Harmful deformation prevention and control method for hydraulic soft rock tunnel

Abstract

The invention discloses a harmful deformation prevention and control method for a hydraulic soft rock tunnel, and the method comprises the steps: carrying out the preliminary classification of the surrounding rock of the tunnel according to the geological survey result of the tunnel, and dividing a deformation control target into four grades; supporting measures which are based on harmful deformation classification and conform to the deformation characteristics of the red-bed soft rock tunnel are provided by considering the characteristics of water physical property, rheological property and the like of the red-bed soft rock; in the construction stage, a soft rock tunnel harmful deformation analysis method under the seepage-rheological coupling effect is adopted for determining the reserved deformation amount, and according to an improved constraint-convergence method, the supporting opportunity is calculated and determined based on a surrounding rock characteristic curve and a safety coefficient; and finally, according to geological conditions exposed by excavation and necessary supplementary survey results, calculating and analyzing the harmful deformation index again, and dynamically adjusting the harmful deformation grade and the support measure of the specific hole section. According to the method, through a scientific supporting mode and dynamic management, tunnel deformation can be effectively controlled, and the adaptability and long-acting stability of red layer soft rock tunnel supporting are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy engineering and tunnel support, and specifically relates to a method for preventing and controlling harmful deformation of a hydraulic soft rock tunnel. Background Art

[0002] The existing tunnel support system lacks dynamic adaptability to the deformation of complex soft rock surrounding rock, and is unable to cope with the long-term deformation of soft rock under complex stress fields and water conditions, which can easily lead to damage to the support structure and delays in project progress. Therefore, a prevention and control method that can be dynamically adjusted is needed to ensure the stability of the tunnel. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preventing and controlling harmful deformation of hydraulic soft rock tunnels, so as to solve the technical problem that the tunnel support system in the prior art lacks dynamic adaptability to the deformation of complex soft rock surrounding rocks and is difficult to cope with the long-term deformation of soft rock under complex stress fields and water effects.

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

[0005] A method for preventing and controlling harmful deformation of a hydraulic soft rock tunnel comprises the following steps:

[0006] Step S1, preliminary classification of surrounding rocks: preliminary classification of tunnel surrounding rocks is performed based on tunnel geological survey results, and the stability of the surrounding rocks is evaluated;

[0007] Step S2, classification of harmful deformation: Based on the preliminary classification results of the surrounding rock in step S1, the harmful deformation index of the soft rock tunnel is calculated by comprehensively considering the material composition, physical and mechanical properties, hydraulic properties and rheological properties of typical red-bed soft rocks, and combining the temporal and spatial distribution characteristics of the deformation of the red-bed soft rock tunnel. The deformation control target is subdivided into four levels of "safe deformation", "first-level harmful deformation", "second-level harmful deformation" and "third-level harmful deformation" according to the harmful deformation index;

[0008] Step S3, formulation of support measures: according to the red layer soft rock hydraulic properties and rheological properties, comprehensive strength-stress ratio, groundwater activity coefficient, rock mass hydraulic properties, tunnel shape coefficient and long-term strength index, and based on the classification of harmful deformation, formulate support measures that meet the deformation characteristics of the red layer soft rock tunnel;

[0009] Step S4, determining the reserved deformation: in the design stage, the initial value of the reserved deformation is determined with reference to the regulations and engineering experience; in the construction stage, the harmful deformation analysis method of soft rock tunnel under the action of seepage-rheology coupling is adopted to obtain the reserved deformation of different tunnel sections through iterative calculation, and dynamic adjustment is performed in combination with deformation monitoring;

[0010] Step S5, determining the support timing: the support timing includes the timing of the initial support and the secondary lining. For the initial support, regardless of the deformation level, it must be carried out in time, and the stress conditions of the surrounding rock must be improved in time to control the development of harmful deformation. For the secondary lining, different support timings are determined according to the deformation level.

[0011] Step S6, dynamic adjustment: Based on the excavation exposure and supplementary survey results, the surrounding rock is classified in detail and basic support measures are determined. Then, a new method is quickly designed based on the harmful deformation support dynamics to dynamically adjust the support system.

[0012] Further optimization, in step S2, the calculation of the harmful deformation index includes the following steps:

[0013] Step S2.1. Definition of harmful deformation index: Harmful deformation index H of soft rock tunnel s The calculation formula is as follows:

[0014]

[0015] 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;

[0016] Step S2.2: Calculate the comprehensive strength stress ratio J σ , the calculation formula is:

[0017]

[0018] In the above formula: R b is the uniaxial compressive strength of rock, obtained from the uniaxial compressive strength test of rock specimens in the laboratory; R cm is the uniaxial compressive strength of rock mass, which is used to characterize the structural characteristics of rock mass; σ0 is the major principal stress value of ground stress, which is obtained through field survey data; k is the ratio of major principal stress to minor principal stress of ground stress.

[0019] Step S2.3: Determine the groundwater activity coefficient J w , as shown in Table 1:

[0020] Table 1 Groundwater activity coefficient J w Value

[0021]

[0022] Step S2.4: Calculate the rock mass hydraulic coefficient J a , the calculation formula is:

[0023]

[0024] In the above formula: rock mass water coefficient J a Generally greater than 1, the larger the hydraulic coefficient, the more obvious the effect of rock mass deterioration when exposed to water.

[0025] I d The disintegration resistance index of soft rock is V d To measure the expansion rate of expansibility, K s To measure the softening coefficient of softening, the above three parameters are obtained through indoor tests. It can be seen from formula (2-1) that when the groundwater influence coefficient is 1, that is, when there is no groundwater in the tunnel, the hydraulic coefficient has no effect on the harmful deformation index.

[0026] Step S2.5 Calculate the tunnel shape factor D i , the calculation formula is:

[0027] D i =λR q (2-4)

[0028] In the above formula: λ is the cross-sectional shape coefficient of the tunnel, λ = 1.0 when the cross-section of the tunnel is horseshoe-shaped, and λ = 0.8 when the cross-section of the tunnel is circular; R q is the equivalent radius of the tunnel. When the tunnel cross-section is horseshoe-shaped, its calculation formula is as follows:

[0029]

[0030] In the above formula, A is the area of ​​the tunnel section.

[0031] The shape of the tunnel has an important influence on the secondary redistribution of surrounding rock stress, and its main influencing factors are the cross-sectional form and size. When the cross-sectional shape of the tunnel is circular, the stress state of the surrounding rock is better. When the tunnel shape is horseshoe-shaped, stress concentration is likely to occur at the arch angle and the foot.

[0032] Step S2.6: Determine the long-term strength reduction factor J c , specifically determined according to the shape of the test specimen:

[0033]

[0034] Further optimization, in step S2, the harmful deformation is graded according to the following standards, specifically:

[0035] 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;

[0036] 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;

[0037] 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;

[0038] When the harmful deformation index is greater than 3.5, it is in the non-extrusion deformation range and is judged as safe deformation.

[0039] Further optimization, in step S3, the proposed support measures are as follows:

[0040] For "safe deformation", the surrounding rock is mainly in an elastic state, and its own bearing capacity can meet the needs of deformation control. The support force mainly comes from the surrounding rock itself, and no requirements are made for secondary lining;

[0041] For the tunnel section with "first-level harmful deformation", the surrounding rock is mainly in an elastic-plastic state, and the instantaneous deformation is relatively large. It is necessary to carry out initial support in time, and the harmful deformation is controlled by the joint bearing of the surrounding rock and initial support. The support force mainly comes from the surrounding rock and initial support.

[0042] For the tunnel section with "secondary harmful deformation", the surrounding rock has obvious rheological effect and significant long-term deformation. It is necessary to timely implement and strengthen the initial support, choose a reasonable time to implement the secondary lining, and control the harmful deformation through the joint bearing of surrounding rock-initial support-secondary lining. The support force comes from the surrounding rock, initial support and secondary lining.

[0043] For the tunnel section with "level 3 harmful deformation", the rheological effect of the surrounding rock is prominent and the long-term deformation is large. It is necessary to promptly apply the initial support combined with anti-yield, and take advance reinforcement and seepage control measures for the surrounding rock. Choose a reasonable time to apply the secondary lining, and control the harmful deformation through the joint bearing of surrounding rock-initial support-secondary lining. The support force comes from the surrounding rock, initial support and secondary lining.

[0044] Further optimization, in step S4, the harmful deformation analysis method of soft rock tunnel under the effect of seepage-rheology coupling is adopted in the construction stage, and the reserved deformation of different tunnel sections is obtained by iterative calculation. The specific process is as follows:

[0045] a) Set the excavation radius of the tunnel and calculate the initial deformation of the tunnel face based on the longitudinal deformation curve.

[0046] b) Then, the radial deformation under the current support conditions and support timing is calculated based on the physical and mechanical properties of the surrounding rock, ground stress and groundwater occurrence status.

[0047] c) Determine whether the secondary lining is invaded based on the excavation radius and radial deformation. If the secondary lining is invaded, the excavation radius of the tunnel needs to be expanded. Conversely, when it is far away from the designed secondary lining, the excavation radius of the tunnel needs to be reduced.

[0048] Further optimization, in step S5, the determination of the support timing specifically includes the following steps:

[0049] Step S5.1, determine the timing of initial support: after the tunnel excavation is completed, the initial support is immediately carried out to quickly change the stress state of the surrounding rock, enhance the stability of the surrounding rock, and control the initial deformation;

[0050] Step S5.2, surrounding rock deformation monitoring: allow the surrounding rock to produce a certain deformation in the initial support stage, use the deformation monitoring system to track the surrounding rock deformation displacement in real time, ensure that the deformation does not exceed the safety range, and prevent harmful deformation from causing surrounding rock instability;

[0051] Step S5.3, determination of the timing of secondary lining: when the surrounding rock deformation enters a stable state, secondary lining construction is carried out;

[0052] Step S5.4, optimization of support timing: During the design phase, while referring to the specifications and standards, the best support timing is determined by comprehensive evaluation in combination with deformation monitoring data and engineering experience.

[0053] Further optimization, in step S5.3, the surrounding rock deformation enters a stable state and satisfies the following conditions:

[0054] a. The horizontal convergence rate around the tunnel should be reduced to less than 0.2 mm / day;

[0055] b. The vertical displacement speed of the tunnel vault or floor is controlled below 0.1 mm / day;

[0056] c. The displacement speed showed a significant slowing trend, and the total displacement reached 90% of the expected value.

[0057] Further optimization, in step S5.3, for the secondary lining, different support timings are determined according to the deformation level, specifically:

[0058] No requirements are made for the “safe deformation” situation;

[0059] In case of "first-level harmful deformation", "digging and lining at the same time" should be carried out as much as possible;

[0060] For "secondary harmful deformation" and "tertiary harmful deformation", the surrounding rock deformation requirements cannot be met after initial support. The disturbance generated during the continued advancement of the face will cause the tunnel support structure to continuously deform, affecting the stability of the tunnel support structure. Secondary lining needs to be applied at the right time to ensure the stability of the surrounding rock. Therefore, by adjusting the support timing of the secondary lining, the purpose of actively regulating the surrounding rock deformation is the key to ensuring the stability of the surrounding rock after tunnel excavation. The support timing control benchmark is established based on the surrounding rock harmful deformation index and the surrounding rock characteristic curve. Set multiple possible appropriate secondary lining support times, calculate the stable deformation and lining safety factors on the improved convergence constraint diagram, and finally select a more appropriate support timing.

[0061] Further optimization, the dynamic adjustment in step S6 specifically includes the following steps:

[0062] Step S6.1, calculation and dynamic adjustment of harmful deformation index: according to the geological conditions revealed by excavation and necessary supplementary survey work, recalculate and analyze various factors of harmful deformation index, and dynamically adjust the harmful deformation level and support measures of specific tunnel sections;

[0063] Step S6.2, seepage-rheology coupling deformation analysis: Based on the calculation results of step S6.1, the seepage-rheology coupling deformation analysis method is used to quickly calculate and verify the support force, instantaneous and long-term deformation of the surrounding rock to ensure the rationality of the reserved deformation and the support system. This step helps evaluate the stability of the support structure under long-term geological effects.

[0064] Step S6.3, application of improved convergence-constraint method: after determining the surrounding rock characteristic curve, the improved convergence-constraint method is used to analyze the support timing, determine the reasonable timing of the secondary lining, and ensure that the surrounding rock deformation is within a safe range and reaches a stable state;

[0065] Step S6.4, support system adjustment and feedback optimization: Combined with the deformation monitoring data of the surrounding rock, the reserved deformation, support strength and timing of the support system are optimized and adjusted in real time to ensure the stability of the tunnel under complex geological conditions.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] According to the results of tunnel geological survey, the present invention preliminarily classifies the tunnel surrounding rock and divides the deformation control target into four levels; by considering the characteristics of red layer soft rock such as hydraulic properties and rheology, a support measure based on the classification of harmful deformation and in line with the deformation characteristics of red layer soft rock tunnel is proposed; during the construction stage, the harmful deformation analysis method of soft rock tunnel under the action of seepage-rheology coupling is used to determine the reserved deformation amount, and the support timing is determined based on the surrounding rock characteristic curve and safety factor calculation according to the "improved constraint-convergence method"; finally, according to the geological conditions revealed by excavation and the necessary supplementary survey results, the harmful deformation index is recalculated and analyzed, and the harmful deformation level and support measures of the specific tunnel section are dynamically adjusted. The method described in the present invention can effectively control tunnel deformation and improve the adaptability and long-term stability of red layer soft rock tunnel support through scientific support methods and dynamic management. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is a schematic diagram of the harmful deformation prevention and control method of hydraulic soft rock tunnel;

[0069] Figure 2 It is a schematic diagram of the improved convergence constraint method under the effect of seepage coupling;

[0070] Figure 3 It is the long-term deformation zoning diagram of the tunnel surrounding rock;

[0071] Figure 4 This is a partial on-site photo of the exit of a tunnel in the Dianzhong Water Diversion Project;

[0072] Figure 5 This is a schematic diagram of the support system for the safe deformation tunnel section;

[0073] Figure 6 This is a schematic diagram of the support system for the first-level harmful deformation tunnel section;

[0074] Figure 7 This is a schematic diagram of the secondary harmful deformation tunnel section support system;

[0075] Figure 8 This is a schematic diagram of the support system for the third-level harmful deformation tunnel section;

[0076] Fig. 9 It is the surrounding rock characteristic curve corresponding to different harmful deformation indexes. DETAILED DESCRIPTION

[0077] 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 partial embodiments of the present invention, rather than all 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.

[0078] A tunnel of the Dianzhong Water Diversion Project is about 18.2 km long, with a diameter of 8.6 m×9.9 m, a general burial depth of 38 to 481 m, and a maximum burial depth of 561 m. The stratum lithology is mainly the Dianzhong red layer. The rock mass is mainly relatively intact. In some areas, the rock mass is broken due to tectonic influences, and the joints and fissures are relatively developed.

[0079] In this embodiment, a tunnel of the Dianzhong Water Diversion Project is taken as an example to describe the harmful deformation prevention and control method of hydraulic soft rock tunnels. Figure 1 As shown, the following steps are included:

[0080] Step S1, preliminary classification of surrounding rocks: Based on the results of tunnel geological survey, preliminary classification of tunnel surrounding rocks is performed, and the stability of surrounding rocks is evaluated.

[0081] In this example, the surrounding rock category is mainly Class IV, accounting for about 40.84%, followed by Class III, accounting for about 35.44%, a small amount of Class V and Class II, accounting for about 19.61%, and special tunnel sections accounting for 4.11%. The widths of the fault zones crossed by the tunnel are 50m and 15m respectively, and several smaller-scale Class III and below structural surfaces are developed. The groundwater is mainly bedrock fissure water, the entire tunnel section is located below the groundwater level, the rock mass is mainly weak to slightly permeable, and the local sections are affected by the structure and faults, and the rock mass is broken.

[0082] Step S2, classification of harmful deformation: Based on the preliminary classification results of the surrounding rock in step S1, the harmful deformation index of the soft rock tunnel is calculated by comprehensively considering the material composition, physical and mechanical properties, hydraulic properties and rheological properties of typical red bed soft rocks, and combining the temporal and spatial distribution characteristics of the deformation of the red bed soft rock tunnel. According to the harmful deformation index, the deformation control target is subdivided into four levels: "safe deformation", "first-level harmful deformation", "second-level harmful deformation" and "third-level harmful deformation".

[0083] In this example, the red strata soft rock in central Yunnan is widely distributed and has great differences in physical and mechanical properties. Based on formulas (2-1)-(2-6), the comprehensive strength stress ratio J of the red strata soft rock in central Yunnan corresponding to different ground stresses is calculated. σ , groundwater activity coefficient J w , rock mass hydraulic coefficient J a , Tunnel shape coefficient D i , Long-term strength reduction factor J c and harmful deformation index H s , and the corresponding deformation levels are shown in Table 2.

[0084] Table 2 Soft rock tunnels under different harmful deformation indexes

[0085] Serial number Ground stress (MPa) <![CDATA[J σ ]]> <![CDATA[J w ]]> <![CDATA[J a ]]> <![CDATA[D i ]]> <![CDATA[J c ]]> Harmful deformation index Grading 1 16.41 0.25 0.66 0.50 1 0.58 0.12 Level 3 harmful deformation 2 7.33 2.30 0.66 0.50 1 0.58 1.14 Secondary harmful deformation 3 7.50 5.10 1.00 0.63 1 0.62 3.16 First level harmful deformation 4 5.74 15.20 1.00 0.5 1 0.58 8.82 Safety deformation

[0086] Step S3: Formulate support measures: Based on the hydraulic properties and rheological properties of the red layer soft rock, the comprehensive strength-stress ratio, the groundwater activity coefficient, the rock mass hydraulic properties, the tunnel shape coefficient and the long-term strength index, and based on the classification of harmful deformation, formulate support measures that meet the deformation characteristics of the red layer soft rock tunnel.

[0087] In this embodiment, some on-site photos of a tunnel exit of the Dianzhong Water Diversion Project are shown in Figure 4 When the water diversion tunnel in this area passes through the red soft rock formation in central Yunnan, there are typical harmful deformation problems of the surrounding rock, such as large deformation of the tunnel surrounding rock, collapse of the top, and water and mud inrush in the fault tunnel section. Figure 4 (a) is a photo of the tunnel surrounding rock undergoing large and harmful deformation; Figure 4 (b)-(d) in the figure are photos of the tunnel surrounding rock that has undergone harmful deformation due to water gushing and mud bursting in the fault tunnel section.

[0088] In this embodiment, the excavation supports corresponding to the four deformation levels of "safe deformation", "first level harmful deformation", "second level harmful deformation" and "third level harmful deformation" are as follows: Figures 5 to 8 As shown. Among them, Figure 5 This is a schematic diagram of the support system for the safe deformation tunnel section. Figure 5 (a) is the excavation and support profile, (b) is the excavation and primary support cross-section, and (c) is the lining shape and reinforcement diagram. Figure 6 This is a schematic diagram of the support system for the first-level harmful deformation tunnel section. Figure 6 (a) is the excavation and support profile, (b) is the excavation and primary support cross-section, and (c) is the lining shape and reinforcement diagram. Figure 7 This is a schematic diagram of the secondary harmful deformation tunnel support system. Figure 7 (a) is the excavation and support profile, (b) is the excavation and primary support cross-section, and (c) is the lining shape and reinforcement diagram. Figure 8 This is a schematic diagram of the support system for the third-level harmful deformation tunnel section. Figure 8 (a) is the excavation and support profile, (b) is the excavation and primary support cross-section, and (c) is the lining shape and reinforcement diagram.

[0089] Step S4, determining the reserved deformation amount, specifically includes the following steps:

[0090] a) Set the excavation radius of the tunnel and calculate the initial deformation of the tunnel face excavation based on the longitudinal deformation curve. Determine the initial deformation of the tunnel face excavation: Based on the longitudinal deformation curve of the surrounding rock in the traditional convergence constraint method. The longitudinal deformation curve of the surrounding rock is determined by theoretical formula or numerical simulation.

[0091] b) Then, the radial deformation under the current support conditions and support timing is calculated based on the physical and mechanical properties of the surrounding rock, ground stress and groundwater occurrence status.

[0092] c) Determine whether the secondary lining is invaded based on the excavation radius and radial deformation. If the secondary lining is invaded, the excavation radius of the tunnel needs to be expanded. On the contrary, when it is far away from the designed secondary lining, the excavation radius of the tunnel needs to be reduced.

[0093] Taking the third-level harmful deformation tunnel section as an example, the initial reserved deformation is set to 120 mm. The above method is used for trial calculation. After three iterations, the final reserved deformation can be obtained as 194 mm. The iteration process is shown in Table 3.

[0094] Table 3 Calculation results of reserved deformation of third-level harmful deformation tunnel

[0095] Serial number Reserved deformation (mm) Secondary lining intrusion (mm) Intrusion amount / reserved deformation (%) 1 120 -35 29.17 2 155 27 17.42 3 182 16 8.79 4 198 -4 2.02

[0096] Step S5, determine the support timing: the support timing includes the timing of the initial support and the secondary lining. For the initial support, regardless of the deformation level, it must be carried out in time, and the surrounding rock stress conditions must be improved in time to control the development of harmful deformation. For the secondary lining, different support timings are determined according to the deformation level. The specific steps include the following:

[0097] Step S5.1, determine the timing of initial support: after the tunnel excavation is completed, the initial support is immediately carried out to quickly change the stress state of the surrounding rock, enhance the stability of the surrounding rock, and control the initial deformation.

[0098] Step S5.2, surrounding rock deformation monitoring: using a deformation monitoring system to track surrounding rock deformation displacement in real time to ensure that the deformation does not exceed a safe range;

[0099] Step S5.3, determination of the timing of secondary lining: when the surrounding rock deformation enters a stable state, the secondary lining construction shall be carried out; when the surrounding rock deformation enters a stable state, the following conditions shall be met:

[0100] a. The horizontal convergence rate around the tunnel should be reduced to less than 0.2 mm / day;

[0101] b. The vertical displacement speed of the tunnel vault or floor is controlled below 0.1 mm / day;

[0102] c. The displacement speed showed a significant slowing trend, and the total displacement reached 90% of the expected value.

[0103] For the secondary lining, different support times are determined according to the deformation level, specifically:

[0104] No requirements are made for the “safe deformation” situation;

[0105] In case of "first-level harmful deformation", "digging and lining at the same time" should be carried out as much as possible;

[0106] For "secondary harmful deformation" and "tertiary harmful deformation", the surrounding rock deformation requirements cannot be met after initial support. The disturbance generated during the continued advancement of the face will cause the tunnel support structure to continuously deform, affecting the stability of the tunnel support structure. Secondary lining needs to be applied at the right time to ensure the stability of the surrounding rock. Therefore, by adjusting the support timing of the secondary lining, the purpose of actively regulating the surrounding rock deformation is the key to ensuring the stability of the surrounding rock after tunnel excavation. The support timing control benchmark is established based on the surrounding rock harmful deformation index and the surrounding rock characteristic curve. Set multiple possible appropriate secondary lining support times, calculate the stable deformation and lining safety factors on the improved convergence constraint diagram, and finally select a more appropriate support timing.

[0107] The convergence constraint method emphasizes that the surrounding rock and the support system jointly bear the loads generated during the excavation process by analyzing the surrounding rock characteristic curve (GRC), the support characteristic curve (SCC) and the surrounding rock longitudinal deformation curve (LDP). This is the core concept of tunnel stability analysis and support design. Due to the diagenetic period, the red layer soft rock in central Yunnan has strong hydraulic properties and obvious long-term deformation characteristics. When the support pressure is small, the rheological deformation is much larger than the elastoplastic deformation. Therefore, in the central Yunnan water diversion project, the initial support is generally carried out simultaneously with the excavation of the face, and then the secondary lining construction is carried out at an appropriate time. It can be seen that choosing the right time for the secondary lining is particularly important. Since the initial support is generally carried out simultaneously with the excavation of the face, the longitudinal deformation curve of the surrounding rock does not need to be considered for the time being. The idea of ​​the improved convergence constraint method under the action of seepage coupling, such as Figure 2 The specific steps are as follows:

[0108] a) Draw the surrounding rock characteristic curve of the tunnel under the action of seepage rheology: Based on the analysis formula of harmful deformation of the tunnel under the action of seepage rheology, calculate the deformation of the tunnel under different support stresses.

[0109] b) Determine the support curves for the initial support and secondary lining: Determine the characteristic equation of the support unit according to the support form and the properties of the support material. For common support structures, this can be calculated by combining the support unit expressions or obtained through empirical formulas.

[0110] c) Determine the initial deformation of the tunnel face excavation: Based on the longitudinal deformation curve of the surrounding rock in the traditional convergence constraint method. The longitudinal deformation curve of the surrounding rock can generally be determined by theoretical formulas or numerical simulations. For red layer soft rock tunnels, initial support is generally started immediately after the face excavation is completed. When the surrounding rock quality is good, support can also be carried out after the face continues to move forward for a period of time.

[0111] d) Selection and analysis of support timing: Due to the low strength of the red layer soft rock and the large rheological deformation, the initial support is generally carried out in real time with the excavation of the face. Therefore, the selection of the secondary lining is the key. First, a set of possible support times is drawn up, the surrounding rock characteristic curve corresponding to the time is calculated, and the intersection of the initial support and the time-effect curve is calculated as the starting point of the secondary lining.

[0112] e) Support effect evaluation: calculate the intersection of the secondary lining support characteristic curve and the permanent deformation, analyze the stress and displacement state of the tunnel surrounding rock, and evaluate the safety and rationality of the support structure.

[0113] The specific derivation process of the analysis formula for harmful deformation of tunnels under seepage rheological action is as follows:

[0114] The analysis of tunnel surrounding rock considering seepage rheology is divided into two parts: instantaneous analysis and seepage rheology analysis. Based on the basic theories of rock mechanics and rheology, the deformation of red bed soft rock can be divided into instantaneous deformation and seepage rheology. i and time-dependent deformation ∈ v The instantaneous deformation can be divided into elastic ∈ e and plastic deformation ∈ p , the time-dependent deformation can be divided into viscoelasticity ∈ ve and viscoplastic deformation ∈ vp :

[0115] ∈=∈ i +∈ v , ∈ i =∈ e +∈ p , ∈ v =∈ ve +∈ vp (8-1)

[0116] Accordingly, the displacement of soft rock tunnels can be divided into instantaneous deformation and long-term deformation:

[0117] u=u i +u v (8-2)

[0118] Set the tunnel support force σ i It can be expressed as:

[0119] σ i =(1-λ)σ0 (8-3)

[0120] Where: σ0 is the in-situ stress of the tunnel surrounding rock; λ is the stress release rate of the surrounding rock after tunnel excavation and support, and its value range is [0,1].

[0121] There are two limits for the stress release rate of the surrounding rock after tunnel excavation and support, namely, the instantaneous failure limit λ I and long-term damage limit λ LWhen λ<λ L When λ L <λ<λ I When λ>λ, a long-term damage zone appears in the tunnel surrounding rock; when λ>λ I When the tunnel surrounding rock is subjected to the flow stress, the long-term damage zone and the instantaneous damage zone appear at the same time. Assuming that the stress of the surrounding rock remains unchanged during the rheological process, the instantaneous and rheological mechanics analytical solutions of the soft rock tunnel under the coupling of seepage stress are established.

[0122] Set the internal water head to h a , the water head at a sufficiently far distance is h0, and the permeability coefficient is the same in all directions. The influence of the deadweight of the surrounding rock is not considered, and the lateral pressure coefficient is assumed to be 1.0, and the radial and tangential stresses are equal to the vertical and horizontal stresses. The research focus of this invention is the radial seepage of the tunnel. Since the buoyancy is relatively small compared to the pore water pressure, the influence of the buoyancy is ignored in the calculation process. When calculating the stress and deformation of the tunnel surrounding rock, the effective stress principle is used for analysis. For deeply buried and long tunnels, since the internal and external water heads are much larger than the tunnel diameter, the seepage is mainly radial. Therefore, the problem is simplified to a stable seepage problem under axisymmetric conditions. The continuity differential equation for tunnel seepage calculation and its corresponding boundary conditions are established as follows:

[0123]

[0124] H(r) r＝R =h a (8-5)

[0125] H(r) r→∞ =h0 (8-6)

[0126] Where: H is the water head within different radius ranges of surrounding rock; R is the inner diameter of the tunnel.

[0127] Based on the solution formula of ordinary differential equations, the general solution is obtained. In order to transform the general solution into a special solution, its boundary conditions need to be brought in. The radius range in formula (8-6) is infinite and there is no way to calculate it, so it is necessary to make appropriate changes and set it to a fixed value. In addition, the pore water pressure on the tunnel surface is 0 during the tunnel construction stage:

[0128] H(r) r＝nR =h0,h a =0 (8-7)

[0129] Where: n is the ratio of the seepage calculation radius to the tunnel radius, which can generally be a number greater than 10. From this, the pore water head inside the surrounding rock can be obtained as:

[0130]

[0131] The tunnel surrounding rock micro-unit is selected to carry out static equilibrium analysis. Considering the effect of seepage force, the classical equation can be written as:

[0132]

[0133] Substituting the pore pressure expression in formula (8-8) into formula (8-9), we can obtain:

[0134]

[0135] Solving the differential equation (8-9) according to the plane strain problem, we can obtain the tangential stress σ θ and radial stress σ r The formula is:

[0136]

[0137] Before calculating the stress and displacement in the elastic-plastic zone of the surrounding rock, it is necessary to determine the critical support stress σ i , that is, the instantaneous failure limit of surrounding rock stress release rate λ I When the surrounding rock stress release rate is greater than the limit value, there is a plastic zone in the surrounding rock around the tunnel; when the surrounding rock stress release rate is less than the limit value, there is no plastic zone in the surrounding rock around the tunnel, which can be determined according to the elastic zone calculation formula (8-3).

[0138] The instantaneous model of the surrounding rock is set to satisfy the Mohr-Coulomb yield criterion:

[0139]

[0140] Where: c is the cohesion of the surrounding rock, is the internal friction angle.

[0141] When the support stress is greater than the critical support stress, the surface of the tunnel satisfies the elastic zone stress calculation formulas (8-11) to (8-12) and the yield criterion (8-13) at the same time:

[0142]

[0143] Substituting formula (8-3) into the instantaneous failure limit λ of the surrounding rock stress release rate can be obtained I :

[0144]

[0145] When the surrounding rock stress release rate is less than the instantaneous damage limit value λ of the surrounding rock stress release rate I , and finally the displacement equation of the tunnel surrounding rock under elastic conditions is:

[0146]

[0147] When the surrounding rock stress release rate is greater than the instantaneous damage limit value λ of the surrounding rock stress release rate I , according to the force balance equation and yield function, the ordinary differential equation of radial stress is established, and finally the equations of radial stress and tangential stress are obtained as follows:

[0148]

[0149] According to the elastic-plastic interface, the plastic and elastic conditions are satisfied at the same time, and the calculation formula of the plastic zone radius can be obtained as follows:

[0150]

[0151] It is worth noting that this equation is a transcendental equation and cannot be directly solved by analytical formula. It can only be solved by setting an initial value and then performing numerical iteration.

[0152] When r>R P When , the surrounding rock is in an elastic state, and the expression of its radial deformation is:

[0153]

[0154] When R P When >r>R, the surrounding rock is in an elastic state, and the expression of its radial deformation is:

[0155]

[0156] Where:

[0157]

[0158] The long-term deformation zones of tunnel surrounding rock under the coupling of seepage and stress are shown in Figure 3 Slightly different from instantaneous failure, when the surrounding rock stress release rate λ<λ I Although the yield strength has not been reached, the surrounding rock may have a long-term damage zone because the long-term strength of the surrounding rock is less than the instantaneous strength. According to the long-term damage limit value λ of the surrounding rock stress release rate L and the instantaneous damage limit λ I , the stress state of the surrounding rock can be divided into three categories. Since the stress remains unchanged during the rheological process, the strain and displacement analysis of the three types of partitions is as follows:

[0159] (1) Deformation analysis in the viscoelastic regionλ<λ L

[0160] Since the deformation of the surrounding rock along the tunnel axis is not considered, the deviatoric stress in the axial direction can be set to 0. The tangential shear stress s θ and radial shear stress s r for:

[0161]

[0162] According to the fractional rheological calculation formula, we can get:

[0163]

[0164] Where:

[0165]

[0166] According to formula (8-11), the radial rheological displacement in the viscoelastic zone is:

[0167]

[0168] By adding the rheological deformation and the transient deformation, the final deformation of the tunnel can be obtained:

[0169] u=u v +u i (8-32)

[0170] Substituting formula (8-28) and (8-31) into the above formula, the displacement u of the viscoelastic zone can be obtained as:

[0171]

[0172] Where G is the shear modulus of the surrounding rock, expressed as:

[0173]

[0174] (2) Long-term deformation analysis of the damage zone I >λ>λ L

[0175] The stress in the long-term damage zone is consistent with the elastic zone in transient mechanical analysis, but when the shear stress reaches the long-term strength, the radius of the long-term damage zone can be obtained. The tangential stress and radial stress satisfy:

[0176]

[0177] Substituting the elastic zone stress formulas (8-11) and (8-12) into (8-35) yields the long-term damage zone radius R L :

[0178]

[0179] When r>R L When R L >r>R, the shear stress exceeds the long-term shear stress σ Y, thus an accelerated rheological zone is generated, and the difference between the shear stress and the long-term shear stress is calculated as:

[0180]

[0181] The interpolation value is recorded as H, and the tangential viscous strain and surrounding rock displacement in the long-term damage zone are further calculated as follows:

[0182]

[0183] Where:

[0184]

[0185] (3) Deformation analysis of instantaneous damage zone λ>λ I

[0186] In the viscoplastic region (R≤r≤R p ), the tunnel surrounding rock forms a viscoplastic zone. According to formulas (8-9) and (8-10) in transient mechanical analysis, the expression of its shear stress can be obtained as follows:

[0187]

[0188] The difference between the shear stress and the long-term shear stress is calculated as:

[0189]

[0190] The rheological deformation caused by shear stress can be obtained:

[0191]

[0192] Where:

[0193]

[0194] Assuming that the rheological deformation in the plastic zone complies with the associated flow criterion, the viscoplastic strain expressions in the tangential and radial directions can be established:

[0195]

[0196] Where Λ represents the viscoplastic multiplier, which can be expressed using the flow rule:

[0197]

[0198] Substituting formula (8-44) and (8-45) into formula (8-53), we can finally get:

[0199]

[0200] C=(N ψ-1)(A1F1+A2F3) (8-55)

[0201] D=(N ψ -1)(A1F2+A2F4) (8-56)

[0202]

[0203] At the interface r = R P This is equivalent to a stress release rate of λ I The support force acts on the radius R P For a tunnel with a displacement of 100 mm, the limit displacement can be obtained according to the long-term damage zone calculation formula:

[0204]

[0205] By adding formula (8-39) and formula (8-57), the final surrounding rock deformation can be obtained as:

[0206]

[0207] The surrounding rock support characteristic curve and longitudinal deformation curve under the action of seepage rheology coupling are consistent with the conventional convergence constraint deformation analysis method. Tunnel deformation is a constraint process formed with the surrounding rock within the limit deformation range of the support system, and the surrounding rock and support system work together as a whole. For red soft rock tunnels, the double-check support form is generally adopted. Due to the complex composition of the surrounding rock-support system, it is difficult to directly apply limit analysis to calculate the support force of the composite support system. In engineering, the maximum support force of each support structure can be added to determine the total support force of the tunnel composite support system:

[0208]

[0209] Where: p shot is the shotcrete support force, p bolt is the anchor support force, p net is the support force of the metal mesh, p rock The supporting force of the rock pressure arch.

[0210] Combined with the research results of tunnel support, the maximum support force, stiffness and maximum deformation of commonly used support forms are shown in Table 4. In addition, for complex support units, the RocSupport program can be used to provide more detailed support unit parameters.

[0211] Table 4 Main characteristic parameters of different surrounding rock support types

[0212]

[0213] The longitudinal deformation curve of the surrounding rock can be expressed by the empirical formula established by Vlachopoulos and Diederichs. The deformation on the tunnel face can generally be expressed as:

[0214]

[0215] Where: U rm is the tunnel wall displacement, R q R is the radius of plastic zone development, m is the radius of maximum plastic zone.

[0216] The deformation U of the surrounding rock on the tunnel surface before the tunnel face (Z>0) and after the tunnel face (Z<0) rz It can be expressed as:

[0217]

[0218] Where: Z is the distance between the tunnel section and the heading face.

[0219] After the excavation of the red layer soft rock tunnel, real-time support is required. According to engineering experience, the initial support is flexible support, which can provide a maximum resistance of 0.5MPa. During the excavation process, the influence of tunnel excavation on the deformation of the surrounding rock can be ignored after it exceeds a certain distance from the face. Therefore, the present invention assumes that the instantaneous deformation of the tunnel is completed in a relatively short time, and ignores the time effect of the face advancement. As the face advances, the initial support comes into contact with the surrounding rock, gradually reaches the maximum resistance, and begins to enter the plastic stage. The elastic deformation in this stage is u s1 As the tunnel face advances further, the initial support deformation increases further. After exceeding the tunnel face advancement influence distance, the plastic deformation generated in this stage is u s2 Then it enters the rheological deformation stage. Assuming that the secondary lining is completed after time t1, the deformation generated during this time period is u s3 Since the initial support has entered the plastic stage and cannot provide more resistance, the surrounding rock pressure is mainly borne by the secondary lining. In this stage, the displacement is relatively small due to the relatively large stiffness of the secondary lining. The deformation in this stage is recorded as u s4 Based on this curve, the following expression can be obtained. According to the principle of seepage rheological constraint analysis, the final deformation u of the initial support can be obtained: F for:

[0220] u F =u s1 +u s2 +u s3 +u s4 (8-63)

[0221] The deformation u1 of the initial support is:

[0222] u1=us1 +u s2 +u s3 (8-64)

[0223] The deformation u2 of the secondary lining is:

[0224] u2=u s4 (8-65)

[0225] Safety factor F of secondary lining s for:

[0226]

[0227] The load sharing ratio SF2 of the secondary lining is:

[0228]

[0229] Based on the derived red layer soft rock surrounding rock support related parameters, it can assist in the prevention and control design of harmful deformation of red layer tunnels in central Yunnan. The initial support deformation u1 should be less than the maximum allowable deformation, the final deformation needs to meet the excavation reserved deformation, and the secondary lining safety factor needs to meet a reasonable safety reserve.

[0230] Step S5.4, optimization of support timing: During the design phase, while referring to the specifications and standards, the best support timing is determined by comprehensive evaluation in combination with deformation monitoring data and engineering experience.

[0231] In this embodiment, based on the preliminary design method of harmful deformation dynamic support, the final reserved deformation beams and secondary support opportunities of four typical soft rock tunnels are obtained, as shown in Table 5.

[0232] Table 5 Secondary lining time of soft rock tunnel under different harmful deformation indexes

[0233] Serial number Harmful deformation index Reserved deformation Secondary lining time 1 0.12 194 120 days after primary lining 2 1.14 85 95 days after primary lining 3 3.16 62 80 days after primary lining 4 8.82 35 No secondary lining required

[0234] Step S6, dynamic adjustment: Based on the excavation exposure and supplementary survey results, the surrounding rock is classified in detail and basic support measures are determined. Then, a new method is quickly designed based on the harmful deformation support dynamics to dynamically adjust the support system.

[0235] In this embodiment, for the actual conditions of four tunnels with different harmful deformation indexes, surrounding rock characteristic curves with different support force conditions and time are drawn as follows: Fig. 9 As shown in the figure, we can see the evolution law of the convergent deformation (u / r) of the tunnel surrounding rock with the change of support force at different periods. It is obvious that with the decrease of the harmful deformation level, the tunnel surrounding rock is less likely to enter the accelerated creep stage.

[0236] Among them, (a) is the surrounding rock characteristic curve of different support force conditions and time corresponding to the safe deformation level. After the excavation of the soft rock tunnel, the tunnel surrounding rock was redistributed in stress. Due to the good quality of the surrounding rock and the low ground stress level, the rock mass is still in an elastic state. The deformation of the surrounding rock is mainly due to the elastic deformation caused by stress redistribution. The difference between instantaneous deformation and permanent deformation is not large, and the values ​​are relatively small.

[0237] Fig. 9 (b) is the surrounding rock characteristic curve of different support force conditions and time corresponding to the first harmful deformation level. In the instantaneous case, even if the support force is very small, it is basically in an elastic working state. When the ratio of support force to ground stress is less than 0.18, long-term rheological failure will occur. Since the ground stress level is not high, the stability of the surrounding rock can be maintained only by initial support.

[0238] Fig. 9 (c) is the surrounding rock characteristic curve of different support force conditions and time corresponding to the second level of harmful deformation. Fig. 9 (d) in the figure is the surrounding rock characteristic curve of different support force conditions and time corresponding to the three levels of harmful deformation.

[0239] Secondary harmful deformation is similar to tertiary harmful deformation, and the single deformation is relatively small. When the ratio of support force to ground stress is less than 0.45, long-term rheological failure will occur in the tunnel surrounding rock. However, the support force required in this case can be met by initial support and choosing the appropriate time for secondary lining.

[0240] Under the condition of level 3 harmful deformation, as the support force gradually decreases, the surrounding rock characteristic curve is divided into three stages of deformation (straight line segment), long-term damage stage (straight line segment) and instantaneous damage stage (curve segment). The overall deformation of the surrounding rock is large. When the ratio of support force to ground stress is less than 0.58, the tunnel surrounding rock will suffer long-term rheological damage. Due to the large initial ground stress of the tunnel, it is difficult to ensure the safety of the tunnel by relying solely on initial support and secondary lining.

[0241] 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 preventing and controlling harmful deformation of hydraulic soft rock tunnels, characterized in that: The following steps are involved: Step S1, preliminary classification of surrounding rocks: preliminary classification of tunnel surrounding rocks is performed based on tunnel geological survey results, and the stability of the surrounding rocks is evaluated; Step S2, classification of harmful deformation: Based on the preliminary classification results of the surrounding rock in step S1, the harmful deformation index of the soft rock tunnel is calculated by comprehensively considering the material composition, physical and mechanical properties, hydraulic properties and rheological properties of typical red-bed soft rocks, and combining the temporal and spatial distribution characteristics of the deformation of the red-bed soft rock tunnel. The deformation control target is subdivided into four levels according to the harmful deformation index: "safe deformation", "first-level harmful deformation", "second-level harmful deformation" and "third-level harmful deformation". Step S3, formulation of support measures: according to the red layer soft rock hydraulic properties and rheological properties, comprehensive strength-stress ratio, groundwater activity coefficient, rock mass hydraulic properties, tunnel shape coefficient and long-term strength index, and based on the classification of harmful deformation, formulate support measures that meet the deformation characteristics of the red layer soft rock tunnel; Step S4, determining the reserved deformation: in the design stage, the initial value of the reserved deformation is determined with reference to the regulations and engineering experience; in the construction stage, the harmful deformation analysis method of soft rock tunnel under the action of seepage-rheology coupling is adopted to obtain the reserved deformation of different tunnel sections through iterative calculation, and dynamic adjustment is performed in combination with deformation monitoring; Step S5, determining the support timing: the support timing includes the timing of the initial support and the secondary lining. For the initial support, regardless of the deformation level, it must be carried out in time, and the stress conditions of the surrounding rock must be improved in time to control the development of harmful deformation. For the secondary lining, different support timings are determined according to the deformation level. Step S6, dynamic adjustment: Based on the excavation exposure and supplementary survey results, the surrounding rock is classified in detail and basic support measures are determined. Then, a new method is quickly designed based on the harmful deformation support dynamics to dynamically adjust the support system.

2. The method for preventing and controlling harmful deformation of hydraulic soft rock tunnels according to claim 1 is characterized in that: In step S2, the calculation of the harmful deformation index includes the following steps: Step S2.

1. Definition of harmful deformation index: Harmful deformation index H of soft rock tunnel s The calculation formula is as follows: 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 S2.2: Calculate the comprehensive strength stress ratio J σ , the calculation formula is: In the above formula: R b is the uniaxial compressive strength of rock, obtained from the uniaxial compressive strength test of rock specimens in the laboratory; R cm is the uniaxial compressive strength of the rock mass, which is used to characterize the structural characteristics of the rock mass; σ0 is the major principal stress value of the ground stress, which is obtained through field survey data; k is the ratio of the major principal stress to the minor principal stress of the ground stress; Step S2.3: Determine the groundwater activity coefficient J w , as shown in Table 1: Table 1 Groundwater activity coefficient J w Value Step S2.4: Calculate the rock mass hydraulic coefficient J a , the calculation formula is: In the above formula: 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; I d The disintegration resistance index of soft rock is V d To measure the expansion rate of expansibility, K s To measure the softening coefficient of the softening property, the above three parameters are obtained through indoor tests; Step S2.5 Calculate the tunnel shape factor D i , the calculation formula is: D i =λR q (2-4) In the above formula: λ is the shape coefficient of the tunnel section, when the tunnel section is horseshoe-shaped, λ = 1.0, when the tunnel 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; Step S2.6: Determine the long-term strength reduction factor J c , specifically:

3. The method for preventing and controlling harmful deformation of hydraulic soft rock tunnels according to claim 2 is characterized in that: In step S2, 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.

4. The method for preventing and controlling harmful deformation of hydraulic soft rock tunnels according to claim 3 is characterized in that: In step S3, the proposed support measures are specifically as follows: For "safe deformation", the surrounding rock is mainly in an elastic state, and its own bearing capacity can meet the needs of deformation control. The supporting force mainly comes from the surrounding rock itself, and no secondary lining is required; For the tunnel section with "first-level harmful deformation", the surrounding rock is mainly in an elastic-plastic state, and the instantaneous deformation is relatively large. It is necessary to carry out initial support in time, and the harmful deformation can be controlled by the joint bearing of the surrounding rock and initial support. The support force mainly comes from the surrounding rock and initial support. For the tunnel section with "secondary harmful deformation", the surrounding rock has obvious rheological effect and significant long-term deformation. It is necessary to timely implement and strengthen the initial support, choose a reasonable time to implement the secondary lining, and control the harmful deformation through the joint bearing of surrounding rock-initial support-secondary lining. The support force comes from the surrounding rock, initial support and secondary lining. For the "third level harmful deformation" tunnel section, the rheological effect of the surrounding rock is prominent and the long-term deformation is large. It is necessary to promptly apply the initial support combined with anti-yield, and take advance reinforcement and seepage control measures for the surrounding rock. Choose a reasonable time to apply the secondary lining, and control the harmful deformation through the joint bearing of surrounding rock-initial support-secondary lining. The support force comes from the surrounding rock, initial support and secondary lining.

5. The method for preventing and controlling harmful deformation of hydraulic soft rock tunnels according to claim 1, characterized in that: In step S4, the harmful deformation analysis method of soft rock tunnel under the effect of seepage-rheology coupling is adopted in the construction stage to obtain the reserved deformation of different tunnel sections through iterative calculation. The specific steps are as follows: a) Set the excavation radius of the tunnel and calculate the initial deformation of the tunnel face based on the longitudinal deformation curve; b) Calculate the radial deformation under the current support conditions and support timing according to the physical and mechanical properties of the surrounding rock, ground stress and groundwater occurrence; c) Determine whether the secondary lining has been invaded based on the excavation radius and radial deformation: If intrusion into the secondary lining occurs, the excavation radius of the tunnel is enlarged; On the contrary, when it is far away from the designed secondary lining, the excavation radius of the tunnel should be reduced.

6. The method for preventing and controlling harmful deformation of hydraulic soft rock tunnels according to claim 1, characterized in that: In step S5, the determination of the support timing specifically includes the following steps: Step S5.1, determine the timing of initial support: after the tunnel excavation is completed, the initial support is immediately carried out to quickly change the stress state of the surrounding rock, enhance the stability of the surrounding rock, and control the initial deformation; Step S5.2, surrounding rock deformation monitoring: using a deformation monitoring system to track surrounding rock deformation displacement in real time to ensure that the deformation does not exceed a safe range; Step S5.3, determination of the timing of secondary lining: when the surrounding rock deformation enters a stable state, secondary lining construction is carried out; Step S5.4, optimization of support timing: During the design phase, while referring to the specifications and standards, the best support timing is determined by comprehensive evaluation in combination with deformation monitoring data and engineering experience.

7. The method for preventing and controlling harmful deformation of hydraulic soft rock tunnels according to claim 6, characterized in that: In step S5.3, the surrounding rock deformation enters a stable state and satisfies the following conditions: a. The horizontal convergence rate around the tunnel should be reduced to less than 0.2 mm / day; b. The vertical displacement speed of the tunnel vault or floor is controlled below 0.1 mm / day; c. The displacement speed showed a significant slowing trend, and the total displacement reached 90% of the expected value.

8. The method for preventing and controlling harmful deformation of hydraulic soft rock tunnels according to claim 6, characterized in that: In step S5.3, for the secondary lining, different support timings are determined according to the deformation level, specifically: No requirements are made for the "safe deformation" situation; In case of "first-level harmful deformation", "dig and line at the same time" should be carried out as much as possible; For "secondary harmful deformation" and "tertiary harmful deformation", multiple possible appropriate secondary lining support times are set. On the improved convergence constraint diagram, the stable deformation and the safety factor of the lining are calculated, and finally a more appropriate support time is selected.

9. The method for preventing and controlling harmful deformation of hydraulic soft rock tunnels according to claim 1, characterized in that: The step S6 specifically includes the following steps: Step S6.1, calculation and dynamic adjustment of harmful deformation index: according to the geological conditions revealed by excavation and necessary supplementary survey work, recalculate and analyze various factors of harmful deformation index, and dynamically adjust the harmful deformation level and support measures of specific tunnel sections; Step S6.2, seepage-rheological coupling deformation analysis: Based on the calculation results of step S6.1, the seepage-rheological coupling deformation analysis method is used to quickly calculate and check the support force, instantaneous and long-term deformation of the surrounding rock to ensure the rationality of the reserved deformation and the support system; Step S6.3, application of improved convergence-constraint method: after determining the surrounding rock characteristic curve, the improved convergence-constraint method is used to analyze the support timing, determine the reasonable timing of the secondary lining, and ensure that the surrounding rock deformation is within a safe range and reaches a stable state; Step S6.4, support system adjustment and feedback optimization: Combined with the deformation monitoring data of the surrounding rock, the reserved deformation, support strength and timing of the support system are optimized and adjusted to ensure the stability of the tunnel under complex geological conditions.

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