Calculation method for surrounding rock pressure of tunnel in rock disc type karst section

Abstract

The invention discloses a method for calculating the surrounding rock pressure of a tunnel in a rock disc type karst section. The method comprises the steps that 1, the thickness of a rock disc between the tunnel and a karst cave is determined; step 2, determining karst cave filler parameters; 3, basic surrounding rock pressure is calculated; 4, calculating original karst cave soil pressure; step 5, determining the safe bedrock thickness of the hidden karst cave around the tunnel, and taking the maximum value of the safe bedrock thickness of the hidden karst cave around the tunnel obtained by checking calculation according to the bedrock bending strength and the safe bedrock thickness of the hidden karst cave around the tunnel obtained by checking calculation according to the bedrock shearing strength; 6, calculating the soil pressure borne by the tunnel lining; and 7, calculating the tunnel surrounding rock pressure. According to the method, uniform calculation of the surrounding rock pressure of the tunnel in the rock disc type karst section can be achieved, the stress of the lining structure is balanced, the influence of the hidden karst cave on the surrounding rock pressure of the tunnel can be reflected, the surrounding rock pressure of the tunnel in the karst section can be calculated more accurately, and the design accuracy and construction safety of the lining structure are improved.

Description

Technical Field

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

[0002] A large number of engineering practices have shown that the design and selection of karst tunnel support structures in karst-developed areas require special caution. Compared with tunnels in other geological conditions, the uniformity of the surrounding rock around the tunnel is greatly reduced due to the presence of karst, which will lead to an increase in the unevenness of the surrounding rock pressure, and then cause the lining structure to be unbalanced or have a large bias, which is very unfavorable to the structural stress. Therefore, when calculating the load of karst tunnels, it is required to consider this unevenness of the surrounding rock pressure, but the traditional surrounding rock pressure calculation method often cannot meet this requirement.

[0003] Therefore, in practical engineering, a theoretically clear, efficient and concise calculation method is urgently needed to accurately calculate the surrounding rock pressure of 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 prior art and to provide a method for calculating the surrounding rock pressure of a tunnel in a slab-type karst area. The method for calculating the surrounding rock pressure of a tunnel in a slab-type karst area can achieve uniform calculation of the surrounding rock pressure of a tunnel in a slab-type karst area, 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 a rock-plate type karst area comprises the following steps.

[0007] Step 1, determine the thickness T of the rock bed between the tunnel and the cave; according to the cave pressure borne by the tunnel lining, determine whether there is a rock bed between the cave and the tunnel, and determine the thickness T of the rock bed between the tunnel and the cave;

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

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

[0010] Step 4, calculating the original cave soil pressure: according to the cave filling material parameters determined in step 2, calculating the original cave soil pressure generated by the cave filling material; at this time, the original cave soil pressure includes the vertical cave soil pressure q and the lateral cave soil pressure e;

[0011] Step 5: Determine the thickness T of the safe rock bed of the hidden karst caves around the tunnels , specifically:

[0012] T s =max(T s1 ,T s2 )

[0013] Where, T s1 The thickness of the safe rock bed of the hidden karst caves around the tunnel calculated based on the rock bed bending strength, in meters;

[0014] T s2 The thickness of the safe rock bed of the hidden karst caves around the tunnel calculated based on the rock bed shear strength, in meters;

[0015] Step 6: Calculate the karst soil pressure on the tunnel lining: The karst soil pressure on the tunnel lining includes the vertical soil pressure q' and the lateral soil pressure E. Then:

[0016] A. When T≥T s When q'=E=0;

[0017] B. When 0<T<T s When q' and E are determined according to the type of hidden caves around the tunnel, specifically:

[0018] (I) When the hidden cave around the tunnel is the hidden cave on the top of the tunnel, the calculation formulas of q' and E are:

[0019]

[0020] E=0

[0021] (ii) When the hidden cave around the tunnel is the hidden cave at the bottom of the tunnel, the calculation formulas of q' and E are:

[0022]

[0023] E=0

[0024] Where, p is the hydrostatic pressure at the top of the rock bed in the cave, unit: kPa;

[0025] (III) When the hidden cave around the tunnel is a hidden cave on the side of the tunnel, the calculation formula of q' is:

[0026] q'=0

[0027] At this time, E is determined based on the positional relationship between the hidden cave on the side of the tunnel and the tunnel;

[0028] Step 7, calculate the tunnel surrounding rock pressure: add the basic surrounding rock pressure in step 3 and the earth pressure on the tunnel lining obtained in step 6 to obtain the tunnel surrounding rock pressure in the rock bed type karst area.

[0029] In step 5, when the hidden cave around the tunnel is the hidden cave on the top of the tunnel, then T s1 and T s2 The calculation formulas are:

[0030]

[0031] In the formula, k s ——Safety factor, which is a set constant;

[0032] γ m ——The weight of the rock mass of the hidden cave, unit: kN / m 3 ;

[0033] l is the rock bed span. For hidden caves on the top of the tunnel, the smaller value between the tunnel excavation span and the cave span is taken, unit: m;

[0034] [σ t ]——the allowable tensile strength of the rock mass, unit: kPa, determined according to the actual measurement results;

[0035] b is the width of the equivalent beam in the simplified mechanical model of tunnels, rock beds and caves, in meters;

[0036] [τ]——The allowable shear strength of the rock mass, unit: kPa, determined based on actual measurement results.

[0037] In step 5, when the hidden cave around the tunnel is the hidden cave at the bottom of the tunnel, then T s1 and T s2 The calculation formulas are:

[0038]

[0039] Where: l is the rock bed span. For hidden caves at the bottom of the tunnel, the smaller value between the tunnel excavation span and the cave span is taken, unit: m.

[0040] In step 5, when the hidden cave around the tunnel is a hidden cave on the side of the tunnel, then T s1 and T s2 The calculation formulas are:

[0041]

[0042] Where: k af ——The active earth pressure coefficient of the filling material in the cave is a set constant;

[0043] γ f ——The weight of the filling material in the cave, unit: kN / m 3 ;

[0044] h——the distance from the surface of the cave filling to the top of the rock bed, unit: m;

[0045] γ w ——Water density in the cave, unit: kN / m 3 ;

[0046] p——hydrostatic pressure at the top of the rock bed in the cave, unit: kPa;

[0047] l is the span of the rock bed. For hidden caves on the side of the tunnel, the smaller value between the tunnel excavation height and the cave height is taken, unit: m.

[0048] In step 4, the lateral cave soil pressure e includes the left arch lateral soil pressure e1, the left bottom lateral soil pressure e′1, the right arch lateral soil pressure e2 and the right bottom lateral soil pressure e′2 generated by the cave filling; the calculation formulas of e1, e′1, e2 and e′2 are respectively:

[0049] e1=γ f h f λ1

[0050]

[0051] e2=γ f h f λ2

[0052]

[0053] Where, h1 and h2 are the depths of the left and right bottoms of the cave filling, respectively, in meters;

[0054] λ1 and λ2 are the left and right lateral pressure coefficients of the cave filling, respectively;

[0055] γ f ——The weight of the filling material in the cave, unit: kN / m 3 ;

[0056] h f ——The thickness of the vault of the cave filling in the tunnel arch, unit: m.

[0057] In step 6, the lateral earth pressure E borne by the tunnel lining includes the left arch of the tunnel lining bearing the lateral earth pressure E1, the left bottom bearing the lateral earth pressure E′1, the right arch bearing the lateral earth pressure E2 and the right bottom bearing the lateral earth pressure E′2; then:

[0058] A. When 0<T<T s , When the hidden cave around the tunnel is a hidden cave on the side of the tunnel and the cave is located on the left side of the tunnel, the calculation formulas of E1, E′1, E2 and E′2 are:

[0059]

[0060] E2=E′2=0

[0061] B. When 0<T<T s , When the hidden cave around the tunnel is a hidden cave on the side of the tunnel and the cave is located on the right side of the tunnel, the calculation formulas of E1, E′1, E2 and E′2 are:

[0062]

[0063] E′1=E1=0.

[0064] In step 2, the surrounding rock grade S of the cave filling is taken as an integer from 1 to 6, corresponding to grade I to VI surrounding rock.

[0065] In step 4, the calculation formula for the vertical cave soil pressure q is:

[0066] q=γ f h q

[0067] in:

[0068] h q =0.45×2 S-1 ×[1+i·(B-5)]

[0069] Where: h q ——Equivalent load height of the cave filling material in the tunnel arch, unit: m;

[0070] γ f ——The weight of the filling material in the cave, unit: kN / m 3 ;

[0071] S——the surrounding rock grade of cave filling;

[0072] B——cavern width, unit: m; when B<5m, let B=5m;

[0073] i——The rate of increase or decrease of surrounding rock pressure when the cave width increases by 1m.

[0074] In step 4, the surrounding rock pressure increase / decrease rate i is determined according to the cave width B.

[0075] The present invention has the following beneficial effects: compared with the traditional surrounding rock pressure calculation method, the present invention can reflect the heterogeneity of the surrounding rock in the karst area, and more accurately calculate the surrounding rock pressure of the tunnel in the rock-plate type karst area through a simplified algorithm, thereby effectively ensuring the accuracy of the structural design and the safety of on-site construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 The structural principle diagram of the calculation of the soil pressure in the karst cave in the present invention is shown.

[0077] Figure 2 A simplified model diagram of the rock bed of the hidden karst cave at the top of the tunnel in the present invention is shown; wherein (a) shows the positional relationship diagram of the tunnel, the rock bed and the hidden karst cave; and (b) is a simplified mechanical calculation model.

[0078] Figure 3 A simplified model diagram of the rock bed of the hidden karst cave at the bottom of the tunnel in the present invention is shown; wherein (a) shows the positional relationship diagram of the tunnel, the rock bed and the hidden karst cave; and (b) is a simplified mechanical calculation model.

[0079] Figure 4 A simplified model diagram of the rock bed of the hidden cave on the side of the tunnel in the present invention is shown; wherein (a) shows the positional relationship diagram of the tunnel, the rock bed and the hidden cave; and (b) is a simplified mechanical calculation model. DETAILED DESCRIPTION

[0080] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific preferred embodiments.

[0081] like Figure 1 As shown, a method for calculating the surrounding rock pressure of a tunnel in a rock-plate type karst area includes the following steps.

[0082] Step 1, determine the thickness T of the rock bed between the tunnel and the cave; according to the cave pressure borne by the tunnel lining, judge whether there is a rock bed between the cave and the tunnel, and determine the thickness T of the rock bed between the tunnel and the cave by drilling or advanced geological prediction.

[0083] 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.

[0084] The surrounding rock grade S of the above-mentioned cave filling is preferably an integer from 1 to 6, corresponding to grade I to VI surrounding rock.

[0085] Step 3: Calculate basic surrounding rock pressure: Calculate basic surrounding rock pressure according to the positional relationship between the cave and the tunnel and the size of the cave, preferably according to the surrounding rock pressure of a general tunnel. When there is a large or giant hidden cave in the arch, and the positional relationship with the tunnel is medium or close, the basic surrounding rock pressure should be calculated according to the shallow buried tunnel, and the arch top burial depth should be determined according to the thickness of the rock bed.

[0086] Step 4: Calculate the original cave soil pressure

[0087] According to the cave filling material parameters determined in step 2, the original cave soil pressure generated by the cave filling material is calculated; at this time, the original cave soil pressure includes the vertical cave soil pressure q and the lateral cave soil pressure e.

[0088] 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.

[0089] The calculation formula of the vertical cave soil pressure q is preferably:

[0090] q=γ f h q

[0091] in:

[0092] h q =0.45×2 S-1 ×[1+i·(B-5)]

[0093] Where: h q ——Equivalent load height of the cave filling in the tunnel arch, unit: m.

[0094] γ f ——The weight of the filling material in the cave, unit: kN / m 3 .

[0095] S——Surrounding rock grade of cave filling.

[0096] B is the width of the cave, unit: m; when B is less than 5m, set B=5m.

[0097] i——The rate of increase or decrease of surrounding rock pressure when the cave width increases by 1m.

[0098] The above-mentioned lateral cave earth pressure e includes the left arch lateral earth pressure e1, the left bottom lateral earth pressure e′1, the right arch lateral earth pressure e2 and the right bottom lateral earth pressure e′2 generated by the cave filling; then the calculation formulas of e1, e′1, e2 and e′2 are preferably:

[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 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] In the formula, 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] Wherein, 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 friction angle of the vertical sliding surface when the cave filling is in an infinite soil mass, shallowly buried state and the surface of the cave filling 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 has the following two calculation 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 surface of the cave filling.

[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 material slopes downward, the calculation formula of the lateral pressure coefficient λ is:

[0126]

[0127] Step 5: Determine the thickness T of the safe rock bed of the hidden karst caves around the tunnel s , specifically:

[0128] T s =max(T s1 ,T s2 )

[0129] Where, T s1 It is the thickness of the safe rock bed for hidden caves around the tunnel obtained by verifying the bending strength of the rock bed, in meters.

[0130] T s2 It is the thickness of the safe rock bed for hidden caves around the tunnel obtained by verifying the shear strength of the rock bed, in meters.

[0131] The hidden caves around the tunnels mentioned above include hidden caves on the top of the tunnel, hidden caves at the bottom of the tunnel and hidden caves on the sides of the tunnel. For each type of hidden caves around the tunnels, there is a corresponding set of T s1 and T s2 , the specific calculation method is as follows.

[0132] 1. Hidden cave at the top of the tunnel

[0133] like Figure 2 As shown in Figure 2, when the hidden cave around the tunnel is the hidden cave on the top of the tunnel, then T s1 and T s2 The calculation formulas are:

[0134]

[0135] In the formula, k s ——Safety factor, which is a set constant.

[0136] γ m ——The weight of the rock mass of the hidden cave, unit: kN / m 3 .

[0137] l is the rock span. For hidden caves on the top of the tunnel, the smaller value between the tunnel excavation span and the cave span is taken, unit: m.

[0138] [σ t ]——the allowable tensile strength of the rock mass, unit: kPa, determined according to the actual measurement results;

[0139] b is the width of the equivalent beam in the simplified mechanical model of tunnels, rock beds and caves, unit: m.

[0140] [τ]——The allowable shear strength of the rock mass, unit: kPa, determined based on actual measurement results.

[0141] 2. Hidden Cave at the Bottom of the Tunnel

[0142] like Figure 3 As shown in the figure, when the hidden cave around the tunnel is the hidden cave at the bottom of the tunnel, then T s1 and T s2 The calculation formulas are:

[0143]

[0144] Where: l is the rock bed span. For hidden caves at the bottom of the tunnel, the smaller value between the tunnel excavation span and the cave span is taken, unit: m.

[0145] 3. Hidden Caves on the Side of the Tunnel

[0146] like Figure 4 As shown in the figure, when the hidden cave around the tunnel is the hidden cave on the side of the tunnel, then T s1 and T s2 The calculation formulas are:

[0147]

[0148] Where: k af ——The active earth pressure coefficient of the filling material in the cave is a set constant.

[0149] γ f ——The weight of the filling material in the cave, unit: kN / m 3 .

[0150] h – distance from the surface of the cave filling to the top of the rock bed, unit: m.

[0151] γ w ——Water density in the cave, unit: kN / m 3 .

[0152] p is the hydrostatic pressure at the top of the rock bed in the cave, unit: kPa.

[0153] l is the span of the rock bed. For hidden caves on the side of the tunnel, the smaller value between the tunnel excavation height and the cave height is taken, unit: m.

[0154] Step 6, calculate the earth pressure on the tunnel lining: the karst cave earth pressure on the tunnel lining includes the vertical earth pressure q' on the tunnel lining and the lateral earth pressure E on the tunnel lining; among them, the lateral earth pressure E on the karst cave includes the lateral earth pressure E1 on the left arch of the tunnel lining, the lateral earth pressure E′1 on the left bottom, the lateral earth pressure E2 on the right arch and the lateral earth pressure E′2 on the right bottom.

[0155] A. When T≥T s When , the lining will not be subjected to additional earth pressure from the cave soil pressure, q'=E=0.

[0156] B. When 0<T<T s When the lining is subjected to additional pressure from the cave soil pressure, the calculation formulas of q' and E can be divided into:

[0157] 1. Hidden cave at the top of the tunnel

[0158]

[0159] E=0

[0160] 2. Hidden Cave at the Bottom of the Tunnel

[0161]

[0162] E=0

[0163] p——hydrostatic pressure at the top of the rock bed in the cave, unit: kPa;

[0164] 3. Hidden Caves on the Side of the Tunnel

[0165] q'=0

[0166] Here, the additional cave pressure on the side is determined according to the relative position of the hidden cave and the tunnel.

[0167] A. When the cave is on the left side of the tunnel:

[0168]

[0169] E2=0

[0170] E′2=0

[0171] B. When the cave is on the left side of the tunnel:

[0172]

[0173] E1=0

[0174] E′1=0

[0175] Step 7, calculate the tunnel surrounding rock pressure: add the basic surrounding rock pressure in step 3 and the cave soil pressure on the tunnel lining obtained in step 6 to obtain the tunnel surrounding rock pressure in the rock bed type karst area.

[0176] Compared with the traditional tunnel surrounding rock pressure calculation method, the present invention can better reflect the influence of hidden caves on tunnel surrounding rock pressure, can more accurately calculate the tunnel surrounding rock pressure in karst areas, and improve the accuracy of lining structure design and the safety of construction.

[0177] 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 belong to the protection scope of the present invention.

Claims

1. A method for calculating surrounding rock pressure of tunnels in rock-plate karst areas, characterized by: The steps include: Step 1, determine the thickness T of the rock bed between the tunnel and the cave; according to the cave pressure borne by the tunnel lining, determine whether there is a rock bed between the cave and the tunnel, and determine the thickness T of the rock bed between the tunnel and the cave; Step 2, determine the cave filling parameters: The cave filling parameters include the surrounding rock grade of the cave filling, the cave filling thickness, the surface state of the cave filling and the physical parameters of the cave filling; Step 3: Calculate basic surrounding rock pressure: Calculate basic surrounding rock pressure based on the position relationship between the cave and the tunnel and the size of the cave; Step 4, calculating the original cave soil pressure: according to the cave filling material parameters determined in step 2, calculating the original cave soil pressure generated by the cave filling material; at this time, the original cave soil pressure includes the vertical cave soil pressure q and the lateral cave soil pressure e; Step 5: Determine the thickness T of the safe rock bed of the hidden karst caves around the tunnel s , specifically: T s =max(T s1 ,T s2 ) Where, T s1 The thickness of the safe rock bed of the hidden karst caves around the tunnel calculated based on the rock bed bending strength, in meters; T s2 The thickness of the safe rock bed of the hidden karst caves around the tunnel calculated based on the rock bed shear strength, in meters; Step 6, calculate the karst soil pressure on the tunnel lining: the karst soil pressure on the tunnel lining includes the vertical soil pressure q' on the tunnel lining and the lateral soil pressure E on the tunnel lining; but: A. When T≥T s When q'=E=0; B. When 0<T<T s When q' and E are determined according to the type of hidden caves around the tunnel, specifically: (I) When the hidden cave around the tunnel is the hidden cave on the top of the tunnel, the calculation formulas of q' and E are: E＝0 (ii) When the hidden cave around the tunnel is the hidden cave at the bottom of the tunnel, the calculation formulas of q' and E are: E＝0 Where, p is the hydrostatic pressure at the top of the rock bed in the cave, unit: kPa; (III) When the hidden cave around the tunnel is a hidden cave on the side of the tunnel, the calculation formula of q' is: q'＝0 At this time, E is determined based on the positional relationship between the hidden cave on the side of the tunnel and the tunnel; Step 7, calculate the tunnel surrounding rock pressure: add the basic surrounding rock pressure in step 3 and the earth pressure on the tunnel lining obtained in step 6 to obtain the tunnel surrounding rock pressure in the rock bed type karst area.

2. The method for calculating surrounding rock pressure of a tunnel in a rocky karst area according to claim 1 is characterized by: In step 5, when the hidden cave around the tunnel is the hidden cave on the top of the tunnel, then T s1 and T s2 The calculation formulas are: In the formula, k s ——Safety factor, which is a set constant; γ m ——The weight of the rock mass of the hidden cave, unit: kN / m 3 ; l is the rock bed span. For hidden caves on the top of the tunnel, the smaller value between the tunnel excavation span and the cave span is taken, unit: m; [σ t ]——the allowable tensile strength of the rock mass, unit: kPa, determined according to the actual measurement results; b is the width of the equivalent beam in the simplified mechanical model of tunnels, rock beds and caves, in meters; [τ]——The allowable shear strength of the rock mass, unit: kPa, determined based on actual measurement results.

3. The method for calculating surrounding rock pressure of a tunnel in a rocky karst area according to claim 2 is characterized by: In step 5, when the hidden cave around the tunnel is the hidden cave at the bottom of the tunnel, then T s1 and T s2 The calculation formulas are: Where: l is the rock bed span. For hidden caves at the bottom of the tunnel, the smaller value between the tunnel excavation span and the cave span is taken, unit: m.

4. The method for calculating surrounding rock pressure of a tunnel in a rocky karst area according to claim 2 is characterized by: In step 5, when the hidden cave around the tunnel is a hidden cave on the side of the tunnel, then T s1 and T s2 The calculation formulas are: Where: k af ——The active earth pressure coefficient of the filling material in the cave is a set constant; γ f ——The weight of the filling material in the cave, unit: kN / m 3 ; h——the distance from the surface of the cave filling to the top of the rock bed, unit: m; γ w ——Water density in the cave, unit: kN / m 3 ; p——hydrostatic pressure at the top of the rock bed in the cave, unit: kPa; l is the span of the rock bed. For hidden caves on the side of the tunnel, the smaller value between the tunnel excavation height and the cave height is taken, unit: m.

5. The method for calculating surrounding rock pressure of tunnels in rock-bed karst areas according to claim 1 is characterized by: In step 4, the lateral cave soil pressure e includes the left arch lateral soil pressure e1, the left bottom lateral soil pressure e′1, the right arch lateral soil pressure e2 and the right bottom lateral soil pressure e′2 generated by the cave filling; the calculation formulas of e1, e′1, e2 and e′2 are respectively: 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; γ f ——The weight of the filling material in the cave, unit: kN / m 3 ; h f ——The thickness of the vault of the cave filling in the tunnel arch, unit: m.

6. The method for calculating surrounding rock pressure of a tunnel in a rocky karst area according to claim 5 is characterized by: In step 6, the lateral earth pressure E borne by the tunnel lining includes the left arch of the tunnel lining bearing the lateral earth pressure E1, the left bottom bearing the lateral earth pressure E′1, the right arch bearing the lateral earth pressure E2 and the right bottom bearing the lateral earth pressure E′2; then: A. When 0<T<T s , When the hidden cave around the tunnel is a hidden cave on the side of the tunnel and the cave is located on the left side of the tunnel, the calculation formulas of E1, E′1, E2 and E′2 are: E2=E′2=0 B. When 0<T<T s , When the hidden cave around the tunnel is a hidden cave on the side of the tunnel and the cave is located on the right side of the tunnel, the calculation formulas of E1, E′1, E2 and E′2 are: E′1=E1=0.

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

8. The method for calculating surrounding rock pressure of a tunnel in a rocky karst area according to claim 7 is characterized by: In step 4, 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 cave filling material in the tunnel arch, unit: m; γ f ——The weight of the filling material in the cave, unit: kN / m 3 ; S——the 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.

9. The method for calculating surrounding rock pressure of a tunnel in a rocky karst area according to claim 8, characterized in that: In step 4, the surrounding rock pressure increase / decrease rate i is determined according to the cave width B.

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