CN114969902A - Active support design method for plateau railway high-ground stress hard rock tunnel - Google Patents
Active support design method for plateau railway high-ground stress hard rock tunnel Download PDFInfo
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Abstract
The invention discloses an active support design method for a high-ground stress hard rock tunnel of a plateau railway, which comprises the following steps of: s1: determining the support type of the hard rock tunnel, and determining the impact load of the hard rock tunnel according to the support type; s2: checking and calculating the safety coefficient according to the impact load of the hard rock tunnel; s3: and (5) finishing the active support design of the hard rock tunnel according to the safety coefficient checking result. Aiming at the difficult problem of designing and constructing a high-ground-stress hard rock tunnel, the invention deduces an impact load calculation method of the rock burst tunnel from the energy release angle, combines loose loads, and provides a load calculation model and a support structure design method of the rock burst tunnel, wherein the support parameters of the rock burst tunnel provided by the design method can meet the requirement of the minimum safety factor of the tunnel specification, so that the tunnel structure is in a safe state and has certain safe reserve.
Description
Technical Field
The invention belongs to the technical field of tunnel support, and particularly relates to an active support design method for a high-ground-stress hard rock tunnel of a plateau railway.
Background
The plateau railway tunnel has the characteristics of long large deformation section and high ground stress, so that the problem of large deformation in the tunnel construction process is more severe, and the accumulated large deformation tunnel engineering experience at the present stage can not be directly suitable for the situation of over-high ground stress level.
The plateau railway javelin section tunnel passes through hard rocks such as granite and limestone for about 394km (47 percent), and the rock burst problem of different degrees exists in total 28 tunnels. The investigation reveals that the maximum horizontal ground stress of the Lashan tunnel in the color season is measured to be 35MPa, and the maximum horizontal ground stress of the Layue tunnel is simulated and predicted to reach 75 MPa. It can be seen that the ground stress level of the plateau railway jalin section far exceeds the existing tunnel engineering, and the design can not be analogized according to the existing engineering.
In view of the above, the invention provides a tunnel active support nursing idea and a corresponding design method based on the existing research results and by combining with engineering practices. An impact load calculation method of the rock burst tunnel is deduced based on an energy method, and meanwhile loose loads are combined to provide a load calculation model of the rock burst tunnel.
Disclosure of Invention
The invention provides an active support design method for a high-ground-stress hard rock tunnel of a plateau railway, aiming at solving the problems.
The technical scheme of the invention is as follows: the active support design method for the high-ground-stress hard rock tunnel of the plateau railway comprises the following steps:
s1: determining the support type of the hard rock tunnel, and determining the impact load of the hard rock tunnel according to the support type;
s2: checking and calculating the safety coefficient according to the impact load of the hard rock tunnel;
s3: and finishing the active support design of the hard rock tunnel according to the safety coefficient checking result.
Further, step S1 includes the following sub-steps:
s11: determining the support type of the hard rock tunnel, determining the rock burst tendency index of the hard rock tunnel based on the support type of the hard rock tunnel, and determining the rock burst grade according to the rock burst tendency index;
s12: determining the quality and impact speed of the blasting blocks of the hard rock tunnel according to different rock blasting grades;
s13: determining a dynamic load factor according to the impact speed of the blasting block of the hard rock tunnel;
s14: and determining the impact load of the hard rock tunnel according to the impact speed and the dynamic load factor of the blasting block.
Further, in step S11, the rock burst tendency index W et The calculation formula of (c) is:
W et ＝Φ SP /Φ ST
in the formula phi SP Representing elastic strain energy released by unloading, phi ST Elastic strain energy representing loss;
in step S11, the method for determining the rockburst level includes: if W et If the grade is more than or equal to 5.0, the rockburst grade is serious rockburst; if W is not more than 2.0 et <5.0, the rock burst grade is medium-low intensity rock burst; if W et <2.0，The rock burst rating is no rock burst.
Further, in step S12, the specific method for determining the quality of the explosive block of the hard rock tunnel includes: determining rock burst influence depths corresponding to different rock burst grades, determining the volume of a burst block according to the rock burst influence depths, and determining the quality of the burst block according to the volume and density of the burst block;
in step S12, the specific method for determining the impact velocity of the explosive block is as follows: and determining the kinetic energy of the explosion block according to the volume of the explosion block, and determining the impact speed of the explosion block according to the kinetic energy of the explosion block.
Further, in step S13, the formula for calculating the dynamic charge factor K is:
wherein Δ represents the maximum deflection of the impacted site, and Δ st The deflection caused by the dead weight is shown, v represents the impact velocity of the explosion block, and g represents the gravity acceleration.
Further, in step S14, the impact load q of the hard rock tunnel Impact of The calculation formula of (2) is as follows:
in the formula, K represents a dynamic charge factor, m represents the mass of the explosive block, g represents the gravity acceleration, and a represents the side length of the explosive block.
Further, in step S2, a safety factor is determined by a load structure method according to the impact load of the hard rock tunnel.
Further, in step S3, the specific method for completing the active support design of the hard rock tunnel includes: and judging whether the safety coefficient is greater than a preset safety coefficient control reference, if so, finishing the active support design of the hard rock tunnel, otherwise, adjusting the support parameters of the hard rock tunnel, and returning to the step S2.
The invention has the beneficial effects that: aiming at the difficult problem of designing and constructing a high-ground-stress hard rock tunnel, the invention deduces an impact load calculation method of the rock burst tunnel from the energy release angle, combines loose loads, and provides a load calculation model and a support structure design method of the rock burst tunnel, wherein the support parameters of the rock burst tunnel provided by the design method can meet the requirement of the minimum safety factor of the tunnel specification, so that the tunnel structure is in a safe state and has certain safe reserve.
Drawings
FIG. 1 is a flow chart of a method for designing an active support for a hard rock tunnel;
FIG. 2 is a test graph of rock burst tendency index;
FIG. 3 is a graph of released kinetic energy fraction versus internal friction angle;
FIG. 4 is a schematic diagram of the application of a load to a rock burst tunnel;
fig. 5 is a schematic diagram of an ANSYS numerical calculation model.
Detailed Description
The embodiments of the present invention will be further described with reference to the accompanying drawings.
Before describing specific embodiments of the present invention, in order to make the solution of the present invention more clear and complete, the definitions of the abbreviations and key terms appearing in the present invention will be explained first:
and (3) a load structure method: the load structure model refers to a calculation method corresponding to the load structure model, wherein the effect of the stratum on the structure is only generated to generate load (including active stratum pressure and passive stratum resistance) acting on the underground building structure, and the lining generates internal force and deformation under the effect of the load.
As shown in fig. 1, the invention provides an active support design method for a high-ground stress hard rock tunnel of a plateau railway, which comprises the following steps:
s1: determining the support type of the hard rock tunnel, and determining the impact load of the hard rock tunnel according to the support type;
s2: checking and calculating the safety coefficient according to the impact load of the hard rock tunnel;
s3: and (5) finishing the active support design of the hard rock tunnel according to the safety coefficient checking result.
In the embodiment of the invention, the stress of the rock around the hole is redistributed due to the tunnel excavation, the radial stress disappears and the tangential stress gradually increases, the rock around the hole is induced to generate surface tensile stress, further shear failure occurs, and the elastic potential energy is converted into kinetic energy to form rock burst. Therefore, the formation of the rock burst is related to the stress state (ground stress and cavern state) of the surrounding rock of the hole and the attribute (stored elastic potential energy) of the surrounding rock, so that the control on the rock burst can be analyzed from the aspects of improving the stress state of the surrounding rock and adjusting the attribute of the surrounding rock. The core idea of rock burst tunnel control is as follows: the radial force is actively provided by using the support, the rock stress state around the tunnel is improved, and the timeliness of the support force is emphasized in order to prevent rock burst caused by support lag.
The impact load calculation on the supporting structure comprises three parts, namely the size of released energy, the size and the speed of a blasting block body and the load acting on the supporting structure.
First, by energy analysis, it is clear how much strain energy is stored in the rock mass and how much of the energy it releases can be converted into explosive mass kinetic energy.
Secondly, the size and speed of the explosive block body are determined. By investigating the occurrence characteristics of the existing rock burst engineering, the characteristics of the rock burst in different grades, such as the shape of the burst block, the size of the block body and the like, can be obtained. On the premise that the kinetic energy of the explosion block is known, the velocity of the explosion block can be obtained by adopting a kinetic energy calculation formula.
Finally, after two key parameters of the size of the explosive block body and the speed of the explosive block are obtained, the size of the load acting on the supporting structure can be calculated by adopting a structural mechanics method.
In addition to the difference in size and speed of the explosive blocks due to the difference in the rock burst occurrence grade, the magnitude of the load acting on the supporting structure is also related to the rigidity of the supporting structure. Even if the same size block acts on the supporting structure at the same speed, the supporting structure has different rigidity, and the size of bearing load and deformation of the supporting structure is different. When the supporting structure has higher rigidity, the deformation of the supporting structure under the impact of the explosion block is small, and the borne impact load is large. When the rigidity of the supporting structure is lower, the deformation of the supporting structure under the impact of the explosion block is large, and the borne impact load is small. Rock burst occurs when the support is not yet applied, and although the burst mass is ejected at a certain speed, no load is applied to the support structure because the support structure is not present.
From the above analysis it can be seen that the impact load acting on the supporting structure is not determinate. In actual engineering, the type and parameters of the supporting structure can be determined by analogy to similar engineering, and the impact load acting on the supporting structure is calculated according to the type and parameters. The safety factor of the supporting structure is determined by a load-structure method, so that the safety of the supporting structure is quantitatively judged. And (3) adjusting the support parameters of the support structure which does not meet the standard requirements of the safety coefficient or has less safety reserve although meeting the requirements, and calculating according to the adjusted support parameters until the safety requirements of the engineering are met.
In the embodiment of the present invention, step S1 includes the following sub-steps:
s11: determining the support type of the hard rock tunnel, determining the rock burst tendency index of the hard rock tunnel based on the support type of the hard rock tunnel, and determining the rock burst grade according to the rock burst tendency index;
s12: determining the quality and the impact speed of the blasting blocks of the hard rock tunnel according to different rock blasting grades;
s13: determining a dynamic load factor according to the impact speed of the blasting block of the hard rock tunnel;
s14: and determining the impact load of the hard rock tunnel according to the impact speed and the dynamic load factor of the blasting block.
In the embodiment of the present invention, in step S11, the rock burst tendency index W et The calculation formula of (2) is as follows:
W et ＝Φ SP /Φ ST
in the formula phi SP Representing elastic strain energy released by unloading, phi ST Elastic strain energy representing loss;
in step S11, the method for determining the rockburst level includes: if W et If the grade is more than or equal to 5.0, the rockburst grade is serious rockburst; if W is not more than 2.0 et <5.0, the rock burst grade is medium-low intensity rock burst; if W et <2.0, the rockburst rating is no rockburst.
In embodiments of the invention, the energy stored in the rock mass is not released entirely as kinetic energy, and some of the energy is dissipated as thermal and surface energy. Different scholars respectively derive a calculation formula of the dissipated energy, but the calculation formula has more parameters and is complex in calculation, and the calculation formula is difficult to obtain in actual engineering. The invention does not consider other energy except kinetic energy, but focuses on how much strain energy accumulated in the rock mass can be converted into kinetic energy and released in a rock burst mode.
The calculation of the magnitude of the released kinetic energy comprises two processes, firstly, external force is applied to do work, the energy is accumulated in a rock body, in the process, a part of energy is used for expanding cracks between degraded surrounding rocks, rock burst can occur only when a critical condition is reached, and in the process of releasing the energy, the part of energy can not be released any more, namely, the strain energy contained in the surrounding rocks comprises elastic strain energy and plastic strain energy; another process is that when the rock burst occurs, part of the energy is released in the form of sound wave energy, heat energy and the like, but not all of the energy is released in the form of kinetic energy. The two processes are analyzed respectively, and finally, the kinetic energy released when the rock burst occurs is determined.
The energy release rate of the first process can be determined experimentally, and the rockburst tendency index test curve is shown in fig. 2. Selecting different W according to different grades of rock burst et The ratio of the elastic strain energy to all the strain energy contained in the rock mass can be calculated according to the value. When the test is carried out under certain conditions, specific tunnel engineering site surrounding rocks are taken, the uniaxial compressive strength test of rocks is carried out, the rock burst tendency index value is obtained, and then the elastic strain energy occupation ratio of the surrounding rock conditions is determined. The ratio of kinetic energy to all elastic strain energy released in the second process, the ratio of kinetic energy to various energy released in the rock shear failure process, and the internal friction angle are related as shown in fig. 3. As can be seen from fig. 3, the proportion of kinetic energy in the released energy is minimum at an internal friction angle of 45 °, and is only 30%. As the internal friction angle approaches 0 ° and 90 °, the proportion of kinetic energy gradually increases until it reaches a maximum value of 60 °. The values can be taken according to the above figure with the magnitude of the internal friction angle known. In the absence of data, the value can be 60 DEG according to the worst condition。
In the embodiment of the present invention, in step S12, the specific method for determining the quality of the explosive block of the hard rock tunnel includes: determining rock burst influence depths corresponding to different rock burst grades, determining the volume of a burst block according to the rock burst influence depths, and determining the quality of the burst block according to the volume and density of the burst block;
in step S12, the specific method for determining the impact velocity of the explosive block is as follows: and determining the kinetic energy of the explosion block according to the volume of the explosion block, and determining the impact speed of the explosion block according to the kinetic energy of the explosion block.
In the embodiment of the invention, the spalling type rock burst body is generally shell-shaped or flaky, the slight ejection type rock burst is a slender elliptic sheet body, and the bursting type rock burst rock body is mostly a block body. Generally, mild and moderate rock bursts are dominated by spalling, and strong and very strong rock bursts are dominated by catapulting. Spalling type rock burst can be spalled for several times, and the characteristics of a single rock burst body are counted only and cannot completely reflect the whole process. Also, exfoliation may be understood as ejection, but at a lower ejection speed. The blocks ejected by the ejection type rock burst are incomplete, more than one block can be ejected from the same explosion pit at one time, and some blocks can be broken into a plurality of blocks after falling to the ground. Comprehensively considering, the size of the blasting block can be more reasonable by analyzing and calculating from the point of view of the blasting pits, and the blasting pits are most common in a V shape.
TB 10003-2016 railway Tunnel design Specification gives the depth of impact at different levels of rock burst as shown in Table 1.
TABLE 1
And selecting the influence depths of different rock burst grades, and calculating the size of the burst block according to a square cone to obtain the volume of the burst block. Rock burst mainly occurs in hard rocks such as granite, limestone, marble rock, gneiss and the like, the density of the rock masses is not greatly different and can be uniformly distributed according to 2.75t/m 3 And (4) taking values. And multiplying the density by the volume to obtain the quality of the explosive block. The resulting calculated burst mass quality is shown in table 2.
TABLE 2
The calculated burst speed is shown in table 3.
TABLE 3
In the embodiment of the present invention, in step S13, the formula for calculating the dynamic charge factor K is:
wherein Δ represents the maximum deflection of the impacted site, and Δ st The deflection caused by the dead weight is shown, v represents the impact velocity of the explosion block, and g represents the gravity acceleration.
In the embodiment of the invention, the support deformation is caused by the fact that the explosion block acts on the support structure at a certain speed, in the process, the height change of the explosion block enables the support structure to have a vertical component of a displacement value at an acting point of the support structure, and the displacement value of the support is very small, so that the gravitational potential energy variation of the explosion block is very small and is not considered. The kinetic energy of the explosive mass is fully converted into strain energy of the structure. Kinetic energy
Strain energy
Then
Wherein m represents the mass of the explosive block, v represents the impact velocity of the explosive block, F represents the maximum impact force, and Delta represents the impacted massMaximum deflection of the site. The calculation is carried out according to the structural mechanics content, and the relation between F and delta is known to be
In the formula, R represents the equivalent radius of the tunnel, E represents the elastic modulus of the supporting structure, and I represents the bending coefficient of the section. In the simultaneous manner, can
In the formula,. DELTA. st Which represents the deflection caused by the self-weight,
the maximum deflection delta of the impacted part and the deflection delta caused by the dead weight st And (5) obtaining the dynamic charge factor K by comparison.
According to a calculation formula of the dynamic load factor K, the dynamic load factor of the impact load acting on the supporting structure is related to the rigidity of the supporting structure. Therefore, the adopted supporting parameters are different, and the impact load acting on the supporting structure is also different.
In the embodiment of the invention, in the step S14, the deadweight of the explosive block is enlarged by the times of the dynamic load factor, and the explosive block is acted on the structure in a uniformly-distributed load mode, namely the impact load q of the hard rock tunnel Impact of The calculation formula of (2) is as follows:
in the formula, K represents a dynamic charge factor, m represents the mass of the explosive block, g represents the gravity acceleration, and a represents the side length of the explosive block.
In the embodiment of the invention, in step S2, a safety factor is determined by using a load structure method according to the impact load of the hard rock tunnel.
In the embodiment of the invention, the hard rock tunnel is most likely to generate rock burst due to the most obvious concentration of compressive stress near the arch crown and the arch bottom. And meanwhile, the probability of rock burst of the vault is higher than that of the vault under the action of gravity. Through the analysis, the impact load acting part is arranged on the vault, and the acting range is half of the length of the explosion block edges on the two sides of the vault.
The rock burst tunnel safety factor detection and calculation adopts a load-structure calculation model, when a load is applied, the surrounding rock pressure calculated according to TB 10003-2016 railway tunnel design specification is applied, then the impact load calculated by the previous section is applied, the action part of the impact load is a vault, and the action range is half of the length of the burst block edges on two sides of the vault. The rockburst tunnel loading is applied as shown in figure 4.
In the embodiment of the present invention, in step S3, the specific method for completing the active support design of the hard rock tunnel includes: and judging whether the safety coefficient is greater than a preset safety coefficient control reference, if so, finishing the active support design of the hard rock tunnel, otherwise, adjusting the support parameters of the hard rock tunnel, and returning to the step S2.
The present invention will be described with reference to specific examples.
And selecting a typical Erlangshan (Bayu) tunnel rockburst section, establishing a load-structure model by adopting the impact load calculation method, and verifying the safety of the load-structure model.
The Erlangshan tunnel is a single-hole double-line tunnel, and rockburst is frequent in the construction process. Within the length of 120m between the flat guide K261+ 820-K261 +940, the phenomena of continuous bursting, stripping and chipping off are serious, a slight ejection phenomenon occurs, the rock burst influences about 1m in depth and belongs to medium rock burst. The section has a buried depth of 430-480 m, a ground stress of 15-20 MPa, class III surrounding rocks, and lithology of limestone, marl interlayer and sandy mudstone.
When the tunnel is firstly tunneled to the tunnel section in the initial construction stage of the section, no attention is paid to the construction unit of the rock burst phenomenon, and no effective prevention and control measures are taken. When the excavation and tunneling reach K261+909, severe rock burst activity occurs, and the construction is interrupted. The post-adjustment construction method adopts the following parameters: firstly, C20 concrete with the thickness of 12 cm; 22, a system mortar anchor rod is 2-2.5 m long, 100cm apart, arranged in a quincunx shape, and a base plate is added; and thirdly, 8cm reinforcing mesh with the interval of 20cm multiplied by 20 cm. And obtain better prevention and treatment effect.
By adopting the impact load calculation method, the explosion block speed is 2.37m/s, and the maximum explosion block volume is 0.33m 3 And according with the field description. And calculating the rock burst impact load to be 31.93kPa by adopting the adjusted parameters. Numerical simulations were performed using Ansys, and the model was established as shown in fig. 5. The calculated safety coefficient is 2.89, is a safety coefficient control standard which is tension control and is higher than the specification 2.7, and accords with the description of obtaining better control effect on site.
When the above load calculation is employed, it should be noted that: the magnitude of the geostress in the above calculation is assumed, and if the magnitude of the geostress is determined in the actual engineering, the actual engineering determination value is adopted. Secondly, the calculation only carries out preliminary research on the impact load acting on the supporting structure, only the effect of the supporting structure is considered in the research, and auxiliary measures such as surrounding rock sprinkling and stress relief are not fully considered.
The invention has the beneficial effects that: aiming at the difficult problem of designing and constructing a high-ground-stress hard rock tunnel, the invention deduces an impact load calculation method of the rock burst tunnel from the energy release angle, combines loose loads, and provides a load calculation model and a support structure design method of the rock burst tunnel, wherein the support parameters of the rock burst tunnel provided by the design method can meet the requirement of the minimum safety factor of the tunnel specification, so that the tunnel structure is in a safe state and has certain safe reserve.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.
Claims (8)
1. A design method for active support of a high-ground-stress hard rock tunnel of a plateau railway is characterized by comprising the following steps:
s1: determining the support type of the hard rock tunnel, and determining the impact load of the hard rock tunnel according to the support type;
s2: checking and calculating the safety coefficient according to the impact load of the hard rock tunnel;
s3: and (5) finishing the active support design of the hard rock tunnel according to the safety coefficient checking result.
2. The active support design method for the high-ground-stress hard rock tunnel of the plateau railway according to claim 1, wherein the step S1 comprises the following sub-steps:
s11: determining the support type of the hard rock tunnel, determining the rock burst tendency index of the hard rock tunnel based on the support type of the hard rock tunnel, and determining the rock burst grade according to the rock burst tendency index;
s12: determining the quality and the impact speed of the blasting blocks of the hard rock tunnel according to different rock blasting grades;
s13: determining a dynamic load factor according to the impact speed of the blasting block of the hard rock tunnel;
s14: and determining the impact load of the hard rock tunnel according to the impact speed and the dynamic load factor of the blasting block.
3. The active support design method for the high-ground-stress hard rock tunnel of the plateau railway as claimed in claim 2, wherein in the step S11, the rockburst tendency index W is et The calculation formula of (2) is as follows:
W et ＝Φ SP /Φ ST
in the formula phi SP Representing elastic strain energy released by unloading, phi ST Elastic strain energy representing loss;
in step S11, the method for determining the rockburst level includes: if W et If the grade is more than or equal to 5.0, the rockburst grade is serious rockburst; if 2.0. ltoreq. W et <5.0, the rock burst grade is medium-low intensity rock burst; if W et <2.0, the rockburst rating is no rockburst.
4. The active support design method for the high-geostress hard rock tunnel of the plateau railway as claimed in claim 2, wherein in the step S12, the specific method for determining the quality of the explosive block of the hard rock tunnel is as follows: determining rock burst influence depths corresponding to different rock burst grades, determining the volume of a burst block according to the rock burst influence depths, and determining the quality of the burst block according to the volume and density of the burst block;
in step S12, the specific method for determining the impact velocity of the explosive block is as follows: and determining the kinetic energy of the explosion block according to the volume of the explosion block, and determining the impact speed of the explosion block according to the kinetic energy of the explosion block.
5. The active support design method for the plateau railway high-geostress hard rock tunnel according to claim 2, wherein in the step S13, the calculation formula of the dynamic load factor K is as follows:
wherein Δ represents the maximum deflection of the impacted site, and Δ st The deflection caused by the dead weight is shown, v represents the impact velocity of the explosion block, and g represents the gravity acceleration.
6. The active support design method for high-geostress hard rock tunnel of plateau railway as claimed in claim 2, wherein in the step S14, the impact load q of the hard rock tunnel Impact of The calculation formula of (c) is:
in the formula, K represents a dynamic charge factor, m represents the mass of the explosive block, g represents the gravity acceleration, and a represents the side length of the explosive block.
7. The active support design method for the high-ground-stress hard rock tunnel of the plateau railway as claimed in claim 1, wherein in the step S2, a safety factor is determined by using a load structure method according to the impact load of the hard rock tunnel.
8. The active support design method for the high-geostress hard rock tunnel of the plateau railway according to claim 1, wherein in the step S3, the concrete method for completing the active support design of the hard rock tunnel is as follows: and judging whether the safety coefficient is greater than a preset safety coefficient control standard, if so, finishing the active support design of the hard rock tunnel, otherwise, adjusting the support parameters of the hard rock tunnel, and returning to the step S2.
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