Design method of tunnel surface supporting structure system

Abstract

The invention discloses a tunnel surface supporting structure system design method, which can quantitatively and accurately determine design parameters of a surface supporting structure system, and form targeted supporting design according to field practice instead of test or experience design for determination. Comprising the following steps: accurately acquiring engineering environment parameters of a tunnel site area, such as physical parameters of surrounding rock, a stress field and engineering characteristics, through data collection and testing; a tunnel deformation control threshold value [delta] is reasonably determined according to the engineering environment and the like, and on this basis, the ring stiffness requirement [S] of a surface layer supporting structure is calculated through a theoretical formula; different design parameters of the surface supporting structure correspond to ring stiffness supply [s] values, and on the basis that the ring stiffness requirement [S] is determined, the matched design parameters, with the ring stiffness supply [s] not smaller than [S], of the surface supporting structure are selected.

Description

Technical Field

[0001] This invention relates to tunnels, and more particularly to a design method for a tunnel surface support structure system, especially applicable to the design of tunnel surface support structure systems in soft rock with large deformation. Background Technology

[0002] In current tunnel support structure systems, steel frames and shotcrete are the two most important components of surface support structures. In my country, the design of surface support structures has traditionally relied on experience-based standard and analogical design methods. Through years of practical refinement, a set of support structure design parameters suitable for general Class I to VI surrounding rock sections has been largely established and improved. However, in some special geological conditions, such as soft rock with large deformation, due to the highly variable geological conditions and limited engineering samples, a set of effective support structure design parameters has not yet been formed. Although in recent years support structure design has gradually shifted towards semi-quantitative and quantitative analytical design methods, such as the allowable stress method, probabilistic reliability design methods based on limit states, and numerical simulation analytical methods based on finite element and finite difference methods, the determination of reasonable design parameters for surface support structures, such as shotcrete thickness, steel frame type, and spacing, remains unresolved. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a design method for a tunnel surface support structure system, which can quantitatively and accurately determine the design parameters of the surface support structure system and form a targeted support design based on the actual site conditions, rather than relying on experimental or experience-based design.

[0004] The technical solution adopted by this invention to solve its technical problem is as follows:

[0005] The present invention provides a design method for a tunnel surface support structure system, comprising the following steps:

[0006] S1. Based on the acquisition of physical and mechanical parameters, geostress field and engineering characteristics of the surrounding rock in the tunnel site area, the tunnel deformation control threshold [δ] is determined according to the actual situation on site. The tunnel deformation control threshold [δ] refers to the allowable value of deformation of the surface support structure.

[0007] S2. Determine the location R of the shear stress peak zone using the following formula:

[0008]

[0009] in

[0010] In the formula: G is the deformation modulus of the surrounding rock, and c is the cohesion. Let P be the internal friction angle, P be the ground stress level in the tunnel site area, and r be the equivalent excavation radius of the tunnel.

[0011] S3. Calculate and determine the ring stiffness requirement [S] of the surface support structure based on the tunnel deformation control threshold [δ]:

[0012] The ring stiffness requirement [S] of the surface support structure refers to the ring stiffness of the surface support structure necessary to stabilize the peak shear stress zone at location R under specific engineering geological conditions in the tunnel site area. It is obtained using the following formula when the horizontal stress = vertical stress = P in the tunnel site area:

[0013]

[0014] in

[0015] S4. The ring stiffness supply [s] of the selected surface support structure shall not be less than the ring stiffness requirement [S] of the surface support structure, and shall be in accordance with the following design parameters:

[0016] The ring stiffness supply [s] of the surface support structure refers to the ring stiffness capacity that the surface support structure can provide under different design parameters of shotcrete and steel frame. The surface support structure is designed in a spectrum through numerical simulation, and is supplemented and improved through model test and field test, and then further fitted to form a theoretical formula.

[0017] The systematic design of the surface support structure includes the ring stiffness supply [s] value corresponding to parameters such as shotcrete grade and thickness, steel frame type and spacing;

[0018] The design parameters for the surface support structure are selected by using the design parameters corresponding to [s]≥K[S], where K is 1.3 to 1.5.

[0019] The beneficial effects of this invention are mainly reflected in the following aspects:

[0020] (1) Under complex engineering geological conditions in the tunnel site area, especially in special adverse geological sections, this method can be used to specifically quantify the design parameters of the surface support structure system, make up for the lack of experience-based design without a large number of data samples, and improve the accuracy of surface support structure design.

[0021] (2) The design parameters are reasonable and the economic benefits are obvious. The design parameters of the surface support structure are accurately quantified, which avoids support failure and rework due to weak support design parameters, or engineering waste due to excessive support design parameters;

[0022] (3) The method is convenient and can quickly determine the support parameters. The systematic design of surface support structures under different support parameters can determine the ring stiffness supply [s] value through a large number of calculations or experiments in the early stage of design, so as to provide a variety of design options; and this method can be further realized as a software platform, so that several reasonable surface support structure design schemes and parameters can be selected based on the clear basic parameters. Attached Figure Description

[0023] This instruction manual includes the following diagram:

[0024] Figure 1 This is a flowchart of a design method for a tunnel surface support structure system according to the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0026] Reference Figure 1 The present invention discloses a design method for a tunnel surface support structure system, comprising the following steps:

[0027] S1. Based on the acquisition of physical and mechanical parameters, geostress field and engineering characteristics of the surrounding rock in the tunnel site area, the tunnel deformation control threshold [δ] is determined according to the actual situation on site. The tunnel deformation control threshold [δ] refers to the allowable value of deformation of the surface support structure.

[0028] S2. Determine the location R of the shear stress peak zone using the following formula:

[0029]

[0030] in

[0031] In the formula: G is the deformation modulus of the surrounding rock, and c is the cohesion. Let P be the internal friction angle, P be the ground stress level in the tunnel site area, and r be the equivalent excavation radius of the tunnel.

[0032] S3. Calculate and determine the ring stiffness requirement [S] of the surface support structure based on the tunnel deformation control threshold [δ]:

[0033] The ring stiffness requirement [S] of the surface support structure refers to the ring stiffness of the surface support structure necessary to stabilize the peak shear stress zone at location R under specific engineering geological conditions in the tunnel site area. It is obtained using the following formula when the horizontal stress = vertical stress = P in the tunnel site area:

[0034]

[0035] in

[0036] S4. The ring stiffness supply [s] of the selected surface support structure shall not be less than the ring stiffness requirement [S] of the surface support structure, and shall be in accordance with the following design parameters:

[0037] The ring stiffness supply [s] of the surface support structure refers to the ring stiffness capacity that the surface support structure can provide under different design parameters of shotcrete and steel frame. The surface support structure is designed in a spectrum through numerical simulation, and is supplemented and improved through model test and field test, and then further fitted to form a theoretical formula.

[0038] The systematic design of the surface support structure includes the ring stiffness supply [s] value corresponding to parameters such as shotcrete grade and thickness, steel frame type and spacing;

[0039] The design parameters for the surface support structure are selected by using the design parameters corresponding to [s]≥K[S], where K is 1.3 to 1.5.

[0040] Example:

[0041] Through data collection and a series of tests, the physical parameters of the surrounding rock were determined (surrounding rock deformation modulus G = 400 MPa, cohesion c = 0.25 MPa, internal friction angle). The stress field (horizontal stress = vertical stress = P = 5 MPa) and engineering characteristics (tunnel equivalent excavation radius r = 5 m) were considered, and the tunnel deformation control threshold [δ] = 0.05 m was reasonably determined based on engineering environmental characteristics and site requirements.

[0042] Through theoretical formulas in The calculated location of the peak shear stress zone is R = 9.26m.

[0043] Through theoretical formulas

[0044] in:

[0045] The ring stiffness requirement of the surface support structure is calculated as [S] = 168.5 MPa.

[0046] By performing a systematic design of the surface support structure through numerical simulation, the ring stiffness supply [s] value under different surface support structure design parameters can be generated.

[0047] Table 1. Systematic Design of Ring Stiffness Supply under Different Surface Support Structure Design Parameters

[0048]

[0049] When selecting reasonable support structure design parameters, the following should be chosen:

[0050] [s]≥1.3~1.5×[S]=219.05~252.75MPa

[0051] The corresponding support parameters.

[0052] Referring to Table 1, the more suitable design parameters are: I20b I-beams, spacing 0.8 / beam, C25 shotcrete, design thickness 30cm; or I20b I-beams, spacing 0.6 / beam, C25 shotcrete, design thickness 25cm. Since two relatively similar parameters exist, further comparison was made based on factors such as economy, and the final selection was: I20b I-beams, spacing 0.6 / beam, C25 shotcrete, design thickness 25cm.

[0053] The present invention has the following innovative features:

[0054] (1) Under complex engineering geological conditions in the tunnel site area, especially in special adverse geological sections, due to the lack of a large amount of engineering practice, we can only use engineering tests to continuously try and optimize design parameters, which is unpredictable. However, this method can specifically quantify the design parameters of the surface support structure system, make up for the lack of experience-based design without a large amount of data samples, and improve the accuracy of surface support structure design.

[0055] (2) The design parameters are reasonable and the economic benefits are obvious. The design parameters of the surface support structure are accurately quantified, which avoids support failure and rework due to weak support design parameters, or engineering waste due to excessive support design parameters.

[0056] (3) The method is convenient and can quickly determine the support parameters. The systematic design of surface support structures under different support parameters can determine the ring stiffness supply [s] value through a large number of calculations or experiments in the early stage of design, so as to provide a variety of design options; and this method can be further realized as a software platform, so that several reasonable surface support structure design schemes and parameters can be selected based on the clear basic parameters.

Claims

1. A design method for a tunnel surface support structure system, comprising the following steps: S1. Based on the acquisition of physical and mechanical parameters, geostress field and engineering characteristics of the surrounding rock in the tunnel site area, the tunnel deformation control threshold [δ] is determined according to the actual situation on site. The tunnel deformation control threshold [δ] refers to the allowable value of deformation of the surface support structure. S2. Determine the location R of the shear stress peak zone using the following formula: in In the formula: G is the deformation modulus of the surrounding rock, and c is the cohesion. Let P be the internal friction angle, P be the ground stress level in the tunnel site area, and r be the equivalent excavation radius of the tunnel. S3. Calculate and determine the ring stiffness requirement [S] of the surface support structure based on the tunnel deformation control threshold [δ]: The ring stiffness requirement [S] of the surface support structure refers to the ring stiffness of the surface support structure necessary to stabilize the peak shear stress zone at location R under specific engineering geological conditions in the tunnel site area. It is obtained using the following formula when the horizontal stress = vertical stress = P in the tunnel site area: in S4. The ring stiffness supply [s] of the selected surface support structure shall not be less than the ring stiffness requirement [S] of the surface support structure, and shall be in accordance with the following design parameters: The ring stiffness supply [s] of the surface support structure refers to the ring stiffness capacity that the surface support structure can provide under different design parameters of shotcrete and steel frame. The surface support structure is designed in a spectrum through numerical simulation, and is supplemented and improved through model test and field test, and then further fitted to form a theoretical formula. The systematic design of the surface support structure includes the ring stiffness supply [s] value corresponding to parameters such as shotcrete grade and thickness, steel frame type and spacing; The design parameters for the surface support structure are selected by using the design parameters corresponding to [s]≥K[S], where K is 1.3 to 1.5.

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