Zoek binnen publicaties
Rainfall boundary condition in a multiphase Material Point Method
The Material Point Method (MPM) is an emerging computational tool to simulate the complex dynamic process of rainfall-induced landslide. In this field, hydraulic boundary conditions play an important role. In recent researches, the average relative velocity of pore water with respect to the solid skeleton is considered as Darcy’s velocity usually. Hence, rainfall intensity (mm/hr) can be assigned to the node of the mesh as a velocity boundary directly. However, the evolution of true velocities of liquid and solid phases has missed so far in the investigation of the landslide process. In order to keep the information of true velocities in the simulation, this paper provided a new solution to estimate the true velocity of the liquid phase at the node of the boundary layer and has been implemented a coupled hydro-mechanical model using MPM. The validation of such implementation was achieved by simulating a 1D infiltration problem and comparing with the MPM results with those obtained through the commercial software PLAXIS. With the help of this newly implemented boundary condition, rainfall-induced landslides can be better investigated using MPM.
Cross-shore intertidal bar behavior along the Dutch coast : laser measurements and conceptual model
Intertidal bars are naturally occurring morphological features along the waterline of sandy beaches. Present quantitative knowledge on intertidal bar behavior is limited, due to the scarcity of data resources and the limitations of traditional survey techniques. To investigate and quantify the cross-shore morphologic behavior of intertidal bars, hourly terrestrial laser scans of Kijkduin beach (The Netherlands) are used and a conceptual evolution intertidal bar model is constructed. In a six-week period in January and February 2017, a pronounced intertidal bar formed at Kijkduin beach and migrated onshore during mild wave conditions and eroded again during storm conditions. The observed maximum shoreward migration was 30 m horizontally with a maximum growth of about 1 m in the vertical direction. Onshore sediment transport fluxes peaked around 2 m3 per m width per day. In the conceptual model proposed here, run-up and overwash processes are dominant for shoreward growth and migration of the bar and submersion processes are responsible for bar destruction.
Rheological analysis of natural and diluted mud suspensions
Natural mud usually exhibits non-Newtonian rheological behaviors like viscoelasticity, thixotropy and yield stress. The history of each mud sample is also an important factor influencing the rheological behavior, as the state of the clay fabric -for a same composition- is dependent on the shear stresses experienced previously by the sample. Several rheological tests including stress ramp-up, oscillatory frequency sweep and structural recovery tests were performed, in order to analyse the rheological fingerprint of the mud samples collected from two different locations of the Port of Hamburg. The yield stress, storage moduli and structural recovery of mud from the same location was studied as a function of density for two series of samples. One series consisted of samples (“natural samples”) taken in-situ as a function of depth (with increasing density as a function of depth) whereas the other one (“diluted samples”) consisted of samples whereby the density was varied by adding in-situ water to the natural sample having the highest density. Significant differences in rheological characteristics were found between the natural and diluted mud samples, that were attributed to the state/composition of the mud’s fabric in each situation but also to the structural rearrangements caused by the preparation of diluted samples.
IALCCE 2020 - The Seventh International Symposium on Life-Cycle Civil Engineering (27-30 October 2020, Tongji University, Shanghai)
Pesticide assessment using passive samplers in two river systems of Cagayan de Oro River Basin, Philippines
Monitoring organic pesticides in surface water using grab water sampling method is ineffective in most cases due to pesticides’ irregular emission and low solubility in water. To address the problem in water sampling method, this study used passive samplers (PS) composed of silicon rubber sheets (SR) and speedisk (SD). SR and SD were used respectively to measure hydrophobic and hydrophilic organic pesticides. These were submerged in river water uninterruptedly for 34 days. Pesticides in PS were extracted and analysed by sensitive analytical instruments HPLC, GC-MS MS and LC-MS MS. Pesticide assessment were conducted in two river systems in Cagayan de Oro River Basin, Philippines where agricultural run-off are unintentionally and continuously disposed from medium to huge plantations. The samplers were able to measure 105 emerging organic pollutants of which, 56 were organic pesticides and 22 organochlorine pesticides (OCP). Out of 56 pesticides, 11 were measured beyond the applied threshold level of 10ng/L. These were boscalid, carbendazim, dimethomorph, metalaxyl, propiconazole, pyrimethanil, diuron, monuron, simazine, dichlorvos and phenamiphos. The 22 OCP, despite being banned or restricted for almost two decades, were measured in ultra-traces of ng-pg/L. The data obtained in this study can be used to establish a baseline background level which is currently absent in most river systems in the Philippines. It is recommended that further study will be conducted using software PBPK or NORMTOX to assess health impacts and implications of the measured pesticides on the communities that are dependent, and continuously exposed to these constituents by these river waters.
Risk-based maintenance of asphalt revetments on flood defences
Revetments protect flood defences against erosion from waves and currents. At several coastal dikes in the Netherlands asphalt has been used as a revetment material for protection against waves. Asphalt concrete revetments can degrade due to several shock-based and continuous degradation processes, for instance wave impacts, uneven settlements, cracking and degradation of the material. When risk-based requirements of flood defences are to be met, this means that it is necessary to define inspection and maintenance strategies such that it is assured the requirements are met throughout the lifetime. In this paper we investigate what risk-based maintenance schemes suffice to meet the standards for an asphalt concrete revetment that is subject to cracking damage. We compare different inspection schemes consisting of different inspection methods with varying Probability of Detection. It is also demonstrated that a different design approach can significantly mitigate the risk posed by cracking of the revetment, especially for older revetments where cracks occur more frequently.