Compensating grouts-Ground improvement
The grout will be injected at a level between the tunnel crown and the structures needed to be protected. Generally, the grout is injected from predrilled holes. These holes will be drilled radially from an access shaft, as shown in figure no:1. Tube-amanchette (TAM) grouting or similar techniques will be used to inject a controlled amount of grout to the soil. Before beginning with the grouting process. Soil should be preconditioned. Preconditioned performed by injecting grout locally so the soil will be compressed or fractured. Preconditioning of soil will allow efficient injection of subsequent grouts, so injections will have immediate effects on the ground. The volume of injected grout should be controlled. The volume of grout injected to soil should be enough to compensate for the change of soil volume due to tunnel construction. Usually, a low amount of grouts used. The amount of injected grout should be controlled to ensure that grout not traveling out of the compensation zone. The volume of injected grout will vary according to ground efficiency.
The grouting process should be monitored by instrumentations on the structures to protect the structure. Monitoring of the process will ensure that the compensating grout is done accurately. Injecting of grout will stop the settlement process, and this will generate a force downward. This force may affect the heading and the lining system of the tunnel. Therefore the level and position of grouting holes should be selected so it will not generate significant stress that can damage tunnel heading or lining system. Similarly, the position of grouting holes should be considered and selected carefully to avoid the damaging of existing tunnels.