KR20040102613A - 2-arch tunnel method controlling the load of tunnel - Google Patents

Abstract

PURPOSE: A two-arch tunnel construction method with load control is provided to construct the tunnel safely by measuring and controlling load of the tunnel to a central support structure, and to reduce the construction period and damage by separating the central support structure into the load control structure and the reinforcing concrete. CONSTITUTION: A central tunnel(1) is excavated, and a load control structure(2) is installed. While excavating a side tunnel(4), load applied to the load control structure is measured and controlled to the desired support load. The load control structure is reinforced with reinforcing concrete(3), and a central supporting structure is finished. The tunnel is constructed safely at a low cost by measuring and controlling the tunnel bearing load to the central supporting structure of a two-arch tunnel. The load control structure is manufactured with a steel structure with a hydraulic screw jack, and the hydraulic jack is removed after checking the final load.

Description

2-ARCH TUNNEL METHOD CONTROLLING THE LOAD OF TUNNEL}

The present invention relates to a two-arch tunnel method and a central support structure (2) for the present method, which is applied to civil engineering such as roads and subways, and more particularly, a load acting on the central support structure (2) when excavating a two-arch tunnel. By constructing and controlling tunnels, economic and safe tunnels are constructed. One embodiment for carrying out this is directed to a central support structure (7) reinforced with a load control structure (2) consisting of a hydraulic screw jack (14) and a roller point (9).

In the civil engineering field, the two-arch tunnel is applied to secure a wide underground space in the horizontal direction such as subway tunnel station and four-lane road tunnel. However, in the conventional two-arch tunnel method, after excavating the central tunnel 1, the central support structure made of reinforced concrete is constructed as a permanent structure, and the side tunnel 4 is excavated. According to this construction method, the existing method has the following problems.

First, the existing two-arch tunnel construction method excessively increases the load on the central support structure, making it difficult to apply to large-depth tunnels that are uneconomical and have large vertical loads.

1 Arch tunnel uses livestock support materials to reduce the loads on the support materials. In designing, it is possible to design tunnels economically by reducing the loads on the support materials by using the load sharing ratio. In general, the applied load sharing ratio is 40-30-30, which means that 40% of the excavation equivalency is all burdened by the ground, 30% is ductile shotcrete and the ground, and the last 30% is rigid. The shotcrete and the ground share. Therefore, it is going to raise the load ratio which the ground shares.

However, in the existing two-arch tunnel, the central support structure and the ground share all 100% of excavation strength by completely hardening the reinforced concrete, which is the central support structure, before the side tunnel is excavated. Therefore, it is made of a design concept that is uneconomical compared to one-arch tunnel. In a tunnel with a depth of several hundred meters where the vertical load is large, the load that the central support structure shares is very large, which causes a lot of difficulties in design.

Second, the existing method does not have a system that can accurately determine the load acting on the central support structure, and even if it is confirmed, it is difficult to take measures against the expected problems.

Since the center supporting structure is composed of reinforced concrete structures, the strain gauge should be attached to the surface of the central supporting structure and the internal reinforcement to check the working load. However, since the construction of the central support structure is completed, it is impossible to reduce the cross section by changing the design according to the measured result when the tunnel load is smaller than the load expected at the time of design. It is also difficult to take countermeasures when design loads are found to be exceeded.

Third, the existing construction method provides a single central support structure type for various tunnel conditions, resulting in uneconomical design and construction.

The ground load to be supported in tunnel excavation is varied by various influence factors such as ground strength, ground deformation characteristics, toffee, side pressure coefficient, construction method, tunnel shape. Therefore, it is almost impossible to accurately estimate the tunnel load at the design stage. In general, one arch tunnel has been proposed and used according to tunnel conditions by many construction experiences, but in the two arch tunnel, there is no such empirical support pattern.

Therefore, the load calculated by the numerical analysis performed with the limited input data is applied and the design is made considering the considerable safety factor. The safest design method is to load all the excavation equivalents to the central support structure, and the general method is to make the central support structure bear 50% of the excavation equivalents. This method is also based on the assumption that the vertical load is simply the toffee load and cannot be seen as an accurate excavation equivalence. As the share of excavation equivalence can be changed by the stiffness difference between the two-arch tunnel sidewall and the central support structure, it is not certain about safety.

Fourth, horizontal excavation pressure is generated during the excavation of the side tunnel, which induces a moment in the central support structure.

When a moment occurs in the central support structure, the compressive stress increases, which is structurally disadvantageous. In underground tunnels, the level of horizontal earth pressure is small due to the flat surface, but in mountain tunnels, the level of horizontal earth pressure due to terrain and ground stress can affect tunnel safety. In addition, horizontal excavation pressure is generated when the side tunnel cannot be excavated at the same time during construction.

Therefore, it is necessary to take countermeasures when excessive horizontal earth pressure is generated, but it is difficult to prepare countermeasures in the existing two-arch tunnel method.

Fifth, since the central support structure is installed as a reinforced concrete permanent structure, damage caused by blasting shock occurs during blasting excavation.

If damage caused by blasting occurs, it is very difficult to repair it. Therefore, mechanical excavation should be carried out as much as possible, and there is considerable limitation in application when construction cost increases and blasting excavation is required.

Sixth, since the side tunnel can be excavated after the installation of the central support structure is completed, the side tunnel can be excavated only 28 days after completion of the installation of the central support structure, thereby increasing the air.

Looking at the design concept of the existing two-arch tunnel containing this problem is as follows. Rather than allowing the tunnel to bear the tunnel bearing load by allowing deformation of the tunnel excavation ground, the deformation is suppressed as much as possible to prevent an increase in tunnel bearing load that may occur after proper deformation. It is problematic to disallow proper strain generation based on the theory that the tunnel support load increases when a loosening zone occurs.

According to the above design concept, the existing two-arch tunnel design was based on the following two assumptions.

First, when the deformation of the central tunnel is tolerated, the tunnel load increases.

Second, the intermediate supporting structure can bear the tunnel supporting load due to the side tunnel excavation.

Therefore, the central support structure should bear a large part of the tunnel support load or tunnel excavation equivalence required to prevent tunnel collapse during tunnel excavation, similar to the concept of the previous ASSM method, without following the tunnel design concept proposed by NATM. will be.

Due to the above problems, the scope of application of 2 arch tunnel is very limited. However, as the depth of the subway deepens, the need for tunnel stations increases, and as the traffic volume increases, the number of lanes adopted from two-way lanes to four lanes increases, and the need for two-arch tunnels increases. Therefore, the development of a method for solving the problems of the existing two-arch tunnel is very urgent situation.

An object of the present invention is to devise in consideration of the problems of the existing two-arch tunnel described above, the tunnel acting by installing a central support structure (7) that can measure and control the load generated by the side tunnel (4) excavation The tunneling method is designed to excavate the side tunnel while measuring and controlling the load.

Another object of the present invention is to separate the central support structure into the load control structure (2) and reinforcement concrete (3) to minimize damage during air shortening and blasting excavation, upper roller point (9), parallel hydraulic To provide a load control structure (2) attached with a screw jack (14).

Based on the concept of NATM, this tunnel method and the central support structure were used to achieve the following technical tasks.

First, secure design verification data by measuring the load acting on the central support structure.

Second, the reduction of the load acting excessively on the central support structure.

Third, the reduction of horizontal seismic pressure acting on the central support structure.

Fourth, minimizing damage caused by blasting excavation.

Fifth, suppression of air increase by installing central support structure.

1 is a perspective view showing an embodiment of a two-arch tunnel construction according to the present invention

Figure 2 is a cross-sectional view showing an embodiment of a two-arch tunnel according to the present invention

Figure 3 is a perspective view showing an embodiment of the load control structure constituting the central support structure according to the present invention

Figure 4 is a cross-sectional view showing an embodiment of the load control structure constituting the central support structure according to the present invention

※ Explanation of code for main part of drawing

1: central tunnel 2: load control structure 3: reinforced concrete

4: side tunnel 5: concrete lining 6: (left) side tunnel

7: Central supporting structure 8: Right tunnel 9: Roller branch

10: support steel plate 11: steel support plate 12: steel plate

13: Steel column 14: Hydraulic screw jack 15: Concrete foundation

16: drain pipe 17: induction drain pipe

1 is a perspective view for explaining an embodiment of the load control two-arch tunnel method, Figure 2 is a cross-sectional view.

The basic procedure of this tunnel method is as follows.

1. Excavate the central tunnel (1) and install the load control structure (2).

In one embodiment, the steel support beam 11, the four-beam steel 12, the steel column 13 of the load control structure is made of H-shaped steel and the specification is 350 × 350 × 19 × 19. The support steel plate 10 is made of a 50 mm thick steel plate with a length of 5.0 m. Roller point (9) is a 10mm diameter, 350mm long round steel bar, both ends are welded to the support steel plate (10) and the inside is painted with grease to facilitate the activity.

When the width of the tunnel is D, the tunnel deformation starts at a distance about 3D from the front of the curtain, and the deformation rapidly increases at the curtain and converges at a position 3D behind the curtain. Therefore, the load control structure 2 is installed at intervals of 1M up to 3D in front of the side tunnel 4. Batch spacing is basically defined as 1.0M, but the spacing can be adjusted according to tunnel conditions.

2. Measure the load acting on the load control structure (2) while excavating the side tunnel (4) and control it to the desired support load.

Tunnel load generated by digging side tunnels is measured by hydraulic gauge attached to load control structure. Since about 30% of the total shear settlement to the curtain is generated, if the load generated on the load control structure installed in front of the curtain is within 30% of the allowable load, the load control is not necessary and the placement interval of the central support structure is considered considering economic efficiency Increase.

When the load exceeds 30% of the allowable load, the tunnel load is adjusted by using a hydraulic screw jack to generate a displacement to the position where the tunnel action load converges. The load for each position is expressed by the following formula F = 1 / [1+ exp ( -x / 0.55)] ^ 1.7. Where x = distance from the barrier, F = center load structure allowable load ratio. This formula proposed by Chern et al (1998) suggests the settlement amount by tunnel location and can be used as the supporting load of the rational location center support structure. If a hydraulic control valve is installed that allows displacement but cannot exceed the set pressure, the displacement can be adjusted automatically.

By measuring and controlling the load acting on the load control structure in the same way as above, it is possible to construct a two-arch tunnel by checking the tunnel load and reducing it when excessive load occurs. In addition, it is possible to verify the feasibility of the design and to change the design by analyzing the load generation trend and performing feedback in comparison with the design conditions.

3. Finally, reinforce the load control structure (2) with reinforcement concrete (3) to complete the central support structure (7).

The load control structure is reinforced with concrete to protect against tunnel fires, vehicle collisions and steel corrosion. In addition, in order to use the central support structure as a permanent structure, it is completed with steel concrete made of load control structure and concrete to secure additional safety factor.

What is important in this method is how much the allowable load of the load control structure is determined. Allowable loads are to be determined taking into account the ultimate bearing capacity and safety factor that the central support structure can support. This is directly related to the cost of construction and directly related to securing the safety factor.

As an example, assuming that the tunnel topi height 100m, tunnel width 25m, and ground unit weight 2.0tf / m ³ , the vertical load of excavation equivalence due to tunnel excavation is 100 × 25 × 2.0 = 5,000 tf / m. In the conventional way, the maximum load on the central support structure is 2,500 tf / m. However, if the load that the central support structure is to support is the ground load that requires additional excavation when constructing with one arch tunnel, the two arch tunnel width is 25m, and the upper half of the tunnel is 25 ^ 2/4 × π ÷ 4 × 2 = 245 tf / m.

Therefore, if the center supporting structure is allowed to be deformed, the load to be supported can be reduced by 90% compared to the existing method when the tunnel topi height is 100m. In addition, if the ground is good, it is self-supporting without reinforcement and no load is generated on the central support structure.

As an example, assuming that the load acting on the central support structure of the two-arch tunnel is the ground load to be additionally excavated during the construction of the one-arch tunnel, the safety factor under construction is applied to Fs = 1.5. Under the above tunnel conditions, the ultimate support load of the central support structure is estimated to be about 375 tf / m and the allowable support load is 250 tf / m. After completion, the safety factor as a permanent structure can be reinforced with reinforced concrete to increase the safety factor Fs = 3.0 or more applied in geotechnical engineering.

3 is a perspective view of the load control structure 2, and FIG. 4 is a sectional view. The main features of the load control structure are as follows.

First, the hydraulic screw jack 14 is installed to measure the tunnel support load and control the working load. One embodiment is to install a gauge that can measure the load acting on the hydraulic screw jack, and the second embodiment is to install a hydraulic control valve that allows displacement but cannot exceed the set pressure. The former focuses on load measurement and is suitable for subway and shaft applications with low top toffee, while the latter focuses on load control and is suitable for large loads.

Hydraulic screw jacks are advantageous for the larger length adjustment range, but they are adopted in consideration of numerical analysis results and expected sedimentary settlements when excavating the central tunnel (1). Support the height to allow adjustment.

Second, in order to minimize vibration damage caused by blasting, it is made of steel and replaceable when damage is caused by blasting shock.

Third, in order to check whether the moment due to the horizontal load is generated by installing the hydraulic screw jack 14 in parallel it is possible to simply and quantitatively confirm the occurrence of horizontal earth pressure.

Fourth, the upper roller point 9 is adopted to minimize the occurrence of horizontal clay pressure. The roller point is applied in the opposite concept to the existing fixed method. In this method, the central support structure receives the vertical force and suppresses the horizontal force burden as much as possible to prevent the increase of the compressive force due to the moment.

Even if the roller point is installed, the load of the hydraulic jacks installed in parallel will be different if the horizontal force is applied. After removing the load with the hydraulic jack, remove the horizontal load acting by applying the same pressure to the two hydraulic jacks installed in parallel.

As described above, in the two-arch tunnel, a safe and economical two-arch tunnel construction can be achieved by measuring the load acting on the central support structure, actively responding to the working load, and releasing the horizontal load. In addition, the present invention can also be applied to the blasting tunnel to solve the problem of damage caused by blasting excavation that can occur in the existing reinforced concrete central support structure.

In particular, the present invention can measure the tunnel load which is the biggest obstacle to the tunnel development will contribute to the development of tunnel technology. In the current design concept, the two-arch tunnel can be applied in the deep-depth tunnel, which is difficult to apply because the load on the central support structure is expected to be very large.

Claims (5)

Tunneling method that enables safe and economical design and construction by measuring and controlling the tunnel support load acting on the central support structure (7) of the 2-arch tunnel The load control structure (2) constituting the central support structure is made of a steel structure with a hydraulic screw jack (14) to measure and control the working load and to support the load even if the hydraulic jack is removed after confirming the final load. rescue Load control structure (2) to prevent damage to the load control structure caused by excessive load and to enable automatic load control by installing a hydraulic control valve capable of maintaining the set pressure (2) The upper point of the load control structure (2) is a roller point (9) that can minimize the generation of the moment of the wall due to the horizontal earth pressure The central support structure is constructed of steel structure during side tunnel excavation to minimize wall damage caused by blasting excavation and then to be reinforced with concrete after completion of excavation.