Settling behAvior of fine-grained bLasted and crushed rOck fRagments
Table of contents
Project Description
Tunnel excavation and rock crushing generate fine mineral particles that may enter rivers, coastal waters, and fjords. SAILOR investigates how salinity, particle size and shape, mineralogy, electrostatic interactions, contaminants, and hydrodynamic conditions control their flocculation and settling. Sediments collected from Norwegian tunnel-construction sites are examined through bulk-settling experiments, microscopy, floc visualization, and ζ-potential measurements. The project aims to identify when fine particles settle near their discharge point and when they remain suspended and spread, supporting environmentally responsible water-treatment and discharge strategies.
The Science: Settle or Spread
The Problem
Fine rock particles released to water bodies during tunnel construction can remain suspended for long periods, increasing turbidity and transporting contaminants away from the discharge point. In Norwegian coastal environments, their fate depends strongly on the transition from freshwater to saline fjord water. Salt can promote particle aggregation and settling, but the response varies substantially between sediments. Particle morphology, mineral composition, surface charge, contaminants, and turbulence jointly determine whether particles form stable flocs or remain dispersed. SAILOR therefore addresses a practical question: under which environmental conditions will tunnel-derived fines settle locally, and under which conditions will they spread through the receiving water body?
Entanglement vs. Electrical Repulsion in the Settling Process
Elongated and irregular particles can interlock or entangle, producing flocs whose settling behaviour depends on particle size and aspect ratio. Conversely, similarly charged surfaces generate electrostatic repulsion, quantified through the ζ-potential, which can maintain dispersion. Coagulation is the destabilization of particles through reduced electrostatic repulsion. Flocculation is their subsequent assembly into larger, settling aggregates. Salinity screens surface charges and can shift the balance from stable suspension towards coagulation, floc formation, and settling.
Schematic representation of the electrical double layer according to DLVO theory. (a) Two negatively charged particles in DI water with a Stern and expanded diffuse layer. Water molecules illustrate the thermally induced Brownian motion. Electrostatic repulsion(VR) dominates over van der Waals attraction(VA); the slipping plane (⇣-Potential) is indicated.(b)Addition of NaCl results in cation adsorption in the Stern layer and compression of the diffuse layer, reducing electrostatic repulsion.(c)Addition of divalent Ca2+ leads to stronger diffuse layer compression and enhanced
Our Methode
SAILOR combines complementary experiments to connect suspension-scale clarification with particle- and floc-scale mechanisms.
Bulk Setting
Changes in transmitted light reveal how rapidly particles leave suspension. This provides a direct measure of clarification and identifies the salinity ranges in which settling is enhanced or suppressed
Transmitted Light Setup
Floc visualization
Microscopic imaging tracks the formation, structure, growth, and breakup of particle aggregates. It links individual particle properties and floc morphology to their effective settling behaviour.
Setup for Visualizing Flocculation
Influence of cement and salinity
The diagram illustrates how salinity and cement contamination modify particle interactions. Salinity generally reduces electrostatic repulsion and promotes aggregation, whereas cement alters water chemistry, surface charge, and floc structure. Their combined effect determines whether compact settling flocs or persistent fine suspensions develop in time.
Representative micrograph images of individual flocs in saltwater(35PSU) observed at different times and shear rates G for pure sediment and sediment containing 9
Project Objectives
- Determine whether tunnel-derived fine sediments settle locally or spread through saline Norwegian fjords.
- Quantify how salinity, particle morphology, surface charge, contaminants, and shear govern flocculation and settling.
- Develop experimentally supported guidance for sediment management, water treatment, and environmentally responsible discharge.
Project Team & Funding
Principal Investigator
Prof. Dr.-Ing. Bernhard Vowinckel (TU Dresden)
Lead Research Associates
- Dr. Franco Tapia
- Dipl.-Ing. Gerit Orzechowski (TU Dresden)
Lead researchers responsible for the experimental campaigns, method implementation, quantitative data analysis, and physical interpretation of particle flocculation and settling.
Funding Body
Norwegian Public Roads Administration (NPRA)