JPH04254694A - Tunnel construction method - Google Patents

Abstract

PURPOSE:To reform the natural ground around the front part of a facing before excavating the facing into the arch of very strong glassy solids. CONSTITUTION:Before excavation, plural guide holes 2 are excavated at given intervals along the circumferential figure of a scheduled excavating cross section A, diagonally upward extending toward the natural ground E above the facing 1a. Electrode bars 3 of low electric resistance are inserted into the guide holes 2 and a heavy electric current is applied to the electrode bars 3. This causes the sections between adjacent electrode bars 3 to be heated and thus silicon in the soil to be melted. Owing to cooling of the melted sections, the arch of mutually integrated glassy solids 5 is formed along the circumference of the scheduled excavating cross section A.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tunnel construction method in which, prior to excavation of a tunnel face, the ground around the front side of the tunnel is modified into an arch made of a high-strength glass-like solid body.

0002

[Prior Art] When excavating a tunnel using the mountain tunnel method in unconsolidated or soft ground, it is necessary to prevent the top of the tunnel from collapsing and subsidence of the ground surface, and to promote self-supporting of the face. Improvements will be made. Conventionally, this improvement method has generally been carried out, for example, by injecting special chemicals, jet grout, or other chemicals around the excavated cross section, or by using hollow bolts to inject chemicals, but this type of injection method is as follows: There were problems described in .

0003

[Problems to be Solved by the Invention] First, this construction method has the problem of contaminating the soil and groundwater with the chemical solution. Furthermore, even if this contamination problem can be ignored, the amount and range of chemical injections depend on the water permeability of the ground and the condition of cracks, making it difficult to predict and manage accurately. For this reason, for example, problems have arisen in terms of safety due to a lack of the expected improvement effect, and conversely, problems in terms of economy and construction period due to an unnecessary increase in the amount of chemical solution injected.

[0004] This invention solves the above problems, and aims to provide a tunnel construction method that can transform the ground itself around a tunnel into a high-strength ground without using chemicals. There is.

[0005]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the construction method of the present invention includes, prior to excavation of a face, a circumferential shape of a planned excavation cross section toward the ground at least on the upper front side of the face. A plurality of electrode rods are inserted at predetermined intervals along the electrode rods, and a current is passed between each electrode rod to generate heat in the area of the ground located between the electrode rods, melting it into a glass-like state. By cooling, the glass-like solid body is formed into an arch shape.

[0006]

[Function] In the above construction method, the arch of the glassy solid body formed inside the ground along the planned cross-sectional shape of the excavation has extremely high strength and prevents the collapse of the top of the tunnel and the subsidence of the ground surface. Serves as a permanent structure for.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIGS. 1(a) and 1(b) show the tunnel construction method of the present invention.

The tunnel 1 in the figure is constructed by the mountain tunnel construction method. This mountain tunnel construction method, as is well known, is a construction method in which a hole is drilled in the face 1a of the tunnel shaft 1 using a rock drill, and then blasting is set there to crush the face 1a while excavating. In this invention method, prior to the above excavation work,
The purpose is to improve at least the ground E on the upper side of the tunnel shaft 1, and first improve the ground E on the upper side of the tunnel face 1a by making multiple improvements at predetermined intervals according to the circumference of the planned excavation cross section Drill the guide hole 2 diagonally upward.

[0009] The length and angle of the guide hole 2 are set to at least several meters to more than ten meters, taking into account the amount of excavation at one time and the thickness of the ground E to be improved. Moreover, it is desirable that the drilling interval between the respective guide holes 2 is set to about 1 to 2 m to 7 to 8 m in consideration of inter-electrode resistance, which will be described later.

[0010] After completion of the drilling work, an electrode rod 3 having low electrical resistance is inserted into each conducting hole 2. Next, each electrode rod 3 and several thousand
When the high current generator 4 of KW power is connected with the polarity alternated between the adjacent electrode rods 3, and then the device 4 is turned on and a large current is caused to flow, the ground existing between the adjacent electrode rods 3 is connected. Joule heat of over 1000°C is generated by the resistance of the mountain E, and this heat melts the silicon components in the soil included in the approximately elliptical area surrounded by diagonal lines in the figure. When the current is cut off in the molten state, the molten part cools down, and an arch of the glassy solids 5 of a predetermined thickness and length is formed along the hatched part in a mutually integrated state, forming the planned excavation cross section A.
are integrally joined along the outer periphery of the Each solid body 5 is glass-like and is integrally formed by connecting them between each electrode 3, so its unconfined compressive strength is 1000 Kg/cm2 or more, making it an extremely high-strength permanent structure. .

[0011] After the above improvement work is completed, the inner circumferential side where the consolidated body 5 is formed is excavated along the planned excavation cross section A using blasting or the like, and is covered once with concrete or the like. complete a cycle of excavation operations. Below, the boring of the guide hole 2 and the insertion of the electrode rod 3 before the excavation work,
Excavation is repeated while forming an arch of the solid body 5 in sequence by applying current.

Furthermore, since the arch of the consolidated body 5 is an extremely strong layer and the melting range varies depending on the geology, it is not formed in direct contact with the outer periphery of the planned excavation cross section A, but rather with a certain degree of unconsolidation. It is desirable to form through layers. For this purpose, if an insulator 3a or the like is provided on the outer periphery of the part of the electrode rod 3 located on the entrance side of the conducting hole 2, as shown in a partially enlarged view in FIG. The portion connecting the insulators 3a remains unmelted and remains as a rock, making subsequent excavation easier and allowing for accurate excavation along cross section A.

[0013] The electrode rod 3 may be introduced by directly penetrating it instead of by drilling and inserting the guide hole 2.

[0014]

Effects of the Invention As explained in detail in the examples above, the tunnel construction method according to the present invention melts and solidifies the ground itself, so there is no need for materials such as chemical solutions, and soil contamination is avoided. It is economical because it does not involve groundwater contamination or groundwater contamination, and it does not require cycle time such as chemical injection time or solidification time, and it is possible to improve the ground in a relatively short time. In addition, in this invention, the improved and strengthened range is predictable to some extent and management is relatively easy, and since an extremely strong arch is formed on the outer circumference of the tunnel, the top of the tunnel There will be no collapse, improving safety during excavation.

[Brief explanation of the drawing]

FIG. 1(a) is a front cross-sectional explanatory view showing a tunnel construction method according to the present invention. (b) is also a side cross-sectional explanatory view.

[Explanation of symbols]

1 Tunnel pit 2 Guide hole 3 Electrode rod 5 Glassy solids

Claims (1)

[Claims] 1. Prior to excavation of a face, a plurality of electrode rods are penetrated at predetermined intervals along the circumference of the planned excavation cross section toward the ground at least on the upper front side of the face, and each electrode The feature is that by passing an electric current between the electrode rods, the parts of the earth located between the electrode rods are heated and melted into a glass-like shape, and then cooled to form a glass-like solid body in an arch shape. construction method for tunnels.