PurposeThis paper aims to develop a probabilistic framework which combines uncoupled cofferdam stability analysis, random forest and Monte Carlo simulation for cofferdam reliability analysis.Design/methodology/approachThe finite element method and limit equilibrium method are used to calculate the seepage field and stability of cofferdam, respectively. Sufficient training and validating random samples are generated to obtain a random forest surrogate model with acceptable accuracy. The calibrated random forest model combined with MCS is used to conduct cofferdam reliability analysis. The proposed methodology is illustrated using a typical cofferdam model.FindingsThe numerical simulation results demonstrate that a larger pore water pressure leads to a lower stability of the cofferdam and vice versa. The increase in the slope angle significantly reduces the stability of cofferdam on the corresponding side, while the stability of cofferdam on the other side is mainly affected by the internal pore water pressure. The increase in the width and height of the reverse pressure platform significantly enhances the stability of cofferdam, and the changes in the angle of the reverse pressure platform affect the stability of cofferdam to some extent. The probability of failure (Pf) of cofferdam increases gradually with increasing vertical and horizontal scales of fluctuation, coefficient of variation, and cross-correlation coefficient when the degradation degree of soil properties is low. It is worth noting that the effect of vertical and horizontal scales of fluctuation, coefficient of variation, and cross-correlation coefficient on the Pf of cofferdam changes significantly when degradation coefficient decreases to a critical value.Practical implicationsA geotechnical engineer could use the proposed method to perform cofferdam reliability analysis.Originality/valueThe reliability of cofferdam can be efficiently and accurately studied using the proposed framework.

In order to study the stress and deformation characteristics of the PLC construction method pile cofferdam structure, this paper takes the deep-water foundation construction of a certain project as the background. The main bridge of the project adopts (90+180+90) m continuous beam arch, and the lower structure of the main bridge adopts a bearing platform and pile group foundation. The plane size of the cofferdam is 29.8mx22.35m, the overall cofferdam is composed of steel pipe piles, Larsen VIW shaped steel sheet piles, purlins, and internal supports. Using finite element software to establish a comprehensive model of the cofferdam space, considering the effects of load combinations such as soil pressure, static water pressure, water flow force, and wave force on the cofferdam, it is divided into 5 working conditions for loading calculation according to different construction stages, and the most unfavorable working conditions are obtained. The structural stress and deformation of the cofferdam are analyzed. The results indicate that the strength and deformation of the deep-water foundation cofferdam meet the requirements. The lateral deformation at the center of the cofferdam structure shows a trend of first increasing and then decreasing. For the purlin and internal support system, the force on the lower support is greater than that on the upper support, and the force on the middle position is greater than that on the two ends. To ensure safe construction, the lower purlin and internal support can choose steel with larger moment of inertia and yield strength.