Technical Assessment For Composite Foundation With Rammed Soil-cement Tapered Columns Reinforced Soft Subsoil Of Expressway

Many soft subsoil reinforcement technologies have emerged in expresswayengineering in recent years, and a great contributions have been made toChinese expressway construction.Geocell and rammed soil-cement taperedcolumns composite foundation is a new type of soft subsoil treatment which hasarisen in2011. The related research on this new reinforcement technology isconducted, and the engineering case of Huang Lan expressway T2bid inGuangZhou NanSha development zone is elaborated in this dissertation. Theprocess flow, technical and economic rationality about composite foundationwith geocell and rammed soil-cement tapered columns treatment the soft subsoilof expressway is evaluated and discussed. The main characteristics contributionof this dissertation is as follows:1. Integrating double direction reinforced composite foundation technique,the foaming methods, rammed soil-cement mixture filling process, pile headtreatment and reinforcement geocell cushion pavement of geocell and rammedsoil-cement tapered columns composite foundation are demonstrated in thisdissertation.2. Large scale model tests of reinforcement geocell cushion were done toexplore the influence of reinforced material and its location on the foundationbearing capacity. In the comparative mode tests of composite foundation withgeocell and rammed soil-cement tapered columns and composite foundationwith geocell and rammed soil-cement columns, the priority of former softsubsoil treatment was discussed. Depending on the engineering case, settlementobservations under a long-term load tests were carried out to prove thereliability of composite foundation with geocell and rammed soil-cementtapered columns and composite foundation with T-shaped mixing columns.3. Based on the engineering case, various economic indicators of softsubsoil reinforced technologies of expressway were assessed. Relying on graycorrelation analysis method, economic indicators comparative analysis of fivereinforced technologies which were the cement deep mixing method, theatmospheric pre pressure method with plastic drainage plate, the crushed stonepile, the loading pre pressure method with packed drain and compositefoundation with geocell and rammed soil-cement tapered columns were discussed. The economic rationalisation of composite foundation with geocelland rammed soil-cement tapered columns was assessed.The main research conclusions are acquired as follows:1) The constructionof pile of rammed soil-cement tapered columns is simple, can resist pile holecollapse risk effectively, improve the rate of pile significantly and has betterapplicability and reliability for engineering projects. Laying reinforced geocellin gravel cushion can apply to the development trend of expressway soft subsoiltreatment.2) Under the same load, the bearing capacity of reinforced geocellgravel cushion is better than the pure gravel cushion. The reinforced location ofgeocell is impact on the bearing capacity of reinforced cushion, the geocell ismore close to the bottom of the cushion, the higher foundation bearing capacitycan be got. Furthermore, it can adjust the uneven settlement of foundation better,which meets the demand of soil improvement of expressway;3) In the samecondition of geological engineering, cement content, pile length and pilevolume, the bearing capacity of composite foundation with geocell and rammedsoil-cement tapered columns is higher than that of the composite foundationwith geocell and rammed soil-cement columns, and the settlement of the formeris obviously smaller than that of the latter. So the composite foundation withgeocell and rammed soil-cement columns has technical priority.4) In thelong-term observation, the settlement of respective soil layers of the T-shapedmixing piles is bigger than that of the rammed soil-cement tapered columns.The composite foundation with geocell and rammed soil-cement taperedcolumns display obviously technical reliability;5) In comparative analysis bygray theory correlation analysis method, the composite foundation with geocelland rammed soil-cement tapered columns is more economic than the other fourpreliminary selections,based on various kinds of economic, technical, andenvironmental indicators.