Slope Instability of the Earthen Levee in Boston, UK: Numerical Simulation and Sensor Data Analysis

The paper presents a slope stability analysis for a heterogeneous earthen levee in Boston, UK, which is prone to occasional slope failures under tidal loads. Dynamic behavior of the levee under tidal fluctuations was simulated using a finite element model of variably saturated linear elastic perfectly plastic soil. Hydraulic conductivities of the soil strata have been calibrated according to piezometers readings, in order to obtain correct range of hydraulic loads in tidal mode. Finite element simulation was complemented with series of limit equilibrium analyses. Stability analyses have shown that slope failure occurs with the development of a circular slip surface located in the soft clay layer. Both models (FEM and LEM) confirm that the least stable hydraulic condition is the combination of the minimum river levels at low tide with the maximal saturation of soil layers. FEM results indicate that in winter time the levee is almost at its limit state, at the margin of safety (strength reduction factor values are 1.03 and 1.04 for the low-tide and high-tide phases, respectively); these results agree with real-life observations. The stability analyses have been implemented as real-time components integrated into the UrbanFlood early warning system for flood protection. Dear Editor in Chief of Computers and Geotechnics, Please find enclosed a manuscript titled " Slope Instability of the Earthen Levee in Boston, UK: Numerical Simulation and Sensor Data Analysis" for consideration. We have developed a finite element module for stability analyses of earthen dikes which are monitored by an early warning system (EWS) for flood protection. The module (called Virtual Dike) employs live sensor data for models calibration and can be run with the real-time input from water level sensors or with predicted high water levels due to upcoming storm surge or river flood. The main objective of the module design is simulating “virtual” sensors time series for normal and abnormal modes (including different kinds of failure) and feeding the Artificial Intelligence component with the obtained series. In order to generate realistic data sets for the AI, the Virtual Dike module is extensively tested and validated on real-life dikes monitored by the early warning system (so far three dikes have been modelled: the Livedike in Groningen, the Netherlands; the Boston levee in UK and the experimental full-scale IJkDijk levee in Bad Nieuweschans, the Netherlands). In the proposed paper we present stability analysis of the Boston levee, which protects the town from floods caused by the raise of water in River Haven. Slope failures are occasionally observed at the site when tidal range reaches its maximum (at winter and spring times). The analysis results indicate that in winter conditions the dike is almost at its limit state, at the margin of safety. The results agree well with the real life observations. We are convinced that this paper is of general interest to the readership of Computers and Geotechnics