Safety depth design method for artificial underground gas storage cavern

Abstract

The application discloses a safe burying depth design method of an artificial underground gas storage hole. The method comprises the following steps: taking the top position of the gas storage hole as a critical burying depth yield point according to the gas storage pressure during the operation period of the gas storage hole, calculating the shortest distance from the critical burying depth yield point to the ground surface, namely the first critical burying depth of the gas storage hole; assuming that the gas storage hole buried in the hard rock underground is cut along the two sides of the diameter under the action of internal pressure, and an upwardly-inclined cutting failure surface is formed, and according to the static balance condition of the tensile stress of the cutting failure surface and the dead weight of the hard rock cone, the second critical burying depth of the gas storage hole is obtained; a tunnel model is established, and the plastic zone of the hard rock around the tunnel model is analyzed by using a numerical simulation method; if the top of the plastic zone of the hard rock around the tunnel model extends to the ground surface, the burying depth is selected as the third critical burying depth of the gas storage hole; and the maximum critical burying depth is selected as the safe burying depth design value. The application reduces the construction excavation amount of the gas storage hole and reduces the construction difficulty.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of artificial hard rock underground gas storage cavern, in particular to a safe burial depth design method of artificial underground gas storage cavern. BACKGROUND

[0002] Under the background of building new energy system, new energy storage is emerging, and the installed capacity is also increasing year by year. Northwest China is rich in photovoltaic and wind energy resources, but water resources are scarce, and there are few pumped storage power stations available for planning. The hard rock strata such as granite, basalt, limestone and sandstone widely distributed in this area have good rock mass quality, high strength and large deformation modulus, which provides good engineering geological conditions for large-scale construction of compressed air energy storage underground gas storage cavern.

[0003] Compressed air energy storage is a technology that uses compressed air as a medium to store excess electricity. During the off-peak period, it uses excess electricity from wind power and the power grid to drive the air compressor to convert electrical energy into internal energy of compressed air and store it in the underground cavern. During the peak period, the high-pressure air is released to convert the potential energy of compressed air into mechanical work of the expander to drive the generator to generate electricity. The artificially excavated underground sealed gas storage cavern has the advantages of flexible site selection, low cost, safety and reliability.

[0004] At present, there are still few successful cases of compressed air energy storage underground sealed caverns in the world. Underground sealed caverns must meet some extreme conditions, such as high pressure resistance (10 MPa or even higher), good air tightness, stable structure, and ability to withstand cyclic pressure and temperature, etc. The underground sealed engineering structure that has been built can withstand smaller internal pressure, and there are still few cases of 10 MPa or even higher cyclic variable high pressure conditions for compressed air storage caverns.

[0005] Since the internal pressure of compressed air energy storage underground gas storage cavern is very high (usually 18-20 MPa), if the Norwegian criterion (i.e., the weight of the overlying rock mass is not less than the internal pressure of the cavern) is used to excavate and construct the gas storage cavern, the burial depth of the underground gas storage cavern will be very large. If the design burial depth of the gas storage cavern is too large, it will not only be difficult to take advantage of the underground gas storage cavern, but also increase the construction difficulty and construction cost. SUMMARY

[0006] In view of the shortcomings of the prior art, the present application provides a safe burial depth design method for artificial underground gas storage cavern. Compared with the Norwegian criterion method which only considers the self-weight of the overlying rock mass, the burial depth of the gas storage cavern calculated is generally smaller, the rock mass bearing capacity is fully utilized under the condition of safety, the excavation amount of the cavern is reduced, the construction difficulty is reduced, and the investment is effectively reduced.

[0007] To achieve the above purpose, the safe burial depth design method for artificial underground gas storage cavern designed by the present application has the following steps:

[0008] S1) Assuming that the maximum principal stress of the gas storage hole buried in the hard rock under the action of internal pressure is vertical, according to the gas storage pressure during the operation period of the gas storage hole, the top position of the gas storage hole is taken as the critical buried depth yield point, the strength relationship of the critical buried depth yield point hard rock satisfies the limit equilibrium state of Mohr-Columb criterion, that is

[0009]

[0010]

[0011] The first critical buried depth of the gas storage hole is obtained from the above two formulas

[0012]

[0013] In the formula,

[0014] h1 represents the shortest distance from the top of the gas storage hole to the ground surface, that is, the first critical buried depth of the gas storage hole,

[0015] φ represents the internal friction angle of the hard rock,

[0016] c represents the cohesion of the hard rock,

[0017] R represents the Mohr circle radius,

[0018] λ represents the gas side pressure coefficient inside the gas storage hole,

[0019] γ represents the unit weight of the hard rock,

[0020] P represents the gas pressure inside the gas storage hole;

[0021] S2) Assuming that the gas storage hole buried in the hard rock under the action of internal pressure is punched and cut along the punching and cutting angle on both sides of the diameter towards the ground surface, forming a hard rock cone between the punching and cutting failure surface on both sides of the gas storage hole and the ground surface and the top of the gas storage hole; Assuming that the tensile stress on the punching and cutting failure surface is fully developed under the limit equilibrium state, only the tensile action of the punching and cutting failure surface is considered, the internal pressure of the gas storage hole, the tensile stress of the punching and cutting failure surface and the self weight of the hard rock cone satisfy the static equilibrium condition, that is

[0022]

[0023] The second critical buried depth of the gas storage hole is obtained from the above formula

[0024]

[0025] In the formula,

[0026] h2 represents the second critical buried depth of the gas storage hole,

[0027] P represents the gas pressure inside the gas storage hole,

[0028] σ t represents the equivalent tensile strength on the punching failure surface,

[0029] c represents the cohesion of hard rock,

[0030] represents the internal friction angle of hard rock,

[0031] θ represents the punching angle,

[0032] d represents the diameter of the gas storage hole,

[0033] γ represents the specific gravity of hard rock;

[0034] S3) a gas storage hole model is established, which adopts a two-dimensional axisymmetric calculation model of a radial section of the gas storage hole, the boundary conditions of the radial section of the gas storage hole are set as follows: the side boundary is fixed as the y axis, the bottom boundary is fixed as the x axis, and the upper surface of the gas storage hole is a free ground surface; a numerical simulation method is used to analyze the plastic zone of the hard rock around the gas storage hole model, a gravity load is applied to the gas storage hole model, and an internal pressure is applied to the inner wall of the gas storage hole to simulate the gas storage process, the extension range of the plastic zone of the hard rock around the gas storage hole at different burial depths is calculated, and if the top of the plastic zone of the hard rock around the gas storage hole extends to the ground surface, the burial depth is selected as the third critical burial depth h3 of the gas storage hole;

[0035] S4) the first critical burial depth, the second critical burial depth and the third critical burial depth obtained in steps S1) to S3) are compared and analyzed, the maximum critical burial depth is selected as the safe burial depth design value of the artificial underground gas storage hole, and the safe burial depth design value h = MAX (h1, h2, h3).

[0036] Further, S5) is further included, according to the safe burial depth design value of the gas storage hole, the buoyancy, shear resistance and gravity of the overlying rock mass of the gas storage hole, and the uplift force caused by the buoyancy and internal pressure of the gas storage hole are calculated to obtain the stability coefficient of the gas storage hole, and the stability of the overlying rock mass is checked through the stability coefficient of the gas storage hole.

[0037] Further, in S5), if the shear resistance of the overlying rock mass is calculated by using the shear friction coefficient and the shear cohesion, and the stability coefficient of the gas storage hole is not less than 3.0, the overlying rock mass is stable, and the burial depth of the gas storage hole is safe; if the shear resistance of the overlying rock mass is calculated by using the shear friction coefficient and the shear cohesion, and the stability coefficient of the gas storage hole is not less than 1.1, the overlying rock mass is stable, and the burial depth of the gas storage hole is safe.

[0038] Further, in S5), the calculation formula of the buoyancy of the overlying rock mass is F br = A c · γ w·z w

[0039] wherein,

[0040] F br represents the overburden rock floating force,

[0041] A c represents the horizontal projection area of the gas storage hole,

[0042] γ w represents the water layer layer unit weight,

[0043] z w represents the upper water level thickness of the gas storage hole;

[0044] The calculation formula of the overburden rock shearing force is

[0045] τ r = L c ·∑z j ·c′ j + L c ·∑σ hj ·f′ j ·z j

[0046] wherein,

[0047] τ r represents the overburden rock shearing force,

[0048] L c represents the horizontal projection perimeter of the gas storage hole,

[0049] z j represents the thickness of the jth layer of rock,

[0050] c′ j represents the shearing resistance cohesion or shearing cohesion of the jth layer of rock,

[0051] σ hj represents the horizontal stress of the jth layer of rock,

[0052] f′ j represents the shearing resistance friction coefficient or shearing friction coefficient of the jth layer of rock;

[0053] The calculation formula of the overburden rock gravity is

[0054] W r = A c ·∑γ j ·z j

[0055] wherein,

[0056] W r represents the overburden rock gravity,

[0057] A c denotes the horizontal projection area of the gas storage cavity,

[0058] γ j denotes the layer unit weight of the jth stratum,

[0059] z j denotes the thickness of the jth stratum;

[0060] The calculation formula of the buoyancy of the gas storage cavity is

[0061] F bc = V c · γ w

[0062] In the formula,

[0063] F bc denotes the buoyancy of the gas storage cavity,

[0064] V c denotes the volume of the gas storage cavity,

[0065] γ w denotes the layer unit weight of the water layer;

[0066] The calculation formula of the uplift force caused by the internal pressure of the gas storage cavity is

[0067] F l = P c · A

[0068] In the formula,

[0069] F l denotes the uplift force caused by the internal pressure of the gas storage cavity,

[0070] P denotes the gas pressure inside the gas storage cavity,

[0071] A c denotes the horizontal projection area of the gas storage cavity;

[0072] The calculation formula of the stability coefficient of the gas storage cavity is

[0073]

[0074] In the formula,

[0075] K denotes the stability coefficient of the gas storage cavity,

[0076] W r denotes the gravity of the overlying rock mass,

[0077] τ r denotes the shear resistance of the overlying rock mass,

[0078] F lrepresents the uplift force caused by the pressure in the gas storage cavity,

[0079] F bc represents the uplift force caused by the pressure in the gas storage cavity,

[0080] F br represents the uplift force caused by the pressure in the gas storage cavity.

[0081] Further, in S5), the horizontal stress σ hj of the jth stratum is calculated by the formula

[0082]

[0083] wherein,

[0084] σ hj represents the horizontal stress of the jth stratum,

[0085] k sj represents the lateral pressure coefficient of the jth stratum,

[0086] γ j-1 represents the unit weight of the j-1th stratum,

[0087] z j-1 represents the thickness of the j-1th stratum,

[0088] γ j represents the unit weight of the jth stratum,

[0089] z j represents the thickness of the jth stratum.

[0090] Further, in S2), the formula for calculating the punch angle θ is

[0091]

[0092] wherein,

[0093] θ represents the punch angle,

[0094] represents the internal friction angle of the hard rock.

[0095] The present application has the advantages of:

[0096] 1. This invention determines the critical burial depth yield point based on the gas storage pressure during the operation of the gas storage tunnel and the Mohr-Columb limit equilibrium state analysis. The distance from the ground surface to the critical burial depth yield point is taken as the first critical burial depth of the gas storage tunnel. Based on the burial depth calculation under the punching shear state of the artificial cavern foundation, the second critical burial depth of the gas storage tunnel is obtained. Numerical simulation is used to analyze the plastic zone of the surrounding rock under the internal pressure of the gas storage tunnel. Based on the burial depth calculation of the expansion and penetration of the plastic zone, the third critical burial depth of the gas storage tunnel is obtained. Finally, the maximum value among the three critical burial depths is selected as the design value of the safe burial depth of the gas storage tunnel.

[0097] 2. The present invention verifies the calculated safe burial depth design value. The specific verification method is as follows: calculate the buoyancy, shear force, and gravity of the overlying rock mass of the gas storage tunnel, as well as the uplift force caused by the buoyancy of the gas storage tunnel and the internal pressure of the gas storage tunnel, to obtain the stability coefficient of the gas storage tunnel. The stability coefficient of the gas storage tunnel is calculated using shear strength and shear resistance respectively. Based on different safety factor standards, the safety of the burial depth of the gas storage tunnel is determined.

[0098] This invention provides a method for designing the safe burial depth of artificial underground gas storage tunnels. It employs a multi-index comprehensive evaluation of the burial depth, considering the mechanical properties of hard rock mass, such as shear resistance, tensile strength, and shear fracture resistance, and introducing the strength index of hard rock. Compared with the Norwegian criterion method, which only considers the self-weight of the overlying rock mass, the calculated design value of the burial depth of the gas storage tunnel is generally smaller. Under the premise of ensuring safety, it makes full use of the bearing capacity of the rock mass, reduces the amount of excavation for gas storage tunnel construction, reduces construction difficulty, and effectively reduces investment. Attached Figure Description

[0099] Figure 1 This invention describes the stress state of a gas storage cavity in hard rock under internal pressure.

[0100] Figure 2 for Figure 1 Stress state analysis diagram of hard rock at critical burial depth yield point under Mohr-Columb limit equilibrium state;

[0101] Figure 3 This is a critical state diagram based on the punching shear resistance of the artificial cavern foundation in this invention;

[0102] Figure 4 This is a finite element analysis diagram based on the plastic zone extension and penetration of the present invention;

[0103] Figure 5 The figure shown is a finite element analysis diagram of the plastic zone expansion and penetration of the present invention for gas storage tunnels at different burial depths in the embodiment. Detailed Implementation

[0104] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0105] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0106] The present invention provides a method for designing the safe burial depth of artificial underground gas storage tunnels, comprising the following steps:

[0107] S1) Assuming the maximum principal stress of a gas storage tunnel buried in underground hard rock under internal pressure is in the vertical direction, and based on the gas storage pressure during the tunnel's operation, the apex of the tunnel is taken as the critical burial depth yield point. Then, the strength relationship of the hard rock at the critical burial depth yield point satisfies the limit equilibrium state of the Mohr-Columb criterion, i.e.

[0108]

[0109]

[0110] From the above two equations, the first critical burial depth of the gas storage tunnel is obtained as follows:

[0111]

[0112] In the formula,

[0113] h1 represents the shortest distance from the apex of the gas storage tunnel to the Earth's surface, i.e., the first critical burial depth of the gas storage tunnel.

[0114] Indicates the internal friction angle of hard rock.

[0115] c represents hard rock cohesion.

[0116] R represents the radius of the Mohr circle.

[0117] λ represents the gas lateral pressure coefficient inside the gas storage tunnel.

[0118] γ represents the unit weight of hard rock.

[0119] p represents the gas pressure inside the gas storage tunnel.

[0120] like Figure 1 The figure shows the stress state of the gas storage cavity in hard rock under internal pressure according to the present invention. Figure 1 In the gas storage tunnel, the maximum principal stress under internal pressure p is in the vertical direction. The apex of the gas storage tunnel is taken as the critical burial depth yield point. The distance from the critical burial depth yield point to the ground is z, where z ≥ h1. Figure 1The stress state analysis of the hard rock at the critical buried depth yield point in the Mohr-Columb limit equilibrium state is shown in the following figure. Figure 2 Figure 2 In the figure, the ordinate τ is the shear stress of the gas storage hole under the action of the internal pressure, the abscissa σ is the principal stress of the gas storage hole under the action of the internal pressure, the p-γz point on the σ axis is the maximum principal stress point of the hard rock at the critical buried depth yield point, and the λγz point on the σ axis is the minimum principal stress point of the hard rock at the critical buried depth yield point. As shown in Table 1, the rock mass mechanical parameter values in the embodiment are taken.

[0121] Table 1: Rock mass mechanical parameter values

[0122]

[0123] In the embodiment, the calculation parameters and c are taken according to the intermediate values of the geological recommended values, considering the material item coefficient, and are reduced by 1.2. The internal pressure p is taken as the maximum operating pressure 18 MPa of the gas storage, the lateral pressure coefficient is 1.8, and based on the relationship formula under the Mohr-Columb limit equilibrium state, the first critical buried depth h1 of the gas storage hole is calculated as 73.1 m.

[0124] S2) Assuming that the gas storage hole buried in the hard rock in the ground is under the action of the internal pressure and the punching shear angle on both sides of the diameter is punched towards the ground, an upwardly inclined punching shear failure surface is formed, and then the hard rock cone is formed between the punching shear failure surface on both sides of the gas storage hole and the ground and the top of the gas storage hole; assuming that the tensile stress on the punching shear failure surface is fully developed under the limit equilibrium state, only the tensile action of the punching shear failure surface is considered, and then the internal pressure of the gas storage hole, the tensile stress of the punching shear failure surface and the self weight of the hard rock cone satisfy the static equilibrium condition, that is,

[0125]

[0126] The second critical buried depth of the gas storage hole is obtained from the above formula as

[0127]

[0128] In the formula,

[0129] h2 represents the second critical buried depth of the gas storage hole,

[0130] P represents the gas pressure inside the gas storage hole,

[0131] σ t represents the equivalent tensile strength on the punching shear failure surface, which is calculated according to the Mohr-Columb strength criterion c represents the cohesion of the hard rock, represents the internal friction angle of the hard rock,

[0132] θ represents the punching angle,

[0133] ​d represents the diameter of the gas storage cavity,

[0134] γ represents the specific gravity of hard rock.

[0135] Specifically, in S2), the calculation formula of the punch angle θ is

[0136]

[0137] In the formula,

[0138] θ represents the punch angle,

[0139] φ represents the internal friction angle of hard rock.

[0140] Figure 3 The critical state diagram is based on the artificial cavity foundation under the state of punch shear. In this embodiment, according to the rock mass mechanical parameters in Table 1 above, considering the material item coefficient 1.2, the second critical buried depth formula of the gas storage cavity is brought in to obtain the second critical buried depth h2=110m of the gas storage cavity.

[0141] S3) Establish a gas storage cavity model, which adopts a two-dimensional axisymmetric calculation model of the radial section of the gas storage cavity, and the boundary conditions of the radial section of the gas storage cavity are set as follows: the fixed side boundary is the y-axis, the fixed bottom boundary is the x-axis, and the upper surface of the gas storage cavity is the free ground surface; the plastic zone of the hard rock around the gas storage cavity model is analyzed by numerical simulation means, the gravity load is applied to the gas storage cavity model, and the internal pressure is applied to the inner wall of the gas storage cavity to simulate the gas storage process, and the extension range of the plastic zone of the hard rock around the gas storage cavity under different buried depths is calculated. If the top of the plastic zone of the hard rock around the gas storage cavity extends to the ground surface, the buried depth is selected as the third critical buried depth h3 of the gas storage cavity.

[0142] A two-dimensional calculation model is established by selecting the cross section of the gas storage cavity, as shown in Figure 4 In this embodiment, the excavation diameter of the gas storage cavity is 12.0m, according to the kinematic hypothesis in rock mechanics, considering the Poisson effect of rock, the lateral pressure coefficient is taken as λ=μ / (1-μ). In terms of load, the gravity load is first applied to the calculation model, and then excavation is considered. The actual operation of the gas storage cavity is considered, and the internal pressure of 18MPa is applied to the inner wall of the gas storage cavity to simulate the gas storage process. Based on the above numerical calculation model, the rock mechanics parameters in Table 1 above are used to calculate the plastic zone extension law of the gas storage cavity under different buried depths, as shown in Figure 5 From Figure 5 It can be seen from the numerical calculation results that according to the plastic zone extension evaluation, the buried depth is selected as the third critical buried depth h3=88m of the gas storage cavity.

[0143] S4) comparing and analyzing the first critical buried depth, the second critical buried depth and the third critical buried depth obtained in steps S1) to S3), and selecting the maximum critical buried depth as the safety buried depth design value of the artificial underground gas storage cavern, the safety buried depth design value h = MAX (h1, h2, h3).

[0144] In the embodiment, the first critical buried depth of the gas storage cavern h1 = 73.1 m, the second critical buried depth of the gas storage cavern h2 = 110 m, and the third critical buried depth of the gas storage cavern h3 = 88 m, so the safety buried depth design value of the gas storage cavern h = MAX (h1, h2, h3) = 110 m.

[0145] According to the Norwegian criterion, the weight of the overlying rock mass is not less than the internal pressure of the gas storage cavern, and according to P = γh4, the overlying rock mass buried depth h4 of the gas storage cavern chamber is calculated to be 671.64 m, and MAX (h1, h2, h3) << h4.

[0146] The application also includes S5), calculating the overlying rock mass buoyancy, shear resistance, gravity of the gas storage cavern, and the lifting force caused by the buoyancy of the gas storage cavern and the internal pressure of the gas storage cavern according to the safety buried depth design value of the gas storage cavern, obtaining the stability coefficient of the gas storage cavern, and checking the stability of the overlying rock mass through the stability coefficient of the gas storage cavern.

[0147] Specifically, in S5), if the shear resistance of the overlying rock mass is calculated by using the shear friction coefficient and the shear cohesive force, and the stability coefficient of the gas storage cavern is not less than 3.0, the overlying rock mass is stable, and the buried depth of the gas storage cavern is safe; if the shear resistance of the overlying rock mass is calculated by using the shear friction coefficient and the shear cohesive force, and the stability coefficient of the gas storage cavern is not less than 1.1, the overlying rock mass is stable, and the buried depth of the gas storage cavern is safe.

[0148] Specifically, considering the adverse effects of the gas storage cavern on the rock mass fissure under the action of high and low pressure cycles, and at the same time to avoid the uncertainty of the fracture surface angle, the result of the vertical shear failure model will be safer.

[0149] The calculation formula of the overlying rock mass buoyancy is

[0150] F br = A c · γ w · z w

[0151] In the formula,

[0152] F br represents the overlying rock mass buoyancy,

[0153] A c represents the horizontal projection area of the gas storage cavern,

[0154] γ w represents the water layer unit weight,

[0155] z w represents the thickness of the upper water level of the gas storage hole;

[0156] The calculation formula of the shear resistance of the overburden is

[0157] τ r = L c ·∑z j ·c′ j + L c ·∑σ hj ·f′ j ·z j

[0158] In the formula,

[0159] τ r represents the shear resistance of the overburden,

[0160] L c represents the horizontal projection perimeter of the gas storage hole,

[0161] z j represents the thickness of the jth stratum,

[0162] c′ j represents the shear resistance or shear cohesion of the jth stratum,

[0163] σ hj represents the horizontal stress of the jth stratum,

[0164] f′ j represents the shear resistance or shear friction coefficient of the jth stratum;

[0165] The calculation formula of the gravity of the overburden is

[0166] W r = A c ·∑γ j ·z j

[0167] In the formula,

[0168] W r represents the gravity of the overburden,

[0169] A c represents the horizontal projection area of the gas storage hole,

[0170] γ j represents the layer unit weight of the jth stratum,

[0171] z j represents the thickness of the jth stratum;

[0172] The calculation formula of the buoyancy of the gas storage hole is

[0173] F bc = V c · γ w

[0174] wherein,

[0175] F bc represents the buoyancy of the gas storage cavity,

[0176] V c represents the volume of the gas storage cavity,

[0177] γ w represents the unit weight of the water layer;

[0178] The calculation formula of the uplift force caused by the internal pressure of the gas storage cavity is

[0179] F l = P·A c

[0180] wherein,

[0181] F l represents the uplift force caused by the internal pressure of the gas storage cavity,

[0182] P represents the gas pressure inside the gas storage cavity,

[0183] A c represents the horizontal projection area of the gas storage cavity;

[0184] The calculation formula of the stability coefficient of the gas storage cavity is

[0185]

[0186] wherein,

[0187] K represents the stability coefficient of the gas storage cavity,

[0188] W r represents the gravity of the overlying rock mass,

[0189] τ r represents the shear resistance of the overlying rock mass,

[0190] F l represents the uplift force caused by the internal pressure of the gas storage cavity,

[0191] F bc represents the buoyancy of the gas storage cavity,

[0192] F br represents the buoyancy of the overlying rock mass.

[0193] Specifically, in S5), the calculation formula of the horizontal stress σ hj of the jth layer of rock is

[0194]

[0195] In the formula,

[0196] σ hj denotes the horizontal stress of the jth layer of rock stratum,

[0197] k sj denotes the lateral pressure coefficient of the jth layer of rock stratum

[0198] γ j-1 denotes the layer unit weight of the j-1th layer of rock stratum,

[0199] z j-1 denotes the thickness of the j-1th layer of rock stratum;

[0200] γ j denotes the layer unit weight of the jth layer of rock stratum,

[0201] z j denotes the thickness of the jth layer of rock stratum.

[0202] In the embodiment, the stability coefficient formula of the gas storage hole is calculated according to the safety buried depth design value 110 m of the gas storage hole, the overburden stability is checked, and the geotechnical mechanics parameters are taken from the values in Table 1. The gas storage pressure is taken as 18 MPa, the shear resistance is calculated by using the shear friction coefficient and the shear fracture cohesion, the obtained stability coefficient of the gas storage hole is 3.3, and the shear resistance is calculated by using the shear friction coefficient and the shear fracture cohesion, the obtained stability coefficient of the gas storage hole is 1.4. It can be seen that when the depth of the hole reaches 110 m, the calculation result can meet the requirement of the stability coefficient.

[0203] The safety buried depth design method of the artificial underground gas storage hole provided by the application comprehensively judges the buried depth of the gas storage hole by using multiple indexes, considers the mechanical properties such as shear resistance, tensile resistance and shear fracture resistance of the hard rock mass, introduces the strength index of the hard rock, and compared with the Norwegian criterion method which only considers the self weight of the overburden rock mass, the calculated buried depth design value of the gas storage hole is generally smaller, the bearing capacity of the rock mass is fully utilized under the condition of ensuring safety, the construction excavation amount of the gas storage hole is reduced, the construction difficulty is reduced, and the investment is effectively reduced.

[0204] The above embodiment is a preferred embodiment of the application, but the embodiment of the application is not limited by the above embodiment, and any change, modification, replacement, combination and simplification made without departing from the spirit and principle of the application should be equivalent replacement, and all should be included in the protection scope of the application.

Claims

1. A method for designing the safe burial depth of an artificial underground gas storage tunnel, characterized in that, Includes the following steps: S1) Assuming the maximum principal stress of a gas storage tunnel buried in underground hard rock under internal pressure is in the vertical direction, and based on the gas storage pressure during the tunnel's operation, the apex of the tunnel is taken as the critical burial depth yield point. Then, the strength relationship of the hard rock at the critical burial depth yield point satisfies the limit equilibrium state of the Mohr-Columb criterion, i.e. From the above two equations, the first critical burial depth of the gas storage tunnel is obtained as follows: In the formula, h1 represents the shortest distance from the apex of the gas storage tunnel to the Earth's surface, i.e., the first critical burial depth of the gas storage tunnel. Indicates the internal friction angle of hard rock. c represents hard rock cohesion. R represents the radius of the Mohr circle. λ represents the gas lateral pressure coefficient inside the gas storage tunnel. γ represents the unit weight of hard rock. P represents the gas pressure inside the gas storage tunnel; S2) Assuming a gas storage tunnel buried in underground hard rock undergoes internal pressure to punch towards the ground along the punching angles on both sides of its diameter, forming an upwardly inclined punching failure surface, then a hard rock cone is formed between the punching failure surfaces on both sides of the gas storage tunnel, the ground, and the top of the gas storage tunnel. Assuming that under the limit equilibrium state, the tensile stress on the punching failure surface is fully utilized, and considering only the tensile effect of the punching failure surface, then the tensile stress of the punching failure surface and the self-weight of the hard rock cone satisfy the static equilibrium condition, i.e. From the above formula, the second critical burial depth of the gas storage tunnel is obtained as follows: In the formula, h2 represents the second critical burial depth of the gas storage tunnel. P represents the gas pressure inside the gas storage tunnel. σ t This represents the equivalent tensile strength on the punching failure surface. c represents hard rock cohesion. Indicates the internal friction angle of hard rock. θ represents the punching angle. d represents the diameter of the gas storage tunnel. γ represents the unit weight of hard rock; S3) Establish a tunnel model. The tunnel model adopts a two-dimensional axisymmetric calculation model of the radial section of the gas storage tunnel. The boundary conditions of the radial section of the gas storage tunnel are set as follows: the side boundary is fixed as the y-axis, the bottom boundary is fixed as the x-axis, and the upper surface of the gas storage tunnel is a free surface. The plastic zone of the hard rock around the tunnel model is analyzed by numerical simulation. Gravity load is applied to the tunnel model, and internal pressure is applied to the inner wall of the gas storage tunnel to simulate the compressed gas storage process. The extension range of the plastic zone of the hard rock around the gas storage tunnel at different burial depths is calculated. If the top of the plastic zone of the hard rock around the tunnel just extends to the ground, then this burial depth is selected as the third critical burial depth h3 of the gas storage tunnel. S4) Compare and analyze the first critical burial depth, the second critical burial depth and the third critical burial depth obtained in steps S1) to S3), and select the maximum critical burial depth as the safe burial depth design value of the artificial underground gas storage tunnel. The safe burial depth design value h = MAX(h1,h2,h3).

2. The method for designing the safe burial depth of artificial underground gas storage tunnels according to claim 1, characterized in that: It also includes S5), which calculates the buoyancy, shear force, and gravity of the overlying rock mass of the gas storage tunnel based on the design value of the safe burial depth of the gas storage tunnel, as well as the uplift force caused by the buoyancy of the gas storage tunnel and the internal pressure of the gas storage tunnel, to obtain the stability coefficient of the gas storage tunnel, and verifies the stability of the overlying rock mass through the stability coefficient of the gas storage tunnel.

3. The method for designing the safe burial depth of artificial underground gas storage tunnels according to claim 2, characterized in that: In S5), if the shear strength of the overlying rock mass is calculated using the shear friction coefficient and shear cohesion, and the stability coefficient of the gas storage tunnel is not less than 3.0, then the overlying rock mass is stable and the burial depth of the gas storage tunnel is safe; if the shear strength of the overlying rock mass is calculated using the shear friction coefficient and shear cohesion, and the stability coefficient of the gas storage tunnel is not less than 1.1, then the overlying rock mass is stable and the burial depth of the gas storage tunnel is safe.

4. The method for designing the safe burial depth of artificial underground gas storage tunnels according to claim 3, characterized in that: In S5), the formula for calculating the buoyancy of the overlying rock mass is: F br =A c ·γ w ·z w In the formula, F br Indicates the buoyancy of the overlying rock mass. A c This represents the horizontal projected area of ​​the gas storage tunnel. γ w Indicates the density of each water layer. z w This indicates the thickness of the water level above the gas storage tunnel; The formula for calculating the shear resistance of the overlying rock mass is as follows: τ r =L c ·∑z j ·c′ j +L c ·∑σ hj ·f′ j ·z j In the formula, τ r Indicates the shear resistance of the overlying rock mass. L c This represents the horizontal projected perimeter of the gas storage tunnel. z j Indicates the thickness of the j-th rock layer. c′ j This represents the shear cohesion, or shear-resistant cohesion, of the j-th rock layer. σ hj This represents the horizontal stress in the j-th rock layer. f′ j This represents the shear friction coefficient, or shear friction coefficient, of the j-th rock layer; The formula for calculating the gravity of the overlying rock is as follows: IN r =A c ·∑γ j ·With j In the formula, W r Indicates the gravity of the overlying rock. A c This represents the horizontal projected area of ​​the gas storage tunnel. γ j This represents the unit weight of the j-th rock layer. z j Indicates the thickness of the j-th rock layer; The formula for calculating the buoyancy of the gas storage tunnel is as follows: F bc =V c ·c w In the formula, F bc Indicates the buoyancy of the gas storage tunnel. V c Indicates the volume of the gas storage cavity. γ w Indicates the unit weight of each water layer; The formula for calculating the uplift force caused by the internal pressure of the gas storage tunnel is as follows: F l =P·A c In the formula, F l This indicates the uplift force caused by the pressure inside the gas storage tunnel. P represents the gas pressure inside the gas storage tunnel. A c This represents the horizontal projected area of ​​the gas storage tunnel. The formula for calculating the stability coefficient of the gas storage tunnel is as follows: In the formula, K represents the stability coefficient of the gas storage tunnel. W r Indicates the gravity of the overlying rock. τ r Indicates the shear resistance of the overlying rock mass. F l This indicates the uplift force caused by the pressure inside the gas storage tunnel. F bc Indicates the buoyancy of the gas storage tunnel. F br This indicates the buoyancy of the overlying rock mass.

5. The method for designing the safe burial depth of artificial underground gas storage tunnels according to claim 4, characterized in that: In S5), the horizontal stress σ of the j-th rock layer hj The calculation formula is In the formula, σ hj This represents the horizontal stress in the j-th rock layer. k sj This represents the lateral pressure coefficient of the j-th rock layer. γ j-1 This represents the unit weight of the (j-1)th rock layer. z j-1 This represents the thickness of the (j-1)th rock layer. γ j This represents the unit weight of the j-th rock layer. z j This represents the thickness of the j-th rock layer.

6. The method for designing the safe burial depth of artificial underground gas storage tunnels according to claim 1, characterized in that: In S2), the formula for calculating the punching angle θ is: In the formula, θ represents the punching angle. This indicates the internal friction angle of hard rock.

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