Experimental Study On Microbial Solidification Of Fiber-doped Calcareous Sand

With the proposal of the "South China Sea Strategy",more and more civil and national defense construction projects are being constructed and developed in the islands of the South China Sea,and the use of calcareous sand as the foundation material in the South China Sea has attracted more and more attention.The main component of natural calcareous sand is calcium carbonate,and it has physical and mechanical properties such as porosity,irregular shape,fragility and low strength,etc.It is difficult to meet the requirements of engineering structure bearing directly with calcareous sand as the basic material.In addition,near-island reef sites are often subject to complex external loads such as wave loads,wind loads,and seismic loads,which are prone to liquefaction of sandy soil,making it difficult to build engineering facilities on the basis of calcareous sandy sites in the South China Sea.In recent years,more and more researches have been carried out on the microbial improvement of sandy soil technology(MICP).Because of its simple operation,small construction disturbance,low cost,and environmental friendliness,the technology has made it suitable for the restoration of ancient buildings and liquefied sandy land.Area reinforcement and other aspects are better used.In this paper,microbe-induced calcium carbonate precipitation technology(MICP)is used to strengthen calcareous sand.Through indoor unconfined compressive strength test and GDS resonance column test,the effects of different fiber types and fiber content on thephysical and mechanical properties of solidified calcareous sand are studied.affect research.The main research contents and conclusions are as follows:(1)The physical and mechanical properties of three different types of fiber cured samples with a fiber content of 0.1% to 0.4% and a gradient increase of 0.05% were tested.The test results show that as the fiber content increases,the calcium carbonate content of the sand column,The dry density and unconfined compressive strength are both "increased first and then decreased".The indexes of the sand column mixed with three fibers(glass,polyester,hemp)reach the maximum value between 0.2% and 0.25%,And the value of the sand column with polyester fiber is the largest,the sand column with glass fiber is the second,and the sand column with hemp fiber is the smallest.On the contrary,the water absorption rate of the sand column shows "first decrease and then increase" with the increase of the fiber content.The three fibers have the smallest content between 0.2% and 0.25%.The sand column with glass fiber is the second,and the smallest with polyester fiber.(2)Three different numbers of grouting wheels,4,6,and 8,were carried out to study the effect of the number of grouting wheels on the physical and mechanical properties of calcareous sand columns.The test results show that: as the number of grouting wheels increases,the calcium carbonate content and dry density in the sand column gradually increase,but the amplitude of the increase decreases somewhat;the compressive strength of the sand column gradually increases,and the incremental The amplitude gradually increases.Comparing the three different fibers,the optimum fiber content is between 0.2% and 0.3%.Under the external load,the fiber-filled sand column mainly shows two forms of "top diagonal cracking failure" and "split failure".The addition of a proper amount of fiber not only improves the strength characteristics of the sand column,but also improves its ductility.In addition,increasing the number of grouting wheels can effectively improve the physical and mechanical properties of the sand column.(3)Based on the indoor GDS resonance column test,the dynamic characteristics of fiber types and dosages on the MICP cured sand column were studied.The research results show that the dynamic shear modulus of the sand column with different types of fibers and dosagegradually increases with the increase of confining pressure,and its dynamic shear modulus gradually decreases with the increase of shear strain,and The faster the decay.The maximum dynamic modulus of the glass fiber-filled sand column is about 0.3%,the polyester fiber is0.3% ? 0.4%,and the hemp is 0.2%.(4)The damping ratio of the solidified sand column decreases with the increase of confining pressure and gradually increases with the increase of the shear strain,and the overall performance is that the damping ratio of pure calcareous sand and hemp-doped fiber sand column is larger than that of glass-doped glass.And polyester fiber sand column.The change law of the damping ratio of fiber-filled sand column can be roughly divided into three stages with the increase of shear strain,namely slowly increasing,rapidly increasing,and steadily increasing.Under the same fiber and confining pressure,the damping ratio of glass-doped and polyester-fiber sand columns generally decreases with the increase of fiber content,and is the smallest in the range of 0.3% to 0.4%.The overall damping of the column is relatively large,and its value is the smallest at the 0.2% dosage.With different types of fibers,admixtures and non-fiber admixtures,the dynamic shear modulus ratio of the sand column gradually attenuates with the increase of the shear strain,and shows the "slow first and then fast" attenuation law.