A method for calculating reasonable burying depth of submarine tunnel

Abstract

This invention provides a method for calculating the reasonable burial depth of a submarine tunnel, belonging to the field of submarine tunnel and underground engineering design and construction technology. The method includes the following steps: Step 1: Obtain the physical and mechanical parameters of the rock strata from top to bottom of the proposed tunnel through survey and exploration data; Step 2: Obtain the information of the proposed tunnel through the tunnel design scheme; Step 3: Calculate the minimum overburden thickness of the tunnel; Step 4: Using seawater load and the physical and mechanical parameters of the rock strata from top to bottom of the proposed tunnel as input conditions, establish a numerical model of the geological structure to simulate the redistribution of surrounding rock stress caused by tunnel excavation. Based on the simulation results, obtain the height H of the overburden strata disturbed during the excavation and support process. S Step 5: Calculate the final minimum overburden thickness for the submarine tunnel. This invention combines top-water coal mining with numerical simulation to determine the reasonable burial depth of the submarine tunnel, taking into account the influence of tunnel support on the burial depth, and conforming to the deformation mechanism of tunnel excavation and support.

Description

Technical Field

[0001] This invention belongs to the field of design and construction technology of submarine tunnels and underground engineering, and specifically relates to a method for calculating the reasonable burial depth of submarine tunnels. Background Technology

[0002] The determination of the reasonable burial depth of undersea tunnels has a significant impact on construction costs and schedules. Currently, the reasonable burial depth of undersea tunnels is mainly determined based on empirical statistics and engineering analogy methods, using empirical formulas from traditional top-water coal mining methods. For example, Chinese invention patent application publication number CN111441822A discloses a method for calculating the reasonable burial depth of underwater mining tunnels, including the following steps: Geological drilling is used to determine the thickness of the silt layer or soft soil layer and the depth of existing fissures in the bedrock surface; the depth of the soft soil cover layer at the top of the tunnel structure and the depth of existing fissures in the bedrock surface are calculated; the water head height and the maximum width of the tunnel arch are measured; based on the rock layer's water-impermeability and permeability coefficient, the rock's strength coefficient, and safety margin, the thickness of the safety protection layer considering the rock layer's water-impermeability and permeability is calculated; based on the foundation coefficient and the minimum resistance line of a single most dangerous explosive charge, the length of the water-conducting fissure in the loosened zone of the surrounding rock caused by drilling and blasting is calculated; and the reasonable burial depth of the mining tunnel is calculated. While this patent can serve as a good criterion for determining the burial depth of undersea tunnels, it fails to consider the supporting effects of tunnel lining and anchor systems, as well as the impact of excavation methods on the surrounding rock strata. This leads to an overestimation of the burial depth derived from empirical formulas for coal mining under water, resulting in increased tunnel construction costs and difficulties. Therefore, relying solely on empirical formulas to determine the burial depth of undersea tunnels is unreasonable. Currently, there is no clearly defined method for determining an economically sound and structurally safe burial depth for undersea tunnels. Summary of the Invention

[0003] This invention addresses the technical problems existing in the prior art by providing a method for calculating the reasonable burial depth of submarine tunnels. It considers the influence of the overburden thickness, applying empirical formulas for the overlying impermeable layer and the height of blasting disturbance to numerical simulations. The numerical simulations also consider the effects of tunnel support and excavation methods. Based on the simulation results, the minimum overburden thickness actually affected by tunnel construction is analyzed. A weighted average is then calculated between this method and the reasonable burial depth obtained from the empirical formulas to determine and guide the determination of the reasonable burial depth of submarine tunnels. This method is well-structured, reasonable, provides reliable results, and is easy to use.

[0004] The technical solution adopted in this invention is: a method for calculating the reasonable burial depth of an undersea tunnel, comprising the following steps:

[0005] Step 1: By investigating and surveying data, obtain the physical and mechanical parameters of the rock strata from top to bottom for the proposed tunnel;

[0006] Step 2: Obtain information about the proposed tunnel through the tunnel design scheme;

[0007] Step 3: Calculate the minimum overburden thickness H of the tunnel.

[0008] H = a + s + h,

[0009] Where a is the depth of the fracture zone on the surface of the submarine tunnel; s is the safe thickness of the water-resistant rock overburden; and h is the height of the blasting disturbance during tunnel excavation.

[0010] Step 4: Load the seawater q w Using the physical and mechanical parameters of the rock strata from top to bottom, the information of the proposed tunnel, and the minimum overburden thickness H as input conditions, a numerical model of the geological structure is established to simulate the redistribution of surrounding rock stress caused by tunnel excavation. Based on the simulation results, the height H of the overburden strata disturbed during the excavation and support process is obtained. S ;

[0011] Step 5: Calculate the final minimum overburden thickness H of the undersea tunnel. min ,

[0012] H min =a+K(s+h)+K S H S ,

[0013] Where K and K S These are the reduction factors for the cover layer height derived from empirical formulas and numerical simulations, respectively.

[0014] Furthermore, in step 1, the physical and mechanical parameters of the rock strata of the proposed tunnel from top to bottom include: surrounding rock grade, surrounding rock unit weight γ, cohesion c, and internal friction angle. Elastic modulus E, Poisson's ratio μ, and elastic resistance coefficient of surrounding rock.

[0015] Furthermore, in step 2, the proposed tunnel information includes: tunnel dimensions, support parameters, and excavation and support sequence.

[0016] Furthermore, in step 3, a is based on the most unfavorable depth of the surface fracture zone in the geological survey data;

[0017]

[0018] In the formula: h1 is the water head height, h2 is the tunnel width, c is the thickness of the strongly weathered rock zone, and f is the PT strength, which is obtained by referring to a table or by sampling test;

[0019]

[0020] In the formula, k is the foundation coefficient; w is the minimum resistance line of a single most dangerous explosive charge; and F(n) is a function of the explosive index of the corresponding explosive charge.

[0021] Furthermore, in step 4, in the simulation results, the ratio of horizontal stress to vertical stress in the surrounding rock after stress redistribution is taken as the horizontal line value as λ, and the error level is taken as ε. Then, the interval corresponding to the (λ-ε, λ+ε) element is defined as the interval where the surrounding rock is less disturbed by excavation after stress redistribution, and the height of the surrounding rock in this interval is h3.

[0022] Hs = s + h - h3.

[0023] Furthermore, in step 4, the seawater pressure is equivalent to a uniformly distributed seawater load q above the seabed. w .

[0024] Furthermore, in step 5, K is set to 0.4, K S Take 0.6.

[0025] Compared with the prior art, the beneficial effects of this invention are:

[0026] 1. This invention combines empirical formulas with numerical simulation results for mutual verification, resulting in high reliability.

[0027] 2. This invention takes into account the effects of surface fissure zone, thickness of safety waterproof layer, blasting disturbance height, tunnel support effect, and excavation method. The method is reasonable, comprehensive, and highly targeted.

[0028] 3. The proposed depth of the undersea tunnel is reasonable, avoiding problems such as increased costs and extended construction period caused by excessive depth.

[0029] 4. This invention is simple to operate, has a clear system, and its calculation process can be achieved using conventional technical means. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention;

[0031] Figure 2 This is a model diagram of an underwater tunnel according to an embodiment of the present invention;

[0032] Figure 3 This is a vertical stress cloud diagram of a tunnel according to an embodiment of the present invention;

[0033] Figure 4 This is a tunnel horizontal stress cloud diagram according to an embodiment of the present invention;

[0034] Figure 5 This is a diagram showing the ratio of horizontal stress to vertical stress at the tunnel roof height according to an embodiment of the present invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Embodiments of the present invention provide a method for calculating the reasonable burial depth of a submarine tunnel, such as... Figure 1 As shown, it includes the following steps:

[0037] Step 1: Based on the survey and exploration data, obtain the physical and mechanical parameters of the rock strata from top to bottom for the proposed tunnel, including: surrounding rock grade; surrounding rock unit weight γ, in kN / m³. 3 Cohesion c, in kPa; Angle of internal friction The units are degrees; elastic modulus E, in Pa; Poisson's ratio μ; elastic resistance coefficient of surrounding rock, in N / m. 3 .

[0038] Step 2: Obtain the information of the proposed tunnel through the tunnel design scheme, including: tunnel size, support parameters, excavation and support sequence.

[0039] Step 3: Calculate the minimum overburden thickness H of the tunnel.

[0040] H = a + s + h,

[0041] Where a is the depth of the surface fracture zone of the submarine tunnel; s is the safe thickness of the water-resistant rock overburden; and h is the height of the blasting disturbance during tunnel excavation.

[0042] a. Based on the most unfavorable depth of the surface fracture zone in the geological exploration data, it is usually taken as 10 to 15 m.

[0043]

[0044] In the formula: h1 is the water head height, in meters; h2 is the tunnel width, in meters; c is the thickness of the strongly weathered rock zone, generally taken as 5 meters; f is the plural strength, obtained from tables or sampling tests, and its value is usually equal to kg / cm². 2 The uniaxial compressive strength of rock is divided by 100.

[0045]

[0046] In the formula, k is the foundation coefficient; w is the minimum resistance line of a single most dangerous explosive charge; and F(n) is a function of the explosive index of the corresponding explosive charge.

[0047] Step 4: Load the seawater q wUsing the physical and mechanical parameters of the rock strata from top to bottom, the proposed tunnel information, and the minimum overburden thickness H as input conditions, a numerical model of the geological structure is established. This model employs a continuous medium model, assuming homogeneous horizontal distribution of the rock strata, using Mohr-Coulomb plane strain elements for the rock mass, isotropic elastic materials for the initial supports, and embedded beam elements for the anchor bolts. The stress and strain of the strata and materials vary within the elastoplastic range. The model simulates the stress and deformation of the surrounding rock and tunnel during the actual excavation and support construction steps. Furthermore, in the geological structure numerical model, the seawater pressure is equivalent to a uniformly distributed seawater load q above the seabed. w .

[0048] The numerical model of the geological structure simulates the redistribution of surrounding rock stress caused by tunnel excavation. The disturbance height is represented by the vertical stress σ at each distribution point along the tunnel axis. h and horizontal stress σ s Determination. Horizontal stress σ s With vertical stress σ h ratio Based on the simulation results, the ratio of horizontal stress to vertical stress in the surrounding rock after stress redistribution is taken as the value of the horizontal line, and the error level is taken as ε, i.e., ε = λ × 5%. Then, the interval corresponding to the (λ-ε, λ+ε) element is defined as the interval where the surrounding rock is less disturbed by excavation after stress redistribution, and the height of the surrounding rock in this interval is h3, which is taken as the height of the surrounding rock with less excavation disturbance.

[0049] Then, calculate the height H of the overlying strata disturbed during the excavation and support process according to the following formula. S .

[0050] Hs = s + h - h3.

[0051] Step 5: Calculate the final minimum overburden thickness H of the undersea tunnel. min This refers to the reasonable burial depth of the undersea tunnel.

[0052] H min =a+K(s+h)+K S H S ,

[0053] Where K and K S These are the reduction factors for the cover layer height derived from empirical formulas and numerical simulations, respectively. K is set to 0.4, K... S Take 0.6.

[0054] The following steps will verify this method using actual numerical data:

[0055] Step 1: Based on the survey and exploration data, the physical and mechanical parameters of the rock strata from top to bottom of the proposed tunnel are obtained, as shown in Table 1.

[0056] Table 1. Physical and mechanical parameters of the rock strata from top to bottom for the proposed tunnel.

[0057]

[0058] Step 2: Based on the tunnel design plan, the information of the proposed tunnel is obtained: the proposed tunnel is a three-lane tunnel with a design speed of 80km / h, an excavation width of 15m, and an excavation height of 9m; the anchor bolts are 3.0m long and spaced at 1.0×1.0 intervals, and the initial support uses C35 20cm thick shotcrete.

[0059] Step 3: Calculate the minimum overburden thickness H of the tunnel, H = a + s + h.

[0060] Where a is the depth of the surface fracture zone of the submarine tunnel, which is taken as 10m;

[0061] s represents the safe thickness of the water-resistant rock overburden layer.

[0062] h represents the height of the blasting disturbance during tunnel excavation.

[0063] In the formula, the subgrade coefficient k of moderately weathered granite is taken as 3000 kPa, the minimum resistance line w = (25~35)d, the borehole diameter d is taken as Φ25, that is, w is taken as 35d = 0.875m, and F(n) = 0.4 + 0.6n 3 If n is 1, then h = 2.6m.

[0064] Therefore, the minimum overburden thickness of the tunnel is H = a + s + h = 25.82m.

[0065] Step 4: Load the seawater q w Using the physical and mechanical parameters of the rock strata from top to bottom, the information of the proposed tunnel, and the minimum overburden thickness H of the tunnel as input conditions, a numerical model of the geological structure is established, such as... Figure 2 As shown.

[0066] The numerical model of the geological structure simulates the redistribution of surrounding rock stress caused by tunnel excavation. The vertical stress cloud diagram of the tunnel is shown below. Figure 3 As shown, the horizontal stress cloud diagram of the tunnel is as follows: Figure 4 As shown, the tunnel excavation process releases vertical stress and increases horizontal stress in the surrounding rock within the tunnel perimeter. The vertical stress above the tunnel initially increases and then decreases. Under the influence of tunnel excavation, the surrounding rock stress undergoes redistribution. After the stress adjustment, the ratio of horizontal stress to vertical stress initially decreases and then increases.

[0067] like Figure 5As shown, after adjusting the surrounding rock stress, the ratio of horizontal stress to vertical stress tends to stabilize at around 0.6. Taking λ = 0.6 and an error level of ±5%, i.e., ε = 0.03, the interval (0.57, 0.63) is defined as the interval with less disturbance after stress redistribution. Therefore, the surrounding rock in the interval of element 13 to 19 is less affected by excavation. In the numerical model of the geological structure, the height h3 of the surrounding rock with less excavation disturbance corresponding to element 13 to 19 is 5.96m.

[0068] Calculate the height H of the overlying strata disturbed during the excavation and support process. S =15.82-5.96=9.86m.

[0069] Step 5: Assume the depth of the surface fracture zone of the subsea tunnel is 10m, K is 0.4, and Ks is 0.6.

[0070] H min =a+K(s+h)+K S H S =10+0.4(13.22+2.6)+0.6*9.86=22.24m.

[0071] The reasonable burial depth of the undersea tunnel calculated in this embodiment is 22.24m.

[0072] The burial depth in the existing technology is H = 25.82m, which is calculated in step 3.

[0073] This invention is nearly 14% better than existing top-water coal mining methods.

[0074] This invention combines top-water coal mining with numerical simulation to determine a reasonable burial depth for submarine tunnels. It takes into account the influence of tunnel support on the burial depth and conforms to the deformation mechanism of tunnel excavation and support. The reasonable burial depth of submarine tunnels determined by this invention can avoid problems such as increased cost, increased construction difficulty, and extended construction period caused by excessive burial depth of submarine tunnels, under the premise of tunnel stability.

[0075] The present invention has been described in detail above through embodiments, but the content described is only an exemplary embodiment of the present invention and should not be considered as limiting the scope of the present invention. The scope of protection of the present invention is defined by the claims. Any technical solutions designed by those skilled in the art using the technical solutions described in the present invention, or designed by those skilled in the art under the inspiration of the technical solutions of the present invention, within the substance and protection scope of the present invention, to achieve the above-mentioned technical effects, or any equivalent changes and improvements made to the scope of the application, should still fall within the patent protection scope of the present invention.

Claims

1. A method for calculating the reasonable burial depth of an undersea tunnel, characterized in that, Includes the following steps: Step 1: By investigating and surveying data, obtain the physical and mechanical parameters of the rock strata from top to bottom for the proposed tunnel; Step 2: Obtain information about the proposed tunnel through the tunnel design scheme; Step 3: Calculate the minimum overburden thickness H of the tunnel. H = a + s + h Where a is the depth of the fracture zone on the surface of the submarine tunnel; s is the safe thickness of the water-resistant rock overburden; and h is the height of the blasting disturbance during tunnel excavation. Step 4: Loading with seawater Using the physical and mechanical parameters of the rock strata from top to bottom, the proposed tunnel information, and the minimum overburden thickness H as input conditions, a numerical model of the geological structure is established. The numerical model adopts a continuous medium model, assuming that the rock strata are homogeneous and horizontally distributed, the rock mass uses Mohr-Coulomb plane strain elements, the initial support uses isotropic elastic materials, and the anchor bolts use embedded beam elements. The stress and strain of the strata and materials vary within the elastoplastic range. The simulation simulates the redistribution of surrounding rock stress caused by tunnel excavation. Based on the simulation results, the height of disturbance of the overburden strata during the excavation and support process is obtained. ; Step 5: Calculate the final minimum overburden thickness for the undersea tunnel. , ， in, and These are the reduction factors for the cover layer height derived from empirical formulas and numerical simulations, respectively. In step 1, the physical and mechanical parameters of the rock strata of the proposed tunnel from top to bottom include: surrounding rock grade, surrounding rock unit weight γ, cohesion c, internal friction angle φ, elastic modulus E, Poisson's ratio μ, and surrounding rock elastic resistance coefficient; In step 2, the proposed tunnel information includes: tunnel dimensions, support parameters, and excavation and support sequence; In step 4, the simulation results are used to determine the ratio of horizontal to vertical stress in the surrounding rock after stress redistribution, which tends towards the horizontal line. If we take the error level ε, then we define the interval corresponding to the (λ-ε, λ+ε) element as the interval where the surrounding rock is less disturbed by excavation after stress redistribution, and the height of the surrounding rock in this interval is h3; Hs = s + h - h3; In step 4, the seawater pressure is equivalent to a uniformly distributed seawater load above the seabed. .

2. The method for calculating the reasonable burial depth of an undersea tunnel as described in claim 1, characterized in that, In step 3, a is based on the most unfavorable depth of the surface fracture zone in the geological survey data; ， In the formula: The water head height, The width of the tunnel. The thickness of the strongly weathered rock zone, The strength is obtained by referring to a table or by sampling test; ， In the formula, k is the subgrade coefficient; w is the minimum resistance line of a single most dangerous explosive charge; This is a function of the explosive exploding index of the corresponding explosive charge.

3. The method for calculating the reasonable burial depth of an undersea tunnel as described in claim 1, characterized in that, In step 5, Take 0.4, Take 0.6.

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