JP2852568B2 - Tunnel excavation method in wet ground - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tunnel excavation method in a wet ground which can stably excavate a soft wet ground saturated with groundwater.

[0002]

2. Description of the Related Art Conventionally, when a tunnel is excavated in a soft wet ground in an urban area, a pipe is pressed into the ground which is about to collapse and flow, and the pipe is safely protected while preventing the ground from collapsing therein. 2. Description of the Related Art A shield method for performing a so-called highly rigid support work for performing an excavation work and a lining work is widely known. However, such a shield method has an economical problem, such as a high manufacturing cost of the shield machine and a high unit price of the lining segment.

[0003] On the other hand, the NATM method, which uses a low-rigidity support and monitors the equilibrium state between the ground and the support by measurement and maximizes the supporting force of the ground itself, is compared with the shield method. It is economical because it is reduced, and has abundant construction results in recent years.

[0004]

However, the adoption of the NATM method has a disadvantage that when the ground is saturated with groundwater, the tunnel face is extremely unstable and difficult to construct. In such a case, a method of excavating a tunnel is usually adopted after lowering the groundwater level, or an auxiliary construction method such as improvement and reinforcement of the ground around the face by injection of a chemical solution, or support for the receiving face from the face is adopted. Although it is adopted, if it is not constructed carefully, it may cause land subsidence, and also leads to an increase in construction costs and a longer construction period,
Especially in urban areas, it is a major problem in construction.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to improve the independence of the face and excavate the excavation stably even when excavating soft and wet ground saturated with groundwater. The purpose is to provide a tunnel excavation method.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned object, and the gist of the present invention is to form a water stop zone in a form surrounding a tunnel to be constructed in advance on a ground to be excavated, The impervious material is sprayed or impregnated on the face of the tunnel in the water stop zone to form a impervious coating, and pore water in the ground to be excavated surrounded by the water stop zone and the impervious covering is formed. Is vacuum dewatered to make the inside of the ground to be excavated a negative pressure with respect to the atmospheric pressure of the already excavated part in the tunnel, excavate the impervious air-permeable part, and newly provide an impervious air-permeable part to the excavated part. A tunnel excavation method in wet ground characterized by excavating a tunnel face while maintaining the negative pressure applied to the ground to be excavated while forming.

[0007] Here, the above-mentioned impervious material refers to a fine-particle material that penetrates into the gaps in the ground to reduce the air permeability of the ground, or a material that forms an impervious coating on the face of the face. Milk, bentonite, resin-based chemicals and the like are preferred.

[0008]

[Function] After surrounding the tunnel excavation ground with the water blocking zone and the impervious air-permeable portion, the pore water in the tunnel excavation ground is vacuum-dewatered to leave the surface remaining on the soil particle surface in this area. The bonding force between the soil particles caused by the surface tension of water increases with a decrease in the water content due to the vacuum dehydration, and the apparent adhesive force that contributes to the shear strength increases,
The shear strength of the ground increases. Further, due to the vacuum dewatering of the pore water, the atmospheric pressure of the already excavated portion in the tunnel exceeds the gap air pressure in the ground where the tunnel is to be excavated, so that the tunnel face acts to be pressed forward.
It acts as a soil retaining effect and improves the independence of the face.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in the order of steps with reference to the accompanying drawings.

First, a pilot tunnel 1,1 is constructed near the ground to be excavated in the wet ground, a chemical injection pipe is extended from the pilot tunnel 1,1, and a chemical solution is injected by a known method to form a tunnel to be excavated. A water-stop zone 2 covering the outer periphery in a cylindrical shape is provided (FIGS. 1a and 1b), and a poorly-permeable material is sprayed on the tunnel face inside the water-stop zone 2 to provide a poorly-permeable coating portion 4 (FIG. 1). (Fig. 2). The formation of the water-stop zone 2 is not limited to the above-mentioned injection of the chemical solution, and a freezing method of freezing the wet ground to strengthen the ground and impermeable the water may be adopted. It is.

Next, the water-stop zone 2 and the impervious air-permeable coating 4
The pore water contained in the ground in the ground 5 to be excavated, which is surrounded by, is vacuum-dehydrated. The pore water is vacuum-dehydrated by inserting a suction pipe 3 from the pilot tunnels 1 and 1 into the ground 5 to be excavated (FIGS. 1a and 1b), or penetrates the tunnel face from the side of the excavated portion 5a. Then, a suction pipe 6 having a large number of water inlets is inserted into the ground 5 to be excavated, and vacuum dewatering is performed by a vacuum pump 8 or the like (FIG. 2).
Due to this vacuum dehydration, a negative pressure is applied to the ground 5 to be excavated with respect to the atmospheric pressure in the excavated portion 5a in the tunnel. In addition, as shown in FIG.
By providing a bulkhead 9 for hermetically shutting off between the ground 5b to be excavated and the ground 5b to be excavated next, the ground 5 to be excavated is substantially sealed by the water blocking zone 2, the poorly permeable covering portion 4, and the bulkhead 9. Therefore, the vacuum dewatering effect can be further enhanced. When the water stop zone 2 is provided, the bulkhead 9 is preferably formed by injecting a chemical solution or the like.

In this state, the impervious air-permeable covering portion 4 is excavated,
The tunnel face is excavated while maintaining the negative air pressure applied to the ground 5 to be excavated while forming a new impervious coating portion 4 at the excavated location. In this excavation, Fig. 2
An excavator or the like schematically showing only the load header 10 at the tip end can be used.
Is provided with a spray nozzle 11 for spraying the impervious material onto the face. Thus, the tunnel face is continuously excavated by the load header 10 while the air-permeable material is sprayed on the tunnel face by the spray nozzle 11.

The following shows the results of experiments on the soil retention effect on the face and the increase in apparent shear strength of the ground by vacuum dewatering of pore water.

Experimental Procedure A partition plate 31 is inserted into an earth tank 30 and an earth retaining beam 32 is installed. The suction hole and the drain hole are sealed in advance. Further, a vinyl sheet 33 is stretched around the partition plate 31 for the purpose of preventing air leakage (make it as air-tight as possible with a gum tape). Sand 34 is charged with a clamshell, then saturated with water and boiled (FIG. 3a). After sufficient boiling, the drain valve 36 'is opened and drained to create a watertight state (FIG. 3).
b). A vinyl sheet is also attached to the upper surface of the sand 34 (to make it as air-tight as possible with a gum tape), and vacuum suction is started by the suction pump 36. The retaining beam 32 and the partition plate 31 are removed. H steel 37, load cell 38, hydraulic jack 3
A loading device 41 consisting of a loading plate 9 and a loading plate 40 is installed, and a load is applied until breakage occurs. The load Q is △
Q is increased at 0.5tf pitch, and suction is always kept at a constant suction pressure during loading (FIG. 3c).

Experimental results Intake pressure p = 0 mmHg ... Case A Intake pressure p = 60 mmHg ... Case B Intake pressure p = 110 mmHg ... Case C Intake pressure p = 150 mmHg ... Case D Absorption as described above. Table 1 and FIG. 4 show the measurement results when the air pressure was changed in four ways.

[0016]

[Table 1]

From Table 1 and FIG. 4, as the intake pressure p increases,
It was confirmed that the apparent shear stress τ including the pressing effect of the face at the time of fracture increased.

[0018]

According to the tunnel excavation method in the wet ground according to the present invention, a water-stop zone and a poorly permeable coating portion are formed on the tunnel face inside the water-stop zone, and the water-stop zone and the water-tight zone are formed. By vacuum dewatering the interstitial water in the ground to be excavated surrounded by the air-covered portion, the apparent adhesive force that contributes to the shear strength increases, and the ground strength increases. Also,
The atmospheric pressure of the excavated portion in the tunnel exceeds the atmospheric pressure in the ground to be excavated due to the vacuum dehydration of the pore water, and the tunnel face is pressed forward to enhance the independence of the face. Therefore, even when excavating soft and wet ground saturated with groundwater, the independence of the face can be improved, and tunnel excavation can be performed stably.

[Brief description of the drawings]

FIG. 1a is a schematic perspective view showing a state in which a water blocking zone is formed from a pilot tunnel in a wet ground and vacuum dewatering of pore water is performed, and FIG. 1b is Ib-Ib in FIG. 1a.
It is sectional drawing.

FIG. 2 is a schematic cross-sectional view of a tunnel showing a process of vacuum-dehydrating pore water in a ground to be excavated from an already excavated portion and newly forming a hardly air-permeable covering portion while excavating a tunnel face.

FIGS. 3A to 3C are explanatory diagrams showing experimental procedures.

FIG. 4 Inlet pressure and apparent shear stress τ at the time of failure
It is a graph which shows the relationship of (tf / m < ² >).

[Explanation of symbols]

 2 water stop zone 4 impervious air-covered section 5 ground to be excavated 9 bulkhead

──────────────────────────────────────────────────続 き Continued on the front page (73) Patent holder 000005924 Mitsui Miike Manufacturing Co., Ltd. 2-1-1, Nihonbashi-Muromachi, Chuo-ku, Tokyo (73) Patent holder 000224787 Dowa Koei Co., Ltd. 31 Chikuko Sakaemachi, Okayama City, Okayama Prefecture No. 10 (73) Patent holder 000140982 Magumi Co., Ltd. 2-58-8 Kita-Aoyama, Minato-ku, Tokyo (72) Inventor Akira Inokuma 1 Asahi Oaza, Tsukuba-shi, Ibaraki Pref.Public Works Research Institute, Ministry of Construction (72) Inventor Inano Shigeru Shigeru, Tsukuba, Ibaraki Pref. 1 Asahi 1 Public Works Research Institute, Ministry of Construction (72) Yoshio Maruyama 2-10-2 Otowa, Bunkyo-ku, Tokyo Japan Advanced Construction Technology Center (72) Inventor Yu Nomura Osaka, Osaka 4-33 Kitahama Higashi, Chuo-ku Obayashi Gumi Co., Ltd. (72) Inventor Masanobu Ochiishi 2-32-14 Chikko Shinmachi, Okayama City, Okayama Prefecture Dowa Koei Co., Ltd. (72) Akiba Kazuo Kagawa 4-6-1 Sendagaya, Shibuya-ku, Tokyo Inside Fujita Co., Ltd. (72) Inventor Hideo Imai 2-1-1 Nihonbashi Muromachi, Chuo-ku, Tokyo Mitsui Miike Works Co., Ltd. (72) Inventor Kusabuka Morito 2-5-8 Kita-Aoyama, Minato-ku, Tokyo Intra-company group (56) References JP-A-3-13690 (JP, A) JP-A-60-51293 (JP, A) (58) Fields surveyed (Int.Cl. ⁶ , DB name) E21D 9/00 E21D 9/04

Claims (1)

(57) [Claims] 1. A water-stop zone is formed in advance in a form surrounding a tunnel to be constructed on a ground to be excavated, and a low-permeability material is sprayed or permeated on a face of the tunnel in the water-stop zone. Forming a coating,
Vacuum dewatering the pore water in the ground to be excavated surrounded by the water blocking zone and the impervious air-covered portion, to make the inside of the ground to be excavated negative pressure with respect to the atmospheric pressure of the excavated part in the tunnel, Excavating the impervious air-permeable portion, excavating a tunnel face while maintaining a negative pressure on the ground to be excavated while forming a new impervious air-covered portion at the excavated portion. Excavation method in wet ground.