Geochemistry of water glass injections

Water glass injection is an effective soil improvement technique for creating temporary water retaining layers or as (permanent) reinforcement of soil for supporting structures. In the past, the civil engineering community has paid particular attention to the strength properties of water glass and the practical aspects of soil injection.

The (geo)chemical background of water glass has, however, mostly been underexposed, while this could potentially answer questions about the application of water glass and hardeners in the soil and the effects on the functioning of drainage systems. The latter in particular regularly causes problems that are difficult to solve and costly. By knowing more about the chemical background, implementation risks can be reduced. In addition, given the 'crowding' in the soil, the simultaneous use of the subsoil for different functions and activities is increasing. Particularly because of the sensitivity of underground energy storage facilities to disturbance, it is becoming increasingly important to increase the efficiency of water glass injection in adjacent construction projects and to monitor and also reduce the influence of the subsurface.

Applications
In the Geotechnical Journal, CRUX published on the chemistry of water glass injections with application in civil engineering. This article (in Dutch) considers common questions that arise during construction. Of these, the lifetime of structural water glass injections is one of the open questions. Based on literature research and experience it is concluded that constructive water glass injections can have a long lifetime (50 to 100 years), but this depends very much on the soil and groundwater composition that is naturally present as well as the design of the injection. CRUX performs project-specific research to estimate the lifetime of water glass injections based on local conditions.

Another common question is the potential clogging risk of drainage wells in construction pits where water glass is used. The potential clogging mechanisms of drainage filters are related to the altered hydrochemistry and an increase in pH of the groundwater in the construction pit. The groundwater composition of the groundwater and mixing of water streams with different hydrochemical composition within the construction pit. Such mixing almost always results in the formation of chemical precipitates that lead to clogging. A management measure to minimize the risk of blockage is to control the mixing ratio in the pumped water by optimizing the position of filters and drainages.

Research
CRUX participates in the knowledge development of the (geo)chemistry in water glass injections by supervising student projects, project-specific studies and research at the universities. In this way the knowledge level on water glass injection is continuously developed.
An example of this is the emerging question about the risk of water glass injections on adjacent CHP systems for large buildings, which are placed ever closer together due to the "crowding" in the city. Whereby precisely those buildings that have large CHP systems are usually buildings with deep underground structures such as parking basements built in deep building pits with or without water glass injections. Assessing influence risks requires a complex analysis of reactive groundwater transport, which is often project-specific. Fortunately, the analysis can also be performed more easily. CRUX, together with Utrecht University, has determined the boundary conditions for the different mass fluxes of erosion from a water glass injection. The results are available through the Hydrogeology Journal. Based on the analysis in this article, the risk of influencing surrounding WKO systems can be estimated. This is relevant for the planning and execution of construction activities that take place right next to existing ATES wells.

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