Pre Injection is cost effective in the following:
- Water Ingress reduction
- Ground zones with fractured rocks or weathered rocks
- Unstable ground
- Structural cracks in concrete
- Unexpected water ingress
- Rehabilitation in concrete structures
The packer is attached to the injection pipes and pushed into the drilled hole. The innermost of the two injection pipes has a tightening lever for fixing the packer. The packer is expanded in the drilled hole using the tightening lever. Cement mixture or chemical substance is injected into the rock’s crack system through the rubber valve in the packer.
- Microfine Cement MICROCEM 8000
- Ultrafine Cement MICROCEM 12000
- Injection Resins RESFOAM 1KM /FOAMJET / MAPEJET SYSTEM
- Desired fluidity
- Setting time / gelling time
- Strength required
Filtration Ability Against Pressure
The coefficient of filtration ability against pressure shows the ability of the fluid to keep the initial characteristics even in the presence of pressure.
In case of heavy ingress of water, it’s better to go for a fast setting injection of resins. Generally, polyurethanes like RESFOAM 1KM or FOAMJET are better. Double component are faster in setting whereas the time of setting of Single component can be controlled if it has to be injected for a longer distance with an accelerator. Also, Nano Silica based injection material is used; it generally has particle sizes of less than 0.1 micron like the Mapejetsystem NS15.
Colloidal silica gel is a “mineral grout” and not a chemical grout It is a stable liquid containing single, sub-microscopic particles of silica oxide. To make it gel, a weak solution of salt water is mixed prior to pumping. The more salt water added, the faster the gel time. It is environmentally friendly and durable, as it is simply composed of quartz sand, water and salt. Having the consistency of water, it penetrates sands and fine fissures very easily. It is extremely user-friendly as a standard cement grout equipment can be used and cleaned with water.
In Grouting the most important is the GIN (Grout Intensity Number). GIN grouting intensity values were defined as the product of the final grouting pressure and absorption per meter for a given single borehole, within a certain period at the end of grouting the result is a constant value.
GIN = PV
where P is the final grouting pressure and V is the ultimate grout take which means the energy consumption per unit grouting period
- Alluvial Soil Grout pressure: low, average 2-4 bar, maximum 7-10 bar
- Cracks in Rock Grout pressure: High, average 30-40 bar, maximum 70-80 bar
Post Injection: Basic features
Reactive mindset: post-injection is conducted when collapses have occured already or uncontorolled water inflow is occuring; or where rehabilitation of leaking tunnels is required; or drilling holes to intersect joints with high water inflow, or pushing slotted pipes into unstable ground masses. These may need specialised drilling equipment such as Odex, Self drilling anchors and packer injections, utilization of expensive, highly reactive chemicals - usually PUs in geotechnical problems and acrylates in rehabilitation problems.
Single Component Polyurethane or Double Component Polyurethanes can be used, or Acrylates. To stop water ingress immediately the Polyurethane can be injected and then acrylates can be injected into joints or cracks. Various Tunnel linings have used the leakage control method with Polyurethanes like RESFOAM / FOAMJET and Mapegel UTT.
Injection in fissures:
- Extremely low viscosity
- Resin should also be injectable when gelling has commenced
- Gelling properties, accurately adjustable
- Acrylates for the injections in and immediately behind deteriorated concrete lining
- Polyurethane (Resfoam 1km) for the improvement of ground, void filling and water seepage reduction
- Taylored cement-based grout for improvement of ground behind concrete and masonry lining
- Sprayable waterproofing membrane on old tunnel lining
- Eventual sprayed concrete
Grouting is a design choice: Pre-injection vs Post Injection
Pre-injection – proactive, relies on effective probing and decision making at the face, cheap materials, 10 to 50 times then post, pre-injection often difficult in soft ground tunneling.
Make the right choice of materials for the right situation at the design stage and tender for it.
Cannot rely on contractors to price for the unforeseen, provisional sums in contracts required giving contractor all available tools necessary to do the job straight away.
Mapei India provides a complete system of Pre Injection and Post Injection for Civil Engineering Projects.