Abstract
The joint force deformation of rock-concrete composite structures is different from that of simple rock specimens or concrete specimens, such as the tunnel surrounding rock-lining concrete, dam foundations, and concrete. In order to study the creep mechanical properties of rock-concrete composite structures under long-duration load, the TFD-2000 microcomputer servo triaxial creep testing machine is used to carry out step loading creep tests on rock-concrete composite specimens (hereinafter referred to as composite specimens) under different confining pressures (including the confining pressures σ3 = 0 MPa). The creep test results show that, under the same confining pressure, when axial deviatoric stress is applied step-by-step according to 10%, 20%, 30%, 40%, 50%, and so forth of the UCS (σ3 = 0 MPa) and TCS (triaxial compressive strength) of the composite specimens, the failure stress that the specimen can bear is closely related to the confining pressure. When the confining pressures are 0 MPa, 7 MPa, 15 MPa, and 22 MPa, respectively, the failure stresses that the composite specimens can bear are 60% (corresponds to 0 MPa), 50%, 30%, and 20% of the TCS under the current confining pressures, respectively. Under the same confining pressure, the initial creep rate of the composite specimen on each step shows a U-shaped change trend. Meanwhile, the instantaneous creep rate and failure creep rate of the specimen increase as the confining pressure increases. When the failure creep rate is excluded, the initial creep rate of other stepped loads at the same confining pressure level decreases step-by-step. The improved Nishihara model can better describe the whole creep process of rock-concrete composite specimens, especially in the accelerating creep step. The testing data and research results in this paper can serve as references for further research on mechanical properties of rock-concrete composite structures.
Highlights
Rough analysis, it is found that the decreasing trend of step loading initial creep rate of rock-concrete composite specimens under different confining pressures can be fitted by using power functions
7 26 39 36 respectively, the initial creep rates meet equations (1)–(4), respectively. e initial creep change trend of rock-concrete composite specimens under different confining pressures obtained through induction and analysis can be used to predict and compare the creep of rock-concrete composite specimens under the same confining pressure
Based on the step loading triaxial creep tests of rock-concrete composite specimens under different confining pressures, with focus on the analysis of the creep rate and its change trend of the rock-concrete composite specimens, the creep process of the rock-concrete composite specimens is described by using the improved Nishihara model, and the following conclusions are obtained: (1) e rock-concrete composite specimen has remarkable creep characteristics; during the creep process, the creep failure stress that the composite specimen can bear is closely related to the confining pressure
Summary
Rock and concrete are two kinds of common building materials, with each containing differences in structure, mechanical properties, and chemical composition. ese two materials are often combined together to bear various complex forces and deformations, such as dam concrete and dam foundation rock, tunnel surrounding rock and shotcrete, and concrete foundation and rock foundation [1,2,3]. There are some other scholars who have carried out relevant researches on the concrete creep He et al [11] analyzed the compression creep mechanical behavior of concrete under the different test conditions. Eir study method is very effective to simplify the complexity of actual engineering and can well simulate mechanical properties of tunnel surrounding rock and concrete lining under long-duration load. The above-mentioned researches mainly focus on the creep mechanical properties of single rock and single concrete or the triaxial compression, shear, and other mechanical properties of rock-concrete composite structures. Erefore, testing data and conclusions in the paper obtained through the relevant creep testing research on the long-duration mechanical properties of rock-concrete composite specimens can greatly enrich the research results of rock-concrete composite specimens and serve as references for the research of rockconcrete composite structures under long-duration load The above-mentioned researches mainly focus on the creep mechanical properties of single rock and single concrete or the triaxial compression, shear, and other mechanical properties of rock-concrete composite structures. ere are few scholars [21, 22] who have studied and analyzed the long-duration mechanical properties of rockconcrete composite structures, that is, the creep properties of rock-concrete composite structures. erefore, testing data and conclusions in the paper obtained through the relevant creep testing research on the long-duration mechanical properties of rock-concrete composite specimens can greatly enrich the research results of rock-concrete composite specimens and serve as references for the research of rockconcrete composite structures under long-duration load
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