Could you please explain:

1. forepoling method
2. cantilever car dump method

Answer:

1. Forepoling is a method of advancing a mine working or tunnel in loose, caving, or running ground, such as water bearing sand or silt, by driving sharp-pointed poles, timbers, sections of steel, or slabs into the ground ahead of, or simultaneously with, the excavation. Forepoling is generally employed under the following conditions: the existence of shallow overburden above the tunnel; the need to restrict ground subsurface settlement; and poor ground conditions.

   There are three different methods of forepoling commonly used in tunneling:

   • Sub-horizontal jet grouting - Jet grouting is used in especially difficult conditions where both weak soils and thin overburden occur. Jet grouting is normally used in sandy or gravel formations.

   • Spiling - The spiling method consists of drilled steel pipes, grout inside the pipes and in voids outside, treated ground by permeation or fracture grouting and steel arch supports. Injection is the essential part of this system in forming the arch-like structure. Grouting is done to strengthen weak and loose soils, to decrease permeability, to reduce subsidence effects caused by dewatering and to stabilize sandy soils.

   • Pipe roof - Forepoling in the pipe roof method is formed in a crown of a tunnel by installing a series of large diameter steel or concrete tubes in an arch or a ring. This is done when overburden is especially thin. Typical installation methods are by pipe jacking and other micro tunneling methods. Pipe roof method pipes are designed to carry longitudinal loads only. They are typically made from open shafts and can be driven parallel to the tunnel axis.

2. The cantilever dump method is a means of transporting spoils from a tunneling operation from the excavation face, through and out of the tunnel. In this method, cars are automatically and continuously transporting spoils out of the tunnel were they automatically tip to the side to expel the spoils to a spoils pile or other spoils transportation operation. It is often used as part of the Sequential Excavation Method (SEM). This method is based upon excavating the tunnel face either in whole or via pilot drives using backhoes or road header equipment. The excavated face is given a temporary lining of shotcrete, reinforced with steel ribs or reinforcing to minimize the relaxation of the in-situ stresses in the soil. The success of this method is dependent on minimizing the time between excavation and lining procedures. The cantilever dump method can be an efficient method for transporting spoils from the excavated face thus facilitating the SEM method. Another method commonly used to transport spoils with the SEM methods is a continuous conveyor system