JP2007309008A - Method of analyzing state change of tunnel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which has an application range with no large limit, and enables analysis on a state change of a tunnel for a long period. <P>SOLUTION: The method includes a step of creating element models by modeling lining concrete and the peripheral natural ground, a step of calculating the distribution of calcium diffusion from a lining structure element model to a natural ground element model, a step of calculating a degree of chemical deterioration resulting in the elution of calcium ions from a cement component of the lining concrete into the natural ground as a damage parameter and setting the calculated parameter on the natural ground element model, a step of calculating a change in deformation characteristics and strength characteristics of the natural ground model as deterioration in the natural ground element model, the change accompanying the diffusion of calcium from the lining structure element model, and a step of calculating the displacement of the lining structure element model accompanied by the deterioration in the natural ground element model. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for analyzing deformations such as internal displacement generated in a tunnel lining structure.

  In Japan, the total number of tunnels including roads and railroads is 10,000 or more, and the total extension distance exceeds 4000 km. Moreover, many of the tunnels currently in use were constructed before the war, and their maintenance is an important issue. In particular, tunnel reinforcement measures are extremely important for improving the proof strength of the lining structure and stabilizing the ground around the tunnel.

  When considering tunnel reinforcement measures, the element model of the finite element method or the finite difference method is used to represent both the natural ground and the lining structure. There is a method to examine the safety of the whole tunnel from the interaction. In this case, an analysis model such as a creep model, a viscoelastic-plastic model, and a ground degradation model is generally applied to handle the temporal deformation behavior of the ground surrounding the tunnel.

  However, in the reinforcement study related to actual maintenance of tunnels, there are almost no cases where the temporal deformation behavior of the ground surrounding the tunnel was examined using a creep model or viscoelastic-plastic model. The reason for this is that when analysis is performed using a creep model or viscoelastic-plastic model, a large amount of information from the tunnel design stage to the present state is required. For example, if disclosure of information required for analysis is restricted, or information required for a long time since construction, such as that built before the war, does not exist, analyze all It becomes difficult.

  On the other hand, in the natural degradation model, it is possible to express the temporal change of natural ground on the assumption that the strength constant decreases over time, improving the proof strength of the lining structure and stabilizing the natural ground around the tunnel. Consideration can be made for planning.

  However, in the natural degradation model, the deformation behavior converges when the stress of the natural ground reaches the residual strength, for example, about 20 years after construction, and the subsequent deformation behavior is examined. Can not do it. In fact, even after 20 years have passed, the degradation of natural ground is still progressing, and its deformation behavior is an essential consideration.

  Moreover, when analyzing using a natural ground degradation model, a comparatively big initial ground pressure is needed. For this reason, when sufficient initial ground pressure cannot be obtained, for example, when the earth cover is small in the tunnel to be analyzed, the amount of displacement of the tunnel due to natural ground degradation will be small, and the deformation phenomenon will be sufficient. There is a possibility that it cannot be expressed. In other words, when applying the natural ground degradation model, it is a condition that the covering of the tunnel is sufficiently secured as the tunnel construction state, and the displacement of the tunnel due to natural ground degradation is sufficiently large. Will be severely limited.

  In view of the above circumstances, an object of the present invention is to provide a method capable of performing a deformation analysis of a tunnel over a long period of time without a large limitation in the application range.

  In order to achieve the above object, a tunnel deformation analysis method according to claim 1 of the present invention is a method for analyzing a tunnel deformation including a concrete lining structure, wherein the lining structure The process of elemental modeling of the body and the surrounding natural ground, the process of calculating the diffusion distribution of the ionized material from the lining structure element model for the natural ground element model, and the ionized material from the cement component of the lining structure The process of setting the chemical degradation degree when it is eluted as a damage parameter and setting it as a natural element model, and the deterioration of the natural element model accompanying the diffusion of ionized substances from the lining structure element model are described above. The method includes a step of simulating according to the damage parameter, and a step of calculating a displacement of the lining structure element model accompanying the deterioration of the natural ground element model.

  The tunnel deformation analysis method according to claim 2 of the present invention is the tunnel deformation analysis method according to claim 1, wherein the damage parameter is generated in a clay mineral in a natural ground as calcium ions are eluted from the lining structure. It is set as a rate of chemical deterioration.

  A tunnel deformation analysis method according to claim 3 of the present invention is the above-described tunnel deformation analysis method according to claim 1, wherein the deformation characteristic change and the strength characteristic change according to the damage parameter are simulated as deterioration of the natural ground element model. The displacement is calculated by applying a plastic pressure caused by the deterioration of the natural ground element model to the lining structure element model.

  According to the present invention, the structural degradation of the ground element model is simulated using the degree of chemical degradation of the natural ground due to the elution of ionized substances from the cement component of the lining structure as a damage parameter. Since the displacement of the lining structure element model accompanying deterioration is calculated, the applicable range does not depend on the dynamic construction conditions of the tunnel, for example, the earth covering must be sufficiently large. Moreover, as long as the lining structure is present, the ionized material is eluted from the cement component of the concrete continuously into the ground, so that the deformation analysis of the tunnel can be performed over a long period of time. become.

  Exemplary embodiments of a tunnel deformation analysis method according to the present invention will be described below in detail with reference to the accompanying drawings.

  First, in order to analyze the deformation behavior of a tunnel over a long period of time even under conditions of small initial ground pressure, it is necessary to construct an analysis model in consideration of the influence of the deformation factors over time. However, as described above, there are various limitations when mechanical conditions such as stress and pressure that directly affect the deformation behavior are used as the deformation factors. Therefore, the present inventor has greatly changed the idea, paying attention to the indirect factor of the chemical degradation degree to the natural ground from the concrete lining structure of the tunnel (hereinafter simply referred to as “lining concrete”), It was assumed that the chemical degradation of the natural ground was a factor causing long-term deformation in the tunnel. More specifically, ionized substances are eluted from the cement component of the lining concrete into the groundwater of the natural ground, and as the ground ion deteriorates due to the eluted ionized material, it enters the tunnel over time. The present invention has been created on the assumption that the extruding behavior occurs.

In the gaps of the lining concrete, calcium ions (Ca ²⁺ ) and hydroxide ions (OH ⁻ ) dissolved from the hydrate contained in the cement component coexist at a certain concentration. When the concentration of calcium ions present in the gap between the lining concrete is higher than the groundwater in the surrounding natural ground, concentration diffusion occurs and calcium ions diffuse into the surrounding natural ground. On the other hand, in lining concrete, from calcium hydroxide (Ca (OH) ₂ ) and calcium silicate hydrate (CSH) as cement components so that the concentration of calcium ions and the concentration of hydroxide ions are kept constant. Dissolution of calcium ions and hydroxide ions occurs. Thereby, it can be considered that the ionized material is constantly supplied from the lining concrete to the surrounding natural ground.

  It can be assumed that, among the ionized materials eluted from the lining concrete, calcium ions have the most influence on the deterioration of natural ground for the following reasons.

(1) Decrease in swelling pressure of natural ground due to ion exchange reaction between groundwater and natural clay minerals The following ions are present between calcium ions eluted in groundwater and Na-montmorillonite, a natural mineral clay mineral. An exchange reaction occurs.
Ca ²⁺ +6 [Na-montmorillonite] = [Ca-montmorillonite] + 2Na ⁺

  This reaction reaches a chemical equilibrium state in a relatively short time of several hours to several weeks. About the influence by this ion exchange reaction, as shown in FIG. 1, it turns out that a swelling pressure falls because sodium ion is substituted by calcium ion. That is, if the surrounding natural ground is under the groundwater before and after the construction of the tunnel, and the Na-montmorillonite in the natural ground is sufficiently saturated, it can be considered that it had swelling properties. Therefore, if this is replaced with calcium ions, the swelling pressure is reduced, and the bearing capacity of the ground around the tunnel is reduced.

(2) Change in consistency due to ion exchange of clay minerals It is known that clay minerals differ in how they are deformed and the degree of resistance (consistency) depending on the water content. The consistency is divided into four stages of liquid state, plastic state, semi-solid state, and solid state, and the boundaries are called the liquid limit, plastic limit, and shrinkage limit, respectively, and given by the water content ratio. This classification is called Atterberg's consistency limit. Fig. 2 shows the Atterberg limit test results of major clay minerals. As is clear from FIG. 2, each clay mineral tends to decrease the water content ratio of the liquid limit and the plastic limit by exchanging calcium ions in the ground water with sodium ions in the clay mineral. It can be seen that the water content at the liquid limit is reduced. In other words, when sodium ions of montmorillonite are replaced with calcium ions, the liquid limit is lowered, for example, what is in a plastic state becomes a liquid state, and the manner of deformation and the degree of resistance greatly change. .

  If the deformation of the surrounding natural ground is stationary at the time of tunnel construction, the effect of this change in consistency is considered to be small, but if the natural ground is deformed in the long term, the deformation method and the degree of resistance will change. It is thought that the effects of doing this cannot be ignored.

(3) Dissolution of clay minerals due to high alkalinity of groundwater Groundwater around the tunnel becomes a high pH environment as calcium ions are eluted from the lining concrete. Under such circumstances, hydrolysis and dissolution of clay minerals as shown below are likely to occur.
3 [Na-montmorillonite] + 11 / 2H ₂ O = 3/2 [kaolinite] + 4H ₂ SiO ₄ + 2Na ⁺
[Kaolinite] + 5H ₂ O = 2Al (OH) ₃ + 2H ₂ SiO ₄

  When considering the matrix (element part) of the natural element model, these dissolutions may lead to a decrease in the volume of the matrix, leading to an increase in substantial stress in the matrix and a decrease in strength (adhesive strength).

  Based on the above consideration, the ground element model for the analysis by the finite element method etc. was formulated as follows. In the following, it is assumed that groundwater exists in the ground around the tunnel, and since the ground is low in permeability, there will be no large groundwater flow, and the influence will be small, so that calcium ions will diffuse. To do.

Assuming that the above-mentioned chemical change has occurred and that the natural ground has deteriorated, such as Na-montmorillonite contained in the natural ground being replaced by Ca-montmorillonite due to the diffusion of calcium ions to the natural ground surrounding the tunnel, The damage parameter, which is the degree, is expressed by the following formula.
Dp = Mc / M0
Here, M0 (mol / m ³ ) is the initial content of Na-montmorillonite. Mc (mol / m ³ ) is the content of Na-montmorillonite after chemical change, and was calculated as follows in each step of the calculation.
Mc ⁽ⁱ⁾ = Mc ^(i-1) -n, DCa, Ac, dt
Here, n, DCa, Ac and dt are the porosity of the natural ground, the calcium ion concentration, the ion substitution rate, and the time interval from the analysis steps (i-1) to (i), respectively.

Using the damage parameters, the deformation characteristics and strength characteristics of the natural ground element model are expressed as follows:
G = G0 ・ Fd
K = K0 ・ Fd
Fd = 1 + (1-Rm) (Dp-1)
C = C0 + (C0-Cres ) (Dp a -1)
Φ = Φ0 + (Φ0−Φres) (Dp ^b −1)
Here, G, K, C, and Φ are the shear elastic modulus, bulk elastic modulus, shear strength, and internal friction angle of the natural ground at the damage parameter Dp. The subscript “0” means the initial strength, and the subscript “res” means the residual strength. Rm, a, and b are constants.

  FIG. 3 is a block diagram showing a configuration of an analysis apparatus applied in the present invention. The analysis device exemplified here is realized by causing a numerical calculation device such as a personal computer to read a program, and an element model generation unit 10, a diffusion distribution calculation unit 11, a parameter setting unit 12, and a deterioration calculation unit 13. The displacement calculation unit 14 is provided. The element model generation unit 10 converts each of the data such as specifications, physical properties, boundary conditions, etc. of the lining concrete and surrounding ground of the tunnel to be analyzed through the input means 20 such as a keyboard into an element model. Is. When a diffusion coefficient is given through the input means 20, the diffusion distribution calculation unit 11 generates calcium ions from the element model of the lining concrete (hereinafter referred to as “covering structure element model”) with respect to the ground element model. A diffusion concentration distribution is calculated. The parameter setting unit 12 calculates the chemical degradation degree when calcium ions are eluted from the cement component of the lining concrete into the natural ground as a damage parameter, and sets this as a natural ground element model. The deterioration calculation unit 13 calculates a change in deformation characteristics and a change in strength characteristics in the ground element model according to the damage parameter from the calcium ion diffusion concentration distribution calculated by the diffusion distribution calculation unit 11. When the deterioration calculation unit 13 calculates the deformation characteristic change and the strength characteristic change in the natural ground element model, the displacement calculation unit 14 is plastic due to the deformation characteristic change and the strength characteristic change in the natural ground element model. Pressure is applied to the lining structure element model to calculate the displacement.

  FIG. 4 is a flowchart showing a procedure of processing performed by the above-described analyzing apparatus. In this analysis device, element modeling of the lining concrete and surrounding ground is performed through the element model generation unit 10 to obtain an initial state at the time of construction (step S100). Next, the analysis apparatus performs a process of calculating the diffusion concentration distribution of calcium ions from the lining structure element model to the natural mountain element model through the diffusion distribution calculation unit 11 (step S101).

  Next, based on the calculated diffusion concentration distribution of calcium ions, the analysis device calculates the degree of chemical deterioration when calcium ions are eluted from the cement component of the lining concrete as a damage parameter through the parameter setting unit 12. This is set in each matrix (element part) of the natural ground element model (step S102), and further, through the deterioration calculation unit 13, the deformation characteristics of the natural ground element model accompanying the diffusion of calcium ions from the lining structure element model and The strength characteristic is simulated according to each damage parameter and the change is calculated (step S103).

  Finally, the displacement calculation unit 14 applies a plastic pressure accompanying the change in the deformation characteristics of the ground element model and the deterioration of the strength characteristics to the lining structure element model to calculate the displacement of the lining structure element model. (Step S104). Thereafter, by repeatedly performing the processing from step S101 until the elapsed years end (step S105), the deformation behavior of the tunnel can be analyzed from the displacement of the lining structure element model. The element model generated by the element model generation unit 10, the diffusion concentration distribution state of calcium ions calculated by the diffusion distribution calculation unit 11, the damage parameters set by the parameter setting unit 12, and the deformation characteristics calculated by the deterioration calculation unit 13 Further, the change of the strength characteristic and the displacement state of the lining structure element model calculated by the displacement calculation unit 14 can be output each time through the output means 30 such as a display or a printer.

  Hereinafter, an embodiment of the present invention in which an actual tunnel is analyzed by the above-described analyzing apparatus will be described.

-Setting of physical properties In this example, as a basic physical property given to the element model generation unit 10, a conventional examination (Hiroo Kumazaka, Toshihiro Asakura, Yoshiyuki Kojima, Tsuyoshi Matsunaga: Tunnel deformation analysis method considering the time dependence of natural ground The conditions used for the tunnel beam-spring model as in the 32nd Symposium on Rock Mechanics (pp.34-40, 2003) , P.215, 1998) and Aidan et al. (Aidan Omer, Tomoyuki Akagi, Takashi Ito, Kamimoto Kawamoto: About the deformation behavior of a tunnel in the squeezing ground and its prediction method, Proceedings of the Japan Society of Civil Engineers, No.448 / III , Pp.73-82, 1992), Tsuji et al. (Yu Shizuka, Tetsuro Esaki, Yasuyuki Yokota, Hidekazu Tsuji): Quantitative analysis of factors influencing the natural ground characteristic curve, Proceedings of the 9th National Symposium on Rock Mechanics , Pp.767-772, 1994) And using a physical property values obtained from the correlation equation. The dilatancy angle was set to ½ of the internal friction angle of the peak strength so that deformation (volume increase) after yielding would not be excessive. The uniaxial compressive strength and shear strength obtained from Cres and Φres in the residual strength state were set to ½ of the correlation values of Aidan et al. The physical properties of the natural ground and the lining concrete used in the analysis are shown in FIG. The diffusion coefficient given to the diffusion distribution calculation unit 11 was set to 1.0 × 10 ⁻⁵ (cm 2 / s) with reference to the diffusion coefficient of the electrolyte in the dilute aqueous solution.

・ Analysis model and boundary conditions In this example, we focus on expressing the phenomenon that plastic pressure acts isotropically on the lining concrete due to long-term deterioration of the surrounding rocks in the tunnel and pushes it into the tunnel. Yes. For this reason, in the element model generation part 10, the lining concrete and the natural ground were each made into an element model as a right half section in consideration of the symmetry condition. FIG. 6 shows the specifications of the tunnel, FIG. 7 shows the analysis region, boundary conditions, and element model division status, and FIG. 8 shows the element modeling and boundary conditions of the lining concrete.

  In addition, it has been clarified from the deformation investigation that the tunnel to be analyzed has a cavity on the back surface of the lining concrete located near the top end. For this reason, as a condition similar to the beam-spring model, three elements of the natural ground element model were hollowed in a range of 30 ° to the left and right with the circle center as the radius from the top of the upper half.

  Regarding the element modeling of contact between lining concrete and natural ground, since the construction of this tunnel is a conventional construction method, it was assumed that the lining concrete and natural ground were not integrated and handled as a slip by Coulomb's law. In addition, since the lining concrete is deformed like a cantilever, it was modeled using interface elements so that the lining concrete and the natural ground can be separated.

  The lining concrete is modeled as a non-linear material according to the Mohr-Coulomb law with the physical properties shown in FIG. 5, and stress exceeding the tensile strength is considered to be generated inside the central part of the side wall. Modeling using interface elements with tensile strength of lining concrete considering opening.

Analysis procedure The analysis in the diffusion distribution calculation unit 11, the deterioration calculation unit 13, and the displacement calculation unit 14 in the present embodiment is as follows.
(1) Initial ground pressure analysis The vertical stress assumed a hydrostatic pressure state with a lateral pressure coefficient of 1 in consideration of its own weight. As the boundary condition, as shown in FIG. 7, the initial stress of each element model is set by applying a distributed load corresponding to the initial ground pressure from the upper and right boundary.

(2) Excavation analysis 100% stress release analysis was performed because the tunnel was constructed by excavating the entire section using the conventional method.

(3) Tunnel deformation analysis after construction Reset the displacement up to the previous step and insert the element model part of the lining concrete. Calculate the diffusion of calcium ions from the lining concrete every year, and analyze the prediction of deformation of the lining structure element model from this diffusion concentration distribution taking into account the deterioration of the ground according to the above damage parameters Carried out.

-Prediction analysis result and consideration (1) About calcium ion concentration distribution FIG. 9 shows the calcium ion concentration distribution in the ground around the tunnel after 30 years calculated by the diffusion distribution calculation unit 11 in color intensity. Yes, FIG. 10 shows the relationship between the distance from the natural wall surface and the calcium ion concentration distribution. As can be seen from these figures, the calcium ions eluted from the lining concrete are distributed in 2 to 3 m near the tunnel, and the concentration increases with the elapsed years.

(2) Distribution of damage parameters FIG. 11 shows the relationship between the distance from the natural ground wall and the distribution of damage parameters. As shown in FIG. 11, the degraded area of the natural ground due to calcium ions eluted from the lining concrete is distributed in 2 to 3 m near the tunnel. This corresponds to the relationship between the distance from the ground wall shown in FIG. 10 and the calcium ion concentration distribution. Moreover, it turns out that the damage parameter of an area | region becomes small with the elapsed years, that is, a deterioration degree becomes large, and this is remarkable near a natural ground wall surface.

(3) Horizontal direction internal air displacement FIG. 12 shows the relationship between the number of years elapsed and the amount of internal air displacement at the internal air displacement measurement position shown in FIG. 6, and FIG. And the amount of horizontal displacement. The broken line in FIG. 12 shows the relationship between the progress variable and the inner air displacement at an average initial displacement speed of 6 mm / year in each inner air displacement measurement of the tunnel. On the other hand, the relationship between the number of years elapsed from the analysis and the amount of displacement in the sky is not a linear relationship, and this place is similar to the average initial displacement speed of 6 mm / year, but the displacement speed is between 10 and 20 years. After that, the S-curve returned to the initial displacement speed again.

  In addition, in the ground degradation model studied previously, the long-term displacement converged in about 22 years, but in this example, the deformation caused by the deformation occurred over 50 years.

  In addition, as shown in FIG. 13, horizontal displacement in the natural ground becomes noticeable at 2 to 3 m near the tunnel corresponding to the decrease of the damage parameter in FIG. Increased results.

  As described above, according to the analysis of the present embodiment, the coverage is not influenced by the dynamic construction conditions of the tunnel, for example, the earth covering must be sufficiently large. It becomes possible to predict the deformation analysis.

  In the above-described embodiment, when the tunnel lining concrete and surrounding ground are modeled, the interface element is used. However, the interface element is not necessarily used. The analysis may be performed by simply modeling the mountain as an element model. Further, the physical properties and specifications in the case of performing the analysis are merely examples, and it goes without saying that they may be changed as appropriate according to the tunnel to be applied.

It is a graph which shows the relationship between the swelling pressure and normal strain of bentonite. It is a chart which shows the Atterberg limit test value of the main clay mineral. It is a block diagram which shows the structure of the analyzer applied by this invention. It is the flowchart which showed the procedure of the process which the analysis apparatus shown in FIG. 3 implements. It is a table | surface which shows the physical-property value of the natural ground applied in the Example of this invention and a concrete lining structure. It is a conceptual diagram which shows the item of the analysis model applied in the Example of this invention. It is a conceptual diagram which shows the division | segmentation condition of the analysis area | region and boundary condition of an analysis model applied in the Example of this invention, and an element model. It is a conceptual diagram shown about the element modeling and boundary condition of a lining structure body in the analysis model applied in the Example of this invention. It is the conceptual diagram which showed the calcium ion density | concentration distribution in the tunnel surrounding natural ground 30 years later in the analysis model applied in the Example of this invention. It is the graph which showed the relationship between the distance from a natural mountain wall surface, and calcium ion concentration distribution. It is the graph which showed the relationship between the distance from a natural ground wall, and distribution of damage parameters. It is the graph which showed the relationship between the elapsed years and the amount of internal space displacement in the internal space displacement measurement position shown in FIG. It is the graph which showed the relationship between the distance from a natural ground wall surface, and the amount of horizontal displacement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Element model production | generation part 11 Diffusion distribution calculating part 12 Parameter setting part 13 Deterioration calculating part 14 Displacement calculating part 17 Basic engineering 20 Input means 30 Output means

Claims (3)

A method for analyzing deformation of a tunnel having a concrete lining structure,
A process of elemental modeling of the lining structure and surrounding ground,
Calculating a diffusion distribution of ionized substances from the lining structure element model for the natural mountain element model;
Calculating the degree of chemical degradation when ionized substances are eluted from the cement component of the lining structure into the natural ground as a damage parameter, and setting this as a natural ground element model;
Simulating the degradation of the ground element model due to the diffusion of ionized material from the lining structure element model according to the damage parameters;
And a step of calculating a displacement of the lining structure element model accompanying the deterioration of the ground element model.   2. The deformation analysis of a tunnel according to claim 1, wherein the damage parameter is set as a rate of chemical deterioration that occurs in clay minerals in a natural ground with the elution of calcium ions from the lining structure. Method.   The deformation characteristic change and the strength characteristic change according to the damage parameters are simulated as deterioration of the natural ground element model, and the plastic pressure resulting from the deterioration of the natural ground element model is applied to the lining structure element model. The tunnel deformation analysis method according to claim 1, wherein the displacement is calculated.

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