Clay Ripening Pilot Study (Kleirijperij): An Overview of Governing Physical Processes, Monitoring, and Modeling
Type:
Presented during:
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
Authors:
E. Meshkati, T. van Kessel, M. van den Heuvel, J. Boganen, N. Nijborg, A. Talmon, M. Nabi, G. Dupuits, P. Vardon, L. Sittoni, W. van der Star
Abstract
"Introduction Excess fluid mud in waterways and coastal systems should not be considered waste but a resource. Thanks to its relatively high clay content, marine (fluid) mud can be reused as a building material for geotechnical development such as dyke reinforcement, counteracting subsidence, and as a substrate for agriculture or nature development. Ripening is a soil formation process that irreversibly converts waterlogged sediment into soil by desiccation and structure development (Vermeulen et al., 2003; Pons and van der Molen, 1973). An alternative international name for the Dutch term 'ripening' is 'initial pedogenesis'. The ripening of dredged sediment consists of physical, chemical, and biological processes. Transforming marine mud into soil comes with several scientific and practical challenges, such as removing salt, organic matter, and possibly pollutants. This extended abstract, accompanied with a presentation, describes some of the key physical ripening processes, their interaction, and the time scale at which they occur in the context of a 25 ha Clay Ripening pilot study (known as pilot Kleirijperij) in the Netherlands. Moreover, a conceptual mathematical formulation for physical dewatering during consolidation and desiccation will be presented. Finally, a one-dimensional large-strain consolidation desiccation model is used to replicate the physical ripening process of the Clay Ripening pilot study. Clay Ripening Pilot study (Kleirijperij) – monitoring From April 2018, about 300,000 m3 of dredged fluid mud from the Ems-Dollard estuary was transferred into 25 different plots (basins) of about 1 ha (100 m × 100 m). Various natural and mechanical ripening scenarios are applied in these plots to identify the most effective way to transform fluid mud to suitable soil for dike construction. The Clay Ripening Pilot (Kleirijperij in Dutch) is conducted at two different locations in the North East of the Netherlands, namely, Delfzijl (using fluid mud from the entrance of the port of Delfzijl) and Kwelder (using mud from the salt marsh Breebaart). Over the past four years, several monitoring campaigns have been carried out to keep track of the temporal change in volume and thickness of the deposit, density, water content, salt content, organic content, groundwater level, drainage, and other key parameters. Overview of governing physical processes When a plot (basin) is filled with fresh (fluid) mud, the deposited mud goes through different physical states from suspension to soil, depending on its initial solid concentration, clay mineralogy, and weather condition, as illustrated schematically in Figure 1. These physical states are: o i) the hindered settling state, in this state, the settling velocity of a floc under gravity becomes smaller than its fall velocity due to hindering effect of the counterflow of water at high floc volume concentration; o ii) the first phase of consolidation, when flocs form a space-filling network (from gelling concentration onwards) and dewatering is governed by gravity-induced excess pore water pressure gradients and permeability at low effective stresses; o iii) the second phase of consolidation, in which effective stress development gradually reduces hydraulic gradients and slows down the dewatering induced by gravity; o iv) the desiccation state, that comes with its typical signature of crust and cracks, in which matric suction caused by evaporation is the main driving force for dewatering. In a mud deposit, water moves from high-pressure regions to low-pressure regions. The driving force for water movement in a one-dimensional vertical system is the gradient of excess pore pressure along with"
Keywords: Kleirijperij, clay ripening, building with mud, desiccation, consolidation