Numerical analysis of the influence of desiccation cracks on the stability of Dutch river dykes

Abstract

With changing climatic conditions, droughts are expected to increase in duration and intensity. Under drying conditions, desiccation cracks can form in clay soil, which is often used as dyke cover and in some cases also for the core of the dyke. These desiccation cracks have a potential impact on the stability of dykes. The main objective of this study is to gain a better insight into the potential influence of desiccation cracks on the macro-stability of Dutch river dykes. With the help of PLAXIS 2D software, a numerical model is used to study the hydraulic response and stability of a dyke with desiccation cracks. It is chosen to simulate the effect of cracks by adjusting soil parameters of the cracked layer. Steady-state scenarios as well as time-dependent scenarios, where high water events are simulated, are studied. The influence of precipitation is also taken into account. For the steady-state case, a maximum decrease of the factor of safety of 5.6% is found. In the time-dependent scenarios, the factor of safety decreases up to 10.8% if a cracked zone with a depth of 2 meters is present. The magnitude of this decrease is mainly depending on the hydraulic conditions and the crack parameters chosen to simulate the effect of cracks. Both inner and outers slope failure is observed. The largest difference between the factor of safety of the cracked and the uncracked dyke occurs when the dyke fails due to outer slope instability as the factor of safety decreased most in the case of a rapid drawdown. From these results it follows that cracks can have a negative impact on the macro-stability of a dyke, but the difference is not unambiguous. Precaution is advised if significant cracks develop at dykes, but smaller cracks are not likely to lead to failure immediately.