Research On Criteria Based On Limit Soil-Retained State Of Filter System With Geotextiles

In practical engineering scenarios such as civil engineering,hydraulic engineering,and environmental engineering,geotextiles are often used as filters.However,there are some limitations in relevant design criteria,resulting in poor filtration performance of filter design in practical applications.This has greatly limited the application of geotextile in practical design,and often due to conservative designs,geotextiles with smaller opening are selected as filters,which inevitably leads to clogging.In practical engineering,there is an urgent need to conduct a series of studies on the upper limit of the pore size of the filter layer,in order to provide more evidence for selecting a filter with reasonable opening to avoid clogging or for developing novel filter materials.Based on the theory of limit soil-retained state,this paper further distinguishes between the theoretical ultimate soil conservation state(State-M)and the acceptable limit soil-retained state(State-V).Based on State-V,a series of relevant experimental studies on the filter with large opening were conducted.The main research work and achievements are as follows:(1)A novel filtration test device was developed to collect soil particles eroding from filtration system,and a series of tests were conducted on different soil samples and hydraulic gradients with different filters.The results indicate that particle migration occurred within the soil and a natural filter layer gradually formed in the soil near the filter to maintain the stability of the filtration system.The limit gradient could be obtained from the series of filter tests of limit soil-retained state.And the combination of opening and hydraulic gradient can be used as the theoretical limit for developing the relevant retained criteria.(2)A novel observation method,the microscopic image analysis method,was introduced.Its related parameter selection and application process were further standardized.The results show that representative grading curves and particle composition could be obtained more efficiently when the volume ratio of dispersant to suspension was1:100.Additionally,the sodium hexametaphosphate solution with mass fraction of 4% was used as the dispersant and the concentration of soil particles in suspension was 4 g/L.(3)Further analysis of soil particles lost through the filter layer were conducted using microscopic image analysis method.The results show that the gradation change of eroded soil particles has an important indicative role for the soil-retained state of the filter system.In other words,the grading curve and particle composition of eroded soil particles are closer to the original soil,indicating that the filtration system is closer to the limit soilretained state.(4)The quantitative limit soil-retained state criteria were established from the perspective of eroded soil particles.The criteria were divided into identification criterion and design criterion.Furthermore,a design process using the criteria in practical engineering was proposed.A series of large-scale slope model tests were conducted to verify the criteria.The results show that when referring to the design criterion,the limit hydraulic gradient could be slightly higher than the design hydraulic gradient where the filter system could also maintain its stability well.Therefore,the design based on the limit soil-retained state design criterion was reliable.