During intense periods of drought, the development of cracks is observed in peat and clay dikes. Asset managers of the dikes increase the inspection frequency in times of drought to be able to monitor these cracks. Significant development of the cracks contributes to the development of different failure mechanisms. In this study, the occurrence of the cracks is predicted at a large spatial scale. An inspection database in which the observations from the last three years are stored is used as the basis. The database contains hundreds of observed cracks including the location and time in which they were observed. The database was extended with attributes such as the precipitation deficit, the peat width at the surface, the orientation of the dike body, the subsidence of the dike body and the soil stiffness. Decision tree algorithms were then used to classify which circumstances will lead to cracks and which circumstances will not. From the resulting decision trees it was deduced that high precipitation deficits, low soil stiffness and the peat width can be used as the main predictors for the occurrence of cracks. Both subsidence of the foundation and the dike body being orientated to the sunny side are also contributors, although less prominent. Time-independent cracking criteria were then used to classify which regions are prone to cracking. Dikes which are rich in peat with a low stiffness were thus highlighted. The Mathews correlation coefficient was used as performance criteria resulting in a 0.3 value for the obtained tree. Application of a random forest increased the coefficient to 0.8. An important conclusion is that proper monitoring of the peat width, soil stiffness and precipitation deficit may result in better asset management. On behalf of more classification validity, it is advised to register negatives during inspections as well. Besides, making a clear distinction between drought-induced cracks and cracks due to macro-instability will reduce the likeliness of the model predicting cracks not related to drought. ... Read more

Maturity model has proven to be helpful for an organization to identify its current capability, strength, and weaknesses through maturity levels. These levels are used to rank the various dimension or process of an organization. However, maturity levels only describe a general description of organization capability. The effect of different maturity levels towards the organizational outcomes is speculated in the basis of the description at each maturity levels. The use of the maturity levels is limited in the pre-determined description. This research is an attempt to foresee the effect of different management maturity towards asset cost and performance by using Dynamic Bayesian Network. The network is developed by using a semi-hypothetical case on grass revetment management. The network models the maintenance process which covers the asset degradation and the influence of different extent of management towards grass condition in time. The degradation probability was determined by using Cooke’s classical model expert judgment. We designed different network involving four management dimension that was translated as model scenarios. The result provides an insight into the potential gain or loss of different management maturity which is beneficial for organizations in evaluating different alternatives of management improvement. ... Read more

Around 55% of The Netherlands is protected by flood defences like dikes. Flood defences must meet requirements which are based on an allowed flood probability. Safety assessments are performed to check whether flood defences meet these requirements. Uncertainties are explicitly included in safety assessments. Uncertainty in soil behaviour is one of the major contributors to failure probability of dikes. Therefore reduction of this uncertainty in soil behaviour leads to potential savings in reinforcement costs. One of the uncertainties in soil behaviour is the effect of aging on the behaviour of soft clays in compression. Compression behaviour of clay is strongly dependent on the transition from overconsolidated to normal consolidated soil behaviour. This transition phase in plain-strain conditions is indicated by the yield stress. The development of the yield stress due to aging is described by isotach models in terms of creep strains and stiffness parameters. Examples of isotach models are the abc-model and PLAXIS’ Soft Soil Creep model (SSC-model). According to those isotach models, a yield stress induced by aging is similar to a yield stress induced by unloading. This study verifies the development of the yield stress predicted by abc-models based on K0-CRS tests. The test material is remoulded, highly organic, silty clay with a liquid limit of 165% and a plastic limit of 56% (OVP-clay). The determination of the abc-parameters is not straightforward. The value for the creep parameter is easily overestimated due to a slow decrease in excess pore water pressure during a constant stress phase, resulting in stress-dependent strains instead of creep strains. The b-parameter is affected by the gradual transition from overconsolidated to normal consolidated behaviour and by the development of structure during aging. The development of structure is not included in the isotach models and could result in a higher yield stress than predicted by the isotach models. The possible increase of the yield stress due to the development of soil structure is not visible in the test results, but the performed tests indicate softening behaviour after aging phases. The SSC-model simulates no increase in lateral stress during aging. Some studies present data showing that the lateral stresses increase under a constant effective stress in time. Unfortunately, the development of lateral stresses cannot be quantified based on the performed tests due to stick and slip behaviour in the K0-ring during laboratory testing. Based on the test can be concluded that a minimum yield stress in time can be predicted based on isotach models. An important note is that a yield stress is always obtained with respect to a certain isotach which is dependent on the loading rate and the creep parameter. The shift of the yield stress from the imposed isotach to the reference isotach is often significant in laboratory tests, but not taken into account. Effects of development of structure during aging should be further investigated: it influences the behaviour of the soil in compression and affects the yield stress determination. ... Read more