JP2005258569A - Strength evaluation method for rc made underground hollow structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method that simply and precisely evaluates the strength appropriateness of an existing tunnel. <P>SOLUTION: The strength evaluation method for a shield tunnel forms endless grooves 33 to a predetermined depth in wall portions 31 of an existing tunnel 3 to form island portions 2 in the wall portions 31 defined by the grooves 33, sets strain gauges 5 on the island portions 2, computes stresses developed in the island portions 2 from measurement results of strain, creates a structural analysis model Md of the tunnel 3, calculates stresses in portions of the model Md corresponding to the island portions, computes a difference δαλk between the structurally calculated stresses σi calculated on the model Md and the stresses σcal computed from the measured strains, and combines coefficients of earth pressure α, λ and k so as to minimize the difference δαλk. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for evaluating the strength of underground structures made of reinforced concrete (hereinafter RC).

  As a structure type of an RC underground structure, for example, a tunnel, a shield tunnel having a circular cross section, a cut-out tunnel having a rectangular shape, and other tunnels are well known. Among these tunnels, when building a cylindrical structure that will be the inner wall surface of a tunnel constructed by RC segments, soil forces acting on the tunnel wall surface in the soil (especially the soil and the structure are in contact) The earth pressure, which is the pressure of the soil acting on the boundary surface of the structure, and the water pressure, which is the pressure exerted by water on the structure, are calculated in design. In this case, the water pressure can be obtained relatively accurately based on Pascal's law, but the earth pressure tends to be inaccurate because the size of the underground soil particles varies from place to place.

  As is well known, a shield tunnel is a segment made of RC (Reinforced Concrete Construction) after excavating natural ground with a shield excavator. This is a tunnel formed by assembling a large number of side-arc shaped block bodies. The excavated tunnel is a tunnel constructed by excavating the earth once, building a tunnel, and then backfilling the earth and sand. Say.

FIG. 18 and FIG. 19 are explanatory diagrams for the calculation method of the design earth pressure (design earth pressure) of the shield tunnel and the open tunnel, respectively.
The meaning of each symbol in these figures is as follows.

(Earth pressure coefficient)
α: Vertical earth pressure coefficient λ: Lateral earth pressure coefficient k: Ground reaction force coefficient (load calculation condition)
H: Distance from the ground surface to the tunnel (also called soil cover)
h: Tunnel height (tunnel outer diameter)
γ: Unit volume of soil (design earth pressure of tunnel)
σv: Pressure due to the weight of the soil applied to the top of the tunnel (referred to as total earth cover pressure, expressed by the formula: γ · H)
σv1: Earth pressure acting in the vertical direction at the top of the tunnel (referred to as vertical earth pressure, expressed as: α · σv)
σv2: Reaction force generated in the bottom plate against the total earth pressure (referred to as the bottom plate reaction force, expressed by the formula: σv1 + tunnel's own weight)
σh1: This means the minimum earth pressure generated in the horizontal direction and is called the minimum side earth pressure (λ · α · σv).

σh2: The maximum earth pressure generated in the horizontal direction, which is called the maximum lateral earth pressure (λα (σv + γ · h).
Note that the ground reaction force coefficient k shown in FIG. 18 has the maximum value in the outer diameter portion in the horizontal direction of the tunnel cross section, and the k value increases as it advances from the maximum value in the tunnel circumferential direction. Then, it gradually becomes smaller as it proceeds toward the apex of the outer peripheral surface of the tunnel.

  The earth pressure coefficients α, λ, and k are well-known numerical values in accordance with various design standards (tunnel standard specifications <shield method, open-cut method> and explanations) established by the Japan Society of Civil Engineers. The numerical values are the basis of the basic design for constructing the tunnel, such as the thickness dimensions of the segments constituting the tunnel and the strength of the aggregate.

The earth pressure generated in the horizontal direction (side earth pressure including σh1 and σh2) becomes higher as it goes downward in the vertical direction.
By the way, the design soil pressures σv, σv1, σv2, σh1, and σh2 of the tunnel calculated by the soil pressure coefficients α, λ, and k are different from each other in the size of underground soil particles as described above. Or due to construction conditions. The following can be considered when the variation in the design earth pressure is large.
(1) If the design earth pressure of the existing tunnel is set excessively compared with the earth pressure actually acting on the tunnel, the existing tunnel can afford the strength and durability, but the waste of material and There is a risk of increasing costs.
(2) On the contrary, when the design earth pressure of the existing tunnel is set to be lower than the earth pressure actually acting on the tunnel, the existing tunnel has no room for strength or durability. For this reason, the case where reinforcement construction is required is considered.

  Conventionally, a technique for measuring earth pressure by placing earth pressure gauges on the ground surface of tunnels and other underground structures is well known. However, measuring instruments such as earth pressure gauges are expensive. Therefore, it can be said that the earth pressure measurement technology so far has poor reliability because the number of acquired data is not sufficient because the device is not widespread. In addition, it is desired to propose a simple and reliable technique as a method for evaluating the strength of underground structures.

  The present invention has been made in view of such circumstances, and the problem to be solved is whether or not the strength of the existing tunnel or other RC hollow structure in the RC structure is set appropriately. An object of the present invention is to provide a method for evaluating the strength of a hollow structure in an RC structure that can be easily and accurately evaluated.

Therefore, the present invention employs the following means.
That is, according to the strength evaluation method for an RC ground hollow structure in the present invention, an endless groove having a predetermined depth is formed in a wall of a tunnel which is an existing RC ground hollow structure, and the groove is formed. The island part which is an isolated region from the surroundings is formed on the wall part, and a strain gauge is placed on the island part. Based on the measurement result of the strain, the degree of stress generated in the island part is obtained, and the structural analysis of the tunnel is performed. Create a model, calculate the stress level of the part corresponding to the island part of the model, and the stress level obtained from the stress level by the structural calculation calculated based on the model and the strain actually measured with the strain gauge (actual strain) The earth pressure coefficient that is the coefficient for earth pressure calculation is combined so that the difference is minimized, and the earth pressure coefficient at the time of the difference obtained by the combination is hollow in the existing RC ground. Applied as earth pressure coefficient of structure The earth pressure acting on the RC underground structure is calculated as the minimum differential earth pressure, the stress level is calculated based on the minimum differential earth pressure, and the calculated stress level (differential minimum stress level). ) On the basis of the predetermined standard 1, the soundness of the RC underground hollow structure is evaluated.

The degree of stress is synonymous with stress, and is an internal resistance force generated inside the object against the earth pressure per unit area of the RC hollow structure in the earth or the structural analysis model.
For earth pressure,
・ Σv: Whole earth pressure (γ ・ H)
・ Σv1: Vertical earth pressure (α ・ σv)
・ Σv2: Bottom reaction force (σv1 + RC's own internal hollow structure weight)
・ Σh1: Minimum lateral earth pressure (λ ・ α ・ σv)
Σh2: Maximum lateral earth pressure (λα (σv + γ · h) is mentioned.

  Where α: vertical earth pressure coefficient, λ: lateral earth pressure coefficient, k: ground reaction force coefficient means earth pressure coefficient, code H: earth covering, h: height of RC hollow structure in the ground Γ: Unit volume of soil means load calculation conditions.

  Therefore, earth pressure is a coefficient for earth pressure calculation so that the difference between the stress degree obtained from the measured strain and the stress degree obtained by calculation for the structural analysis model of the RC underground hollow structure is minimized. The earth pressure when the difference is the minimum is applied to the existing RC underground hollow structure as the earth pressure coefficient of the existing RC underground hollow structure. Calculate. And the soundness of the existing RC underground hollow structure is judged by comparing the calculated earth pressure with the design earth pressure actually applied to the existing RC underground hollow structure.

The following (A) and (B) are given as predetermined standards for determining the soundness level.
(A) Absolute value of the stress level based on the design earth pressure actually applied to the existing RC underground hollow structure> Absolute value of the minimum differential stress → In this case, the RC underground hollow structure There is no need to reinforce things.
(B) Absolute value of the stress level based on the earth pressure (design earth pressure) actually applied to the existing RC ground hollow structure in the existing RC site ≤ absolute value of the stress level at the time of the differential minimum → In this case, the RC site Examine the need for reinforcement of the hollow inner structure.

  In the calculation, if the absolute value of the stress level based on the design earth pressure is equal to the absolute value of the stress level based on the absolute value of the minimum differential stress level, reinforcement is unnecessary, but in consideration of safety. In this case, the necessity for reinforcement shall be considered.

  The endless groove means a groove formed in a direction orthogonal to the wall portion of the RC underground hollow structure and having no interruption in the direction in which the groove extends on the wall surface. The endless groove formed in the RC underground hollow structure is formed by, for example, directing a highly rigid hollow cylinder perpendicular to the wall portion and press-fitting it while rotating. By doing so, an endless groove having a width corresponding to the thickness of the hollow cylindrical body and having a cross-sectional shape and a ring shape can be secured in the wall portion. Needless to say, the shape is not limited as long as it is an endless groove. By forming the endless groove, the region surrounded by the endless groove is isolated from the surroundings (that is, the island portion in this specification), and the non-enclosed region (that is, the RC in-ground structure main body Part of the island where no island is formed). When the endless groove is ring-shaped, the surrounding area becomes a circular cylinder having a circular cross section, and is connected to the RC underground structure main body only at the bottom, that is, the surrounding area in a cantilever shape. Will be supported against the non-going area. Depending on the size of the endless groove (the size depends on the depth and length of the endless groove), the degree of freedom of the surrounding area increases, and earth pressure received when it is integrated with the non-enclosed area You will be released from the external force. As a result, distortion occurs in the Go region. It is well known that the stress level can be easily calculated by calculating the strain, and the calculated stress level is compared with the minimum differential stress level based on the strain obtained by actual measurement. The appropriateness of the stress level of the existing RC underground structure can be understood by referring to the items (A) and (B) described above.

More details are as follows.
(1) A step of obtaining a stress degree from an actually measured strain of an existing RC underground hollow structure, a step of obtaining a stress degree of a structural analysis model of the RC underground hollow structure, and a difference between both stress degrees A method for evaluating the strength of a hollow structure in an RC structure, comprising: a step of obtaining a combination of earth pressure coefficients that are coefficients for earth pressure calculation so that the difference is minimized.
(2) A step of forming an endless groove having a predetermined depth in the wall portion of the existing RC underground hollow structure, and forming an island portion which is an isolated region from the surroundings by forming the endless groove. And a step of placing a strain gauge on the island, a step of obtaining a stress level generated in the island before the endless groove is formed based on a strain measurement result by the strain gauge, and the RC A structural analysis model of the underground hollow structure was created, and the stress level of the part corresponding to the island portion of the model was determined, and the stress level and the measured strain obtained from the structural calculation based on the structural analysis model A strength evaluation method for an RC underground hollow structure having a step of obtaining a difference in stress degree and a step of combining a soil pressure coefficient that is a coefficient for earth pressure calculation so that the difference is minimized.
(3) A step of forming an endless groove having a predetermined depth in the wall portion of the existing RC underground hollow structure, and forming an island portion that is an isolated region from the surroundings by forming the endless groove. And a step of placing a strain gauge on the island, and a step of measuring a stress level that has actually occurred in the island before the endless groove is formed based on a measurement result of the strain by the strain gauge, Creating a structural analysis model of the RC ground hollow structure, calculating a cross-sectional force of an island-corresponding portion of the model, a stress level based on the calculated cross-sectional force, and the island RC in-ground hollow having a step of obtaining a difference between the stress level actually generated in the part and a step of combining a soil pressure coefficient that is a coefficient for soil pressure calculation so that the difference is minimized Strength evaluation method for structures.
(4) Even if the island portion is formed, the predetermined depth is formed in a range in which the residual rate of the strain becomes 0, and the diameter of the endless groove is equal to the diameter of the crushed stone in the RC ground hollow structure. A strength evaluation method for a hollow structure in RC-made ground, characterized in that it is determined on the basis of the above.
(5) Earth pressure acting on the existing RC underground structure when the earth pressure coefficient when the difference is minimized is applied as the earth pressure coefficient of the existing RC underground hollow structure A method for evaluating the strength of a hollow structure in an RC ground, characterized by having a step of calculating the earth pressure as a minimum differential earth pressure.
(6) A method for evaluating the strength of a hollow structure in an RC structure, comprising a step of calculating the stress level based on the minimum differential earth pressure as the minimum differential stress level.
(7) The strength evaluation of the RC underground hollow structure characterized by evaluating the strength of the RC underground hollow structure by determining the minimum differential stress level based on a predetermined standard. Method.
(8) The strength evaluation of the RC underground hollow structure characterized in that the formation portion of the island portion is formed on the axial extension line at a location where the reinforcing bar of the RC underground hollow structure does not have a reinforcing bar. Method.
(9) The strain is measured at 1 to n dispersed locations in the RC ground hollow structure, and the average value thereof is set as the actually measured strain of the RC ground hollow structure. RC strength evaluation method for underground hollow structures.
(10) The RC ground-internal hollow structure is a shield tunnel, an open-cut tunnel or a shaft, and the strength evaluation method for the RC ground-in hollow structure.
(11) The measured strain measured by the strain gauge includes a tunnel axial strain in the tunnel axial direction and a tunnel transverse strain in the tunnel transverse direction. Evaluation methods.
(12) The strain in the axial direction of the tunnel and the strain in the transverse direction of the tunnel are detected by arranging strain gauges, which are constituent elements of the strain gauge, in the axial direction and the transverse direction of the tunnel, respectively. A method for evaluating the strength of a hollow structure in an RC structure, wherein the strain gauge is arranged in a direction and the twist of the tunnel is measured.

  According to the strength evaluation method of the RC ground hollow structure of the present invention, the actual earth pressure acting on the tunnel or other existing RC ground hollow structures, the earth pressure determined by design, Thus, it is possible to evaluate whether or not the strength of the existing tunnel or other RC ground hollow structure is set appropriately.

Hereinafter, embodiments of the present invention (hereinafter, embodiments) will be described with reference to the accompanying drawings.
FIG. 1 shows a shield that is an RC underground structure using an island forming device 1 that forms an island part 2 used in the strength evaluation method for an existing RC hollow structure according to the present invention. FIG. 3 is a perspective view showing a state where an island part 2 is formed in a tunnel 3.

  The shield tunnel 3 is formed by a number of segments 4 that are constituent elements thereof, and the segments 4 are arranged in the circumferential direction and the longitudinal direction (tunnel axis direction) of the tunnel 3. Further, the adjacent segments 4 in the tunnel longitudinal direction are displaced from each other in the tunnel circumferential direction (see FIG. 5). The groups of segments 4 in the circumferential direction are arranged so that every other group is in the same position in the longitudinal direction.

  Since the island forming device 1 is described in Japanese Patent Application No. 2003-343071 by the applicant of the present application, a detailed description thereof will be omitted, but if briefly described with reference to FIG. The cylindrical cutter 1a having an open hollow cylindrical shape is rotated by a drive motor, and the cutter 1a is caused to enter the hollow structure in the RC ground. It is an apparatus to form.

2, 3 and 4 are respectively a cross-sectional view, an enlarged cross-sectional view and a front view of the main part of the tunnel in which the island part 2 is formed.
The island part 2 is a specific area formed in the wall part 31. More specifically, the island part 2 presses the cylindrical cutter 1a of the island part forming device 1 perpendicularly to the wall part 31 of the shield tunnel 3 and press-fits into the wall part 3 while rotating the cylindrical cutter 1a in this state. This is a region surrounded by the wall portion 31 by an endless groove (a groove without interruption in the direction in which the groove extends) 33 formed in the wall portion 31.

  If the endless groove 33 is formed by the cylindrical cutter 1a, the endless groove 33 has a groove width W corresponding to the thickness of the cylindrical cutter 1a (FIG. 3). , See FIG. 4). Needless to say, the shape of the endless groove 33 is not limited to the ring shape. By forming the endless groove 33, it can be divided into an island part 2 which is an area surrounded by the endless groove 33 and a non-enclosed area (that is, a part of the tunnel body where the island part 2 is not formed) 3a. The shape of the island part 2 which is the surrounding area is a columnar shape. And the island part 2 is supported with respect to the non-enclosed area | region 3a in the state connected to the tunnel main body only at the bottom part, ie, cantilever shape.

  Moreover, the formation location of the island part 2 is made into the location which does not have the reinforcing bar of the RC structure inside hollow structure on the axial direction extension line. This is to prevent the cylindrical cutter 1a from colliding with the reinforcing bar. In order to know where the reinforcing bars are buried in the tunnel, the design drawing of the tunnel may be used, or an ultrasonic detector or other reinforcing bar probe may be used.

The size of the island portion 2 is determined by the depth De of the endless groove and the diameter Di of the island portion. In this embodiment, both are 50 mm (see FIGS. 3 and 4), but the dimensions are not limited to those dimensions, and the dimensions vary depending on the size of the tunnel. In short, even if the island portion 2 is formed, the predetermined depth is formed in a range where the residual strain rate becomes 0, and the diameter of the endless groove is based on the diameter of the crushed stone contained in the hollow structure in the RC structure. It is preferable to determine it. For example, if the endless groove has a depth of approximately 50 mm to 100 mm and a diameter of approximately 50 mm to 100 mm, it is suitable for obtaining the stress level. It is.
(About depth)
(Minimum depth)
FIG. 20 shows a general change tendency of the stress strain of the island part due to the formation of the groove in the RC structure. The vertical axis indicates the residual ratio (%) of the stress strain, and the horizontal axis is cut when the island part is formed. FIG. 5 is a stress strain residual ratio (%) — cutting depth / diameter diagram, which is a value (ratio) obtained by dividing the endless groove 33 by the diameter of the island portion 2. The graph of FIG. 20 is obtained from analysis and experiments in which a groove is formed after a known stress is generated in advance in the RC structure, and the residual degree of stress in the island portion is confirmed. It can be seen that the stress applied to the island portion is released when the depth of the endless groove 33 is about 1.0 or more, that is, about the diameter of the island portion 2 or more. Therefore, it can be seen that the endless groove 33 needs to be formed at least larger than the diameter of the island portion 2 in order to obtain an accurate value of the stress strain generated in the island portion 2.
(Maximum depth)
From the verification of the minimum depth, as the endless groove 33 is deeper, the measured strain becomes more stable and reliability is obtained. However, the target structure is a tunnel, and water pressure is usually applied to the rear surface. That is, if the endless groove is too deep, problems such as water leakage from the back surface may occur. That is, it is necessary to consider the thickness of the RC structure of the target tunnel for the maximum depth. Empirically, it is considered to be about 1/2 of the tunnel wall thickness. As can be seen from the verification of the minimum depth and the maximum depth, the numerical value of 50 to 100 mm of the depth suggests a range in which the tunnel is not damaged such as water leakage. Therefore, as long as the damage is not given, the numerical range is not limited.

(About diameter)
(Minimum diameter)
The minimum diameter is 50 mm based on the measurement accuracy of the strain gauge. That is, the measurement accuracy of the strain gauge shown in the garden 10 is affected by the diameter of crushed stone in the concrete. The diameter of this crushed stone is about 20 mm. In order not to be affected, the length of the strain gauge needs to be 2.0 to 3.0 times this diameter. Therefore, the minimum diameter of the endless groove is about 50 mm.
(Maximum diameter)
The maximum diameter is set to 100 mm based on the arrangement of the reinforcing bars. Reinforcing bars for general RC structures are arranged at intervals of about 150 mm. Therefore, since it is necessary to form the island part 2 avoiding the reinforcing bars, the maximum diameter is about 100 mm.

  The greater the depth of the endless groove 33, the higher the degree of freedom of the island portion 2, and it is released from external force such as earth pressure received when it is integrated with the non-enclosed region 3a. As a result, the island 2 is distorted. If the strain is known, the stress level can be obtained. The degree of stress is an internal resistance force generated inside a material when an external force is applied to the material. By forming the island part 2 in the RC segment 4, the island part 2 is released from the RC segment 4 and no external force is applied to the island part 2, so that no stress is generated in the island part 2. And how much stress was acting on the island part 2 before formation of the island part 2 can be calculated | required by calculation from distortion. A method of measuring strain by forming the island portion 2 is called a stress release method. Note that the endless groove 33 is closed after the strain measurement is completed.

  The degree of stress obtained by calculation based on the strain obtained by the stress release method is compared with the degree of stress obtained by calculating for the structural analysis model of the RC underground hollow structure. At that time, the appropriateness of the stress level of the existing RC in-ground structure is determined in consideration of a predetermined standard.

  5-8 shows an example of an island part formation location. 5 is a side view of the shield tunnel 3, FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 5, FIG. 7 is a cross-sectional view taken along the line VII-VII in FIG. It is.

The seventeen locations (i) to (l) shown in FIGS. 6 to 8 are island formation locations in the shield tunnel 3. Among the segments M, L, and R shown by hatching in FIG. 5, the segment group M in the central portion includes a segment K type at the ceiling, a segment B type-2 at the bottom, and a side peripheral portion as shown in FIG. It consists of segment A type-1, A type-2, B type-1, and B type-3. Of these segments, the segment A type-1, A type-2, B type-1, B type-3 have islands 2 formed in the vicinity of the boundary and near the center, and the bottom segment. In the B-type-2, an island 2 is formed at the center.

  One segment group R (the group on the right side in FIG. 5) on both sides of the segment group M includes the center of the other segment 4 except for the segment K type and A type-1 as shown in FIG. The island part 2 is formed.

  In the other segment group (the group on the left side of FIG. 5), an island 2 is formed at the center of each segment 4 except for segment K type and B type-3 as shown in FIG. Yes.

  In each island part 2 in these locations (i) to (l), a strain which is a constituent element of a strain gauge (a part of the strain gauge) indicated by reference numeral 5 in FIG. 9 and FIG. The gauges 5 are arranged in the axial direction of the shield tunnel 3, the transverse direction, and the intermediate direction (45 degree direction) between these axial directions and transverse directions, respectively. The twist degree of the shield tunnel 3 can be measured by the strain gauge 5 arranged in the 45 degree direction. In attaching the strain gauge, the tip surface 2a of the island 2 is flattened. Thereafter, the elastic coefficient Ec of the segment 4 is measured by a known elastic wave method. After the measurement, the island forming device 1 is installed and the strain is measured for each island. The strain measured by the strain gauge 5 is called measured strain.

  In the strength evaluation method of the shield tunnel according to the present embodiment, based on the measurement results of the transverse strain and the axial strain (hereinafter referred to as tunnel transverse strain and tunnel axial strain) by the strain gauge. Then, the degree of stress generated in the island part 2 is obtained from the measured strain. Then, a structural analysis model of the shield tunnel 3 is created, and the stress level of the portion corresponding to the island portion is calculated from the model, and the stress calculated from the structural calculation calculated based on the structural analysis model and the measured strain A combination of earth pressure coefficients (α: vertical earth pressure coefficient, λ: lateral earth pressure coefficient, k: ground reaction force coefficient), which is a coefficient for earth pressure calculation so that the difference in degree is obtained I do. Then, the earth pressure acting on the existing shield tunnel is calculated using the earth pressure coefficient when the difference is the minimum. The calculated earth pressure is defined as the minimum differential earth pressure, based on the stress level calculated based on the minimum differential earth pressure (hereinafter referred to as the minimum differential stress level) and the earth pressure coefficient actually used for the existing shield tunnel. The soundness of the shield tunnel is judged by comparing the degree of stress calculated based on the earth pressure (hereinafter, the actual design earth pressure) (hereinafter, the actual design stress).

  The tunnel transverse strain II1 and the tunnel axial strain II2 obtained by the stress release method, that is, obtained by actual measurement, include the stress strain ε1 caused by the load (earth pressure) and the temperature drying shrinkage strain ε2. (Temperature drying shrinkage strain means that the temperature and humidity are constant on the natural ground side of the tunnel, while those on the inside are indefinite. This is the change in strain.)

  Therefore, in order to obtain the stress strain ε1, it is necessary to correct the tunnel transverse strain II1 and the tunnel axial strain II2 in consideration of the temperature drying shrinkage strain ε2, and the stress strain ε1, the temperature drying shrinkage strain ε2 and the tunnel transverse direction. The relationship between the strain II1 and the relationship between the stress strain ε1, the temperature drying shrinkage strain ε2, and the tunnel axial strain II2 are expressed by (Equation 1) and (Equation 2), respectively.

  II1, II2, ε1, and ε2 are expressed by the following (Expression 1) to (Expression 4), and by solving the simultaneous equations of (Expression 1) and (Expression 2), a stress strain ε1 is obtained (Expression 3). It is done. In (Expression 1) to (Expression 4), ν is the Poisson's ratio of concrete.

Note that (Expression 1) and (Expression 2) are established based on the assumptions shown in the following (i) to (iii). (I) Since there is a load effect in the tunnel transverse direction, stress strain occurs. And distortion also arises in the tunnel axis direction by the well-known Poisson effect.
(Ii) Since no load is applied in the tunnel axis direction, no stress strain occurs.
(Iii) The temperature drying strain is the same in the tunnel transverse direction and the tunnel axis direction.

Although Equation 4 does not affect the direct determination of stress strain, it is described because the simultaneous equations are solved.
In order to obtain the concrete stress degree σi of the shield tunnel 3 from the stress strain ε1, it is calculated from (Equation 5). ε1 is a strain generated in the transverse direction due to the load action of the tunnel, and this is multiplied by the elastic modulus Ec of the segment measured by the elastic wave method to obtain the stress level σi of the concrete of the island portion 2 that is the measurement position. .

   Measurement results of tunnel transverse strain II1 and tunnel axial strain II2 measured with strain release by the stress release method for the previous 17 islands 2, stress strain ε1, temperature drying shrinkage strain ε2, and concrete stress Table 1 shows the degree σi.

In Table 1, data on the twist of the shield tunnel 3 is omitted.
Next, calculation of the concrete stress degree σcal of the shield tunnel 3 by structural calculation will be described. In the description, the structural analysis model of the shield tunnel will be described with reference to FIGS.

  As is well known, the shield tunnel 3 is mainly configured by connecting RC segments 4 with a number of joints (for example, a segment joint 3b made of a rotary spring, a ring joint 3c made of a shear spring, and a number of bolts (not shown) (see FIG. 11 and FIG. 12).

  Then, in the structural analysis model Md of the shield tunnel 3 as shown in FIG. 12, a well-known beam-spring model calculation method in which the RC segment 4, the joints 3b and 3c are modeled is used. As the specifications of the model Md, different values are used depending on the thickness of the RC segment 4 and the sizes of bolts and springs. The stress σcal of tunnel concrete by structural calculation is calculated by computer software by inputting design load into this model. The stress σcal of the tunnel concrete by the structural calculation is the cross section obtained by calculating the cross-sectional force of the portion corresponding to the island portion of the structural analysis model Md of the RC hollow structure in the RC created as described above. It can be calculated as a stress level based on force. Since the calculation method of the stress level based on the cross-sectional force is a well-known matter, the description is omitted here. Further, the method for obtaining the design load of the shield tunnel 3 (method for calculating the design earth pressure obtained in the design) is the same as that in FIG.

  Next, the optimum tunnel load condition is searched from the difference (error) δαλk between the stress degree σi of the island portion 2 formed dispersed in the n places and the concrete stress degree σcal of the shield tunnel by the structural calculation. In order to perform the search, the following (formula 6) is used.

  However, δαλk is a deviation (N / mm 2) with respect to the average of σ i, and n is the number of island portions in the shield tunnel and the structural analysis model (in this embodiment, the island portion 2 is a location (as described above) B) There are 17 locations from (b) to (b)). [sigma] i- [sigma] cal.i indicates the difference between the stress degree [sigma] i obtained from the measured strain and the stress degree [sigma] cal.i obtained by calculation for the structural analysis model Md. By forming the islands in a dispersed manner, the stress level generated in the islands can be averaged more appropriately.

  (Equation 6) means that strain measurement is performed at 1 to n locations in the shield tunnel 3 to obtain a measured stress level (σ), and the difference between the stress level σcal based on the structural calculation of the corresponding location. The geometric mean is defined as the accuracy of the earth pressure coefficient (α, λ, k).

  From (Equation 6), when δαλk is large, the accuracy of the earth pressure coefficient (α, λ, k) is deteriorated, and when δαλk is small, the accuracy of the earth pressure coefficient (α, λ, k) is good. For example, the average absolute value of the measured stress (σ) is about 3N / mm2, but if δαλk is about 3N / mm2, the accuracy of the earth pressure coefficient (α, λ, k) is 100%, The accuracy with respect to the actual measurement of the earth pressure coefficient (α, λ, k) is poor. However, if δαλk is about 1 N / mm 2, the accuracy with respect to the actual measurement of the earth pressure coefficient (α, λ, k) is 33%, and it can be said that the accuracy is relatively good.

Next, the search for optimum tunnel load conditions will be described.
Structural analysis of 2500 cases (= 50 × 50) is performed by changing the earth pressure coefficients α and λ as follows. The stress level σcal at the same location (17 locations) as the on-site measurement is obtained. Here, k = 0 is assumed. (When k is taken into account, 2500 cases are similarly calculated for the set k value.)
0.02 ≦ α ≦ 1.0 (50 cases set at intervals of 0.02)
0.02 ≦ λ ≦ 1.0 (50 cases set at intervals of 0.02)
Since the interval is 0.02, there are 2500 cases. Therefore, the number of cases is not limited and can be freely selected depending on the interval.

  Among the δαλk of 2500 cases, the minimum combination of α and λ is extracted and the earth pressure constant at the examination point (α: vertical earth pressure coefficient, λ: lateral earth pressure coefficient, k: The optimum value of the ground reaction force coefficient.

  An estimated image of 2500 cases is shown in FIG. In FIG. 13, the X coordinate, the Y coordinate, and the Z coordinate indicate the vertical earth pressure coefficient α, the error δαλk, and the side earth pressure coefficient λ, respectively. As can be seen from FIG. 13, when 2500 cases are combined, a bowl-shaped locus (graph) is obtained. FIG. 13 is an image diagram and does not necessarily have such a form.

FIG. 14 is a vertical earth pressure coefficient-side earth pressure coefficient diagram in which the vertical earth pressure coefficient is taken on the vertical axis and the side earth pressure coefficient is taken on the horizontal axis, and the acting load of the shield tunnel 3 is estimated. Results are shown.
Further, for the shield tunnel 3, a combination (α = 0.72, λ = 0.98, k = 0.0) such that δαλk = 0.84 shown in FIG. 14 is the optimum value (δαλk is the minimum value). It can be seen that it is. Each region in FIG. 14 indicates a divided region of δαλk, and is divided every 2 N / mm 2 in the range of 0 to 20 N / mm 2.

  Next, the soundness of the shield tunnel 3 is illustrated with reference to FIGS. 15 to 17 using the optimum value. 15 to 17, for the segment groups L, M, and R of the shield tunnel 3, the vertical axis represents the stress level, and the horizontal axis represents the angle (0 ° to 360 °) in the circumferential direction of the shield tunnel 3. It is a stress degree-angle diagram. In these diagrams, the symbol (black circle) means the stress degree σi obtained from the strain obtained by actual measurement by the stress release method, and the broken line locus (graph) indicated by the broken line indicates the circumference of the shield tunnel 3. Trajectory (structural calculation) showing the stress distribution when the optimum values (α = 0.72, λ = 0.98, k = 0.0) obtained by structural calculation in the direction of 0 ° to 360 ° in the direction are applied (Trajectory based on optimum value).

  The solid line locus (graph) indicated by the solid line is the result of the structural calculation of the design load (α = 1.00, λ = 0.70, k = 0.0 in this example) when the shield tunnel 3 is designed. It is a locus (trajectory based on a load condition at the time of designing a shield tunnel) showing stress distribution over a range of 0 ° to 360 ° in the circumferential direction of the shield tunnel 3.

The evaluation of the soundness of the shield tunnel 3 is determined by comparing these symbols (black circles) and each locus.
In the case of this example, it can be seen that the absolute value of the solid locus is larger than the absolute value of the broken locus in any segment group L, M, R. Therefore, since it can be said that the shield tunnel 3 according to the present embodiment generates only a stress smaller than the stress assumed in the design stage, it can be determined that at least the stress is in a safe state. On the contrary, when the absolute value of the solid line locus is smaller than the absolute value of the broken line locus, it is considered that the shield tunnel 3 has no room for strength or durability. The arrow indicates the difference between the stress degree σi obtained from the measured strain and the stress degree σcal.i obtained by calculation for the structural analysis model Md. The longer the arrow, the larger the difference.

The following (A) and (B) are judgment criteria (predetermined criteria) for evaluating the soundness of the shield tunnel 3.
(A) Absolute value of the stress level based on the design earth pressure actually applied to the existing RC underground hollow structure> Absolute value of the minimum differential stress → In this case, the RC underground hollow structure There is no need to reinforce things.
(B) Absolute value of the stress level based on the earth pressure (design earth pressure) actually applied to the existing RC ground hollow structure in the existing RC site ≤ absolute value of the stress level at the time of the differential minimum → In this case, the RC site Examine the need for reinforcement of the hollow inner structure.

The shield tunnel strength evaluation method according to the present embodiment described above can be said to be the shield tunnel strength evaluation method described below.
(1)
(1-1) a step of obtaining a stress level from the measured strain of the existing shield tunnel 3 measured by the strain gauge 5;
(1-2) obtaining a stress level by calculation for the structural analysis model of the shield tunnel 3;
(1-3) obtaining a difference between both stress levels;
(1-4) A method for evaluating the strength of a shield tunnel, including a step of combining earth pressure coefficients that are coefficients for earth pressure calculation related to the calculation so that the difference is minimized.
(2)
(2-1) a step of forming an endless groove 33 having a predetermined depth in the wall 31 of the existing shield tunnel 1 and forming the island 2 in the wall 31 by forming the endless groove 33;
(2-2) placing the strain gauge 5 of the strain gauge on the island 2;
(2-3) a step of calculating the stress degree σi generated in the island portion 2 based on the strain measurement result by the strain gauge by calculation;
(2-4) Creating a structural analysis model Md of the shield tunnel 3 and obtaining a stress degree σcal of an island-corresponding portion of the structural analysis model Md;
(2-5) obtaining a difference δαλk between the stress degree σcal by the structural calculation obtained based on the structural analysis model Md and the stress degree σi obtained from the measured strain;
(2-6) A method for evaluating the strength of a shield tunnel, including a step of combining earth pressure coefficients that are coefficients for earth pressure calculation so that the difference δαλk is minimized.
(3)
(3-1) forming an endless groove 33 having a predetermined depth in the wall 31 of the existing shield tunnel 3 and forming the island 2 in the wall 31 by forming the endless groove 33;
(3-2) a step of placing a strain gauge 5 of a strain gauge on the island 2;
(3-3) a step of measuring the degree of stress actually generated in the island portion 2 based on the strain measurement result by the strain gauge;
(3-4) creating a structural analysis model Md of the shield tunnel 3 and calculating the cross-sectional force of the island portion of the model Md;
(3-5) obtaining a difference δαλk between the stress degree σcal based on the calculated sectional force and the stress degree σi actually generated in the island part 2;
(3-6) A method for evaluating the strength of a shield tunnel, including a step of combining earth pressure coefficients that are coefficients for earth pressure calculation so that the difference is minimized.
(4) In the shield tunnel strength evaluation method, the earth pressure coefficient (α: vertical earth pressure coefficient, λ: side earth pressure coefficient, k: ground reaction force coefficient) when the difference δαλk is minimized is used as the shield tunnel. When applied as an earth pressure coefficient of 3, the earth pressure acting on the shield tunnel 3 is calculated as a minimum differential earth pressure.
(5) Moreover, the strength evaluation method of the shield tunnel which has a step which calculates the stress degree based on the said soil pressure at the time of the minimum difference as a stress level at the time of the minimum difference.

  Note that the present invention is not limited to the illustrated examples described above, and various modifications can be made without departing from the scope of the present invention. For example, in the present embodiment, a shield tunnel has been disclosed, but an open-cut tunnel or a shaft may be used.

  According to the strength evaluation method of the shield tunnel according to the present embodiment, the actual earth pressure acting on the tunnel and other existing RC hollow structures in the RC ground and the earth pressure determined in the design are quantitatively calculated. It can be compared, and it can be evaluated whether or not the strength of the existing tunnel or other RC ground hollow structure is set appropriately.

It is a perspective view which shows the state which forms the island part using the island part formation apparatus which concerns on this invention. It is a cross-sectional view of a shield tunnel in which islands are formed. It is a principal part enlarged view of FIG. 2, Comprising: It is a figure which shows the longitudinal cross-section of an island part. It is the figure seen from the arrow IV direction of FIG. It is a side view of a shield tunnel, and is a figure which emphasizes and shows the segment to which the strength evaluation method of the shield tunnel concerning the present invention was applied. FIG. 6 is a sectional view taken along line VI-VI in FIG. 5. It is the VII-VII sectional view taken on the line of FIG. It is the VIII-VIII sectional view taken on the line of FIG. It is a longitudinal cross-sectional view which shows the state which attached the strain gauge to the island part surface. It is the figure seen from the arrow X direction of FIG. It is a perspective view of the segment which is a shield tunnel and its structural member. It is a perspective view of the structural analysis model of a shield tunnel. It is an image figure of the coordinate body formed when the difference of the stress degree of an island part and the concrete stress degree of the shield tunnel by structure calculation is put in many three-dimensional coordinates. It is a vertical earth pressure coefficient-side earth pressure coefficient diagram in which a vertical earth pressure coefficient is taken on the vertical axis and a lateral earth pressure coefficient is taken on the horizontal axis. It is a stress degree-angle diagram which takes the stress degree on the vertical axis and takes the angle (0 ° to 360 °) in the circumferential direction of the shield tunnel on the horizontal axis for the segment group L of the shield tunnel. It is a stress degree-angle diagram which takes the stress degree on the vertical axis and takes the angle (0 ° to 360 °) in the circumferential direction of the shield tunnel on the horizontal axis for the segment group M of the shield tunnel. FIG. 4 is a stress degree-angle diagram in which the stress level is taken on the vertical axis and the angle (0 ° to 360 °) in the circumferential direction of the shield tunnel is taken on the horizontal axis for the segment group R of the shield tunnel. It is explanatory drawing about the calculation method of the earth pressure (design earth pressure) on the design of a shield tunnel. It is explanatory drawing about the calculation method of the earth pressure (design earth pressure) in the design of a shaft and an open-cut tunnel. It is a stress strain residual rate (%)-cutting depth / diameter diagram.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Island part formation apparatus 2 Island part 3 Shield tunnel (RC inside underground hollow structure)
3a Non-enclosed area 3b Segment joint 3c Ring joint 4 Segment 5 Strain gauge 31 Wall 33 Endless groove
II1 Tunnel transverse strain
II2 Tunnel axial strain ε1 Stress strain ε2 Temperature drying shrinkage strain σi Shield tunnel stress degree Ec Elastic coefficient α Vertical earth pressure coefficient λ Side earth pressure coefficient k Ground reaction force coefficient δαλk Difference between stress degree σi and stress degree σcal H Distance from surface to tunnel (also called soil cover)
h Tunnel height γ Unit volume of soil σv Pressure due to the weight of soil applied to the tunnel top σv1 Earth pressure σv2 acting in the vertical direction at the tunnel top σv2 Reaction force σh1 generated at the bottom against the total soil pressure Pressure σh2 Maximum lateral earth pressure Md Structural analysis model ν Poisson's ratio of concrete

Claims (12)

A step of obtaining a stress degree from an actually measured strain of the existing RC underground hollow structure;
Obtaining a stress level for the structural analysis model of the RC underground structure in the hollow structure;
Obtaining a difference between both stress levels;
A method for evaluating the strength of a hollow structure in an RC structure having a step of combining earth pressure coefficients that are coefficients for earth pressure calculation so that the difference is minimized. Forming an endless groove having a predetermined depth in the wall portion of the existing RC ground hollow structure, and forming an island portion that is an isolated region from the surroundings by forming the endless groove;
Placing a strain gauge on the island,
Obtaining a stress level generated in the island portion before the endless groove is formed based on a measurement result of strain by the strain gauge;
Creating a structural analysis model of the RC in-ground hollow structure, obtaining a stress level of an island equivalent portion of the model; and
Obtaining a difference between a stress degree obtained from the structural calculation obtained based on the structural analysis model and a stress degree obtained from the measured strain;
A method for evaluating the strength of a hollow structure in an RC structure having a step of combining earth pressure coefficients that are coefficients for earth pressure calculation so that the difference is minimized. Forming an endless groove of a predetermined depth in the wall portion of the existing RC ground hollow structure, and forming an island portion which is an isolated region from the surroundings by forming the endless groove;
A step of placing a strain gauge on the island;
Measuring the degree of stress actually generated in the island part before the endless groove is formed based on the measurement result of strain by the strain gauge;
Creating a structural analysis model of the RC ground hollow structure, and calculating the cross-sectional force of the island portion of the model;
Obtaining a difference between the stress level based on the calculated sectional force and the stress level actually generated in the island part;
A method for evaluating the strength of a hollow structure in an RC structure having a step of combining earth pressure coefficients, which are coefficients for earth pressure calculation, so that the difference is minimized.   Even if the island portion is formed, the predetermined depth is formed in a range where the residual strain rate is 0, and the diameter of the endless groove is based on the diameter of crushed stone contained in the RC hollow structure The strength evaluation method for a hollow structure in RC-made ground according to any one of claims 2 to 3, wherein   When the earth pressure coefficient when the difference is minimized is applied as the earth pressure coefficient of the existing RC underground hollow structure, the earth pressure acting on the existing RC underground structure is calculated as the difference maximum. 5. The strength evaluation method for a hollow structure in RC building according to any one of claims 1 to 4, further comprising a step of calculating as a small earth pressure.   The strength evaluation method for RC hollow structure in RC building according to claim 5, further comprising a step of calculating a stress level based on the minimum differential earth pressure as a minimum differential stress level.   The strength of the RC ground hollow structure according to claim 6, wherein the strength of the RC ground hollow structure is evaluated by comparing the difference stress at the time of minimum with a predetermined standard. Evaluation methods. The RC site according to any one of claims 2 to 7, wherein the island portion is formed at a location where the reinforcing bar is not formed in the hollow structure inside the RC site on the axial extension line. Strength evaluation method for hollow inner structure.   The method for evaluating the strength of an RC underground hollow structure according to any one of claims 1 to 8, wherein strain measurement is performed at 1 to n dispersed locations in the RC hollow underground structure. .   10. The RC underground underground hollow structure strength evaluation method according to claim 1, wherein the RC underground hollow structure is a shield tunnel, an open-cut tunnel, or a shaft.   The RC strain according to any one of claims 2 to 10, wherein the measured strain measured by the strain gauge includes a tunnel axial strain in a tunnel axial direction and a tunnel transverse strain in a tunnel transverse direction. Strength evaluation method for underground hollow structures.   The tunnel axial strain and the tunnel transverse strain are detected by arranging strain gauges, which are components of the strain gauge, in the axial and transverse directions of the tunnel, respectively, and in the intermediate direction between these axial and transverse directions. A strain gauge is arranged and the twist condition of a tunnel is measured, The strength evaluation method of the RC underground hollow structure in any one of Claims 1-11 characterized by the above-mentioned.

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