JP2003314188A - Method for predicting settlement in excavation of tunnel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for predicting settlement in a relatively simple manner when excavation of a tunnel is carried out by adopting an auxiliary method. <P>SOLUTION: The method for predicting the settlement is available in excavation of the tunnel by adopting the auxiliary method employing longer section preliminary installed works, leg reinforcing works, etc., and setting timbering on an excavated wall surface. According to the method, the settlement is predicted based on a ground characteristic curve A showing the relationship between timbering internal pressure and wall surface deformation, and a timbering characteristic curve B showing the relationship between the timbering internal pressure and the settlement. Reinforcement in a cross sectional direction, by virtue of execution of the auxiliary method is reflected on the natural ground characteristic curve A as an arch effect, and reinforcement in a longitudinal sectional direction, by virtue of execution of the auxiliary method is reflected on the timbering characteristic curve B as a beam effect. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting a subsidence amount in tunnel excavation, and more particularly to a method for predicting a subsidence amount when an auxiliary construction method such as a long pre-bearing work is adopted for tunnel excavation.

[0002]

2. Description of the Related Art In tunnel excavation, it is customary to employ a numerical analysis method based on a finite element method such as FEM when predicting the amount of subsidence that accompanies excavation.

However, such a conventional method of predicting the amount of subsidence in tunnel excavation has the following technical problems.

[0004]

That is, subsidence due to tunnel excavation occurs as a result of complicated intertwining of various conditions such as ground conditions (deformation coefficient, strength characteristics), overburden, tunnel diameter, and support work. However, there is a problem that it is difficult to model the numerical analysis that meets all of these conditions, and it is difficult to match the analysis result with the actual subsidence amount.

In particular, in recent urban tunnels, an auxiliary construction method such as a long length pre-bearing construction is adopted. However, if such an auxiliary construction method is adopted, it is more difficult to model and the settlement amount is predicted. Currently, there is no established method.

The present invention has been made in view of such conventional problems, and an object of the present invention is to relatively easily predict the subsidence amount when an auxiliary construction method is adopted. It is to provide a method of predicting the amount of settlement in tunnel excavation that can be performed.

[0007]

In order to achieve the above object, the present invention employs an auxiliary construction method such as a long tip receiving work and leg reinforcement work to excavate a tunnel and support the excavation wall surface. In the method of predicting the amount of subsidence in tunnel excavation to be installed, based on the ground characteristic curve indicating the relationship between the bearing internal pressure and the wall deformation amount, and the bearing characteristic curve indicating the relationship between the external force acting on the bearing and the bearing deformation amount. The basic configuration is to predict the subsidence amount, and the reinforcement in the cross-section direction due to the construction of the auxiliary construction method is reflected as an arch effect in the natural characteristic curve, and the longitudinal cross-section direction along with the construction of the auxiliary construction method. The beam effect of the reinforcement is reflected in the support characteristic curve.

According to the method of predicting the amount of subsidence in tunnel excavation constructed as described above, as is clear from a comparison with the construction work to be described later, the amount of subsidence can be predicted relatively easily when the auxiliary construction method is adopted. can do.

The arch effect in the cross-sectional direction is obtained by setting a thick cylinder model in an infinite medium assuming an annular ground reinforcement region on the outer periphery of the excavation surface, and using the elasticity theory to calculate the rock mass characteristics. Can be calculated.

The wall surface deformation amount of the rock mass characteristic curve can be calculated as the excavation affected deformation amount by subtracting the deformation amount due to the initial ground pressure.

The support characteristic curve can be calculated on the basis of the crown subsidence amount of the support work due to stress release during excavation and the leg subsidence amount of the support work.

The crown settlement can be calculated based on this thin-walled cylindrical model by setting the relationship between the external force and the settlement amount associated therewith as a thin-walled cylindrical model.

As for the leg subsidence amount, the ground reaction force coefficient is calculated according to the degree of reinforcement of the leg portion, and the relation between the subsidence amount and the supporting work axial force can be set using the coefficient.

When predicting the subsidence amount, the crown subsidence amount is corrected by the data of tunnel excavation of similar geology and the preceding subsidence rate α estimated from the subsidence amount measurement during the preceding excavation to obtain the total subsidence amount. The amount of subsidence can be calculated.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 1 to 10 show an embodiment of a method of predicting a subsidence amount in tunnel excavation according to the present invention.

The prediction method shown in the figure is based on the relationship between the tunnel internal pressure and the displacement, that is, the natural characteristic curve A showing the relationship between the support internal pressure and the wall deformation amount, and the external force (equal to the internal pressure) acting on the support. Characteristic curve B showing the relationship between
Focusing on and, the basic concept is to find the amount of convergent displacement in the tunnel (the amount of subsidence) that is the intersection of these curves (the point where both curves are balanced). In the case of this embodiment, the upper half of the tunnel is excavated.

When the ground surface subsidence amount is to be obtained, the ground surface subsidence amount and the crown subsidence amount are measured at the time of performing the construction work,
The amount of land subsidence is predicted from the ratio of the amount of land subsidence and the amount of subsidence obtained from the measurement results.

FIG. 1 shows an example of tunnel excavation to which the prediction method of this embodiment is applied. In the tunnel excavation shown in the same figure, a long length receiving work and a leg reinforcing work are adopted as auxiliary construction methods.

In the long front receiving work, a plurality of fore piles 1 having a predetermined length are formed in an umbrella shape toward the front side of the face in the upper half of the tunnel excavation. This fore pile 1
With the progress of tunnel excavation, are installed so that their ends overlap with each other in the tunnel axial direction with a predetermined gap.

On the inner surface of the excavated tunnel, an arch-shaped steel supporter 2 is installed, and in order to reinforce its leg side, a foot pile 3 is provided below the excavated wall surface as a leg reinforcement work. Is formed toward.

In tunnel excavation adopting such an auxiliary construction method, ideally, the effect of the long front receiving work for forming the fore pile 1 is a shell effect as shown in FIGS. This is approximately considered to be a combined effect of the arch effect in the cross-section direction shown in FIG. 2 and the beam effect in the cross-section direction shown in FIG.

When predicting the amount of subsidence, the arch effect in the cross-sectional direction shown in FIG. 2 assumes a natural rock reinforcement area 4 around the tunnel, and this natural rock reinforcement area 4 is used as a displacement suppressing effect. evaluate.

In other words, the lateral arch effect is that the ground reinforcement region 4 having a certain thickness around the tunnel excavation is formed by injecting the cast steel pipe / ground improvement material when forming the fore pile 1. The deformation coefficient of the natural ground increases due to the formation of the natural ground reinforced region 4, and this is evaluated as the displacement suppressing effect.

Further, when predicting the amount of subsidence, the beam effect in the direction of the longitudinal section shown in FIG. 3 is evaluated as the preceding subsidence rate related to the rigidity of the long front receiving work (fore pile 1).
The ground displacement due to tunnel excavation occurs as a preceding displacement before the face reaches the face, and is usually displayed as a stress release rate in the two-dimensional FEM analysis using the concept of equivalent initial ground pressure.

When this concept is used, the preceding settlement rate changes greatly depending on the supporting work to be installed. However, in actual construction work so far, the preceding settlement rate changes greatly regardless of the supporting work to be installed. The current situation is not doing it.

Therefore, in the method of predicting the amount of subsidence according to the present embodiment, such a problem in the FEM analysis is eliminated and the direct preceding subsidence rate α can be focused and evaluated so as to be more realistic.

Further, since the preceding subsidence is considered to be related to the beam effect of the long front receiving work (fore pile 1) placed in front of the face, the preceding subsidence rate is set to the long front receiving work (fore pile 1). ) The stiffness of

However, the preceding subsidence rate α greatly contributes to the stability of the ground in the uncut state from the stress relief during excavation to the installation of the supporting work 2 in the long pre- receiving work (fore pile 1). Therefore, it is decided to define it as the settlement rate up to +1 m of the face advance for the upper half convergence value (in general, the advance settlement rate is the face advance +0 m for the final convergence value).
The subsidence rate is up to. ).

On the other hand, as shown in FIG. 4, the leg reinforcement work forming the footpile 2 is supported by the foot support 2 against the earth load transmitted to the support support foot ground through the support support 2. By improving the mountain, it has the effect of improving the ground bearing capacity and suppressing the amount of foot subsidence.

As a result, the amount of crown subsidence and the amount of ground subsidence are suppressed. With regard to the effect of the leg reinforcement work, the displacement suppressing effect is evaluated by assuming a ground improvement region in the leg ground and assuming that the ground reaction force coefficient κ in this region increases.

Next, a specific procedure and method for predicting the amount of subsidence will be described. FIG. 5 shows a procedure for predicting the amount of subsidence. In the subsidence amount prediction method of the present embodiment, first, the natural characteristic curve A and the support characteristic curve B are calculated in consideration of the effects of the auxiliary construction method as described above.

Calculation of natural characteristic curve A (steps 1 and 2)
Then, a long receiving work (fore pile 1) around the tunnel
In order to evaluate the arch effect in the cross-sectional direction due to, the ground reinforcement region 4 is set.

Assuming that the ground reinforcement region 4 exists concentrically with the circular excavation surface (assuming that the tunnel cross section is circular), an infinite medium as shown in FIG. Assuming a thick-walled cylinder model in 1), the natural characteristic curve A (relationship between the bearing internal pressure P _a and the wall surface deformation amount u _a ) is calculated based on the elasticity theory under the basic conditions of this model.

The relational expression between the support internal pressure P _a and the wall surface deformation amount u _a used in this calculation is shown below.

[0035]

[Formula 1] However, this equation also includes deformation due to initial ground pressure
Therefore, it is necessary to subtract this amount of deformation from the above equation. First
The amount of deformation due to the ground pressure is u_{a, 0}Is P_a= P ₀As
Calculated from this, the amount of deformation due to excavation u_a´ is next
Growls u_a´ ＝ u_a-U_{a, 0} The support characteristic curve B is the support internal pressure P._a(External force acting on the support
And the subsidence amount s (corresponding to the deformation amount of the support)
In this calculation, the subsidence amount s is
Crown subsidence s of primary support due to release stress during excavation₁When,
Leg subsidence s_TwoAnd calculate separately (steps 3-6)
It

[0036] With respect to the crest subsidence s _1, the thickness of the primary支保(支保Engineering 2), since smaller than the tunnel excavation radius, modeled with thin cylindrical as shown in FIG. 7, the external force P _{a (支保} (Equal to internal pressure P _a ) and the amount of subsidence s ₁ that accompanies it
The relationship is established and the calculation is performed based on this.

Regarding the leg subsidence amount s ₂ , the ground reaction force coefficient κ is calculated according to the degree of reinforcement of the leg (placing density, placing length, diameter, etc. of the foot pile 3), and it is used. , Fig. 8
In the model shown in, the relationship between the subsidence amount s ₂ and the supporting work axial force T (leg working load) is set.

[0038] Consequently, shoring axial force T, because represented by excavation radius a and支保pressure P _a, subsidence s ₂ can be represented by a function of支保pressure P _a. From the above, the total subsidence amount s _a of the top end, which is the sum of the subsidence amount and the leg subsidence amount of the primary support (supporting work 2) due to excavation, is _a function of the support internal pressure P _a as shown below. Becomes

[0039]

[Formula 2] Furthermore, at the time of installation of the primary support (support 2), the ground deformation due to tunnel excavation has already occurred. Therefore, considering the ratio of the amount of settlement (preceding settlement rate α) occurring in front of the face. , The total subsidence amount s _a ′ is shown as follows. s _a ′ = s _a + α · s _a ′ s _a ′ = s _a / (1-α) Note that the preceding settlement rate α in this case is the data for tunnel excavation of similar geology and the amount of settlement during the preceding excavation. Estimate from measurements.

When the ground characteristic curve A and the support characteristic curve B are calculated as described above, next, in step 7, the input value is set. At this time, in addition to items such as soil cover and tunnel radius a determined from the geometric conditions, measurement results and test results associated with the preceding excavation are input so that these can be reflected (step 8, 9).

When the input value is set, next, in step 10, the crown settlement amount is calculated. As shown in FIG. 9, the amount of crown settlement is the above-mentioned amount of deformation affected by excavation u _a
′ And the total subsidence amount s _a ′ are equal to each other, that is, the subsidence amount at the convergence point C of the subsidence or deformation.

In FIG. 9, if the auxiliary construction method is used and the type is different, the slope of the ground characteristic curve A changes due to the difference in the arch effect in the cross-sectional direction, and at this time, the support work 2 and the leg reinforcement Even if the work is the same, since the preceding settlement amount changes due to the difference in the beam effect in the longitudinal section direction, the difference in the settlement amount that occurs as a result of these differences,
The forecast of subsidence amount according to the auxiliary construction method is reflected.

The prediction result of the subsidence amount obtained as described above is used, for example, to predict the subsidence amount of the unconstructed section, and the subsidence utilization prediction of the ground surface is, for example, as shown in FIG. It is calculated by the ratio of the crown subsidence and the ground subsidence obtained from the measurement result (step 11).

In this case, since the ratio of the crown subsidence amount to the ground surface subsidence amount largely depends on the soil cover and excavation cross section, it is preferable to use the measurement result having the relationship shown in FIG. desirable.

FIG. 11 shows the result of comparison between the predicted value and the measured value, which was applied to an actually constructed tunnel in order to confirm the validity of the prediction method of this embodiment. In the construction tunnel, various types of auxiliary methods, such as injection type steel pipe front receiving method (trevi tube method), high pressure injection steel pipe front receiving method (trevijet method), and leg jet grout are used for the legs. However, all of them were processed by the prediction method of this example, and the predicted value was calculated.

The predicted value is somewhat different depending on the magnitude of the squat measurement value, but there is a high correlation of R ² = 0.8 with the measured value / predicted value = 1, and the effectiveness of the prediction method of this embodiment is high. Is confirmed,
This prediction method can also be used as a judgment material when adopting an auxiliary construction method for the purpose of suppressing ground subsidence.

[0047]

As described above in detail, according to the method of predicting the amount of subsidence in tunnel excavation according to the present invention, the amount of subsidence can be relatively easily predicted when the auxiliary construction method is adopted. At the same time, it can be used as a judgment material when adopting an auxiliary construction method for the purpose of suppressing ground subsidence.

[Brief description of drawings]

FIG. 1 is an explanatory view of a tunnel and an auxiliary construction method to which a subsidence amount prediction method in tunnel excavation according to the present invention is applied.

FIG. 2 is an explanatory diagram showing an arch effect in a cross-sectional direction of the auxiliary construction method shown in FIG.

FIG. 3 is an explanatory diagram showing a beam effect in a vertical cross-section direction of the auxiliary method shown in FIG.

FIG. 4 is an explanatory view of leg reinforcement work of the auxiliary construction method shown in FIG. 1.

FIG. 5 is a flowchart showing the procedure of the prediction method of the present invention.

FIG. 6 is an explanatory diagram of a thick-walled cylindrical model with an arch effect shown in FIG. 2.

FIG. 7 is an explanatory diagram of a thin-walled cylindrical model when evaluating the amount of subsidence due to release stress during excavation in the prediction method of the present invention.

FIG. 8 is an explanatory diagram of a squat model when calculating a leg squat amount in the prediction method of the present invention.

FIG. 9 is an explanatory diagram for obtaining a final subsidence amount in the prediction method of the present invention.

FIG. 10 is a graph showing the relationship between soil cover and subsidence ratio used when predicting ground subsidence from the final subsidence obtained by the prediction method of the present invention.

FIG. 11 is a graph showing the prediction method of the present invention and the measurement result of the actual work.

[Explanation of symbols]

1 Fore pile (long length receiving work) 2 support work 3 foot pile 4 Ground reinforcement area A natural characteristic curve B Support characteristic curve

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tadashi Ninomiya             2-15-2 Konan, Minato-ku, Tokyo Co., Ltd.             Obayashi Head Office

Claims (7)

[Claims] 1. A method of predicting the amount of subsidence in tunnel excavation, which employs an auxiliary construction method such as a long length receiving work and leg reinforcement work to install a support work on the excavation wall surface. Natural characteristic curve showing the relationship with the amount of deformation,
Based on a support characteristic curve showing the relationship between the external force acting on the support and the amount of support deformation, the basic configuration is to predict the settlement amount, and the reinforcement in the cross-sectional direction along with the construction of the auxiliary construction method is used as an arch effect. A method of predicting a subsidence amount in tunnel excavation, which is reflected in the natural characteristic curve and is also reflected in the support characteristic curve as a beam effect of reinforcement in a vertical cross-sectional direction associated with the construction of the auxiliary construction method. 2. The arch effect in the cross-sectional direction is set by a theory of elasticity by setting a thick cylinder model in an infinite medium assuming an annular ground reinforcement region on the outer periphery of the excavation surface. A method for predicting subsidence in tunnel excavation, which is characterized by calculating mountain characteristics. 3. The prediction of the subsidence amount in tunnel excavation according to claim 2, wherein the wall deformation amount of the rock mass characteristic curve is calculated as an excavation affected deformation amount by subtracting the deformation amount due to the initial ground pressure. Method. 4. The support characteristic curve is calculated on the basis of a crown subsidence amount of the support work due to stress release during excavation and a leg subsidence amount of the support work. Method of subsidence amount in tunnel excavation in Japan. 5. The tunnel excavation according to claim 4, wherein the crown settlement is set as a thin-walled cylinder model by setting a relationship between an external force and a settlement amount associated therewith, and is calculated based on the thin-walled cylinder model. Method of subsidence in Japan. 6. The leg subsidence amount is characterized by calculating a ground reaction force coefficient in accordance with the degree of reinforcement of the leg portion and using the calculated coefficient to set the relationship between the subsidence amount and the supporting work axial force. Claim 4
A method for predicting subsidence in tunnel excavation as described. 7. When predicting the subsidence amount, the crown subsidence amount is corrected by the data of tunnel excavation of similar geology, or the preceding subsidence rate α estimated from the subsidence measurement at the time of preceding excavation. And calculating the total subsidence amount.
A method for predicting subsidence in tunnel excavation as described.