| The local agro-drainage ditch slope is collapse serious under the condition of seepage due to alternating cycle of drying-wetting and freezing-thawing in Yellow River irrigating district of Ningxia,where deposited with drift sand layer.At present,the grass-soil willow pile protection technique has been commonly used in this area,but after two or three years,partial damage often occurs;while adopting the dry masonry slope protection technique often accompanies the disadvantage of high engineering cost and lacking of construction material.Geotextile soilbags is a better choice because it has the advantages of low cost,easy to take materials,fast construction speed and little influence on the surrounding environment.It is widely used in slope control,coastal protection and other projects at home and abroad.Based on the reinforcement effect of geotextile soilbags technique,this thesis presents the application of this technique to slope stabilization project of agro-drainage ditch,solving the problem of slope easily collapsed.Farmland drainage ditches in Dongfanghong Village irrigation area of Shaogang Town,Qingtongxia City,Ningxia were selected as the experimental objects,summarizes the literuaterue achievements of geotextile soilbags technology in the past,related mechanical properties were tested when soil samples were taken at different positions on the ditch slope of the test area,such as the direct shear test,the interface friction test between two kinds of Geotextiles and soil,and the unconfined compression test of geotextile soilbags in different water content.Then filter ability test with five kinds of geotextiles and soil were tested for the filtration properties in different hydraulic gradients by self-made gradient ratio test instrument.Finally through the self-made large-scale permeability test equipment,the permeability coefficient of the geotextile soilbags masonry structure in the vertical direction and horizontal direction was tested by selecting 8 different masonry composite structures formed by two different sizes under three different hydraulic gradients.On this basis,a test section of geotextile soilbags ditch slope with length of 100 m was constructed on the farmland drainage ditch in the test area.Two in-situ monitoring test sections were arranged on the geotextile soilbags ditch section and located on the upper part of the soilbags ditch which was grass-soil willow pile section to monitor the slope protection effect of different masonry modes.On the basis of collating and analyzing the laboratory test,in-site survey data and the latest relevant research literature,the calculation model ofupper limit solution for the stability analysis of the drainage ditch slope with geotextile soilbagsmasonry was established,where the ditch bottom contains drift sand interlayer,and seepage flow was considered at the same time according to the characteristics of farmland drainage channel and thespecific geological conditions in Ningxia Yellow River irigation district.The stability of geotextile soilbags retaining slope with pile and non-pile were simulated and analyzed by using optumG2 limit analysis software.The main research results and conclusions are as follows:(1)Direct shear interface friction tests were carried out with soil samples at different locations of the ditch and two kinds of geotextiles which are white leather fabric and black polypropylene fibers,respectively.The results show that the friction coefficient of the contact surface between geotextile and soil sample decreases with the increase of moisture content.The unconfined compressive strength of geotextile soilbags under wet condition is better than that under dry condition,and the allowable deformation before failure is larger.The additional cohesion of geotextile soilbags in longitudinal and latitudinal directions is about 18?21kPa and 15?17kPa after compressive deformation,respectively,which is beneficial to resist slope deformation and failure.(2)Under different hydraulic gradients,the test of soil-geotextile filtration performance shows that seepage has a great influence on the stability of soil particles in the local area near the filter.But at a distance from the filtering layer,seepage has little influence on soil structure,and the soil is basically stable.The performance of white leather is the most remarkable when the hydraulic gradient is low.(3)The permeability tests of geotextile soilbags structures with different masonry modes shows that the permeability coefficient in horizontal direction is greater than that in vertical direction,and in both directions is greater than that in undisturbed soil,which indicates that the ditch protected by geotextile soilbags is feasible to discharge the groundwater of irrigation area.(4)The two in-situ monitoring datas from geotextile soilbags sections and grass-soil willow pile sections that have been arranged in the same ditch show that the pore water pressure of grass-soil willow pile section is higher than the geotextile soilbags section at the same depth.The earth pressures of geotextile masonry structure at different depths have been illustrated on the distribution characteristic of large portion in the middle but a small at both top and bottom of soilbags wall.Monitoring results show that geotextile soilbags not only control the swelling deformation of slope soil after immersion,but also avoid the occurrence of penetrating cracks due to loss of water.Since geotextile soilbags has the tensile strength and the reinforcement function,it can effectively prevent the local collapse caused by the excessive deformation because of freezing-thawing of soil and the filtering erosion by seepage pressure.(5)Based on the geotextile soilbags slope with pile support and non-pile support in the experiment ditch where the stratum has drift sand interbed,the stability of farmland drainage ditches which protected by geotextile soilbags is simulated and analyzed under seepage conditions by utilizing the upper limit solution model.The results showed that the slope stability coefficient of geotextile soilbags retained with pile support is larger than that non-pile support under the different channel water level and groundwater depth.With the change of water head difference between ditch water level and groundwater depth,the range of stability coefficient of geotextile soilbags revetment without piles varies more widely than that of with piles.The results of laboratory and in-site experiments and numerical calculation show that the sliding strength and discharging field groundwater are all better by using geotextile soilbags technology,so the achievements will be expected to provide fundament for the practice of farmland drainage control project in Yellow River irrigation district of Ningxia. |
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