| The construction of the South China Sea project is related to the development and utilization of marine resources,and it is of great strategic significance to China.However,the South China Sea project is different from the land project.Due to the scarcity of geotechnical engineering materials and the huge cost of land transportation,the construction of island and reef projects in the South China Sea is facing severe challenges.Calcareous sand is a special geotechnical medium rich in calcium carbonate or other refractory carbonates.Its particles have the characteristics of high porosity,irregular shape,easy to cement,easy to break,etc.If it is directly used as foundation backfill In actual projects,uneven settlement of the ground is prone to occur,and it will lead to safety accidents.As a new type of cementitious material,polyurethane foam adhesive has the characteristics of high strength,good toughness,fast reaction speed,good durability and environmental protection.It is often used as a reinforcement material in geotechnical engineering for guarding,railway subgrade and other projects.In view of the engineering problems caused by the special mechanical properties of calcareous sand and the excellent properties of polymers as a new type of cementitious material,which is used to solidify and improve the calcareous and backfill.In order to provide theoretical guidance for the treatment of calcareous sand foundation in the construction of South China Sea project,direct shear tests,dynamic triaxial tests and SEM microscopy are carried out to study the shear strength?dynamic characteristics and curing improvement mechanism of solidified calcareous sand.The relevant work is as follows:(1)Observation of the microscopic characteristics of calcareous sand after solidification of polyurethane foam adhesive,and explanation of the mechanism of action of solidified calcareous sand of polyurethane foam adhesive.Considering that the calcareous sand particles are fragile,and the polyurethane foam adhesive needs to be fully and evenly mixed with the calcareous sand particles.In the process of sample preparation,the method of artificial mixing and layered compaction is put forward.(2)Through SEM microstructure test,observe the morphology of solidified calcareous sand with different grades and different polyurethane foam adhesive content.Studies have shown that the content of coarse and fine particles in calcareous sand has a significant effect on the bonding method of polyurethane foam adhesive;The way for polyurethane foam adhesive to improve the shear strength of calcareous sand is mainly to cover the surface of calcareous sand particles with polyurethane foam adhesive,and gradually change the contact form between calcareous sand particles(from point contact to surface contact),and Strengthen the cementation between particles.(3)A series of direct shear tests were carried out to study the shear strength characteristics of solidified calcareous sand samples with different gradations and different polyurethane foam adhesive content.The relationship between particle grading,polyurethane foam content and cohesion,internal friction angle of polyurethane foam adhesive solidified calcareous sand samples are established,respectively.The results show that the larger the polyurethane foam adhesive content,the shear strength envelope of the polymer-cured calcareous sand upward and parallel,and the shear strength of the polymer-cured calcareous sand is greatly improved;The greater the content of coarse particles in the particles,the larger the pores,the more obvious the polymer reaction,and the more obvious the change in strength.(4)The influence law of different confining pressure and different polymer content on dynamic characteristics such as dynamic elastic modulus and equivalent damping ratio of polyurethane foam adhesive improved calcareous sand is studied by GDS dynamic triaxial test.The results show that: The stress-strain backbone curve of the modified calcareous sand improved by polyurethane foam adhesive can be described by hyperbolic function;with the increase of dynamic strain,the dynamic elastic modulus of the modified calcareous sand decreases,the damping ratio increases;With the confining pressure and the polyurethane foam adhesive content increases,the dynamic elastic modulus of the calcareous sand is increased,and the damping ratio is decreased;When the dynamic strain is large,the effect of the amount of polyurethane foam adhesive on the damping ratio is obvious. |
PDF Full Text Request