Development of a nature-based Geo-engineering solution to reduce soil permeability in-situ

Stability of dikes is a national security issue for densely populated low-lying countries situated in delta areas, like the Netherlands. One of the dominant dike failuremechanisms in the Netherlands is piping, where high seepage flow rates transport sand particles and subsequently form a ’pipe’ under a dike structure. As such, one manner to reinforce dike lies in the modification of the seepage flow field. Though many of conventional approaches have demonstrated varied degree of success in creating flow barrier, which is a subsurface structure that can alter the seepage flow field, they are commonly costly in terms of energy and labour. Facing the ever-growing awareness of climate change as well as the large economic scale of the dike stability issue in the Netherlands, the development of alternative techniques is thus desired. The focus of this research project is to develop a cost-effective, robust and environmentally compatible technology for insitu permeability reduction of sub-surface systems. We took inspiration from nature, where a natural soil stratification process (namely Podzolization) shows the viability of organo-metallic complexes precipitation in reducing soil permeability in-situ. The aim of the research presented in this thesis is to quantitatively study the feasibility of using Podzolization-derived approaches to install flow barrier in dikes. Chapter 2 of this thesis presents two approaches for applying organo-metallic complexes to reduce soil permeability in-situ, which are derived from the detailed analysis of Podzolization and the flocculation process between metal salt with organic matter. The first approach bases on the in-situ mixing and reaction between two components (i.e., aluminium (Al) and organic matter (OM) solutions), while the second approach makes use of the direct injection of Al-OM flocs. To understand the feasibility of using these approaches to install flow barrier on site, a 3D process-oriented model was developed. An important aspect of this model development is to incorporate engineering conditions on site into the simulation of processes. A series of scenario analyses were therefore performed with the model in order to facilitate the design and evaluation of the full-scale experiments where the two delivery approaches were applied to install a flow barrier in two dikes.