| Due to its low cost,light structure and convenient construction,soil nailing wall has become a main form of slope support.Traditional soil nails are usually made of steel bars and steel pipes,but their application is limited due to their easy corrosion and poor corrosion resistance.Glass Fiber Reinforced Polymer(GFRP)bar has the advantages of light weight,high strength and strong corrosion resistance,which can effectively avoid the shortcomings of traditional soil nailing and become one of the preferred materials for soil nailing wall nails.Based on the test section of GFRP soil nailing wall on Xiyang underground pipe gallery slope,the stress-strain relationship,tensile strength and elastic modulus of GFRP bars were studied through indoor tensile test.The failure mode analysis of soil nails in the field pull-out test and the internal force detection of soil nails in the excavation process evaluated the feasibility of GFRP bars for soil nail wall support;The internal force of the pallet in the limit state of soil nailing was analyzed by using the thin plate bending and small hole expansion theory combined with numerical simulation.The above tests mainly prove that GFRP bars are feasible for soil nailing wall support,and obtain the research results are as follows :1.The indoor tensile strength test of GFRP bars was carried out.The stress-strain relationship of GFRP bars was linear elastic,and the ultimate tensile strength was 391.5 MPa and the elastic modulus was 7 MPa.GFRP bars failure longitudinal cracking and glass fiber fracture.2.The field test section of GFRP soil-nailed wall was carried out in the underground pipe gallery slope of Xiyang Development Zone.Through the field pullout test of soil nail,the pullout bearing capacity of soil nail meets the design requirements,and the connection strength between soil nail and tray also meets the design requirements.When the ultimate bearing capacity of the pull-out test was carried out,the connection failure between the GFRP rod body and the tray was shown,and the tray also showed radial cracking.In order to improve the connection performance between GFRP rod body and pallet,the corresponding improvement measures are put forward,such as increasing the nut buckle length,pre-cutting groove at the end of the nut cone,and increasing the hoop constraint on the outer side of the nut.The test results show that the corresponding improvement measures are effective.3.In order to study the mechanical mechanism of GFRP soil-nailed wall in the process of pipe gallery slope excavation,the project cooperated with Professor Shi Bin team of Nanjing University.The distributed fiber grating sensing technology was used to monitor the internal force of GFRP soil nailing in the whole period of pipe gallery slope excavation.The construction process of grouting,spray surface,excavation,crane loading and the influence of pressure on soil nailing stress at the bottom of the main structure of the underground pipe gallery were explored.The influence of slope creep on soil nailing was analyzed.The test results show that the spraying surface layer of the pipe gallery slope only affects the shallow stress of the soil nail within the spraying area,and the excavation of the lower soil has a great influence on the internal force of the upper soil nail.The gradual excavation of the slope leads to the gradual transfer of the peak stress of the soil nail to the end of the soil nail.4.Using the theory of thin plate bending and small hole expansion of elastic mechanics to analyze the internal force of the pallet in the limit state of soil nails,at the same time,the finite element method is used to carry out a numerical simulation.The theoretical calculation is consistent with the numerical simulation results.The results show that the maximum tray stress is the radial stress at the bottom of the inner wall,which is consistent with the test results.The optimization plan for the tray material and cross-section is proposed,which provides theoretical guidance for the improvement of the tray. |
