Analysis of Mechanics Characteristic of Mold Bag Sand+Steel Pipe Piles Combined Cofferdam with Low Water Resistance Ratio on Soft Foundation
On the basis of summarizing the common section types of the existing underwater tunnel mold bag sand cofferdam,aiming at the problems of large section size and high water resistance ratio of mold bag sand combined cofferdam on soft soil foundation,the cofferdam engineering at the interface section of a typical immersed tube tun-nel on soft soil foundation in Guangzhou is taken as the background,a combined scheme of mold bag sand and steel pipe pile with low water resistance ratio of was proposed.At the same time,the mechanism of the steel pipe pile was analyzed,the mechanical characteristics were discussed,as well as its sensitivity to factors such as filling thickness of mold bag,elastic modulus of mold bag and internal friction angle of filling sand.The results of analysis indicate that:1)The combined cofferdam scheme with low water resistance ratio is reasonable.Compared with the conven-tional plan,the settlement of the outer cofferdam has significantly increased in this plan.But the influence on the internal force of the mold bag is smaller and the overall stability is good;2)Both the settlement value at the top of the cofferdam and the tension value of the mold bag increase with the increase of the filling thickness of the mold bag;3)The larger the elastic modulus of mold bag,the smaller the settlement value at the top of the cofferdam,but the larger the tension value of the mold bag;4)There is an inverse nonlinear relationship between the settlement at the top of the cofferdam,the tension of the mold bag,and the internal friction angle of the filled sand.It is recom-mended to control the filling thickness of the mold bag within the range of 0.5～0.7 m on soft soil foundation,with a friction angle of no less than 28 ° inside the filled sand,and to enhance the control of settlement and stability at the top of the cofferdam by laying high-strength geogrid at the bottom.
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