| In recent years,polypropylene spunbonded needle-punched geotextiles have gradually developed into a hot spot in spunbonded needle-punched production process,and it is also an innovation point and difficulty in nonwoven geotextiles production process.The typical technology of polypropylene spunbonded needle-punched geotextiles production is to combine melt spinning with needle-punched consolidation technology to form the unique three-dimensional pore structure of polypropylene continuous filament.However,in the field of special geotechnical engineering,there is a lack of research on polypropylene spunbonded needled geotextiles.There is a lack of research on the structural and hydraulic properties of polypropylene spunbonded needled geotextiles in domestic and foreign academic and engineering circles.At present,most polyester spunbonded needled geotextiles are used in our country,but the major defect of polyester geotextiles is poor alkali resistance,hydrolysis will occur under alkaline conditions.The polypropylene spunbonded needled geotextile has outstanding alkali resistance,especially under the condition of acid and alkali has an irreplaceable role.Therefore,this topic on polypropylene spunbonded needled geotextile research,in order to replace polyester spunbonded needled geotextile.This paper is to prepare polypropylene and polyester spunbonded needled geotextile under the condition of spunbonded needling technology,and to prepare polypropylene fiber needled geotextile using the short fiber needling consolidation technology.The structural properties and related hydraulic properties of the geotextiles are mainly studied.The surface and section morphology of polypropylene spunbonded needled geotextiles were observed and analyzed.And the geotextiles made under different processes are further studied and prepared by the new one-step composite technology of geotextiles/polyethylene(PE film)composite geomembrane,and the corresponding performance test and comparative analysis are carried out.The geo-composite mechanism,breaking mechanism and tensile properties of the composite geomembrane were also studied.Thus,it can provide theoretical basis for the production of polypropylene spunbonded needled geotextiles and related engineering applications.According to the application of the actual project in the early stage and on the basis of this requirement,this paper studied the mechanical properties of polypropylene spunbonded needled geotextile,polyester spunbonded needled geotextile,polypropylene staple fiber needled geotextile in three surface density(design value is 200g/m~2,400g/m~2,600g/m~2)respectively.At the same time,the performance of the three kinds of composite geomembrane prepared on the three surface densities(design values are 500g/m~2,700g/m~2,900g/m~2)was also studied.Including tensile,tearing,breaking and penetration properties.The performance of the products under the same surface density is compared and analyzed,and the corresponding conclusions are drawn,which can provide reference for engineering design and application.At the same time,the performance and difference between CBR bursting and spherical bursting are studied and analyzed.The results show that:(1)the internal filament of spunbonded needled filament net is locked in the form of"?"knots.When the cloth sample is stretched and broken,the first is the extension of the filament laid in disorder,and then the destruction of the fiber tangles and knots in the form of"?"between the filaments,and finally the filament is broken.(2)when the surface density is 200g/m~2and 400g/m~2,the breaking strength of npolypropylene spunbonded needle-punched geotextiles is less than that of polyester spunbonded needle-punched geotextiles and polypropylene staple fiber needle-punched geotextiles,the latter two are about 1.3?1.7 times of the former.However,when the surface density is 600g/m~2,the maximum strength reaches 53.86k N/m,which is related to the mesh formation and needle consolidation technology.The tearing strength and bursting strength of polypropylene spunbonded needled geotextile(CBR bursting strength and spherical bursting strength)are greater than that of polyester spunbonded needled geotextile and polypropylene staple fiber needled geotextile.(3)The study of CBR bursting performance and spherical bursting performance shows that the strength and elongation of the CBR bursting strength and elongation of polypropylene spunbonded needling,polyester spunbonded needling and polypropylene staple fiber needling geotextile are all greater than that of spherical bursting strength.The bursting strength of CBR is about 1.6?2.5 times that of the spherical bursting,and the elongation is about 1.3?2.1 times that of the spherical bursting.The difference of the two kinds of bursting strength is mainly due to the difference of shear force and stress area when the geotextiles are bursting(CBR bursting area is1962.5mm~2,and the spherical bursting area is 490.63mm~2).In addition,the relationship between bursting strength and bursting area is not directly proportional.The results also show that:(4)the composite of hot-melt PE extruded film and geotextile increases the strength of the composite geomembrane.Its breaking strength,tearing strength and breaking strength are all higher than that of single geotextile.The permeability coefficient of polypropylene spunbonded needle punched cloth/PE composite membrane is very small.The geotextile on one side of the composite geomembrane forms a drainage channel,while the PE membrane on the other side plays a major role in anti-seepage.(5)The composite mechanism of composite geomembrane is that under the dual action of hot melt and pressure,hot melt PE extruded film and geotextile after calender composite and rolling,molten PE on the surface of the geotextile partial penetration.A large number of fibers are hot bonded with the hot melt film,so that some of the fibers on the surface of the geotextile are embedded in the PE film,and effectively compound with the hot melt PE film in the fiber network area,that is,consolidation.Finally,the PE film formed by cooling has a binding effect on the fibers in the fiber net,which restricts the elongation of the fiber net and greatly increases the tensile strength of the film.The composite geomembrane stretching process includes two parts:one is the fracture of the main body of the geotextile in the composite geomembrane;The other is the fracture of PE film.(6)The mechanical properties of polypropylene spunbonded needle-punched cloth/PE composite film are better than those of polyester spunbonded needle-punched cloth/PE composite film and polypropylene staple fiber needle-punched cloth/PE composite film.The tearing strength and bursting strength are both greater than the other two,and the bursting strength of CBR is greater than that of spherical bursting.The performance comparison law of the composite film is similar to that of the single geotextile. |
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