| The glass fiber reinforced polymer (GFRP), as a green environmental protection anchoring material conforms to national sustainable development strategies, possesses several advantages of lightweight, high strength and corrosion resistance. It is confirmed to be a reasonable substitute for steel to solve complex geological problems. Consequently, the GFRP has gradually been widely used in the areas of road slope, excavation, mining and tunnel supporting and have received more and more attention on anchorage techniques research recently.GFRP material is a multiphase material, and its mechanical properties and failure mechanism are closely related to some influencing factors such as the performance and the ratio of components and their macro dimensions. The parameters are usually obtained by macroscopic mechanical tests, but the stress-strain field on the micro scales at the same order of magnitude can not be informed. Multiscale research method was used to analyze the micro damage mechanism of GFRP in the process of stress and the correlation of macro structural mechanics response, which will improve the study on the damage formation and the crack propagation mechanism. The demand for the durability of materials is as equally important as for the mechanical properties. When used in anchorage engineering, the steel bars are usually found corroded due to complex geotechnical environment, which can lead to the reduction of the bearing capacity of the structure and even to failure, and also can result in environment pollution. At present, the GFRP reinforcement is mostly applied tentatively in geotechnical engineering, in other words, the study on its durability does not provide adequacy technical support to replace the steel. Therefore, it is necessary to research the durability of GFRP soil nail under complex geotechnical environment (alkali, salt), so as to indicate its resistance ability for environmental changes and long-term performance in anchorage engineering. For GFRP is a heterogeneous and anisotropic material, the existing theory of reinforcement is not suitable to be used indiscriminately to analyze the bond anchorage properties of GFRP bars. In addition, the bond between the anchor and the anchor solid is influenced by the overburden pressure in geotechnical engineering, especially for the GFRP bar with low modulus. Therefore, it will be more practical to study the impact on the anchorage performance of GFRP bars when the mortar constraint condition changes.The GFRP is considered to substitute steel as soil nail. In order to investigate its performance from the perspective of engineering applicability, three typical researches are carried out, of which one is multiscale research on mechanical properties of GFRP, the second is study on durability and service life prediction of GFRP under complicated geological engineering environment and the last is to research the influence on the anchoring performance of GFRP under mortar constraint condition. An advanced research method is adopted which is combined with laboratory experiments, theoretical analysis, numerical simulation and demonstration projects tests. Finally, the crucial technical problems will be solved in the application of GFRP in anchorage. According to the results, some conclusions are as follows:(1)It is obtained in multi-scale mechanical test that the formation of apparent crack, the adhesion of internal components as well as the changes in strain tensile test can accurately reflect the development of the material damage and also there is a certain correlation between them. In addition, the matrix stress transmission effect of vinylester bar is superior to that of unsaturated polyester bar, the former has better fracture toughness. Under a same stress level, the degree of progressive damage of unsaturated polyester bar is higher. Moreover, the cyclic loading experiments can quantitatively reflect the cumulative damage of the bar. It is found that when loaded the residual strain of unsaturated polyester bar is larger than that of vinylester bar, and the tensile strength are reduced by almost 10% under cyclic loading effects.(2)When under corrosive environments, the mechanical properties of GFRP bar is proved to reduce in varying degrees, among which the impact on bars when under saline environment is larger than that under alkaline conditions. And the unsaturated polyester bars performed significantly better than the vinylester bars to resist the effect of corrosive environment. It can be gained when using Arrhenius model to predict the service life under corrosive environments that the vinylester bars can still posses nearly 50% of the tensile strength after being soaked in weak alkaline solution(pH=10) for 1000 days, and the decay rate of its strength presented a decreasing trend.(3)According to the results of pullout test under mortar constraint conditions, it can be obtained that the ultimate drawing force on the single function of loading under strong constraint conditions has increased 77% compared to the conditions without constraint, and also the depth of anchorage has increased from 0.6m to 1.0m. It is also confirmed that the mortar constraint applied in the circumferential directions can effectively improve the shear strength of the mortar. Moreover, part of the mortar can continuously bear load even after being damaged by shear stress and the GFRP bars used as soil nails can reserve ample strength.(4)The research achievements on application of GFRP soil nail show that:GFRP bar is a great substitute for steel using in anchorage to achieve better supporting effect, which can make the coefficient of slope stability increased by 26.8%. In accordance with technical specification for retaining and protection of foundation excavations, the drawing force of the bar is far below its ultimate load, and the GFRP soil nail with higher strength reserves compared with steel. The results of pullout test on four GFRP soil nails indicates that the standard values of axial tension calculated from steel nail is a conservative estimate for GFRP soil nail. The soil nails can efficiently share the soil stress, and the smaller the distance between nails is, the more evenly the effect on sharing loads will be. And it's also founded that the parameters of soil nails and the test procedure are the main factors on the displacement at the end of soil nail.(5)FBG sensing technology is very convenient to monitor soil nail and suitable for long-term observation. The results of GFRP soil nail at slope indicates that the vinylester GFRP soil nails have comparatively less decrease in strength after used for nearly three years long. Hence, it can be concluded that the vinylester GFRP soil nails have excellent durability and can be popularized and applied for long-term use. |
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