Study On Characteristics Of Interface Between Geogrid Reinforced Calcareous Sand And The Particle Breakage

With the advancement of the the Belt and Road and the South China Sea development strategy,a large number of infrastructure projects have been started in the South China Sea region and the surrounding Indian Ocean region.In the island environment,engineering fillers used for infrastructure construction mainly use calcareous sand nearby.However,calcareous sand differs greatly from land sand in terms of production environment,geological process,chemical composition,and other aspects.Triaxial experimental studies on geosynthetic reinforced calcareous sand have shown that reinforced materials such as geotextiles and geogrids can effectively enhance the overall strength of calcareous sand,but there is still a lack of research on the interaction between the reinforcement and soil interface under the failure of grid pull-out,There is also a lack of research on the interface characteristics of reinforced calcareous sand through large-scale direct shear or pull-out tests.Therefore,in order to scientifically construct island foundation engineering,this article uses pull-out tests as a means to study the interface mechanical properties of grid reinforced calcareous sand.The main research content includes the following:(1)Introduced the large-scale pulling equipment used in the experiment,and provided improvement measures for clamping plates and airbag structures to address the issues of grid damage and airbag damage during the experiment.The basic physical and mechanical properties of calcareous sand and land-based sand were measured,and it was found that there were a large number of irregular particles in the calcareous sand since 0.35 mm,and the shear strength of calcareous sand was higher than that of ordinary sand;And by observing the particle morphology of calcareous sand through scanning electron microscopy,it was found that there are defects such as pores,ducts,and erosion in the calcareous sand.(2)A pull-out test was conducted on bidirectional polypropylene(PP)grid reinforced calcareous sand,and the reinforcement effect under different normal stresses was evaluated according to the standard working conditions recommended by ASTM specifications.It was found that the reinforcement effect of calcareous sand is very significant and superior to that of land-based sand;Taking into account the effects of initial relative density and pull-out rate,it is found that the fluctuation in pull-out strength of reinforced calcareous sand between 0.1mm/min-1mm/min is smaller than that of reinforced land-based sand,and is less affected by the pull-out rate.However,the initial relative density has a greater impact on the quasi cohesive force between the interface peak and residual strength.(3)A pull-out test was conducted on unidirectional high-density polyethylene(HDPE)grids and reinforced calcareous sand with warp knitted basalt grids,and compared with reinforced land-based sand.It is concluded that the reinforcement effect of unidirectional grids is weakest due to the influence of excessive transverse rib spacing and actual reinforcement length;The basalt fiber grid has the best reinforcement effect for calcareous sand,but the nodes are too fragile to fully utilize the grid label strength;The pulling rate has little effect on the reinforcement effect of different grids,while the relative density has the greatest impact on the reinforcement effect of basalt grids.(4)Based on the experience of previous studies on the thickness of shear bands,a selfmade grid frame method was adopted to extract sand from different regions,and the shear bands of reinforced soil were divided and screened.It was found that particle breakage generally occurs in the direct contact area of reinforced soil,with particle sizes concentrated within the range of 0.8mm～1.2mm;And attempt to propose the concept of pull-out energy,observing that the degree of particle breakage is distributed in a stepped shape around the normal stress level;Combining the screening data of different pulling stages,it is found that the crushing of bidirectional PP grating and basalt fiber grating has been basically completed before reaching the peak resistance to pulling,while the crushing degree of unidirectional grid reinforcement tends to be influenced by the pulling displacement.