A method for constructing a tunnel across a large-span unfillable deep karst cave section

Abstract

The present invention provides a method for constructing a tunnel across a large-span unfillable deep cave segment, by excavating a nearshore support platform, constructing a platform support starting segment on the nearshore support platform, respectively constructing a first anchoring assembly and a second anchoring assembly on both sides of the excavated tunnel segment, sequentially hoisting all the supporting spanning segments, excavating a farshore support platform on the cave wall of the target cave away from the platform support starting segment, constructing a platform support ending segment, constructing a tunnel main structure on the top of the basic spanning platform, dismantling the first anchoring assembly, the second anchoring assembly and all anchor cables, so as to complete the construction of the tunnel segment corresponding to the target cave. The present application solves the problem that a working platform cannot be set up when constructing a large-span unfillable cave from a single direction, fully utilizing the strength of the rock mass as an anchoring pier, saving materials and facilitating construction, and can be set up in a targeted manner according to the calculation of caves of different spans, with a wide range of application, and can be promoted for similar projects.

Description

Technical Field

[0001] The present application relates to the field of tunnel technology, and in particular to a method for constructing a tunnel across a large-span unfillable deep karst cave section. Background Art

[0002] In the process of tunnel construction, especially as my country's highway construction gradually shifts to the southwestern mountainous areas, the highway-tunnel ratio in this area is high, and caves are frequently encountered during tunnel construction. According to the longitudinal span of the cave along the tunnel and the distance from the bottom boundary of the cave to the tunnel design elevation, the caves are divided into four types: small-span shallow caves, large-span shallow caves, small-span deep caves and large-span deep caves.

[0003] For the tunnel construction methods of the first three types of karst cave sections, there are relatively mature engineering technologies that can be applied. For example, for the first three types of karst caves, construction solutions such as filling, setting pillars to reduce spans, and drilling in the air can be used. However, for large-span deep karst caves (span greater than 15m, depth greater than 30m), there are characteristics such as the development boundary along the longitudinal span of the tunnel is very large, the bottom boundary is very deep and difficult to explore, and there may be water channels at the bottom. The previous filling, drilling in the air, setting pillars to reduce spans and other solutions are not applicable. Only a one-way crossing solution can be used. However, due to the large longitudinal span of the karst cave, the opposite bank foundation construction cannot be carried out on the excavated side of the karst cave. Therefore, there is currently no mature solution for the construction method of tunnels through large-span deep karst caves. How to safely, economically and conveniently build tunnels in this type of karst cave has become a problem that urgently needs to be solved.

[0004] In view of this, it is necessary to propose a tunnel construction method across a large-span unfillable deep cave section to solve or at least alleviate the above-mentioned defects. Summary of the invention

[0005] The main purpose of the present application is to provide a method for constructing a tunnel across a large-span unfillable deep karst cave section, so as to solve the technical problem that there is no mature solution for the existing technology for the method for constructing a tunnel through a large-span deep karst cave.

[0006] To achieve the above-mentioned purpose, the present application provides a method for constructing a tunnel across a large-span unfillable deep cave section, comprising the steps of:

[0007] S1, excavating a nearshore support platform at the boundary of the excavated tunnel section close to the target cave, and constructing a platform support starting section on the nearshore support platform;

[0008] S2, respectively applying a first anchoring assembly and a second anchoring assembly on both sides of the excavated tunnel section;

[0009] S3, erect the i-th pair of anchor cables corresponding to the i-th support span segment, use the i-th pair of anchor cables to splice the i-th support span segment to the end of the platform support starting segment, and then apply the corresponding design prestress to the i-th pair of anchor cables; wherein i is a positive integer, the initial value of i is 1, and the i-th pair of anchor cables includes two anchor cables respectively arranged on both sides of the excavated tunnel segment and anchor cables , anchor cable One end of the anchor cable is anchored on the i-th supporting span segment, and the other end is anchored on the first anchor assembly. One end of is anchored on the i-th supporting span segment, and the other end is anchored on the second anchoring assembly;

[0010] S4, erecting the i+1th pair of anchor cables corresponding to the i+1th supporting span segment, splicing the i+1th supporting span segment to the end of the i-th supporting span segment using the i+1th pair of anchor cables, and then applying the corresponding designed prestress to the i+1th pair of anchor cables; wherein the i+1th pair of anchor cables includes two anchor cables respectively arranged on both sides of the excavated tunnel segment and anchor cables , anchor cable One end of the anchor cable is anchored on the i+1th supporting span segment, and the other end is anchored on the first anchor assembly. One end of is anchored on the (i+1)th supporting span segment, and the other end is anchored on the second anchoring assembly;

[0011] S5, determine whether the i+1th supporting span segment is the last supporting span segment, if so, proceed to step S6, if not, assign i+1 to i, and return to step S4;

[0012] S6, excavating a far-shore support platform on the wall of the target cave away from the platform support start segment, and constructing a platform support end segment on the far-shore support platform; wherein the platform support end segment and the last support span segment are spliced, and the platform support start segment, the platform support end segment and all support span segments together constitute a basic span platform;

[0013] S7, constructing the main structure of the tunnel on the top of the foundation spanning platform, and when the strength of the main structure of the tunnel reaches the designed strength, removing the first anchoring assembly, the second anchoring assembly and all anchor cables to complete the construction of the tunnel section corresponding to the target cave.

[0014] Preferably, applying the corresponding designed prestress to the first pair of anchor cables in step S3 specifically comprises the following steps:

[0015] Obtain the maximum self-weight load and construction load of the first supporting span segment;

[0016] Determine the total vertical load value received by the first supporting span segment according to the self-weight load and the maximum load value during the construction period;

[0017] According to the anchor The anchor cable is anchored at the position of the first supporting span segment and the position of the first anchor assembly. The tilt angle , according to the total vertical load and the inclination angle Determine the anchor cable Axial force on , and according to the axial force Determine the anchor cable Apply the corresponding design prestress;

[0018] According to the anchor Anchor cable anchored at the first support span segment and the second anchor assembly The tilt angle , according to the total vertical load and the inclination angle Determine the anchor cable Axial force on , and according to the axial force Determine the anchor cable Apply the corresponding design prestress.

[0019] Preferably, the first anchor assembly includes a first anchor pier and a second anchor pier arranged on the same side of the excavated tunnel section, the first anchor pier includes a first anchor head, a first connecting steel plate, a first fixed pulley and a plurality of first anchor rods; wherein, the first anchor head is pre-buried in the tunnel side wall, the first connecting steel plate is connected to the outer end surface of the first anchor head, the first fixed pulley is connected to the outer wall surface of the first connecting steel plate, the first anchor head has a plurality of first through holes for the first anchor rods to pass through, the first anchor rod includes a first connecting end and a first anchoring end arranged opposite to each other along its own extension direction, the first anchoring end is anchored in the tunnel surrounding rock, the first connecting end passes through the first through hole and is connected to the first connecting steel plate;

[0020] The second anchor pier includes a second anchor head, a second connecting steel plate, a second fixed pulley and a plurality of second anchor rods; wherein, the second anchor head is pre-buried in the tunnel side wall, the second connecting steel plate is connected to the outer end surface of the second anchor head, the second fixed pulley is connected to the outer wall surface of the second connecting steel plate, the second anchor head has a plurality of second through holes for the second anchor rods to pass through, the second anchor rod includes a second connecting end and a second anchoring end arranged opposite to each other along its own extension direction, the second anchoring end is anchored in the tunnel surrounding rock, and the second connecting end passes through the second through hole and is connected to the second connecting steel plate.

[0021] Preferably, the second anchor assembly includes a third anchor pier and a fourth anchor pier arranged on the same side of the excavated tunnel section, wherein the third anchor pier includes a third anchor head, a third connecting steel plate, a third fixed pulley and a plurality of third anchor rods; wherein the third anchor head is pre-buried in the tunnel side wall, the third connecting steel plate is connected to the outer end face of the third anchor head, the third fixed pulley is connected to the outer wall face of the third connecting steel plate, the third anchor head has a plurality of third through holes for the third anchor rod to pass through, the third anchor rod includes a third connecting end and a third anchoring end arranged relatively along its own extension direction, the third anchoring end is anchored in the tunnel surrounding rock, and the third connecting end passes through the third through hole and is connected to the third connecting steel plate;

[0022] The fourth anchor pier includes a fourth anchor head, a fourth connecting steel plate, a fourth fixed pulley and multiple fourth anchor rods; wherein, the fourth anchor head is pre-buried in the tunnel side wall, the fourth connecting steel plate is connected to the outer end face of the fourth anchor head, the fourth fixed pulley is connected to the outer wall face of the fourth connecting steel plate, the fourth anchor head has multiple fourth through holes for the fourth anchor rod to pass through, the fourth anchor rod includes a fourth connecting end and a fourth anchoring end relatively arranged along its own extension direction, the fourth anchoring end is anchored in the tunnel surrounding rock, and the fourth connecting end passes through the fourth through hole and is connected to the fourth connecting steel plate.

[0023] Preferably, the plurality of first anchor rods are in the shape of an inverted frustum that is small on the outside and large on the inside, and / or the plurality of second anchor rods are in the shape of an inverted frustum that is small on the outside and large on the inside.

[0024] Preferably, the number of required support spanning segments is obtained by the following steps:

[0025] Get the vertical span of the target cave ;

[0026] Using formula The number of supporting span segments required to span the target cave ; Among them, the length of each support span segment is 6m.

[0027] Preferably, the nearshore supporting platform is 3 m long and 13 m wide along the longitudinal direction of the tunnel, and the farshore supporting platform is 3 m long and 13 m wide along the longitudinal direction of the tunnel.

[0028] Preferably, the center height of the first anchor pier is 8m from the design elevation of the tunnel and 9m from the proximal boundary of the target cave; the center height of the second anchor pier is 1m from the design elevation of the tunnel and 14m from the proximal boundary of the target cave.

[0029] Preferably, the center height of the third anchor pier is 8m from the design elevation of the tunnel, and the horizontal distance from the proximal boundary of the target cave is 9m; the center height of the fourth anchor pier is 1m from the design elevation of the tunnel, and the horizontal distance from the proximal boundary of the target cave is 14m.

[0030] Compared with the prior art, this application has the following beneficial effects:

[0031] The present invention provides a method for constructing a tunnel across a large-span unfillable deep cave segment, by excavating a nearshore support platform, constructing a platform support starting segment on the nearshore support platform, respectively constructing a first anchoring assembly and a second anchoring assembly on both sides of the excavated tunnel segment, sequentially hoisting all the supporting spanning segments, excavating a farshore support platform on the cave wall of the target cave away from the platform support starting segment, constructing a platform support ending segment, constructing a tunnel main structure on the top of the basic spanning platform, dismantling the first anchoring assembly, the second anchoring assembly and all anchor cables, so as to complete the construction of the tunnel segment corresponding to the target cave. The present application solves the problem that a working platform cannot be set up when constructing a large-span unfillable cave from a single direction, fully utilizing the strength of the rock mass as an anchoring pier, not needing to construct a large-volume gravity anchor pier, saving materials and facilitating construction, and can be set up in a targeted manner according to the calculation of caves of different spans, with a wide range of applications, and can be promoted for similar projects. This application adopts supporting spanning segments, such as Bailey beams, which can achieve rapid assembly and spanning, fast construction speed, greatly save construction period, and ensure construction progress; all construction steps of this application are implemented in the excavated space, without adding too many engineering entities, and the anchor cables and anchor pier components can be recycled and reused, which has obvious economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0033] Figure 1 A schematic diagram of a process of a tunnel construction method in one embodiment of the present application;

[0034] Figure 2 This is a schematic diagram of the structure before the construction of the nearshore support platform in one embodiment of the present application;

[0035] Figure 3 It is a schematic diagram of the structure after the nearshore support platform and the first anchoring assembly are constructed in one embodiment of the present application;

[0036] Figure 4This is a schematic diagram of the structure after the first supporting span segment is hoisted in one embodiment of the present application;

[0037] Figure 5 This is a schematic diagram of the structure after the last supporting span segment is hoisted in one embodiment of the present application;

[0038] Figure 6 This is a schematic diagram of the structure after the construction of the remote shore support platform in one embodiment of the present application;

[0039] Figure 7 It is a schematic diagram of the structure after the main structure of the tunnel is constructed in one embodiment of the present application;

[0040] Figure 8 This is a schematic structural diagram of a first anchoring assembly in one embodiment of the present application;

[0041] Fig. 9 This is one of the schematic diagrams of the connection between the anchor end and the supporting spanning segment in one embodiment of the present application;

[0042] Fig.10 This is the second schematic diagram of the connection between the anchor end and the supporting span segment in one embodiment of the present application;

[0043] Fig.11 This is the third schematic diagram of the connection between the anchor end and the supporting span segment in one embodiment of the present application.

[0044] The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings.

[0045] Description of Figure Numbers:

[0046] 10. Excavated tunnel section; 110. Nearshore support platform; 20. Target cave; 210. Farshore support platform; 30. First anchor assembly; 310. First anchor pier; 311. First anchor head; 312. First connecting steel plate; 313. First fixed pulley; 314. First anchor rod; 3141. First connecting end; 3142. First anchor end; 320. Second anchor pier; 40. Anchor cable; 41. Anchor cable anchor end; 411. Connection assembly; 4111. Anchor beam; 41111. First Mounting plate; 41112, second mounting plate; 41113, third mounting plate; 41114, fourth mounting plate; 4112, connecting drop plate; 412, anchor; 4121, anchor body; 4122, first pad; 4123, second pad; 4124, third pad; 413, anchor cable segment; 42, anchor cable tensioning end; 510, platform support starting segment; 520, support span segment; 530, platform support ending segment; 60, foundation span platform; 70, tunnel main structure. DETAILED DESCRIPTION

[0047] It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0048] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0049] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0050] In addition, the descriptions of "right part", "middle part" and the like in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "right part" and "middle part" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0051] Please see attached Figures 1 to 8 In one embodiment of the present application, a method for constructing a tunnel across a large-span unfillable deep cave section comprises the following steps:

[0052] S1, excavating a nearshore support platform 110 at the boundary of the excavated tunnel section 10 close to the target cave 20, and constructing a platform support starting segment 510 on the nearshore support platform 110; Figure 2 As shown, a support platform is first excavated near the boundary of the target cave 20 as a construction platform for the platform support starting segment 510 to be constructed, wherein the size of the nearshore support platform 110 matches the size of the platform support starting segment 510. As a preferred example, the platform support starting segment 510 is 3 meters long in the longitudinal direction of the tunnel, the nearshore support platform 110 is 3 meters long in the longitudinal direction of the tunnel, and the width in the transverse direction of the tunnel is 13 meters.

[0053] S2, respectively apply the first anchoring assembly 30 and the second anchoring assembly (not shown) on both sides of the excavated tunnel section 10; wherein, the first anchoring assembly 30 and the second anchoring assembly are respectively located on the left and right sides of the excavated tunnel section 10, preferably, the first anchoring assembly 30 and the second anchoring assembly are symmetrically arranged on both sides of the excavated tunnel section 10.

[0054] As a preferred embodiment, the first anchor assembly 30 includes a first anchor pier 310 and a second anchor pier 320 arranged on the same side of the excavated tunnel section 10, the first anchor pier 310 includes a first anchor head 311, a first connecting steel plate 312, a first fixed pulley 313 and a plurality of first anchor rods 314; wherein, the first anchor head 311 is pre-buried in the tunnel side wall, the first connecting steel plate 312 is connected to the outer end surface of the first anchor head 311, the first fixed pulley 313 is connected to the outer wall surface of the first connecting steel plate 312, the first anchor head 311 has a plurality of first through holes (not shown) for the first anchor rod 314 to pass through, the first anchor rod 314 includes a first connecting end 3141 and a first anchoring end 3142 arranged opposite to each other along its own extension direction, the first anchoring end 3142 is anchored in the tunnel surrounding rock, and the first connecting end 3141 passes through the first through hole and is connected to the first connecting steel plate 312;

[0055] The second anchor pier 320 includes a second anchor head (not shown in the figure), a second connecting steel plate (not shown in the figure), a second fixed pulley (not shown in the figure) and a plurality of second anchor rods (not shown in the figure); wherein, the second anchor head is pre-buried in the tunnel side wall, the second connecting steel plate is connected to the outer end surface of the second anchor head, the second fixed pulley is connected to the outer wall surface of the second connecting steel plate, the second anchor head has a plurality of second through holes (not shown in the figure) for the second anchor rods to pass through, the second anchor rod includes a second connecting end (not shown in the figure) and a second anchoring end (not shown in the figure) arranged opposite to each other along its own extension direction, the second anchoring end is anchored in the tunnel surrounding rock, and the second connecting end passes through the second through hole and is connected to the second connecting steel plate.

[0056] Specifically, the structure of the second anchor pier 320 is similar to that of the first anchor pier 310, and will not be described in detail here. The first connecting steel plate 312 provides a connection basis for both the anchor rod and the first fixed pulley 313. The first fixed pulley 313 is used for winding the anchor cable 40 to convert the force direction so that the structural system can be completed in the excavated tunnel space. The second anchor pier 320 is similar to the first anchor pier 310 in structure, and will not be described in detail here. The spatial positions of the second anchor pier 320 and the first anchor pier 310 in the excavated tunnel section 10 are preferably spaced a certain distance apart along the longitudinal direction of the tunnel. It should be noted that, if Figure 3-6As shown, the first anchor pier 310 and the second anchor pier 320 are located on the same side along the tunnel excavation direction. As a preferred example, the center height of the first anchor pier 310 is 8m from the tunnel design elevation, and the horizontal distance from the proximal boundary of the target cave 20 is 9m. The center height of the second anchor pier 320 is 1m from the tunnel design elevation, and the horizontal distance from the proximal boundary of the target cave 20 is 14m.

[0057] As another preferred embodiment, the second anchoring assembly comprises a third anchor pier (not shown) and a fourth anchor pier (not shown) arranged on the same side of the excavated tunnel section, wherein the third anchor pier comprises a third anchor head (not shown), a third connecting steel plate (not shown), a third fixed pulley (not shown) and a plurality of third anchor rods (not shown); wherein the third anchor head is pre-buried in the tunnel side wall, the third connecting steel plate is connected to the outer end face of the third anchor head, the third fixed pulley is connected to the outer wall face of the third connecting steel plate, the third anchor head has a plurality of third through holes for the third anchor rods to penetrate, the third anchor rod comprises a third connecting end and a third anchoring end arranged oppositely along its own extension direction, the third anchoring end is anchored in the tunnel surrounding rock, and the third connecting end penetrates the third through hole and is connected to the third connecting steel plate;

[0058] The fourth anchor pier includes a fourth anchor head (not shown in the figure), a fourth connecting steel plate (not shown in the figure), a fourth fixed pulley (not shown in the figure) and multiple fourth anchor rods (not shown in the figure); wherein, the fourth anchor head is pre-buried in the tunnel side wall, the fourth connecting steel plate is connected to the outer end face of the fourth anchor head, the fourth fixed pulley is connected to the outer wall face of the fourth connecting steel plate, the fourth anchor head has multiple fourth through holes for the fourth anchor rod to pass through, the fourth anchor rod includes a fourth connecting end and a fourth anchoring end relatively arranged along its own extension direction, the fourth anchoring end is anchored in the tunnel surrounding rock, and the fourth connecting end passes through the fourth through hole and is connected to the fourth connecting steel plate.

[0059] Specifically, the third anchor pier is symmetrically arranged with the first anchor pier 310, and the fourth anchor pier is symmetrically arranged with the second anchor pier 320, which will not be described in detail here. As a preferred example, the center height of the third anchor pier is 8m from the tunnel design elevation, and the horizontal distance from the near end boundary of the target cave 20 is 9m, and the center height of the fourth anchor pier is 1m from the tunnel design elevation, and the horizontal distance from the near end boundary of the target cave 20 is 14m.

[0060] S3, erect the i-th pair of anchor cables 40 corresponding to the i-th support spanning segment 520, use the i-th pair of anchor cables 40 to splice the i-th support spanning segment 520 to the end of the platform support starting segment 510, and then apply the corresponding designed prestress to the i-th pair of anchor cables 40; wherein i is a positive integer, the initial value of i is 1, and the i-th pair of anchor cables 40 includes two anchor cables respectively arranged on both sides of the excavated tunnel section 10 and anchor cables , anchor cable One end of the anchor cable is anchored on the i-th supporting span segment 520, and the other end is anchored on the first anchoring assembly 30. One end of is anchored on the i-th supporting span segment 520, and the other end is anchored on the second anchoring assembly;

[0061] As a preferred embodiment, applying the corresponding designed prestress to the first pair of anchor cables 40 in step S3 specifically includes the following steps:

[0062] Obtain the maximum self-weight load and construction load of the first supporting span segment 520;

[0063] Determine the total vertical load value received by the first supporting span segment 520 according to the deadweight load and the maximum load value during the construction period;

[0064] According to the anchor The anchor cable is anchored at the position of the first support spanning segment 520 and the position of the first anchor assembly 30 to determine the anchor cable. The tilt angle , according to the total vertical load and the inclination angle Determine the anchor cable Axial force on , and according to the axial force Determine the anchor cable Apply the corresponding design prestress;

[0065] According to the anchor The anchor cable is anchored at the position of the first support spanning segment 520 and the position of the second anchor assembly. The tilt angle , according to the total vertical load and the inclination angle Determine the anchor cable Axial force on , and according to the axial force Determine the anchor cable Apply the corresponding design prestress.

[0066] The design prestress of this embodiment is based on a calculation formula derived from the principle of mechanics, which comprehensively considers actual loads such as the deadweight load of the supporting span segment 520 and the maximum load during the construction period. The design prestress obtained according to the method of this embodiment can ensure the safety of the construction process, avoid blindly determining according to experience, and quickly guide the construction.

[0067] S4, erecting the i+1th pair of anchor cables 40 corresponding to the i+1th supporting span segment 520, splicing the i+1th supporting span segment 520 to the end of the i-th supporting span segment 520 using the i+1th pair of anchor cables 40, and then applying the corresponding designed prestress to the i+1th pair of anchor cables 40; wherein the i+1th pair of anchor cables 40 includes two anchor cables respectively arranged on both sides of the excavated tunnel section 10 and anchor cables , anchor cable One end of the anchor cable is anchored on the (i+1)th supporting span segment 520, and the other end is anchored on the first anchor assembly 30. One end of is anchored on the (i+1)th supporting spanning segment 520, and the other end is anchored on the second anchoring assembly;

[0068] S5, determine whether the i+1th supporting span segment 520 is the last supporting span segment 520, if yes, proceed to step S6, if no, assign i+1 to i, and return to step S4;

[0069] Specifically, when constructing the support spanning segment 520, the first support spanning segment 520 is constructed first, that is, when i takes the initial value 1, the first pair of anchor cables 40 corresponding to the first support spanning segment 520 is erected, and the first support spanning segment 520 is spliced ​​to the end of the platform support starting segment 510 by using the first pair of anchor cables 40, and then the first pair of anchor cables 40 is applied with the corresponding design prestress, and then the second pair of anchor cables 40 corresponding to the second support spanning segment 520 is erected, and the second pair of anchor cables 40 is used to splice the first support spanning segment 520 to the end of the platform support starting segment 510. The cable 40 splices the second supporting span segment 520 to the end of the platform supporting starting segment 510, and then applies the corresponding designed prestress to the second pair of anchor cables 40, and then determines whether the second supporting span segment 520 is the last supporting span segment 520. If so, the last supporting span segment 520 has reached the vicinity of the far end boundary of the target cave 20. At this time, the far shore supporting platform 210 corresponding to S6 can be constructed on the last supporting span segment 520 with the help of construction equipment.

[0070] It should be noted that, in order to improve the stability of the supporting span segment 520 during hoisting, a pair of anchor cables 40 is arranged corresponding to each supporting span segment 520 in the present application. Preferably, each pair of anchor cables 40 is symmetrically connected to both sides of the supporting span segment 520, and each pair of anchor cables 40 is applied simultaneously. For example, in order to simplify the diagram, Figures 3 to 6 Only a single-side connection diagram is shown, that is, one anchor cable 40 of a pair of anchor cables 40 is connected to the first anchor pier 310 and the second anchor pier 320 .

[0071] S6, excavating a far-shore support platform 210 on the wall of the target cave 20 away from the platform support start segment 510, and constructing a platform support end segment 530 on the far-shore support platform 210; wherein the platform support end segment 530 and the last support span segment 520 are spliced, and the platform support start segment 510, the platform support end segment 530 and all the support span segments 520 together constitute a basic span platform 60;

[0072] As a preferred example, the length of the far shore support platform 210 along the longitudinal direction of the tunnel is 3 m, and the width along the transverse direction of the tunnel is 13 m.

[0073] S7, construct the tunnel main structure 70 on the top of the foundation spanning platform 60, and when the strength of the tunnel main structure 70 reaches the design strength, remove the first anchoring assembly 30, the second anchoring assembly and all anchor cables 40 to complete the construction of the tunnel section corresponding to the target cave 20.

[0074] The present application solves the problem that a working platform cannot be set up in a single-direction construction of a large-span unfillable karst cave, and fully utilizes the strength of the rock mass as an anchor pier, saving materials and facilitating construction. It can be set up in a targeted manner according to calculations of karst caves of different spans, has a wide range of applications, and can be promoted for similar projects. All construction steps of the present application are implemented in the excavated space, without adding too many engineering entities, and the anchor cable 40 and the anchor pier assembly can be recycled and reused, which is obviously economical.

[0075] Furthermore, the plurality of first anchor rods 314 are in the shape of an inverted frustum that is small on the outside and large on the inside, and / or the plurality of second anchor rods are in the shape of an inverted frustum that is small on the outside and large on the inside.

[0076] As a preferred embodiment, Figure 8 As shown, multiple first anchor rods 314 are in the shape of an inverted cone with a small outside and a large inside, and multiple second anchor rods are in the shape of an inverted cone with a small outside and a large inside, wherein the direction from the outside to the inside refers to the direction from the inside of the tunnel to the surrounding rock. The inverted cone shape with a small outside and a large inside is adopted to enhance the anchoring force of the anchor rod in the surrounding rock. When the anchor rod is inserted and fixed, due to the inverted cone shape with a small outside and a large inside, the surrounding rock exerts a greater squeezing and friction force on it, thereby improving the stability and bearing capacity of the anchor rod, and laying a stable foundation for the lifting and support of the spanning segment 520 by the anchor cable 40.

[0077] Further, the number of required support spanning segments 520 is obtained by the following steps:

[0078] Get the longitudinal span of the target cave 20 , using the formula The number of supporting spanning segments 520 required for spanning the target cave 20 ; Wherein, the length of each supporting span segment 520 is 6m. As a specific example, for example, the longitudinal span L of the target cave 20 is measured to be 18m, and the number n of the supporting span segments 520 calculated by the above formula is 3, and the length of each supporting span segment 520 is 6m. For another example, the longitudinal span L of the target cave 20 is measured to be 22m, and the number n of the supporting span segments 520 calculated by the above rounding-up formula is 4, so 4 supporting span segments 520 are sufficient between the platform supporting starting segment 510 and the platform supporting ending segment 530.

[0079] Furthermore, each anchor cable 40 includes an anchor cable anchoring end 41 and an anchor cable tensioning end 42 . The anchor cable anchoring end 41 is used to connect with the supporting spanning segment 520 , and the anchor cable tensioning end 42 is used to connect with the anchor assembly and apply corresponding prestress to the anchor cable 40 .

[0080] As a preferred embodiment, the anchor cable anchoring end 41 includes a connecting component 411, an anchor 412 and an anchor cable segment 413, wherein the connecting component 411 is connected (for example, welded) to the bottom of the supporting span segment 520, the anchor cable segment 413 is connected to the anchor 412, and the anchor 412 is connected to the connecting component 411.

[0081] Specifically, since the contact connection portion between the anchor cable anchoring end 41 and the support spanning segment 520 is a key stress-bearing area, such as Figures 9 to 11 As shown, the anchor cable anchoring end 41 in this embodiment includes a connecting component 411, an anchor 412 and an anchor cable segment 413. As a preferred embodiment, the connecting component 411 includes an anchoring beam 4111 extending laterally along the supporting span segment 520 and two connecting drop plates 4112 arranged at intervals laterally along the supporting span segment 520, wherein the connecting drop plates 4112 are in the shape of a right-angled triangle, the top surface of the connecting drop plates 4112 is connected to the bottom of the supporting span segment 520, the anchoring beam 4111 is connected to a right-angled surface of the connecting drop plates 4112, the anchor cable segment 413 is arranged to pass between the two connecting drop plates 4112, and the anchor 412 is connected to the anchoring beam 4111 so that the anchor cable 40 and the supporting span segment 520 are arranged at an angle to adapt to the position of the anchor pier assembly.

[0082] As a preferred embodiment, the anchoring beam 4111 includes a first mounting plate 41111 and a second mounting plate 41112 arranged in parallel and spaced apart, a third mounting plate 41113 and a fourth mounting plate 41114 arranged in parallel and spaced apart, and the anchor 412 includes an anchor body 4121, a first pad 4122 and a second pad 4123; wherein, the first mounting plate 41111 and the second mounting plate 41112 extend in the transverse direction of the support span segment 520, the first mounting plate 41111 and the connecting drop plate 4112 are connected at a right angle, and the third mounting plate 41113 and the fourth mounting plate 41114 are arranged in parallel and spaced apart. 3 and the fourth mounting plate 41114 are connected between the first mounting plate 41111 and the second mounting plate 41112, the first mounting plate 41111 is provided with a first through hole (not shown in the figure) for the anchor body 4121 to partially pass through, the second mounting plate 41112 is provided with a second through hole (not shown in the figure) for the anchor body 4121 to pass through, the first pad 4122 is connected to the outer wall of the second mounting plate 41112, and the second pad 4123 is connected to the outer wall of the first mounting plate 41111, and the connection method can be either welding or bolt connection.

[0083] Furthermore, the anchor 412 also includes a third pad 4124 connected to the outer wall of the anchor body 4121, the third pad 4124 is located between the first pad 4122 and the second pad 4123, one end of the third pad 4124 is connected to the third mounting plate 41113, and the other end is connected to the fourth mounting plate 41114.

[0084] It is worth noting that, through the anchor cable anchoring end 41 in this embodiment, on the one hand, the anchor 412 can be prevented from directly contacting the supporting span segment 520, thereby avoiding direct contact between the two to produce a large stress concentration. On the other hand, with the help of the inclined surface of the connecting drop plate 4112, a suitable installation angle is provided for the first mounting plate 41111, and then the first pad 4122 is connected to the outer wall of the second mounting plate 41112, and the second pad 4123 is connected to the outer wall of the first mounting plate 41111, which can provide a stable and reliable installation foundation for the anchor 412, thereby ensuring the reliability of the anchor cable 40. When different angles are required, the corresponding connecting drop plate 4112 can be selected to quickly solve the inclination angle requirement of the anchor cable 40.

[0085] To further illustrate the technical solution of this application, this application also provides a specific example for reference:

[0086] Step 1: It is measured that the longitudinal span of the target cave 20 along the tunnel is about 18m. According to the span of the target cave 20, it is determined according to the above formula that a total of 1 platform support starting segment 510, 3 support span segments 520, and 1 platform support ending segment 530 are required. The lengths of the platform support starting segment 510 and the platform support ending segment 530 are both 3m. A total of 3 pairs of steel strand anchor cables 40 are required, and the horizontal spacing of the anchor cables 40 along the longitudinal direction of the tunnel is 6m.

[0087] Step 2: According to the tunnel construction limit, the center height of the first anchor pier 310 on the side wall of one side of the tunnel is determined to be 8m from the tunnel design elevation and 9m from the near end boundary of the target cave 20. The center height of the second anchor pier 320 on the same side of the tunnel is 1m from the tunnel design elevation and 14m from the near end of the target cave 20. The third anchor pier and the first anchor pier 310 are symmetrically arranged on both sides of the tunnel, and the fourth anchor pier and the second anchor pier 320 are symmetrically arranged on both sides of the tunnel.

[0088] Step 3: Using finite element software to calculate, the total value of all vertical loads during the construction phase is 1207 kN, including equipment load of 500 kN, construction live load of 270 kN, and the deadweight of all supporting spanning segments of 520 mm, 437 kN.

[0089] The present embodiment adopts three pairs of anchor cables 40, and three stages of assembly construction conditions are set accordingly. Each pair of anchor cables 40 is symmetrically arranged in the supporting span segment 520. It is calculated that when assembling the first supporting span segment 520, the axial force of each anchor cable 40 of the first pair of anchor cables 40 is 350 kN. When assembling the second supporting span segment 520, the axial force of each anchor cable 40 of the first pair of anchor cables 40 is 640 kN, and the axial force of each anchor cable 40 of the second pair of anchor cables 40 is 430 kN. When assembling the third supporting span segment 520, the axial force of each anchor cable 40 of the first pair of anchor cables 40 is 446 kN, the axial force of each anchor cable 40 of the second pair of anchor cables 40 is 709 kN, and the axial force of each anchor cable 40 of the third pair of anchor cables 40 is 661 kN, the anchor cable 40 uses 12 strands of φ9mm steel strands with a tensile strength of 1470MPa, and the anchor cable 40 is anchored by the beam bottom anchoring method. In the assembly condition of each supporting span segment 520, the prestressing force of the anchor cable 40 is 70%~80% of the design axial force.

[0090] Step 4: Design the size of the anchor pier according to the calculated anchor cable 40 force. In this example, the anchor pier consists of 16 anchor rods with a length of 10m and a diameter of 108×6mm + an anchor head with a diameter of 2m×2m×3m. Specifically, drill holes for anchor rods in the side wall of the tunnel with a drilling depth of 10m, drive 16 φ108×6mm steel pipes at an angle of 10~15°, and inject cement-waterglass double liquid slurry along the entire length of the steel pipe to make it completely bonded with the surrounding rock mass. A 2m×2m×3m (width×height×depth) anchor head cavity is excavated at the end of the anchor rod (close to the inner end of the tunnel), the anchor head is embedded in the anchor head cavity, a 1.5m×1.5m×4cm thick connecting steel plate is embedded on the side wall surface and welded firmly to the connecting ends of all anchor rods, C50 concrete is poured, the anchor rod and the anchor head are combined to form an inverted cone anchor pier, and a fixed pulley block is welded at the embedded steel plate. The number of grooves of the fixed pulley block can be selected according to the number of anchor cables 40. Repeat the above construction steps to complete the construction of the side wall anchoring system (i.e., the second anchoring assembly) on the other side of the tunnel.

[0091] Step 5: After the first anchor pier 310 and the second anchor pier 320 are completed, a nearshore support platform 110 with a length of 3 m and a width of 13 m along the longitudinal direction of the tunnel is excavated at the proximal boundary of the target cave 20, and the platform support starting segment 510 is hoisted to the designed position of the nearshore support platform 110, and the platform support starting segment 510 is anchored to the rock mass by bolts, and C30 concrete is poured and a joint for assembling the next segment is reserved;

[0092] Step six: erect the first pair of steel strand anchor cables 40, anchor them to the designed position of the first supporting span segment 520, rotate and lower the first supporting span segment 520 to the designed position through the first pair of steel strand anchor cables 40 and connect it to the platform supporting starting segment 510, and apply 280 kN prestress to each anchor cable 40 of the first pair of steel strand anchor cables 40.

[0093] Step seven: erect a second pair of steel strand anchor cables 40, anchor them to the designed position of the second supporting span segment 520, rotate and lower the second supporting span segment 520 to the designed position through the second pair of steel strand anchor cables 40 and connect it to the first supporting span segment 520, apply 512 kN prestress to each anchor cable 40 of the first pair of steel strand anchor cables 40, and apply 344 kN prestress to each anchor cable 40 of the second pair of steel strand anchor cables 40.

[0094] Step eight: erect the third pair of steel strand anchor cables 40, anchor them to the designed position of the third supporting span segment 520, rotate and lower the third supporting span segment 520 to the designed position and connect it to the second supporting span segment 520 through the third pair of steel strand anchor cables 40, apply 357 kN prestress to each anchor cable 40 of the first pair of steel strand anchor cables 40, apply 567 kN prestress to each anchor cable 40 of the second pair of steel strand anchor cables 40, and apply 528 kN prestress to each anchor cable 40 of the third pair of steel strand anchor cables 40.

[0095] Step nine: Through the above construction, the third supporting span segment 520 (the last supporting span segment 520) has reached the far boundary of the target cave 20, and the far shore supporting platform 210 is constructed at the far boundary of the target cave 20. The far shore supporting platform 210 is 3m long along the longitudinal length of the tunnel and 13m wide along the transverse width of the tunnel. The platform supporting end segment 530 is installed, and the platform supporting end segment 530 is anchored to the rock mass by bolts, and concrete is poured to support the platform supporting end segment 530 at the end of the target cave 20.

[0096] Step 10: construct the tunnel main structure 70 on the top of the foundation spanning platform 60, including the bottom plate, side walls and arch top. The permanent bottom plate structure can be in the form of concrete rib beams, arch bridges, composite beams, etc.

[0097] Step 11: When the permanent structure strength reaches the design strength, remove the first anchor assembly 30, the second anchor assembly and all anchor cables 40, complete the tunnel crossing the large-span unfillable target cave 20 project, and carry out subsequent construction according to the design documents.

[0098] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for constructing a tunnel across a large-span unfillable deep karst cave section, characterized in that: Includes steps: S1, excavating a nearshore support platform at the boundary of the excavated tunnel section close to the target cave, and constructing a platform support starting section on the nearshore support platform; S2, respectively applying a first anchoring assembly and a second anchoring assembly on both sides of the excavated tunnel section; S3, erect the i-th pair of anchor cables corresponding to the i-th support span segment, use the i-th pair of anchor cables to splice the i-th support span segment to the end of the platform support starting segment, and then apply the corresponding design prestress to the i-th pair of anchor cables; wherein i is a positive integer, the initial value of i is 1, and the i-th pair of anchor cables includes two anchor cables respectively arranged on both sides of the excavated tunnel segment and anchor cables , anchor cable One end of the anchor cable is anchored on the i-th supporting span segment, and the other end is anchored on the first anchor assembly. One end of is anchored on the i-th supporting span segment, and the other end is anchored on the second anchoring assembly; S4, erecting the i+1th pair of anchor cables corresponding to the i+1th supporting span segment, splicing the i+1th supporting span segment to the end of the i-th supporting span segment using the i+1th pair of anchor cables, and then applying the corresponding designed prestress to the i+1th pair of anchor cables; wherein the i+1th pair of anchor cables includes two anchor cables respectively arranged on both sides of the excavated tunnel segment and anchor cables , anchor cable One end of the anchor cable is anchored on the i+1th supporting span segment, and the other end is anchored on the first anchor assembly. One end of is anchored on the (i+1)th supporting span segment, and the other end is anchored on the second anchoring assembly; S5, determine whether the i+1th supporting span segment is the last supporting span segment, if so, proceed to step S6, if not, assign i+1 to i, and return to step S4; S6, excavating a far-shore support platform on the wall of the target cave away from the platform support start segment, and constructing a platform support end segment on the far-shore support platform; wherein the platform support end segment and the last support span segment are spliced, and the platform support start segment, the platform support end segment and all support span segments together constitute a basic span platform; S7, constructing a tunnel main structure on the top of the foundation spanning platform, and when the strength of the tunnel main structure reaches the design strength, removing the first anchoring assembly, the second anchoring assembly and all anchor cables to complete the construction of the tunnel section corresponding to the target cave; In step S3, applying the corresponding designed prestress to the first pair of anchor cables specifically comprises the following steps: Obtain the maximum self-weight load and construction load of the first supporting span segment; Determine the total vertical load value received by the first supporting span segment according to the self-weight load and the maximum load value during the construction period; According to the anchor The anchor cable is anchored at the position of the first supporting span segment and the position of the first anchor assembly. The tilt angle , according to the total vertical load and the inclination angle Determine the anchor cable Axial force on , and according to the axial force Determine the anchor cable Apply the corresponding design prestress; According to the anchor Anchor cable anchored at the first support span segment and the second anchor assembly The tilt angle , according to the total vertical load and the inclination angle Determine the anchor cable Axial force on , and according to the axial force Determine the anchor cable Apply the corresponding design prestress.

2. The method for constructing a tunnel across a large-span unfillable deep cave section according to claim 1, characterized in that: The first anchor assembly comprises a first anchor pier and a second anchor pier arranged on the same side of the excavated tunnel section, the first anchor pier comprises a first anchor head, a first connecting steel plate, a first fixed pulley and a plurality of first anchor rods; wherein the first anchor head is pre-buried in the tunnel side wall, the first connecting steel plate is connected to the outer end surface of the first anchor head, the first fixed pulley is connected to the outer wall surface of the first connecting steel plate, the first anchor head has a plurality of first through holes for the first anchor rods to pass through, the first anchor rod comprises a first connecting end and a first anchoring end arranged oppositely along its own extension direction, the first anchoring end is anchored in the tunnel surrounding rock, the first connecting end passes through the first through hole and is connected to the first connecting steel plate; The second anchor pier includes a second anchor head, a second connecting steel plate, a second fixed pulley and a plurality of second anchor rods; wherein, the second anchor head is pre-buried in the tunnel side wall, the second connecting steel plate is connected to the outer end surface of the second anchor head, the second fixed pulley is connected to the outer wall surface of the second connecting steel plate, the second anchor head has a plurality of second through holes for the second anchor rods to pass through, the second anchor rod includes a second connecting end and a second anchoring end arranged opposite to each other along its own extension direction, the second anchoring end is anchored in the tunnel surrounding rock, and the second connecting end passes through the second through hole and is connected to the second connecting steel plate.

3. The method for constructing a tunnel across a large-span unfillable deep karst cave section according to claim 2, characterized in that: The second anchoring assembly comprises a third anchor pier and a fourth anchor pier arranged on the same side of the excavated tunnel section, the third anchor pier comprises a third anchor head, a third connecting steel plate, a third fixed pulley and a plurality of third anchor rods; wherein the third anchor head is pre-buried in the tunnel side wall, the third connecting steel plate is connected to the outer end face of the third anchor head, the third fixed pulley is connected to the outer wall face of the third connecting steel plate, the third anchor head has a plurality of third through holes for the third anchor rod to pass through, the third anchor rod comprises a third connecting end and a third anchoring end arranged opposite to each other along its own extension direction, the third anchoring end is anchored in the tunnel surrounding rock, the third connecting end passes through the third through hole and is connected to the third connecting steel plate; The fourth anchor pier includes a fourth anchor head, a fourth connecting steel plate, a fourth fixed pulley and multiple fourth anchor rods; wherein, the fourth anchor head is pre-buried in the tunnel side wall, the fourth connecting steel plate is connected to the outer end face of the fourth anchor head, the fourth fixed pulley is connected to the outer wall face of the fourth connecting steel plate, the fourth anchor head has multiple fourth through holes for the fourth anchor rod to pass through, the fourth anchor rod includes a fourth connecting end and a fourth anchoring end relatively arranged along its own extension direction, the fourth anchoring end is anchored in the tunnel surrounding rock, and the fourth connecting end passes through the fourth through hole and is connected to the fourth connecting steel plate.

4. The method for constructing a tunnel across a large-span unfillable deep karst cave section according to claim 3, characterized in that: The plurality of first anchor rods are in the shape of an inverted frustum that is small on the outside and large on the inside, and / or the plurality of second anchor rods are in the shape of an inverted frustum that is small on the outside and large on the inside.

5. The method for constructing a tunnel across a large-span unfillable deep karst cave section according to claim 1, characterized in that: The number of required support span segments is obtained by the following steps: Get the vertical span of the target cave ; Using formula The number of supporting spanning segments required to span the target cave ; Among them, the length of each support span segment is 6m.

6. The method for constructing a tunnel across a large-span unfillable deep karst cave section according to claim 1, characterized in that: The near-shore supporting platform is 3 m long and 13 m wide along the longitudinal direction of the tunnel, and the far-shore supporting platform is 3 m long and 13 m wide along the longitudinal direction of the tunnel.

7. The method for constructing a tunnel across a large-span unfillable deep karst cave section according to claim 2, characterized in that: The center height of the first anchor pier is 8m from the design elevation of the tunnel, and the horizontal distance from the proximal boundary of the target cave is 9m. The center height of the second anchor pier is 1m from the design elevation of the tunnel, and the horizontal distance from the proximal boundary of the target cave is 14m.

8. The method for constructing a tunnel across a large-span unfillable deep karst cave section according to claim 3, characterized in that: The center height of the third anchor pier is 8m from the design elevation of the tunnel, and the horizontal distance from the proximal boundary of the target cave is 9m. The center height of the fourth anchor pier is 1m from the design elevation of the tunnel, and the horizontal distance from the proximal boundary of the target cave is 14m.

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