CN111425252A - Tunnel construction soft rock large deformation grading method - Google Patents
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Abstract
The invention discloses a tunnel structure soft rock large deformation grading method which comprises the steps of obtaining the topographic and geomorphic, stratigraphic and lithological properties, geological structure and ground stress information of a tunnel section to be researched; judging whether the tunnel section to be researched meets set conditions, if so, entering the next step, and if not, ending the algorithm; judging whether the acquired ground stress data is complete, if so, entering the last step, and otherwise, entering the next step; primarily judging the large deformation grade of the surrounding rock structure of the tunnel section to be researched as I grade, II grade and III grade or not generating large deformation; acquiring the ground stress data which is not acquired before the tunnel to be researched by adopting field measurement or numerical inversion; and calculating the rock mass strength-stress ratio according to the maximum normal stress in the vertical hole axis direction and the rock mass strength, and judging the large deformation level of the tunnel surrounding rock structure to be researched in detail according to the rock mass strength-stress ratio.
Description
Technical Field
The invention belongs to the field of geological investigation of tunnel engineering, and particularly relates to a tunnel structure soft rock large deformation grading method.
Background
With the rapid development of underground engineering construction in the fields of traffic, water conservancy, energy and the like, a large number of deeply buried long and large tunnels emerge. The problem of large deformation of the surrounding rock of the tunnel is very prominent due to the complex geological structure background and the special mechanical property of the surrounding rock, and the safety and the long-term service stability of the tunnel structure are seriously threatened. Since the first serious large deformation of the surrounding rock occurs on the new Prolun tunnel I line in the beginning of the 20 th century, the large deformation disaster cases of the surrounding rock occur frequently in tunnel engineering at home and abroad, and great potential safety hazards and economic losses are brought to engineering construction.
Scholars at home and abroad develop a great deal of research work aiming at the problem of large deformation of the tunnel surrounding rock and obtain abundant research results, and define, define and grade the large deformation of the surrounding rock by adopting various indexes from different angles, so that the scholars do not form a unified understanding on the large deformation generation mechanism and the grading method. But numerous engineering examples show that: the large deformation of the surrounding rock often occurs in low-strength weak surrounding rocks such as fault fracture zones, low-grade metamorphic rocks and coal-series stratums, and is typical embodiment of extreme deformation and damage of the surrounding rock under the condition of high ground stress, and the inoculation of the surrounding rock is influenced by factors such as ground stress environment, geological structure, surrounding rock properties, hydrological conditions and dynamic disturbance.
It is worth noting that key control factors of large deformation of surrounding rocks, such as the lithology and structural characteristics of the surrounding rocks, high ground stress environment, geological conditions, hydrological conditions and the like, are closely related to the structure activity around the tunnel. In addition, the large deformation of the surrounding rock has the characteristics of progressive development, long duration, high deformation speed and the like, and the intrinsic power of the large deformation of the surrounding rock is derived from the structural stress formed by the mountain-making movement. It can be said that the factors of crustal stress distribution, geological structure, stratum lithology and the like of the structure motion control are the fundamental conditions for driving the occurrence of large deformation inoculation of the tunnel surrounding rock. Therefore, the strength-stress ratio cannot comprehensively represent and reflect the influence of the factors on the large deformation, and the classification method only considering the strength-stress ratio cannot accurately classify the large deformation of the tunnel surrounding rock.
Disclosure of Invention
Aiming at the defects in the prior art, the tunnel structure soft rock large deformation grading method provided by the invention considers the rock body performance of the tunnel section to be researched from multiple angles, so that the finally obtained soft rock large deformation grading is closer to the true value.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that:
the method for grading the large deformation of the soft rock in the tunnel construction comprises the following steps:
s1, acquiring the topographic and geomorphic, stratigraphic and lithological, geological and geostress data of the tunnel section to be researched;
s2, judging whether the surrounding rock of the tunnel section to be researched meets the set condition for constructing the large deformation of the soft rock according to the ground stress, the stratigraphic lithology and the geological structure data of the tunnel section to be researched, if so, performing the step S3, otherwise, the surrounding rock does not generate the large deformation, and finishing the algorithm;
s3, judging whether the geostress data obtained in the surveying process is complete, if so, entering the step S6, otherwise, entering the step S4;
s4, according to geological structure, rock natural strength, rock stratum thickness, rock stratum attitude and geophysical prospecting abnormal characteristic data, primarily judging the large deformation level of the surrounding rock structure of the tunnel section to be researched as I level, II level and III level or not to generate large deformation;
s5, acquiring the ground stress which is not acquired before the tunnel to be researched by adopting field measurement or numerical inversion;
s6, calculating the rock mass strength-stress ratio according to the maximum normal stress in the direction perpendicular to the hole axis and the rock mass strength, and determining the tectonic large deformation level of the tunnel surrounding rock to be researched according to the rock mass strength-stress ratio.
The invention has the beneficial effects that: when the safety and stability of the tunnel section to be researched are determined, the initial judgment is firstly carried out on the tunnel section to be researched through the ground stress, the stratigraphic lithology and the geological structure, the deformation grade of the rock is initially judged on the basis of the geological structure, the natural strength of the rock, the thickness of the rock, the rock formation occurrence and the geophysical prospecting abnormal characteristics under the condition that the possibility that the rock is deformed is determined, the strength-stress ratio of the integrity degree, the ground stress and the rock strength is combined, and then the final grading of the rock is obtained according to the strength-stress ratio.
According to the scheme, the rock mass is considered from 5 influence factors of stratum era, structural plane occurrence, rock strength, rock thickness and rock integrity, so that the large deformation grading of the tunnel section to be researched is more prepared and reliable; in the tunnel engineering, a supporting structure which is more favorable for improving the safety and stability of a tunnel section to be researched can be adopted in the tunnel excavation or later-stage tunnel maintenance process based on more accurate deformation grade conditions, so that the possibility of surrounding rock large deformation disasters in the tunnel is reduced.
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FIG. 1 is a flow chart of a tunnel construction soft rock large deformation grading method.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
Referring to fig. 1, fig. 1 shows a flow chart of a tunnel construction soft rock large deformation grading method; as shown in fig. 1, the method S includes steps S1 to S6.
In step S1, acquiring the topographic and geomorphic, stratigraphic and lithological, geological and geostress data of the tunnel segment to be researched; stratum era information, rock stratum thickness and attitude, included angle between rock stratum surface and tunnel axis direction and rock natural uniaxial compressive strength RcIntensity of rock mass Rcm(ii) a The geological structure comprises a fault fracture zone, the position and the property of a fold core part and an included angle between a structural surface and the axial direction of the tunnel.
The structural surface mentioned in the scheme generally refers to an important structural surface of a tunnel section to be researched, such as a fault and a weak interlayer which have a large influence on deformation, and if the tunnel section to be researched has no fault and the weak interlayer, the rock stratum surface is a main structural surface.
When the ground stress is obtained, any actual measurement method such as a hydraulic fracturing method, an acoustic emission method, a flat jack method and the like is generally adopted to obtain the ground stress.
In step S2, according to the geostress, the stratigraphic lithology and the geological structure data of the tunnel segment to be researched, it is determined whether the surrounding rock of the tunnel segment to be researched meets the set condition for constructing the large deformation of the soft rock, if so, step S3 is performed, otherwise, the surrounding rock does not generate the large deformation, and the algorithm is ended.
According to the scheme, the tunnel segment to be researched can be primarily screened under the set conditions of the step S2, and then the subsequent research is carried out under the condition that the tunnel segment to be researched is deformed, so that the on-site survey cost is reduced.
Step S1 and step S2 of the present solution can be understood as macro judgment in the present solution construction soft rock large deformation grading method.
When the method is implemented, the set conditions of the scheme at least comprise that the horizontal ground stress of the tunnel section to be researched is larger than the vertical ground stress; preferably, the set conditions further comprise that the lithology of the stratum is extremely soft rock, softer rock or broken hard rock, and/or that the passing area of the tunnel section to be researched is a fault broken zone, a fold core part, a joint dense zone, a bedding rock layer or a gentle dip rock layer.
When the lithology and the rock mass hardness degree of a tunnel section to be researched are determined, reference is mainly made to national standard of the people's republic of China: the classification is carried out by the classification standard of the engineering rock mass (GB/T50218-2014), and the classification standard refers to the following tables 1 and 2:
TABLE 1 grading of rock hardness
TABLE 2 division table of rock integrity
In step S3, the earth stress data associated with large deformation grading obtained during the survey (the complete earth stress includes the maximum positive stress σ of the vertical hole axis)maxMaximum horizontal principal stress σHMinimum horizontal principal stress σh) If the integrity is not complete, the step S6 is executed, otherwise, the step S4 is executed;
when the tunnel safety is investigated, the tunnel safety is usually required to be surveyed on the spot for many times, and the relatively complete data can be collected.
In step S4, according to the geological structure, the natural rock strength, the rock stratum thickness, the rock stratum attitude and the geophysical prospecting abnormal characteristics, the large deformation level of the surrounding rock structure of the tunnel section to be researched is primarily judged to be I level, II level and III level or not to generate large deformation; here, the first order is a slight large deformation, the second order is a moderate large deformation, and the third order is a severe large deformation.
Step S3 and step S4 of the present scheme can be understood as the initial judgment in the method for constructing the soft rock large deformation grading.
The classification of the tunnel section to be researched is realized mainly based on the following table 3:
table 3 structural soft rock large deformation grading initial judging table
In step S5, in-situ measurement or numerical inversion is used to obtain the geostress data that is not obtained before the tunnel to be studied;
step S5, if the earth stress which is not collected can be obtained by adopting a survey mode, the earth stress can be obtained by adopting the survey as much as possible, and thus, the collected data is relatively more accurate; if the residual ground stress can not be obtained by the surveying method, the residual ground stress is obtained by a numerical inversion method.
In step S6, calculating a rock mass strength-stress ratio according to the maximum normal stress in the direction perpendicular to the hole axis and the rock mass strength, and determining the tectonic large deformation level of the tunnel surrounding rock to be researched according to the rock mass strength-stress ratio; the relation between the strength-stress ratio of the rock mass and the large deformation grade of the structure is referred to table 4.
TABLE 4 structural soft rock large deformation grading Standard
When the rock mass of the tunnel to be researched is a fault affected zone, a fold core part, a turning end, a joint dense zone, a geophysical prospecting IV or V grade abnormal zone, the damage degree grade is heavier, and the rock mass integrity index is 0.45; when the rock mass of the tunnel to be researched is a fault fracture zone, a dense fold zone with frequent occurrence change or a geophysical V-level abnormal zone, the damage degree grade is serious, the damage degree grade of the rest situations is divided into slight, and the rock mass integrity index is 0.65.
The steps S4 to S6 of the present scheme can be understood as the detailed judgment (also the correction of the initial judgment) in the method for constructing the soft rock large deformation classification.
In an embodiment of the invention, before calculating the strength-stress ratio of the rock mass, the step S6 further includes classifying the structural influence degree of the surrounding rock of the tunnel segment to be researched into a mild, a heavy or a severe degree according to the stratigraphic lithology and geological structure of the tunnel to be researched;
and then calculating the rock mass strength-stress ratio according to the influence degree grade of the tunnel to be researched:
when the degree of influence is serious, the formula for calculating the strength-stress ratio of the rock mass is as follows:
M＝Rcm/σmax(1)
when the influence degree grade is heavy or slight, the formula for calculating the strength-stress ratio of the rock mass is as follows:
M＝a1a2a3a4Rcm/σmax＝a1a2a3a4KvRc/σmax(2)
wherein M is the strength-stress ratio of the rock mass; a is1The influence coefficient of the stratum era is shown; a is2Is a small included angle influence coefficient; a is3The rock strength influence coefficient; a is4Is the formation thickness influence coefficient; rcmThe rock mass strength; kvIs the rock integrity index; rcThe natural uniaxial compressive strength of the rock; sigmamaxThe maximum positive stress in the direction perpendicular to the hole axis.
The method calculates the rock mass strength-stress ratio pertinently by adopting different formulas under different geological conditions, and carries out structural large deformation classification according to the calculation result, thus having strong operability and high reliability of the classification result.
The stratum era influence coefficient of the scheme is selected through stratum era information, and how to select the influence coefficient is shown in a table 5; the small included angle influence coefficient is selected through the included angle between the structural surface and the tunnel axis, the small included angle influence is not considered in the wrinkle core part in the selection process, and how to select the small included angle influence coefficient is shown in a table 6; the rock strength influence coefficient is selected in table 7, and the rock thickness influence coefficient is selected in table 8.
TABLE 5 formation age influence coefficients
| Stratum era | From the third to the Jurassic period | From the period of trismus to the period of cambrian | Before earthquake denier |
| a1 | 1.1 | 1.0 | 0.9 |
TABLE 6 Small Angle influence coefficient
TABLE 7 rock Strength Effect coefficients
| Rock natural uniaxial compressive strength (MPa) | Rc≤5 | 5＜Rc≤15 | 15＜Rc≤30 | Rc＞30 |
| a3 | 0.9 | 1.0 | 1.1 | 1.2 |
TABLE 8 formation thickness coefficient of influence
In implementation, the method for acquiring the optimal rock mass strength comprises the following steps:
when the degree of influence is serious, the rock mass strength RcmThe acquisition method comprises the following steps:
if rock natural uniaxial compressive strength RcNot more than 15MPa, rock mass strength Rcm0.8-1.8MPa, if the natural uniaxial compressive strength of the rock is more than 15 and R is less thancNot more than 30MPa, rock strength Rcm1.8-3.0MPa, the natural uniaxial compressive strength R of rockcGreater than 30MPa, rock strength RcmIs 3.0-4.2 MPa;
when the influence degree is in a slight or heavy grade, the rock mass strength RcmObtaining by adopting any one of the following three methods:
the method comprises the steps of firstly, carrying out direct measurement of a field load plate test;
and the second method is to carry out an on-site shear test or a direct shear test according to the Mohr-Coulomb criterion:
wherein, cpThe peak cohesive force of the rock mass;
the peak internal friction angle of the rock mass;
3) calculating rock mass strength R according to rock mass integrity index obtained by table look-up 9 or rock mass and rock mass elastic wave longitudinal wave propagation velocity obtained by actual measurementcm：
Wherein v ispmThe propagation speed of longitudinal waves of elastic waves in the rock mass; v. ofprIs the propagation velocity of longitudinal waves of elastic waves in the rock.
TABLE 9 rock strength in severe zone affected by geological structure
In implementation, the scheme preferably selects the maximum positive stress sigma in the direction vertical to the hole axismaxThe acquisition method comprises the following steps:
maximum positive stress σ in the vertical hole axis when the failure level is slight or heavymaxThe obtaining method comprises the following steps:
calculating the in-situ maximum horizontal initial normal stress sigma of the vertical hole body according to the stress ellipsoidHorizontal max：
Wherein σHIs the maximum horizontal principal stress; sigmahIs the minimum horizontal principal stress; theta is an included angle between the maximum horizontal main stress and the axial direction of the tunnel;
comparing the in-situ maximum horizontal initial normal stress sigma of the vertical hole bodyHorizontal maxAnd vertical ground stress συThe maximum force of the two is selected as the maximum positive stress sigma of the vertical hole axismax；
Maximum positive stress σ of vertical hole axis when failure level is severemaxThe calculation formula of (2) is as follows:
σmax＝γH (6)
wherein gamma is the volume weight of the rock; h is the tunnel buried depth.
Compared with the existing grading method, the method is more reliable and comprehensive in consideration of the influence of the structure on the large deformation of the surrounding rock, closely related to the engineering geological investigation, in accordance with the engineering practice, strong in operability, quite objectivity and high in grading result reliability, and further adopts proper safety support measures for the research tunnel section to improve the safety and stability of the tunnel section to be researched.
The accuracy of the large deformation grading of the scheme is illustrated by taking a Lixiang line middle meaning tunnel and a salt edge tunnel as examples:
yili incense thread middle-meaning tunnel
The local stress of the pseudo-tunnel region in the Lixiang line is mainly structural stress, the lithology is mainly softer rock or softer rock, and large deformation grading work needs to be carried out. The circuit is located at the left side 650-1000 m of the back fracture (active fracture) of the dragon coil-arbor and passes through approximately in parallel, and the width of the fracture zone is 150-300 m. Looking up a table 3, wherein the tunnel large deformation division conditions are 0-30 degrees of wing part small included angle and medium-thickness layer shape; the uniaxial compressive strength of the rock is 10MPa, so the initial judgment level of large deformation of the medium-meaning tunnel structure is I level.
The new structure of the large deformation generation section of the medium-meaning tunnel moves strongly, the line is parallel to the scission of the west foot of the Yulong snow mountain, the superposition effect of multi-stage structure movement is experienced, the rock mass is mostly in a flaky structure, joint cracks develop, generally develop 3-5 groups of joints, mainly compressive joints, local sections develop with joint dense zones, the rock mass is broken loosely, the level of the large deformation influence degree of the geological structure is serious, and the rock mass strength stress ratio is calculated by adopting a corresponding formula.
In practical measurement, the uniaxial compressive strength of the rock is 10MPa, and the rock mass strength R is obtained by looking up a table 9cm＝0.8+[(1.8-0.8)/(15-0)]× (10-0) ═ 1.47MPa, and the maximum positive stress sigma in the direction perpendicular to the hole axis is calculated by the formula (1)max8.4MPa, and obtaining M-R by calculation according to a corresponding formula when the grade is seriouscm/σmaxAnd (4) 1.47/8.4-0.175, and further, the grade of large deformation of the soft rock of the medium-meaning tunnel construction is classified into II grade.
Second, salt side tunnel
The salt side tunnel region ground stress is mainly structural stress, lithology is schist, gneiss, ash, dark gray, lamellar and flaky, strong weathering to weak weathering is mainly, lithology is softer, and large deformation grading work is needed. The included angle between the rock stratum layer direction and the line direction is 0-25 degrees, the layer surface is inclined to the left bedding layer of the line, and interlayer combination is poor; joints develop to a great extent, most joints are 3 groups or more, the joints are disordered and irregular, and the rock mass is cut into fragments and blocks. Natural uniaxial compressive strength R of rockcAnd looking up a table 3 under the pressure of 18.27MPa, wherein the initial judgment level of the large deformation of the salt side tunnel structure is I level.
The salt side tunnel is located in the northern section of regional active fracture anaphora-green juice river active fracture, the fold structure develops, the joints are disorderly and dense, the influence degree of the geological structure on large deformation is relatively high, and therefore the corresponding formula is adopted for calculation.
Mainly including quartz schists, gneiss, lamellate and lamellate along the tunnel, looking up 5 to obtain stratum epoch influence coefficient a10.9; the included angle between the dominant structural surface and the axis of the hole is 0-25 degrees, and a small included angle influence coefficient a is obtained by looking up a table 620.75; natural uniaxial compressive strength R of rockcLooking up 7 to obtain the rock strength influence coefficient a under 18.27MPa31.1 as the ratio; the rock stratum is in a thin layer shape and a sheet shape, and the rock stratum thickness influence coefficient a is obtained according to the step S640.75; the influence degree of the geological structure on the large deformation is heavy, and the rock integrity index K is obtained according to the table 9v0.45; the rock mass strength R is calculated by the formula (2)cm＝KvRc0.45 × 18.27.27-8.22 MPa, maximum normal stress sigma perpendicular to the hole axismax23.35MPa, and calculating according to a formula to obtain M ═ a1a2a3a4Rcm/σmax0.9 × 0.75 × 1.1 × 0.75 × 8.22.22/23.3 is 0.20, and the large deformation grade of the soft rock of the salt side tunnel structure is classified into II grade.
In practice, the large deformation grade of the Yitong tunnel in the Lixiang line is grade II, the large deformation grade of the salt side tunnel is grade II, the large deformation grade obtained by adopting the scheme is completely coincided with the actual large deformation condition, and the large deformation condition of the tunnel to be researched can be accurately confirmed by the visible scheme, so that the tunnel construction and maintenance process is guaranteed, an accurate supporting mode is adopted according to the constructed large deformation grade, and the safety of the tunnel is guaranteed.
Claims (8)
1. The tunnel structure soft rock large deformation grading method is characterized by comprising the following steps:
s1, acquiring the topographic and geomorphic, stratigraphic and lithological, geological and geostress data of the tunnel section to be researched;
s2, judging whether the surrounding rock of the tunnel section to be researched meets the set condition for constructing the large deformation of the soft rock according to the ground stress, the stratigraphic lithology and the geological structure data of the tunnel section to be researched, if so, performing the step S3, otherwise, the surrounding rock does not generate the large deformation, and finishing the algorithm;
s3, judging whether the geostress data obtained in the surveying process is complete, if so, entering the step S6, otherwise, entering the step S4;
s4, according to geological structure, rock natural strength, rock stratum thickness, rock stratum attitude and geophysical prospecting abnormal characteristic data, primarily judging the large deformation level of the surrounding rock structure of the tunnel section to be researched as I level, II level and III level or not to generate large deformation;
s5, acquiring the ground stress data which are not acquired before the tunnel to be researched by adopting field measurement or numerical inversion;
s6, calculating the rock mass strength-stress ratio according to the maximum normal stress in the direction perpendicular to the hole axis and the rock mass strength, and determining the tectonic large deformation level of the tunnel surrounding rock to be researched according to the rock mass strength-stress ratio.
2. The grading method for large deformation of soft rock for tunnel construction according to claim 1, wherein the set conditions at least include that the horizontal ground stress of the tunnel section to be studied is greater than the vertical ground stress.
3. The method for grading large deformation of soft rock in tunnel construction according to claim 2, wherein the set conditions further comprise that the lithology of the stratum is very soft rock, softer rock or broken hard rock, and/or that the passing area of the tunnel section to be researched is a fault fracture zone, a fold core part, a joint dense zone, a bedding rock layer or a gentle dip rock layer.
4. The method for grading large deformation of tunnel tectonic soft rock according to claim 1, characterized in that, before calculating the strength-stress ratio of rock mass in step S6, the method further comprises grading the degree of structural influence of surrounding rock of the tunnel segment to be researched into slight, heavy or serious according to the stratigraphic lithology and geological structure of the tunnel to be researched;
and then, calculating the rock mass strength-stress ratio according to the structural influence degree grade of the tunnel surrounding rock to be researched:
when the degree of influence is serious, the formula for calculating the strength-stress ratio of the rock mass is as follows:
M＝Rcm/σmax
when the influence degree grade is heavy or slight, the formula for calculating the strength-stress ratio of the rock mass is as follows:
M＝a1a2a3a4Rcm/σmax＝a1a2a3a4KvRc/σmax
wherein M is the strength-stress ratio of the rock mass; a is1The influence coefficient of the stratum era is shown; a is2Is a small included angle influence coefficient; a is3The rock strength influence coefficient; a is4Is the formation thickness influence coefficient; rcmThe rock mass strength; kvIs the rock integrity index; rcThe natural uniaxial compressive strength of the rock; sigmamaxIs the maximum positive stress perpendicular to the hole axis.
5. The tunnel construction soft rock large deformation grading method according to claim 4, characterized in that the method for obtaining the rock body strength comprises the following steps:
when the degree of influence is serious, the rock mass strength RcmThe acquisition method comprises the following steps:
if rock natural uniaxial compressive strength RcLess than or equal to 15, rock mass strength Rcm0.8-1.8, if the natural uniaxial compressive strength of the rock is more than 15 and RcLess than or equal to 30, rock mass strength Rcm1.8-3.0, the natural uniaxial compressive strength R of rockcGreater than 30, rock mass strength Rcm3.0-4.2;
when the influence degree is in a slight or heavy grade, the rock mass strength RcmObtaining by adopting any one of the following three methods:
the method comprises the steps of firstly, carrying out direct measurement of a field load plate test;
and the second method is to carry out an on-site shear test or a direct shear test according to the Mohr-Coulomb criterion:
wherein, cpThe peak cohesive force of the rock mass;
the peak internal friction angle of the rock mass;
3) calculating rock mass strength R according to rock mass integrity index or rock mass and rock mass elastic wave longitudinal wave propagation velocity obtained by actual measurementcm：
Wherein v ispmThe propagation speed of longitudinal waves of elastic waves in the rock mass; v. ofprIs the propagation velocity of longitudinal waves of elastic waves in the rock.
6. The method for grading large deformation of soft rock in tunnel construction according to claim 4 or 5, wherein the maximum positive stress σ in the vertical hole axis directionmaxThe acquisition method comprises the following steps:
maximum positive stress σ in the direction perpendicular to the hole axis when the degree of failure is of the order of slight or heavymaxThe obtaining method comprises the following steps:
calculating the in-situ maximum horizontal initial normal stress sigma of the vertical hole body according to the stress ellipsoidHorizontal max：
Wherein σHIs the maximum horizontal principal stress; sigmahIs the minimum horizontal principal stress; theta is an included angle between the maximum horizontal main stress and the axial direction of the tunnel;
comparing the in-situ maximum horizontal initial normal stress sigma of the vertical hole bodyHorizontal maxAnd vertical ground stress συThe maximum force of the two is selected as the maximum positive stress sigma in the direction vertical to the hole axismax；
Perpendicular to the axis of the hole when the level of damage is severeMaximum positive stress sigmamaxThe calculation formula of (2) is as follows:
σmax＝γH
wherein gamma is the volume weight of the rock; h is the tunnel buried depth.
7. The method for grading large deformation of soft rock in tunnel construction according to claim 1, wherein the lithology of the stratum comprises stratum time information, thickness and attitude of the stratum, included angle between the stratum surface and the axial direction of the tunnel and natural uniaxial compressive strength R of the rockcIntensity of rock mass Rcm(ii) a The geological structure comprises a fault fracture zone, the position and the property of a fold core part and an included angle between a structural surface and the axial direction of the tunnel.
8. The grading method for large deformation of soft rock in tunnel construction according to claim 7, wherein the structural surface comprises a bedding surface, a sheet surface, a weak sandwich surface, a fault surface and/or a joint crack surface.
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