Unsupported primary support opening support structure and method for T-shaped tunnel intersection with arches

Abstract

The invention relates to an unsupported primary support hole opening support structure and a construction method for an intersection of an arch-intersecting T-type tunnel, comprising a composite steel ring beam, an advanced pipe shed, a hollow anchor rod, a steel plate belt and a shotcrete layer; wherein the composite steel ring beam is arranged in the primary support thickness space of the main tunnel, and a pre-buried steel pipe is arranged inside the composite steel ring beam as a guide, positioning and fixing device for the advanced pipe shed, and under the protection of the composite steel ring beam and the advanced pipe shed, the main steel frame of the intersection can be dismantled in blocks and the rock mass can be excavated, and at the same time, the steel plate belt is arranged closely to the advanced pipe shed, the hollow anchor rod is driven and the shotcrete layer is covered, so as to form a spatial shed protection structure of "horizontally forming an arch and longitudinally forming a beam", which can effectively bear the surrounding rock load of the "triangular cantilever area" of the arch-intersecting T-type tunnel, smoothly realize the unsupported primary support hole opening of the intersection, and can completely avoid the risks of collapse and roof fall caused by the construction of traditional hole opening schemes, and has high engineering, economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the field of urban rail transit design and construction, and in particular to an unsupported primary support hole support structure and a construction method which can effectively avoid the risks of landslide and roof collapse in the "triangular cantilever area surrounding rock" at the intersection of arches in a T-shaped tunnel. Background Art

[0002] Due to its functional positioning and service requirements, the underground subway station needs to lead out at least 2 conventional entrances and exits, 2 sets of air ducts and 1 fire safety exit from the station. Among them: Due to the limitations of the main station hall floor height and arch structure, the entrances and exits, air ducts and other auxiliary passages are often in an arch-intersecting state with the main tunnel. When the T-shaped intersection hole construction breaks the integrity of the primary support structure of the main tunnel, the surrounding rock in the arch-intersecting area is prone to form a "triangular" cantilever support blind area. The cantilever length is related to the intersection position of the T-shaped intersection tunnel arch, generally in the range of 1.8 to 2.9 meters, equivalent to the length of 3 to 6 steel frame spacing. For such a large cantilever support blind area in the underground tunnel, once the hole opening support measures are improperly selected, it is very easy to induce roof collapse and landslide accidents, seriously threatening the lives and safety of workers and causing immeasurable economic losses. It has attracted more and more attention and attention from engineers in the industry. At present, the three commonly used hole opening support measures and construction methods for the intersection of arch-intersecting T-shaped tunnels are facing different degrees of deficiencies and disadvantages. The specific analysis is as follows:

[0003] (1) Using the secondary lining structure to open a hole: Although the middle plate platform can be used to set up a gate-shaped vertical support to temporarily eliminate the support blind spot of the "triangular cantilever area surrounding rock", the intersection structure still faces the construction risk of instability due to the removal of the support when it is closed and molded. In addition, artificial construction joints are formed at the closing position, and it is necessary to reserve steel connectors and embedded waterstops in advance. The construction of the auxiliary channel is very easy to contaminate the existing finished materials, which is not conducive to the stress of the complex structure of the intersection and cannot ensure the quality of waterproof construction. In addition, from the perspective of construction organization and construction period and efficiency, the excavation of the auxiliary channel and the main tunnel cannot be carried out simultaneously, which seriously restricts the subsequent construction and decoration, mechanical and electrical installation professionals to enter the site for construction, reduces efficiency, and delays the construction period, which is neither economical nor reasonable.

[0004] (2) Adjust the main arch excavation profile to meet the requirements of the vertical wall initial support opening. The vertical wall initial support opening can ensure that the auxiliary steel frame directly supports the main truncated steel frame without facing the support blind spot of the "triangular cantilever area surrounding rock". However, the main arch excavation profile becomes flatter and the curvature becomes smaller, which leads to a worse initial support arch effect, which is not conducive to the control of the initial support structure stress and the stability of the surrounding rock, and may even induce the initial support strength and stiffness instability. In addition, two section conversions are required when the main tunnel of the intersection transitions with the standard sections on both sides, which is extremely unfavorable for construction organization and risk control. The subsequent secondary lining formwork construction belongs to the category of large-volume concrete construction due to the outward excavation profile of the main body. The hydration heat generated can easily cause temperature shrinkage stress inside the concrete and form harmful cracks that destroy the structural integrity.

[0005] (3) Directly support the opening with the primary support by utilizing the self-bearing capacity of the surrounding rock: This method of opening the hole is suitable for surrounding rocks with good integrity and stability. However, the main primary support after truncation can only achieve self-stabilization by relying on the bonding strength between the shotcrete and the surrounding rock. Even if the advanced pipe shed is set up, it cannot be welded with the main primary support to form a reliable overall load-bearing structure. The support blind spot of the "triangular cantilever area surrounding rock" still exists. Once the surrounding rock is broken or the geological changes suddenly, the consequences will be disastrous. Only vertical support can be set up to temporarily avoid risks, but the risk of dismantling the support later is higher. The secondary lining has to be built by buried support, which is difficult to guarantee the waterproof quality and structural durability. The flood rectification faced in the later operation is more difficult and costly. Summary of the invention

[0006] In view of the above-mentioned defects and shortcomings of the existing support schemes for opening holes at intersections of T-shaped tunnels where arches intersect; the present invention provides a support structure for opening holes without initial support at intersections of T-shaped tunnels and a construction method; the "horizontal arch and longitudinal beam" spatial bearing structure formed by the support structure can effectively bear the surrounding rock load in the triangular cantilever area where arches intersect, and smoothly realize the initial support and no-support opening of tunnels at intersections. Compared with the traditional opening method, there is no need to face the construction risk of instability due to removal of supports; at the same time, the excavation and support of the auxiliary passage and the main tunnel can be carried out simultaneously, and the construction period is shortened.

[0007] The technical solution adopted by the present invention to solve the above technical problems is: a non-supported primary support opening support structure at the intersection of arch-intersecting T-shaped tunnels, comprising a main tunnel and an auxiliary passage intersecting with the main tunnel in a T-shaped arch, wherein the support structure comprises a composite steel ring beam, an advanced pipe shed, a steel plate belt and a hollow anchor rod; wherein:

[0008] The composite steel ring beam is fixed inside the primary support structure of the main tunnel at the intersection of the T-shaped tunnel. The shape of the composite steel ring beam matches the intersection line of the arches of the T-shaped tunnel. A plurality of pre-buried steel pipes are evenly arranged in the circumferential direction inside the composite steel ring beam.

[0009] The advanced pipe sheds respectively pass through the embedded steel pipes, and one end of the pipe shed is welded and fixed to the embedded steel pipe, and the other end passes through the surrounding rock of the triangular cantilever area where the arches intersect, and is placed in the unexcavated soil of the front auxiliary channel;

[0010] The steel bar strips are provided in plurality and are respectively fixed vertically on the pipe wall of the advanced pipe shed;

[0011] The hollow anchor rods are arranged in an intermittent manner with the advance pipe shed in the annular direction, and an anchor rod tray is arranged at the end of the hollow anchor rod. The anchor rod tray and the hollow anchor rod can fix the steel plate strip and the advance pipe shed on the surrounding rock base surface of the triangular cantilever area where the arches intersect.

[0012] Furthermore, a sprayed concrete layer with a thickness of 300-350 mm is provided on the surface of a supporting structure composed of an advanced pipe shed, a steel plate belt and a hollow anchor rod located on the surrounding rock of the triangular cantilever area where the arches intersect.

[0013] Furthermore, the length of the advanced pipe shed passing through the surrounding rock of the triangular cantilever area where the arches intersect is not less than 3m; and an auxiliary channel steel frame is provided within the overlapping range between the advanced pipe shed and the unexcavated soil of the auxiliary channel.

[0014] Furthermore, the steel bar strip is composed of two threaded steel bars arranged in parallel, and the two threaded steel bars are respectively arranged on both sides of the hollow anchor rod and are welded and fixed to the pipe wall of the advanced pipe rack.

[0015] Furthermore, the composite steel ring beam is a lattice structure formed by welding a double-arranged I-beam and two tie plates respectively connected to the I-beam.

[0016] Furthermore, the hollow anchor rod has a diameter of 25 mm and is arranged in a plum blossom shape of 1.2 m×1.2 m. The dimensions of the anchor rod tray are 150 mm in length, 150 mm in width and 12 mm in thickness, and the steel bar plate can be fixed to the advanced pipe shed with buckles and locks.

[0017] The present invention also provides a method for constructing a non-supported initial support opening at an arch-intersecting T-shaped tunnel intersection based on the above-mentioned support structure, comprising the following construction steps:

[0018] S1: excavate along the main tunnel to the intersection of the T-shaped tunnel and construct the corresponding initial support structure;

[0019] S2, close to the opening side of the rear auxiliary channel, lay out and measure, and locate the intersection line of the leading main tunnel and the arch of the rear auxiliary channel;

[0020] S3, using the intersection line of the arches as the excavation boundary line of the upper step of the main tunnel, continue to excavate forward, construct support and drive locking anchors to stabilize the arch foot;

[0021] S4, processing prefabricated composite steel ring beams, the shape of which is adapted to the intersection of the arches, and the ground trial assembly can be used for on-site construction only after it meets the assembly error requirements;

[0022] S5, when the tunnel face is excavated to 1 times the span of the auxiliary passage in front of the T-shaped intersection, the rock mass suitable for the installation space of the combined steel ring beam is excavated in a circular manner along the excavation edge line of the upper step, and a combined steel ring beam with several pre-buried steel pipes is erected and fixed by welding to the primary support grid steel frame of the main tunnel;

[0023] S6: Continue to excavate downward to the bottom elevation of the upper step of the rear auxiliary passage and construct the corresponding initial support structure;

[0024] S7: Remove the initial support of the advanced pipe shed installation point and expose the embedded steel pipe, clean the foreign matter filled inside and install the advanced pipe shed, weld one end of the advanced pipe shed to the combined steel ring beam as a whole, and pass the other end through the surrounding rock of the triangular cantilever area where the arches intersect, and place it in the unexcavated soil of the front auxiliary passage;

[0025] S8: Cut off the lower part of the composite steel ring beam in blocks to provide initial support for the main tunnel first, and then excavate and build the upper steps of the auxiliary passage;

[0026] S9: The excavation depth of the rear auxiliary channel is controlled at 0.5m. As the excavation progresses, steel plate strips, hollow anchor rods, and hollow trays are applied, and a sprayed concrete layer is applied to timely seal the surrounding rock of the triangular cantilever area where the arches intersect;

[0027] S10: Continue to excavate the rear auxiliary channel forward, requiring that an auxiliary channel steel frame must be erected within the overlapping length of the rear auxiliary channel main tunnel and the advanced pipe shed to form a structural pressure bearing support for the advanced pipe shed;

[0028] S11: So far, the construction of the initial support opening of the entire arch-intersecting T-shaped tunnel intersection has been completed.

[0029] In the above scheme, in step S5, the interior of the embedded steel pipe is pre-filled with non-woven fabrics or textile bags to prevent the spray mix from blocking the pipeline, which is convenient for the later advanced pipe shed construction.

[0030] Furthermore, after step S11, the following construction steps are also included: after the tunnel is fully opened, the waterproof material of the T-shaped tunnel intersection structure is laid, the steel bars are tied, and the secondary lining is molded.

[0031] Compared with the prior art, the present invention has the following advantages and effects:

[0032] 1. The non-supported initial support hole opening support structure of the intersection of arch-intersecting T-type tunnels described in the present invention comprises a composite steel ring beam, an advanced pipe shed, a hollow anchor rod, a steel plate belt and a shotcrete layer; wherein, the composite steel ring beam is arranged in the initial support thickness space of the main tunnel, and a pre-buried steel pipe is arranged inside the composite steel ring beam as a guiding, positioning and fixing device of the advanced pipe shed. Under the protection of the composite steel ring beam and the advanced pipe shed, the main steel frame of the intersection can be dismantled in blocks and the rock mass can be excavated. At the same time, a steel plate belt is arranged closely to the advanced pipe shed, a hollow anchor rod is driven and a shotcrete layer is covered to form a "horizontally arched and longitudinally beamed" space shed protection structure, which can effectively bear the surrounding rock load of the "triangular cantilever area" of the arch-intersecting T-type tunnel, smoothly realize the non-supported initial support hole opening of the intersection, and can completely avoid the risks of collapse and roof collapse caused by the dismantling construction of the traditional hole opening scheme. The construction risk of the project itself is completely controllable, which makes up for the shortcomings and gaps of the traditional hole opening support design scheme, and has high engineering, economic and social benefits.

[0033] 2. In the unsupported primary support opening construction method for the intersection of T-shaped tunnels with intersecting arches described in the present invention, the excavation and support of the main tunnel and the auxiliary passage can be carried out simultaneously, forming a flow operation with the secondary lining formwork without interfering with each other, ensuring that the existing finished structure and waterproof materials are not polluted or damaged by the excavation and support construction, and the construction organization is relatively more flexible, which can significantly shorten the construction period and alleviate the pressure of the civil engineering construction period.

[0034] 3. In the non-supported initial support hole opening construction method for the intersection of T-shaped tunnels where arches intersect described in the present invention, under the protection of the combined steel ring beam and the advanced pipe shed, the initial support hole is directly opened along the intersection line of the arches, which will not change the excavation contour of the main tunnel, and the main longitudinal construction does not need to face the section conversion; the initial support structure is reasonably and reliably stressed, ensuring smooth and convenient excavation and support of the main body, and avoiding harmful cracks caused by the hydration heat of large-volume concrete construction.

[0035] 4. In the unsupported primary support opening construction method for the T-shaped tunnel intersection where arches intersect described in the present invention, the secondary lining structure of the T-shaped intersection is constructed simultaneously by mold casting, avoiding the formation of artificial waterproof construction joints by setting two layers of reinforced ring beams, which can significantly improve the structural stress and waterproof quality, ensure the durability of the structure, and greatly reduce the economic cost and time cost of later operation and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention 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 invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0037] Figure 1 It is a transverse cross-sectional view of a T-shaped tunnel intersection where arches intersect according to an embodiment of the present invention.

[0038] Figure 2 It is a side view of a T-shaped tunnel intersection with intersecting arches according to an embodiment of the present invention.

[0039] Figure 3 It is a structural schematic diagram of a combined steel ring beam combined with an advanced pipe shed in an unsupported primary support opening support structure at an intersection of arches in a T-shaped tunnel according to an embodiment of the present invention.

[0040] Figure 4 It is a partial enlarged view of the unsupported primary support opening support structure A at the intersection of the T-shaped tunnel with arches intersecting according to an embodiment of the present invention.

[0041] Explanation of reference numbers: 1a, left pilot pit on the upper level of the main tunnel; 1c, middle pilot pit on the upper level of the main tunnel; 1b, right pilot pit on the upper level of the main tunnel; 2a, left pilot pit on the middle level of the main tunnel; 2c, middle pilot pit on the middle level of the main tunnel; 2b, right pilot pit on the middle level of the main tunnel; 3a, left pilot pit on the lower level of the main tunnel; 3c, middle pilot pit on the lower level of the main tunnel; 3b, right pilot pit on the lower level of the main tunnel; 4, initial support; 5, upper step of the auxiliary passage; 6, lower step of the auxiliary passage; 7, composite steel ring beam; 7a, I-beam; 7b, tie plate; 7e, embedded steel pipe; 8, advanced pipe shed; 9, surrounding rock in the triangular cantilever area where arches intersect; 10a, hollow anchor rod; 10b, steel plate and strip; 10c, shotcrete layer; 11, steel frame of the auxiliary passage. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with embodiments. The following embodiments are for explanation of the present invention but the present invention is not limited to the following embodiments.

[0043] Example 1: Figures 1 to 4 As shown, a non-supported primary support opening support structure for a T-shaped tunnel intersection with arches includes a main tunnel and an auxiliary passage to be excavated that intersects the main tunnel in a T-shaped arch. The support structure includes a composite steel ring beam 7, an advanced pipe shed 8, a steel plate belt 10b and a hollow anchor rod 10a; wherein:

[0044] like Figure 2 , 3 As shown, the composite steel ring beam 7 is fixed inside the primary support structure of the main tunnel at the intersection of the T-shaped tunnel. The shape of the composite steel ring beam 7 matches the intersection line of the arches of the T-shaped tunnel. A number of pre-buried steel pipes 7e are evenly arranged in the circumferential direction inside the composite steel ring beam 7.

[0045] like Figure 1 , 2As shown in 3, the advanced pipe shed 8 passes through the embedded steel pipe 7e respectively, and one end of the pipe shed is welded and fixed to the embedded steel pipe 7e, and the other end passes through the surrounding rock 9 of the triangular cantilever area where the arches intersect, and is placed in the unexcavated soil of the front auxiliary channel;

[0046] like Figure 4 As shown, a plurality of steel plate strips 10b are provided, which are respectively fixed vertically on the pipe wall of the advance pipe shed 8; the hollow anchor rods 10a are arranged in an interval manner with the advance pipe shed 8 in the circumferential direction, and an anchor rod tray is provided at the end of the hollow anchor rod 10a. The anchor rod tray and the hollow anchor rod 10b can fix the steel plate strips 10b and the advance pipe shed 8 on the base surface of the surrounding rock 9 in the triangular cantilever area where the arches intersect.

[0047] Specifically, in the unsupported primary support opening support structure of the T-type tunnel intersection described in this embodiment 1, the composite steel ring beam 7 is a lattice structure formed by welding a double-arranged I-beam 7a and two tie plates 7b respectively connected to the I-beam 7a; the steel plate strip 10b is composed of two threaded steel bars arranged in parallel, and the two threaded steel bars are respectively arranged on both sides of the hollow anchor rod 10a, and are welded and fixed to the pipe wall of the advanced pipe shed 8; the hollow anchor rod 10a has a diameter of 25 mm and is arranged in a plum blossom shape of 1.2 m×1.2 m. The dimensions of the anchor rod tray are 150 mm in length, 150 mm in width, and 12 mm in thickness, and the steel plate strip 10b can be locked and fixed to the advanced pipe shed 8.

[0048] Furthermore, if Figure 1 , 4 As shown, in this embodiment 1, the length of the advance pipe shed 8 passing through the surrounding rock of the triangular cantilever area where the arches intersect is not less than 3m, and an auxiliary channel steel frame 11 is provided in the range where the advance pipe shed 8 and the unexcavated soil of the auxiliary channel overlap each other, so as to form a structural pressure-bearing support for the advance pipe shed 8; the surface of the support structure composed of the advance pipe shed 8, the steel plate belt 10b and the hollow anchor rod 10a located on the surrounding rock 9 of the triangular cantilever area where the arches intersect is provided with a sprayed concrete layer 10c with a thickness of 300-350mm, and the sprayed concrete layer 10c can effectively seal the surrounding rock of the triangular cantilever area where the arches intersect, thereby improving the overall stability and safety of the support structure.

[0049] In the support structure described in the present embodiment 1, the composite steel ring beam 7 is built into the primary support space of the preceding main tunnel during excavation and welded to the main steel frame, serving as a supporting structure to cut off the main steel frame when the initial support of the T-shaped intersection is opened, and also serves as a pressure bearing of the advanced pipe shed; on the other hand, the advanced pipe shed 8 uses the composite steel ring beam 7 and the unexcavated stratum in front as the two end supports, respectively, which can effectively avoid the surrounding rock collapse and roof fall accidents in the triangular cantilever area where the arches intersect during excavation; the composite steel ring beam 7 The spatial shed bearing support structure of "horizontally forming an arch and longitudinally forming a beam" formed by the interconnection of the advance pipe shed 8, the hollow anchor rod 10a, the steel plate 10b and the shotcrete 10c jointly maintains the stability of the surrounding rock in the triangular cantilever area where the T-shaped tunnel arches intersect before the secondary lining formwork of the intersection, and successfully realizes the initial support opening without support at the intersection. Compared with the traditional opening method, there is no need to face the construction risk of instability due to support removal; at the same time, the excavation and support of the auxiliary channel and the main tunnel can be carried out simultaneously, and the construction period is short.

[0050] Example 2: Figures 1 to 4 As shown, a method for constructing a non-supported initial support opening at an intersection of a T-shaped tunnel with intersecting arches comprises the following construction steps:

[0051] S1, excavate along the upper left pilot pit 1a of the main tunnel to the T-shaped intersection and apply 350mm thick initial support 4, and the upper right pilot pit 1b of the main tunnel lags behind the upper left pilot pit 1a of the main tunnel by 15m in excavation and support;

[0052] S2, close to the side of the opening of the rear auxiliary passage, lay out and measure, and locate the intersection line of the arch of the upper left pilot pit 1a of the main tunnel and the upper step 5 of the auxiliary passage;

[0053] S3, using the intersection line of the arches as the excavation boundary line of the upper step rock mass of the left pilot pit 1a on the upper level of the main tunnel, continue to excavate forward, support and drive locking anchors to stabilize the arch foot;

[0054] S4, processing prefabricated composite steel ring beam 7, the shape of the composite steel ring beam 7 is adapted to the intersection line of the arch, and the ground trial assembly can be used for on-site construction only after meeting the assembly error requirements; wherein: the composite steel ring beam 7 is welded by I-beam 7a with a specification of I-25a double-arranged and 10mm thick gusset plate 7b, and the I-beam 7a and the gusset plate 7b are provided with embedded steel pipes 7e that can meet the 89mm diameter of the advanced pipe shed 8. The embedded steel pipe 7e needs to be filled with non-woven fabrics or textile bags to prevent the spraying and mixing from clogging the pipeline, so as to facilitate the construction of the advanced pipe shed 8 in the later stage. The inner diameter of the embedded steel pipe 7e is 10mm larger than the outer diameter of the advanced pipe shed 8, and has the dual functions of guiding, positioning and fixing the pipe shed. No external insertion angle is required when the pipe shed is constructed, which can reduce the over-excavation amount and initial lining masonry amount of the steps 5 on the auxiliary channel;

[0055] S5, when the upper left pilot pit 1a of the main tunnel is excavated to the tunnel span of the auxiliary passage 1 times in front of the T-shaped intersection, the surrounding rock of the installation space of the composite steel ring beam 7 is excavated in a circular manner along the excavation edge line of the upper step, and the composite steel ring beam 7 is erected and welded to the grid steel frame of the primary support 4 of the main tunnel;

[0056] S6, continue to excavate the lower step rock mass of the left pilot pit 1a of the upper layer of the main tunnel at the intersection to the bottom elevation of the upper step 5 of the auxiliary passage, and apply the remaining initial support 4;

[0057] S6: Continue to excavate downward until the bottom elevation of the upper step of the rear auxiliary passage, and construct the corresponding initial support structure;

[0058] S7, breaking the initial support 4 of the 89mm diameter advanced pipe shed 8 installation point and exposing the embedded steel pipe 7e, cleaning the internal filling foreign matter and installing the advanced pipe shed 8, one end of the advanced pipe shed 8 is welded to the combined steel ring beam 7 as a whole, and the other end passes through the surrounding rock 9 of the triangular cantilever area where the arches intersect, and is placed in the unexcavated soil of the front auxiliary passage;

[0059] S8, cut off the initial support 4 at the bottom of the composite steel ring beam 7 in blocks, and then follow the excavation to go up the step 5 of the auxiliary passage;

[0060] S9, the excavation progress of the upper step 5 of the rear auxiliary passage is controlled to be 0.5m. As the excavation progresses, multiple steel plate strips 10b consisting of two 28mm diameter threaded steel bars and a 25mm diameter hollow anchor rod 10a are applied, and 300mm thick sprayed shotcrete 10c is applied to timely close the surrounding rock 9 of the triangular cantilever area where the arches intersect; wherein: the two threaded steel bars in the steel plate strip are arranged side by side at 35mm on both sides of the hollow anchor rod 10a, and are applied and welded to the advanced pipe shed 8. During welding, the pipe wall of the advanced pipe shed 8 must not be penetrated to avoid reducing the longitudinal bearing capacity of the pipe shed structure;

[0061] S10, continue to excavate the rear auxiliary channel forward, requiring that the auxiliary channel steel frame 11 must be erected within the overlapping length range of the auxiliary channel and the advanced pipe shed 8, so as to form a structural pressure bearing support for the advanced pipe shed 8;

[0062] S11, so far, the unsupported initial support opening construction of the entire arch-to-arch T-intersection has been completed, and the remaining upper left, middle and right pilot pits 1a, 1c, 1b of the main tunnel, the middle left, middle and right pilot pits 2a, 2c, 2b of the main tunnel, the lower left, middle and right pilot pits 3a, 3c, 3b of the main tunnel and the lower step 6 of the auxiliary passage are excavated, and the corresponding system support structure is constructed;

[0063] S12: After the tunnel is fully opened, the waterproof material of the intersection structure will be laid, the steel bars will be tied and the secondary lining will be molded.

[0064] In the construction method described in the second embodiment, the composite steel ring beam 7 is pre-buried in the initial support thickness space during the excavation of the main tunnel. When the heading face is constructed to the front of the T-intersection and is not less than 1 times the span of the auxiliary passage, the initial support base surface of the advance pipe shed arrangement point is manually broken and the tunnel entry pipe shed is constructed. Under the protection of the steel ring beam and the advance pipe shed, the main steel frame of the tunnel portal is dismantled in blocks and the rock mass is excavated. Immediately following the excavation of the surrounding rock in the triangular cantilever area where the arches intersect, steel plate strips and hollow anchor rods are constructed closely adjacent to the advance pipe shed and covered with a sprayed concrete layer. The composite steel ring beam and the advance pipe shed are combined to form a spatial shed protection bearing structure with "horizontal arch and longitudinal beam". Compared with the traditional two-lining tunnel exit or straight wall initial exit tunnel exit scheme, the support and opening measures described in the present invention can ensure the stability of the surrounding rock in the triangular cantilever area of ​​the T-shaped tunnel intersection where the arches intersect, achieve the purpose of non-support initial support tunnel opening, shorten the construction period, improve construction efficiency, improve structural stress, and ensure waterproof quality.

[0065] In addition, it should be noted that the shapes and names of the parts and components of the specific embodiments described in this specification may be different. Any equivalent or simple changes made based on the structure, features and principles described in the patent concept of the present invention are included in the protection scope of the patent of the present invention. The technicians in the technical field of the present invention can make various modifications or supplements to the specific embodiments described or replace them in a similar manner, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for constructing a tunnel without primary support at an intersection of arches in a T-shaped tunnel, characterized in that Based on the application of an unsupported primary support opening support structure for an arch-intersecting T-shaped tunnel intersection, the support structure includes a main tunnel and an auxiliary passage intersecting with the main tunnel in a T-shaped arch, a composite steel ring beam, an advanced pipe shed, a steel plate belt and a hollow anchor rod; wherein: The composite steel ring beam is fixed inside the primary support structure of the main tunnel at the intersection of the T-shaped tunnel. The shape of the composite steel ring beam matches the intersection line of the arches of the T-shaped tunnel. A plurality of pre-buried steel pipes are evenly arranged in the circumferential direction inside the composite steel ring beam. The advanced pipe sheds respectively pass through the embedded steel pipes, and one end of the advanced pipe shed is welded and fixed to the embedded steel pipe, and the other end passes through the surrounding rock of the triangular cantilever area where the arches intersect, and is placed in the unexcavated soil of the front auxiliary channel; The steel bar strips are provided in plurality and are respectively fixed vertically on the pipe wall of the advanced pipe shed; The hollow anchor rods are arranged in an intermittent manner with the advance pipe shed in the annular direction, and an anchor rod tray is arranged at the end of the hollow anchor rod. The anchor rod tray and the hollow anchor rod can fix the steel plate strip and the advance pipe shed on the surrounding rock base surface of the triangular cantilever area where the arches intersect; The construction method comprises the following construction steps: S1: excavate along the main tunnel to the intersection of the T-shaped tunnel and construct the corresponding initial support structure; S2, close to the opening side of the rear auxiliary channel, lay out and measure, and locate the intersection line of the leading main tunnel and the arch of the rear auxiliary channel; S3, using the intersection line of the arches as the excavation boundary line of the upper step of the main tunnel, continue to excavate forward, construct support and drive locking anchors to stabilize the arch foot; S4, processing prefabricated composite steel ring beams, the shape of which is adapted to the intersection of the arches, and the ground trial assembly can only be used for on-site construction after it meets the assembly error requirements; S5, when the tunnel face is excavated to 1 times the span of the auxiliary passage in front of the T-shaped intersection, the rock mass suitable for the installation space of the composite steel ring beam is excavated in a circular manner along the excavation edge line of the upper step, and a composite steel ring beam with several pre-buried steel pipes is erected and fixed by welding to the primary support grid steel frame of the main tunnel; S6: Continue to excavate downward to the bottom elevation of the upper step of the rear auxiliary passage and construct the corresponding initial support structure; S7: Remove the initial support of the advanced pipe shed installation point and expose the embedded steel pipe, clean the foreign matter filled inside and install the advanced pipe shed, weld one end of the advanced pipe shed to the combined steel ring beam as a whole, and pass the other end through the surrounding rock of the triangular cantilever area where the arches intersect, and place it in the unexcavated soil of the front auxiliary passage; S8: Cut off the lower part of the composite steel ring beam in blocks to provide initial support for the main tunnel, and then excavate and step up the auxiliary passage; S9: The excavation depth of the rear auxiliary channel is controlled at 0.5m. As the excavation progresses, steel plate strips, hollow anchor rods, and hollow trays are applied, and a sprayed concrete layer is applied to timely seal the surrounding rock of the triangular cantilever area where the arches intersect; S10: Continue to excavate the rear auxiliary channel forward, requiring that an auxiliary channel steel frame must be erected within the overlapping length of the rear auxiliary channel main tunnel and the advanced pipe shed to form a structural pressure bearing support for the advanced pipe shed; S11: So far, the construction of the initial support opening of the entire arch-intersecting T-shaped tunnel intersection has been completed.

2. The method for constructing a T-shaped tunnel intersection without primary support according to claim 1, characterized in that: The surface of the support structure consisting of advanced pipe sheds, steel plate belts and hollow anchor rods located on the surrounding rock of the triangular cantilever area where the arches intersect is provided with a sprayed concrete layer with a thickness of 300-350mm.

3. The method for constructing a T-shaped tunnel intersection without primary support according to claim 1, characterized in that: The length of the advanced pipe shed passing through the surrounding rock of the triangular cantilever area where the arches intersect is not less than 3m; an auxiliary channel steel frame is provided within the overlapping range between the advanced pipe shed and the unexcavated soil of the auxiliary channel.

4. The method for constructing a T-shaped tunnel intersection without primary support according to claim 1, characterized in that: The steel bar strip is composed of two threaded steel bars arranged in parallel. The two threaded steel bars are respectively arranged on both sides of the hollow anchor rod and are welded and fixed on the pipe wall of the advanced pipe shed.

5. The method for constructing a T-shaped tunnel intersection without primary support according to claim 1, characterized in that: The composite steel ring beam is a lattice structure formed by welding double-arranged I-beams and two tie plates respectively connected to the I-beams to form a lattice structure.

6. The method for constructing a T-shaped tunnel intersection without primary support according to claim 1, characterized in that: The hollow anchor rod has a diameter of 25 mm and is arranged in a plum blossom shape of 1.2 m × 1.2 m. The anchor rod tray has a length of 150 mm, a width of 150 mm, and a thickness of 12 mm. The steel plate can be fixed to the advanced pipe shed with buckles and locks.

7. The method for constructing a T-shaped tunnel intersection without primary support according to claim 1, characterized in that: In step S5, the interior of the embedded steel pipe is pre-filled with non-woven fabrics or textile bags to prevent the spray mix from blocking the pipeline, which is convenient for the later advanced pipe shed construction.

8. The method for constructing a tunnel without primary support at an intersection of arches in a T-shaped tunnel according to claim 1, characterized in that: After step S11, the following construction steps are also included: after the tunnel is fully connected, the waterproof material of the T-shaped tunnel intersection structure is laid, the steel bars are tied, and the secondary lining is molded.

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