Nowadays, most of the large commercial/residential building structures and infrastructure projects such as road and rail tunnels, UG metro rails, mining tunnels, dams, hydro power projects, etc., involve huge underground constructions. During construction, design modification and adaptation of these structures are common, and civil engineers and project managers often encounter challenging issues and hazards on account of poor geology and groundwater constraints. Water flow under the ground is mostly unpredictable, abrupt, and destructive, which can have catastrophic consequences to structural integrity and longevity. Moreover, such projects are always expensive to build and need continual and high standards of maintenance.
Once water finds its way into the workplace (shaft, basement, tunnel, etc.), it seems to be very complicated to stop it. As soon as one leak is plugged, the water finds another gap, and a new leak appears in a formerly dry point.
Amongst the various options, Polyurethane injection grouting is the most frequently used defence against water ingress in tunnels or other underground structures, and as a remedial option to improve or restore the mechanical and sealing properties of soil and rocks. This has created a demand for high-performance grouting materials.
It is possible to use a wide range of techniques and products to control water ingress into underground structures and mining works. There are many products available for waterproofing, consolidation, sealing, bolting, crack and joint repairing, bonding and cavity filling. However, selection of the right grouting techniques, materials, and suitable equipment is of utmost importance for the successful and permanent arresting of leakages or say it different: what to use where and how?
Generally, the following parameters amongst others should be considered while deciding on grouting in below grade structures subjected to substantial water leakages, and for consolidation of rocks/soil.
– permeability or porosity of the concrete/rock mass or soil
– crack width
– substrate or crack movement
– water pressure and flow rate (amount of water infiltration)
– injection method as well as the right choice of materials and equipment’s mechanical properties, ambient temperature, etc.
Polyurethane (PU) injection grouts have become very popular over the last couple of decades, and are considered to be the most effective solution to inhibit heavy water leakages in below-grade or water retaining structures, as well as make the construction permanent sealed against water ingress. For decades, the polyurethane grouting was done using expanding polyurethane to cut off water flow through joints or cracks, and to fill voids beneath or behind the subsurface of the excavated area. The grout is injected with high pressure through a pre-drilled hole, which then expands to fill the crack or void. Polyurethane grouts can be used for both leak sealing structures against high water flow and ground consolidation.
PU grouting is performed to improve or restore the physical and mechanical properties of rock, soil, or building materials in construction. The main advantage of polyurethane is its versatility, and by the right choice of the raw materials, different properties can be given to the formulations: foam or a solid resin, hydrophobic or hydrophilic, rigid or flexible, short or long reaction time and low viscosities. Generally, water-reactive polyurethane is (with or without the addition of a catalyst) injected into the ground and cured with the water in the ground, yielding a foam.
Water-reactive polyurethane grouts are designed to react with water and depending on whether it is hydrophobic or hydrophilic expand in-place, forming a tight, impermeable, elastomeric seal that immediately stops the flow of water. Hydrophobic polyurethane grouts have the tendency that they start leaking again after short or long time. In a lot of countries, it is no longer accepted that it starts leaking again.
Further, as they are valid in many global areas, the standard requests a permanent seal of the leak. In the EU, a 10 years guarantee should be given on the injection work. Therefore, the standard is described as:
First stop or react the water away by using a foaming PU system
Then, seal it off with a solid resin: a flexible PU, a structural PU or EP
The consequence for this standard includes a need for 2 different injection systems, 2 different pumps and 2 packers.
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