Issue 41

S. Zhao et alii, Frattura ed Integrità Strutturale, 41 (2017) 412-423; DOI: 10.3221/IGF-ESIS.41.52 422 2. The concrete test blocks with the addition of carbon fiber cannot have a good dispersion of the fiber in the mixing process, and the strength of the test blocks compared with that of the test blocks with containing ordinary concrete decreases significantly. The pressure value gets a decline rapidly decline after reaching a certain point during the compressive process, but the test blocks do not reflect obvious damage, and retaining their original shape. Compared with the strength of the ordinary concrete, the strength of the steel fiber- reinforced concrete increases significantly. But from a macroscopic observation, the destruction of the steel fiber concrete is more thorough, and the damage interface is relatively clear. 3. As the thermal conductivity materials, the addition of the industrial graphite and the scrap copper slag can improve the thermal conductivity of the pile, but it can also reduce the mechanical properties of the pile. It is necessary to control the amount within a certain range. It is infeasible not feasible to add too much graphite just to improve the thermal conductivity of the pile. 4. From an analysis of the experimental data analysis, the best- experimental program performing test group can be determined, which is the No. 5 test group with composite Portland cement selected as the cementitious material, and steel fiber as the reinforcement material, that is to say, the material. The material mixing ratio of the energy pile after optimization isA 2 B 2 C 3 D 1 . 5. The A static loading test is carried out towards on the three test piles. The results show that the effect of the heat transfer tubes on the compressive strength of the pile is far greater than the its theoretical influence. From According to the theoretical calculations data, the strength of the second group of test piles shall should be 97.5% of that of the first group of test piles. While Meanwhile in the static loading test, the strength of the second group of test piles is 80.7% of that of the first group of test piles. For the third group of piles with steel fiber, the result shows that the test strength of the piles in the third group is not only decreased, but also slightly improved, so as to which verifies the correctness of the material mixing ratio A 2 B 2 C 3 D 1 . 6. The thermal conductivity of the test blocks in the fourth and fifth group is improved greatly. The thermal conductivity of the block in Group 5 is over twice than that in Group 1; the heat storage coefficient of the first group of materials is 19.3 W / (m 2 • K) , the heat storage coefficient of the fifth group of materials is 30.6 W / (m 2 • K) . That is to say, the thermal storage capacity of the energy pile using a mixing ratio of A 2 B 2 C 3 D 1 is 1.6 times than that of the ordinary reinforced concrete pile, whose effect of heat storage is relatively better. A CKNOWLEDGMENTS his work was supported by the National Natural Science Foundation of China (Grant No.51606084); Ji Lin Sheng Jiao Yu Ting Science and Technology Research [2016] (Grant No. 149); Ji Lin Sheng Ke Ji Ting QingNian Science and Technology Research [2016] (Grant No. 20160520028JH); Zhu Jian Bu Science and Technology Research [2016] (Grant No. 2016-K1-30). R EFERENCES [1] Denis, M., Philippe, P., The effect of borehole inclination on fluid and ground temperature for GLHE systems, Geothermic, 38(4) (2009) 392-398. [2] Zhan, N.Y., Xu, P.W., Influence of building envelop on natural convection and heat transfer when con sidering indoor heat transfer and radiation coupled in natural convection, Acta Energiyae Solaris Sinica, 32(4) (2011) 501-507. [3] Novoselac, A., Burley, B.J., Srebric, J., Development of new and validation of existing convection correlations for rooms with displacement ventilation systems, Energy and Buildings, 38(3) (2006) 163-173. [4] Franco, A., Moffat, R., Toledo, M., Herrera, P., Numerical sensitivity analysis of thermal response tests (TRT) in energy piles, Renewable Energy, 86 (2016) 985-992. [5] Caulk, R., Ghazanfari, E., Mccartney, J.S., Parameterization of a calibrated geothermal energy pile model, Geomechanics for Energy and the Environment, 5 (2016) 1-15. [6] Brahim, T., Jemni, A., A Two-Dimensional Steady State Roll Heat Pipe Analyses for Heat Exchanger Applications, International Journal of Heat and Technology, 30(2) (2012) 115-119. [7] Peng, X., Natural ventilation and energy efficiency in building, Industrial Construction, 37(3) (2013) 5-9. [8] Singh, S.N., Flow and heat transfer studies in a double-pass counter flow solar air heater, International Journal of Heat and Technology, 31(2) (2013) 37-42. T