A new method for determining the support and excavation methods of highway tunnels

Abstract

The present invention discloses a novel method for determining the support and excavation methods of highway tunnels. After a tunnel cycle is completed and a new face is exposed, the RMR level of the face surrounding rock is determined; the tunnel support method is determined based on the face surrounding rock RMR grading results and the degree of rock fragmentation; and the final tunnel excavation method is determined based on the modified Nguyen model of surrounding rock self-stabilization time according to the face surrounding rock RMR grading results. The method for determining the tunnel support and excavation methods in the present invention can greatly simplify the tunnel design work. In addition, the determination of the tunnel self-stabilization time in the present invention provides a new approach to tunnel construction and excavation methods.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and in particular to a method for determining a new highway tunnel support mode and excavation mode. Background Art

[0002] With the continuous development of my country's economy, tunnel engineering has developed rapidly. Currently, the most widely used construction method for mountain tunnels in my country is the New Austrian Tunneling Method (NATM), proposed by Austrian researchers in the 1950s. In recent years, my country has introduced the New Austrian Tunneling Method (NATM), a geotechnical controlled deformation analysis method, which is currently being promoted and applied in my country.

[0003] The new method was proposed by Italian scholar Professor Pietro in the 1970s. Its core idea is that the deformation of the advance core soil is the main cause of tunnel deformation. Its design and construction procedures are divided into five steps: investigation stage, diagnosis stage, treatment stage, implementation stage, and testing stage. Among them, the diagnosis stage requires the use of mathematical methods to predict the stability of the tunnel advance core soil and select the tunnel support type based on the stability of the advance core soil. However, mathematical methods are difficult to use and difficult to implement in the field. In addition, the new method design and construction procedures only explain the method for determining the tunnel support form, and the tunnel excavation method is not explained in detail. During on-site construction, the excavation method must be determined based on the actual situation. Summary of the Invention

[0004] In view of the above-mentioned problems, the present invention aims to provide a method for determining a new highway tunnel support method and excavation method to solve the problems existing in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A new method for determining the support mode and excavation mode of a highway tunnel is characterized by comprising the following steps:

[0007] S1: After a tunnel cycle is completed and a new tunnel face is exposed, the RMR level of the surrounding rock at the tunnel face is determined;

[0008] S2: Determine the tunnel support method based on the RMR classification results of the surrounding rock mass at the tunnel face, the degree of rock fragmentation, and whether the tunnel is located in a special area;

[0009] S3: Based on the RMR classification results of the surrounding rock at the tunnel face, the final tunnel excavation method is determined based on the modified Nguyen model of surrounding rock self-stabilization time.

[0010] Furthermore, the specific operation of step S1 includes the following steps:

[0011] S101: Take multiple rock blocks at the tunnel face and conduct load strength tests to determine the point load strength of the surrounding rock at the tunnel face;

[0012] S102: measuring grade parameters of the surrounding rock of the tunnel face, wherein the grade parameters include the length, width, roughness, weathering degree, filling condition, occurrence and distance between discontinuities on the tunnel face;

[0013] S103: Calculate the RQD value of the surrounding rock of the tunnel face based on the distance between discontinuous surfaces on the tunnel face.

[0014] RQD=115-3.3J V

[0015] J V =1 / S1+1 / S2+……1 / S n

[0016] Where, J V is the number of joints per unit volume; S1, S2, ..., S n is the distance between discontinuities on the tunnel face;

[0017] S104: Observe the tunnel face and determine the tunnel face state, where the tunnel face state includes dry, damp, wet, dripping, and flowing;

[0018] S105: Calculate the RMR level of the surrounding rock at the tunnel face based on the results of steps S101 to S104.

[0019] Furthermore, when the RMR level of the surrounding rock of the face is II and the rock mass is slightly crushed, the support method is as follows: the arch pre-support adopts 7-12 fully grouted rock anchors with a length of 6.0m, a longitudinal spacing of 1.2m, and a transverse spacing of 2.05m; the primary support adopts 20cm thick steel fiber shotcrete; the secondary lining adopts 40cm thick plain concrete, and the invert arch adopts 70cm thick plain concrete.

[0020] Furthermore, when the tunnel face surrounding rock mass RMR level is II-III and the rock mass is moderately crushed, the support method is as follows: the primary support uses 20cm thick steel fiber shotcrete and two 160 I-beam steel arch frames with a longitudinal spacing of 1.2±10%m; the secondary lining uses 40cm thick plain concrete, and the invert arch uses 70cm thick plain concrete;

[0021] When the tunnel face surrounding rock RMR classification is II-III and is located in a special area, the support method is as follows: the arch crown pre-support adopts 39±10 steel pipes with a diameter of 114.3mm and a wall thickness of 10mm; the primary support adopts 20cm thick steel fiber shotcrete and a steel arch frame composed of two 160 I-beams with a longitudinal spacing of 1.0m; the secondary lining adopts plain concrete with a thickness of 40cm to 110cm, and the invert arch adopts plain concrete with a thickness of 70cm.

[0022] Furthermore, when the tunnel face surrounding rock mass RMR level is III-IV and the rock mass is moderately to highly fractured, the support method is as follows: the primary support uses 20cm thick steel fiber shotcrete and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.2±10%m; the secondary lining uses 65cm thick plain concrete and the invert uses 80cm thick reinforced concrete;

[0023] When the RMR level of the surrounding rock of the face is III-IV and the rock mass is moderately crushed, the support method is as follows: the arch crown pre-support adopts 7-12 fully grouted rock anchors with a length of 6.0m, a longitudinal spacing of 1.4m, and a transverse spacing of 2.05m; the primary support adopts 20cm thick steel fiber shotcrete and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.4±10%m; the secondary lining adopts 65cm thick plain concrete, and the invert arch adopts 80cm thick reinforced concrete.

[0024] Furthermore, when the tunnel face surrounding rock mass RMR level is IV and is located in a special area, the support method is as follows: the arch crown pre-support uses 39±10 steel pipes with a diameter of 114.3mm and a wall thickness of 10mm; the primary support uses steel fiber shotcrete with a thickness of 20cm and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.0m; the secondary lining uses reinforced concrete with a thickness of 40cm to 110cm, and the invert arch uses reinforced concrete with a thickness of 80cm;

[0025] When the RMR level of the surrounding rock of the tunnel face is IV or above and it is not located in a special area, the support method is as follows: the arch crown pre-support adopts 39±10 steel pipes with a diameter of 114.3mm and a wall thickness of 10mm; the primary support adopts 20cm thick steel fiber shotcrete and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.0m; the advanced core soil reinforcement adopts 55±10% glass fiber conduits with a length of 18.0m; the secondary lining adopts 65cm thick reinforced concrete, and the invert arch adopts 80cm thick reinforced concrete.

[0026] Furthermore, the special section includes low cover layer, tunnel axis parallel to the slope, broken rock mass, strong water gushing and proximity to fault zone.

[0027] Furthermore, the specific operation of step S3 includes the following steps:

[0028] S301: Determine the preliminary tunnel excavation method based on the RMR classification results of the surrounding rock at the tunnel face;

[0029] S302: Constructing a modified Nguyen model based on the surrounding rock self-stabilization time to calculate the tunnel self-stabilization time;

[0030] S303: Compare the tunnel stabilization time with the time required for different preliminary tunnel excavation methods determined in step S301 to determine the final tunnel excavation method.

[0031] Furthermore, in step S301, the preliminary tunnel excavation method includes a full-face excavation method, a two-bench method, and a three-bench method.

[0032] Furthermore, the specific operation of constructing the modified Nguyen model based on the surrounding rock self-stabilization time in step S302 includes the following steps:

[0033] S3021: Modify the coefficients of the Nguyen model according to the tunnel depth;

[0034] In the case of deep burial, Nguyen's correction coefficient is K = A1H -3.333 , where A1 = 4.75E + 23RMR -7.75 , where H is the depth of the tunnel and E is the elastic modulus of the surrounding rock at the tunnel face;

[0035] In the case of shallow burial, Nguyen's correction factor is K = A2RMR -7.751 , where A2 = 4.58E + 23H -3.333 ;

[0036] S3022: Based on the coefficients of the modified Nguyen model, the modified Nguyen model is constructed as

[0037]

[0038]

[0039] Where, L(Kt * ) represents the unsupported span in deep burial conditions; L * (Kt * ) represents the unsupported span in shallow burial conditions; γ is the rock mass, α and δ are the parameters of the Nguyen model, α = 0.700, δ = 0.005, For displacement.

[0040] The beneficial effects of the present invention are:

[0041] The novel method for determining support and excavation methods for highway tunnels, presented in this paper, determines the tunnel support method based on the face rock mass RMR classification and the degree of rock fragmentation. The final tunnel excavation method is determined based on the face rock mass RMR classification and a modified Nguyen model of surrounding rock stabilization time, significantly simplifying tunnel design. The method for determining tunnel stabilization time provides new insights into tunnel construction and excavation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the support method when the tunnel face surrounding rock RMR level is II and the rock mass is slightly crushed in the present invention;

[0043] Figure 2 This is a schematic diagram of the support method when the tunnel face surrounding rock RMR level is II-III and the rock mass is moderately crushed in the present invention;

[0044] Figure 3 This is a schematic diagram of the support method when the tunnel face surrounding rock RMR classification is II-III and is located in a special area in the present invention;

[0045] Figure 4 This is a schematic diagram of the support method when the tunnel face surrounding rock RMR level is III-IV and the rock mass is moderately to highly broken in the present invention;

[0046] Figure 5 Schematic diagram of the support method when the tunnel face surrounding rock RMR level is III-IV and the rock mass is moderately crushed in the present invention;

[0047] Figure 6 This is a schematic diagram of the support method when the tunnel face surrounding rock RMR level is IV and is located in a special area in the present invention;

[0048] Figure 7 This is a schematic diagram of the support method when the tunnel face surrounding rock RMR level is IV or below and is not located in a special area;

[0049] Figure 8 is the relationship curve between RMR and tunnel self-stabilization time in the present invention;

[0050] Figure 9 The relationship between the tunnel depth and the correction coefficient when RMR=100, 90, 70, 60 in the present invention;

[0051] Figure 10 The relationship between the tunnel depth and the correction coefficient when RMR=50, 40, 30, 20 in the present invention;

[0052] Figure 11 is the relationship curve between RMR and coefficient A in the present invention;

[0053] Figure 12 This is the cross section of the tunnel face in the first embodiment of the present invention;

[0054] Figure 13 This is the face condition of the exit section of Tunnel No. 2 in Example 2 of the present invention;

[0055] Figure 14 This is the face condition after 30-meter tunnel excavation in Example 2 of the present invention;

[0056] Figure 15 This is the face condition after excavating a 40-meter tunnel in Example 2 of the present invention;

[0057] Figure 16 This is the situation of the tunnel face at about 300 meters of excavation in Example 2 of the present invention. DETAILED DESCRIPTION

[0058] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0059] A new method for determining the support mode and excavation mode of a highway tunnel comprises the following steps:

[0060] S1: After a tunnel cycle is completed and a new tunnel face is exposed, the RMR level of the surrounding rock at the tunnel face is determined;

[0061] Specifically, S101: Take multiple rock blocks at the tunnel face and perform load strength tests to obtain point load strengths of the multiple rock blocks. Delete three of the highest and three of the lowest, and calculate the arithmetic average of these values ​​as the point load strength of the surrounding rock of the tunnel face, providing the required data for calculating the RMR level.

[0062] S102: Using tools such as a compass, a ruler, and a geological hammer, the grade parameters of the surrounding rock of the tunnel face are measured. The grade parameters include the length, width, roughness, weathering degree, filling condition, occurrence, and distance between discontinuities on the tunnel face, providing the data required for calculating the RMR grade.

[0063] S103: Calculate the RQD value of the surrounding rock of the tunnel face based on the distance between discontinuous surfaces on the tunnel face, providing the required data for calculating the RMR grade;

[0064] RQD=115-3.3J V

[0065] J V =1 / S1+1 / S2+……1 / S n

[0066] Where, J Vis the number of joints per unit volume; S1, S2, ..., S n is the distance between discontinuities on the tunnel face;

[0067] S104: Observe the tunnel face and determine the tunnel face condition, where the tunnel face condition includes dry, damp, wet, dripping, and flowing, providing data required for calculating the RMR level;

[0068] S105: Based on the results of steps S101 to S104, find the corresponding points in Table 1-5 below, and sum them to calculate the RMR level of the surrounding rock at the tunnel face.

[0069] Table 1 Geomechanical classification RMR evaluation points and classification

[0070]

[0071] Table 2 Discontinuity surface condition indicators

[0072]

[0073] Table 3 Influence of discontinuity on tunnel excavation

[0074]

[0075] Table 4 Correction points of discontinuity

[0076]

[0077] Table 5 Rock mass categories determined by RMR values

[0078]

[0079] Furthermore, S2: Determine the tunnel support method based on the RMR classification results of the surrounding rock mass at the tunnel face and the degree of rock fragmentation, and whether the tunnel is located in a special area;

[0080] Specifically,

[0081] (1) When the RMR level of the surrounding rock of the tunnel face is II and the rock mass is slightly broken, the support method is as follows: the arch pre-support adopts 7-12 fully grouted rock anchors with a length of 6.0m, a longitudinal spacing of 1.2m, and a transverse spacing of 2.05m; the primary support adopts 20cm thick steel fiber shotcrete; the secondary lining adopts 40cm thick plain concrete, and the invert arch adopts 70cm thick plain concrete. Figure 1 shown.

[0082] (2) When the RMR level of the surrounding rock of the face is II-III and the rock mass is moderately crushed, the support method is as follows: the primary support adopts 20cm thick steel fiber shotcrete, two 160 I-beam steel arch frames, with a longitudinal spacing of 1.2±10%m; the secondary lining adopts 40cm thick plain concrete, and the invert arch adopts 70cm thick plain concrete. Figure 2 As shown;

[0083] (3) When the RMR classification of the surrounding rock of the tunnel face is II-III, and there are relatively dangerous areas such as low overburden, parallel between the tunnel axis and the slope, broken rock mass, strong water inrush, and proximity to fault zones, the support method is as follows: the arch pre-support adopts 39±10 steel pipes with a diameter of 114.3mm and a wall thickness of 10mm; the primary support adopts steel fiber shotcrete with a thickness of 20cm, and a steel arch frame composed of two 160 I-beams with a longitudinal spacing of 1.0m; the secondary lining adopts plain concrete with a thickness of 40cm to 110cm, and the invert arch adopts plain concrete with a thickness of 70cm. Figure 3 shown.

[0084] (4) When the RMR level of the surrounding rock of the face is III-IV and the rock mass is moderately to highly broken, the support method is as follows: the arch crown pre-support adopts 7-12 fully grouted rock anchors, the primary support adopts 20cm thick steel fiber shotcrete, and the steel arch frame is composed of two 180 I-beams with a longitudinal spacing of 1.2±10%m; the secondary lining adopts 65cm thick plain concrete, and the invert arch adopts 80cm thick reinforced concrete (specifically steel fiber shotcrete). Figure 4 As shown;

[0085] (5) When the RMR level of the surrounding rock of the face is III-IV and the rock mass is moderately crushed, the support method is as follows: the arch pre-support adopts 7-12 fully grouted rock anchors with a length of 6.0m, a longitudinal spacing of 1.4m, and a transverse spacing of 2.05m; the primary support adopts 20cm thick steel fiber shotcrete and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.4±10%m; the secondary lining adopts 65cm thick plain concrete and the inverted arch adopts 80cm thick reinforced concrete. Figure 5 shown.

[0086] (6) When the RMR level of the surrounding rock of the tunnel face is IV, the tunnel axis is parallel to the slope, the rock mass is broken, the water inrush is strong, and the area is close to the fault zone, the support method is as follows: the arch pre-support adopts 39±10 steel pipes with a wall thickness of 10mm and a diameter of 114.3mm; the primary support adopts steel fiber sprayed concrete with a thickness of 20cm, and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.0m; the secondary lining adopts reinforced concrete with a thickness of 40cm to 110cm, and the invert arch adopts reinforced concrete with a thickness of 80cm. Figure 6As shown;

[0087] (7) When the RMR level of the surrounding rock of the tunnel face is IV or above, the support method is as follows: the arch pre-support adopts 39±10 steel pipes with a wall thickness of 10mm and a diameter of 114.3mm; the primary support adopts 20cm thick steel fiber shotcrete and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.0m; the advanced core soil reinforcement adopts 55±10% glass fiber conduits with a length of 18.0m; the secondary lining adopts 65cm thick reinforced concrete, and the invert arch adopts 80cm thick reinforced concrete. Figure 7 shown.

[0088] Furthermore, S3: according to the RMR classification results of the surrounding rock at the tunnel face, the final tunnel excavation method is determined based on the modified Nguyen model of surrounding rock self-stabilization time.

[0089] Specifically, S301: determining a preliminary tunnel excavation method based on the RMR classification result of the surrounding rock of the tunnel face, wherein the preliminary tunnel excavation method includes a full-face excavation method, a two-bench method, and a three-bench method;

[0090] The relationship between the RMR classification results and the excavation method is shown in Table 6 below.

[0091] Table 6 Different excavation methods and their applicable scope

[0092]

[0093] As can be seen from Table 5, the initial tunnel excavation method can be determined based on the different RMR values ​​of the tunnel surrounding rock. However, the same RMR classification result also corresponds to multiple excavation schemes. For example, for surrounding rock with an RMR of 51, both full-face excavation and two-bench excavation can be used. Therefore, it is necessary to further select the excavation method based on the tunnel stabilization time. The tunnel stabilization time is calculated according to the modified Nguyen model of surrounding rock stabilization time. Therefore, the following steps are required.

[0094] S302: Constructing a modified Nguyen model based on the surrounding rock self-stabilization time to calculate the tunnel self-stabilization time;

[0095] The relationship between the self-stabilization time and RMR classification proposed by Bieniawski is shown in the attached Figure 8 As shown, extract Figure 8 The data points are shown in Table 7 below. Based on the data in Table 7, the Nguyen model is modified to a certain extent.

[0096] Table 7 RMR and self-stabilization time data points

[0097] RMR Support span l(m) Elastic modulus E(GPa) Self-stabilization time t(h) 100 30 100 1000000 90 24 80 31000 80 22 60 6000 70 20.2 40 1150 60 14 20 200 50 10.3 10 20 40 8 5.6 6 30 5 3.16 1.2 20 3 1.78 0.2

[0098] In Table 7, the elastic modulus is calculated according to the formula Calculated.

[0099] In order to substitute the above data points into the Nguyen model, it is also necessary to set the rock mass density, Poisson's ratio, allowable displacement, and α and δ. Using RMR as the classification standard, when RMR>60, the rock mass density γ=26500N / m3, and the allowable displacement u=0.01m; when 40<RMR<60, the rock mass density γ=25500N / m3, and the allowable displacement u=0.02m; when RMR<40, the rock mass density γ=24500N / m3, and the allowable displacement u=0.03m. The Poisson's ratio is uniformly set to 0.3. Based on the rock type of the supporting project, refer to α and δ given by Nguyen, and take α=0.700 and δ=0.005.

[0100] In addition to the above parameter settings, the tunnel depth is also a parameter in the Nguyen model. The correction coefficient of the Nguyen model will also change according to the tunnel depth.

[0101] Substitute the data points and assumed rock mass conditions into the Nguyen model, assuming tunnel depths H of 20m, 50m, 100m, 150m, 200m, 250m, 300m, 400m, and 500m. When RMR = 80, the calculated results are shown in Table 8. The calculated results are compared with the corresponding data points to obtain the corresponding correction factors.

[0102] Table 8 Calculation results and correction coefficients when RMR=80

[0103]

[0104] The relationship between the correction coefficient and the tunnel depth when RMR=80 is K=1.24E+09H -3.333 , the correlation coefficient of this relationship is 1, which means it has a high correlation.

[0105] Similarly, the relationship between the correction coefficient and the tunnel depth is calculated when RMR = 100, 90, 70, 60, 50, 40, 30, 20. The results are shown in the attached figure. Figure 9 and attached Figure 10 As shown in the figure, the relationship between the burial depth and the correction coefficient under different RMR is summarized as K = AH -3.333 It can be found that only the coefficient A is different in this relationship. At the same time, it is found that the size of the coefficient A and the RMR also have a certain pattern. Using the same method, the relationship between the coefficient A and RMR is fitted with a function, and the results are shown in Table 9 and the attached table. Figure 11 shown.

[0106] Table 9 Different RMR and their corresponding coefficient A

[0107]

[0108] In summary, in the case of deep burial, Nguyen's correction coefficient is K = A1H -3.333 , where A1 = 4.75E + 23RMR - 7 .75 ;

[0109] In the case of shallow burial, Nguyen's correction coefficient is K = A2RMR -7.751 , where A2 ＝ 4.58E+23H -3.333 ;

[0110] According to the coefficients of the modified Nguyen model, the modified Nguyen model can be obtained as follows:

[0111]

[0112]

[0113] Where, L(Kt * ) represents the unsupported span in deep burial conditions; L * (Kt * ) represents the unsupported span in shallow burial conditions; γ is the rock mass, α and δ are the parameters of the Nguyen model, α = 0.700, δ = 0.005, For displacement.

[0114] S303: Compare the self-stabilization time of the tunnel with the time required for different preliminary tunnel excavation methods determined in step S301, ensure that the obtained self-stabilization time is greater than the time required by the excavation method adopted, and determine the final tunnel excavation method.

[0115] Example 1:

[0116] The starting and ending pile numbers of the No. 2 tunnel in the F3 section of the E60 highway in Georgia are PK3+122.5-PK4+750 in the AT direction, with a total length of 1627.5m. The starting and ending pile numbers in the TA direction are PK3+117.2-PK4+741.5, with a total length of 1621.3m. The PK4+300 section in the AT direction of the No. 2 tunnel was selected, and the cross-section face photo is attached. Figure 12 shown.

[0117] The specific operation of determining the tunnel support mode and excavation mode by applying the method in Example 1 includes the following steps:

[0118] S1: After a tunnel cycle is completed and a new tunnel face is exposed, the RMR level of the surrounding rock of the tunnel face is determined. Prepare tools such as a compass, geological hammer, and ruler in advance.

[0119] Specifically, 15 rock blocks of appropriate size at the tunnel face were selected and the point load strengths were calculated to be 2.44 MPa, 4.53 MPa, 2.24 MPa, 5.59 MPa, 3.58 MPa, 4.41 MPa, 3.78 MPa, 4.89 MPa, 3.98 MPa, 3.30 MPa, 5.61 MPa, 5.70 MPa, 2.20 MPa, 3.86 MPa, and 2.15 MPa. By removing the three maximum and minimum values ​​and calculating the arithmetic mean, the average point load strength of the rock mass is 3.86 MPa.

[0120] Using tools such as a compass, ruler, and geological hammer, we measured and estimated the length, roughness, weathering level, filling, occurrence, and spacing of the main discontinuities on the tunnel face. We found two main groups of discontinuities on the face. The first group had an average spacing of 20 to 30 cm and a length of approximately 6 meters. These discontinuities were filled with hard materials such as quartz, had rough joints, were moderately weathered, and dipped at an angle of 260° to 50°. The second group had similar properties to the first, with a dip angle of 85° to 60°.

[0121] The measured distance between discontinuous surfaces is 40cm to 50cm, the number of joints per unit volume is 4.5, and the calculated RQD value is 90%.

[0122] Observe the palm face, which is moist.

[0123] According to the above data, the RMR of the rock mass is calculated to be 42, and the rock mass is Class III surrounding rock.

[0124] S2: Due to the high degree of fracture and RMR of the surrounding rock mass, the following support method was used: the primary support was constructed with 20cm thick steel fiber shotcrete and a steel arch frame consisting of two 180mm I-beams, with a longitudinal spacing of 1.2±10%m. The secondary lining was constructed with 65cm thick plain concrete, and the invert was constructed with 80cm thick reinforced concrete.

[0125] S3. According to the RMR grade and Table 1 in Example 1, the applicable excavation methods for the tunnel are full-face excavation and two-bench excavation.

[0126] Since the unsupported span of the tunnel is about 8m and the RMR value is 42, Figure 1 The tunnel self-stabilization time is about 10 hours.

[0127] According to on-site statistics, one excavation cycle using the full-face method takes approximately 17 hours, while the two-bench method takes approximately 9.5 hours. The two-bench method requires less time than the tunnel's stabilization time, ensuring the tunnel remains stable until excavation is complete. Therefore, the two-bench method was chosen for tunnel excavation.

[0128] Example 2:

[0129] The tunnel of Georgia's E60 highway is located in a granite area and is constructed using a new method. The tunnel passes through a broken zone and low overburden several times. During construction, the tunnel face conditions should be judged in a timely manner based on the tunnel face conditions and the appropriate support method should be selected to ensure safe and economical tunnel construction.

[0130] After the No. 2 tunnel exit section was exposed at the tunnel face, it was observed that there was a weak interlayer filled with clay in the tunnel face. The tunnel face was highly weathered to completely weathered. Figure 13 As shown in the figure, the vault is experiencing severe block fall, and the tunnel face is located at the tunnel portal. The advanced core soil is in a short-term stable state. Calculations indicate that the surrounding rock grade is IV, with a GSI value of approximately 40. Therefore, the support method described in Example 1, "when the tunnel face surrounding rock RMR grade is IV and located in a special area," is applicable.

[0131] After 30m of tunnel excavation, the tunnel face condition showed a trend of improvement. There was a small fault on the tunnel face. The rock on the left was moderately weathered and moderately broken, while the rock on the right was completely weathered. Figure 14 As shown in the figure. After calculation, the RMR level is III-IV, the GSI is about 45, and according to the direction of the fault, the fully weathered part on the right side of the tunnel face will become smaller and smaller. Therefore, the tunnel face surrounding rock is suitable for the support method of "the tunnel face surrounding rock RMR level is III-IV, and the rock mass is moderately to highly broken". After continuing to excavate for 10m (total excavation of 40m), the tunnel face is as shown in the figure below. Figure 15 As shown, the fully weathered rock on the right half has almost disappeared.

[0132] At about 300m of excavation, the tunnel face is moist, the rock strength is strong, slightly weathered, slightly broken, most joints are closed, and a few joints are filled with hard materials such as quartz, such as the attached Figure 16 The rock grade is calculated to be III, and the GSI is about 53. Therefore, the support method described in Example 1, "when the tunnel face surrounding rock RMR grade is II-III and the rock mass is moderately crushed," is applicable.

[0133] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A new method for determining the support and excavation methods of a highway tunnel, characterized in that: The following steps are included: S1: After a tunnel cycle is completed and a new tunnel face is exposed, the RMR level of the surrounding rock at the tunnel face is determined; S2: Determine the tunnel support method based on the RMR classification results of the surrounding rock mass at the tunnel face, the degree of rock fragmentation, and whether the tunnel is located in a special area; S3: Based on the RMR classification results of the surrounding rock at the tunnel face, the final tunnel excavation method is determined based on the modified Nguyen model of surrounding rock self-stabilization time; The specific operations of step S1 include the following steps: S101: Take multiple rock blocks at the tunnel face and conduct load strength tests to determine the point load strength of the surrounding rock at the tunnel face; S102: measuring grade parameters of the surrounding rock of the tunnel face, wherein the grade parameters include the length, width, roughness, weathering degree, filling condition, occurrence and distance between discontinuities on the tunnel face; S103: Calculate the RQD value of the surrounding rock of the tunnel face based on the distance between discontinuous surfaces on the tunnel face. RQD=115-3.3J V J V =1 / S1+1 / S2+……1 / S n Where, J V is the number of joints per unit volume; S1, S2, ..., S n is the distance between discontinuities on the tunnel face; S104: Observe the tunnel face and determine the tunnel face state, where the tunnel face state includes dry, damp, wet, dripping, and flowing; S105: Calculate the RMR level of the surrounding rock at the tunnel face based on the results of steps S101 to S104; The specific operation of step S3 includes the following steps: S301: Determine the preliminary tunnel excavation method based on the RMR classification results of the surrounding rock at the tunnel face; S302: Constructing a modified Nguyen model based on the surrounding rock self-stabilization time to calculate the tunnel self-stabilization time; S303: comparing the tunnel stabilization time with the times required for different preliminary tunnel excavation methods determined in step S301 to determine a final tunnel excavation method; The specific operations based on the modified surrounding rock self-stabilization time Nguyen model in step S302 include the following steps: S3021: Modify the coefficients of the Nguyen model according to the tunnel depth; In the case of deep burial, Nguyen's correction coefficient is K = A1H -3.333 , where A1 = 4.75E + 23RMR -7.75 , where H is the depth of the tunnel and E is the elastic modulus of the surrounding rock at the tunnel face; In the case of shallow burial, Nguyen's correction factor is K = A2RMR -7.751 , where A2 = 4.58E + 23H -3.333 ; S3022: Based on the coefficients of the modified Nguyen model, the modified Nguyen model is constructed as Where, L(Kt * ) represents the unsupported span in deep burial conditions; L * (Kt * ) represents the unsupported span in shallow burial conditions; γ is the rock mass, α and δ are the parameters of the Nguyen model, α = 0.700, δ = 0.005, For displacement.

2. The method for determining the support and excavation methods of a new highway tunnel according to claim 1 is characterized in that: When the RMR level of the surrounding rock of the face is II and the rock mass is slightly crushed, the support method is as follows: the arch crown pre-support adopts 7-12 fully grouted rock anchors with a length of 6.0m, a longitudinal spacing of 1.2m, and a transverse spacing of 2.05m; the primary support adopts 20cm thick steel fiber shotcrete; the secondary lining adopts 40cm thick plain concrete, and the invert arch adopts 70cm thick plain concrete.

3. The method for determining the support and excavation methods of a new highway tunnel according to claim 2 is characterized in that: When the tunnel face surrounding rock mass RMR level is II-III and the rock mass is moderately crushed, the support method is as follows: the primary support uses 20cm thick steel fiber shotcrete and two 160 I-beam steel arch frames with a longitudinal spacing of 1.2±10%m; the secondary lining uses 40cm thick plain concrete, and the invert uses 70cm thick plain concrete; When the tunnel face surrounding rock RMR classification is II-III and is located in a special area, the support method is as follows: the arch crown pre-support adopts 39±10 steel pipes with a diameter of 114.3mm and a wall thickness of 10mm; the primary support adopts 20cm thick steel fiber shotcrete and a steel arch frame composed of two 160 I-beams with a longitudinal spacing of 1.0m; the secondary lining adopts plain concrete with a thickness of 40cm to 110cm, and the invert arch adopts plain concrete with a thickness of 70cm.

4. The method for determining the support and excavation methods of a new highway tunnel according to claim 3 is characterized in that: When the tunnel face surrounding rock mass RMR is III-IV and the rock mass is moderately to highly fractured, the support method is as follows: the primary support uses 20cm thick steel fiber shotcrete and two 180 I-beam steel arch frames with a longitudinal spacing of 1.2±10%m; the secondary lining uses 65cm thick plain concrete, and the invert uses 80cm thick reinforced concrete. When the RMR level of the surrounding rock of the face is III-IV and the rock mass is moderately crushed, the support method is as follows: the arch crown pre-support adopts 7-12 fully grouted rock anchors with a length of 6.0m, a longitudinal spacing of 1.4m, and a transverse spacing of 2.05m; the primary support adopts 20cm thick steel fiber shotcrete and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.4±10%m; the secondary lining adopts 65cm thick plain concrete, and the invert arch adopts 80cm thick reinforced concrete.

5. The method for determining the support and excavation methods of a new highway tunnel according to claim 4 is characterized in that: When the tunnel face surrounding rock mass RMR is IV and located in a special area, the support method is as follows: the arch crown pre-support uses 39 ± 10 steel pipes with a diameter of 114.3 mm and a wall thickness of 10 mm; the primary support uses 20 cm thick steel fiber shotcrete and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.0 m; the secondary lining uses reinforced concrete with a thickness of 40 cm to 110 cm, and the invert uses reinforced concrete with a thickness of 80 cm. When the RMR level of the surrounding rock of the tunnel face is IV or above and it is not located in a special area, the support method is as follows: the arch crown pre-support adopts 39±10 steel pipes with a diameter of 114.3mm and a wall thickness of 10mm; the primary support adopts 20cm thick steel fiber shotcrete and a steel arch frame composed of two 180 I-beams with a longitudinal spacing of 1.0m; the advanced core soil reinforcement adopts 55±10% glass fiber conduits with a length of 18.0m; the secondary lining adopts 65cm thick reinforced concrete, and the invert arch adopts 80cm thick reinforced concrete.

6. A method for determining a new highway tunnel support method and excavation method according to claim 3 or 5, characterized in that: The special sections include low cover, tunnel axis parallel to the slope, broken rock mass, strong water gushing and proximity to fault zones.

7. The method for determining the support and excavation methods of a new highway tunnel according to claim 1 is characterized in that: In step S301, the preliminary tunnel excavation method includes full-face excavation method, two-bench method and three-bench method.

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