| Over the past decade,offshore,port and wharf and other offshore projects have developed rapidly,and many new technologies of cofferdam have been developed.However,any cofferdam has to face the problem of cofferdam stability.The most important factor for the stability of cofferdam is the shear strength.In the stability analysis,the stability of the cofferdam is usually analyzed by undraining shear strength.In view of this,the effective stress method is improved,and a more reasonable theoretical formula is obtained.Combined with the spot monitoring data and numerical simulation,the stability of the soft foundation cofferdam is further studied.The main contents and results are as follows.(1)On the basis of reviewing the development of the theory of soil shear strength,the methods of undraining strength analysis are briefly summarized by experts and scholars at home and abroad.Through formula deduction and example analysis,consolidation stress method based on fracture surface is put forward.Based on the theoretical knowledge of the excess pore water pressure and the effective stress method,the reasonable shear strength of the soft soil in the active and passive areas is deduced.A numerical example is given to show that the method is feasible and the method is more reasonable than the standard and the effective consolidation stress method proposed by Shen Zhujiang through practical engineering.The method is applied to the Jiangmen port,and the result is consistent with reality.(2)The spot data of the public Wharf Engineering in the main port area of Jiangmen are analyzed in detail,including the vacuum under the membrane,the surface settlement,the deeply horizontal displacement,the stratified settlement and the pore water pressure.The construction of the cofferdam is guided through the deformable law of the foundation,the stability of the vacuum and the change of the pore pressure.The influence of continuous sea construction and vacuum change on the surface settlement and deep horizontal displacement of cofferdam is emphatically analyzed.The following suggestions are made for similar projects using vacuum preloading to reinforce soft foundation: 1)vacuum must be stabilized in design value;2)as for surface settlement and deep horizontal displacement,especially when the surrounding areas affect the stability of the project,we must focus on monitoring so as to make timely response when there are problems;3)strictly control filling or loading rate and avoid excessive speed,which will affect the stability of soft foundation cofferdam.(3)The safety calculation function of PLAXIS 2D is applied to analyze the influence of vacuum change and reinforcement on the stability of cofferdam,which is reflected by safety factor,and combined with the deformation of cofferdam,a numerical analysis is carried out.In the numerical simulation analysis,the vacuum has the greatest influence on the stability in the beginning and middle stage,and the enough vacuum and the days vacuum stability can make the cofferdam maintain high stability after unloading the vacuum.Geotextile reinforced effect in vacuum condition,the effect is not obvious,and in the vacuum after unloading,the safety coefficient of reinforced significantly improved reinforcement method and conventional drainage consolidation under the comparison of vacuum preloading,the latter is more obvious,that is to say,in order to ensure the overall stability of the cofferdam,it can use the method of reinforcement to compensate for unstable vacuum or the short days of vacuum stability. |
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