Design method and construction method of transverse opposite-pulling system of triangular area of non-middle-guide multi-arch tunnel

Abstract

The invention relates to a design method and a construction method of a transverse opposite-pulling system of a triangular area of a non-middle-guide multi-arch tunnel, and belongs to the technical field of multi-arch tunnel design and construction. The design method comprises the steps that a calculation model of the non-middle-guide multi-arch tunnel is established, and the initial support arc length corresponding to the distribution range of a surrounding rock plastic zone of a triangular area above the non-middle-guide multi-arch tunnel after construction is completed is obtained through calculation; horizontally and uniformly distributed loads are applied to surrounding rock within the distribution range of a plastic zone of a triangular zone above the middle-guide-free multi-arch tunnel, and the horizontally and uniformly distributed load corresponding to the minimum value of the area of the plastic zone is found; calculating the total pre-tension force required by a transverse opposite-pull system in the triangular area of the non-middle-guide multi-arch tunnel; and counter-pulling anchor rods of a transverse counter-pulling system of the triangular area of the non-middle-guide multi-arch tunnel are designed. The reinforcement effect can be achieved on the surrounding rock of the triangular area above the multi-arch tunnel, the surrounding rock of the triangular area can be in a strong constraint state so that the stability and ultimate bearing capacity of the surrounding rock can be improved, deformation of the surrounding rock of the triangular area above the middle-guide-free multi-arch tunnel and development of a plastic zone can be effectively controlled, and the method has important significance on guaranteeing the safety of a tunnel structure.

Description

Technical Field

[0001] The invention belongs to the technical field of the design and construction of connected-arch tunnels, and particularly relates to a design method and a construction method for a transverse tension system in the triangular area of a non-middle-guide connected-arch tunnel. Background Art

[0002] Due to its unique structural form, the non-middle-guide connected-arch tunnel has strong topographic adaptability in highway tunnel construction, can effectively solve the problem of the connection of the two ends of the tunnel in highway construction, avoid the sub-frame at the intersection, and improve the space utilization rate. In addition, since it does not require the excavation of the middle guide tunnel and the construction of the middle partition wall, the construction process is simplified, the construction cost is reduced, and the leakage of water through the middle partition wall is prevented; and after the support structure is completely constructed, the structural stress of the non-middle-guide connected-arch tunnel is more reasonable compared with that of the middle-guide connected-arch tunnel. Therefore, the non-middle-guide connected-arch tunnel has become the optimal solution under many limited conditions.

[0003] However, the treatment of the triangular area above the leading tunnel and the trailing tunnel of the non-middle-guide connected-arch tunnel has always been a difficult problem. As the area with the most construction disturbances and also the blind area of reinforcement, the surrounding rock in the triangular area is extremely prone to collapse deformation and plastic failure, which increases the additional stress acting on the support structure, and thus easily causes the cracking of the secondary lining of the leading tunnel and the collapse of the initial support of the trailing tunnel. Therefore, how to propose an effective reinforcement technology for the triangular area of the non-middle-guide connected-arch tunnel to control the deformation of the surrounding rock in the triangular area and the development of the plastic zone has important engineering significance for tunnel construction. Summary of the Invention

[0004] In order to solve the deficiencies of the prior art, the invention provides a design method and a construction method for a transverse tension system in the triangular area of a non-middle-guide connected-arch tunnel. The method uses tension bolts to reinforce the plastic surrounding rock in the triangular area, and improves its stability and ultimate bearing capacity through the reinforcement and strong constraint effects, effectively controlling the deformation of the surrounding rock in the triangular area and the development of the plastic zone, and ensuring the safety of the tunnel structure.

[0005] To achieve the above object, the technical solution adopted by the invention is as follows:

[0006] A design method for a transverse tension system in the triangular area of a non-middle-guide connected-arch tunnel includes the following steps:

[0007] Step (1), according to the design drawings of the tunnel lining section, establish a numerical calculation model of the stratum-structure method for the non-middle-guide connected-arch tunnel, and calculate the initial support arc length Lp corresponding to the distribution range of the plastic zone of the surrounding rock in the triangular area above the non-middle-guide connected-arch tunnel after the construction is completed (as shown in Figure 2 shown, Figure 9 (a), the red part in the triangular area above the non-middle-guide connected-arch tunnel is the plastic zone);

[0008] Step (2): In the calculation model established in step (1), apply a uniformly distributed horizontal load P to the surrounding rock within the distribution range of the plastic zone (i.e., Lp) in the triangular area above the mid - guide - less multi - arch tunnel, and adjust the value of P to conduct trial calculations on the model, so as to find the minimum value A of the plastic zone area. MIN The corresponding uniformly distributed horizontal load is denoted as the optimal solution P of the uniformly distributed horizontal load. m ;

[0009] Step (3): Using the initial support arc length Lp obtained in step (1) and the optimal solution P of the uniformly distributed horizontal load obtained in step (2), m calculate the total pre - tension P required for the transverse tension - resisting system in the triangular area of the mid - guide - less multi - arch tunnel. total ;

[0010] Step (4): Design the tension - resisting bolts for the transverse tension - resisting system in the triangular area of the mid - guide - less multi - arch tunnel, including determining the bolt arrangement method, the number of bolts, the bolt length, and the bolt pre - tension.

[0011] Furthermore, preferably, in step (2), the method for determining the optimal solution P m is as follows:

[0012] Adjust the value of P to conduct trial calculations on the model. When conducting trial calculations on the model, the uniformly distributed horizontal load is P i , and the corresponding plastic zone area of the surrounding rock in the triangular area is A i , where i = 0, 1, 2, 3, …, M, and M is the total number of trial calculations;

[0013] Use equation (1) to fit the variation law of the plastic zone area A with the load P:

[0014]

[0015] In equation (1), A amp is the initial amplitude, A 0 is the equilibrium point, a is the attenuation factor, ω is the angular frequency, is the phase, and all of the above are fitting parameters;

[0016] Using the fitted equation (1), find the uniformly distributed horizontal load corresponding to the minimum value A of the plastic zone area, and this uniformly distributed horizontal load is denoted as the optimal solution P of the uniformly distributed horizontal load. MIN m .

[0017] Furthermore, preferably, in step (2), M should be not less than 6.

[0018] Furthermore, preferably, in step (3), the calculation method for the total pre - tension P required for the transverse tension - resisting system in the triangular area of the mid - guide - less multi - arch tunnel is as follows: total

[0019] Ptotal = P m ·Lp (2)

[0020] In formula (2), P m is the optimal solution of the horizontal uniformly distributed load, kN / m; Lp is the length of the initial support arc, m.

[0021] Furthermore, preferably, in step (4), the arrangement method of the anchor bolts adopts a plum blossom arrangement;

[0022] The pretension of the anchor bolt is calculated by formula (2):

[0023] P s = P total / N (3)

[0024] In the formula, P s is the pretension of a single pair of tension anchor bolts; N is the number of pairs of tension anchor bolts arranged per meter along the longitudinal direction of the tunnel in the triangular area of the non-middle-guide continuous arch tunnel.

[0025] The present invention also provides a construction method for the transverse tension system in the triangular area of the non-middle-guide continuous arch tunnel. The transverse tension system in the triangular area of the non-middle-guide continuous arch tunnel designed by using the design method of the transverse tension system in the triangular area of the non-middle-guide continuous arch tunnel includes the following steps:

[0026] S1, Excavate the upper bench of the advanced tunnel, and the excavation height is greater than 2.0 m;

[0027] S2, Install the system anchor bolts on the upper bench of the advanced tunnel;

[0028] S3, Install the steel frame on the upper bench of the advanced tunnel, hang the steel mesh, and weld the longitudinal connecting bars; Install channel steel at the corresponding positions of the tension anchor bolts, and reserve round holes at the corresponding positions where the anchor bolts pass through the channel steel. Clamp both ends of the channel steel on the flanges of the adjacent two sets of steel frames close to the surrounding rock side, and weld the contact parts between the web of the channel steel and the flanges of the adjacent two sets of steel frames firmly;

[0029] S4, Mark the drilling positions, and use a pneumatic drill to drill horizontally from the right side of the upper bench of the advanced tunnel towards the side of the subsequent tunnel. The angle and depth of the drilling need to be strictly controlled to ensure that the anchor bolts can be accurately inserted and extend not less than 30 cm beyond the designed initial support surface of the subsequent tunnel;

[0030] S4, After the drilling is completed, clean the holes;

[0031] S6, Insert the anchor bolts into the holes in the surrounding rock through the round holes of the channel steel, with both ends exposed 29 - 31 cm from the designed initial support surface. The insertion length of the anchor bolts needs to meet the design requirements and shall not be shorter than 95% of the designed length;

[0032] S7, Install the grout plug and the anchor backing plate on the anchor bolts;

[0033] S8, Use a grouting machine to inject grout into the hole until the grout overflows from the hole opening;

[0034] S9, After grouting is completed, tighten the grout plug and install nuts at the ends of the tie-back bolts. Use a torque wrench to apply the initial stress until the anchor plate is in close contact with the channel steel;

[0035] S10, Initial tensioning of the bolts: After the grout has solidified, use a torque wrench to tighten the nuts to tension the bolts until the tensile force reaches 30% of the designed anchoring force;

[0036] S11, Complete the initial support and secondary lining construction of the pilot tunnel according to the designed excavation support sequence;

[0037] S12, Use the same steps as S1 - S11 to process the subsequent tunnel;

[0038] S13, Tension the bolts of the subsequent tunnel to ensure that the bolts reach the designed anchoring force, and then cut off the excess length of the bolts;

[0039] S14, Construction of subsequent processes: After the transverse tie-back system in the triangular area of the non-middle-guide continuous arch tunnel is constructed according to the above steps, the excavation and support processes of the lower bench of the subsequent tunnel can be carried out in sequence.

[0040] In the present invention, establishing a numerical calculation model of the stratum-structure method for a non-middle-guide continuous arch tunnel is the basic method and model for tunnel numerical simulation. It can be achieved by using existing technologies, and the present invention does not impose special restrictions on this.

[0041] In step (2) of the present invention, when i = 0, P i = 0, A i = 5.3754, which is calculated from step (1).

[0042] In the present invention, the bolt length and bolt quantity are determined according to the specific layout method in accordance with the tunnel lining section design drawings.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] The present invention provides a design method and a construction method for a transverse tension system in the triangular area of a non-middle-guide multi-arch tunnel. The prior art has not proposed an effective design method for the tension bolts used for reinforcing the surrounding rock in the triangular area above the multi-arch tunnel. In view of this problem, the design method of the present invention can quickly calculate the pre-tension of the tension bolts, thereby providing a theoretical basis for the reasonable design of the bolt length, the number of bolts, and the layout method. After the on-site implementation of the transverse tension system of the present invention, the deformation and the development of the plastic zone of the surrounding rock in the triangular area above the multi-arch tunnel can be effectively controlled. Taking the embodiment of this article as an example, arranging 17 tension bolts with a pre-tension of 143 kN per meter of the triangular area of the surrounding rock can reduce the area of the plastic zone to 0, thereby significantly improving the stability and safety of the tunnel and the support structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a flow chart of the design and construction method of the transverse tension system in the triangular area of the non-middle-guide multi-arch tunnel of the present invention;

[0046] Figure 2 is a schematic diagram of applying the horizontal uniform load of the calculation model of the present invention;

[0047] Figure 3 is a schematic diagram of the mechanical reinforcement principle of the triangular area of the non-middle-guide multi-arch tunnel of the present invention;

[0048] Figure 4 is a schematic diagram of the variation law of the plastic zone area shown by the fitting function of the present invention with the horizontal uniform load;

[0049] Figure 5 is a schematic diagram of the construction process of the non-middle-guide multi-arch tunnel of the present invention;

[0050] Figure 6 is a large-scale drawing of the tension bolts of the transverse tension system in the triangular area of the non-middle-guide multi-arch tunnel of the present invention;

[0051] Figure 7 is a schematic diagram of the arrangement of the tension bolts of the transverse tension system in the triangular area of the non-middle-guide multi-arch tunnel of the present invention;

[0052] Figure 6 and Figure 7 In, 1 - tension bolt (the exposed part is processed into a thread, and the processing length is 300 mm), 2 - nut, 3 - anchor backing plate, 4 - protection wrapped with non-woven fabric, 5 - end position of the one-time drilling of the bolt, 6 - longitudinal connecting member of channel steel, 7 - drilling hole, 8 - part of the bolt embedded in the surrounding rock, 9 - anchoring agent slurry, 10 - surrounding rock, 11 - anchoring end of the advanced tunnel, 12 - surrounding rock in the triangular area, 13 - anchoring end of the subsequent tunnel, 14 - steel frame;

[0053] Figure 8 is the stratum-structure method calculation model of the non-middle-guide multi-arch tunnel in the application example;

[0054] Figure 9 It is the plastic zone distribution calculated for different levels of uniformly distributed load P in the application example; the red area in the figure is the plastic zone;

[0055] Figure 10 It is the fitting result of the plastic zone area calculated for different levels of uniformly distributed load in the application example; Specific implementation manner

[0056] The present invention will be further described in detail below in conjunction with the embodiments.

[0057] Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those not specified in the embodiments regarding specific techniques or conditions, they shall be carried out according to the techniques or conditions described in the literature in the art or according to the product specifications. For those materials or equipment without indicating the manufacturer, they are all conventional products that can be obtained by purchase.

[0058] Embodiment 1

[0059] The design method of the transverse tension system in the triangular area of the middle - guide - less connected - arch tunnel includes the following steps:

[0060] Step (1), according to the design drawings of the tunnel lining section, establish a numerical calculation model of the stratum - structure method for the middle - guide - less connected - arch tunnel, and calculate the initial support arc length Lp corresponding to the distribution range of the plastic zone of the surrounding rock above the triangular area of the middle - guide - less connected - arch tunnel after construction is completed;

[0061] Step (2), in the calculation model established in step (1), apply a horizontal uniformly distributed load P to the surrounding rock within the distribution range of the plastic zone in the triangular area above the middle - guide - less connected - arch tunnel, and adjust the value of P to conduct a trial calculation on the model, so as to find the minimum value A of the plastic zone area MIN corresponding horizontal uniformly distributed load, and this horizontal uniformly distributed load is denoted as the optimal solution P of the horizontal uniformly distributed load m ;

[0062] Step (3), using the initial support arc length Lp obtained in step (1) and the optimal solution P of the horizontal uniformly distributed load obtained in step (2) m , calculate the total pre - tension P required for the transverse tension system in the triangular area of the middle - guide - less connected - arch tunnel total ;

[0063] Step (4), design the tension bolts for the transverse tension system in the triangular area of the middle - guide - less connected - arch tunnel, including the determination of the bolt arrangement method, the number of bolts, the bolt length, and the bolt pre - tension.

[0064] Embodiment 2

[0065] The design method of the transverse tension system in the triangular area of the middle - guide - less connected - arch tunnel includes the following steps:

[0066] Step (1): According to the design drawings of the tunnel lining section, establish a numerical calculation model of the stratum-structure method for the non-middle-guide connected-arch tunnel, and calculate the initial support arc length Lp corresponding to the distribution range of the plastic zone of the surrounding rock in the triangular area above the non-middle-guide connected-arch tunnel after construction is completed.

[0067] Step (2): In the calculation model established in step (1), apply a horizontal uniform load P to the surrounding rock within the distribution range of the plastic zone in the triangular area above the non-middle-guide connected-arch tunnel, and adjust the value of P to conduct a trial calculation on the model, so as to find the minimum value A of the plastic zone area. MIN The corresponding horizontal uniform load is recorded as the optimal solution P of the horizontal uniform load. m ;

[0068] Step (3): Use the initial support arc length Lp obtained in step (1) and the optimal solution P of the horizontal uniform load obtained in step (2). m to calculate the total pre-tension P required for the transverse tie-back system in the triangular area of the non-middle-guide connected-arch tunnel. total ;

[0069] Step (4): Design the tie-back bolts for the transverse tie-back system in the triangular area of the non-middle-guide connected-arch tunnel, including determining the bolt arrangement method, the number of bolts, the bolt length, and the bolt pre-tension.

[0070] In step (2), the method for determining the optimal solution P m is as follows:

[0071] Adjust the value of P to conduct a trial calculation on the model. When conducting the trial calculation of the model, the horizontal uniform load is P i , and the corresponding plastic zone area of the surrounding rock in the triangular area is A i , i = 0, 1, 2, 3,..., M, where M is the total number of trial calculations;

[0072] Use Equation (1) to fit the variation law of the plastic zone area A with the load P:

[0073]

[0074] In Equation (1), A amp is the initial amplitude, A 0 is the equilibrium point, a is the attenuation factor, ω is the angular frequency, is the phase, and all of the above are fitting parameters;

[0075] Use the fitted Equation (1) to find the horizontal uniform load corresponding to the minimum value A of the plastic zone area, and this horizontal uniform load is recorded as the optimal solution P of the horizontal uniform load. MIN ; m .

[0076] In step (2), M should be not less than 6.

[0077] In step (3), the total pre-tension force P required for the transverse tie-back system in the triangular area of the non-middle-guidance multi-arch tunnel total is calculated as follows:

[0078] P total = P m ·Lp (2)

[0079] In formula (2), P m is the optimal solution of the horizontal uniform load, kN / m; Lp is the length of the initial support arc, m.

[0080] In step (4), the arrangement of the anchor bolts is in a plum blossom pattern;

[0081] The pre-tension force of the anchor bolts is calculated by formula (2):

[0082] P s = P total / N (3)

[0083] In the formula, P s is the pre-tension force of a single tie-back anchor bolt; N is the number of tie-back anchor bolts arranged per meter along the longitudinal direction of the tunnel in the triangular area of the non-middle-guidance multi-arch tunnel.

[0084] Example 3

[0085] A construction method for the transverse tie-back system in the triangular area of the non-middle-guidance multi-arch tunnel, using the transverse tie-back system design method for the triangular area of the non-middle-guidance multi-arch tunnel described in Example 1 or Example 2, includes the following steps:

[0086] S1, Excavate the upper bench of the leading tunnel, and the excavation height is greater than 2.0 m;

[0087] S2, Install the system anchor bolts on the upper bench of the leading tunnel;

[0088] S3, Install the steel frame on the upper bench of the leading tunnel, hang the steel mesh, and weld the longitudinal connecting bars; Install the channel steel at the corresponding positions of the tie-back anchor bolts, and reserve round holes at the corresponding positions where the anchor bolts pass through the channel steel. Clamp both ends of the channel steel on the flanges of the adjacent two sets of steel frames close to the surrounding rock side, and weld the contact parts between the web of the channel steel and the flanges of the adjacent two sets of steel frames firmly;

[0089] S4, Mark the drilling positions, and use a pneumatic drill to drill horizontally from the right side of the upper bench of the leading tunnel towards the trailing tunnel side. The angle and depth of the drilling need to be strictly controlled to ensure that the anchor bolts can be accurately inserted and extend no less than 30 cm beyond the designed initial support surface of the trailing tunnel;

[0090] S5, After the drilling is completed, clean the holes;

[0091] S6. Insert the anchor bolt into the surrounding rock hole through the round hole of the channel steel. The two ends should protrude 29 - 31 cm from the designed primary support surface. The inserted length of the anchor bolt should meet the design requirements and shall not be shorter than 95% of the designed length.

[0092] S7. Install the grout stopper and the anchor backing plate on the anchor bolt.

[0093] S8. Use a grouting machine to inject the grout into the hole until the grout overflows from the hole mouth.

[0094] S9. After the grouting is completed, tighten the grout stopper and install nuts at the ends of the tie-back anchor bolts. Use a torque wrench to apply the initial stress until the anchor backing plate is in close contact with the channel steel.

[0095] S10. Initial tension of the anchor bolt: After the grout has solidified, use a torque wrench to tighten the nuts to tension the anchor bolts until the tensile force reaches 30% of the designed anchoring force.

[0096] S11. Complete the construction of the primary support and the secondary lining of the pilot tunnel according to the designed excavation and support sequence.

[0097] S12. Use the same steps as S1 - S11 to process the following tunnel.

[0098] S13. Tension the anchor bolts of the following tunnel to ensure that the anchor bolts reach the designed anchoring force, and then cut off the excess length of the anchor bolts.

[0099] S14. Construction of subsequent processes: After the construction of the transverse tie-back system in the triangular area of the non-middle-guide continuous arch tunnel is completed according to the above steps, the subsequent processes (excavation and support processes of the lower bench of the following tunnel) can be carried out in sequence.

[0100] Example 4

[0101] A design method for the transverse tie-back system in the triangular area of a non-middle-guide continuous arch tunnel, including the following steps:

[0102] I. Determination of the pre-tension of the transverse tie-back system in the triangular area of the non-middle-guide continuous arch tunnel:

[0103] Step (1). Through the design drawings of the tunnel lining section, establish a "stratum - structure" method calculation model for the non-middle-guide continuous arch tunnel, and calculate the initial support arc length Lp corresponding to the distribution range of the plastic zone of the surrounding rock in the triangular area above the non-middle-guide continuous arch tunnel after the construction is completed.

[0104] Step (2). In the calculation model established in step (1), apply a horizontal uniform load P (such as Figure 2 ) to the surrounding rock within the distribution range of the plastic zone in the triangular area above the non-middle-guide continuous arch tunnel, and adjust the value of P to conduct trial calculations on the model to find the optimal solution P m . This optimal solution P m should minimize the distribution area of the plastic zone of the surrounding rock in the triangular area after the model calculation is completed.

[0105] Step (3), calculate the total pre-tension force P required for the transverse tie-back system in the triangular area of the middle-guide-free multi-arch tunnel total .

[0106] II. Design of tie-back bolts for the transverse tie-back system in the triangular area of the middle-guide-free multi-arch tunnel:

[0107] Step (4), the design of tie-back bolts for the transverse tie-back system in the triangular area of the middle-guide-free multi-arch tunnel includes the determination of bolt arrangement method, bolt quantity, bolt length, and bolt pre-tension force.

[0108] In step (2), the determination method of the optimal solution P m is as follows:

[0109] According to the rock mechanics theory, before the tunnel excavation, the stress state of a point in the surrounding rock of the triangular area above the middle-guide-free multi-arch tunnel is as Figure 3 shown. Considering only the self-weight, the acting forces on the top and bottom surfaces of the micro-element are both σ 1 =γz, and the acting force on the side surface of the micro-element is σ 3 =λγz, where γ is the unit weight of the rock, λ is the lateral pressure coefficient, and z is the buried depth. Its stress state is as Figure 3 shown in ① of

[0110] As the tunnel is excavated, the lateral constraint of the surrounding rock in the triangular area gradually disappears, that is, σ 3 gradually decreases. According to the Mohr-Coulomb failure criterion, when σ 3 decreases to σ 3' , when the stress circle is tangent to the shear strength line, the rock mass fails and becomes unstable (as Figure 3 shown in ② of

[0111]

[0112] In the formula, R P is the compressive strength of the rock mass; σ 3 is the lateral constraint force; c is the cohesion of the rock mass; is the internal friction angle.

[0113] If horizontal acting forces are applied to the surrounding rock in the triangular area by adding tie-back bolts during the tunnel excavation process to increase σ 3 , the stress state of the rock mass will be below the envelope line and will not fail. However, if the applied lateral stress becomes the major principal stress and is too large, and the stress circle is tangent to the shear strength line, the rock mass will still fail (as Figure 3 shown in ③ of

[0114] Therefore, in order to improve the stability and ultimate bearing capacity of the surrounding rock in the triangular area above the non-central guide double-arch tunnel, the applied horizontal distributed load P should be able to provide sufficient lateral restraint stress, but the lateral restraint stress should not be so great as to cause rock mass damage.

[0115] Determine the optimal solution P for horizontal load distribution m The method is to find a horizontal average load P that minimizes the distribution area of ​​the plastic zone. This load is the optimal solution P for the horizontal average load that meets safety and economic conditions. m Since the plastic zone area of ​​the surrounding rock in the triangular area above the non-central guide double-arch tunnel shows a change rule of decreasing first and then increasing with the horizontal average load P, the P value should be adjusted to test the model for no less than 6 times, and the calculated plastic zone area should fall as much as possible within the optimal solution P for the horizontal average load. m The corresponding plastic zone area on both sides, that is, the calculation results can reflect the change law that the plastic zone area first decreases and then increases with the horizontal evenly distributed load.

[0116] The horizontal average load in the model calculation is P i (i=0,1,2,3,…≥6), the area of ​​the plastic zone of the surrounding rock in the corresponding triangle is A i (i=0,1,2,3,…≥6), the following formula is used to fit the variation law of the plastic zone area A with the load P: when i=0, P i =0, A i =5.3754

[0117]

[0118] In the formula, A amp is the initial amplitude, A 0 is the equilibrium point, a is the attenuation factor, ω is the angular frequency, is the phase, and the above are all fitting parameters.

[0119] This formula can intuitively reflect the change rule of the plastic zone area A(P) as the independent variable P first decreases rapidly and then increases slowly. The minimum value of the plastic zone area A MIN The corresponding horizontal average load is the optimal solution of horizontal average load P m (like Figure 4 ).

[0120] In step (3), the total pre-tension force P required for the transverse tension system in the triangular area of ​​the tunnel without a central guide arch is total The calculation method is as follows:

[0121] P total =P m ·Lp

[0122] Where P mis the optimal solution of the horizontal uniformly distributed load (kN / m), and Lp is the length of the initial support arc (m).

[0123] In step (4), the arrangement method, quantity, length, and determination method of the pre-tension of the anchor bolts in the transverse tie-back system of the triangular area of the middle-guide-less connected-arch tunnel are as follows:

[0124] The arrangement method of the anchor bolts is in a plum blossom pattern; the length and quantity of the anchor bolts are determined according to the specific arrangement method from the design drawings of the tunnel lining section; the pre-tension of the anchor bolts is calculated by the following formula:

[0125] P s = P total · / N

[0126] In the formula, P s is the pre-tension of a single tie-back anchor bolt; N is the number of tie-back anchor bolts arranged per meter longitudinally in the triangular area of the middle-guide-less connected-arch tunnel.

[0127] A construction method for the transverse tie-back system in the triangular area of a middle-guide-less connected-arch tunnel. This construction method for the transverse tie-back system in the triangular area of a middle-guide-less connected-arch tunnel is based on the above-mentioned design method for the transverse tie-back system in the triangular area of a middle-guide-less connected-arch tunnel, and includes the following steps:

[0128] S1, Excavation of the upper bench of the leading tunnel: The leading tunnel is excavated in a circular shape with section I, and the excavation height is greater than 2.0 m (such as Figure 5 ).

[0129] S2, Installation of system anchor bolts: The system anchor bolts of the upper bench of the leading tunnel are installed according to the conventional construction steps.

[0130] S3, Erection of steel arch frames: The steel arch frames of the upper bench of the leading tunnel are constructed, the steel mesh is hung, and the longitudinal connecting bars are welded; channel steels are installed at the corresponding positions (in a plum blossom pattern) of the tie-back anchor bolts, and round holes are reserved at the corresponding positions where the anchor bolts pass through the channel steels. The two ends of the channel steels are clamped on the flanges of two adjacent sets of steel arch frames close to the surrounding rock side, and the contact parts between the web of the channel steel and the flanges of the two adjacent sets of steel arch frames are welded firmly.

[0131] S4, Drilling: Mark the drilling positions (in a plum blossom pattern), and use a pneumatic drill to drill horizontally from the right side of the upper bench of the leading tunnel towards the side of the trailing tunnel. The angle and depth of the drilling need to be strictly controlled to ensure that the anchor bolts can be accurately inserted and extend not less than 30 cm beyond the designed initial support surface of the trailing tunnel.

[0132] S5, Hole cleaning: After drilling, the rock powder and accumulated water in the hole need to be cleaned to ensure that the hole is clean without debris.

[0133] S6, Installation of anchor bolts: Insert the anchor bolts into the holes in the surrounding rock through the round holes of the channel steels, with both ends protruding 30 cm beyond the designed initial support surface (such as Figure 6 and Figure 7), the insertion length of the anchor rod shall meet the design requirements and shall not be shorter than 95% of the design length.

[0134] S7, Install the grout stopper and anchor plate: Install the grout stopper and anchor plate on the anchor rod to ensure that the grout will not leak during grouting and can provide sufficient anchoring force.

[0135] S8, Grouting: Use a grouting machine to inject the grout into the hole until the grout overflows from the hole mouth. During the grouting process, it is necessary to control the grouting pressure and the amount of grout to ensure that the grout can fill the anchor hole and penetrate into the cracks.

[0136] S9, Tighten the grout stopper and install the nut: After the grouting is completed, tighten the grout stopper and install the nut at the end of the tie-back anchor rod. Use a torque wrench to apply the initial stress until the anchor plate is in close contact with the channel steel.

[0137] S10, Initial tension of the anchor rod: After the grout has solidified, use a torque wrench to tighten the nut to tension the anchor rod. The tension force should not be too large, and it is sufficient to reach 30% of the design required anchoring force.

[0138] S11, Construction of the lining of the pilot tunnel: Complete the construction of the initial support and the secondary lining of the pilot tunnel according to the designed excavation support sequence (such as Figure 5 ).

[0139] S12, Carry out the following operations for the upper bench excavation, installation of system anchor rods, drilling, hole cleaning, installation of anchor rods, installation of grout stoppers and anchor plates, grouting, etc. of the following tunnel using the same steps.

[0140] S13, Tie-back of the anchor rods: Tension the anchor rods of the following tunnel by tightening the nuts with a torque wrench to ensure that the anchor rods reach the design required anchoring force, and then cut off the excess length of the anchor rods.

[0141] S14, Construction of subsequent processes: After the construction of the transverse tie-back system in the triangular area of the non-middle-guide continuous arch tunnel is completed according to the above steps, the excavation and support processes of the lower bench of the following tunnel can be carried out in sequence.

[0142] Application example

[0143] This example provides a design method for precast reinforced bars for the invert lining of a tunnel, including the following steps:

[0144] Step (1), Taking the Class V surrounding rock as an example, establish a "stratum-structure" method calculation model for the non-middle-guide continuous arch tunnel through the tunnel lining section design drawings, such as Figure 8 shown; After calculation, the initial support arc length Lp = 5.4m corresponding to the plastic zone distribution range of the surrounding rock in the triangular area above the non-middle-guide continuous arch tunnel after construction is obtained, as Figure 2 shown;

[0145] Step (2), apply a uniformly distributed horizontal load P (such as Figure 2 ) on the surrounding rock within the plastic zone distribution range of the triangular area above the middle - guide - less connected - arch tunnel in the calculation model, and adjust the value of P to conduct trial calculations on the model to find the optimal solution P m of the uniformly distributed horizontal load. The optimal solution P m of the uniformly distributed horizontal load should minimize the distribution area of the plastic zone of the surrounding rock in the triangular area after the model calculation ends;

[0146] The determination method of the optimal solution P m of the uniformly distributed horizontal load is as follows:

[0147] Adjust the value of P to conduct trial calculations on the model no less than 6 times, and the calculated plastic zone area of the surrounding rock in the triangular area should fall on both sides of the plastic zone area corresponding to the optimal solution P m as much as possible, that is, the calculation results should be able to reflect the change law that the plastic zone area of the surrounding rock in the triangular area above the connected - arch tunnel first decreases and then increases with the uniformly distributed horizontal load P. After calculation, the results are as Figure 9 shown in Table 1.

[0148] Table 1 Plastic zone areas obtained by calculating different uniformly distributed horizontal loads

[0149] Horizontal uniformly distributed load P (kN / m) 0 200 400 800 1000 1500 2000 <![CDATA[Plastic zone area A (m 2 )]]> 5.38 1.42 0.16 0.12 0.37 1.43 3.17

[0150] Use the following formula to fit the change law of the plastic zone area A with the uniformly distributed horizontal load P in Table 1:

[0151]

[0152] In the formula, A amp is the initial amplitude, A 0 is the equilibrium point, a is the attenuation factor, ω is the angular frequency, is the phase, and all of the above are fitting parameters.

[0153] The fitting result is as follows, and the function graph is as Figure 10 shown.

[0154]

[0155] From Figure 10 it can be seen that initially, the plastic zone area of the triangular area of the model is 5.38 m 2 . As the uniformly distributed horizontal load increases, the plastic zone area first decreases rapidly and then increases slowly. Among them, the bc section of the curve indicates that when the uniformly distributed horizontal load increases from b to c, the plastic zone area is always 0, that is, the load corresponding to point b is the desired optimal solution, and at this time P m = 450 kN / m.

[0156] Step (3), calculate the total pre - tension P total required for the transverse tension - resistant system in the triangular area of the middle - guide - less connected - arch tunnel;

[0157] Total pre-tension force P required for the transverse tie-back system in the triangular area of a non-middle-guide multi-arch tunnel total The calculation method is as follows:

[0158] P total = P m ·Lp = 450×4.5 = 2430 kN

[0159] In the formula, P m is the optimal solution of the horizontal uniformly distributed load (kN / m), and Lp is the length of the initial support arc within the plastic zone distribution range of the surrounding rock in the triangular area (m).

[0160] Step (4) Design of the tie-back bolts for the transverse tie-back system in the triangular area of a non-middle-guide multi-arch tunnel:

[0161] The design of the tie-back bolts for the transverse tie-back system in the triangular area of a non-middle-guide multi-arch tunnel includes the determination of the bolt arrangement method, the number of bolts, the bolt length, and the bolt pre-tension force.

[0162] Specifically:

[0163] The bolt arrangement method is in a plum blossom pattern. The bolt length and the number of bolts are determined according to the specific arrangement method from the design drawing. As Figure 5 shown, the tie-back bolts adopt Φ32 prestressed threaded steel, and the circumferential and longitudinal spacings are 60 cm×50 cm. The bolt pre-tension force is calculated by the following formula:

[0164] P s = P total / N = 2430 / (2×6 + 5) = 143 kN

[0165] In the formula, P s is the pre-tension force of a single tie-back bolt; N is the number of tie-back bolts arranged per meter along the longitudinal direction of the tunnel in the triangular area of the non-middle-guide multi-arch tunnel.

[0166] This example also proposes a construction method for the transverse tie-back system in the triangular area of a non-middle-guide multi-arch tunnel; as Figure 1 shown, this construction method for the transverse tie-back system in the triangular area of a non-middle-guide multi-arch tunnel includes the following steps:

[0167] Step 1, Excavation of the upper bench of the pilot tunnel: The pilot tunnel is excavated with a circular cross-section I, and the excavation height is greater than 2.0 m (as Figure 5 ).

[0168] Step 2, Installation of the systematic bolts: The systematic bolts of the upper bench of the pilot tunnel are driven according to the conventional construction steps.

[0169] Step 3, erect steel arch: Install the steel arch of the upper bench of the pilot tunnel, hang the steel mesh, and weld the longitudinal connecting bars; Install channel steel at the corresponding positions (in a plum blossom pattern) of the tie-back bolts, and reserve round holes at the corresponding positions where the bolts pass through the channel steel. Clamp both ends of the channel steel on the flanges of two adjacent steel arches close to the surrounding rock side, and weld the contact parts between the web of the channel steel and the flanges of two adjacent steel arches firmly.

[0170] Step 4, drilling: Mark the drilling positions (in a plum blossom pattern), and use a pneumatic drill to drill from the right side of the upper bench of the pilot tunnel horizontally towards the rear tunnel side. The angle and depth of the drilling need to be strictly controlled to ensure that the bolt can be accurately inserted and extend no less than 30 cm beyond the designed primary support surface of the rear tunnel.

[0171] Step 5, hole cleaning: After drilling, clean the rock powder and accumulated water in the hole to ensure that the hole is clean without debris.

[0172] Step 6, install bolts: Insert the bolts into the holes of the surrounding rock through the round holes of the channel steel, with both ends protruding 30 cm beyond the designed primary support surface (as Figure 6 and Figure 7 ), and the inserted length of the bolts needs to meet the design requirements and shall not be shorter than 95% of the designed length.

[0173] Step 7, install grout plug and anchor plate: Install a grout plug and an anchor plate on the bolt to ensure that the grout will not leak during grouting and can provide sufficient anchoring force.

[0174] Step 8, grouting: Use a grouting machine to inject the grout into the hole until the grout overflows from the hole mouth. During the grouting process, control the grouting pressure and grouting volume to ensure that the grout can fill the anchor hole completely and penetrate into the cracks.

[0175] Step 9, tighten the grout plug and install the nut: After grouting, tighten the grout plug and install a nut at the end of the tie-back bolt. Use a torque wrench to apply the initial stress until the anchor plate is in close contact with the channel steel;

[0176] Step 10, initial tensioning of bolts: After the grout has solidified, use a torque wrench to tighten the nut to tension the bolts. The tension force should not be too large, and reaching 30% of the designed anchoring force is sufficient.

[0177] Step 11, lining construction of the pilot tunnel: Complete the construction of the initial support and secondary lining of the pilot tunnel according to the designed excavation and support sequence (as Figure 5 ).

[0178] Step 12, carry out the following operations for the upper bench excavation of the rear tunnel, installation of system bolts, drilling, hole cleaning, bolt installation, installation of grout plug and anchor plate, grouting, etc. using the same steps.

[0179] Step 13, tie-back of anchor bolts: Use a torque wrench to tighten the nuts to tension the anchor bolts in the subsequent tunnel, ensuring that the anchor bolts reach the designed anchoring force, and then cut off the excess length of the anchor bolts.

[0180] Step 14, construction of subsequent processes: After the transverse tie-back system in the triangular area of the middle-guide less multi-arch tunnel is constructed according to the above steps, the excavation and support processes of the lower bench of the subsequent tunnel can be carried out in sequence.

[0181] The present invention provides a design method and a construction method for a transverse tie-back system in the triangular area of a middle-guide less multi-arch tunnel. The prior art has not proposed an effective design method for the tie-back anchor bolts used for the reinforcement of the surrounding rock in the triangular area above the multi-arch tunnel. To address this issue, the design method of the present invention can quickly calculate the pre-tension of the tie-back anchor bolts, thereby providing a theoretical basis for the reasonable design of the anchor bolt length, the number of anchor bolts, and the layout method. After the on-site implementation of the transverse tie-back system of the present invention, the deformation of the surrounding rock and the development of the plastic zone in the triangular area above the multi-arch tunnel can be effectively controlled. Taking the embodiment of this article as an example, arranging 17 tie-back anchor bolts with a pre-tension of 143 kN per meter of the triangular area surrounding rock can reduce the plastic zone area to 0, thus significantly improving the stability and safety of the tunnel and the support structure.

[0182] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. The design method of the transverse tension system in the triangular area of ​​the non-central guide double-arch tunnel is characterized by: The steps include: Step (1), according to the tunnel lining section design drawings, a stratum-structure method numerical calculation model of the tunnel without central guide arch is established, and the initial support arc length Lp corresponding to the distribution range of the surrounding rock plastic zone in the triangular area above the tunnel without central guide arch after the construction is completed is calculated; Step (2), in the calculation model established in step (1), a horizontal average load P is applied to the surrounding rock within the distribution range of the plastic zone in the triangular area above the non-central guide arch tunnel, and the value of P is adjusted to perform trial calculations on the model, so as to find the minimum value A of the plastic zone area. MIN The corresponding horizontal average load is recorded as the optimal solution of the horizontal average load P m ; Step (3): using the initial support arc length Lp obtained in step (1) and the optimal solution P for the horizontal average load obtained in step (2) m , calculate the total pre-tension force P required for the transverse tension system in the triangular area of ​​the tunnel without a central guide arch total ; Step (4) is to design the tensioning anchors of the transverse tensioning system in the triangular area of ​​the non-central guide arch tunnel, including the determination of the anchor arrangement, the number of anchors, the anchor length and the anchor pre-tension.

2. The method for designing a transverse tension system in a triangular area of ​​a non-central guide double-arch tunnel according to claim 1 is characterized in that: In step (2), the optimal solution P m The method of determining is as follows: Adjust the P value to test the model. When testing the model, the horizontal average load is P i , the corresponding plastic zone area of ​​the triangular surrounding rock is A i , i=0,1,2,3,…,M, M is the total number of trials; Formula (1) is used to fit the variation law of the plastic zone area A with the load P: In formula (1), A amp is the initial amplitude, A0 is the equilibrium point, a is the attenuation factor, ω is the angular frequency, is the phase, and the above are all fitting parameters; Using the fitted formula (1), we can find the minimum value of the plastic zone area A: MIN The corresponding horizontal average load is recorded as the optimal solution of the horizontal average load P m .

3. The method for designing a transverse tension system in a triangular area of ​​a non-central guide double-arch tunnel according to claim 2 is characterized in that: In step (2), M should be no less than 6.

4. The method for designing a transverse tension system in a triangular area of ​​a non-central guide double-arch tunnel according to claim 1 is characterized in that: In step (3), the total pretension force P required for the transverse tension system in the triangular area of ​​the tunnel without a central guide arch is total The calculation method is as follows: P total =P m ·Lp (2) In formula (2), P m is the optimal solution for horizontally distributed load, kN / m; Lp is the initial support arc length, m.

5. The method for designing the transverse tension system of the triangular area of ​​a non-central guide double-arch tunnel according to claim 1 is characterized in that: In step (4), the anchor rods are arranged in a plum blossom shape; The anchor pretension is calculated by formula (2): P s =P total / N(3) Where P s is the pre-tension of a single tension anchor rod; N is the number of tension anchor rods arranged in the triangular area of ​​the tunnel without a central guide arch per meter along the longitudinal direction of the tunnel.

6. A method for constructing a transverse tension system in a triangular area of ​​a non-central guide multi-arch tunnel, characterized in that: The lateral tensioning system for the triangular area of ​​a non-central guide double-arch tunnel designed by the design method for the lateral tensioning system for the triangular area of ​​a non-central guide double-arch tunnel according to any one of claims 1 to 5 comprises the following steps: S1, excavation of steps on the first tunnel, excavation height greater than 2.0m; S2, driving the anchor bolts of the step system on the pilot hole; S3, construct the step steel frame on the pilot hole, hang the steel mesh, and weld the longitudinal connecting bars; install the channel steel at the corresponding position where the tension anchor rods are arranged, and reserve circular holes at the corresponding positions where the anchor rods pass through the channel steel, clamp the two ends of the channel steel on the flanges of the two adjacent steel frames close to the surrounding rock, and weld the contact parts between the web of the channel steel and the flanges of the two adjacent steel frames firmly; S4, mark the drilling position, use a pneumatic drill to drill horizontally from the right side of the upper step of the tunnel leading hole to the side of the rear tunnel, and the drilling angle and depth must be strictly controlled to ensure that the anchor rod can be accurately inserted and can extend out of the designed initial support surface of the rear tunnel by no less than 30cm; S5, after the drilling is completed, the hole is cleaned; S6, insert the anchor rod into the surrounding rock hole through the circular hole of the channel steel, with both ends exposed 29-31cm above the designed initial support surface. The insertion length of the anchor rod must meet the design requirements and shall not be shorter than 95% of the designed length; S7, install the grout stopper and anchor pad on the anchor rod; S8, injecting slurry into the hole using a grouting machine until the slurry overflows the hole; S9, after grouting is completed, tighten the stop plug and install the nut at the end of the tension anchor rod, and use a torque wrench to apply initial stress until the anchor plate and the channel steel are in close contact; S10, initial tensioning of anchor rods: after the slurry solidifies, tighten the nut with a torque wrench to tension the anchor rods until the tensioning force reaches 30% of the design anchoring force; S11, complete the initial support of the pilot tunnel and the construction of the secondary lining according to the designed excavation and support sequence; S12, using the same steps as S1 to S11 to process the back hole; S13, tension the anchor rods in the rear tunnel to ensure that the anchor rods reach the designed anchoring force, and then cut off the excess length of the anchor rods; S14, subsequent construction process: After the transverse tensioning system of the triangular area of ​​the non-central guide multi-arch tunnel is constructed according to the above steps, the excavation and support processes of the steps under the rear tunnel can be carried out in sequence.

Images