Calculation method for surrounding rock pressure of small-clear-distance tunnel

Abstract

The invention provides a small-clear-distance tunnel surrounding rock pressure calculation method, and aims to solve the problem that the existing small-clear-distance tunnel surrounding rock pressure calculation is complicated and improve the existing small-clear-distance tunnel surrounding rock pressure calculation method. According to Hp and hq, dividing the burial depth condition of the tunnel into deep burial, shallow burial and ultra-shallow burial; when the tunnel is deeply buried, a method for calculating the surrounding rock pressure of the deeply-buried small-clear-distance tunnel is adopted; when the tunnel is shallowly buried, judging whether bias voltage exists in the tunnel or not; if the unsymmetrical pressure does not exist, a calculation method of the non-unsymmetrical pressure surrounding rock pressure of the shallow-buried small-clear-distance tunnel is adopted; if the bias voltage exists, adopting a calculation method of the bias voltage surrounding rock pressure of the shallow-buried small-clear-distance tunnel; when ultra-shallow burying is carried out, whether bias voltage exists or not is judged; if the bias voltage does not exist, a calculation method of the non-bias voltage surrounding rock pressure of the ultra-shallow buried small-clear-distance tunnel is adopted; and if the bias voltage exists, a calculation method of the bias voltage surrounding rock pressure of the ultra-shallow-buried small-clear-distance tunnel is adopted.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel surrounding rock, in particular to a method for calculating the surrounding rock pressure of a small-clearance tunnel. Background Art

[0002] my country's "Highway Tunnel Design Code, Volume 1, Civil Engineering" (JTG 3370.1-2018) provides a calculation method for the surrounding rock pressure of small clearance tunnels. However, the calculation method in the code has the following problems:

[0003] (1) The current calculation method of surrounding rock pressure in tunnels with small clearance is not the same as that of single-hole tunnels and multi-arch tunnels;

[0004] The calculation method for surrounding rock pressure of single-hole tunnel adopts the empirical formula method. As early as the 1980s, the "Railway Tunnel Design Code" (TBJ3-85) adopted this method to calculate surrounding rock pressure. It has been used for many years and is widely accepted in the transportation industry.

[0005] The calculation method of surrounding rock pressure of multi-arch tunnels and small clearance tunnels appeared relatively late, and first appeared in the "Highway Tunnel Design Code" (JTG / T D70-2010). It is a calculation method derived based on the Prochitz method, and there are some problems in its use. Tian Zhiyu et al. published "Revision Opinions on the Structural Calculation Articles of "JTG D70-2010 Highway Tunnel Design Code" in "Modern Tunnel Technology" in 2017, pointed out the problems, and fed back the opinions to the compilation group of "Highway Tunnel Design Code".

[0006] The calculation method of surrounding rock pressure of multi-arch tunnel in the "Highway Tunnel Design Code, Volume 1, Civil Engineering" (JTG 3370.1-2018) has made a comprehensive and systematic revision of the calculation method in the "Highway Tunnel Design Code" (JTG / T D70-2010). The new method is based on the empirical formula method of single-hole tunnels and derives the calculation formula of surrounding rock pressure of multi-arch tunnels. The calculation method of surrounding rock pressure of multi-arch tunnels in the current code has clear derivation logic, concise and reasonable formulas, which is easy for technical personnel to use and is consistent with the calculation method of surrounding rock pressure of single-hole tunnels.

[0007] The calculation method for surrounding rock pressure of small-clearance tunnels in the "Highway Tunnel Design Code, Volume 1, Civil Engineering" (JTG 3370.1-2018) is just a partial modification of the calculation method in the "Highway Tunnel Design Code" (JTG / T D70-2010). The formula is complicated and inconvenient to use, and is inconsistent with the calculation method for surrounding rock pressure of single-hole tunnels and multi-arch tunnels.

[0008] In summary, the current calculation method for surrounding rock pressure of single-hole tunnels and multi-arch tunnels is one system, while the calculation method for surrounding rock pressure of small clearance tunnels is another system, and the three do not form an organic whole.

[0009] (2) Some calculation results violate industry consensus and are inconsistent with engineering practice;

[0010] According to the calculation method of surrounding rock pressure of small and medium clearance tunnels and multi-arch tunnels in the "Highway Tunnel Design Code, Volume 1, Civil Engineering" (JTG 3370.1-2018), the internal force of the lining structure, crack width and safety factor are finally obtained. The calculation results show that, whether it is a shallow or deep buried condition, when all calculation parameters except the clearance are taken as the same, the surrounding rock pressure, structural axial force, structural bending moment, and crack width of the small clearance tunnel with a clearance of 6m are larger than those of the 3m clearance, while the safety factor is smaller than that of the 3m clearance. At the same time, whether it is a shallow or deep buried condition, when all calculation parameters are taken as the same, the surrounding rock pressure, structural axial force, and structural bending moment of the small clearance tunnel with a clearance of 6m are larger than those of the multi-arch tunnel. The above results obviously violate the consensus of the industry and are inconsistent with the actual engineering.

[0011] (3) The calculation method of surrounding rock pressure in small clearance tunnels is not a unified and coordinated whole;

[0012] In the "Highway Tunnel Design Code, Volume 1, Civil Engineering" (JTG 3370.1-2018), whether it is a single-hole tunnel or a multi-arch tunnel, the surrounding rock pressure calculation formulas for the shallow buried non-biased condition and the shallow buried biased condition are different, but in the case of non-biased pressure (surface slope is 0), as long as the calculation parameters are taken as the same, the results calculated by the two are the same; in other words, for single-hole tunnels and multi-arch tunnels, the shallow buried non-biased condition is a special form of the shallow buried biased condition, and the two are a unified and coordinated whole.

[0013] However, the surrounding rock pressure calculation formulas for the shallow non-biased pressure condition and the shallow biased pressure condition of the small clearance tunnel are different. In the non-biased case, the calculation parameters are taken as the same, and the results calculated by the two are also different. In other words, for the small clearance tunnel, the shallow non-biased pressure condition and the shallow biased pressure condition are unrelated to each other, and the two are not a unified and coordinated whole.

[0014] Therefore, it is necessary to derive a concise and correct calculation method for the surrounding rock pressure of small-clearance tunnels based on the calculation method for the surrounding rock pressure of single-hole tunnels, to ensure the accuracy of the calculation results of small-clearance tunnels, and to form a whole with the calculation method for the surrounding rock pressure of single-hole tunnels and multi-arch tunnels. Summary of the invention

[0015] The technical problem to be solved by the present invention is to provide a method for calculating the surrounding rock pressure of a small-clearance tunnel. Aiming at the problems that the existing calculation method of the surrounding rock pressure of a small-clearance tunnel is complicated and some contents are wrong, the existing method for calculating the surrounding rock pressure of a small-clearance tunnel is improved.

[0016] The technical solution adopted by the present invention to solve its technical problem is:

[0017] A method for calculating surrounding rock pressure of a small clearance tunnel is provided. The implementation process of the method is as follows:

[0018] (1) For an actual small clearance tunnel project, according to H p 、h q The tunnel depth is divided into deep, shallow and ultra-shallow.

[0019] (2) When the burial depth H>H p When the tunnel is deeply buried, the calculation method of surrounding rock pressure of deep buried small clear distance tunnel is adopted;

[0020] (3) When h q <Burial depth H≤H p When the tunnel is shallowly buried, determine whether there is bias pressure in the tunnel; if there is no bias pressure, the calculation method of non-bias pressure surrounding rock pressure of shallow buried small clear distance tunnel is adopted; if there is bias pressure, the calculation method of bias pressure surrounding rock pressure of shallow buried small clear distance tunnel is adopted;

[0021] (4) When the burial depth H≤h q When the tunnel is in ultra-shallow buried condition, it is determined whether there is bias pressure; if there is no bias pressure, the calculation method of non-bias pressure surrounding rock pressure of ultra-shallow buried small clear distance tunnel is adopted; if there is bias pressure, the calculation method of bias pressure surrounding rock pressure of ultra-shallow buried small clear distance tunnel is adopted.

[0022] The depth of the deep and shallow burial boundary H p The judgment is as follows:

[0023] H p =(2~2.5)h q (one)

[0024] In formula (1), H p is the depth of the boundary between deep and shallow burial of small clearance tunnel, in meters; H is taken for the surrounding rock of grade IV to VI p =2.5h q ; For the surrounding rock of grade Ⅰ~Ⅲ, take H p =2h q ;h q is the equivalent height of the load;

[0025] The h q The expression is as follows:

[0026]

[0027] In formula (2), q0=q+q′, where q is the basic vertical pressure of the surrounding rock; q′ is the additional vertical pressure of the surrounding rock; and γ is the weight of the surrounding rock.

[0028] When the burial depth H>H p The calculation method of surrounding rock pressure of deep buried small clearance tunnel is as follows:

[0029] 1. Vertical Pressure

[0030] The vertical pressure includes the basic surrounding rock vertical pressure q and the additional surrounding rock vertical pressure q′;

[0031] The basic surrounding rock vertical pressure q is the surrounding rock pressure at the bottom of the stable collapse arch formed by a single hole, which is assumed to be a uniformly distributed load;

[0032] The additional surrounding rock vertical pressure q′ is: when the clear distance is 0, the surrounding rock pressure at the lower part of the collapsed arch formed by the left and right holes minus the basic surrounding rock vertical pressure, multiplied by the correction coefficient.

[0033] Under different surrounding rock levels, small clearance tunnels are divided into Class A, Class B and Class C according to the clearance, the surrounding rock levels include Class III surrounding rock, Class IV surrounding rock and Class V surrounding rock, and the clearance is the double-hole clearance;

[0034] Case 1: When the net distance between the two holes is 0, the left and right holes together form a collapse arch. The calculation formula for the collapse arch height is as follows:

[0035]

[0036] Case 2: When the double-tunnel clearance is the boundary value of B- and C-level small-clearance tunnels, the left and right tunnels each form a collapse arch. The calculation formula for the collapse arch height is as follows:

[0037]

[0038] Case 3: When the surrounding rock pressure of the A and B class small clearance tunnels is between Case 1 and Case 2, its size is related to the clearance;

[0039] The calculation formulas for the basic surrounding rock vertical pressure q and the additional surrounding rock vertical pressure q′ of the deep-buried small clearance tunnel are as follows:

[0040]

[0041]

[0042] In formulas (III) to (VI), B t is the width of a single tunnel; 2B t is the height of the collapsed arch when calculating the width; Bt is the height of the collapsed arch when calculating the width; S is the surrounding rock grade, which is an integer from 1 to 6; i1 and i2 are respectively t , 2B t is the rate of increase or decrease of surrounding rock pressure when calculating width; ξ is the correction factor of interlayer rock in additional load; η is the correction factor of clear distance of additional load;

[0043] 2. Lateral pressure

[0044] The lateral pressure of surrounding rock acting on the outside of the lining is:

[0045]

[0046] The lateral pressure of surrounding rock acting on the inner side of the lining is:

[0047]

[0048] In formulas (VII) and (VIII), λ is the lateral pressure coefficient, H t is the height of a single-hole tunnel.

[0049] When the burial depth H≤h q When the tunnel is divided into non-biased tunnel and biased tunnel, the calculation formula of the surrounding rock pressure of the ultra-shallow small clearance tunnel without biased pressure is as follows:

[0050] 1. Vertical Pressure

[0051] q=γH (IX)

[0052] In formula (9), q is the vertical uniform pressure, the unit is kN / m 2 ; γ is the weight of surrounding rock, unit is kN / m 3 ; H is the tunnel depth, which refers to the distance from the top of the tunnel to the ground, in meters;

[0053] 2. Lateral pressure

[0054]

[0055]

[0056] In formula (10), e1 and e′1 are the lateral pressures at the top and bottom of the tunnel, respectively, in kN / m 2 , H t is the tunnel height, in m; λ is the lateral pressure coefficient; Calculate the friction angle for the surrounding rock.

[0057] The calculation method of surrounding rock pressure of the ultra-shallow buried small clearance tunnel bias pressure is as follows:

[0058] 1. Vertical Pressure

[0059] qi =γh i (eleven)

[0060] In formula (XI), i = 1, 2, 3 or 4; q1, q2, q3, q4 are the vertical pressures on the left side of the left hole, the right side of the left hole, the left side of the right hole, and the right side of the right hole, respectively, in kN / m 2 ;

[0061] 2. Lateral pressure

[0062]

[0063] In formula (XII), i = 1, 2, 3 or 4; e1, e2, e3, e4 are the lateral pressures of the surrounding rock of the left tunnel, the left tunnel, the right tunnel, the left tunnel, and the right tunnel, in kN / m 2 .

[0064] When h q <Burial depth H≤H p When the tunnel is divided into non-biased tunnel and biased tunnel, the surrounding rock pressure calculation method of the shallow buried small clearance tunnel without biased pressure is as follows:

[0065] 1. Vertical Pressure

[0066] Includes outer vertical pressure and inner vertical pressure;

[0067] (1) The calculation formula of the outer vertical pressure is as follows:

[0068]

[0069] (2) The formula for calculating the inner vertical pressure is as follows:

[0070] q2=q1+ξη(q-q1)

[0071]

[0072] In formulas (13) and (14), q1 is the vertical pressure of the surrounding rock outside the shallow-buried small-clearance tunnel, in kN / m 2 ; q2 is the vertical pressure of the surrounding rock inside the shallow tunnel with small clearance, in kN / m 2 ; γ is the weight of surrounding rock, unit is kN / m 3 ; H is the tunnel depth, which refers to the distance from the tunnel top to the ground; λ is the lateral pressure coefficient; θ is the friction angle on both sides of the arch rock and soil column; B t is the width of the single-hole tunnel; β is the rupture angle when the maximum thrust is generated on the left side of the left hole, the right side of the left hole, the left side of the right hole, and the right side of the right hole; is the friction angle calculated for the surrounding rock; ξ is the correction coefficient for the interlayer rock in the additional load; η is the correction coefficient for the additional load clearance; q is the vertical pressure of the surrounding rock of the shallow buried small clearance tunnel when the clearance is 0;

[0073] 2. Lateral pressure

[0074]

[0075]

[0076] In formulas (15) and (16), e1 and e1′ are the lateral pressures of the surrounding rock at the top and bottom of the tunnel on the left side of the left tunnel (right side of the right tunnel); e2 and e′2 are the lateral pressures of the surrounding rock at the top and bottom of the tunnel on the right side of the left tunnel (left side of the right tunnel); H t is the tunnel height; v is the coefficient of increase in lateral pressure of the interlayer rock.

[0077] In the above formula;

[0078]

[0079] The calculation method of surrounding rock pressure of the shallow buried small clearance tunnel eccentric pressure is as follows:

[0080] 1. Vertical Pressure

[0081] (1) The calculation of q1 does not consider the influence of the right tunnel and is based on a single-tunnel shallow buried biased tunnel. The formula is as follows:

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] In formula (18), Q1 is the total vertical pressure of the left tunnel, in kN / m; W1 is the weight of the rock and soil overlying the left tunnel, in kN / m; q1 is the vertical pressure on the left tunnel side, in kN / m 2 ; λ1, λ2, λ3, λ4 are the lateral pressure coefficients of the left side of the left tunnel, the right side of the left tunnel, the left side of the right tunnel, and the right side of the right tunnel respectively; β1, β2, β3, β4 are the rupture angles when the maximum thrust is generated on the left side of the left tunnel, the right side of the left tunnel, the left side of the right tunnel, and the right side of the right tunnel respectively, among which β1=β3, β2=β4; α is the ground slope; θ is the friction angle on both sides of the arch rock and soil column;

[0090] (2) The calculation of q1 takes into account the influence of the right hole, and the calculation formula is as follows:

[0091] q2=q′2+ξη(q″2-q′2)

[0092]

[0093]

[0094] In formula (19), q2 is the vertical pressure on the right side of the left hole, in kN / m 2 ; q′2 is the vertical pressure on the right side of the left tunnel of the shallow-buried bias-pressure separated tunnel, in kN / m 2 , the derivation process is the same as q1; q″2 is the average vertical pressure of the surrounding rock of the shallow buried bias pressure small clear distance tunnel when the buried depth is h2 and the clear distance is 0, the unit is kN / m 2 ;

[0095] (3) The calculation of q3 takes into account the influence of the left hole, and the calculation formula is as follows:

[0096] q3=q'3+ξη(q3"-q'3)

[0097]

[0098]

[0099] In formula (XX), q3 is the vertical pressure on the left side of the right hole, in kN / m 2 ; q′3 is the vertical pressure on the left side of the right tunnel of the shallow-buried bias-pressure separated tunnel, in kN / m 2 , the derivation process is the same as q1; q″3 is the average vertical pressure of the surrounding rock of the shallow buried bias pressure and small clear distance tunnel when the buried depth is h3 and the clear distance is 0;

[0100] (4) The calculation of q4 does not consider the influence of the left tunnel and is calculated as a single-tunnel shallow buried bias pressure tunnel. The calculation formula is as follows:

[0101]

[0102]

[0103]

[0104] In formula (XXI), Q4 is the total vertical pressure of the right tunnel, in kN / m; W4 is the weight of the rock and soil overlying the right tunnel, in kN / m; q4 is the vertical pressure on the right side of the right tunnel, in kN / m 2 ;

[0105] 2. Lateral pressure

[0106]

[0107]

[0108] In formulas (XXII) and (XXIII), i = 1, 2, 3, 4; e1, e2, e3, e4 are the lateral pressures of the surrounding rock on the left side of the left tunnel, the right side of the left tunnel, the left side of the right tunnel, and the right side of the right tunnel, respectively, in kN / m 2 ; e11, e′2, e′3, e′4 are the lateral pressures of the tunnel bottom surrounding rock on the left side of the left tunnel, the right side of the left tunnel, the left side of the right tunnel, and the right side of the right tunnel, respectively, in kN / m 2 ;v i It is the coefficient of increase of lateral pressure of the interlayer rock.

[0109] In the above formula:

[0110]

[0111] The beneficial effects of the present invention are:

[0112] 1. The formula is simple and clear, easy to use and easy for users to understand.

[0113] 2. Based on the current calculation method of surrounding rock pressure of single-hole tunnel and referring to the derivation model of surrounding rock pressure calculation method of multi-arch tunnel, a calculation method of surrounding rock pressure of small-clearance tunnel is proposed; when the calculation parameters such as tunnel geometric dimensions, surrounding rock conditions, and support materials are consistent, the maximum vertical pressure of small-clearance tunnel calculated under various working conditions is between that of multi-arch tunnel and separated tunnel, that is, the proposed calculation method of surrounding rock pressure of small-clearance tunnel forms an organic whole with the calculation methods of surrounding rock pressure of single-hole tunnel and multi-arch tunnel.

[0114] 3. The shallow buried non-biased pressure condition and the shallow buried biased pressure condition are interrelated. Although the surrounding rock pressure calculation formulas for the shallow buried non-biased pressure condition and the shallow buried biased pressure condition are different, under the non-biased pressure condition (the surface slope is 0), the calculation results of the two are consistent, forming a unified and coordinated whole. This is consistent with the situation of single-hole tunnels and multi-arch tunnels, and also proves that the method of the present invention itself is unified and coordinated.

[0115] 4. Through the calculation method of surrounding rock pressure of small clear distance tunnel, under deep burial conditions, the additional vertical stress and the lateral pressure on the inner side of the lining gradually decrease with the increase of clear distance, and the basic vertical pressure and the lateral pressure on the outer side of the lining remain unchanged with the change of clear distance; under shallow burial conditions, the vertical pressure and the lateral pressure gradually decrease with the increase of clear distance until they are the same as those of the separated tunnel; that is, whether it is shallow burial conditions or deep burial conditions, when all calculation parameters except the clear distance are taken as the same, as the clear distance of the tunnel increases, the tunnel surrounding rock pressure, structural bending moment axial force, and crack width gradually decrease, the safety factor gradually increases, and the safety of the tunnel structure increases, which is in line with the industry consensus.

[0116] 5. The method for calculating surrounding rock pressure of small clearance tunnels proposed in the present invention solves the problems existing in the existing calculation methods and can better describe the surrounding rock pressure characteristics of small clearance tunnels.

[0117] 6. According to the comparative analysis between the field measured data and the calculated data, compared with the standard method, the surrounding rock pressure calculated by the method proposed in the present invention is closer to the measured value, can better reflect the actual surrounding rock pressure of the small clearance tunnel, and is consistent with the actual project. BRIEF DESCRIPTION OF THE DRAWINGS

[0118] Figure 1 This is a schematic diagram of surrounding rock pressure of a deep-buried tunnel with small clearance;

[0119] Figure 2 This is a schematic diagram of the collapse arch curve of a small clearance tunnel;

[0120] Figure 3 This is a schematic diagram of surrounding rock pressure in an ultra-shallow non-biased small clearance tunnel;

[0121] Figure 4 This is a schematic diagram of surrounding rock pressure in an ultra-shallow buried, biased, and small-clearance tunnel;

[0122] Figure 5 This is a schematic diagram of surrounding rock pressure in a shallow-buried, non-biased, small-clearance tunnel;

[0123] Figure 6 This is a schematic diagram of surrounding rock pressure in a shallow buried, biased, small clearance tunnel;

[0124] Figure 7 Schematic diagram of the mean vertical pressure of the surrounding rock of a shallow buried bias pressure tunnel with small clearance when the buried depth is h2 and the clearance is 0;

[0125] Figure 8 Schematic diagram of the mean vertical pressure of the surrounding rock of a shallow buried bias pressure tunnel with small clearance when the buried depth is h3 and the clearance is 0;

[0126] Fig. 9 This is the excavation outline and clearance diagram of a tunnel;

[0127] Fig.10 This is a comparison chart of surrounding rock pressure of a tunnel;

[0128] Fig.11 This is the inner contour of a tunnel;

[0129] Fig.12 This is a schematic diagram of surrounding rock pressure for deep-buried tunnels with small clearance using the old method;

[0130] Fig.13 This is a comparative analysis diagram of vertical pressure in deep buried tunnels with small clearance between the new and old methods. DETAILED DESCRIPTION

[0131] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0132] Example 1

[0133] Under different surrounding rock levels, highway small clearance tunnels are divided into Class A, Class B and Class C according to the clearance. The surrounding rock levels include Class III surrounding rock, Class IV surrounding rock and Class V surrounding rock. The clearance is the double-hole clearance. The classification of small clearance can be shown in Table 1.

[0134]

[0135]

[0136] In Table 1, B Z B is the net distance between the two holes; t It is the excavation width of the pilot tunnel (existing tunnel).

[0137] The bedrock of a tunnel section is mainly limestone, dolomite limestone, siltstone and shale. The rock mass is relatively intact to broken, and the grade and stability of the surrounding rock are poor to relatively poor. A typical section of the small clear distance tunnel section was selected for comparative analysis of the on-site monitoring data, the calculation data of the new method of the present invention, and the standard original calculation method.

[0138] The surrounding rock level of the selected typical section is Grade IV (silty mudstone), the left and right net distance of the typical section is 5m, the left hole is buried at a depth of 339.8mm, and the right hole is buried at a depth of 345.2. The calculated section is as follows: Fig. 9 As shown in the following table 2; the material parameters involved in the calculation refer to the "Highway Tunnel Design Code Volume 1 Civil Engineering" (JTG 3370.1), "Highway Tunnel Design Rules" (JTG / T D70), and "Detailed Survey Report of a Certain Tunnel", as shown in the following table 2.

[0139]

[0140] Table 2

[0141] Taking a typical section as an example, the surrounding rock pressure is calculated using the new method proposed in the present invention.

[0142] Step 1: Calculate the height of the collapse arch:

[0143] Theoretically, when the clear distance between the two tunnels is 0, the left and right tunnels form a collapse arch together. In this case, the surrounding rock pressure of the small clear distance tunnel is the largest. When the clear distance between the two tunnels is the boundary value of the B and C level small clear distance tunnels, the left and right tunnels form a collapse arch respectively. In this case, the surrounding rock pressure of the small clear distance tunnel is the same as that of the separated tunnel. The surrounding rock pressure of the A and B level small clear distance tunnels should be between the above two.

[0144] like Figure 2As shown in (a), case 1: when the net distance between the two holes is 0, the left and right holes form a collapse arch together, which is the most unfavorable case. The calculation formula of the collapse arch height is as follows:

[0145]

[0146] like Figure 2 As shown in (b), case 2: when the double-tunnel clearance is the boundary value of the B- and C-level small-clearance tunnels, the left and right tunnels each form a collapse arch, which is the most favorable situation. The calculation formula for the collapse arch height is as follows:

[0147]

[0148] In formulas (1) and (2), S is the surrounding rock grade, which is an integer from 1 to 6. When there is a surrounding rock BQ or [BQ] value, S can be replaced by [S]. The calculation of [S] is as follows:

[0149] or

[0150]

[0151] i1 and i2 are respectively t , 2B t To calculate the surrounding rock pressure increase and decrease rate when the width is calculated, the value is taken according to Table 3;

[0152]

[0153] Table 3

[0154] like Figure 2 (c) shows case 3: when the surrounding rock pressure of the A and B class small clearance tunnels is between case 1 and case 2.

[0155] Step 2: Calculate the basic surrounding rock vertical pressure and additional surrounding rock vertical pressure:

[0156]

[0157]

[0158] In formulas (3) and (4), ξ is the correction coefficient of the intermediate rock for the additional load. When the intermediate rock is stable and can provide effective support to the surrounding rock above it (the initial support deformation on the side of the pilot tunnel close to the intermediate rock is less than 120% of the initial support deformation on the other side), ξ = 0.2 to 0.3. Otherwise (the initial support deformation on the side of the pilot tunnel close to the intermediate rock is greater than 150% of the initial support deformation on the other side), ξ = 0.6 to 0.7. In general, ξ = 0.3 to 0.6. In this calculation, 0.3 is taken.

[0159] η is the additional load clearance correction coefficient, and the calculation formula is as follows:

[0160]

[0161] In formula (5), B′ z It is the boundary value between Class B and C small clearance tunnels (m), and Class III surrounding rock is taken as 0.6B t , the IV grade surrounding rock is taken as 0.8B t , Grade V surrounding rock is taken as 1.0B t ; B Z is the tunnel clearance (m);

[0162] q0=q+q′=234.59+34.85=269.44kN / m 2 (6)

[0163] Step 3: Calculate the equivalent load height and the depth of the boundary between deep and shallow buried tunnels with small clearance as follows:

[0164]

[0165] H p =2.5h q =26.04m (8)

[0166] In formulas (7) and (8), H p is the depth of the shallow-buried boundary of a small-clearance tunnel, in meters; for the surrounding rock of grade IV to VI, H p =2.5h q ; For the surrounding rock of grade Ⅰ~Ⅲ, take H p =2h q ;h q is the equivalent height of the load.

[0167] Step 4: Determine the tunnel depth:

[0168] In this case, H>H p , so the tunnel depth is determined to be deep.

[0169] Step 5: Use the calculation method of surrounding rock pressure of deep buried small clearance tunnel. The surrounding rock pressure diagram is as follows: Figure 1 shown.

[0170] The basic surrounding rock vertical pressure acting on the top of the lining is q=234.59kN / m2, and the additional surrounding rock vertical pressure is q'=34.85kN / m2.

[0171] The lateral pressure of surrounding rock acting on the outside of the lining is:

[0172]

[0173] The lateral pressure of surrounding rock acting on the inner side of the lining is:

[0174]

[0175] In formulas (9) and (10), λ is the lateral pressure coefficient. For single-hole tunnels with the same depth, the value is taken according to Table 4. H t is the height of a single-hole tunnel (m); in this example calculation, the lateral pressure coefficient is taken as 0.3.

[0176] Confining pressure level Ⅰ、Ⅱ Ⅲ Ⅳ Ⅴ Ⅵ Side pressure coefficient λ 0 ＜0.15 0.15～0.3 0.3～0.5 0.5～1.0

[0177] Table 4

[0178] If the burial depth H≤h q When the tunnel is judged as an ultra-shallow tunnel, it is further judged whether there is bias pressure in the tunnel; if there is no non-bias pressure, the calculation method of non-bias pressure surrounding rock pressure of ultra-shallow tunnel with small clearance is adopted. The schematic diagram of surrounding rock pressure is shown in Figure 3 As shown; if there is bias pressure, the calculation method of bias pressure surrounding rock pressure of ultra-shallow buried small clearance tunnel is adopted. The schematic diagram of surrounding rock pressure is shown in Figure 4 shown.

[0179] If h q <Burial depth H≤H p When the tunnel is , it is determined to be a shallow tunnel, and further judge whether there is bias pressure in the tunnel; if there is no non-bias pressure, the calculation method of non-bias pressure surrounding rock pressure of shallow tunnel with small clearance is adopted. The surrounding rock pressure diagram is shown in Figure 5 As shown; if there is bias pressure, the calculation method of bias pressure surrounding rock pressure of shallow buried small clear distance tunnel is adopted. The schematic diagram of surrounding rock pressure is shown in Figure 6 shown.

[0180] The calculation method of surrounding rock pressure of shallow buried small clearance tunnel involves the friction angle θ on both sides of the arch rock and soil column. If there is no measured data, the value can be taken according to Table 5:

[0181]

[0182] Table 5

[0183] In the calculation method of the eccentric pressure surrounding rock pressure of the shallow buried small clear distance tunnel, q″2″ is the average vertical pressure of the surrounding rock of the shallow buried eccentric pressure small clear distance tunnel when the buried depth is h2 and the clear distance is 0, that is, the tunnel width is 2B t The average vertical pressure of the surrounding rock of a shallow-buried single-hole tunnel with bias pressure, in kN / m 2 ,like Figure 7 As shown, the derivation process is as follows:

[0184]

[0185]

[0186]

[0187] In equations (11) to (13), Q2 is the total vertical pressure of the double holes when the burial depth is h2 and the clear distance is 0 (kN / m); W2 is the weight of the rock and soil overlying the double holes when the burial depth is h2 and the clear distance is 0 (kN / m).

[0188] q″3″ is the average vertical pressure of the surrounding rock of a shallow buried bias pressure tunnel with small clearance when the buried depth is h3 and the clearance is 0, that is, the tunnel width is 2B t The average vertical pressure of the surrounding rock of a shallow-buried single-hole tunnel with bias pressure, in kN / m 2 ,like Figure 8 As shown, the derivation process is as follows:

[0189]

[0190]

[0191]

[0192] In formulas (14) to (16), Q3 is the total vertical pressure of the double holes when the burial depth is h3 and the clear distance is 0 (kN / m); W3 is the weight of the rock and soil overlying the double holes when the burial depth is h3 and the clear distance is 0 (kN / m).

[0193] The calculated values ​​of surrounding rock pressure of the final typical section using the new method of the present invention and the standard method are shown in Table 6.

[0194]

[0195] Table 6

[0196] According to the decomposition of surrounding rock pressure, the standard value and the new method calculated value of the surrounding rock pressure at the buried point are calculated, and the standard calculated value, the new method calculated value and the field measured value are compared respectively; the tunnel surrounding rock pressure comparison chart is shown in Fig.10 As shown, 1. The surrounding rock pressure of the left tunnel: the field measured values ​​a are 21.0, 99.9, 77.0, 116.7, and 26.2; the values ​​b calculated by the new method are 136.9, 245.6, 252.0, 220.8, and 126.7; the standard calculated values ​​c are 228.8, 498.5, 439.6, 294.8, and 144.9; 2. The surrounding rock pressure of the right tunnel: the field measured values ​​d are 30.8, 125.8, 107.6, and 13 6.8, 31.6; the calculated values ​​e by the new method are 126.7, 220.8, 252.0, 245.6, 136.9; the calculated values ​​by the standard are 144.9, 294.8, 439.6, 498.5, 228.8; it can be seen that the calculated values ​​by the new method are smaller than the calculated values ​​by the standard and are closer to the field test results. At the same time, the force distribution of the test results is closer to the calculated values ​​by the new method. Therefore, the calculation method proposed in the present invention is more in line with the force mode of the actual project.

[0197] Example 2

[0198] The new method of the present invention is compared with the existing method for calculating surrounding rock pressure of small clearance tunnels.

[0199] S1. Calculation parameters

[0200] S1.1 Structural parameters

[0201] For the convenience of comparative analysis, the secondary lining of all calculation conditions is 60cm thick C30 reinforced concrete, and the reinforcement parameters are:

[0202] 22@20cm, its inner contour is as follows Fig.11 shown.

[0203] S1.2. Material parameters

[0204] The materials involved in the calculation are mainly rock, soil, and structure (concrete, steel bars). The corresponding material parameters are taken from the "Highway Tunnel Design Code, Volume 1, Civil Engineering" (JTG 3370.1) and "Highway Tunnel Design Rules" (JTG / T D70), as shown in Tables 7 to 8.

[0205] Surrounding rock level BQ value Bulk density γ(kN / m3) Elastic resistance coefficient k(kPa / m) Calculate the friction angle φc (°) Level Ⅴ surrounding rock 200 18 180×103 45

[0206] Table 7 is the geotechnical material parameter table

[0207]

[0208] Table 8 is the support material parameter table S1.3, load sharing ratio

[0209] The secondary lining load sharing ratio is 70%.

[0210] S2. Calculation conditions are shown in Table 9.

[0211]

[0212] Table 9 is the calculation condition table S3, and the calculation results are compared and analyzed as shown in Table 10.

[0213]

[0214] Table 10 shows the calculation results of deep buried working condition. Table S3.1 shows the vertical pressure comparison of deep buried working condition. Fig.13 As shown, we can know:

[0215] 1. The basic pressure values ​​of vertical pressure calculated by the new and old methods are the same.

[0216] 2. The additional pressure value q' of the vertical pressure calculated by the new method gradually decreases with the increase of the clear distance, and becomes 0 when the clear distance is ≥12m (the dividing value between the small clear distance tunnel of Class V surrounding rock Class B (medium impact) and the small clear distance tunnel of Class C (slight impact)). Its changing trend is in line with the consensus of the industry.

[0217] 3. Fig.12 As shown, the additional pressure values ​​q2 and q2' of the vertical pressure calculated by the old method first increase and then decrease with the increase of the clear distance, and become 0 when the clear distance is ≥8m. The change trend does not conform to the consensus of the industry.

[0218] The reason for this result is that the calculation formula of the additional load in the old method has problems, as shown below:

[0219]

[0220]

[0221] When q2<0, take q2=0, and when q′2<0, take q′2=0.

[0222] In formula (17), In the most unfavorable case, only the common equilibrium arch formed above the left and right caverns is considered, and the collapse arch height when the bearing effect of the rock column in the middle is not considered is calculated as follows:

[0223]

[0224] B wp is the horizontal projection length of the outer fracture surface (m), which can be calculated as follows:

[0225]

[0226] B np is the horizontal projection length of the inner edge fracture surface (m), which can be calculated as follows:

[0227]

[0228] P z is the supporting force of the middle rock column on the upper rock mass, calculated as follows;

[0229]

[0230] In formula (18), K z is the safety factor of the support capacity of the intermediate rock column, generally K z —=2;

[0231] B zp is the effective bearing width of the middle rock column (m), calculated as follows:

[0232] B zp =B z -2B np

[0233] is the converted strength of the rock mass in the middle rock column (kPa), calculated according to the following formula:

[0234]

[0235] In formula (19), P i is the active support resistance of the support structure to the rock column (kPa); is the internal friction angle of the rock mass in the middle rock column (°); It is the uniaxial compressive design strength of the rock mass in the middle rock column (kPa).

[0236] when hour, Its value increases with the increase of the clear distance; when hour, Its value remains constant as the clearance increases. The changing pattern of B np Same.

[0237] when When P z =0; when When P z Increases with the increase of clearance.

[0238] Therefore, when When q2 and q′2 are affected The influence of increases with the increase of the clear distance; when When q2 and q′2 are affected P z The impact of As the clearance increases and remains constant, P z It increases with the increase of the clear distance, so q2 and q'2 decrease with the increase of the clear distance.

[0239] S4. Combining the above

[0240] Regardless of vertical pressure, lateral pressure, structural internal force, and crack width, the calculation results of the old method first increase and then decrease with the increase of the clear distance, and the calculation results of the safety factor first decrease and then increase with the increase of the clear distance. The change trend does not conform to the industry consensus, while the change law of surrounding rock pressure, structural internal force, etc. of the new method remains consistent with the change of the clear distance, which conforms to the objective law. This proves the rationality of the new method proposed by the present invention itself.

[0241] At the same time, taking the 6m clearance as an example, the internal force value of the small clearance tunnel structure calculated by the new method is 8.1% greater than the axial force value of the separated tunnel structure, and the bending moment value is 10.1% greater than the axial force value of the separated tunnel structure; the internal force value of the small clearance tunnel structure calculated by the old method is 72.3% greater than the axial force value of the separated tunnel structure, and the bending moment value is 84.8% greater than the axial force value of the separated tunnel structure. The minimum safety factor of the small clearance tunnel structure calculated by the new method is 9.4% less than the minimum safety factor of the separated tunnel structure; the minimum safety factor of the small clearance tunnel structure calculated by the old method is 47.3% less than the minimum safety factor of the separated tunnel structure. The maximum crack width of the small clearance tunnel structure calculated by the new method is 11.3% greater than the maximum crack width of the separated tunnel structure; the maximum crack width of the small clearance tunnel structure calculated by the old method is 394.3% greater than the maximum crack width of the separated tunnel structure. This shows that the old method and the calculation method of the surrounding rock pressure of the separated tunnel in the specification are independent calculation systems, and there are obvious differences from the actual engineering.

[0242] The method for calculating surrounding rock pressure of small-clearance tunnels proposed in the present invention constitutes a unified and coordinated whole, and is the same system as the method for calculating surrounding rock pressure of single-hole tunnels and multi-arch tunnels in the current design specifications, and the calculation results are in line with the consensus of the industry.

[0243] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calculating surrounding rock pressure of a small clearance tunnel, characterized by: The implementation process of this method is as follows: (1) For an actual small clearance tunnel project, according to H p 、h q The tunnel depth is divided into deep, shallow and ultra-shallow. (2) When the burial depth H>H p When the tunnel is deeply buried, the calculation method of surrounding rock pressure of deep buried small clear distance tunnel is adopted; (3) When h q <Burial depth H≤H p When the tunnel is shallowly buried, determine whether there is bias pressure in the tunnel; If there is no bias pressure, the calculation method of non-bias pressure surrounding rock pressure of shallow buried small clear distance tunnel is adopted; if there is bias pressure, the calculation method of bias pressure surrounding rock pressure of shallow buried small clear distance tunnel is adopted; (4) When the burial depth H≤h q When the tunnel is extremely shallow, determine whether there is bias pressure; If there is no bias pressure, the calculation method of non-biased surrounding rock pressure of ultra-shallow buried small clear distance tunnel is adopted; if there is bias pressure, the calculation method of biased surrounding rock pressure of ultra-shallow buried small clear distance tunnel is adopted.

2. The method for calculating surrounding rock pressure of a small clearance tunnel according to claim 1, characterized in that: The depth of the deep and shallow burial boundary H p The judgment is as follows: H p =(2~2.5)h q (one) In formula (1), H p is the depth of the boundary between deep and shallow burial of small clearance tunnel, in meters; H is taken for the surrounding rock of grade IV to VI p =2.5h q ; For the surrounding rock of grade Ⅰ~Ⅲ, take H p =2h q ;h q is the equivalent height of the load; The h q The expression is as follows: In formula (2), q0=q+q′, where q is the basic vertical pressure of the surrounding rock; q′ is the additional vertical pressure of the surrounding rock; and γ is the weight of the surrounding rock.

3. The method for calculating surrounding rock pressure of a small clearance tunnel according to claim 1, characterized in that: When the burial depth H>H p The calculation method of surrounding rock pressure of deep buried small clearance tunnel is as follows:

1. Vertical Pressure The vertical pressure includes the basic surrounding rock vertical pressure q and the additional surrounding rock vertical pressure q′; Under different surrounding rock levels, small clearance tunnels are divided into Class A, Class B and Class C according to the clearance, the surrounding rock levels include Class III surrounding rock, Class IV surrounding rock and Class V surrounding rock, and the clearance is the double-hole clearance; Case 1: When the net distance between the two holes is 0, the left and right holes together form a collapse arch. The calculation formula for the collapse arch height is as follows: Case 2: When the double-tunnel clearance is the boundary value of B- and C-level small-clearance tunnels, the left and right tunnels each form a collapse arch. The calculation formula for the collapse arch height is as follows: Case 3: When the surrounding rock pressure of the A and B class small clearance tunnels is between Case 1 and Case 2, its size is related to the clearance; The calculation formulas for the basic surrounding rock vertical pressure q and the additional surrounding rock vertical pressure q′ of the deep-buried small clearance tunnel are as follows: In formulas (III) to (VI), B t is the width of a single tunnel; 2B t is the height of the collapsed arch when calculating the width; B t is the height of the collapsed arch when calculating the width; S is the surrounding rock grade, which is an integer from 1 to 6; i1 and i2 are respectively t , 2B t is the rate of increase or decrease of surrounding rock pressure when calculating width; ξ is the correction factor of interlayer rock in additional load; η is the correction factor of clear distance of additional load; 2. Lateral pressure The lateral pressure of surrounding rock acting on the outside of the lining is: The lateral pressure of surrounding rock acting on the inner side of the lining is: In formulas (VII) and (VIII), λ is the lateral pressure coefficient, H t is the height of a single-hole tunnel.

4. The method for calculating surrounding rock pressure of a small clearance tunnel according to claim 1, characterized in that: When the burial depth H≤h q When the tunnel is divided into non-biased tunnel and biased tunnel, the calculation formula of the surrounding rock pressure of the ultra-shallow small clearance tunnel without biased pressure is as follows:

1. Vertical Pressure q=γH (IX) In formula (9), q is the vertical uniform pressure, the unit is kN / m 2 ; γ is the weight of surrounding rock, unit is kN / m 3 ; H is the tunnel depth, which refers to the distance from the top of the tunnel to the ground, in meters; 2. Lateral pressure In formula (10), e1 and e′1 are the lateral pressures at the top and bottom of the tunnel, respectively, in kN / m 2 , H t is the tunnel height, in m; λ is the lateral pressure coefficient; Calculate the friction angle for the surrounding rock.

5. A method for calculating surrounding rock pressure of a small clearance tunnel as claimed in claim 4, characterized in that: The calculation method of surrounding rock pressure of the ultra-shallow buried small clearance tunnel bias pressure is as follows:

1. Vertical Pressure q i =γh i (eleven) In formula (XI), i = 1, 2, 3 or 4; q1, q2, q3, q4 are the vertical pressures on the left side of the left hole, the right side of the left hole, the left side of the right hole, and the right side of the right hole, respectively, in kN / m 2 ; 2. Lateral pressure In formula (XII), i = 1, 2, 3 or 4; e1, e2, e3, e4 are the lateral pressures of the surrounding rock of the left tunnel, the left tunnel, the right tunnel, the left tunnel, and the right tunnel, in kN / m 2 .

6. The method for calculating surrounding rock pressure of a small clearance tunnel according to claim 1, characterized in that: When h q <Burial depth H≤H p When the tunnel is divided into non-biased tunnel and biased tunnel, the surrounding rock pressure calculation method of the shallow buried small clearance tunnel without biased pressure is as follows:

1. Vertical Pressure Includes outer vertical pressure and inner vertical pressure; (1) The calculation formula of the outer vertical pressure is as follows: (2) The formula for calculating the inner vertical pressure is as follows: q2=q1+ξη(q-q1) In formulas (13) and (14), q1 is the vertical pressure of the surrounding rock outside the shallow-buried small-clearance tunnel, in kN / m 2 ; q2 is the vertical pressure of the surrounding rock inside the shallow tunnel with small clearance, in kN / m 2 ; γ is the weight of surrounding rock, unit is kN / m 3 ; H is the tunnel depth, which refers to the distance from the tunnel top to the ground; λ is the lateral pressure coefficient; θ is the friction angle on both sides of the arch rock and soil column; B t is the width of the single-hole tunnel; β is the rupture angle when the maximum thrust is generated on the left side of the left hole, the right side of the left hole, the left side of the right hole, and the right side of the right hole; is the friction angle calculated for the surrounding rock; ξ is the correction coefficient for the interlayer rock in the additional load; η is the correction coefficient for the additional load clearance; q is the vertical pressure of the surrounding rock of the shallow buried small clearance tunnel when the clearance is 0; 2. Lateral pressure In formulas (15) and (16), e1 and e′1 are the lateral pressures of the surrounding rock at the top and bottom of the tunnel on the left side of the left tunnel (right side of the right tunnel); e2 and e′2 are the lateral pressures of the surrounding rock at the top and bottom of the tunnel on the right side of the left tunnel (left side of the right tunnel); H t is the tunnel height; ν is the lateral pressure increase coefficient of the interlayer rock; In the above formula; 7. A method for calculating surrounding rock pressure of a small clearance tunnel as claimed in claim 6, characterized in that: The calculation method of surrounding rock pressure of the shallow buried small clearance tunnel eccentric pressure is as follows:

1. Vertical Pressure (1) The calculation of q1 does not consider the influence of the right tunnel and is based on a single-tunnel shallow buried biased tunnel. The formula is as follows: In formula (18), Q1 is the total vertical pressure of the left tunnel, in kN / m; W1 is the weight of the rock and soil overlying the left tunnel, in kN / m; q1 is the vertical pressure on the left tunnel side, in kN / m 2 ; λ1, λ2, λ3, λ4 are the lateral pressure coefficients of the left side of the left tunnel, the right side of the left tunnel, the left side of the right tunnel, and the right side of the right tunnel respectively; β1, β2, β3, β4 are the rupture angles when the maximum thrust is generated on the left side of the left tunnel, the right side of the left tunnel, the left side of the right tunnel, and the right side of the right tunnel respectively, where β1=β3, β2=β4; α is the ground slope; θ is the friction angle on both sides of the arch rock and soil column; (2) The calculation of q1 takes into account the influence of the right hole, and the calculation formula is as follows: q2=q'2+ξη(q'2-q'2) In formula (19), q2 is the vertical pressure on the right side of the left hole, in kN / m 2 ; q′2 is the vertical pressure on the right side of the left tunnel of the shallow-buried bias-pressure separated tunnel, in kN / m 2 , the derivation process is the same as q1; q″2 is the average vertical pressure of the surrounding rock of the shallow buried bias pressure small clear distance tunnel when the buried depth is h2 and the clear distance is 0, the unit is kN / m 2 ; (3) The calculation of q3 takes into account the influence of the left hole, and the calculation formula is as follows: q3=q'3+ξη(q'3-q'3) In formula (XX), q3 is the vertical pressure on the left side of the right hole, in kN / m 2 ; q′3 is the vertical pressure on the left side of the right tunnel of the shallow-buried bias-pressure separated tunnel, in kN / m 2 , the derivation process is the same as q1; q″3 is the average vertical pressure of the surrounding rock of the shallow buried bias pressure and small clear distance tunnel when the buried depth is h3 and the clear distance is 0; (4) The calculation of q4 does not consider the influence of the left tunnel and is calculated as a single-tunnel shallow buried bias pressure tunnel. The calculation formula is as follows: In formula (XXI), Q4 is the total vertical pressure of the right tunnel, in kN / m; W4 is the weight of the rock and soil overlying the right tunnel, in kN / m; q4 is the vertical pressure on the right side of the right tunnel, in kN / m 2 ; 2. Lateral pressure In formulas (XXII) and (XXIII), i = 1, 2, 3, 4; e1, e2, e3, e4 are the lateral pressures of the surrounding rock on the left side of the left tunnel, the right side of the left tunnel, the left side of the right tunnel, and the right side of the right tunnel, respectively, in kN / m 2 ; e′1, e′2, e′3, e′4 are the lateral pressures of the tunnel bottom surrounding rock on the left side of the left tunnel, the right side of the left tunnel, the left side of the right tunnel, and the right side of the right tunnel, respectively, in kN / m 2 ; ν i is the coefficient of lateral pressure increase of the interlayer rock; In the above formula:

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