| A large number of fine tailings stored in tailing reservoirs will lead to dry beach slope to slow down,frequent dusty weather,increase of the seepage line and dams stability decrease,which seriously threaten the life and property safety of the surrounding residents and the surrounding ecological environment.Geotextile tube technology provides ideas for effectively solving the problem of dam construction with fine tailings.Improving filling characteristics and interface mechanical properties of fine tailings geotextile tube can not only turn fine tailings into treasures and shorten the construction period,but also provide guarantee for the safe operation of tailings dams.Simultaneously,it will contribute to the ecological civilization construction advocated by our country and escort beautiful China.This thesis starts with more(improving utilization rate of fine tailings),faster(quick consolidation of geotextile tubes)and stronger(improving mechanical strength of geotextile tubes).The research on filling characteristics and interface mechanical properties of fine tailings geotextile tube with low cement content was carried out through a combination of field investigation,theoretical analysis,laboratory test and field test.The main results of this thesis are summarized as follows:(1)Filling tests of geotextile tubes were carried out.The evaluation model of geotextile tube filling characteristics was constructed,and the quantitative evaluation of water permeability and sand retention for geotextile tubes was realized.The optimum cement content was determined to be 3%to improve the filling characteristics of the fine tailings geotextile tube.In the early stage of geotextile tube filling(the first two hours),drainage caused by hydrostatic pressure played a major role,accounting for about sixty to eighty percent of the total discharge volume.In the later stage,the water was squeezed out of the geotextile tube by the weight of the consolidated tailings.During the filling construction of the geotextile tube,measures such as tapping the surface of the geotextile tube and stepping on the top of the geotextile tube can be taken to speed up the drainage of the geotextile tube.(2)Microscopic tests of consolidated tailings were performed.The improvement of filling characteristics of geotextile tube with low cement content was attributed to the appearance of composite particles composed of coarse tailings,hydration film and fine tailings.Fibrous calcium silicate hydrate wound some fine tailings particles in the hydrated calcium silicate fiber mass,and some fine tailings particles were also adhered to the surface of the hydrate film.Composite particles not only alleviated the phenomenon of fine tailings blocking the surface of geotextile tube materials,but also improved the pore size of consolidated tailings and provided a smooth channel for drainage.(3)Interface pull-out tests of geotextile tube material were completed.The interfacial shear properties of geotextile tube materials were affected by the interface combination type of geotextile tube materials and the dry-wet state,and the former had a significant effect on the occlusal friction angle,while the latter macroscopically showed the influence on the sliding friction angle.The quasi-friction angle of the W-shaped interface(the latitude lines on the interface are parallel to the drawing direction)could be as high as 37.7°(dry)and 35.4°(wet).Compared with the J-shaped interface(the longitude lines on the interface are parallel to the drawing direction),the quasifriction angle was increased by 82.9%and 86.6%.Therefore,when sewing the geotextile tube,especially the small size geotextile tube or the geotechnical bag with small length-width ratio,it was suggested that the latitude of the geotextile tube material should be parallel to the shear direction of the geotextile tube.(4)Uniaxial compression tests and interface pull-out tests of geotextile tube were carried out under different cement contents and consolidation time.The optimum cement content to improve the mechanical properties of fine tailings geotextile tube was determined to be 3%,and the optimum consolidation time was to be 7 days.The influence mechanism of cement content and consolidation time on the interfacial shear characteristics of fine tailings geotextile tube was as follows.The coverage and thickness of hydrate films were expanded,which improved the skeleton structure and compactness of the consolidated tailings.Furthermore,the wrapping of geotextile tube materials to the consolidated tailings reduced the energy consumption due to its deformation.Finally,the normal stress transferred to the surface of the geotextile tube increased,which led to a more stable interlocking structure on the geotextile tube interface.(5)The prediction model of the interface friction angle of the geotextile tube was provided,which considered cement content,interface friction angle of geotextile tube materials,consolidation time and friction angle of consolidated tailings.The model error could be controlled within 5%.The influence coefficients of the first two factors were as high as 0.660 and 0.455.(6)The control equation of the geotextile tube interface was established.A progressive failure model of geotextile tube interface was constructed.A method to determine model parameters was put forward and model validation was completed.The evolution law of interface failure of geotextile tube was revealed in final.(7)The conventional dam and geotextile tube dam were constructed in Fengshuigou Tailing Reservoir.The cracks spread from the crest to the slope in the conventional dam,and the fault cracks appeared on the inside of the dam crest.The geotextile tube dam only appeared local cracks in the backfill soil on the inside of the dam crest.The height of the seepage line at the same position was about 1/30 of the conventional dam,which showed obvious advantages.There are 91 pictures,19 tables and 163 references in this thesis. |
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