A method for determining the thickness of reinforced concrete lining in the underground docking section of a shield tunnel.

Abstract

This invention provides a method for determining the thickness of reinforced concrete in the underground connection section of a tunnel boring machine (TBM), comprising the following steps: 1) determining the diameter d1 of the TBM; 2) determining the shield shell thickness δ1; 3) determining the tunnel burial depth h1; 4) determining the natural unit weight γ of the soil above the groundwater level and the depth h2 of the groundwater level from the ground surface; 5) determining the saturated unit weight γ of the soil below the groundwater level. sat And effective unit weight γ'; 6) Determine the overburden load P0 of the tunnel; 7) Determine the vertical earth pressure P at the shield arch crown: P=P0+Σγ i h i +Σγ' j h j 8) Determine the allowable compressive stress σ1 of the shield material; 9) Determine the pressure P1 that the shield can withstand; 10) Determine the pressure P2 that the cast-in-place reinforced concrete lining needs to withstand: P2 = P - P1; 11) Determine the thickness of the cast-in-place reinforced concrete:

Description

Technical Field

[0001] This invention provides a method for determining the thickness of the reinforced concrete lining in the underground docking section of a shield tunnel, which solves the problem of determining the thickness of the cast-in-place reinforced concrete lining after the shield is removed and the shield shell is retained when using underground docking of shield tunnels. Background Technology

[0002] With the development of my country's rail transit, shield tunneling has become increasingly sophisticated. Simultaneously, the demand for tunnels has significantly increased. Under construction conditions such as large spans, sea-crossing tunnels, and situations where it's impossible to install working shafts mid-span, the "opposite-advancing, underground docking, and shell dismantling" shield-to-ground docking technology has become a new development trend. Domestic examples of shield-to-ground docking construction include the Shiziyang Tunnel project of the Guangzhou-Shenzhen-Hong Kong Express Rail Link and the Qingdao Metro Line 8 project. Shield-to-ground docking technology has extremely high requirements for structural safety. After removing the cutterhead at the docking section, the shield shell remains in the tunnel, and then reinforced concrete lining is poured on-site for reinforcement. Due to the presence of the shield shell, the thickness of the cast-in-place reinforced concrete lining at the docking section can be less than the thickness of the tunnel segments. However, in existing engineering practice, there is a lack of clear standards for selecting the thickness of the cast-in-place reinforced concrete lining, which has certain shortcomings. Therefore, it is necessary to study a new method to determine the thickness of the cast-in-place reinforced concrete lining. Summary of the Invention

[0003] The main technical problem to be solved by the present invention is to provide a method for determining the thickness of the cast-in-place reinforced concrete lining in the underground docking section of a shield tunnel, which can determine the required thickness of the cast-in-place reinforced concrete lining under different construction conditions and geological conditions.

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

[0005] A method for determining the thickness of reinforced concrete in the underground docking section of a shield tunnel includes the following steps:

[0006] 1) Determine the diameter d1 of the tunnel boring machine;

[0007] 2) Determine the thickness δ1 of the shield shell;

[0008] 3) Determine the tunnel's burial depth h1;

[0009] 4) Determine the natural unit weight γ of the soil above the groundwater level and the depth h2 of the groundwater level from the ground surface;

[0010] 5) Determine the saturated unit weight γ of the soil below the groundwater level. sat and effective severe γ'; γ' = γ sat -γ w , where γ w The unit weight of groundwater is taken as 9.8 kN / m³. 3 ;

[0011] 6) Determine the overburden load P0 over the tunnel;

[0012] 7) Determine the vertical earth pressure P at the crown of the shield tunnel: P = P0 + ∑γ i h i +∑γ' j h j ;

[0013] 8) Determine the allowable compressive stress σ1 of the shield material:

[0014] Where 0.5 is a reduction factor considering the shield shell under long-term unfavorable underground conditions;

[0015] η is the weld coefficient, which is 0.8 for straight seam pipes;

[0016] The safety factor is set to 2.0;

[0017] 9) Determine the pressure P1 that the shield can withstand:

[0018] Where σ1 is the allowable compressive stress of the steel used in the shield shell;

[0019] 0.3 is a reduction factor considering the removal of the tunnel boring machine, leaving only the shield shell.

[0020] 10) Determine the pressure P2 that the cast-in-place reinforced concrete lining needs to withstand: P2 = P - P1.

[0021] 11) Determine the thickness δ of the cast-in-place reinforced concrete:

[0022] Where: σ2 is the allowable compressive stress of concrete;

[0023] 0.2 is the reduction factor for allowable stress;

[0024] 1.5 is the safety factor considering overall safety.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] 1) This invention makes full use of materials. Considering that after the shield shell is retained in the underground docking section, the thickness of the cast-in-place reinforced concrete is required after the shield shell bears part of the pressure, instead of directly using the thickness of the tunnel segments. Therefore, this invention fully considers that the existence of the shield shell and the cast-in-place reinforced concrete share the pressure, and fully considers utilizing the strength of the shield shell material.

[0027] 2) This invention takes into account that the required thickness of cast-in-place reinforced concrete is reduced after the shield shell is retained in the underground docking section. Therefore, reducing the amount of concrete used can reduce construction costs and avoid unnecessary material expenditures.

[0028] 3) The formulas used in this invention to calculate the pressure borne by the shield and determine the thickness of the cast-in-place reinforced concrete are concise, clear, and straightforward. Through reasonable calculations, the thickness of the cast-in-place reinforced concrete is determined, and the calculation results are safe and reliable. This avoids the consequences caused by improper determination of the thickness of the cast-in-place reinforced concrete. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the derivation of formula P1;

[0030] Figure 2 A schematic diagram illustrating the derivation of the δ formula; Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0034] refer to Figure 1 and Figure 2 This embodiment provides a method for determining the thickness of reinforced concrete poured in the underground docking section of a shield tunnel, including the following steps:

[0035] 1) Determine the diameter d1 of the tunnel boring machine;

[0036] The diameter of the tunnel boring machine (TBM) is determined based on the type and variety of TBMs used in the project. Currently, TBMs come in various diameters, including 6.3m, 8.8m, and 15.01m.

[0037] 2) Determine the shield thickness δ1;

[0038] The thickness of the shield shell is determined based on the type and variety of tunnel boring machine used in the actual project.

[0039] 3) Determine the tunnel's burial depth h1;

[0040] The tunnel burial depth is determined based on the tunnel design data and relevant design parameters.

[0041] 4) Determine the natural unit weight γ of the soil above the groundwater level and the depth h2 of the groundwater level from the ground surface;

[0042] Soil samples were taken from above the groundwater level during drilling. Density tests were conducted in the laboratory to calculate the density ρ of the soil above the groundwater level. This density ρ was then multiplied by the gravitational acceleration g to calculate the natural unit weight γ of the soil above the groundwater level. Based on geological exploration data, the depth h2 of the groundwater level from the surface was determined.

[0043] 5) Determine the saturated unit weight γ of the soil below the groundwater level. sat And effective severe γ': γ'=γ sat -γ w , where γ w The unit weight of groundwater is taken as 9.8 kN / m³. 3 ;

[0044] By sampling soil samples below the groundwater level during drilling and conducting density tests in the laboratory, the density ρ1 of the soil above the groundwater level was calculated. Multiplying this density by the gravitational acceleration g, the saturated unit weight γ of the soil below the groundwater level was then calculated. sat Then, the effective unit weight γ' of the soil below the groundwater level is calculated using the above formula.

[0045] 6) Determine the overburden load P0 of the tunnel:

[0046] Based on the specific construction conditions and project background, determine the specific type of overburden load on the tunnel and the corresponding calculation method.

[0047] 7) Determine the vertical earth pressure P at the crown of the shield tunnel: P = P0 + ∑γ i h i +∑γ' j h j ;

[0048] The calculation is based on the unit weight of each soil layer at the top of the shield and the corresponding soil layer depth. That is, the natural unit weight of the soil above the groundwater level or the effective unit weight below the groundwater level is multiplied by the corresponding soil layer depth and then superimposed. Finally, the overburden load of the tunnel is added.

[0049] 8) Determine the allowable compressive stress σ1 of the shield material: Where 0.5 is a reduction factor considering the shield shell under long-term unfavorable underground conditions;

[0050] η is the weld coefficient, which is 0.8 for straight seam pipes;

[0051] The yield strength is determined by the type of steel used in the shield material and the thickness of the shield.

[0052] The safety factor is set to 2.0.

[0053] 9) Determine the pressure P1 that the shield can withstand:

[0054] Where σ1 is the allowable compressive stress of the steel used in the shield shell;

[0055] 0.3 is a reduction factor considering the removal of the tunnel boring machine, leaving only the shield shell.

[0056] The shield is cut along its length, and the upper half of a unit length is analyzed. It is subjected to a uniform external pressure P1, and the thickness of the shield is δ1.

[0057] 10) Determine the pressure P2 that the cast-in-place reinforced concrete lining needs to withstand: P2 = P - P1;

[0058] All the total pressure is borne by the shield shell and the cast-in-place reinforced concrete remaining in the tunnel. Therefore, subtracting the pressure that the shield shell can withstand from the total pressure calculated above, the remainder is the pressure that the cast-in-place reinforced concrete must withstand.

[0059] 11) Determine the thickness δ of the cast-in-place reinforced concrete:

[0060] Where: σ2 is the allowable compressive stress of concrete;

[0061] 0.2 is the reduction factor for allowable stress;

[0062] 1.5 is the safety factor considering overall safety.

[0063] Example

[0064] A railway tunnel project employs a shield tunneling method involving underground docking and shell dismantling. This invention is needed to determine the thickness of the cast-in-place reinforced concrete lining for the docking section after retaining the original shield shell. Based on the model and type of the shield tunneling machine, its diameter is d1 = 6.3m, the shield shell thickness is δ1 = 40mm, and the shield shell is made of Q235 steel with an allowable compressive stress of σ1 = 45MPa. According to the tunnel design data, the tunnel depth is h1 = 20.4m. On-site drilling revealed that the groundwater level is h2 = 3.2m above the ground surface. Soil samples were taken from both above and below the groundwater level and density tests were conducted in the laboratory. The density of the soil above the groundwater level was measured to be ρ = 1.87g / cm³. 3 The density of the soil below the groundwater level is ρ1 = 1.94 g / cm³. 3 Multiplying each by the gravitational acceleration g, we obtain the unit weight of the soil above the groundwater level as γ = 18.3 kN / m³. 3 The saturated unit weight of the soil below the groundwater level is γ. sat =19.0kN / m 3 Therefore, the effective unit weight of the soil below the groundwater level is γ' = 9.2 kN / m³. 3 Based on engineering experience, the overburden load of the tunnel is taken as P0 = 20 kPa. Therefore, the vertical earth pressure at the shield arch crown is P = 236.8 kPa. According to the above formula, the pressure that the shield shell can withstand is calculated to be P1 = 171.4 kPa; therefore, the pressure that the cast-in-place reinforced concrete lining needs to withstand is P2 = 65.4 kPa. The concrete used is C50, and its allowable eccentric compressive stress is σ2 = 16.8 MPa. Substituting these values ​​into the above formula, the thickness of the cast-in-place reinforced concrete lining can be calculated as δ = 91 mm.

[0065] A subway tunnel project employs a shield tunneling method involving underground docking and shell dismantling. This invention's method is needed to determine the thickness of the cast-in-place reinforced concrete lining for the docking section after retaining the original shield shell. Based on the model and type of the tunnel boring machine (TBM), its diameter is d1 = 7.0m, the shield shell thickness is δ1 = 45mm, and the shield shell is made of Q345B grade steel with an allowable compressive stress of σ1 = 63MPa. According to the tunnel design data, the tunnel depth is h1 = 24.6m. On-site drilling revealed that the groundwater level is h2 = 3.6m above the ground surface. Soil samples were taken from both above and below the groundwater level and density tests were conducted in the laboratory. The density of the soil above the groundwater level was measured to be ρ = 1.98g / cm³. 3 The density of the soil below the groundwater level is ρ1 = 2.14 g / cm³. 3 Multiplying this by the acceleration due to gravity g, we obtain the unit weight of the soil above the groundwater level as γ = 19.4 kN / m³. 3 The saturated unit weight of the soil below the groundwater level is γ.sat =21.0kN / m 3 Therefore, the effective unit weight of the soil below the groundwater level is γ' = 11.2 kN / m³. 3 Based on engineering experience, the overburden load of the tunnel is taken as P0 = 20 kPa. Therefore, the vertical earth pressure at the shield arch crown is P = 325.1 kPa. According to the above formula, the pressure that the shield shell can withstand is calculated to be P1 = 243 kPa; therefore, the pressure that the cast-in-place reinforced concrete lining needs to withstand is P2 = 82.1 kPa. The concrete used is C45, and its allowable eccentric compressive stress is σ2 = 15.0 MPa. Substituting these values ​​into the above formula, the thickness of the cast-in-place reinforced concrete lining can be calculated as δ = 142 mm.

[0066] The above description is merely a preferred embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention by those skilled in the art within the scope of the technology disclosed in the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A method for determining the thickness of reinforced concrete in the underground connection section of a shield tunnel, comprising the following steps: 1) Determine the diameter d1 of the tunnel boring machine; 2) Determine the shield thickness δ1; 3) Determine the tunnel's burial depth h1; 4) Determine the natural unit weight γ of the soil above the groundwater level and the depth h2 of the groundwater level from the ground surface; 5) Determine the saturated unit weight γ of the soil below the groundwater level. sat and effective severe γ'; γ'=γ sat -γ w , where γ w The unit weight of groundwater is taken as 9.8 kN / m³. 3 ; 6) Determine the overburden load P0 of the tunnel; 7) Determine the vertical earth pressure P at the crown of the shield tunnel: P = P0 + ∑γ i h i +∑γ' j h j ; γ i The natural unit weight of the soil above the groundwater level, γ' j h is the effective unit weight of the soil below the groundwater level. i h is the depth of the soil layer above the groundwater level. j The depth of the soil layer below the groundwater level; 8) Determine the allowable compressive stress σ1 of the shield material: in, 0.5 is a reduction factor considering the long-term adverse underground conditions of the shield shell; η is the weld coefficient; the yield strength is determined by the type of steel used in the shield material and the shield thickness; the safety factor is taken as 2.0; 9) Determine the pressure P1 that the shield can withstand: Where σ1 is the allowable compressive stress of the steel used in the shield shell; 0.3 is the reduction factor considering the removal of the tunnel boring machine and only the shield shell remaining; the shield shell is cut along the length direction, and the upper half of the unit length is analyzed, subjected to a uniform external pressure P1, and the thickness of the shield shell is δ1. 10) Determine the pressure P2 that the cast-in-place reinforced concrete lining needs to withstand: P2 = P - P1; 11) Determine the thickness δ of the cast-in-place reinforced concrete: Where: σ2 is the allowable compressive stress of concrete; 0.2 is the reduction factor of allowable stress; 1.5 is the safety factor considering overall safety.

2. The method for determining the thickness of reinforced concrete in the underground docking section of a shield tunnel according to claim 1, characterized in that: In step 4, soil samples above the groundwater level are taken from the drilling site and density tests are conducted in the laboratory. The density ρ of the soil above the groundwater level is calculated, and multiplied by the gravitational acceleration g to calculate the natural unit weight γ of the soil above the groundwater level. Based on the geological exploration data, the depth h2 of the groundwater level from the ground surface is determined.

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