Experimental Study On Mechanical Properties Of Polyurethane Foam Adhesive Improved Calcareous Sand

The engineering construction of the South China Sea area involves the development of marine resources,national development,national defense construction and other major core interests.Different from land engineering construction,the geotechnical engineering materials in the South China Sea are scarce,the cost of transporting from land is huge,which brings severe challenges to the construction.Calcareous sand is a porous,irregular,easily broken calcium carbonate or insoluble carbonate geotechnical medium.If calcareous sand is directly used as foundation backfill soil,it is easy to appear the phenomenon of irregular settlement of foundation.Polyurethane foam is a new type of cementitious material with good material properties,such as fast strength improvement,low density,high adhesion,good toughness,environmental protection and durability,and it is often used as reinforcement material for granular soil in embankment engineering.In view of the engineering problems caused by the easy crushing of calcareous sand particles and the excellent mechanical properties of the new curing agent of polyurethane foam,which is used to solidify and improve the calcareous sand backfill.In order to provide scheme design and technical reference for calcareous sand foundation treatment in the construction of airport runway and other projects in South China Sea,consolidation test,unconfined compressive strength test,conventional triaxial test and microstructure test are carried out to study the mechanical properties under static load and curing improvement mechanism of solidified calcareous sand.The relevant work is as follows:(1)The crushing test of calcareous sand soil is carried out.Through the change of particle size distribution before and after compression,the crushing law of calcareous sand particles is analyzed.Then combined with the fractal model,the crushing behavior of calcareous sand particles is evaluated.The results show that the calcareous sand particles are also broken under a small pressure(50 kPa).(2)Polyurethane foam is used to cure and improve calcareous sand,and combined with the microscopic morphology of polyurethane foam solidified calcareous sand,the improvement mechanism of polyurethane foam to calcareous sand is explained preliminarily.Then,the method of artificial mixing and layered compaction is put forward.In the process of sample preparation,not only the fragility of calcareous sand particles should be considered,but also the uniform mixing of polyurethane foam and particles should be taken into account.(3)One dimensional consolidation test is carried out to study the deformation characteristics of polyurethane foam solidified calcareous sand samples.The relationship between polyurethane foam content and compression coefficients,compression modulus,deformation modulus of polyurethane foam solidified calcareous sand samples are established,respectively.It is found that the larger the amount of the polyurethane foam is,the better the compressive deformation ability of the polyurethane foam solidified calcareous sand samples is.(4)The unconfined compressive test and conventional triaxial test of polyurethane foam solidified calcareous sand are carried out.The stress-strain curves of polyurethane foam solidified cured calcareous sand is obtained,and the strength characteristics of polyurethane foam solidified calcareous sand is studied.Meanwhile,the functional relationship between peak strength and polyurethane foam content is obtained,and the relationship between shear strength index and polyurethane foam content is analyzed.The results show that the polyurethane foam can not only significantly improve the cohesive force of calcareous sand samples,but also significantly improve the internal friction angle.In addition,the stress-strain curves of polyurethane foam solidified calcareous sand samples are described by Duncan-Chang model.