Method for discriminating soft rock deformation based on harmful deformation index

Abstract

The invention discloses a soft rock deformation discrimination method based on a harmful deformation index. The method comprises the following steps: calculating a comprehensive strength-stress ratio; determining an activity coefficient of underground water; calculating a rock mass water rational coefficient; determining a tunnel shape coefficient according to the tunnel section shape; determining a long-term strength reduction coefficient; the above factors are comprehensively considered, the harmful deformation index of the soft rock tunnel is calculated, and the surrounding rock deformation category is determined according to the obtained harmful deformation index in contrast with a soft rock tunnel harmful deformation grading table. According to the method, the physical and mechanical characteristics, geological conditions, hydrological environment and time effect of the surrounding rock of the soft rock tunnel are comprehensively considered, the defect that dynamic factors and environmental influence are neglected in a traditional method is overcome, deformation recognition is more comprehensive and accurate, the risk prediction capacity is effectively improved, and the risk prediction efficiency is improved. A new thought and method are provided for deformation identification and classification in soft rock tunnel engineering, and valuable reference is provided for application of similar engineering.

Description

Technical Field

[0001] The invention belongs to the technical field of soft rock tunnel engineering, and in particular, relates to a method for identifying and grading harmful deformation of a red layer soft rock tunnel. Background Art

[0002] Soft rock tunnels often experience large deformations during excavation, and corresponding support is required according to different deformation conditions, so it is very important to accurately and quickly determine the deformation type. The traditional method of determining large deformations of soft rocks is mainly based on strength-stress ratio analysis. However, a single stress-strength ratio indicator usually cannot accurately reflect the occurrence environment and complexity of the surrounding rock, and a more accurate solution is needed. Summary of the invention

[0003] The purpose of this invention is to propose a method for distinguishing soft rock deformation based on harmful deformation index, overcome the limitations of traditional methods, comprehensively consider factors such as the physical and mechanical properties of the surrounding rock and the characteristics of the occurrence environment, and accurately identify and evaluate the stability of the surrounding rock and the risk of large deformation.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A method for determining soft rock deformation based on a harmful deformation index comprises the following steps:

[0006] Step S1: Calculate the comprehensive strength stress ratio J by combining lithology, geostress field and rock mass structural characteristics σ :

[0007]

[0008] In the above formula, R b is the uniaxial compressive strength of rock, R cm is the uniaxial compressive strength of rock mass, σ 0 is the major principal stress value of the geostress, and k is the ratio of the major principal stress to the minor principal stress of the geostress.

[0009] Step S2: Determine the activity coefficient J of groundwater w , as shown in Table 1:

[0010] Table 1 Groundwater activity coefficient J w Value

[0011]

[0012]

[0013] Step S3: According to the three indicators of disintegration, expansion and softening, the disintegration resistance index I d , expansion rate V d, softening coefficient K s To characterize and calculate the rock mass water coefficient J a :

[0014]

[0015] In the above formula, the rock mass water coefficient J a It is generally greater than 1. The larger the hydraulic coefficient is, the more obvious the effect of rock degradation when exposed to water is.

[0016] Step S4: Determine the tunnel shape coefficient D according to the tunnel cross-sectional shape i :

[0017] D i =λR q

[0018] In the above formula, λ is the shape coefficient of the tunnel section. Since there are many horseshoe-shaped sections, λ = 1.0 when the tunnel section is horseshoe-shaped, but λ = 0.8 when the tunnel section is circular. q is the equivalent radius of the tunnel.

[0019] When the cross section is horseshoe-shaped, the calculation formula is as follows:

[0020]

[0021] Where A is the area of ​​the tunnel section.

[0022] Step S5: According to the attenuation law of surrounding rock strength under long-term load, the long-term strength reduction factor J is obtained by laboratory test or numerical simulation analysis. c , specifically:

[0023]

[0024] In the above formula, σ c It refers to the maximum strength value at which rock can remain stable without being damaged under continuous load.

[0025] Step S6: Considering the basic mechanical properties of soft rock in tunnels, the characteristics of the environment and the time effect, the harmful deformation index H of soft rock tunnels is proposed. s :

[0026]

[0027] Where: J σ is the comprehensive strength stress ratio, J w is the groundwater activity coefficient, J a is the rock mass water resistance coefficient, D i is the tunnel shape factor, J c is the long-term strength reduction factor.

[0028] Step S7: According to the obtained harmful deformation index, the harmful deformation classification table of soft rock tunnels is compared, as shown in Table 2, to determine the surrounding rock deformation category.

[0029] Table 2: Classification of harmful deformation in soft rock tunnels

[0030] Grading Main description Safety deformation The rock mass has good strength and integrity, and the surrounding rock itself can remain stable First level harmful deformation The surrounding rock has large deformation, but the deformation rate is relatively small and stable over a period of time. Secondary harmful deformation The surrounding rock has large deformation and a high deformation speed. If the support is not strengthened in time, it will be destroyed quickly. Level 3 harmful deformation The surrounding rock deforms greatly, the deformation rate is very fast, and a large amount of water and soil are gushing out.

[0031] Further optimization, in step S3, the three indicators of disintegration, expansion and softening are obtained by the following method:

[0032] The disintegration resistance index I was obtained by testing the disintegration resistance of rock samples. d ; The expansion rate V is obtained according to the cementation characteristics and weathering degree of the rock d The soft rock samples were immersed in water for 48 hours to become saturated samples. The saturated samples and natural samples were subjected to uniaxial compression tests. The ratio of their compressive strengths is the softening coefficient K. s .

[0033] Further optimization, in step S4, when the tunnel cross section is horseshoe-shaped, λ=1.0, and when the tunnel cross section is circular, λ=0.8; R q is the equivalent radius of the tunnel. When the tunnel cross-section is horseshoe-shaped, its calculation formula is as follows:

[0034]

[0035] In the above formula: A is the area of ​​the tunnel section.

[0036] Further optimization, in step S5, the specific process is as follows:

[0037] S5.1: Carry out triaxial mechanical tests on rock mass under seepage conditions to obtain mechanical parameters of rock mass seepage-stress coupling tests;

[0038] S5.2: Carry out triaxial rheological mechanical tests under different osmotic pressure conditions using the obtained mechanical parameters to obtain triaxial rheological test curves under different osmotic pressure conditions;

[0039] S5.3: By analyzing the rheological test data under different stress levels, a series of stress-strain isochronal curves are drawn; when the curve has an obvious inflection point, the curve segments on both sides of the inflection point are linearly fitted, and the stress value corresponding to the intersection of the two fitting straight lines is the long-term strength σ of the rock. c ;

[0040] S5.4: Calculation of long-term strength reduction factor J of rock mass c :

[0041]

[0042] Further optimization, in step S7, the harmful deformation is graded according to the following standards, specifically:

[0043] When the harmful deformation index is 0-0.5, it is an extremely severe extrusion deformation range and is judged as level 3 harmful deformation;

[0044] When the harmful deformation index is between 0.5 and 1.5, it is a severe extrusion deformation range and is judged as secondary harmful deformation;

[0045] When the harmful deformation index is between 1.5 and 3.5, it is in the medium extrusion deformation range and is judged as first-level harmful deformation;

[0046] When the harmful deformation index is greater than 3.5, it is in the non-extrusion deformation range and is judged as safe deformation.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The present invention comprehensively considers the physical and mechanical properties of the surrounding rock of soft rock tunnels, geological conditions, hydrological environment and time effects, overcomes the shortcomings of traditional methods that ignore dynamic factors and environmental influences, thereby making deformation identification more comprehensive and accurate, effectively improving the risk prediction ability, and providing new ideas and methods for deformation identification and classification in soft rock tunnel projects, providing valuable reference for the application of similar projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flow chart of the method for distinguishing soft rock deformation based on harmful deformation index according to the present invention;

[0050] Figure 2 This is the relationship between the collapse resistance index and the number of cycles of the red bed soft rock in central Yunnan in this example;

[0051] Figure 3 It is the triaxial rheological test curve under different osmotic pressure conditions;

[0052] Figure 4 It is the stress-strain isochronous curve;

[0053] Figure 5 This is a statistical chart of harmful deformation of water diversion in central Yunnan;

[0054] Figure 6 This is a curve diagram for predicting extrusion deformation based on the harmful deformation index. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] like Figure 1 As shown, a method for determining soft rock deformation based on harmful deformation index comprises the following steps:

[0057] Step S1: Measure the uniaxial compressive strength R of the rock sample through experiments b , uniaxial compressive strength of rock mass R cm As well as the values ​​of major principal stress and minor principal stress of geostress.

[0058] In this embodiment, according to the construction practice of the Chuxiong section of the Dianzhong Water Diversion Project, 50 cases of large deformation of soft rock in the tunnel of the Chuxiong section of the Dianzhong Water Diversion Project were collected. As shown in Table 3, the ground stress, rock / rock mass strength, etc. of 10 groups of cases are given.

[0059] Table 3 Statistics of squeeze deformation characteristics of soft rock layer in the tunnel of Dianzhong Water Diversion Project

[0060]

[0061] According to the data in the example, calculate the comprehensive strength stress ratio J of each group σ :

[0062]

[0063] Step S2: According to the description of groundwater status in each instance, obtain each group of groundwater activity coefficients J w ;

[0064] Step S3: First, the rock samples are subjected to a disintegration resistance test to obtain a relationship diagram between the disintegration resistance index of the red bed soft rock in central Yunnan and the number of cycles, such as Figure 2 As shown, the disintegration resistance coefficient I of each group is obtained. d Secondly, most of the long and large diversion tunnels of the Dianzhong Water Diversion Project pass through weakly weathered to fresh rock mass, and the rock expansion is less affected. d ; Secondly, the soft rock sample was immersed in water for 48 hours to become a saturated sample. The saturated sample and the natural sample were subjected to uniaxial compression tests respectively. The ratio of the compressive strength of the two is the softening coefficient K s , the test results are shown in Table 4.

[0065] Table 4 Statistics of average values ​​of red layer soft rock softening test

[0066]

[0067] Finally, calculate the hydraulic coefficient J of each rock mass group a :

[0068]

[0069] Step S4: First, calculate the equivalent radius R of each group of tunnels according to the area of ​​the tunnel section q ; Secondly, determine the shape coefficient of each group of tunnel sections according to the shape of the tunnel section. When the section is horseshoe-shaped, λ = 1.0, and when the section is circular, λ = 0.8; Finally, calculate the shape coefficient D of each group of tunnels i :

[0070] D i =λR q

[0071] Step S5: First, triaxial mechanical tests of red bed soft rock under different confining pressures (5.0 MPa, 7.0 MPa and 10.0 MPa) and different seepage pressures (1.0 MPa, 2.0 MPa, 3.0 MPa) are carried out. The test scheme is shown in Table 5.

[0072] Table 5: Triaxial mechanical test scheme for red bed soft rock under seepage conditions

[0073]

[0074]

[0075] Secondly, the seepage stress coupling test of red soft rock under confining pressure of 5.0, 7.0, 10.0 MPa and seepage pressure of 1.0, 2.0, 3.0 MPa was carried out. The mechanical parameters of the seepage stress coupling test of red soft rock were calculated by fitting using the classic Mohr-Coulomb criterion, and the results are shown in Table 6.

[0076] Table 6 Mechanical parameters of red layer soft rock

[0077]

[0078] Thirdly, based on the triaxial mechanical test results of red bed soft rock, triaxial rheological mechanical tests were carried out under different seepage pressure conditions, and triaxial rheological test curves under different seepage pressure conditions were obtained. The results are as follows: Figure 3 As shown. Among them, Figure 3 (a) is the rheological test curve at confining pressure of 10.0 MPa and osmotic pressure of 1.0 MPa, (b) is the rheological test curve at confining pressure of 10.0 MPa and osmotic pressure of 2.0 MPa, and (c) is the rheological test curve at confining pressure of 10.0 MPa and osmotic pressure of 3.0 MPa.

[0079] Again, by analyzing the rheological test data at different stress levels, a series of stress-strain isochronal curves were drawn. The results are as follows: Figure 4 As shown, Figure 4 (a) is the curve of confining pressure 10.0MPa and seepage pressure 1.0MPa, (b) is the curve of confining pressure 10.0MPa and seepage pressure 2.0MPa, and (c) is the curve of confining pressure 10.0MPa and seepage pressure 3.0MPa. When the curve has an obvious inflection point, the curve segments on both sides of the inflection point are linearly fitted, and the stress value corresponding to the intersection of the two fitting straight lines is the long-term strength of the rock. The results are shown in Table 7.

[0080] Table 7: Triaxial rheological parameters of red bed soft rock under seepage pressure conditions

[0081]

[0082] Finally, when the test specimen is a complete rock block, the long-term strength reduction factor J c for:

[0083]

[0084] Step S6: Calculate the harmful deformation index of each group, the formula is:

[0085]

[0086] Step S7: First, the harmful deformation index of 50 instance data is statistically analyzed to obtain the large deformation index and deformation law. The results are as follows: Figure 5 As shown, Figure 5 (a) is the value result of harmful deformation, the horizontal axis is the case number, the vertical axis is the corresponding deformation (unit: mm), (b) is the statistical result of the occurrence location of harmful deformation, (c) is the statistical result of surrounding rock category, and (d) is the statistical result of geological body type.

[0087] The deformation area is divided into four intervals according to the harmful deformation index: the interval with a harmful deformation index of 0 to 0.5 is an extremely severe extrusion deformation interval (level three harmful deformation); the interval with a harmful deformation index of 0.5 to 1.5 is a severe extrusion deformation interval (level two harmful deformation); the interval with a harmful deformation index of 1.5 to 3.5 is a moderate extrusion deformation interval (level one harmful deformation); the interval with a harmful deformation index greater than 3.5 is a no extrusion deformation interval (safe deformation).

[0088] Secondly, the example data is fitted in the form of an exponential function to obtain the extrusion deformation prediction curve based on the harmful deformation index. The results are as follows: Figure 6 As shown; Finally, the fitting degree R is obtained by calculation and analysis 2=0.86, and the example data is predicted by fitting curve formula, specifically, the prediction curve is fitted by the data obtained from these 50 groups of examples; and then compared with the 50 groups of tunnel soft rock deformation statistical example data in this example. Applied to the 50 groups of tunnel soft rock deformation statistical examples in this example, the number of correct prediction groups is 43 groups, and the accuracy rate is 86%. When the classification standard of strength-stress ratio is used alone, the number of correct prediction groups is 31 groups, and the accuracy rate is only 62%. Therefore, compared with the single strength-stress-intensity ratio index, the proposed prediction method based on large deformation index improves the accuracy rate by more than 30%.

[0089] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for distinguishing soft rock deformation based on harmful deformation index, characterized in that: The following steps are involved: Step S1: Calculate the comprehensive strength stress ratio J by combining lithology, geostress field and rock mass structural characteristics σ : In the above formula, R b is the uniaxial compressive strength of rock, Rc m is the uniaxial compressive strength of rock mass, σ0 is the major principal stress value of ground stress, k is the ratio of major principal stress to minor principal stress of ground stress; Step S2: Determine the activity coefficient J of groundwater w , as shown in Table 1; Table 1 Groundwater activity coefficient J w Value Step S3: Calculate the rock mass hydraulic coefficient J based on the three indicators of disintegration, expansion and softening. a : In the above formula, the rock mass water coefficient J a Generally greater than 1, the larger the hydraulic coefficient, the more obvious the effect of rock mass degradation when exposed to water; d The disintegration resistance index of soft rock is V d To measure the expansion rate of expansibility, K s The softening coefficient is a measure of softening properties; Step S4: Determine the tunnel shape coefficient D according to the tunnel cross-sectional shape i , the calculation formula is: Di=λRq In the above formula, λ is the cross-sectional shape coefficient of the tunnel, and Rq is the equivalent radius of the tunnel; Step S5: Determine the long-term strength reduction factor J c , specifically: In the above formula, σ c It refers to the maximum strength value at which rock can remain stable without damage under continuous load. Step S6: Calculate the harmful deformation index H of the soft rock tunnel by combining the factors obtained in steps S1-S5 s : In the above formula, J σ is the comprehensive strength stress ratio, J w is the groundwater activity coefficient, J a is the rock mass water resistance coefficient, D i is the tunnel shape factor, J c is the long-term strength reduction factor; Step S7: Determine the surrounding rock deformation category according to the harmful deformation index obtained in step S6 and the harmful deformation classification table of soft rock tunnels; the harmful deformation classification of soft rock tunnels is shown in Table 2; Table 2 Classification of harmful deformation of soft rock tunnels 2. The method for determining soft rock deformation based on harmful deformation index according to claim 1, characterized in that: In step S3, the three indicators of disintegration, expansion and softening are obtained by the following method: The disintegration resistance index I is obtained by testing the disintegration resistance of rock samples. d ; The expansion rate V is obtained according to the cementation characteristics and weathering degree of the rock d The soft rock samples were immersed in water for 48 hours to become saturated samples. The saturated samples and natural samples were subjected to uniaxial compression tests. The ratio of their compressive strengths is the softening coefficient K. s .

3. The method for determining soft rock deformation based on harmful deformation index according to claim 2, characterized in that: In step S4, when the tunnel cross section is horseshoe-shaped, λ=1.0, and when the tunnel cross section is circular, λ=0.8; R q is the equivalent radius of the tunnel. When the tunnel cross-section is horseshoe-shaped, its calculation formula is as follows: In the above formula, A is the area of ​​the tunnel section.

4. The method for determining soft rock deformation based on harmful deformation index according to claim 3 is characterized in that: In step S5, the specific process is as follows: S5.1: Carry out triaxial mechanical tests on rock mass under seepage conditions to obtain mechanical parameters of rock mass seepage-stress coupling tests; S5.2: Carry out triaxial rheological mechanical tests under different osmotic pressure conditions using the obtained mechanical parameters to obtain triaxial rheological test curves under different osmotic pressure conditions; S5.3: By analyzing the rheological test data under different stress levels, a series of stress-strain isochronal curves are drawn; when the curve has an obvious inflection point, the curve segments on both sides of the inflection point are linearly fitted, and the stress value corresponding to the intersection of the two fitting straight lines is the long-term strength σ of the rock. c ; S5.4: Calculation of long-term strength reduction factor J of rock mass c :

5. The method for determining soft rock deformation based on harmful deformation index according to claim 4, characterized in that: In step S7, the harmful deformation is graded according to the following standards, specifically: When the harmful deformation index is 0-0.5, it is an extremely severe extrusion deformation range and is judged as level 3 harmful deformation; When the harmful deformation index is between 0.5 and 1.5, it is a severe extrusion deformation range and is judged as secondary harmful deformation; When the harmful deformation index is between 1.5 and 3.5, it is in the medium extrusion deformation range and is judged as first-level harmful deformation; When the harmful deformation index is greater than 3.5, it is in the non-extrusion deformation range and is judged as safe deformation.

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