A method for calculating surrounding rock pressure of tunnels in exposed karst areas

Abstract

The present invention discloses a method for calculating the surrounding rock pressure of tunnels in exposed karst areas, comprising the following steps: 1. determining whether the cave and the tunnel intersect; if the cave and the tunnel intersect, the area is exposed karst; 2. determining the parameters of the cave filling material; 3. calculating the basic surrounding rock pressure; 4. calculating the earth pressure borne by the tunnel lining: because the cave and the tunnel intersect, the earth pressure borne by the tunnel lining is equal to the earth pressure in the cave; the earth pressure in the cave includes vertical earth pressure in the cave and lateral earth pressure in the cave; the vertical earth pressure in the cave is related to the tunnel's burial depth; and 5. calculating the surrounding rock pressure of the tunnel. The present invention can achieve uniform calculation of the surrounding rock pressure of tunnels in exposed karst areas, ensuring balanced stress on the lining structure.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel engineering, in particular to a method for calculating the surrounding rock pressure of a tunnel in an exposed karst area. Background Art

[0002] Exposed karst areas refer to situations where tunnels intersect with karst structures. A large number of engineering practices have shown that the design and selection of support structures for karst tunnels in karst-developed areas require special caution. Compared with tunnels with other geological conditions, due to the presence of karst structures, the surrounding rock around the tunnel has cavities or fillings with properties that are quite different from those of the surrounding rock, resulting in a significant reduction in the uniformity of the surrounding rock. This will lead to an increase in the unevenness of the surrounding rock pressure, which in turn will cause the lining structure to be subjected to uneven stress or a large bias, which is very unfavorable to the stress of the structure. Therefore, when calculating the load of a karst tunnel, it is required to consider this unevenness of the surrounding rock pressure. However, in the traditional surrounding rock pressure calculation method, the rock mass around the tunnel is regarded as uniform in nature, and it is impossible to clearly calculate the surrounding rock pressure of tunnels in karst areas.

[0003] Therefore, in practical engineering, a theoretically clear, efficient and concise calculation method is urgently needed to accurately calculate the surrounding rock pressure of exposed karst tunnels. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned existing technologies and provide a method for calculating the surrounding rock pressure of tunnels in exposed karst areas. The method for calculating the surrounding rock pressure of tunnels in exposed karst areas can achieve uniform calculation of the surrounding rock pressure of tunnels in exposed karst areas, so that the lining structure is subjected to balanced force.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for calculating surrounding rock pressure of a tunnel in an exposed karst area comprises the following steps.

[0007] Step 1: Determine whether the cave and the tunnel intersect: Determine whether the cave and the tunnel intersect based on the cave pressure on the tunnel lining. If the cave and the tunnel intersect, it is an exposed karst and proceed to step 2. Otherwise, terminate the calculation.

[0008] Step 2: Determine cave filling parameters: cave filling parameters include surrounding rock grade, cave filling thickness, cave filling surface state, and cave filling physical parameters;

[0009] Step 3: Calculate the basic surrounding rock pressure: Calculate the basic surrounding rock pressure based on the positional relationship between the cave and the tunnel and the size of the cave.

[0010] Step 4: Calculate the earth pressure on the tunnel lining: Since the cave intersects the tunnel, the earth pressure on the tunnel lining is equal to the earth pressure in the cave. The earth pressure in the cave includes the vertical earth pressure q and the lateral earth pressure e. The vertical earth pressure q is related to the tunnel depth, specifically:

[0011] A. When the tunnel is deeply buried, the calculation formula for the vertical cave soil pressure q is:

[0012] q=γ f h q

[0013] in:

[0014] h q =0.45×2 S-1 ×[1+i·(B-5)]

[0015] Where: h q ——Equivalent load height of the cave filling in the tunnel arch, unit: m.

[0016] γ f ——The density of the filling material in the cave, unit: kN / m 3 .

[0017] S——Surrounding rock grade of cave filling.

[0018] B is the width of the cave, unit: m; when B is less than 5m, let B = 5m.

[0019] i——The rate of increase or decrease of surrounding rock pressure when the cave width increases by 1m.

[0020] B. When the tunnel is in a shallow buried state, the calculation formula for the vertical cave soil pressure q is:

[0021]

[0022] Where h f ——The thickness of the vault of the cave filling in the tunnel arch, unit: m.

[0023] θ is the friction angle of the vertical sliding surface of the cave filling, unit: °.

[0024] λ0——lateral pressure coefficient of the cave filling in the tunnel arch.

[0025] Step 5: Calculate the tunnel surrounding rock pressure: Add the basic surrounding rock pressure obtained in step 3 to the earth pressure on the tunnel lining obtained in step 4 to obtain the tunnel surrounding rock pressure in the exposed karst area.

[0026] In step 2, the surrounding rock grade S of the cave filling is an integer from 1 to 6, corresponding to grade I to VI surrounding rock.

[0027] In step 4, if there is no measured value for the friction angle θ of the vertical sliding surface of the cave filling, it is taken according to the S value, specifically:

[0028] A. When S=1, 2, 3, in, Calculate the internal friction angle for the cave filling, unit: °.

[0029] B. When S=4,

[0030] C. When S=5,

[0031] D. When S=6,

[0032] In step 4, the surrounding rock pressure increase / decrease rate i is determined according to the cave width B. The specific method for determining the value is as follows:

[0033] A. When B≤5, i=0.2.

[0034] B. When 5<B<14, i=0.1.

[0035] C. When B≥14 and the tunnel is excavated using separate pilot tunnels, i=0.07.

[0036] D. When B≥14 and the tunnel adopts up and down steps or one-time excavation, i=0.12.

[0037] In step 4, the lateral cave earth pressure e includes the left arch lateral earth pressure e1, the left bottom lateral earth pressure e1', the right arch lateral earth pressure e2, and the right bottom lateral earth pressure e'2 generated by the cave filling. The calculation formulas for e1, e1', e2, and e'2 are:

[0038] e1=γ f h f λ1

[0039]

[0040] e2=γ f h f λ2

[0041]

[0042] Where h1 and h2 are the depths of the left and right bottoms of the cave filling, respectively, in meters.

[0043] λ1 and λ2 are the left and right lateral pressure coefficients of the cave filling, respectively.

[0044] In step 4, let the lateral pressure coefficient λ = λ0, λ1 or λ2, then λ is calculated according to the soil type and buried state of the cave filling.

[0045] When the cave filling is an infinite soil mass and is deeply buried, the calculation formula of the lateral pressure coefficient λ is:

[0046]

[0047] Where, Calculate the internal friction angle for each cave filling.

[0048] When the cave filling is an infinite soil mass, is in a shallow buried state, and the surface of the cave filling is inclined upward, the calculation formula of the lateral pressure coefficient λ is:

[0049]

[0050] Where, α is the angle between the surface of the cave filling and the horizontal plane, unit: °.

[0051] When the cave filling is an infinite soil mass, is in a shallow buried state, and the surface of the cave filling is inclined downward, the calculation formula of the lateral pressure coefficient e is:

[0052]

[0053] Where θ0 is the vertical sliding surface friction angle when the cave filling is in an infinite soil mass, shallowly buried state and the cave filling surface is inclined downward, and is calculated by the following formula:

[0054]

[0055] When the cave filling is a finite soil mass and is shallowly buried, the lateral pressure coefficient λ can be calculated using the following two methods:

[0056] A. When the surface of the cave filling is inclined upward, the calculation formula of the lateral pressure coefficient λ is:

[0057]

[0058] in:

[0059] m=tanα

[0060] Where, δ is the angle between the lateral earth pressure and the horizontal line, unit: °.

[0061] m – slope of the cave filling surface.

[0062] n is the slope of the line connecting the intersection of the cavity wall and the surface of the cave filling, and the intersection of the cavity wall and the tunnel surface.

[0063] μ——The friction coefficient between the cavity wall and the cave filling.

[0064] B. When the surface of the cave filling is inclined downward, the calculation formula of the lateral pressure coefficient λ is:

[0065]

[0066] The present invention has the following beneficial effects: compared with the traditional surrounding rock pressure calculation method, it can more accurately calculate the surrounding rock pressure of the tunnel in the exposed karst area, effectively ensuring the accuracy of the structural design and the safety of on-site construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 The structural principle diagram of the calculation of the soil pressure in the cave in the present invention is shown. DETAILED DESCRIPTION

[0068] The present invention will be further described in detail below with reference to the accompanying drawings and specific preferred embodiments.

[0069] A method for calculating surrounding rock pressure of a tunnel in an exposed karst area comprises the following steps.

[0070] Step 1: Determine whether the cave and the tunnel intersect: Determine whether the cave and the tunnel intersect based on the cave pressure on the tunnel lining. If the cave and the tunnel intersect, it is an exposed karst and proceed to step 2. Otherwise, terminate the calculation.

[0071] Step 2: Determine the parameters of the cave filling: The parameters of the cave filling include the surrounding rock grade of the cave filling, the thickness of the cave filling, the surface state of the cave filling, and the physical parameters of the cave filling.

[0072] In this embodiment, the surrounding rock grade S of the cave filling is preferably an integer from 1 to 6, corresponding to grades I to VI surrounding rock.

[0073] Step 3: Calculate basic surrounding rock pressure: Calculate basic surrounding rock pressure based on the positional relationship between the cave and the tunnel and the cave size. It is preferably calculated according to the general tunnel surrounding rock pressure, which will not be repeated here.

[0074] Step 4: Calculate the earth pressure on the tunnel lining: Since the cave intersects the tunnel, the earth pressure on the tunnel lining is equal to the earth pressure in the cave.

[0075] like Figure 1 As shown in Figure 3, the cave soil pressure includes the vertical cave soil pressure q and the lateral cave soil pressure e.

[0076] The vertical cave soil pressure q is related to the tunnel burial depth, specifically:

[0077] A. When the tunnel is deeply buried, the calculation formula for the vertical cave soil pressure q is:

[0078] q=γ f h q

[0079] in:

[0080] h q =0.45×2 S-1 ×[1+i·(B-5)]

[0081] Where: h q ——Equivalent load height of the cave filling in the tunnel arch, unit: m.

[0082] γ f ——The density of the filling material in the cave, unit: kN / m 3 .

[0083] S——Surrounding rock grade of cave filling.

[0084] B is the width of the cave, unit: m; when B is less than 5m, let B = 5m.

[0085] i is the rate of increase or decrease of surrounding rock pressure when the cave width increases by 1 m. It is preferably determined according to the cave width B, as shown in Table 1 below.

[0086] Table 1

[0087]

[0088] B. When the tunnel is in a shallow buried state, the calculation formula for the vertical cave soil pressure q is:

[0089]

[0090] Where h f ——The thickness of the vault of the cave filling in the tunnel arch, unit: m.

[0091] λ0——lateral pressure coefficient of the cave filling in the tunnel arch.

[0092] θ is the friction angle of the vertical sliding surface of the cave filling, in degrees. When there is no measured value, it is preferably determined based on the S value, specifically:

[0093] A. When S=1, 2, 3,

[0094] B. When S=4,

[0095] C. When S=5,

[0096] D. When S=6,

[0097] Where, Calculate the internal friction angle for the cave filling, unit: °.

[0098] The above-mentioned lateral cave earth pressure e includes the lateral earth pressure e1 on the left arch, the lateral earth pressure e1' on the left bottom, the lateral earth pressure e2 on the right arch, and the lateral earth pressure e'2 on the right bottom generated by the cave filling. The calculation formulas for e1, e1', e2, and e'2 are:

[0099] e1=γ f h f λ1

[0100]

[0101] e2=γ f h f λ2

[0102]

[0103] Where h1 and h2 are the depths of the left and right bottoms of the cave filling, respectively, in meters.

[0104] λ1 and λ2 are the left and right lateral pressure coefficients of the cave filling, respectively.

[0105] In this embodiment, the lateral pressure coefficient λ is set to λ0, λ1 or λ2, and λ is calculated according to the soil type and buried state of the cave filling.

[0106] 1. When the cave filling is an infinite soil mass and is deeply buried, the calculation formula of the lateral pressure coefficient λ is:

[0107]

[0108] Where, Calculate the internal friction angle for each cave filling.

[0109] 2. When the cave filling is an infinite soil mass, is in a shallow buried state, and the surface of the cave filling is inclined upward, the calculation formula of the lateral pressure coefficient λ is:

[0110]

[0111] Where, α is the angle between the surface of the cave filling and the horizontal plane, unit: °.

[0112] 3. When the cave filling is an infinite soil mass, is in a shallow buried state, and the surface of the cave filling is inclined downward, the calculation formula of the lateral pressure coefficient λ is:

[0113]

[0114] Where θ0 is the vertical sliding surface friction angle when the cave filling is in an infinite soil mass, shallowly buried state and the cave filling surface is inclined downward, and is calculated by the following formula:

[0115]

[0116] When the cave filling is a finite soil mass and is shallowly buried, the lateral pressure coefficient λ can be calculated using the following two methods:

[0117] A. When the surface of the cave filling is inclined upward, the calculation formula of the lateral pressure coefficient λ is:

[0118]

[0119] in:

[0120] m=tanα

[0121] Where, δ is the angle between the lateral earth pressure and the horizontal line, unit: °.

[0122] m – slope of the cave filling surface.

[0123] n is the slope of the line connecting the intersection of the cavity wall and the surface of the cave filling, and the intersection of the cavity wall and the tunnel surface.

[0124] μ——The friction coefficient between the cavity wall and the cave filling.

[0125] B. When the surface of the cave filling is inclined downward, the calculation formula of the lateral pressure coefficient λ is:

[0126]

[0127] Step 5: Calculate the tunnel surrounding rock pressure: Add the basic surrounding rock pressure obtained in step 3 to the earth pressure on the tunnel lining obtained in step 4 to obtain the tunnel surrounding rock pressure in the exposed karst area.

[0128] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the scope of protection of the present invention.

Claims

1. A method for calculating surrounding rock pressure in tunnels in exposed karst areas, characterized by: The steps include: Step 1: Determine whether the cave and the tunnel intersect: Based on the cave pressure on the tunnel lining, determine whether the cave and the tunnel intersect. If the cave and the tunnel intersect, it is an exposed karst and proceed to step 2; otherwise, terminate the calculation. Step 2: Determine cave filling parameters: cave filling parameters include surrounding rock grade, cave filling thickness, cave filling surface state, and cave filling physical parameters; Step 3: Calculate basic surrounding rock pressure: Calculate basic surrounding rock pressure based on the positional relationship between the cave and the tunnel and the cave size; Step 4: Calculate the earth pressure on the tunnel lining: Since the cave intersects the tunnel, the earth pressure on the tunnel lining is equal to the earth pressure in the cave. The earth pressure in the cave includes the vertical earth pressure q and the lateral earth pressure e. The vertical earth pressure q is related to the tunnel depth, specifically: A. When the tunnel is deeply buried, the calculation formula for the vertical cave soil pressure q is: q=γ f h q in: h q =0.45×2 S-1 ×[1+i·(B-5)] Where: h q ——Equivalent load height of the karst filling material in the tunnel arch, unit: m; γ f ——The density of the filling material in the cave, unit: kN / m 3 ; S - surrounding rock grade of cave filling; B——cavern width, unit: m; when B<5m, let B=5m; i——the rate of increase or decrease of surrounding rock pressure when the cave width increases by 1m; B. When the tunnel is in a shallow buried state, the calculation formula for the vertical cave soil pressure q is: Where h f ——The thickness of the vault of the karst filling material in the tunnel arch, unit: m; θ——friction angle of the vertical sliding surface of the cave filling, unit: °; λ0——lateral pressure coefficient of the karst filling material in the tunnel arch; Step 5: Calculate the tunnel surrounding rock pressure: Add the basic surrounding rock pressure obtained in step 3 to the earth pressure on the tunnel lining obtained in step 4 to obtain the tunnel surrounding rock pressure in the exposed karst area.

2. The method for calculating surrounding rock pressure of a tunnel in an exposed karst area according to claim 1, characterized in that: In step 2, the surrounding rock grade S of the cave filling is an integer from 1 to 6, corresponding to grade I to VI surrounding rock.

3. The method for calculating surrounding rock pressure in an exposed karst tunnel according to claim 2, characterized in that: In step 4, if there is no measured value for the friction angle θ of the vertical sliding surface of the cave filling, it is taken according to the S value, specifically: A. When S=1, 2, 3, in, Calculate the internal friction angle for the cave filling, unit: °; B. When S=4, C. When S=5, D. When S=6, 4. The method for calculating surrounding rock pressure of a tunnel in an exposed karst area according to claim 1, characterized in that: In step 4, the surrounding rock pressure increase / decrease rate i is determined according to the cave width B. The specific method for determining the value is as follows: A. When B≤5, i=0.2; B. When 5<B<14, i=0.1; C. When B ≥ 14 and the tunnel is excavated using separate pilot tunnels, i = 0.07; D. When B≥14 and the tunnel adopts up and down steps or one-time excavation, i=0.

12.

5. The method for calculating surrounding rock pressure of a tunnel in an exposed karst area according to claim 1 is characterized by: In step 4, the lateral cave earth pressure e includes the left arch lateral earth pressure e1, the left bottom lateral earth pressure e1', the right arch lateral earth pressure e2, and the right bottom lateral earth pressure e'2 generated by the cave filling. The calculation formulas for e1, e1', e2, and e'2 are: e1=γ f h f λ1 e2=γ f h f λ2 Where h1 and h2 are the depths of the left and right bottoms of the cave filling, respectively, in meters; λ1 and λ2 are the left and right lateral pressure coefficients of the cave filling, respectively.

6. The method for calculating surrounding rock pressure of a tunnel in an exposed karst area according to claim 5, characterized in that: In step 4, let the lateral pressure coefficient λ = λ0, λ1 or λ2, then λ is calculated according to the soil type and buried state of the cave filling.

7. The method for calculating surrounding rock pressure of a tunnel in an exposed karst area according to claim 6, characterized in that: When the cave filling is an infinite soil mass and is deeply buried, the calculation formula of the lateral pressure coefficient λ is: Where, Calculate the internal friction angle for each cave filling.

8. The method for calculating surrounding rock pressure of a tunnel in an exposed karst area according to claim 7, characterized in that: When the cave filling is an infinite soil mass, is in a shallow buried state, and the surface of the cave filling is inclined upward, the calculation formula of the lateral pressure coefficient λ is: Where, α is the angle between the surface of the cave filling and the horizontal plane, unit: °.

9. The method for calculating surrounding rock pressure of a tunnel in an exposed karst area according to claim 8, characterized in that: When the cave filling is an infinite soil mass, is in a shallow buried state, and the surface of the cave filling is inclined downward, the calculation formula of the lateral pressure coefficient λ is: Where θ0 is the vertical sliding surface friction angle when the cave filling is in an infinite soil mass, shallowly buried state and the cave filling surface is inclined downward, and is calculated by the following formula:

10. The method for calculating surrounding rock pressure of a tunnel in an exposed karst area according to claim 8, characterized in that: When the cave filling is a finite soil mass and is shallowly buried, the lateral pressure coefficient λ can be calculated using the following two methods: A. When the surface of the cave filling is inclined upward, the calculation formula of the lateral pressure coefficient λ is: in: m=tanα Where, δ is the angle between the lateral earth pressure and the horizontal line, unit: °; m – slope of the cave filling surface; n is the slope of the line connecting the intersection of the cavity wall and the surface of the cave filling, or the intersection of the cavity wall and the tunnel surface; μ——the friction coefficient between the cavity wall and the cave filling; B. When the surface of the cave filling is inclined downward, the calculation formula of the lateral pressure coefficient λ is:

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