JP7045952B2 - Tunnel construction method and tunnel support structure - Google Patents

Description

The present invention relates to a tunnel construction method and a tunnel support structure.

Mountain tunnel construction methods such as NATM are equipped with sprayed concrete sprayed on the ground surface exposed by excavation, steel support works assembled along the ground surface, rock bolts placed on the ground, etc. Safety is ensured by tunnel support.
In a tunnel covered with large earth, the amount of deformation of the ground around the tunnel increases, and a large earth pressure may act on the tunnel support. The same applies to fault crush zones and tunnels formed by excavating expansive terrain.
It is estimated that a large stress is applied to the support structure in the tunnel within 24 hours after excavation. Therefore, in a tunnel where a large stress is expected to act, sprayed concrete that develops strength at an early stage may be adopted in order to ensure the safety of the tunnel. For example, Patent Document 1 discloses sprayed concrete having a compressive strength of 15 N / mm ² or more at a material age of 3 hours.

Japanese Unexamined Patent Publication No. 2008-137817

However, even in the case of sprayed concrete that develops strength at an early stage, there is a risk that cracks will occur or local fracture will occur due to deformation of the ground after excavation.
An object of the present invention is to propose a tunnel construction method and a tunnel support structure that can secure the stability of the tunnel interior in tunnel excavation under a ground condition where a large ground pressure acts.

The tunnel construction method of the present invention for solving the above-mentioned problems includes an excavation step of excavating the ground and a support step of spraying concrete on the ground surface exposed by the excavation of the ground. The sprayed concrete contains moderate heat cement, blast furnace slag powder, silica fume powder, a high-performance water reducing agent, an aggregate, a quick-setting agent, and water, and the age of the sprayed concrete is 24. The Young's modulus of time is 20000 N / mm ² or less, and the compressive strength at 28 days of age is 70 N / mm ² or more.
Further, the tunnel support structure of the present invention includes steel support works built at intervals along the tunnel axial direction and sprayed concrete sprayed on the ground. The steel support is formed of a steel material and a contractible member. Further, the sprayed concrete contains moderate heat cement, blast furnace slag powder, silica fume powder, a high-performance water reducing agent, an aggregate, a quick-setting agent, and water, and is a material of the sprayed concrete. The Young's modulus at 24 hours of age is 20000 N / mm ² or less, and the compressive strength at 28 days of age is 70 N / mm ² or more.

According to the present invention, since the Young's modulus at the initial age of the sprayed concrete (within 24 hours of age) is low, it is possible to follow the deformation of the ground. Therefore, it is possible to prevent the sprayed concrete from cracking and compression fracture. As a result, it is possible to ensure the stability of the air inside the tunnel when excavating the tunnel under the ground conditions where a large earth pressure acts.

(A) is a cross-sectional view showing a tunnel according to the present embodiment, and (b) is a vertical sectional view showing a support structure of the tunnel. (A) is a perspective view showing sprayed concrete, and (b) is a perspective view showing a steel support. It is a stress model diagram of the tunnel used for the calculation. It is a characteristic curve diagram of the ground and the support.

In this embodiment, as shown in FIG. 1A, the support structure of the tunnel 1 constructed by NATM (tunnel support structure 2) will be described. Since the tunnel 1 is constructed in an environment of high soil cover and high ground pressure, it is expected that the ground G will be significantly deformed. In the present embodiment, local fracture is suppressed by adopting the tunnel support structure 2 capable of following the deformation of the ground G.
As shown in FIG. 1 (b), the tunnel support structure 2 of the present embodiment includes a steel support structure 3, a sprayed concrete 4, and a lock bolt 5. The steel support 3 and the sprayed concrete 4 are formed in an arch shape (horseshoe shape). The shapes of the steel support 3 and the sprayed concrete 4 are not limited, and may be, for example, a ring shape. The tunnel support structure 2 may be combined with an auxiliary construction method as needed.

Steel support works 3 are built at intervals along the tunnel axial direction. The steel support 3 of the present embodiment is formed by combining a plurality of steel materials 6 and a contractible member 7. The arrangement pitch of the steel support 3 is appropriately determined according to the ground condition (ground grade, etc.).
The steel material 6 is formed by processing H-shaped steel. The cross-sectional dimensions of the H-shaped steel constituting the steel material 6 are not limited, and may be appropriately determined according to the ground conditions. Further, the material constituting the steel material 6 is not limited to the H-shaped steel.
The contractible member 7 has a lower rigidity than the steel material 6, and is interposed between the steel materials 6. The number and arrangement of the contractible members 7 to be installed in the steel support 3 is not limited, but it is desirable to arrange them symmetrically. The contractible member 7 has a material that deforms while maintaining a constant load strength. Therefore, the steel support 3 makes it possible to maintain the internal pressure of the tunnel 1 even during contractibility. The contractible member 7 of the present embodiment has a main body 71 formed of a hardened mortar containing cement, a porous material, and water, and a reinforcing body which is a fiber sheet provided around the main body 71. It is a columnar member made of 72. The cross-sectional shape of the main body 71 is not limited, and may be, for example, circular or rectangular. Further, the main body portion 71 is not limited to mortar, and may be, for example, concrete. Further, the reinforcing body 72 may have a plurality of fiber sheets laminated on the reinforcing body 72. A woven fabric made of polypropylene fiber is used for the fiber sheet. The material constituting the fiber sheet is not limited, and may be, for example, a woven fabric such as an aramid fiber or a polyethylene fiber. Further, the reinforcing body 72 is not limited to the fiber sheet, and may be, for example, a tubular member. The structure of the contractible member 7 is not limited, and may be, for example, a hardened fiber-reinforced concrete body having innumerable bubbles, a member in which a steel pipe having a multi-layer structure is deformed while buckling, or the like. ..

The sprayed concrete 4 is sprayed on the ground G (around the tunnel) exposed by excavation of the ground G. The sprayed concrete 4 contains moderate heat cement, blast furnace slag powder, silica fume powder, high-performance water reducing agent, aggregate, quick-setting agent, and water, and is predetermined with respect to the ground G. It is sprayed on the thickness. The sprayed concrete 4 of the present embodiment has a Young's modulus of 20000 N / mm ² or less at 24 hours of age and a compressive strength of 70 N / mm ² or more at 28 days of age.
The sprayed concrete 4 has a water powder ratio (W / P) of water and powder (moderate heat cement, blast furnace slag powder and silica fume powder) of 15% or more and 25% or less. From the viewpoint of increasing the spray compressive strength, the water powder ratio is preferably 20.0% or less, more preferably 18.0% or less, and more preferably 16.5% or less. More preferred. Further, the plastic viscosity of the base concrete (or base mortar) excluding the quick-setting admixture is 5 Pa · s or more and 25 Pa · s or less, and the yield value is 0.01 Pa · s or more and 15 Pa · s or less.

Moderate heat cement is so-called moderate heat Portland cement. Moderate heat cement has a lower heat of hydration than ordinary Portland cement. In the present embodiment, the blending amount of moderate heat Portland cement in the powder is 40% by weight or more. The blending amount of moderate heat cement is not limited.
As the blast furnace slag powder, one containing 1 wt% or more and 10 wt% or less of particles of 90 μm or more that do not pass through a sieve having a nominal opening of 90 μm specified in JIS Z8801-1 is used. The blast furnace slag powder is blended so that the blending amount in the powder is 5% by weight or more. The blending amount of the blast furnace slag powder is not limited.
The silica fume powder is blended so that the blending amount in the powder is 5% by weight or more. The blending amount of silica fume powder is not limited.

As the high-performance water reducing agent, one containing a polycarboxylic acid ether-based compound is used. The high-performance water reducing agent is not limited, and for example, naphthalene sulfonic acid-based compound, melamine sulfonic acid-based compound, amino sulfonic acid-based compound, alkylallyl sulfonic acid-based compound and derivatives or modified products thereof, polyether. Derivatives, polyglycol derivatives, ester compounds, and those containing a mixture thereof as a main component can be used. The composition of the high-performance water reducing agent is 1 part by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the powder. The amount of the high-performance water reducing agent to be blended is not limited.
Fine aggregate and coarse aggregate are used as the aggregate. The material constituting the fine aggregate is not limited as long as the particle size is 0.85 to 0.60 mm or less, and for example, natural aggregate such as river sand and mountain sand, crushed sand, and blast furnace slag fine bone. Materials can be used. Gravel or crushed stone is used for the coarse aggregate. The blending amount of the aggregate may be appropriately determined. Further, the coarse aggregate may be blended as needed.
Use a liquid quick-setting agent. Examples of the liquid quick-setting admixture include aluminate-based, water-soluble aluminum salt-based, and the like. Further, the material constituting the quick-setting admixture is not limited, and for example, powdered materials such as calcium aluminate-based, calcium sulfate-based, and aluminate-based may be used.
The material contained in the sprayed concrete 4 is not limited, and for example, an admixture, a fiber, an admixture, and the like may be contained in addition to the above-mentioned materials. Examples of such an admixture include limestone fine powder, quartz fine powder, silica stone fine powder, rock fine powder, gypsum and the like. Further, examples of the fiber include steel fiber and organic fiber. Further, as the admixture, there are an AE agent, an AE water reducing agent, a fluidizing agent, an antifoaming agent, a thickening agent, a foaming agent and the like.

A plurality of lock bolts 5 are arranged at predetermined intervals in the circumferential direction of the tunnel. The length, bolt diameter, casting pitch, etc. of the lock bolt 5 are not limited, and may be appropriately set according to the ground conditions. Further, the lock bolt 5 may be installed as needed and may be omitted. Further, instead of the lock bolt 5, a fore polling method, an AGF method, or the like may be adopted.

Next, the construction method of the tunnel 1 will be described. The tunnel construction method of the present embodiment includes an excavation process and a support process.
The excavation process is a process of excavating the ground G to form an excavation pit in the ground. The excavation method of the tunnel 1 is not limited, and is selected from the blasting excavation method, the mechanical excavation method, and the like according to the ground conditions and the surrounding environment. Further, the excavation method for the tunnel 1 is not limited, and for example, a full-section excavation method, a bench cut method, or an advanced shaft method may be adopted.
The support step is a step of forming the tunnel support structure 2 in the excavation pit. In the tunnel support structure 2, the steel support work 3 is built after the primary spraying 41 (a part of the sprayed concrete 4) is performed on the ground surface (around the tunnel) exposed by the excavation of the ground G. Further, it is formed by casting a secondary spray 42 (the remaining portion of the spray concrete 4) and a lock bolt 5. The steel support 3 is built at a predetermined interval from the steel support 3 built in the previous construction cycle. The lock bolt 5 is placed by drilling a lock bolt hole in the ground G around the tunnel 1 and inserting the lock bolt 5 into the lock bolt hole. The sprayed concrete 4 does not necessarily have to be divided into a plurality of layers (primary spray 41 and secondary spray 42), and may be only one layer. Further, the lock bolt 5 may be placed together with the construction of the steel support work 3 after the construction of the primary spray 41.

According to the tunnel support structure 2 of the present embodiment, the Young's modulus at the initial material age (within 24 hours of the material age) of the sprayed concrete 4 is low, and the contractible member 7 is interposed in the steel support structure 3. Therefore, it is possible to follow the deformation of the ground G. Therefore, even if the ground G is deformed after the tunnel support structure 2 is formed, the sprayed concrete 4 may be cracked or compression fracture may occur by following the deformation of the ground G. Can be prevented. As a result, it is possible to ensure the stability of the air inside the tunnel when excavating the tunnel under the ground conditions where a large earth pressure acts.
Since the sprayed concrete 4 follows the deformation of the ground G as a whole, stress is not locally concentrated. Therefore, the sprayed concrete 4 is not locally damaged.

The following shows the calculation results performed to understand the influence of the Young's modulus at the initial age of the sprayed concrete 4 on the construction of the support work. In this calculation, the stress generated in the sprayed concrete 4 was calculated from the characteristic curve for the material ages of about 7 to 8 hours, 12 hours, 24 hours, and 28 days, and compared with the compressive strength of the sprayed concrete 4.
As a condition of calculation, it was assumed that the overburden was 200 m and the sprayed concrete 4 was sprayed on the tunnel 1 having a circular cross section with an excavation radius of 4000 mm with a spray thickness of 200 mm (see FIG. 3). At this time, the unit volume weight of the ground G was set to 1.8 t / m ³ , and the deformation coefficient of the ground G was set to 2500 N / mm ² . Further, H-150 was used as the steel support work 3, and the arrangement interval was set to 1 m. It was also assumed that the support structure and the ground pressure show elastic behavior.

The calculation was performed according to the following procedure.
First, the characteristic curve L1 of the ground G is created by the equation 1 (see FIG. 4). Equation 1 consists of the relationship between the radial stress (σ _γ ) _a of the tunnel 1 and the wall surface displacement u _a when the ground G is in an elastic state.

Next, the leading displacement when the release force acts on the support is calculated, and the starting point of the support characteristic curve is determined (see FIG. 4). The preceding displacement was set to be 40% of the total wall surface displacement when the tunnel support structure 2 was not installed, assuming that the displacement was 1 m (0.1 × D) ahead of the face.
Subsequently, the characteristic curve L2 of the tunnel support structure 2 was created by the equation 2 (see FIG. 4).

Next, the load acting on the primary support (sprayed concrete 4) and the amount of displacement of the wall surface are calculated from the intersection (point of equilibrium state) between the characteristic curve L1 of the ground G and the characteristic curve L2 of the tunnel support structure 2. .. As the load and the amount of displacement on the wall surface, the numerical values read from the graph of FIG. 4 may be used.
Subsequently, using the formula 3, the stress generated in the sprayed concrete 4 for about 7 to 8 hours, 12 hours, 24 hours, and 28 days is calculated from the load acting on the sprayed concrete 4. The calculated stress is shown in Table 2.

After calculating the stress generated in the sprayed concrete 4, it is compared with the compressive strength f _c'of the sprayed concrete 4. For the compressive strength, the test results obtained by loading with a load control of a loading speed of 0.6 ± 0.4 N / mm2 / s using an Amsler type testing machine according to JIS A1149 were used. Table 1 shows the composition of the concrete (sprayed concrete 4) used in the test. Tests were conducted with three specimens for each age. The specimen was a cylinder having a diameter of 100 × 200 mm.
Table 2 shows the relationship between the calculation results of the sprayed concrete 4 and the compressive strength. In addition, the stress generated in the sprayed concrete 4 exceeding the compressive strength of the sprayed concrete 4 (σ _θ c / f _c '≧ 1) was regarded as NG.
As shown in Table 2, it was confirmed that according to the sprayed concrete 4 of the present embodiment, the required compressive strength is exhibited against the acting stress at the young age.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and each of the above-mentioned components can be appropriately changed without departing from the spirit of the present invention.
In the above embodiment, the case where the contractible member 7 is interposed in the steel support 3 has been described, but the contractible member 7 may be installed as needed.

1 Tunnel 2 Tunnel support structure 3 Steel support 4 Sprayed concrete 5 Lock bolt 6 Steel 7 Shrinkable member

Claims (2)

The excavation process for excavating the ground and
It is a tunnel construction method that includes a support process that sprays concrete on the ground surface exposed by excavation of the ground.
The sprayed concrete contains moderate heat cement, blast furnace slag powder, silica fume powder, high-performance water reducing agent, aggregate, quick-setting agent, and water.
A tunnel construction method, wherein the sprayed concrete has a Young's modulus of 20000 N / mm ² or less at a material age of 24 hours and a compressive strength of 70 N / mm ² or more at a material age of 28 days. Steel timbers built at intervals along the tunnel axis,
It is a tunnel support structure equipped with sprayed concrete sprayed on the ground.
The steel support is formed of a steel material and a contractible member.
The sprayed concrete contains moderate heat cement, blast furnace slag powder, silica fume powder, high-performance water reducing agent, aggregate, quick-setting agent, and water.
A tunnel support structure characterized in that the Young's modulus of the sprayed concrete at a material age of 24 hours is 20000 N / mm ² or less, and the compressive strength at a material age of 28 days is 70 N / mm ² or more.

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