Experimental Study On Interfacial Friction Characteristics Of FRP Composite Pile-weathered Red Sandstone Soil

Fiber Reinforced Polymers(FRP)is a composite material made of fiber-reinforced polymer matrix.It has been gradually applied in engineering.Compared with traditional steel and concrete piles,FRP composite piles have unique advantages.Such as high durability,high strength,light weight,etc.The friction characteristic of the pile-soil interface is an important factor that affects the bearing capacity of the pile foundation.However,at this stage,the research on the friction characteristics of FRP materials under different load modes and in different soils is not complete,so the FRP materials It is of great significance to conduct friction test research on the interface with soil.Therefore,in this paper,two FRP materials(CFRP,GFRP)are used as the pile interface and the red sandstone weathered soil is the soil interface.Interfacial friction tests are carried out to analyze the influence of different factors on the interface friction characteristics and pile bearing capacity.The main research contents and results are as follows:(1)The Shear TracⅢ indoor large-scale direct shear instrument was used to carry out interfacial friction characteristics tests under different vertical pressures,different soil moisture contents,and different soil dry densities,and the shear stress-displacement response and shear deformation laws under different conditions were obtained.The results show that the stressstrain curve changes under different conditions are similar.At the beginning of shearing,the shearing stress rises rapidly with the increase of the shearing displacement,and then slowly decreases when the shearing stress reaches the peak value,and finally stabilizes.Stress softening;under the same conditions,the greater the vertical pressure,the more obvious the shear shrinkage phenomenon.(2)Based on the FRP material-red sandstone weathered soil interface friction test results,the friction characteristics of the FRP material-red sandstone weathered soil interface under different soil moisture contents and dry densities were analyzed,and the interfacial stress-strain relationship,friction coefficient,and interface friction angle were obtained.The law of response to changes in these factors.It can be found that the CFRP and GFRP-soil interface have similar friction characteristics in response to changes in moisture content and dry density;the interface friction strength reaches the maximum near the optimal soil moisture content.When the moisture content is greater than the optimal moisture content,the interface strength will be Weakening occurs when exposed to water.(3)Combining the FRP material-red sandstone weathered soil interface friction angle and quasi-cohesive force obtained from the friction test,a finite element simulation software Midas GTS NX was used to establish a pile foundation numerical model considering the friction characteristics of the pile-soil interface,and the FRP composite material was analyzed.The vertical bearing capacity of a single pile responds with the change of the interface parameters of the pile-soil interaction,and the law of the change of the bearing capacity of the FRP composite pile with the change of the interface parameters is obtained.