Mechanical Experiments Of Time-dependent Properties And Study On Constitutive Model Of Marble In Jinping

With the process of the western development, major conservancy and hydropowerprojects have also been constructed and large embedded depth of rock engineering comeforth continuously. The ground pressure conditions and geological conditions of theprojects are also more complex. Compared with the shallow projects, the mechanicalproperties of deep projects have great difference, which mainly shows in: rib spalling,brittle expansion and rock burst will occur after excavation unloading; the rock masshave obvious creep characteristics. The production of the phenomenon has a commoncharacteristic, namely: with the increase of the time, the mechanical properties of therock mass change correspondingly. Therefore, it is necessary to conduct the time-relatedunloading test and creep test. In view of this, the author has done some research on thetime effect of unloading test and mechanical properties test of the deep-lying diversiontunnel marble in Jinping Ⅱ hydropower station. The main research contents andconclusions obtained are as follows:(1) Unload confining pressure tests were carried out to study the time-dependentproperties of Jinping marbles. The lateral deformation is the main reasons that result inthe damage of rock; both elastic modulus and Poisson’s ratio of rock exhibit a non-linerrelationship with the confining pressure. Elastic modulus of rock is proportional to theunloading confining pressures, however, the Poisson’s ratio just has an oppositerelationship with it.(2) The axial compressive load was applied step by step. The experiment resultsshowed that the lateral deformation is about2-3times of axial deformation, whichshall be a preferable indicator for prediction of the mechanical stability ofexcavation-induced rock deformation; the Poisson’s ratio changes with time, and keepsgrowing under a certain pressure; when the strength of the rocks exceed a certainthreshold, the rock deteriorates with time, and the strength of the rocks hasapproximately a negative exponent relation with time.(3) The damage characteristics and failure mechanism was analyzed through dataarrangements, and the time-dependent properties of rock strength was purified. Thedamage theory and fractional order theory was introduced in the creep model, with combination of previous research results, an applicable constitutive model of damagetime-dependent property based on fractional order theory was constructed for thismarble.