Study On Failure Mode And Stability Analysis Method Of The Cofferdam With Geotextile Bags On Soft Foundation

With the rapid economic development in China, increasing number of engineering projects like coastal reclamation, port and wharf have been implemented in recent years. In the meantime, the applications of cofferdam with geotextile bags, due to its unique advantages in engineering application, have increased. However, huge ambiguity exists on the issue of failure mode of the cofferdam with geotextile bags and the stability analysis method lags behind engineering practices, both of which limit further development of cofferdam application in construction projects.In this paper, the failure mode of the cofferdam with geotextile bags on soft foundation have been summarized and detailed analysis method was proposed for each failure mode correspondently. The main works in this study are listed below:(1) Using the ANSYS finite element software, possible failure modes of the cofferdam with geotextile bags were simulated under different conditions, and damage situations from practical engineering accidents were also investigated. Combine with the result of centrifugal model tests, it can be summarized that three types of failure mode existed form the cofferdam failure analyses: the arc sliding failure mode, the linear sliding failure mode, and the soft soil extrusion failure mode. Furthermore, the patterns of each failure mode have been characterized.(2) Morgenstern- Price(M-P) method in the theory of limit equilibrium was used for the arc sliding failure mode calculation. The actual damage situation of geotextile bags confirmed that Sweden method was the most accurate model to describe actual situation.(3) Geo-Studio software was used to compare the Sweden method, Netherland method and the Superficial Cohesion method by modeling analysis. The calculation result showed that safety factor calculated by the Superficial Cohesion method was the largest. However, the results calculated by Sweden method was close to the results from Netherland method. When using the Superficial Cohesion method to simplify the calculation, the allowable safety factor should be increased by 5%~15% by engineering experience.(4) The calculation formula of linear sliding failure mode was deduced. And, by taking advantage of the results from an example calculation, the correlation between the safety factor and the depth or the angle of the sliding surface was studied.(5) Based on the ultimate bearing capacity calculation method proposed by Prandtl and Ressiner, the correlation formula between maximum depth of the soft soil extrusion failure surface and the width of load was deduced. And an example calculation demonstrated the deduced correlation between safety factor and width of load.(6) The proposed calculation method was tested in an actual engineering project in Tianjin, and calculation results were compared with the measured data. Comparison showed that the proposed calculation method was correct and reasonable.