Grouting is one of the original trenchless rehabilitation methods and has been in use for over 50 years. Through this method, sewers are repaired and sealed without excavation resulting in financial savings and reduced time taken to execute a repair.
The most common use of grouting in trenchless projects is to seal leaking sewers. A leaking sewer can contaminate the surrounding ground with its contents if the groundwater pressure is low. However, in cases where the groundwater pressure is high, water leaks into the sewer adding to the flow and overloading downstream processing units. Some reports say that as much as 50% of the waste water reaching treatments plants comes from groundwater entering leaking sewer pipes. It is not only water that enters these leaks, but fine sand particles too. Sand particles build up in the sewer over time creating blockages in the system.
Here are the ways grouting is used in trenchless projects.
Injection grouting is the original trenchless repair method using grout to seal leaking pipes and sewers. It is a simple process involving the use of a packer on the inside of the pipe to inject grout through the defect. The grout fills the leak in the pipe wall or joint and enters the surrounding soil. As it hardens, it stabilises the soil and forms a tight seal in the defect.
In the early days, injection grouting was seen as a temporary repair, but as technology has improved and engineering practices have been refined, injection grouting has found its place as a repair method that can be expected to last. Injection pressure, grout additives, packer design and the injection technique itself have all been refined to improve the performance of this trenchless rehabilitation method.
Injection grouting is also used as a precursor to Cured-in-place-pipe (CIPP). By using injection grouting, the external pipe can be leak proofed thus preventing any water ingress, which could affect the curing of the pipe sleeve for CIPP.
Sliplining and Grouting
Sliplining, is a trenchless rehabilitation method whereby a smaller diameter pipe is inserted into a leaking pipe in order to provide a new leak free carrier for the product. Pipes used for sliplining are typically High Density Polyethylene (HDPE) or Polyvinyl Chloride (PVC). The operation is carried out by jacking the new pipe into the old, or by winching it through from the destination end. Once the slipline pipe is in position, grout is used to seal the gap between the new pipe and the old.
It is important to grout the gap between the pipes because this will prevent the collapse of the older, leaking pipe over time into the newer pipe. Grouting the gap provides increased strength to the inner pipe and protection from the surrounding environment. Different types of grout can be chosen depending on whether the pipes are to be fused together for strength or whether the purpose is mainly to keep the smaller pipe in position.
A disadvantage of the sliplining and grouting method of repair, is that any lateral connections have to be reinstated after installation. This requires excavation and manual intervention at each lateral connection.
Jet grouting is a trenchless construction method used to stabilise ground in advance of further construction activity. Jet grouted columns are created in the ground by injecting a cement mixture (grout) at high pressure and flow rate into the soil. As the grout sets, it forms a stable column in the ground. A number of columns are normally created alongside each other depending on the engineering requirements for the specific project.
Jet grouting systems are classified as single fluid (grout), double fluid (air together with grout) or triple fluid (air, water and grout). Triple fluid systems are the most effective as the air and water jets remold the soil around the drill string, while the grout is injected separately. This generates a more even distribution of grout into the soil and a more solid column of grout.
Jet grouting is used to construct horizontal barriers, underpin foundations, and stabilise ground where trenchless construction is in process.
Shoring and Grouting
Shoring is the process of supporting the walls of an excavation or other sloped ground in order to prevent collapse of the soil and injury to workers or damage to property. A number of different methods are used for shoring depending on the depth of the excavation and the condition of the ground. Grout is used along with soil anchors to seal a sloping face of soil. Soil nails are typically metal rods that are drilled into the ground at a slightly downwards angle, and then grouted into position. A concrete spray is then applied to the surface and the combination of the grouted in nails and surface grout covering provides stability to the soil.
Grouting is an integral component of trenchless projects
Grouting is a well established method used in trenchless projects in many different ways. It’s long history of effectiveness and usefulness to seal leaks, and provide stability to excavations or unstable ground is sure to keep it on the forefront of trenchless projects for many years to come.