| Crack problem of hydraulic tunnel lining concrete is being paid more attention in recent years. Previous studies have indicated that temperature is the main cause of lining concrete cracks. Compared with the common hydraulic mass concrete, hydraulic tunnel lining concrete mostly uses the technic of pumping, which needs large dosage of cement leading to high adiabatic temperature rise. At the same time, hydraulic tunnel lining concrete is a kind of thin-wall structure with great heat delivery surface and base restrained block. Although heat can be taken away quickly from the surface, the half ripe age is small, eventually bring the highest temperature out in short time and rapid temperature decrease after the temperature peak. Creep in the aspect of mechanics key factor is also small which has limited ability to relieve local stress concentration. As indicated by data of engineering practices, the temperature crack appears easily due to the features above. So the temperature crack control is highly needed. Temperature crack control is a kind of extremely complex technical problem. Based on the predecessors' researches, the creep and relaxation which are important mechanic factors of concrete have been studied on the calculation theory methods. The FEM calculation method of the temperature field of important temperature control measure pipe cooling in the process of calculating temperature stress and the temperature control measures of lining concrete with cooling pipes combined with specific engineering are also studied. The research contents are as follows:1. Analyze the basic function of concrete creep mechanics based on the generalized Kelvin model with variable coefficients, study and choose the dirichlet series formula of creep with physical significance and strictly corresponding to the model, study the optimization selection of each parameter of creep model, deduce the function of relaxation rate, propose a method to use the relaxation rate to calculate the relaxation, by using some experimental data, compare the common creep expression and the superposition algorithm, analyze the influence of creep and creep temperature stress calculation at the early age of lining concrete pouring based on the continuous retardation spectrum theory.2. Propose the creep model including initial load time, observation time, age and lag-time taken account into the unit of generalized Kelvin model with variable coefficients, analyze the characteristic of the proposed creep model, study the characteristic of each unit and the fitting precision under the situation of no more loading-unloading.3. Analyze and structure the heat balance equation near the cooling pipes, use the theory of equivalent heat conduction to deduce the average temperature of any interval, propose an iterative algorithm to calculate the temperature rise along the cooling pipes by the temperature gradient of concrete near the cooling pipes, suggest the algorithm above to improve the calculating precision of real temperature filed calculation of concrete with cooling pipes under fixed mesh size.4. Introduce the direct simulation finite element method to calculate the temperature field of concrete with cooling pipes into the hydraulic tunnel lining concrete, study the Xiluodu hydraulic tunnel side wall lining concrete with cooling pipes during the construction, contrast the calculation results to the local testing results, use the direct simulation finite element method to analyze the advantages and disadvantages of lining concrete of the under construction Baihetan hydropower station diversion tunnel non-pressure section, analyze the sensitivity of pipe spacing, inlet water temperature and flow, propose some optimized schemes of cooling parameters, propose a difference analytical method to solve the problem that each representative node location under different pipe spacing is not at the same height, providing some important references for temperature control of lining concrete with cooling pipes. |
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