A method for calculating the depth of underground gas storage caverns based on dilatational failure

Abstract

The application discloses a kind of underground gas storage cavern depth calculation method based on expansion and crack failure in the technical field of high-pressure gas storage cavern, comprising the following steps: assuming that the failure mode of the overburden of gas storage cavern under the action of internal gas pressure is expansion and crack failure, cracks along one side of the gas storage cavern, the overburden rotates and lifts around the origin of the other side, calculates the lifting torque and anti-lifting torque with the origin, and establishes the torque balance equation, constructs the correlation calculation formula of the gas pressure in the cavern and the minimum burial depth and distance coefficient, and calculates the numerical value of the minimum burial depth of the cavern using the trial method, and the calculation accuracy meets the engineering requirements. Under the premise of ensuring the safety of the gas storage cavern, the minimum burial depth of the cavern can be accurately calculated, thereby saving investment and shortening the construction period, and the engineering benefit is remarkable.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-pressure gas storage cavern, in particular to a buried depth calculation method for underground gas storage cavern. BACKGROUND

[0002] Underground cavern gas storage is a new type of energy storage, which has the following benefits: first, it can save land occupation and has little impact on the environment; second, it can use surrounding rock to bear part of the internal gas pressure, reducing the thickness of the lining structure; third, it is not restricted by terrain conditions.

[0003] Underground cavern gas storage has great development potential and broad market prospects, but the buried depth of high-pressure gas storage cavern has a great impact on the amount of civil engineering, especially the excavation length of the ventilation hole, construction shaft and other auxiliary caverns, which in turn has a great impact on the project cost. If the Norwegian criteria for water conservancy tunnel of water and electricity (the weight of overlying rock is not less than the internal pressure of the hole) is followed, the strength of the rock mass is not considered, and only the weight of the rock mass is considered. For an internal gas pressure of 10 MPa, the rock mass buried depth is greater than 300 m, which will greatly increase the length of the traffic hole or construction shaft for underground cavern construction, thereby increasing the construction cost.

[0004] Therefore, how to accurately calculate the minimum buried depth of the underground gas storage cavern to reduce the construction difficulty and construction cost has become a technical problem to be solved by those skilled in the art. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a buried depth calculation method for underground gas storage cavern based on dilatant failure to solve the technical problem that the existing buried depth calculation method for gas storage cavern cannot accurately calculate the minimum buried depth.

[0006] The technical solution adopted by the present application is: a buried depth calculation method for underground gas storage cavern based on dilatant failure, comprising the following steps:

[0007] Take the AB vertical plane on one side of the gas storage cavern as the split plane, and rotate and lift the overlying rock mass ABOC upward with the O point on the other side of the gas storage cavern as the origin; the AB vertical plane is tangent to the gas storage cavern, and the C point is located directly above the O point;

[0008] Calculate the shear resistance τ and the gravity G of the overlying rock mass ABOC when it is rotated and lifted, calculate the shear moment M corresponding to the shear resistance τ, the gravity G and the internal gas pressure P of the cavern with the O point as the origin τ , the gravity moment M G and the gas pressure moment M P , and establish the moment balance equation:

[0009] Wherein, G, τ and gas storage hole depth H exist function relation, L=N*D, L is the horizontal distance of the origin O from the underground gas storage hole, unit m, D is the diameter of the underground gas storage hole, unit m; N is the distance coefficient;

[0010] The trial method is used, the gas pressure P in the hole chamber corresponding to different depths and different distance coefficients N is calculated according to the moment balance equation, when the minimum value of the gas pressure in the hole chamber under a certain depth is equal to the design pressure P0 of the gas in the hole chamber, the depth at this time is the minimum depth H of the underground gas storage hole min ;

[0011] Wherein, L=N*D, L is the horizontal distance of the origin O from the underground gas storage hole, unit m, D is the diameter of the underground gas storage hole, unit m; N is the distance coefficient.

[0012] Preferably, the shear force τ is calculated according to the following formula:

[0013]

[0014] Wherein, c i Is the cohesion of the i layer of rock-soil, unit KPa; H i Is the thickness of the i layer of rock-soil, unit m; K i Is the ratio coefficient of horizontal ground stress and dead weight stress; γ m Is the specific weight of the m layer of rock-soil; unit kN / m 3 ; H m Is the thickness of the m layer of rock-soil, unit m; Is the internal friction angle of the i layer of rock-soil, unit °, and n is the total number of rock-soil layers above the gas storage hole.

[0015] Preferably, the gravity G is calculated according to the following formula:

[0016]

[0017] Wherein, γ i Is the specific weight of the i layer of rock-soil; unit kN / m 3 ; H i Is the thickness of the i layer of rock-soil, unit m; D is the diameter of the underground gas storage hole, unit m; L is the distance of the origin from the underground gas storage hole, unit m.

[0018] The beneficial effects of the application are:

[0019] The present application is based on dilatant failure, and a torque balance equation is established for the overlying rock mass of the gas storage cavity in a critical state, a related calculation formula of the gas pressure in the cavity, the minimum buried depth and the distance coefficient is constructed, the numerical value of the minimum buried depth of the cavity can be calculated by using the trial method, the calculation precision meets the engineering needs, compared with the existing cavity buried depth calculation method, the cavity buried depth can be reduced under the premise of ensuring the safety of the gas storage cavity, the investment is saved and the construction period is shortened, and the engineering benefit is remarkable. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The calculation model of the underground high-pressure gas storage cavity buried depth calculation method based on dilatant failure of the present application. DETAILED DESCRIPTION

[0021] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings. These embodiments are only used to illustrate the present application, and are not limiting to the present application.

[0022] In the description of the present application, it should be noted that the orientations or positional relationships indicated by the terms 'center', 'longitudinal', 'transverse', 'upper', 'lower', 'front','rear', 'left', 'right','vertical', 'horizontal', 'top', 'bottom', 'inner', 'outer' and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms 'first','second' are only for description purposes, and cannot be understood as indicating or implying relative importance.

[0023] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms'mounting', 'connection', 'connection' should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection, it can be mechanical connection, or electrical connection, it can be direct connection, or indirect connection through intermediate medium, it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0024] In addition, in the description of the present application, unless otherwise specified, the meaning of 'a plurality of' is two or more.

[0025] The inventor found through long-term research that the failure mode of the overlying rock mass of the high-pressure gas storage cave is bulging and cracking failure, which is different from the calculation mode of Terzaghi mountain pressure in classical rock-soil mechanics, but is similar to the ground cracks caused by the upward surge of volcanic magma or gas and the ground cracking caused by the rupture of underground high-pressure water pipelines. When the overlying rock mass undergoes bulging and cracking failure, the cracking surface is located on one side of the underground cave, and the overlying rock mass rotates upward around a point on the other side of the underground cave as the origin.

[0026] An underground gas storage cave depth calculation method based on bulging and cracking failure is shown in the embodiment, which comprises the following steps: Figure 1

[0027] It is assumed that the overlying rock mass ABOC undergoes bulging and cracking failure under the action of the internal gas pressure of the cave, the vertical surface AB on one side of the gas storage cave is the cracking surface, and the overlying rock mass ABOC rotates upward around the point O on the other side of the gas storage cave as the origin. The vertical surface AB is tangent to the gas storage cave, and the point C is directly above the point O.

[0028] The shear resistance τ of the overlying rock mass ABOC when rotating and lifting is calculated, as well as the gravity G of the overlying rock mass ABOC, and the shear resistance moment M τ , the gravity moment M G and the gas pressure moment M P corresponding to the shear resistance τ, the gravity G and the internal gas pressure P of the cave are calculated with the point O as the origin. The gas storage cave is in the state of just lifting as the critical state of the overlying rock mass ABOC, and the moment balance equation is established:

[0029] The internal gas pressure P corresponding to different depths H and different distance coefficients N is calculated according to the moment balance equation by using the trial method. When the minimum value of the internal gas pressure of the cave under a certain depth is equal to the design pressure P0 of the internal gas of the cave, the depth at this time is the minimum depth H min of the underground gas storage cave.

[0030] Wherein, G and τ have a functional relationship with the depth H of the gas storage cave, L=N*D, L is the horizontal distance from the origin O to the underground gas storage cave, unit: m, D is the diameter of the underground gas storage cave, unit: m; N is the distance coefficient.

[0031] Based on the bulging and cracking failure, the moment balance equation of the overlying rock mass of the gas storage cave in the critical state is established, the related calculation formula of the internal gas pressure of the cave and the minimum depth and the distance coefficient is constructed, the numerical value of the minimum depth of the cave can be calculated by using the trial method, the calculation is accurate and meets the engineering needs, compared with the existing cave depth calculation method, the cave depth can be reduced under the premise of ensuring the safety of the gas storage cave, the investment and the construction period are saved, and the engineering benefit is remarkable.

[0032] Specific embodiment 1 is shown in​Figure 1 As shown, a method for calculating the burial depth of underground gas storage cavities based on expansion and fracture failure includes the following steps:

[0033] Assuming that the overlying rock mass ABOC undergoes expansion and cracking failure under the pressure inside the cavern, the failure mode is as follows: the vertical plane AB on one side of the gas storage cavern is taken as the crack surface, that is, the crack extends upward from the gas storage cavern to the ground along the vertical plane AB on the left side of the overlying rock mass ABOC, and the overlying rock mass ABOC rotates and rises upward with point O on the right side of the gas storage cavern as the origin; the vertical plane AB is tangent to the left side of the gas storage cavern, the horizontal plane where point O is located is tangent to the top of the gas storage cavern, and point C is located directly above point O.

[0034] Calculate the shear force τ and gravity G experienced by the overlying rock mass ABOC during rotational uplift, and calculate the shear moment M corresponding to the shear force τ with point O as the origin. τ Calculate the gravitational moment M corresponding to gravity G with point O as the origin. G Calculate the gas pressure moment M corresponding to the gas pressure P inside the cavern, with point O as the origin. P .

[0035] Specifically, the shear force τ can be calculated using any known method. The following is a detailed explanation of one such method as an example. The formula for calculating the shear force τ is as follows:

[0036]

[0037] Among them, c i H represents the cohesion of the i-th soil and rock layer, in kPa; i K represents the thickness of the i-th soil and rock layer, in meters. i γ is the proportionality coefficient between horizontal ground stress and self-weight stress; m The unit weight of the m-th soil and rock layer; unit: kN / m 3 H m The thickness of the m-th soil and rock layer is given in meters. denoted as the internal friction angle of the i-th soil and rock layer, in degrees, and n is the total number of soil and rock layers above the gas storage tunnel.

[0038] Shear moment M τ The calculation formula is:

[0039] M τ =τ×(D+L)

[0040] The formula for calculating gravity G is:

[0041]

[0042] Where, γ i The unit weight of the i-th soil and rock layer; unit: kN / m³ 3 Hi is the thickness of the i-th rock-soil layer, unit m; D is the diameter of the underground gas storage cavern, unit m; L is the horizontal distance from the origin O to the underground gas storage cavern, unit m.

[0043] Gravity moment M G The calculation formula is:

[0044]

[0045] Gas pressure moment M P The calculation formula is:

[0046]

[0047] When the underground gas storage cavern is in a critical state just after uplift, the overlying rock mass ABOC is in a critical state, and the following moment balance exists:

[0048] M G +M τ =M P

[0049] Substitute the shear moment M τ , the gravity moment M G and the gas pressure moment M P into the moment balance equation, and the following equation can be obtained:

[0050]

[0051] where D is the diameter of the underground gas storage cavern, unit m; L is the horizontal distance from the origin to the underground gas storage cavern, unit m; P is the internal gas pressure of the cavern, unit MPa.

[0052] Using the internal gas design pressure P0 of the gas storage cavern, the cavern diameter D and the rock mass mechanical parameters, etc., the minimum burial depth calculation formula of the overlying rock mass ABOC in the critical state is obtained

[0053] Substitute L=N*D into the minimum burial depth calculation formula, and the minimum burial depth H min and the distance coefficient N are obtained:

[0054] H min =f(N)

[0055] The above formula shows that under the conditions of given internal gas pressure of the cavern, cavern diameter, rock-soil layer thickness and strength parameters, the minimum burial depth of the underground cavern is a function of the distance coefficient.

[0056] Adopting the trial method, the gas pressure P in the chamber corresponding to different buried depths H and different distance coefficients N is calculated according to the moment balance equation, when the minimum value of the gas pressure P in the chamber under a certain buried depth is equal to the design gas pressure P0 in the chamber, the buried depth is the minimum buried depth H of the underground gas storage chamber min ; that is, the buried depth H and the distance coefficient N (that is, L=N*D) are taken as known variables to substitute into the moment balance equation, the minimum value of the gas pressure in the chamber when N takes any value under the same buried depth is calculated, when the minimum value of the gas pressure in the chamber is equal to the design gas pressure P0 in the chamber, the value of the buried depth H is the minimum buried depth H of the underground gas storage chamber min .

[0057] Wherein, L=N*D, L is the horizontal distance from the origin O to the underground gas storage chamber, unit m, D is the diameter of the underground gas storage chamber, unit m; N is the distance coefficient, the value range of N can be 0.1-1.2.

[0058] With reference to the embodiment, a proposed gas storage and energy storage project is located in the northwest region, the terrain undulates slightly, the site rock-soil body is distributed in three layers (n=3) from top to bottom, which are aeolian sand layer, sandy gravel layer and gneiss layer, and the physical and mechanical parameters of the rock-soil layer are shown in Table 1.

[0059] Table 1 Physical and mechanical parameters of rock-soil body

[0060]

[0061] The maximum gas pressure in the designed gas storage chamber is 10 MPa, the calculation result is shown in Table 2 according to the above formula; it can be seen from Table 2 that when the buried depth is 122.5 m, the minimum value of the gas pressure in the chamber is 10.032 MPa, and the buried depth just meets the requirement of the design gas pressure P0=10 MPa of the chamber, that is, the minimum buried depth is 122.5 m.

[0062] Table 2 Calculation results of chamber internal gas pressure corresponding to different buried depths and distance coefficients

[0063]

[0064]

[0065] Note that, according to Table 2, when the chamber buried depth H is fixed, the gas pressure P in the chamber calculated according to the moment balance equation decreases first and then increases with the increase of the distance coefficient N.

[0066] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled persons in the art, without departing from the technical principles of the present application, a number of improvements and replacements can be made, and these improvements and replacements should also be considered as the protection scope of the present application.

Claims

1. A method for calculating the depth of a gas storage cavern based on dilatational failure, characterized in that, Comprise the following steps: With the AB vertical plane of one side of the gas storage hole as the split plane, the overlying rock mass ABOC is rotated and lifted upward with the O point of the other side of the gas storage hole as the origin; the AB vertical plane is tangent to the gas storage hole, and the C point is located directly above the O point; The shear force τ and the gravity G suffered by the overburden rock mass ABOC during the rotation uplift are calculated, and the shear moment M corresponding to the shear force τ, the gravity G and the gas pressure P inside the chamber are calculated with O point as the origin τ , the gravity moment M G and the gas pressure moment M P , and the moment balance equation is established: Wherein, G, τ and the depth H of the gas storage hole exist a functional relationship, L=N*D, K is the horizontal distance from the origin O to the underground gas storage hole, unit m, D is the diameter of the underground gas storage hole, unit m; N is the distance coefficient; The trial method is used to calculate the gas pressure P in the chamber corresponding to different depths H and different distance coefficients N according to the moment balance equation. When the minimum value of the gas pressure in the chamber at a certain depth is equal to the design pressure P0 of the gas in the chamber, the depth at this time is the minimum depth H of the underground gas storage chamber min ; The calculation formula of the shear force τ is as follows: wherein c i is cohesion of the i-th layer of rock-soil, unit KPa; H i is thickness of the i-th layer of rock-soil, unit m; K i is a proportional coefficient of horizontal ground stress and dead weight stress; Y m is specific weight of the m-th layer of rock-soil, unit kN / m 3 ; H m is thickness of the m-th layer of rock-soil, unit m; is internal friction angle of the i-th layer of rock-soil, unit °, and n is total number of layers of rock-soil above the gas storage cavity. The calculation formula of the gravity G is as follows: wherein Y i is the unit kN / m 3 ; H i is the thickness of the i-th layer of rock-soil, unit m; D is the diameter of the underground gas storage cavern, unit m; L is the distance from the origin to the underground gas storage cavern, unit m.

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