Permeability Test Study Of Pebbled Filters

The filter in engineering of takeing water from underground shall be lightweight and corrosion-resistant.the gravel filter can get the characteristic like that by changing the material of the gravle part and liner pipe.It has been widely used in geothermal mining,sand well restoration,hydrological observation and other projects.It eliminates the step of filling gravel.It is confirmed that using graval pipe can get a good well-forming effect in Cangzhou saline-alkali soil improved engineering,whose hole trajectory is horizontal.And it has been further applied in the mining of non-solid minerals in the sea,and it has good sand control effect.Most research of the gravel filter is about how to improve the bonding strength of gravel layer and the liner pipe,tensile strength,compressive strength,pecies of the liner pipe,he overall structure of the gravel pipe(single layer or double layer)?and sand control effect etc.Gravle layer palys the main roles when preventing sand intrusion into the wellbore.By now,there is no detailed study about the permeability of it.Improve the permeability of the gravle layer can icrease the output of the resource mining,which is significant in economic.In this paper,on the basis of the existing sand-resistance test of the gravel-attached filter,the particle size range and fine particle content of the quartz sand used to make the gravel-attached layer are adjusted indoors for its permeability characteristics in the loose state.Experimental research;and use the original sample after the test to make a gravel body,while studying the permeability characteristics of the gravel body,compare with the permeability characteristics of the bulk structure.This paper adopts the method of combining qualitative and quantitative analysis to obtain some conclusions and understandings on the permeability characteristics of the gravel-attached filter.It has a certain reference in theory and practice for further improving the permeability characteristics of the gravel-attached filter.(1)With the continuous decrease of the particle size,the permeability coefficients of the granular structure and the gravel structure are continuously reduced,and the change is the largest in the range of medium sand(0.25-0.5mm),and in the fine sand(0.075-0.25 mm)The range changes slightly.The change points of the permeability coefficient of the quartz sand used in the experiment are around 0.3?0.45mm and0.13?0.16mm,respectively,and the magnitude of the permeability coefficient changes from 10^-1 to 10^-2,10^-2 to 10^-3.(2)When the particle size range is determined,as the content of fine particles increases,the permeability coefficients of the granular structure and the gravel structure are continuously reduced.The decrease amplitude of the permeability coefficients is larger with the increases of diameter difference between the fine particles and the coarse particles.(3)The influence of gradation on the permeability coefficient is greater than the influence of particle size on the permeability coefficient.The content of fine particles is an aspect of the gradation.The permeability coefficient of the 0.3-0.6mm sample is0.085cm/s when the ratio of coarse and fine particles reaches 1:9,Slightly less than the permeability coefficient of the 0.3-0.45mm sample is 0.091cm/s.The permeability coefficient of the 0.224-0.6mm sample when the ratio of coarse and fine particles reaches 1:9 is 0.027cm/s,which is significantly smaller than the permeability coefficient of the 0.224-0.355mm sample,which is 0.049cm/s.(4)When the particle size and content of fine particles are the same,the permeability of the granular structure is better than that of the gravel structure.In the range of medium-fine sand,the permeability of the gravel structure is better than that of the granular structure.