Method for determining optimal initial support timing of underground works

Abstract

The application discloses a method for determining an optimal primary support time of underground engineering, proposes a concept of plastic volume rate, determines the optimal primary support time through a sudden change point of a plastic volume rate change curve with a surrounding rock release rate, takes a displacement release rate as a link, combines a surrounding rock longitudinal deformation convergence curve, determines a supporting structure following a working face distance index as a support time criterion, quantitatively and explicitly determines the optimal primary support time of the surrounding rock, and establishes a method for determining the primary support time of the underground engineering layered excavation based on the plastic volume rate, thereby breaking through a problem that a displacement evolution critical state is difficult to find in a method for determining the primary support time based on the displacement release rate and the method cannot be applied to the determination of the primary support time of different layers in the layered excavation of the underground powerhouse, and providing a reference for the layered and stepped excavation design and construction of large underground engineering.

Description

Technical Field

[0001] This invention relates to the field of tunnels and underground engineering, and specifically to a method for determining the optimal timing for initial support in underground engineering. Background Technology

[0002] The stability of underground engineering projects is a crucial concern in their construction. According to the New Austrian Tunneling Method (NATM), the optimal timing for initial support refers to when support should be implemented after tunnel excavation to ensure both the self-supporting capacity of the surrounding rock and minimal stress on the support structure. Supporting too early prevents the rock's self-supporting capacity from being fully utilized, resulting in excessive support pressure, increased costs, and reduced construction efficiency. Conversely, untimely support leads to excessive deformation and instability of the surrounding rock. Therefore, choosing the appropriate initial support timing directly impacts the full utilization of the rock's self-supporting capacity, thereby reducing project costs and improving construction efficiency.

[0003] Previous studies on the timing of initial support during underground engineering excavation have explored this topic in depth through theoretical analysis, laboratory experiments and numerical simulations, and field monitoring. However, these studies have the following shortcomings: 1) Theoretical analyses contain too many idealized assumptions and cannot reflect the actual conditions of underground engineering sites under complex geological conditions; moreover, most theoretical analyses can only provide qualitative explanations of support timing and cannot yield quantitative results; 2) Laboratory experiments and numerical simulations are mostly biased towards qualitative evaluation of support effects and fail to provide effective and feasible control conditions or selection methods; 3) Field monitoring is a relatively conventional and effective means of determining support timing, but in practice, it faces the difficulty of continuously monitoring the deformation of the surrounding rock immediately after blasting; 4) These studies have failed to provide effective and feasible control conditions or selection methods, therefore these methods are difficult to apply to actual engineering projects; 5) Existing research results are mostly focused on tunnel excavation and have limitations when applied to the phased excavation of large-scale underground engineering projects.

[0004] Since the stress release of the surrounding rock during tunnel excavation is macroscopically manifested as the deformation of the surrounding rock, there is a close relationship between the stress release rate and the deformation convergence during the excavation process. Based on this, some scholars have used two-dimensional and three-dimensional numerical simulation methods to analyze the spatial deformation characteristics of the surrounding rock in the cross-section and longitudinal section after tunnel excavation, based on the basic theory of convergence-constraint method. They have proposed a method to determine the optimal support timing by taking the abrupt change point of the displacement release rate in the curve of the relationship between displacement release rate and stress release rate of the surrounding rock as the basis for determining the timing of the initial support, and taking the distance between the monitoring section and the working face in the longitudinal convergence deformation curve of the surrounding rock as the criterion for selecting the support timing. This method has been applied to actual engineering projects. However, this method has the following problems: 1) It is only applicable to general underground projects with small cross-sections that only require one excavation; 2) For large underground projects with large cross-sections that require layered excavation, such as underground powerhouses, the trend of displacement release rate with the stress release rate of the surrounding rock is not obvious, and it is difficult to find the critical state of displacement evolution.

[0005] In summary, there is an urgent need for a method to determine the optimal timing for initial support in underground engineering projects, in order to solve the problem of determining the optimal support timing in existing technologies. Summary of the Invention

[0006] The purpose of this invention is to provide a method for determining the optimal timing of initial support in underground engineering, thereby solving the problem of determining the optimal support timing in the prior art. The specific technical solution is as follows:

[0007] A method for determining the optimal timing for initial support in underground engineering includes the following steps:

[0008] Step S1: Based on the construction data, establish two-dimensional and three-dimensional numerical calculation models of the underground project, and arrange multiple monitoring points on the excavation section of the two-dimensional numerical calculation model; arrange monitoring sections at the center of the axis of the three-dimensional numerical calculation model;

[0009] Step S2: Based on the two-dimensional numerical calculation model, the full-section excavation simulation of the i-th layer of the underground project is carried out. The displacement release rate corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock is determined according to the simulation results under different surrounding rock stress release rates.

[0010] Step S3: Based on the three-dimensional numerical calculation model, the i-th layer of the underground project is simulated by step excavation to obtain the displacement of each monitoring point during the step excavation process. After processing the displacement of each monitoring point, the longitudinal convergence deformation curve of the surrounding rock is obtained, which shows the relationship between the distance from the working face to the monitoring section and the displacement release rate.

[0011] Step S4: Based on the displacement release rate determined in Step S2 and the longitudinal convergence deformation curve of the surrounding rock in Step S3, find the corresponding distance between the working face and the monitoring section as the optimal time for the first support of the i-th layer.

[0012] Step S5: Apply the corresponding support to the two-dimensional and three-dimensional numerical calculation models using the optimal initial support timing obtained in step S4, and obtain the final state after excavation and support of the i-th layer. Use the final state after the simulation of the i-th layer excavation as the initial state of the next layer excavation.

[0013] Step S6: Let i = i+1, repeat steps S2 to S5 to determine the optimal time for initial support of the (i+1)th layer excavation.

[0014] Step S7: Repeat step S6 to determine the optimal timing for initial support of each excavation layer.

[0015] In the preferred embodiment of the above technical solution, in step S1, four monitoring points are arranged on the excavation section of the two-dimensional numerical calculation model.

[0016] In the preferred embodiment of the above technical solution, step S2 includes:

[0017] Step S2.1: Based on the simulation results under different surrounding rock stress release rates, plot the relationship curves between the plastic volume fraction of the surrounding rock and the stress release rate of the surrounding rock on the cross section and the relationship curves between the displacement release rate of the surrounding rock and the stress release rate of the surrounding rock on the longitudinal section.

[0018] Step S2.2: Determine the stress release rate of the surrounding rock corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock based on the steep increase point of the curve relating the plastic volume fraction of the surrounding rock to the stress release rate of the surrounding rock. Determine the displacement release rate corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock based on the curve relating the stress release rate of the surrounding rock to the displacement release rate.

[0019] In the preferred embodiment of the above technical solution, the definition of the plastic volume fraction ξ of the surrounding rock in step S2.1 is as shown in Equation 1):

[0020]

[0021] Where: V p V represents the volume of the surrounding rock that underwent plastic deformation after excavation. E This refers to the total volume of the excavation advance.

[0022] In the preferred embodiment of the above technical solution, the displacement release rate λ in step S2.2 is defined as shown in Equation 2):

[0023] λ=(u x / u ∞ )×100% 2);

[0024] Where: u x Let u be the displacement of the surrounding rock under any stress release rate. ∞ This indicates the displacement when the stress release rate of the surrounding rock is 100%.

[0025] In the preferred embodiment of the above technical solution, in step S2.1, by sequentially applying different surrounding rock stress release rates, the relationship curves between the plastic volume fraction of the surrounding rock and the surrounding rock stress release rate, as well as the relationship curves between the displacement release rate and the surrounding rock stress release rate under different surrounding rock stress release rates during the excavation of the i-th layer are obtained.

[0026] Among them, the stress release rates of the surrounding rock were applied in sequence as follows: 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%.

[0027] In the preferred embodiment of the above technical solution, in step S3, the displacement of each monitoring point during the step-by-step excavation process is obtained, and the displacement change curve is obtained based on the displacement of each monitoring point. After the displacement change curve is uniformized, the longitudinal convergence deformation curve of the surrounding rock is obtained, which is related to the distance between the working face and the monitoring section and the displacement release rate.

[0028] In the preferred embodiment of the above technical solution, in step S4, the distance between the working face and the monitoring section corresponding to the displacement release rate determined in step S2 on the longitudinal convergence deformation curve of the surrounding rock is taken as the optimal time for initial support.

[0029] The application of the technical solution of the present invention has the following beneficial effects:

[0030] The optimal support timing method of this invention proposes the concept of plastic volume ratio. The optimal initial support timing is determined by the abrupt change point in the curve of plastic volume ratio versus surrounding rock release rate. Using displacement release rate as a link, and combining it with the longitudinal deformation convergence curve of the surrounding rock, the distance between the support structure and the working face is determined as the criterion for support timing. This quantitatively clarifies the optimal initial support timing for the surrounding rock and establishes a method for determining the initial support timing of layered excavation in underground engineering based on plastic volume ratio. This method overcomes the difficulties of finding the critical state of displacement evolution and the inability to apply it to determining the initial support timing of different layers in layered excavation of underground powerhouses, which are problems encountered in previous methods based on displacement release rate. It provides a reference for the design and construction of layered and step-by-step excavation in large-scale underground engineering projects. The method of this invention can be directly applied to the construction design of large-scale underground engineering projects, significantly improving excavation efficiency and economic benefits while ensuring structural safety. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] In the attached diagram:

[0033] Figure 1 This is a schematic diagram of the numerical model in this embodiment; (a) illustrates the two-dimensional numerical calculation model, and (b) illustrates the three-dimensional numerical calculation model.

[0034] Figure 2 This is a schematic diagram of the support structure in this embodiment;

[0035] Figure 3 This is a schematic diagram of the arrangement of monitoring points and monitoring sections in this embodiment. (a) shows the monitoring points; (b) shows the monitoring sections.

[0036] Figure 4 This is a curve diagram showing the relationship between determining the optimal timing for the first layer of support;

[0037] Figure 5 This is a graph showing the relationship between determining the optimal timing for the second layer of support.

[0038] Figure 6 This is a curve diagram showing the relationship between determining the optimal timing of the third layer of support;

[0039] in, Figures 4 to 6 In the figure, (a) is the curve showing the relationship between plastic volume fraction and surrounding rock stress release rate; (b) is the curve showing the relationship between surrounding rock displacement release rate and surrounding rock stress release rate; (c) is the curve showing the relationship between surrounding rock displacement and the distance between the monitoring section and the tunnel face; and (d) is the curve showing the relationship between displacement release rate and the distance between the monitoring section and the tunnel face.

[0040] Figure 3 In the diagram, 1 represents a monitoring point; 2 represents a monitoring section. Detailed Implementation

[0041] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0042] Example:

[0043] A method for determining the optimal timing for initial support in underground engineering includes the following steps S1 to S7, such as... Figures 1 to 6 As shown, the details are as follows:

[0044] Step S1: As Figures 1 to 3 As shown, based on the construction data, two-dimensional and three-dimensional numerical calculation models of the underground project are established, and multiple monitoring points are arranged on the excavation section of the two-dimensional numerical calculation model; a monitoring section is arranged at the center of the axis of the three-dimensional numerical calculation model. Specifically, considering the results of the underground project survey and the designed excavation scheme, two-dimensional and three-dimensional numerical calculation models of the underground project (taking an underground powerhouse as an example in this embodiment) are established, and four monitoring points are arranged on the excavation section of the two-dimensional model; a monitoring section is arranged at the center of the axis of the three-dimensional calculation model.

[0045] Step S2: As Figure 4As shown, based on a two-dimensional numerical calculation model, a full-section excavation simulation is performed on the i-th layer of the underground engineering. The displacement release rate corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock is determined based on the simulation results under different surrounding rock stress release rates. Step S2 specifically includes steps S2.1 and S2.2, as follows:

[0046] Step S2.1: Based on the two-dimensional numerical calculation model, a full-section excavation simulation is performed on the i-th floor of the factory building (where i = 1, i.e., excavation starts from the first floor). During the simulation, different surrounding rock stress release rates are considered. Based on the simulation results under different surrounding rock stress release rates, the relationship curves between the plastic volume fraction ξ of the surrounding rock and the stress release rate δ of the surrounding rock on the cross section and the relationship curves between the displacement release rate λ of the surrounding rock and the stress release rate δ of the surrounding rock on the longitudinal section are plotted respectively.

[0047] In step S2.1, the definition of the plastic volume fraction ξ of the surrounding rock is shown in Equation 1):

[0048]

[0049] Where: V p V represents the volume of the surrounding rock that underwent plastic deformation after excavation. E The total volume of the excavation advance;

[0050] The definition of the surrounding rock displacement release rate λ is shown in Equation 2):

[0051] λ=(u x / u ∞ )×100% 2);

[0052] Where: u x Let u be the displacement of the surrounding rock under any stress release rate. ∞ This represents the displacement when the surrounding rock stress release rate is 100%.

[0053] Specifically, by sequentially applying different surrounding rock stress release rates, the relationship curves between the plastic volume fraction of the surrounding rock and the surrounding rock stress release rate, as well as the relationship curves between the displacement release rate and the surrounding rock stress release rate under different surrounding rock stress release rates in the first layer excavation are obtained. In this embodiment, preferably, surrounding rock stress release rates of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% are applied sequentially.

[0054] In step S2.1, the following points need to be explained:

[0055] 1) The volume ratio of the plastic zone is the ratio of the volume of the plastic zone to the volume of the excavated body. A two-dimensional numerical calculation model of the tunnel is established. The tunnel is excavated in one go, and the excavation load is released in stages (the excavation load is released in 10 stages, with load release rates of 10%, 20%, ..., 90%, 100%). After numerical calculation, the volume ratio of the plastic zone corresponding to different load release rates can be determined by the fish language.

[0056] 2) As the excavation load release rate increases, the surrounding rock displacement continues to increase, and the plastic zone appears from nothing. After reaching a certain excavation load release rate, both the displacement increment and the plastic zone increase rapidly. The time when the excavation load release rate occurs at the point of sudden change in the volume fraction of the plastic zone is the optimal time for initial support. The displacement release rate corresponding to this load release rate is the displacement release rate corresponding to the optimal support time.

[0057] Step S2.2: Based on step S2.1, determine the stress release rate corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock in step S2.1 according to the steep increase point of the curve relating plastic volume fraction of the surrounding rock to stress release rate of the surrounding rock (the steep increase point is the point in the curve relating plastic volume fraction of the surrounding rock to stress release rate where the slope increases relatively sharply for different stress release rates). Then, find the corresponding displacement release rate in the curve relating stress release rate of the surrounding rock to displacement release rate based on this stress release rate. Thus, the displacement release rate corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock can be determined.

[0058] Step S3: Based on the three-dimensional numerical calculation model, the i-th layer (i.e., the first layer) of the underground project is simulated by step excavation (i.e., gradually advancing from one end of the chamber to the other end) to obtain the displacement change curve of each monitoring point during the step excavation process. After the displacement change curve is uniformized, the longitudinal convergence deformation curve of the surrounding rock is obtained, which is related to the distance between the working face and the monitoring section and the displacement release rate (the optimal timing of the initial support can be obtained based on the distance of the support structure following the working face).

[0059] Step S4: Based on the displacement release rate determined in Step S2 and the longitudinal convergence deformation curve of the surrounding rock in Step S3, the optimal initial support timing is determined by finding the corresponding distance between the support structure and the working face as the criterion for selecting the support timing. Specifically, the optimal initial support timing for the i-th layer is determined by the distance between the working face and the monitoring section corresponding to the displacement release rate in Step S2 on the longitudinal convergence deformation curve of the surrounding rock. The explanation for Step S4 is: Support timing is a time concept. In practice, it is difficult to specify exactly when to perform support; therefore, the distance between the support structure and the working face is used as the support timing indicator.

[0060] Step S5: Apply the corresponding support to the two-dimensional and three-dimensional numerical calculation models using the optimal initial support timing of the i-th layer obtained in step S4, and obtain the final state after excavation and support of the i-th layer (i.e., the first layer). Use the final state after the excavation simulation of the i-th layer as the initial state for the excavation of the next layer (i.e., the i+1 layer, i.e. the second layer).

[0061] Step S6: Let i = i+1, repeat steps S2 to S5 to determine the optimal timing for the initial support of the (i+1)th layer. The explanation of steps S5 and S6 here is: through step S5, the final state of the previous layer is used as the initial state of the next layer, and the optimal timing for the initial support of the next layer (i+1) is determined in the same way as the initial support of the ith layer.

[0062] Step S7: Repeat step S6 to determine the optimal initial support timing for each excavation layer in sequence. In other words, the optimal initial support timing for each layer can be determined sequentially in the above manner. In this embodiment, there are six excavation layers, which means that the support timing for all six layers needs to be determined.

[0063] The following is the calculation process of the optimal support timing determination method in this embodiment, combined with a specific case:

[0064] Establish two-dimensional and three-dimensional computational models:

[0065] like Figures 1 to 3 As shown, based on the actual situation of an underground powerhouse project, two-dimensional and three-dimensional numerical calculation models were established respectively. The burial depth of the underground powerhouse was selected as 200m, and the cross-sectional dimensions of the powerhouse were 58m (height) × 27m (width), with excavation carried out in 6 layers. The boundary dimensions of the two-dimensional numerical calculation model were 200m × 200m, and four monitoring points were arranged on the excavation cross-section of the two-dimensional model. The length of the tunnel axis in the three-dimensional numerical calculation model was 100m, and a monitoring section (e.g., [missing information]) was arranged at the center of the axis of the three-dimensional powerhouse calculation model. Figure 3 As shown). Support scheme (such as...) Figure 2 (As shown) The system uses ordinary mortar anchor bolts Ф32 / Ф28@1.5×1.5, L=9m / 6m, arranged in a quincunx pattern, with 15cm thick shotcrete and Φ8@200×200 steel mesh. The stress relief method is used to excavate different layers of the two-dimensional model sequentially; then, in 3m increments, different layers of the three-dimensional model are excavated in stages.

[0066] In this embodiment, the numerical calculation model adopts the Mohr-Coulomb elastoplastic model. The surrounding rock of the main powerhouse cavern is mainly Class III surrounding rock. According to the field test and exploration report, the rock mass calculation parameters are shown in Table 1.

[0067] Table 1 Numerical Calculation Parameters for Rock Mass

[0068]

[0069] The numerical calculation parameters for the ordinary mortar anchor bolts in the system are shown in Table 2.

[0070] Table 2 Numerical Calculation Parameters for Mortar Anchor Bolts

[0071]

[0072] The timing for the first layer of excavation and support is determined, such as Figure 4 As shown:

[0073] Using a two-dimensional model, by applying different surrounding rock stress release rates (10%, 20%, 30%, ..., 80%, 90%, 100%), the variation curves of plastic volume fraction under different surrounding rock stress release rates during the excavation of the first layer were obtained (e.g., Figure 4 (as shown in (a)) and the variation curves of displacement release rate under different surrounding rock stress release rates (as shown in (a)). Figure 4 (as shown in (b)).

[0074] Depend on Figure 4 As can be seen from (a), during the first layer of excavation, the plastic volume fraction of the surrounding rock begins to increase sharply when the stress release rate reaches 80%. Therefore, the optimal initial support timing corresponds to a stress release rate of 80%. According to... Figure 4 (b) shows that the optimal initial support timing corresponds to a rock displacement release rate of 79.5%.

[0075] A three-dimensional model was used to simulate the step-by-step excavation of the first layer, and the deformation convergence curve of the surrounding rock during the first layer excavation was obtained, as shown in the figure. Figure 4 (c)

[0076] The deformation convergence curve of the surrounding rock was homogenized to obtain the longitudinal displacement release rate curve of the surrounding rock during the excavation process, as shown in the figure. Figure 4 (d) Based on the previously determined optimal initial support, the actual displacement release rate is 79.5%, combined with... Figure 4 (d) can be used to find that the distance between the monitoring section corresponding to the displacement release rate and the working face is 14.8m, which means that the distance between the support structure and the working face corresponding to the optimal initial support time for the first layer of excavation is 14.8m.

[0077] Apply appropriate support to the model based on the determined optimal timing for initial support, obtain the final state after the first layer of excavation and support, and use the final state after the simulation of the first layer of excavation as the initial state for the second layer of excavation.

[0078] The timing for the second layer of excavation and support is determined, such as... Figure 5 As shown:

[0079] Using a two-dimensional model, by applying different surrounding rock stress release rates (10%, 20%, 30%, ..., 80%, 90%, 100%), the variation curves of plastic volume fraction under different surrounding rock stress release rates during the second layer excavation were obtained (e.g., Figure 5 (a) and the variation curves of displacement release rate under different surrounding rock stress release rates are shown in Figure 1. Figure 5 (b)

[0080] Depend on Figure 5 As can be seen from (a), during the excavation of the second layer, the plastic volume fraction of the surrounding rock begins to increase sharply when the stress release rate reaches 70%. Therefore, the optimal initial support timing corresponds to a stress release rate of 70%. According to... Figure 5 (b) shows that the optimal initial support timing corresponds to a rock displacement release rate of 60.5%.

[0081] A three-dimensional model was used to simulate the step-by-step excavation of the second layer, and the deformation convergence curve of the surrounding rock during the second layer excavation was obtained. Figure 5 (c)

[0082] The deformation convergence curve of the surrounding rock was homogenized to obtain the longitudinal displacement release rate curve of the surrounding rock during the excavation process, as shown in the figure. Figure 5 (d) Based on the previously determined optimal initial support, the actual corresponding displacement release rate is 60.5%, combined with... Figure 5 (d) can be used to find that the distance between the monitoring section corresponding to the displacement release rate and the working face is 4.9m, which means that the distance between the support structure and the working face corresponding to the optimal initial support time for the second layer of excavation is 4.9m.

[0083] Apply the corresponding support to the model according to the determined optimal timing of the initial support, obtain the final state after the second layer of excavation and support, and use the final state after the simulation of the second layer of excavation as the initial state of the third layer of excavation.

[0084] The timing for the third layer of excavation and support has been determined, such as... Figure 6 As shown:

[0085] Using a two-dimensional model, by applying different surrounding rock stress release rates (10%, 20%, 30%, ..., 80%, 90%, 100%), the variation curves of plastic volume fraction under different surrounding rock stress release rates during the excavation of the third layer were obtained (e.g., Figure 6 (a) and the variation curves of displacement release rate under different surrounding rock stress release rates are shown in Figure 1. Figure 6 (b)

[0086] Depend on Figure 6As can be seen from (a), during the excavation of the third layer, the plastic volume fraction of the surrounding rock began to increase sharply when the stress release rate reached 70%. Therefore, the optimal initial support timing corresponds to a stress release rate of 70%. According to... Figure 6 (b) shows that the optimal initial support timing corresponds to a rock displacement release rate of 59.5%.

[0087] A three-dimensional model was used to simulate the step-by-step excavation of the third layer, and the deformation convergence curve of the surrounding rock during the third layer excavation was obtained. Figure 6 (c)

[0088] The deformation convergence curve of the surrounding rock was homogenized to obtain the longitudinal displacement release rate curve of the surrounding rock during the excavation process, as shown in the figure. Figure 6 (d) Based on the previously determined optimal initial support, the actual displacement release rate is 59.5%, combined with... Figure 6 (d) can be used to find that the distance between the monitoring section corresponding to the displacement release rate and the working face is 4.8m, which means that the distance between the support structure and the working face corresponding to the optimal initial support time for the third layer of excavation is 4.8m.

[0089] Apply the corresponding support to the model according to the determined optimal timing of the initial support, obtain the final state after the third layer of excavation and support, and use the final state after the simulation of the third layer of excavation as the initial state of the fourth layer of excavation.

[0090] As can be seen from the above, the support timing for the first to third layers can be obtained based on the above calculations. Since the method for determining the support timing for the fourth to sixth layers is the same as that for the first layer, this embodiment will not elaborate further. The support timing for each layer in this embodiment can be found in Table 3.

[0091] Table 3. Determined support timing for each layer.

[0092] Timing of support 14.8m 4.9m 4.8m 4.8m 4.9m 5.8m

[0093] The optimal initial support timing scheme for the underground powerhouse ultimately formed in this embodiment can provide important reference value for the design and construction of actual underground engineering projects.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the optimal timing for initial support in underground engineering, characterized in that, Includes the following steps: Step S1: Based on the construction data, establish two-dimensional and three-dimensional numerical calculation models of the underground project, and arrange multiple monitoring points on the excavation section of the two-dimensional numerical calculation model; arrange monitoring sections at the center of the axis of the three-dimensional numerical calculation model; Step S2: Based on the two-dimensional numerical calculation model, perform the calculation on the first... Full-section excavation simulation was conducted for each layer, and the displacement release rate corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock was determined based on the simulation results under different surrounding rock stress release rates. Step S3: Based on the three-dimensional numerical calculation model, the underground engineering is carried out using a step-by-step excavation method. Layer-by-layer simulated excavation was used to obtain the displacement of each monitoring point during the step-by-step excavation process. After processing the displacement of each monitoring point, the longitudinal convergence deformation curve of the surrounding rock, which is related to the distance between the face of the tunnel and the monitoring section and the displacement release rate, was obtained. Step S4: Based on the displacement release rate determined in Step S2, and based on the longitudinal convergence deformation curve of the surrounding rock in Step S3, find the corresponding distance between the working face and the monitoring section as the first... The optimal time for initial support of the layer; Step S5: Apply corresponding support to the two-dimensional and three-dimensional numerical calculation models using the optimal initial support timing obtained in Step S4, and obtain the... The final state after layer excavation and support will be the first The final state after the layer excavation simulation is used as the initial state for the next layer excavation; Step S6: Let Repeat steps S2 to S5 to determine the first... The optimal time for initial support during layered excavation; Step S7: Repeat step S6 to determine the optimal timing for initial support for each excavation layer. Step S2 includes: Step S2.1: Based on the simulation results under different surrounding rock stress release rates, plot the relationship curves between the plastic volume fraction of the surrounding rock and the stress release rate of the surrounding rock on the cross section and the relationship curves between the displacement release rate of the surrounding rock and the stress release rate of the surrounding rock on the longitudinal section. Step S2.2: Determine the stress release rate of the surrounding rock corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock based on the steep increase point of the curve relating the plastic volume fraction of the surrounding rock to the stress release rate of the surrounding rock. Determine the displacement release rate corresponding to the abrupt change point of the plastic volume fraction of the surrounding rock based on the curve relating the stress release rate of the surrounding rock to the displacement release rate.

2. The method for determining the optimal initial support timing in underground engineering according to claim 1, characterized in that, In step S1, four monitoring points are arranged on the excavation section of the two-dimensional numerical calculation model.

3. The method for determining the optimal timing for initial support in underground engineering according to claim 1, characterized in that, In step S2.1, the plastic volume fraction of the surrounding rock The definition is shown in Equation 1): 1）； in: This refers to the volume of the surrounding rock that underwent plastic deformation after excavation. This refers to the total volume of the excavation advance.

4. The method for determining the optimal timing of initial support in underground engineering according to claim 1 or 3, characterized in that, In step S2.2, the displacement release rate The definition is shown in Equation 2): 2）； in: Let represent the displacement of the surrounding rock under any stress release rate. This indicates the displacement when the stress release rate of the surrounding rock is 100%.

5. The method for determining the optimal timing of initial support in underground engineering according to claim 1, characterized in that, In step S2.1, by sequentially applying different surrounding rock stress release rates, the first... Curves showing the relationship between plastic volume fraction of surrounding rock and stress release rate of surrounding rock under different stress release rates in layered excavation, as well as the relationship between displacement release rate of surrounding rock and stress release rate of surrounding rock. Among them, applied sequentially , , , , , , , , as well as The stress release rate of the surrounding rock.

6. The method for determining the optimal timing for initial support in underground engineering according to claim 1, characterized in that, In step S3, the displacement of each monitoring point during the step-by-step excavation process is obtained, and the displacement change curve is obtained based on the displacement of each monitoring point. After the displacement change curve is homogenized, the longitudinal convergence deformation curve of the surrounding rock is obtained, which shows the relationship between the distance from the working face to the monitoring section and the displacement release rate.

7. The method for determining the optimal initial support timing in underground engineering according to claim 6, characterized in that, In step S4, the optimal initial support timing is determined by the distance between the working face and the monitoring section corresponding to the displacement release rate determined in step S2 on the longitudinal convergence deformation curve of the surrounding rock.

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