model of the Jointed rock masses under compression and shear... 

Exponential correlations were established for the prediction of uniaxial compressive strength ratio/ratio of static and dynamic elastic modulus of rock mass from the intact rock uniaxial compressive strength/elastic modulus and joint factor (Ramamurthy, 1993), which includes joint frequency, joint inclination andjoint strength. These relations are useful in characterisation of jointed rock mass by knowing the intact rock properties and the joint factor. 

In this paper the compressive strength/elastic modulus of the jointed rock mass was estimated as a function of intact rock strength/modulus and joint factor. The joint factor reflects the combined effect of joint frequency, joint inclination and joint strength. Therefore, having known the intact rock properties and the joint factor, jointed rock properties can be estimated. The test results indicated that the rock mass strength decreases with an increase in the joint frequency and a sharp transition was observed from brittle to ductile behaviour with an increase in the number of joints. It was also found that the rocks with planar anisotropy exhibit the highest strength in the direction perpendicular to the anisotropy and the lowest at an inclination of 30o-45o in jointed samples. The anisotropy of the specimen influences the dynamic elastic modulus more than the static elastic modulus. The results were also compared well with the published works of different authors for different type of rocks. 

It is attempted to evaluate uniaxial compressive strength (UCS) and elastic modulus of rock mass as a function of UCS or elastic modulus of intact rock and j oint factor. Figure 14 shows the variation of (the ratio of UCS of jointed rock to the intact rock) with joint factor (Jj.) for tested material. The term joint factor (Jj.), introduced by Ramamurthy (1993), which reflects the combined effect of j oint frequency, joint inclination and joint roughness (or wall strength) and is expressed as ... 

The major advantage of the seismic refraction method is that the derived sound velocity of an individual layer correlates very well to the compactness of the sediment or to the Unconfined Compressive Strength rock strength (UCS). However, whereas the UCS value is a rock strength property the seismic sound velocity is more a rock mass characteristic that may strongly be affected by joints, fractures and other discontinuities. These properties in combination with the UCS determine the dredgeability of rock. 

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