Study And Application Of Filtration Fabrics On Geotechnical Drainage Board

Widely attention has been paid to geotechnical drainage board in recent years for its significant effects in the reinforcement of soft soil foundation.Drainage board is formed by a plastic core board and filtration fabrics outside the core board,both parts are crucial to the performance of drainage board.Present researches are focused on engineering application and influence of core board,this study,however,mainly concentrated on the performance of filtration fabrics.PET fibers with good mechanical property and aging quality are used in this study.Spunbond technique is selected as the manufacturing process under the requirement of mechanical properties. Both the material and the process are introduced in the article.The filtration and permeation mechanism of geotechnical drainage filtration membranes are analyzed in the article.Filtration mechanism is composed of two parts,one is the utilization of small pores to prevent soil from getting across,the other is filtration by the natural filtration layer formed near geofabrics.As for the permeation mechanism of fiber media with high porosity like nonvewens,fibers are considered as separated units in the fluid.Navier-Stokes equation was used to analyze the force from fluid to fibers.A numerical model was established in this article.Results show that water permeability is in direct ratio to fiber density and square of fiber diameter,in inverse ratio to areal density of geofabrics.Darcy's Law was used to measure the mechanism of permeation.Laminar flow should be maintained to guarantee accuracy;therefore,Reynolds experiment was used to distinguish turbulent flow from laminar flow.Abundant experiments demonstrated that minimum standard deviation could be reached when cross-head was 5cm.Moreover,water permeability could be used to avoid the influence of filter thickness,thus,engineering needed index could be obtained.In the manufacturing process of filtration membranes,a variety of parameters are related to products quality.We selected spinning velocity,areal density,thermal-bonding area,roller pressure to analyze their effects on mechanical and hydraulics properties of the products. Underlying reason of those effects was investigated to guide practical production.Furthermore, aging properties of PET filters were also investigated under the temperature condition of 200℃, 180℃,160℃w ith d ifferent t ime p eriods.Aging e quation w as e stablished a nd d egradation products were analyzed.In the end of this article,we iterated the application of drainage boards in Shanghai Qingcaosha Drinking Water Source Engineering,according to our analyze and calculation,C type drainage board with a length of 21-25cm and a spacing of 1.4m should be placed in a triangular state.To the extent of our observation,this method has a high efficiency,low cost,easy construction and slight disturbance,could be used as a reference to later construction.