A method for distinguishing soft rock deformation based on harmful deformation index

Abstract

The present invention discloses a method for identifying soft rock deformation based on a harmful deformation index, comprising calculating a comprehensive strength-stress ratio; determining a groundwater activity coefficient; calculating a rock mass hydraulic coefficient; determining a tunnel shape coefficient based on the tunnel cross-sectional shape; and determining a long-term strength reduction coefficient. Taking all of the above factors into consideration, the harmful deformation index of the soft rock tunnel is calculated, and the surrounding rock deformation category is determined based on the obtained harmful deformation index and a table for harmful deformation classification of soft rock tunnels. The present invention comprehensively considers the physical and mechanical properties, geological conditions, hydrological environment, and time effects of the surrounding rock of the soft rock tunnel, overcoming the shortcomings of traditional methods that ignore dynamic factors and environmental influences. This method makes deformation identification more comprehensive and accurate, effectively improving risk prediction capabilities, and provides new ideas and methods for deformation identification and classification in soft rock tunnel projects, providing valuable reference for applications in similar projects.

Description

Technical Field

[0001] The present 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 bed soft rock tunnel. Background Art

[0002] Soft rock tunnels often experience large deformations during excavation, requiring appropriate support based on the specific deformation conditions. Therefore, accurate and rapid determination of deformation types is crucial. Traditional methods for determining large deformation in soft rock rely primarily on strength-to-stress ratio analysis. However, this single stress-to-strength ratio metric often fails to accurately reflect the surrounding rock's occurrence and complexity, necessitating a more accurate solution. Summary of the Invention

[0003] The purpose of this invention is to propose a method for distinguishing soft rock deformation based on the 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, σ0 is the major principal stress value of ground stress, and k is the ratio of major principal stress to minor principal stress of ground stress.

[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 Ks To characterize and calculate the rock mass hydraulic coefficient J a :

[0014]

[0015] In the above formula, the rock mass hydraulic 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.

[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 through 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 occurrence environment and the time effect, the soft rock tunnel harmful deformation index H 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 coefficient, J c is the long-term strength reduction factor.

[0028] Step S7: Determine the surrounding rock deformation category by comparing the obtained harmful deformation index with the harmful deformation classification table for soft rock tunnels, as shown in Table 2.

[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 deformation is large, the deformation rate is relatively small and stable over a period of time Secondary harmful deformation The surrounding rock deformation is large and has 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 gush out

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

[0032] The rock samples were tested for disintegration resistance and the disintegration resistance index I was obtained. d ; The expansion rate V is obtained based on 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. Uniaxial compression tests were performed on the saturated samples and the natural samples respectively. The ratio of the compressive strength of the two 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: Conduct triaxial mechanical tests on rock mass under seepage conditions to obtain mechanical parameters of rock mass seepage-stress coupling tests;

[0038] S5.2: Conduct triaxial rheological tests under different osmotic pressures using the obtained mechanical parameters to obtain triaxial rheological test curves under different osmotic pressures;

[0039] S5.3: By analyzing the rheological test data at different stress levels, a series of stress-strain isochronal curves are drawn. When a clear inflection point appears on the curve, the curve segments on both sides of the inflection point are linearly fitted. The stress value corresponding to the intersection of the two fitted lines is the long-term strength σ of the rock. c ;

[0040] S5.4: Calculate the 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 0.5-1.5, it is a severe extrusion deformation range and is determined to be a secondary harmful deformation;

[0045] When the harmful deformation index is 1.5 to 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 to be 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, overcoming the shortcomings of traditional methods that ignore dynamic factors and environmental influences, thereby making deformation identification more comprehensive and accurate, effectively improving risk prediction capabilities, and providing new ideas and methods for deformation identification and classification in soft rock tunnel projects, providing a valuable reference for the application of similar projects. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0051] Figure 3 The triaxial rheological test curves under different osmotic pressure conditions;

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

[0053] Figure 5 This is a statistical chart of harmful deformation caused by 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] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0056] like Figure 1 As shown, a method for determining soft rock deformation based on a harmful deformation index includes 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 example, based on the construction experience of the Chuxiong section of the Dianzhong Water Diversion Project, 50 cases of large deformation in soft rock tunnels in the Chuxiong section of the Dianzhong Water Diversion Project were collected. As shown in Table 3, the in-situ stress and rock / rock mass strength of 10 of these cases are given.

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

[0060]

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

[0062]

[0063] Step S2: Based on the groundwater state description of each instance, obtain each group of groundwater activity coefficients J w ;

[0064] Step S3: First, the rock sample is 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 diversion tunnels of the Dianzhong Water Diversion Project pass through weakly weathered to fresh rock mass, and the rock expansion is relatively weak, so the expansion rate V d ; Again, the soft rock sample was immersed in water for 48 hours to become a saturated sample. The uniaxial compressive test was performed on the saturated sample and the natural sample 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 bed soft rock softening test

[0066]

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

[0068]

[0069] Step S4: First, calculate the equivalent radius R of each group of tunnels based on the area of ​​the tunnel section q ; Secondly, determine the shape coefficient of each tunnel section according to the tunnel section shape. When the section is horseshoe-shaped, λ = 1.0; when the section is circular, λ = 0.8; Finally, calculate the shape coefficient D of each tunnel section 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, and 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] Next, seepage-stress coupling tests were conducted on the red-bed soft rock at confining pressures of 5.0, 7.0, and 10.0 MPa and seepage pressures of 1.0, 2.0, and 3.0 MPa. The classical Mohr-Coulomb criterion was used for fitting, and the mechanical parameters of the seepage-stress coupling tests for the red-bed soft rock were calculated. The results are shown in Table 6.

[0076] Table 6 Mechanical parameters of red bed 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 a confining pressure of 10.0 MPa and an osmotic pressure of 1.0 MPa, (b) is the rheological test curve at a confining pressure of 10.0 MPa and an osmotic pressure of 2.0 MPa, and (c) is the rheological test curve at a confining pressure of 10.0 MPa and an osmotic pressure of 3.0 MPa.

[0079] Again, by analyzing the rheological test data under different stress levels, a series of stress-strain isochronal curves were drawn. The results are as follows: Figure 4 As shown, Figure 4 (a) shows the curve for a confining pressure of 10.0 MPa and an osmotic pressure of 1.0 MPa, (b) shows the curve for a confining pressure of 10.0 MPa and an osmotic pressure of 2.0 MPa, and (c) shows the curve for a confining pressure of 10.0 MPa and an osmotic pressure of 3.0 MPa. When a clear inflection point appears on the curve, a linear fit is performed on the curve segments on both sides of the inflection point. The stress value corresponding to the intersection of the two fitted 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 using the formula:

[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) shows the magnitude of harmful deformation, the horizontal axis is the case number, and the vertical axis is the corresponding deformation (unit: mm); (b) shows the statistical results of the occurrence location of harmful deformation; (c) shows the statistical results of surrounding rock types; and (d) shows the statistical results of geological body types.

[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 the extremely severe extrusion deformation interval (level three harmful deformation); the interval with a harmful deformation index of 0.5 to 1.5 is the severe extrusion deformation interval (level two harmful deformation); the interval with a harmful deformation index of 1.5 to 3.5 is the moderate extrusion deformation interval (level one harmful deformation); the interval with a harmful deformation index greater than 3.5 is the no extrusion deformation interval (safe deformation).

[0088] Secondly, the exponential function is used to fit the example data to obtain the extrusion deformation prediction curve based on the harmful deformation index. The results are as follows: Figure 6 As shown; Finally, the calculation and analysis obtained the fitting degree R 2= 0.86. A curve fitting formula was used to predict the case data. Specifically, a prediction curve was fitted to the data from these 50 cases. This curve was then compared and validated with the 50 sets of statistical data from tunnel soft rock deformation in this example. Applied to these 50 cases, 43 correct predictions were made, with an accuracy rate of 86%. However, using only the strength-stress ratio classification criterion resulted in 31 correct predictions, with an accuracy rate of only 62%. Therefore, compared to the single strength-stress ratio metric, the proposed prediction method based on the large deformation index improves accuracy by over 30%.

[0089] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for determining soft rock deformation based on a 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 the rock mass, σ0 is the major principal stress value of the in-situ stress, and k is the ratio of the major principal stress to the minor principal stress of the in-situ 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 hydraulic coefficient J a Generally greater than 1, the larger the hydraulic coefficient is, the more obvious the effect of rock degradation when exposed to water is; d The disintegration resistance of soft rock is measured by the disintegration resistance index, 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 soft rock tunnel harmful deformation index H 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 coefficient, J c is the long-term strength reduction factor; Step S7: Determine the surrounding rock deformation category based on the harmful deformation index obtained in step S6 and the harmful deformation classification table for soft rock tunnels. The harmful deformation classification for 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 rock samples were tested for disintegration resistance and the disintegration resistance index I was obtained. d ; The expansion rate V is obtained based on 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. Uniaxial compression tests were performed on the saturated samples and the natural samples respectively. The ratio of the compressive strength of the two 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; 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, characterized in that: In step S5, the specific process is as follows: S5.1: Conduct triaxial mechanical tests on rock mass under seepage conditions to obtain mechanical parameters of rock mass seepage-stress coupling tests; S5.2: Conduct triaxial rheological tests under different osmotic pressures using the obtained mechanical parameters to obtain triaxial rheological test curves under different osmotic pressures; S5.3: By analyzing the rheological test data at different stress levels, a series of stress-strain isochronal curves are drawn. When a clear inflection point appears on the curve, the curve segments on both sides of the inflection point are linearly fitted. The stress value corresponding to the intersection of the two fitted lines is the long-term strength σ of the rock. c ; S5.4: Calculate the 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 classified 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 0.5-1.5, it is a severe extrusion deformation range and is determined to be a secondary harmful deformation; When the harmful deformation index is 1.5 to 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 to be safe deformation.

Images