CN113886919A - Method for determining support design of ultra-large span underground cavern based on energy field balance - Google Patents
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Abstract
The invention relates to a method for determining a support design of a super-large span underground cavern based on energy field balance, which comprises the following steps: (1) through a field loading test, acquiring an energy value of a unit rock mass loaded to be damaged in a large-span cavern body range; (2) calculating stress and strain fields of the large-span cavern full-section excavation without a support working condition, and determining an unstable region in the cavern; (3) respectively calculating stress and strain fields of the cavern under different excavation schemes, and obtaining the excavation scheme with the smallest area of the unstable region by comparison and selection as an optimal excavation scheme; (4) on the basis of the optimal excavation scheme, calculating the stress and strain field of the cavern under the working condition of taking supporting measures; and continuously adjusting and optimizing the support measures to enable the support measures when the area of the energy unstable region is zero to serve as a final support scheme for the oversized underground cavern. The invention takes the energy as the index for judging the stability of the rock mass, accords with the destructive characteristic and the stability mechanism of the substance, and has reasonable and reliable design method.
Description
Technical Field
The invention relates to the field of tunnel underground engineering design and construction, in particular to a method for determining an optimal supporting scheme of an oversized underground cavern based on energy field balance.
Background
For tunnel cavern underground engineering, the design and construction usually adopt a qualitative and quantitative method, the qualitative generally adopts an engineering comparison method, and the quantitative generally adopts stratum-structure, load-structure and other methods; for the underground cavern with the ultra-large span, particularly the span of more than 40m, because of few engineering cases, an engineering similarity method cannot be used as a design basis, while a stratum-structure method in a quantitative analysis method is difficult to judge the destruction basis and the destruction form, and the load in a load-structure method depends on an empirical formula and is not suitable for the underground cavern with the span.
In summary, most of the existing design methods are empirical formulas, and the stability of the rock mass is judged by two independent indexes of strength and deformation, and the method is suitable for conventional caverns, but for the oversized underground cavern, certain limitations exist because the method cannot provide definite load and has no reliable damage index.
Disclosure of Invention
Based on the above limitations of the conventional design method applied to the support design of the huge-span cavern, the invention provides a method for designing the huge-span underground cavern by using an energy field formed by combining stress and strain as an evaluation index.
The technical scheme adopted by the invention for solving the technical problems is as follows: a method for determining a support design of a super-large span underground cavern based on energy field balance specifically comprises the following steps:
s1, determining the maximum principal stress sigma of the planned ultra-large span underground cavern by means of field measurement1And minimum principal stress σ3；
S2, obtaining rock mass test blocks to be built in the hole area, the middle part and the tail part of the super-large span underground cavern in a drilling mode; uniaxial loading compression test and maximum principal stress sigma are carried out on rock mass test block1And minimum principal stress σ3Carrying out a triaxial loading compression experiment under confining pressure; obtaining the energy value of a single rock test block loaded to a destruction state in the oversized underground cavern through calculation;
s3, establishing a three-dimensional calculation model of the oversized underground cavity in the steps S1 and S2 by using a computer, calculating stress and strain fields of the oversized underground cavity under the full-section excavation and no support working condition, determining rock mass energy values of all units of the cavity, comparing the rock mass energy values of all units of the cavity with the energy values of the rock mass test blocks determined in the step S2 when the rock mass test blocks are loaded to a failure state, and determining an unstable region S in the oversized underground cavity;
s4, drawing up an excavation scheme of the ultra-large span underground cavern, determining an unstable region S in each excavation scheme according to the method in the step S3, and taking the excavation scheme with the minimum area of the unstable region S as an optimal excavation scheme; the proposed excavation of the underground cavern with the ultra-large span comprises the following steps: a reserved medium rock pillar method, a step method and a pilot tunnel enlarging and excavating method.
S5, applying support measures to the oversized underground cavern under the excavation scheme obtained by screening in the step S4, calculating the stress and strain value of the cavern after support according to the calculation method in the step S3, and determining an unstable region S of the cavern;
and S6, adjusting and optimizing the support measures until the unstable area S of the cavern is zero, and taking the support measures at the moment as a final support design scheme for drawing up the super-large underground cavern.
Further, in step S1: method for measuring and determining maximum principal stress sigma of planned super-large-span underground cavern by adopting hydrofracturing ground stress method1And minimum principal stress σ3。
Further, step S2 is specifically: at least three groups of rock mass test blocks are respectively selected in the area of the oversized underground cavity opening, the middle part of the cavity and the tail part of the cavity, and the number of the test blocks in each group of rock mass test blocks is more than or equal to 3; respectively carrying out uniaxial loading compression test and confining pressure sigma on each group of rock mass test blocks1And σ3The triaxial loading compression test; obtaining the energy values of all rock mass test blocks under the three loading working conditions, wherein the calculation formula is as follows:
wherein: eiMaximum principal stress sigma for confining pressure1In a triaxial loading compression experiment, calculating energy values of each rock mass test block when the rock mass test block is loaded to damage; ejMinimum principal stress sigma for confining pressure3In a triaxial loading compression experiment, calculating energy values of each rock mass test block when the rock mass test block is loaded to damage; ekCalculating the energy value of each rock mass test block when the rock mass test block is loaded to be damaged in the uniaxial compression test;
specifically, in the above formula: delta is the stress value in the loading process of the rock mass test block, and epsilon is the rock mass test block loadedStrain values in the course, longitudinal being parallel to the loading direction and transverse being perpendicular to the loading direction, deltav、δhFor longitudinal and transverse stress values, epsilon, of rock mass test block during loadingv、εhLongitudinal and transverse strain values, epsilon, of rock mass test block in the loading processvmax is the sum delta of the longitudinal delta-epsilon curve of the rock mass test blockvStrain value, δ, corresponding to maxvmax is the maximum stress value in the longitudinal delta-epsilon curve of the rock mass test block, epsilonhmax is the longitudinal load to δvThe transverse strain value of the test block at max, and n is the number of rock mass test blocks under 3 loading working conditions;
respectively calculating the average value of energy under three loading working conditions,
take its minimum value
The energy value of a single rock block test block which is over-large and spans the underground cavern when the test block is loaded to be damaged is used.
Further, in step S2, the rock mass test blocks are all cylindrical test blocks with a diameter and a height of 100 mm.
Further, in step S3, the calculation model unit of the oversized underground cavern adopts a tetrahedron, the side lengths are all 1m, the rock mass energy value of each unit is calculated by drawing a delta-epsilon curve of each unit in x, y and z directions and the following calculation formula:
wherein: epsilon1x、ε1y、ε1zFor super large span of cavern and delta1x、δ1y、δ1zCorresponding strain value, δ1x、δ1y、δ1zThe initial stress values of the ultra-large underground cavern in the x, y and z directions are obtained; epsilon2x、ε2y、ε2zFor super large span of cavern and delta2x、δ2y、δ2zThe corresponding strain value is set according to the strain value,δ2x、δ2y、δ2zthe maximum stress value delta of the rock mass test block in the x, y and z directions in a delta-epsilon curvex、δy、δzIs the stress of the cavity in the x, y, z directions, epsilonx、εy、εzStrain of the cavern in x, y and z directions;
the energy E is more than 0.5EdThe unit area of (a) is defined as an unstable area S; edAnd loading the energy value of the single rock block test block which is over-large and spans the underground cavern until the test block is damaged.
And further, the span of the super-span underground cavern is more than or equal to 40 m.
Preferably, in step S3, the rock energy value of each unit of the super-large underground cavern is a rock energy value near the vault, arch shoulder or arch foot area of the cavern.
Further, in step S6, the optimizing the supporting measures includes: on the basis of the original support measures, the anchoring force of a prestressed anchor cable is increased, anchor rods are lengthened, the thickness of sprayed concrete is thickened or an arch frame is erected.
Compared with the prior art, the invention has the following advantages and effects:
1. in the method for designing and determining the support of the oversized underground cavern based on the energy field balance, the energy value of a single rock test block loaded to a failure state is determined by carrying out a field loading compression experiment on the rock test block in the range of the planned oversized underground cavern body, and the energy value is used as an index for judging the stability of the rock, so that the method conforms to the material failure characteristic and the stability mechanism, and the support scheme determined based on the energy index is particularly suitable for the oversized underground cavern.
2. According to the invention, through a computer three-dimensional model, the energy values of all units of the planned super-large span underground cavern under the full-section excavation and no-support working condition are calculated, and are compared with the energy values obtained by experiments when a single rock test block is loaded to a failure state, and the energy unstable region S existing in the cavern is determined.
3. According to the method for designing and determining the support of the oversized underground cavern based on the energy field balance, on the basis of the optimal excavation scheme obtained through screening, the support of the unstable region S of the cavern is continuously strengthened aiming at the weak region of the cavern by applying a preliminary support measure, calculating the unstable region S of the proposed cavern and gradually strengthening the support measure until the unstable region S of the cavern is zero, so that the cavern gradually reaches a reliable stable state, and the finally obtained support scheme has the advantages of strong support stability, reasonability and reliability.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 shows the maximum principal stress σ of the rock mass test block confined pressure in step S2 according to the embodiment of the present invention1And (3) obtaining a longitudinal delta-epsilon curve in a triaxial loading compression test.
FIG. 2 shows the maximum principal stress σ of the rock mass test block confined pressure in step S2 according to the embodiment of the present invention1And (3) obtaining a transverse delta-epsilon curve in a triaxial loading compression test.
Fig. 3 is a stress field cloud chart (a) and a strain field cloud chart (b) of the ultra-large span underground cavern full-section excavation and under the non-support working condition in step S3 of the embodiment of the invention.
Fig. 4 is a stress cloud chart of the ultra-large span underground cavern full-section excavation in step S3 in the embodiment of the invention, in the X direction (diagram a), the Y direction (diagram b), and the Z direction (diagram c) under the working condition of no support.
Fig. 5 is a schematic diagram of an energy unstable region S (block portion) in the step S3 of the embodiment of the present invention, which is excavated over a full section of an ultra-large span underground cavern and under a non-support working condition.
FIG. 6 is a conventional step-by-step excavation scheme (the sequence number represents an excavation step sequence) for a super-large span underground cavern in the embodiment of the invention, and the diagram A is a reserved mid-column method; b is a step method; and C, a pilot hole enlarging and excavating method.
Fig. 7 is a schematic diagram of an unstable area S of a cavern under the condition of preliminary bracing construction by a reserved middle-edge column method.
Fig. 8 is a schematic diagram of a super-large span underground cavern supporting structure when the reserved mid-column-method unstable region S is zero.
Detailed Description
The present invention will be described in further detail with reference to examples, which are illustrative of the present invention and are not to be construed as being limited thereto.
Example 1: as shown in fig. 1 to 8, a method for determining a support design of an ultra-large span underground cavern based on energy field balance comprises the following steps:
s1, obtaining the maximum principal stress sigma of the planned 50-meter ultra-large span underground cavern field by adopting a hydrofracturing ground stress measuring method1And minimum principal stress σ3；
Wherein: sigma1＝6.2Mpa；σ3＝1.72Mpa；
S2, obtaining rock mass test blocks to be built at the opening, the middle part and the tail part of the super-large underground cavern in a drilling mode, and carrying out a uniaxial loading compression experiment and a maximum principal stress sigma1And minimum principal stress σ3In the field loading compression experiment, the energy value of a single rock mass test block loaded to a failure state in the ultra-large underground cavity is obtained through calculation;
the specific scheme is as follows: selecting 10 groups of rock mass test blocks in the range of the ultra-large span underground cavern body; wherein: taking 3 groups of holes, 4 groups of holes in the middle and 3 groups of holes at the tail, wherein 3 rock mass test blocks are taken from each group; respectively carrying out confining pressure sigma on rock mass test blocks of each group1Three-axis loading compression experiment under 6.2Mpa, confining pressure sigma3A triaxial loading compression experiment and a uniaxial loading compression experiment under 1.72 Mpa; and calculating the energy value of each rock mass test block of each group when the rock mass test blocks are loaded to a failure state under the three loading working conditions, wherein the calculation formula is as follows:
in the above formula: eiCalculating the energy value of each group of rock mass test blocks when the rock mass test blocks are loaded to be damaged in a triaxial loading compression experiment with the maximum confining pressure main stress of 6.2 Mpa; ejCalculating the energy value of each group of rock mass test blocks when the rock mass test blocks are loaded to be damaged in a triaxial loading compression experiment with the minimum principal stress of confining pressure of 1.72 Mpa; ekCalculating the energy value of each group of rock mass test blocks when the rock mass test blocks are loaded to be damaged in the uniaxial compression test; delta is the stress value in the loading process of the rock mass test block, epsilon is the strain value in the loading process of the rock mass test block, the longitudinal direction is parallel to the loading direction, the transverse direction is vertical to the loading direction, and delta isv、δhFor longitudinal and transverse stress values, epsilon, of rock mass test block during loadingv、εhLongitudinal and transverse strain values, epsilon, of rock mass test block in the loading processvmax is the sum delta of the longitudinal delta-epsilon curve of the rock mass test blockvStrain value, δ, corresponding to maxvmax is the maximum stress value in the longitudinal delta-epsilon curve of the rock mass test block, epsilonhmax is the longitudinal load to δvThe transverse strain value of the test block at max;
Eiexample of calculation: taking the first test block of the first group of test blocks at the opening section to carry out confining pressure sigma1Obtaining longitudinal and transverse delta-epsilon curves of the test (6.2 Mpa) through a triaxial loading compression test, and obtaining delta through graphs shown in figures 1 and 2v max＝22.3Mpa；εvmax＝0.011，εhmax is 0.018, and the energy value is calculated as:
the other test blocks can be calculated respectively as follows:
Ei＝(279，290，301...269)(i＝1，2，3..30)；
the calculation result of the triaxial loading compression experiment with the minimum confining pressure main stress of 1.72MPa for each group of rock mass test blocks is as follows:
Ej＝(186，193，201...176)(j＝1，2，3..30)；
in the uniaxial compression test, calculating the energy value of each group of rock mass test blocks when the rock mass test blocks are loaded to be damaged:
Ek＝(135，169，211...173)(k＝1，2，3..30)；
Ej、Ekthe longitudinal delta-epsilon curve and the transverse delta-epsilon curve of the triaxial loading compression test with the minimum principal stress of 1.72MPa and the longitudinal delta-epsilon curve of the uniaxial compression test can be respectively drawn, and reference is made to EiCalculating an example to obtain;
respectively calculating the average energy value under three loading conditions:
take its minimum value
The numerical value is the energy value when the oversized cross-chamber rock mass test block is loaded to a failure state, and the unit of the energy is kj.
S3, establishing a three-dimensional calculation model unit of the oversized underground cavern by using computer software (such as MIDAS/GTS NX or FLAC 3D) in steps S1 and S2, wherein the three-dimensional calculation model unit of the oversized underground cavern adopts a tetrahedron, the side length is 1m, the calculation parameters select geological parameters in a geological survey report, the stress and strain field of the oversized underground cavern under the full-section excavation and no support working condition is calculated, the rock mass energy value of each unit of the cavern is determined, and the rock mass energy value of each unit of the cavern is compared with the energy value of the rock mass test block determined in the step S2 when the rock mass test block is loaded to the destruction state, so that an unstable region S in the oversized underground cavern is determined;
specifically, a total stress field cloud picture of the ultra-large span underground cavern under the full-section excavation and support-free working condition is shown in fig. 3(a), and a total strain field cloud picture is shown in fig. 3 (b). Drawing delta-epsilon curves of each unit (a rock mass unit near a vault A, a shoulder B or a foot arch area) of the cavern in the X direction, the Y direction and the Z direction, and calculating the energy value of each unit by using stress clouds in the X direction, the Y direction and the Z direction as shown in figure 4:
S4, drawing up an excavation scheme of the ultra-large span underground cavern, determining an unstable region S in each excavation scheme according to the method in the step S3, and taking the excavation scheme with the minimum area of the unstable region S as an optimal excavation scheme;
specifically, as shown in fig. 6, the conventional excavation scheme includes a reserved middle pillar method, a three-step method, and a pilot tunnel enlarging method, the stress and strain values of the caverns under the 3 excavation schemes are respectively calculated, the unstable region S in each excavation scheme is obtained according to the calculation method in step (3), and the unstable region S obtained by the reserved middle pillar method is obtained by comparing and selecting the smallest area, that is, the reserved middle pillar method is the optimal excavation scheme.
S5, applying a preliminary support measure to the oversized underground cavern under the optimal excavation scheme obtained by screening in the step S4, calculating the stress and strain value of the cavern after support according to the calculation method in the step S3, and determining an unstable region S of the cavern;
specifically, the preliminary supporting measures can be that the length L of a construction prestressed anchor cable is 15m @7m, the anchoring force F is 500kN, the anchor rod L is 3m @7m, and the thickness h of sprayed concrete is 10 cm; obtaining an unstable region S under the supporting working condition of the cavern according to the calculation method of the step S3, wherein the area of the unstable region S is smaller than that of the unstable region S under the full-section excavation and supporting-free working condition, as shown in the square part of FIG. 7;
and S6, adjusting and optimizing the support measures until the unstable area S of the cavern is zero, and taking the support measures at the moment as a final support scheme for drawing up the super-large underground cavern.
Specifically, on the basis of the preliminary support in the step, the support measures are gradually strengthened, the stress and strain values of the cavern are respectively calculated, and the support measure for making the area of the unstable region S zero is finally obtained according to the calculation method in the step S3, as shown in fig. 8, the unstable region S disappears; the support measure at this time is that the length L of the prestressed anchor cable is 25m @5m, the anchoring force F is 1500kN, the anchor rod L is 6m @5m, and the thickness h of the sprayed concrete is 20cm, and the support measure can be used as the optimal support measure for the oversized underground cavern in the embodiment.
The method for determining the support design of the oversized-span underground cavern based on the energy field balance in the embodiment 1 takes energy as an index for judging the stability of a rock mass, accords with the material destruction characteristics and the stability mechanism, is reasonable and reliable, can quickly determine the optimal excavation and support scheme of the oversized-span underground cavern with the span of more than 40m, and has important theoretical guiding significance for actual tunnel underground engineering design and construction.
In addition, it should be noted that the specific embodiments described in the present specification may differ in the shape of the components, the names of the components, and the like. All equivalent or simple changes of the structure, the characteristics and the principle of the invention which are described in the patent conception of the invention are included in the protection scope of the patent of the invention. Various modifications, additions and substitutions for the specific embodiments described may be made by those skilled in the art without departing from the scope of the invention as defined in the accompanying claims.
Claims (8)
1. A method for determining a support design of an oversized underground cavity based on energy field balance is characterized by comprising the following steps:
s1, determining the maximum principal stress sigma of the planned ultra-large span underground cavern by a field measurement mode1And minimum principal stress σ3；
S2, obtaining rock mass test blocks to be built in the hole area, the middle part and the tail part of the super-large span underground cavern in a drilling mode; respectively carrying out uniaxial loading compression test and maximum principal stress sigma on the rock mass test block1And minimum principal stress σ3Carrying out a triaxial loading compression experiment under confining pressure; obtaining the energy value of a single rock test block loaded to a destruction state in the oversized underground cavern through calculation;
s3, establishing a three-dimensional calculation model of the oversized underground cavity in the steps S1 and S2 by using a computer, calculating stress and strain fields of the oversized underground cavity under the full-section excavation and no support working condition, determining rock mass energy values of all units of the cavity, comparing the rock mass energy values of all units of the cavity with the energy values of the rock mass test blocks determined in the step S2 when the rock mass test blocks are loaded to a failure state, and determining an unstable region S in the oversized underground cavity;
s4, drawing up an excavation scheme of the ultra-large span underground cavern, determining an unstable region S in each excavation scheme according to the method in the step S3, and taking the excavation scheme with the minimum area of the unstable region S as an optimal excavation scheme;
s5, applying support measures to the oversized underground cavern under the excavation scheme obtained by screening in the step S4, calculating the stress and strain value of the cavern after support according to the calculation method in the step S3, and determining an unstable region S of the cavern;
and S6, adjusting and optimizing the support measures until the unstable area of the cavern is zero, and taking the support measures at the moment as a final support design scheme for drawing up the super-large underground cavern.
2. The method for determining the support design of the ultra-large span underground cavern based on the energy field balance as claimed in claim 1, wherein in the step S1: method for measuring and determining maximum principal stress sigma of planned super-large-span underground cavern by adopting hydrofracturing ground stress method1And minimum principal stress σ3。
3. The method for determining the support design of the ultra-large span underground cavern based on the energy field balance as claimed in claim 1, wherein the step S2 is specifically as follows: at least three groups of rock mass test blocks are respectively selected at the opening, the middle part and the tail part of the oversized underground cavern, and the number of the test blocks in each group of rock mass test blocks is more than or equal to 3; respectively carrying out uniaxial loading compression test and confining pressure sigma on rock mass test blocks of each group1And σ3The triaxial loading compression test; obtaining the energy values of all rock mass test blocks under the three loading working conditions, wherein the calculation formula is as follows:
wherein: eiMaximum principal stress sigma for confining pressure1In a triaxial loading compression experiment, calculating energy values of each rock mass test block when the rock mass test block is loaded to damage; ejMinimum principal stress sigma for confining pressure3In a triaxial loading compression experiment, calculating energy values of each rock mass test block when the rock mass test block is loaded to damage; ekCalculating the energy value of each rock mass test block when the rock mass test block is loaded to be damaged in the uniaxial compression test;
specifically, in the above formula: delta is the stress value in the loading process of the rock mass test block, epsilon is the strain value in the loading process of the rock mass test block, the longitudinal direction is parallel to the loading direction, the transverse direction is vertical to the loading direction, and delta isv、δhFor longitudinal and transverse stress values, epsilon, of rock mass test block during loadingv、εhLongitudinal and transverse strain values, epsilon, of rock mass test block in the loading processvmax is the sum delta of the longitudinal delta-epsilon curve of the rock mass test blockvStrain value, δ, corresponding to maxvmax is the maximum stress value in the longitudinal delta-epsilon curve of the rock mass test block, epsilonhmax is the longitudinal load to δvThe transverse strain value of the test block at max, and n is the number of rock mass test blocks under 3 loading working conditions;
respectively calculating the average value of energy under three loading working conditions,
take its minimum value
The energy value of a single rock block test block which is over-large and spans the underground cavern when the test block is loaded to be damaged is used.
4. The method for determining the supporting design of the oversized underground cavern based on the energy field balance as claimed in claim 3, wherein in the step S2, the rock mass test blocks are all cylindrical test blocks with the diameter and the height of 100 mm.
5. The method for determining the supporting design of the ultra-large span underground cavern based on the energy field balance as claimed in claim 3, wherein in the step S3, the calculation model units of the ultra-large span underground cavern adopt tetrahedrons, the side lengths are all 1m, the rock mass energy value of each unit is obtained by drawing delta-epsilon curves of each unit in x, y and z directions and calculating by the following calculation formula:
wherein: epsilon1x、ε1y、ε1zFor super large underground crossing over caverns and delta1x、δ1y、δ1zCorresponding strain value, δ1x、δ1y、δ1zThe initial stress values of the ultra-large underground cavern in the x, y and z directions are obtained; epsilon2x、ε2y、ε2zFor super large span of underground cavern and delta2x、δ2y、δ2zCorresponding strain value, δ2x、δ2y、δ2zThe maximum stress value delta of the rock mass test block in the x, y and z directions in a delta-epsilon curvex、δy、δzIs the stress value of the cavern in the x, y and z directions, epsilonx、εy、εzStrain of the cavern in x, y and z directions;
the energy E is more than 0.5EdThe unit area of (a) is defined as an unstable area S; edAnd loading the energy value of the single rock block test block which is over-large and spans the underground cavern until the test block is damaged.
6. The method for determining the support design of the ultra-large span underground cavern based on the energy field balance as claimed in claim 1, wherein the span of the ultra-large span underground cavern is more than or equal to 40 m.
7. The method for determining the support design of the ultra-large span underground cavern based on the energy field balance as claimed in claim 5, wherein in the step S3, the rock energy values of the units of the ultra-large span underground cavern are rock energy values near the vault, arch shoulder or arch foot area of the cavern.
8. The method for determining the support design of the ultra-large span underground cavern based on the energy field balance as recited in claim 5, wherein in the step S6, the optimization of the support measures comprises: on the basis of the original support measures, the anchoring force of a prestressed anchor cable is increased, anchor rods are lengthened, the thickness of sprayed concrete is thickened or an arch frame is erected.
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