BORING ELASTIC MODULUS METHOD FOR ROCK MASS MECHANICAL CHARACTERISTICS AT NUCLEAR ISLAND

The biggest advantage of drill test method is to obtain the rock mechanics characteristics such as deformation modulus and elastic modulus. They are the crucial parameters for engineering support design and engineering safety evaluation. This paper is based on a nuclear island construction project. It uses the boring elastic modulus method for rock mass mechanics characteristic. It finds that the method is good to reflect the rock mass structure characteristic and the stress-strain curve of test has a relative good regularity. The curve can be described as follows. In low pressure stage, the stress-strain curve is non-linear relation with a quick deformation. In medium pressure stage, it needs a certain pressure to force the drill wall and bearing plates of boring elastic modulus equipment to contact completely when the pressure increases and cracks close. In high pressure stage, the stress-strain curve is a linear relation. Meanwhile, with the influence of rock mass structure itself, the deformation modulus and elastic modulus vary at different depths. In a further study on the deformation modulus and elastic modulus at nuclear island, it is known that the anisotropy is not evident in granite ranging from weak weathering to fresh. However, some of the test section affected by cracks and joint cutting can show relative low rock mass modulus, bigger rock modulus ratio and stronger in anisotropy. Finally, this paper provides the rock mass modulus in weak weathering to fresh conditions as follows. At the weak weathering condition. The standard value of NS deformation modulus is 24.021.61GPa; the standard value of EW deformation modulus is 23.921.56GPa and the comprehensive value of deformation modulus is 23.971.10GPa. At the fresh condition, the standard value of NS elastic modulus is 45.152.58GPa; the standard value of EW elastic modulus is 44.252.57GPa and the comprehensive value of elastic modulus is 44.701.79GPa.