Calculation method of surrounding rock pressure and increase / decrease rate of super-long span tunnel considering partial excavation

Abstract

The present invention discloses a method for calculating the surrounding rock pressure and increase / decrease rate of a super-large span tunnel considering partial excavation. The method considers the temporal and spatial distribution characteristics of the surrounding rock pressure of the super-large span tunnel excavated in sections, defines the pilot tunnel influence coefficient to consider the influence of the pilot tunnel construction on the surrounding rock pressure of the subsequent pilot tunnel, obtains the modified surrounding rock pressure increase / decrease rate for calculating the overall surrounding rock pressure of the tunnel using the pilot tunnel surrounding rock pressure, and establishes a modified surrounding rock pressure increase / decrease rate expression related to the surrounding rock level. The calculation method has high reliability and accuracy, can provide a reference for the design and construction of super-large span tunnels excavated in sections, and can provide a basis for the improvement of relevant Chinese standards.

Description

Technical Field

[0001] The invention relates to traffic fields such as highway tunnels and underground engineering technologies, and relates to a method for calculating surrounding rock pressure and increase / decrease rate of a super-large span tunnel taking partial excavation into consideration. Background Art

[0002] With the development of my country's transportation industry, more and more single-hole four-lane ultra-long span tunnels are being built in mountainous highways, urban peripheries and economically developed areas. Compared with ordinary two-lane and three-lane tunnels, ultra-long span tunnels have larger spans and flatter structures. In particular, they are affected by partial excavation during construction, which makes the surrounding rock pressure more complicated. The calculation method of surrounding rock pressure is a basic research topic in the field of tunnel engineering and is also the key to the design of tunnel support structures. The traditional theoretical formulas and empirical formulas for calculating surrounding rock pressure are mainly for medium and small span tunnels, and neither of them considers the influence of partial excavation on surrounding rock pressure. Some scholars have studied the calculation method of surrounding rock pressure of ultra-large span tunnels.

[0003] Surrounding rock pressure is the force acting on the support structure during the process of loosening or deformation of the surrounding rock mass into the cave caused by underground cave excavation. Its calculation method is the key to the design of tunnel support structure and is also a basic research topic in the field of tunnel engineering. For a long time, domestic and foreign scholars have conducted in-depth research on the calculation method of tunnel surrounding rock pressure, and obtained the size and temporal and spatial distribution law of surrounding rock pressure, which is conducive to the development and correction of empirical formulas and theoretical calculations. Since super-large span tunnels are excavated in sections and not completed in one excavation, it is obviously not completely appropriate to directly apply the traditional surrounding rock pressure calculation formula to the determination of super-large span tunnel surrounding rock pressure.

[0004] In his 2006 paper “Research on Load Pattern and Application of Flat Extra-Large Section Highway Tunnels”, Qu Haifeng believed that when a super-large span tunnel is excavated in sections, the loosening zone is not a static single area, but a dynamic loosening zone that develops with the construction process. It is the result of the mutual influence and development of the loosening zones of each pilot tunnel. The pilot tunnel influence coefficient η is used to measure the degree of aggravation of the surrounding rock pressure of the pilot tunnel, where η = q 先 / q 后In order to show the influence of the excavation of the rear pilot tunnel on the surrounding rock pressure of the pilot tunnel, the calculation formulas for the surrounding rock pressure of the super-large span tunnel were derived based on the Prochner theory, the Tayzaghi theory and the surrounding rock pressure calculation method of the Tunnel Design Code. The range of the influence coefficient η of the pilot tunnel was obtained when the three pilot tunnels were excavated first with the side pilot and then the middle pilot: 1.0<η<1.8 according to the Prochner theory, and 1.0<η<2.3 according to the highway tunnel code. In 2011, Yan Zongxue revised the derived formula of Qu Haifeng by considering the stress path and unloading effect in the "Study on Stress Path and Spatial Effect of Large Section Tunnel Construction". The above surrounding rock pressure calculation methods for the partial excavation of super-large span tunnels are all derived under the premise of considering the influence of the excavation of the rear pilot tunnel on the surrounding rock pressure of the pilot tunnel. The value of the pilot tunnel influence coefficient η mainly depends on the experience of engineering technicians and experts, lacks the support of engineering measured data, and the calculation formula is complicated.

[0005] In summary, the current calculation method for the surrounding rock pressure of ultra-large span tunnels is still imperfect. There is an urgent need for a calculation method for the surrounding rock pressure of ultra-large span tunnels that is practical, has clear physical meaning of parameters, is simple and practical, and takes partial excavation into consideration to provide support for tunnel parameter design. Summary of the invention

[0006] In view of the above problems, the present invention proposes a method for calculating the surrounding rock pressure and increase / decrease rate of super-large span tunnels taking into account partial excavation. After theoretical analysis and on-site actual monitoring and analysis, the present invention found that when the super-large span tunnel with grade IV and grade V surrounding rock is partially excavated, the construction of the rear pilot tunnel has little effect on the calculation of the surrounding rock pressure of the pilot tunnel, and the surrounding rock pressure of the rear pilot tunnel is greater than that of the pilot tunnel. The reason is that under the constraint of the initial support of the pilot tunnel, the excavation of the rear pilot tunnel has a limited impact on the surrounding rock and support structure of the pilot tunnel that has entered a stable state, while the surrounding rock of the rear pilot tunnel has experienced the disturbance of two excavations of the former and latter pilot tunnels, and the degree of mechanical property degradation is more serious.

[0007] The technical solution of the present invention is as follows:

[0008] A method for calculating the surrounding rock pressure increase rate of a super-large span tunnel excavated in sections comprises the following steps:

[0009] 【1】The equivalent height of the tunnel's overall surrounding rock pressure is calculated based on the pilot tunnel parameters

[0010] h q =0.45×2 S-1 [1+i(b 先 -5)]η (1)

[0011] Where S is the surrounding rock grade, which is integers of 1, 2, 3, 4, 5, and 6. 先 is the width of the pilot tunnel, i is the rate of increase or decrease of surrounding rock pressure, and η is the influence coefficient of the pilot tunnel.

[0012] 【2】The equivalent height of the tunnel's overall surrounding rock pressure is calculated based on the tunnel span parameters

[0013] h q =0.45×2 S-1 [1+i'(B-5)] (2)

[0014] Where B is the tunnel excavation span, and i' is the corrected surrounding rock pressure increase or decrease rate.

[0015] 【3】Let formula (1) and (2) be equal, and obtain the corrected surrounding rock pressure increase rate

[0016]

[0017] Where b 先 It is the width of the pilot tunnel when calculating the surrounding rock pressure according to tunnel regulations.

[0018] In the calculation method of the surrounding rock pressure increase rate of the super-large span tunnel excavated in sections, the method for obtaining the pilot tunnel influence coefficient η is to set up a pressure box on site to measure the surrounding rock pressure stability value q of the pilot tunnel and the rear pilot tunnel respectively. 先 and q 后 , we get the influence coefficient of the pilot tunnel η=q 后 / q 先 .

[0019] In the calculation method of the increase rate of surrounding rock pressure of the above-mentioned partially excavated super-large span tunnel, when supporting the super-large span tunnel according to the support parameters required by the tunnel regulations, the influence coefficient η of the surrounding rock pilot tunnel of level IV is taken as 1.12, and the influence coefficient η of the surrounding rock pilot tunnel of level V is taken as 1.28.

[0020] A method for calculating surrounding rock pressure using the surrounding rock pressure increase rate. The special feature is that surrounding rock pressure q = 0.45 × 2 S-1 [1+i′(B-5)]γ; where γ is the bulk density of surrounding rock, S is the surrounding rock grade, which is taken as integers of 4, 5, or 6; B is the tunnel width; i′ is the corrected rate of increase or decrease of surrounding rock pressure after considering the influence of partial excavation.

[0021] The above-mentioned method for calculating surrounding rock pressure is characterized in that: i'=0.017×(S-1), where S is 4 or 5.

[0022] The beneficial technical effects of the present invention are as follows:

[0023] 1. The present invention provides a method for calculating the surrounding rock pressure of a partially excavated ultra-large span tunnel based on quantitative analysis of measured data. The results calculated by this method can not only reliably envelop the surrounding rock pressure values ​​of each measuring point of the first and second pilot tunnels, but also have considerable accuracy. By using the calculation formula provided by the present invention, the surrounding rock pressure increase and decrease rate can be conveniently and quickly calculated according to the surrounding rock level, and then the surrounding rock pressure of the partially excavated ultra-large span tunnel can be calculated, providing an important reference for tunnel design and construction.

[0024] 2. The parameter calculation method provided by the present invention is established based on the actual measurement and analysis results of the temporal and spatial distribution characteristics of the surrounding rock pressure of the super-large span tunnel excavated in sections. Under the constraint of the initial support of the pilot tunnel (designed and constructed according to the tunnel regulations in the construction of super-large span tunnels), the excavation of the subsequent pilot tunnel has a limited impact on the surrounding rock and support structure of the pilot tunnel that has entered a stable state. However, the surrounding rock of the subsequent pilot tunnel has experienced the disturbance of the two excavations of the pilot tunnel, and the degree of mechanical property degradation is more serious, which leads to the general η>1 (where η=q 后 / q 先 ), the surrounding rock pressure of the rear pilot tunnel is generally greater than that of the pilot tunnel, thus scientifically understanding and obtaining this parameter, laying the foundation for subsequent tunnel design and construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the typical time curve of the IV level surrounding rock pressure measured on site in the present invention;

[0026] Figure 2 It is the typical time curve of the V-level surrounding rock pressure measured on site in the present invention;

[0027] Figure 3 This is a schematic diagram of the buried position of the pressure box in the upper step bulkhead method construction;

[0028] Figure 4 This is a schematic diagram of surrounding rock pressure during the construction of the upper step bulkhead method;

[0029] In the figure: 1-pressure box; 2-pilot hole; 3-rear pilot hole; 4-temporary support. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail by comparing specific embodiments and engineering applications. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] On the contrary, the present invention covers any substitution, modification, equivalent and scheme made on the essence and scope of the present invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the detailed description of the present invention below. Those skilled in the art can fully understand the present invention without the description of these details.

[0032] In the design and construction of super-large span tunnels, it is necessary to calculate the surrounding rock pressure parameters on site. Compared with single-hole two-lane and three-lane tunnels, single-hole four-lane super-large span tunnels have the characteristics of larger excavation span, flatter structure and more complex construction process. At the same time, the partial excavation method is generally adopted during the construction process. The multiple disturbances of the surrounding rock and the mutual influence between the complex processes make the size and action mode of the surrounding rock pressure of the super-large span tunnel unclear, which directly affects the reasonable formulation of the support type and parameters of the super-large span tunnel and the construction safety.

[0033] As described in the background of the present invention, Qu Haifeng proposed to use the pilot tunnel influence coefficient η to measure the degree of pressure aggravation of the surrounding rock of the pilot tunnel, where η = q 先 / q 后 It indicates the influence of the excavation of the subsequent pilot tunnel on the surrounding rock pressure of the pilot tunnel, and the range of the pilot tunnel influence coefficient η is obtained when the three pilot tunnels are excavated first with the side pilot and then with the middle pilot: 1.0<η<1.8 according to the Proctor theory, and 1.0<η<2.3 according to the highway tunnel design specification, which means that the excavation of the subsequent pilot tunnel will have a greater impact on the surrounding rock pressure of the pilot tunnel. 先 represents the surrounding rock pressure value of the pilot tunnel, q 后 Indicates the surrounding rock pressure value of the rear pilot tunnel.

[0034] The inventor has been engaged in the practice of ultra-large span tunnels for a long time. The results of field measurements on several domestic tunnels show that for grade IV and grade V surrounding rock, the construction of the rear pilot tunnel has little effect on the calculation of the surrounding rock pressure of the pilot tunnel, and the surrounding rock pressure of the rear pilot tunnel is greater than that of the pilot tunnel. The typical results are shown in Figure 1 and Figure 2 . It can be seen from the figure that when the super-large span tunnel is excavated in sections with grade IV and grade V surrounding rocks, the trend of surrounding rock pressure change over time is basically the same, and they all experience three stages: rapid growth, slow growth, and gradual stability. The surrounding rock pressure of the pilot tunnel increases sharply within 3 to 5 days after excavation, and then enters a slow growth, and enters a stable state before the excavation of the rear pilot tunnel; when the rear pilot tunnel is excavated, the surrounding rock pressure of the pilot tunnel does not change significantly as a whole, and only a certain degree of fluctuation occurs at individual points; the excavation of the lower step and the removal of temporary support procedures have no obvious effect on the surrounding rock pressure of the leading and trailing pilot tunnels. After the construction of the invert, the surrounding rock pressure of each measuring point enters a stable state. The field test results show that the excavation of the rear pilot tunnel has no significant effect on the surrounding rock pressure of the pilot tunnel.

[0035] According to the measured data in Table 1, the influence coefficient of the pilot tunnel is calculated as η = q 后 / q 先 It represents the influence coefficient of the pilot tunnel. The average influence coefficient η of the pilot tunnel with grade IV surrounding rock is 1.12, and the average influence coefficient η of the pilot tunnel with grade V surrounding rock is 1.28.

[0036] Table 1 Influence coefficient η of pilot tunnels in each section

[0037]

[0038] Note: 1. “-” indicates missing data of measuring point;

[0039] 2. “※” indicates that the data is the surrounding rock pressure value at the top of the pilot tunnel in the double-side wall pilot tunnel method;

[0040] 3.3. “ / ” indicates that the data were corrected and eliminated according to the Chauveiller criterion in the statistical significance analysis method.

[0041] The reason is that in the construction of super-large span tunnels, after the pilot tunnel is excavated and the initial support is completed, the pilot tunnel needs to be reinforced with initial support according to the tunnel regulations. Common support parameters are shown in Table 2. Under the constraint of the initial support of the pilot tunnel, the excavation of the subsequent pilot tunnel has limited impact on the surrounding rock and support structure of the pilot tunnel that has entered a stable state. However, the surrounding rock of the subsequent pilot tunnel has experienced the disturbance of two excavations of the pilot tunnels, and the degree of mechanical property degradation is more serious.

[0042] The following introduces the method for calculating surrounding rock pressure of a super-large span tunnel of the present invention by taking the above-step CD method as an example.

[0043] Table 2 Support parameters of super-long span tunnels

[0044]

[0045]

[0046] Taking the step-middle partition method as an example, the following is a calculation step of surrounding rock pressure of a super-large span tunnel excavated in parts according to the present invention:

[0047] 【1】Measure and obtain the influence coefficient η of the pilot tunnel

[0048] like Figure 3 and Figure 4 As shown in the figure, the pressure boxes were placed on site to measure the surrounding rock pressure stability values ​​of the pilot tunnel and the rear pilot tunnel, and the pilot tunnel influence coefficient η = q was calculated. 后 / q 先 , where q 先 represents the surrounding rock pressure value of the pilot tunnel, q 后 Indicates the surrounding rock pressure value of the rear pilot tunnel.

[0049] In a typical super-long span highway tunnel, a field test of surrounding rock pressure was carried out by partial excavation method. The layout of pressure box 1 is as follows: Figure 3 According to the surrounding rock pressure stability value after the excavation of pilot tunnel 2 and before the removal of temporary support 4 and the surrounding rock pressure stability value after the excavation of rear pilot tunnel 3, the influence coefficient of rear pilot tunnel excavation on the surrounding rock pressure of pilot tunnel η=q is calculated. 后 / q 先 .

[0050] 【2】Using pilot tunnel parameters to express the equivalent height of the overall tunnel load

[0051] The surrounding rock pressure value of the subsequent pilot tunnel is used as the surrounding rock pressure of the entire tunnel to achieve the envelope of the surrounding rock pressure values ​​of each pilot tunnel in the tunnel, and the equivalent height formula of the overall tunnel load based on the pilot tunnel is obtained.

[0052] Use the equivalent height h of the pilot hole load 先 The equivalent height of the rear tunnel load h 后 =ηh 先 , then the equivalent height of the overall load of the tunnel is

[0053] h q =ηh 先 (η≥1)

[0054] Since the excavation span of the pilot tunnel is less than 14m, it is reasonable to use the formula in the tunnel specification to calculate the surrounding rock pressure of the pilot tunnel. Then the surrounding rock pressure of the pilot tunnel is used to represent the equivalent height of the overall surrounding rock pressure of the tunnel. The calculation formula is:

[0055] h q =0.45×2 S-1 [1+i(b 先 -5)]η

[0056] Where S is the surrounding rock grade, i is the surrounding rock pressure increase and decrease rate when the surrounding rock pressure calculation formula of deep buried tunnels is used to calculate the surrounding rock pressure of small and medium span tunnels; b 先 is the width of the pilot hole.

[0057] 【3】Correct the surrounding rock pressure increase and decrease rate i in the tunnel specification formula

[0058] Use the formula obtained in step [2] to correct the surrounding rock pressure increase and decrease rate in the surrounding rock pressure calculation formula recommended by the tunnel specification, obtain the corrected surrounding rock pressure increase rate i', and establish an expression for i' related to the surrounding rock grade.

[0059] The pilot tunnel influence coefficient η obtained by analyzing the surrounding rock pressure measured on site is applicable not only to the normal bearing state, but also to the ultimate bearing state of the pilot tunnel. First, the surrounding rock pressure calculation formula of the small-span tunnel (excavation span less than 14m) in the tunnel regulations is used to calculate the surrounding rock pressure of the pilot tunnel, and then the surrounding rock pressure of the subsequent pilot tunnel is calculated using the pilot tunnel influence coefficient η, and the larger surrounding rock pressure value of the previous and subsequent pilot tunnels is regarded as the surrounding rock pressure of the entire tunnel. Finally, the surrounding rock pressure obtained is substituted into the surrounding rock pressure calculation formula of the super-large span tunnel (excavation span greater than 14m) in the tunnel regulations, and the surrounding rock pressure increase and decrease rate is calculated in reverse, thereby realizing the correction of the surrounding rock pressure increase and decrease rate i during the partial excavation of the super-large span tunnel. The detailed calculation process is described as follows.

[0060] According to the calculation formula of surrounding rock pressure of deep buried tunnel in tunnel regulations, the equivalent load height of surrounding rock pressure is calculated by using the overall excavation span B of the tunnel, and then:

[0061] h q =0.45×2 S-1 [1+i'(B-5)]

[0062] When the tunnel excavation span B is used to calculate the surrounding rock pressure, the corrected surrounding rock pressure increase rate is

[0063]

[0064] Substituting the η values ​​of the IV and V surrounding rocks obtained by actual measurement in Table 1 into the above formula, the corresponding i' values ​​are obtained, as shown in Table 3. At the same time, the relationship between i' and the surrounding rock grade is constructed as shown in Table 4, and then the relationship between i' and the surrounding rock grade S is established:

[0065] i'=0.017×(S-1)

[0066] The surrounding rock grade S is 4 or 5.

[0067] Table 3. Increase and decrease rate of surrounding rock pressure i' in tunnels constructed by partial excavation method

[0068]

[0069] Table 4 Values ​​of surrounding rock pressure increase and decrease rate i'

[0070]

[0071] 【4】Determination of shallow and deep burial and horizontal pressure

[0072] Defining equivalent load height h for super-long span tunnels with partial excavation and shallow and deep buried tunnels q The surrounding rock pressure of shallow tunnels and the horizontal average pressure of super-large span tunnels are calculated with reference to tunnel regulations.

[0073] According to the method provided by the present invention, the increase and decrease rate i' of the surrounding rock pressure of the super-long span tunnel considering partial excavation is re-determined, and the relationship between i' and the surrounding rock grade is given. In engineering, i' can be calculated after determining the surrounding rock grade and substituted into the tunnel specification formula to calculate the surrounding rock pressure.

[0074] Taking the YK2+133 section of Laohushan Tunnel as an example, the surrounding rock level is Grade V, the excavation span is 20.0m, and the surrounding rock weight is 18kN / m 3 .

[0075] Corrected surrounding rock pressure increase and decrease rate

[0076] i'=0.017×(S-1)=0.017×(5-1)=0.068

[0077] Width influence factor

[0078] ω=1+i(B-5)=1+0.068×(20.0-5)=2.0

[0079] Vertically distributed pressure

[0080] q=0.45×2 S-1 ω·γ=0.45×2 5-1 ×2×18=0.259MPa

[0081] The surrounding rock pressure of the deep buried test section was calculated using the tunnel gauge, Qu Haifeng formula, Yan Zongxue formula and the method proposed in this paper, and the results are listed in Table 5. It can be seen that the calculation method proposed in this invention achieves the envelope of the measured surrounding rock pressure and is closer to the measured value.

[0082] Table 5 Comparison of measured and calculated results of test section

[0083]

[0084]

[0085] The present invention proposes a method for calculating the surrounding rock pressure of a super-large span tunnel with partial excavation based on quantitative analysis of measured data. The result calculated by this method can not only reliably encompass the surrounding rock pressure values ​​of each measuring point of the leading and trailing pilot tunnels, but also has considerable accuracy, and can better reflect the actual situation of the surrounding rock pressure during the construction of a super-large span highway tunnel with partial excavation method, and can provide an important reference for tunnel design and construction.

Claims

1. A method for calculating surrounding rock pressure and increase / decrease rate of a super-long span tunnel considering partial excavation, characterized in that: The following steps are involved: Step 1: Calculate the equivalent height of the tunnel's overall surrounding rock pressure based on the pilot tunnel parameters h q =0.45×2 S-1 [1+i(b 先 -5)]h (1) Where S is the surrounding rock grade, which is taken as integers of 1, 2, 3, 4, 5, and 6; i is the rate of increase or decrease of surrounding rock pressure; and η is the influence coefficient of the pilot tunnel; Step 2: Calculate the equivalent height of the tunnel's overall surrounding rock pressure based on the tunnel span parameters h q =0.45×2 S-1 [1+i'(B-5)] (2) Where B is the tunnel excavation span, i' is the corrected surrounding rock pressure increase and decrease rate; Step 3: Let formula (1) and (2) be equal to obtain the corrected surrounding rock pressure increase and decrease rate: Where b 先 It is the width of the pilot tunnel when calculating the surrounding rock pressure according to tunnel regulations.

2. The method for calculating surrounding rock pressure and increase / decrease rate of a super-large span tunnel considering partial excavation according to claim 1 is characterized in that: The method for obtaining the pilot tunnel influence coefficient η is to set up a pressure box on site and measure the surrounding rock pressure stability value q of the pilot tunnel and the rear pilot tunnel respectively. 先 and q 后 , the pilot tunnel influence coefficient η=q 后 / q 先 .

3. The method for calculating surrounding rock pressure and increase / decrease rate of a super-large span tunnel considering partial excavation according to claim 2 is characterized in that: When supporting the super-large span tunnel according to the support parameters required by the tunnel regulations, the influence coefficient η of the pilot tunnel of grade IV surrounding rock is taken as 1.12, and the influence coefficient η of the pilot tunnel of grade V surrounding rock is taken as 1.

28.

4. The method for calculating surrounding rock pressure and increase / decrease rate of a super-long span tunnel considering partial excavation according to any one of claims 1 to 3, characterized in that: The surrounding rock pressure is q=0.45×2 S-1 [1+i′(B-5)]γ Where γ is the bulk density of surrounding rock, S is the surrounding rock grade, which is taken as integers of 4, 5, or 6; and B is the tunnel width.

5. The method for calculating surrounding rock pressure and increase / decrease rate of a super-long span tunnel considering partial excavation according to claim 4 is characterized in that: i'=0.017×(S-1), where S is 4 or 5.

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