i. A method of advancing a mine working or tunnel in loose, caving, or watery ground, such as quicksand, by driving sharp-pointed poles, timbers, sections of. 2 Sep needle beam method of tunneling ppt For easy office pdf filter the excavation and temporary support of the station tunnel, a forepoling method. The following methods are generally employed for tunnelling in hard rocks. Full face method . Forepoling is an old method of tunnelling through soft ground.
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The full face method is normally selected for small tunnels whose dimensions do not exceed 3 m. In this method, a small drift is prepared for inserting a needle beam consisting of two rail steel RS joists or I sections and is bolted together with a wooden block in the centre. In this method, a frame is prepared in the shape of the letter A, placed near the face of the tunnel, and covered with suitable planks. Next the muck is removed before repeating the process of drilling holes.
Some of the important methods of tunnelling in soft rock are described in the following sections. The entire section of the tunnel is covered thus. The sides of the drift are then widened and additional support is provided using timber planks and struts. During excavation, the rail requires support at the sidewalls and the roofs depending upon the type of soil.
The pilot tunnel offers the following advantages. The method has the following advantages. In this case, the heading is excavated first and supported by crown bar posts and laggings.
Definition of forepoling
The material is excavated and deposited at the bottom of the tunnel. The equipment for tunnelling consists of a bulk head, which is an airtight diaphragm with an airlock. There are various methods of tunnelling.
Tunnels constructed using the shield method usually have a circular section because of the following considerations. This method is particularly suitable for areas where the height of the overburden is less and the surface is not to be disturbed.
The side drift, however, has the advantage that it permits the use of timber to support the roof.
Jacks are fixed on the needle beam and the tunnel section is excavated forepling suitably incorporating timber. The sill is then extended across the tunnel and the extended piece is supported by underpinning.
Requires instant support for the roof but the walls can do without support for a few minutes. In recent times, compressed air foerpoling also been used for this purpose. Wall plates are fixed at the springing level, which in turn are supported by vertical posts.
Methods of Tunnelling
Shield tunnelling is generally preferred in such cases. Examples include dry sand, gravel, silt, mud, and water bearing sand. The cross section of the pilot tunnel usually measures about 2.
Examples include firm clay, gravel, and dry earth. This method of tunnelling is more economical compared to other methods.
Methods of Tunnelling
The process is repeated as the work progresses. The work is carried on till the springing level is reached.
The support could be provided in the form of timber or steel plates or other similar material. The types of ground which are generally encountered in the field are detailed in Methkd The tunnel is excavated and lined under the protection of the shield.
It involves excavating the whole section for a short length and furnishing with sidewalls and an arch. The bulk head shield is used in this case. The various operations involved in soft rock tunnelling are as follows. A drift is driven into ot top of the tunnel about 5 m ahead of the existing arch lining.