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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Some of the important methods of tunnelling in soft rock are described in the following sections.
The support could be provided in the form of timber or steel plates or other similar material. The sides are excavated next and supported by crown bars and posts. This method is similar to the American method except that the roof load is supported by underpinning instead of using vertical posts.
The sidewalls and face of the tunnel can do without support for one or two hours, but the roof can last only a few minutes. Tunnelling may be basically divided into two main groups. These are described in detail in the subsequent sections. 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. The method, however, requires the construction of an additional tunnel and therefore the time and cost of construction are higher as compared to the methods described before.
Requires instant support for the roof but the walls can do without support for a few minutes. The pilot tunnel offers the following advantages. The material is excavated and deposited at the bottom of the tunnel. The drift is subsequently widened. Poles are then inserted at the top of the frame up.
This method is used for long tunnels, particularly those at great depths, where the walls of the excavation may yield under the weight of the cover. Field experience has shown that the central drift is the best choice, as it offers better ventilation and requires lower quantities of explosives. This method is possibly the most modern method of tunnelling. The equipment for tunnelling consists of a bulk head, which is an airtight diaphragm with an airlock.
In recent times, compressed air has also been used for this purpose. A shield is a device meant for excavation that is to be carried out beneath waterbearing strata.
Requires instant support throughout the excavation. The method has the following advantages.
Methods of Tunnelling
In the linear plate method Fig. A drift is driven into the top of the tunnel about 5 m ahead of the existing arch lining. Proper forrepoling should be taken to ensure that the material does not block the propelling jacks and other equipment.
The use of pressed steel plates is a recent development.
The various operations involved in soft rock tunnelling are as follows. The method has to be meticulously repeated in sequence and there is no short cut for the same.
Definition of forepoling
The excavation is carried out on the tunnelung and the excavated portion is suitably supported by timber. The needle beam is placed horizontally with its front end supported on the drift and the rear end supported on a vertical post resting on the lining of the tunnel. The bulk head shield is used in this case.
Forepoling is an old method of tunnelling through soft ground. Excavation is carried out and the soil is removed immediately after the excavation.
Definition of forepoling – glossary
During excavation, the rail requires support at the sidewalls and the roofs depending upon the type of soil. The side drift, however, has the advantage that it permits the use of timber to support the foreppling. In this method, the excavation is carried out along the perimeter or periphery of the section.
In this case, the heading is excavated first and supported by crown bar posts and laggings. The types of ground which are generally encountered in the field are detailed in Table Other details regarding tunnelling in such a soil are the same as for sand.
In this case, tunnelling is of the open type. The sides of the drift are then widened and additional support is provided using timber planks and struts. The determination of this value depends more on experience than on technical considerations. This method is particularly suitable for areas where the height of the overburden is less and the surface is forepolinb to be disturbed.