Research On Underwater Anti-Dispersion Ultra-Thin Annular Retaining Wall Material

With the increasing requirements of large structures for the bearing capacity of pile foundations,the diameter of infill piles is increasing,and the mud retaining wall used in traditional construction methods is difficult to meet the construction requirements.In order to adapt to the development of large diameter piles,a layer of ultra-thin ring concrete retaining wall can be cast underwater instead of mud retaining wall by using steel cage + wire mesh as the inner mold.In this paper,we develop a submerged ultra-thin ring-shaped retaining wall material with dispersion resistance,large flow and adjustable setting time for the structural characteristics of this new submerged ultra-thin ring-shaped retaining wall.The main work is as follows:(1)The effectiveness of various flocculants and their compatibility with water reducing agents were compared by net slurry test with fluidity and anti-dispersity as indicators.After the comparison,it was decided to use 15 w viscosity of HPMC with polycarboxylate superplasticizer system as the anti-dispersant of underwater ultra-thin ring-shaped retaining wall material.Since the addition of anti-dispersant will introduce air in the slurry and reduce the strength of the material,this paper determines the use of high quality polyether defoamer as an auxiliary agent to significantly increase the strength and improve the flowability through comparative tests.(2)In order to obtain submerged ultra-thin annular retaining wall materials with better dispersion resistance and fluidity,the effect of admixtures on the fluidity,dispersion resistance and strength of the materials was investigated by single and multiple admixtures of fly ash,granulated blast furnace slag powder,silica fume and metakaolin in the mortar.Except for silica fume,each admixture will adversely affect the dispersibility while improving the fluidity.Fly ash,GGBS and metakaolin were all effective in improving late strength,but fly ash was detrimental to the development of early strength.By conducting full factorial experiments,the optimum dopant substitution for fluidity and dispersion resistance was obtained as 5% for fly ash,15%for mineral powder and 15% for metakaolin.(3)On the basis of the above research,combined with the actual engineering practice,this paper adopts the method of orthogonal experiment to optimize the design of single-mixed fly ash and compound fly ash and GGBS retaining wall materials,and comes up with three kinds of best matching ratio with different characteristics.Under the premise of good anti-dispersant,the slump extension of the retaining wall material can be up to 465 mm,and the 28 d compressive strength is above 20 MPa.(4)In order to solve the problem of slow setting caused by the anti-dispersant,a variety of pro-setting components were selected for the study.The results show that lithium carbonate and aluminum sulfate can adjust the setting time of the material in a wide range,and the use of aluminum sulfate can shorten the setting time to 3.1h,but its dosing is too large for liquidity.The underwater ultra-thin annular retaining wall material studied in this paper was successfully applied in the 5m large diameter pile foundation retaining wall project of Qingshan River Special Bridge.The material prepared on site has good anti-dispersion and fluidity performance,and no blockage occurred in the casting,which is fully adapted to the construction of 5m large diameter pile foundation retaining wall.