Testing Study On Deformation Characteristics Of Layered Rockmass

Layered rockmass is a kind of heterogeneous and discontinuous material with orthotropic mechanical property and its deformation is mainly subjected to bedding planes and the combination pattern of layers. In engineering practices, plate-loading test is widely carried out to study rockmass deformation property. However, this method has a principal disadvantage that the resulted deformation modulus is a kind of equivalent modulus that can't reflect single layer's deformation property and is related with testing conditions such as loading area and pressure and so, is of great uncertainty.In this paper, convention plate-loading test, plate-loading test with a central hole, in-situ tri-axial test, acoustic wave measurement and numerical simulation are carried out to comprehensively study the deformation characteristics of layered rockmass in Shuibuya hydropower station in Qingjiang River and the rockmass in Baihetan hydropower station in Jinsha River. The main achievements are as follows:1)In the base of summarizing the methods and techniques of in-situ deformation tests, some test techniques are improved by applying multi-points displacement sensor with 0.05% precision and anchoring detector in plate-loading test with a central hole and large-sized hydraulic pressure pillow in in-situ tri-axial test.2)Acquired knowledge about the deformation characteristics of layered rockmass include:①In plate-loading condition, the deformation curve of medium-bedded or thick-bedded hard rockmass is nearly linear with small permanent deformation, meaning approximate elastic behavior, and the curve of composite rockmass is concave with much permanent deformation because of the nonlinear deformation of soft layers and bedding planes. In tri-axial tests with principal stressσ1 normal to bedding plane, theε1-σ1 curve is convex, and more large the lateral stress is, more steep the curve.②The deformation modulus of soft layered rockmass relate to stress state, the moduli resulted from tri-axial tests would increase while confining pressure increasing and are greater than the ones from plate-loading tests.③The magnitudes of different layer's moduli vary severely showing obvious heterogeneousness.④Deformation modulus closely relate to loading area and the relationship depend on the combination pattern of layers.⑤Deformation modulus is orthotropic, the modulus in the direction paralleling bedding plane is obviously bigger than the one in the vertical direction.3)A new modulus numerical inversion method based on plate-loading test with a central hole is developed and successfully applied in the deformation characteristic study of the engineering rockmass in Baihetan hydropower station acquiring the moduli of unloaded rockmass and undisturbed rockmass of column-jointed basalt.