| The study of deep soft rock’s creep law and failure mechanism under complicated geological conditions is very important, and it provide the theoretical basis of underground engineering and the development of deep surrounding rock supporting. With the underground engineering and mining becomes deeper and deeper, the shallow creep theory of rock and the experience have been unable to suit the needs of practical production. The environment deep soft rock facing is more complex compared with the shallow rock, the high temperature, the complex stress field and the multi medium all affect the behavior of creep. It brings more problems and more time to do creep test, and it is difficult to determine the influence of creep parameters. Similar test provides a new method to research the underground geotechnical engineering. Using the model test based on the similarity criteria, we can establish the relationship between the prototype and the model with the mechanical parameters. This paper studies a similar material with low elastic modulus to simulate soft rock creep characteristics. We can determine the main influence factors of soft rock creep rapidly and cheap using the model test method to simulate the creep behavior of soft rock.The similarity criteria for model test carried out on the basis of the prototype; by it we can carry out similar material creep test to establish the relationship between the model and the prototype. At first, we adjust the ratio of latex cement and determine the similar material suitable by compared the parameter results of the model and prototype test. Then deduce the creep deformation and failure mechanism of soft rock based on the similar material’s creep test results.This paper is based on the background of NSTC project which title is "Study on the rheology softening theory of asphalt, rubber-plastic and soft rock material and their Simulation experimentation", etc. This paper establish a similarity index similar test which the soft rock similar principles followed, and let it as the theoretical basis guiding ratio of similar materials and carrying out the similar tests. Let SBR as the cementing agent of latex cement to make similar material, and determine suitable materials ratio to simulate the creep properties of soft rock through the mechanical experiments, then determine similar maintenance mode and test method for materials. Then study the effect of the temperature on the creep behavior by the DMTS test, set up the temperature-stress model of soft rock creep. By SEM test of soft rock and similar material, we study the micro features similar microstructure and failure character after creep. Using FLAC software, we carried out the numerical simulation of creep, We proved that the creep behavior of latex cement can simulate the soft rock well. The test results, the parameter fitting and numerical simulation results verify each other, and all of them are consistent with the similarity criterion. The result shows that the latex cement creep test at20℃is suit to simulate the creep behavior of soft rock in50℃. The creep law of soft rock at other temperature can be introduced according to the time temperature equivalent principle. We can carry out more tests on the material to study the creep law for soft rock, it will guide the practical engineering. The researches in this paper are as follows:1. According to the similarity theory, we can deduce the similarity criterion at linear elastic stage and soft rock creep stage by dimension analysis method, and considering the effects of temperature, the density. Research on the similarity criteria, we can determine the relationship between physical parameters testing required depends on the similarity, fully considering the temperature, time, stress and density similarity on similar trials may cause. The similarity criteria for material selection ratio similar to determine significance, also can verify the reliability of similar test through the prototype test and model test results;2. Choosing the latex cement as similar materials for soft rock creep phenomenon, using three kinds of latex compounding latex cement and verify similarity law of its creep behavior and soft rock, consider the SBR and the cement as binder as a main part of similar materials, and sand as aggregate, then study the ratio of the similar material, the specimens of maintenance and the test condition. This paper designed and produced a special mould and device for similar material according to the characteristics of soft rock and similar standard sample material requirements. It included a frame and independent mold, the specimens should be compacted and push out better. Mold forming one seamless, overcome the adverse effects of sample die docking may lead to mold is not tight and difficult to be compacted. The mould and device ensure the accuracy of standard sample size of similar material, and greatly improve production efficiency;3. Carry out the similar test. Test the soft rock mechanics character, then study the basic mechanical properties and creep characteristics of soft rock; deduce the time-creep and temperature-creep relationship by using the time temperature equivalent theory of soft rock test at different temperature. Carry out the uniaxial creep test of SBR latex cement with different sand content, and creep tests were performed on different temperature, different ratio by using DMTS. Study the creep curve affected by sand content and temperature, determine the cement:SBR:sand ratio at1:0.2:2as the soft rock similar material. The similar material has the latex’s good creep properties and the strength of cement which can simulate the soft rock creep well, there is a high degree of similarity to prototype and model; at the same time, and it proves that the latex cement has high temperature sensitive, sand content is too large, the compressive strength of latex cement decreased. Observe the fracture of soft rock’s natural state and the creep damaged state by SEM, analysis the microstructure of soft rock creep failure mechanism Using SEM to observation the microstructure of the latex cement and creep after the destruction, it shows that the latex cement and soft rock has certain similarities in microscopic structure. By similar test, we can creep find the creep law of soft rock rapidly and accurately.4. Based on similar material creep deformation law of soft rock, this paper deduces the constitutive equation and creep equation of Burges model, then use Oringin software to numerical merged into the main physical parameters of test parameters to creep; choose3D Burgers model as creep model, let the compliance as the medium to fit the shift factors at different temperatures, then establish the soft rock creep compliance expression at the same stress conditions at any temperature.5. Using FLAC software simulates the uniaxial creep test and the tunnel structure of the prototype and model, we prove that latex cement test parameters at20℃fit the soft rock creep rule at50℃. Through the numerical simulation we verified the creep displacement, prototype and model the distribution of stress and the creep rate suit for the similarity criterion well. The result shows that the similar material can simulate the prototype material well. |
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