Disturbance isolation and anti-floating construction method for up-down crossing tunnel under ultra-small clear distance condition

Abstract

The invention discloses a disturbance isolation and anti-floating construction method for upper and lower crossed tunnels under the ultra-small clear distance condition, and belongs to the technical field of tunnel construction. A closed anti-floating system comprising an arch part local thickening reinforcing ring, an arch foot annular component and an inverted arch anti-floating anchor rod is formed in a lower tunnel crossed section; a reinforcing layer is arranged on the vault, and a flexible buffer layer is arranged on the side wall, so that the overall rigidity and the floating resistance of the lower tunnel are remarkably improved; the excavation disturbance of the upper tunnel is preferentially dispersed and consumed in the upper structure and the middle partition surrounding rock through the combination of a left lower pilot tunnel, a right lower pilot tunnel, high-modulus grouting of the middle partition surrounding rock and a truss type bearing system of longitudinal anchor rods and crossed inclined steel bar anchor rods at the bottom of the upper tunnel; vertical rigidity transition is formed, a rigid bridge is prevented from being formed between the upper tunnel and the lower tunnel, and the risk that disturbance loads are directly transmitted to the lower tunnel is reduced.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction technology, specifically relating to a disturbance isolation and anti-uplift construction method under ultra-small clearance conditions of intersecting tunnels. Background Technology

[0002] With the large-scale construction of urban rail transit and municipal integrated utility tunnels, it is common for tunnels of different lines and functions to be intersected in limited underground spaces. When upper and lower tunnels intersect obliquely in the plane and the vertical clearance is small, the excavation disturbance of the later-constructed tunnel can easily be transmitted to the earlier-constructed tunnel, causing additional deformation and redistribution of internal forces in the earlier-constructed tunnel. This can lead to risks of defects such as crown cracking, invert heave, and secondary lining leakage, making it difficult to guarantee both construction safety and operational safety. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a disturbance isolation and anti-uplift construction method under the condition of ultra-small clearance between intersecting tunnels, which can significantly reduce the additional impact of the excavation disturbance of the upper tunnel on the lower tunnel, and control the risk of overall uplift and lining cracking of the lower tunnel.

[0004] To achieve the above objectives, the present invention provides the following technical solution: The present invention discloses a method for disturbance isolation and anti-uplift construction under ultra-small clearance conditions for intersecting tunnels, characterized by comprising the following steps: Step (1), lower tunnel excavation and support, the lower tunnel is excavated in sections along the designed line, and the single-cycle advance and blasting energy are controlled; after each cycle of excavation is completed, shotcrete is sprayed immediately, steel arch frame and steel mesh are installed, system anchor bolts are arranged, and the initial support reinforcement layer is formed; Step (2): Local reinforcement of the tunnel arch crown and arch waist. Within the area affected by the tunnel intersection, supplementary arch frames are added between the existing steel arch frames. The supplementary arch frames are connected to the original arch frames by welding plates to form a continuous skeleton. Circumferential reinforcing bars or ring beams are set at the arch foot and welded to the arch frames on both sides to form the lower connection foundation of the arch reinforcement ring and the invert arch area to form an integral stress closed ring. On the outside of the densified arch frame, steel fiber sprayed concrete is used to thicken the arch crown and arch waist as a whole. The secondary spray layer is tightly combined with the initial support to form a continuous arch crown secondary lining reinforcement layer in the longitudinal direction. Step (3): Construction of the anti-buoyancy anchoring components for the invert arch of the lower tunnel. The anchoring hole positions are laid out at a certain longitudinal interval on the bottom surface of the invert arch. Anchor holes are drilled vertically downward or inclined downward from inside the invert arch. Bottom anchors are placed in the holes and the holes are filled with cement-based grout to form an anchor body. When binding the invert arch and the bottom plate reinforcement, the exposed end of the anchor is connected to the invert arch reinforcement mesh and the circumferential reinforcement component at the arch foot. The anchor is connected to the invert arch structure by pouring concrete for the invert arch and the bottom plate, forming an anti-buoyancy system of invert arch-bottom plate-anchor-deep surrounding rock. It forms a closed rigid anti-buoyancy ring with the circumferential reinforcement component at the arch foot and the locally thickened reinforcement ring of the arch. Step (4): The flexible buffer layer of the lower tunnel sidewall and the secondary lining arch reinforcement layer are formed by setting a thin layer of flexible or compressible material on the inner side of the initial support. During the secondary lining construction, high-performance concrete and dense reinforcement are used along the tunnel axis at the arch top of the lower tunnel to form an arch reinforcement layer, so that the arch stiffness of the intersection section is higher than that of the transition sections on both sides. Step (5): Excavation and support of the pilot tunnel at the bottom of the upper tunnel. Before the upper tunnel is excavated to the intersection, the outline of the pilot tunnel is laid out according to the lower left and right positions of the upper tunnel design section. First, the pilot tunnel at the bottom of the left side of the upper tunnel is excavated using small-foot weak blasting or mechanical tunneling. After the excavation is completed, shotcrete is sprayed, steel arches are installed, steel mesh and system anchors are arranged to form stable support. After the support of the left pilot tunnel is stable, the pilot tunnel at the bottom of the right side of the upper tunnel is excavated in the same way, and the surrounding rock in the middle is also kept open. The left and right pilot tunnels are continuously constructed along the entire length of the intersection and extend to both ends to form two stable lateral beams. Step (6): High modulus grouting reinforcement of the central partition surrounding rock. After the initial support of the left and right pilot tunnels is completed, high modulus cement-based grouting is used to reinforce the central partition surrounding rock and its surrounding surrounding rock as a whole. The surrounding rock in the area of ​​the lower tunnel arch is only treated with conventional stabilization to form a vertical stiffness transition. Step (7): Construction of the truss-type steel reinforcement connection system for the central diaphragm surrounding rock. Several sets of truss-type anchor units are arranged in the reinforced central diaphragm surrounding rock. Each set includes two parallel longitudinal anchors and two cross-shaped oblique steel anchors. The two longitudinal anchors are arranged on the inner support of the left and right guide tunnels. Step (8): The main body of the upper tunnel and the secondary lining are excavated in sections. Starting from one end of the intersection, the main body of the upper tunnel is excavated in sections using a small advance method. After each cycle of excavation is completed, concrete is sprayed immediately, steel arches are installed, and the support of the left and right pilot tunnels is welded to the truss anchor points. After the deformation of the initial support of the upper tunnel intersection tends to stabilize, the secondary lining is constructed using the trolley segmented pouring method. The initial support of the left and right pilot tunnels and the truss anchor rods therein are completely wrapped in the lining concrete, so that the truss anchor rod system becomes part of the permanent structure of the upper tunnel.

[0005] Furthermore, in step (1), before excavating the section where the upper and lower tunnels intersect, advance drilling and advance small guide pipes are used to investigate the geological conditions ahead and pre-reinforce the weak sections, so as to provide a stable foundation for subsequent strengthening measures.

[0006] Further, in step (7), two longitudinal anchor rods are arranged on the inner support of the left and right pilot tunnels. Four endpoints A, B, C, and D are laid out at the same horizontal elevation: A and B are the two ends of the first longitudinal anchor rod, and C and D are the two ends of the second longitudinal anchor rod. A horizontal hole is drilled from A to the vicinity of B in the direction of the right pilot tunnel. A fully threaded high-strength steel bar anchor rod is inserted into the hole and grouted. Both ends extend into the support of the left and right pilot tunnels and are welded and fixed to the steel arch or steel mesh to form the first longitudinal anchor rod. On the same horizontal plane, a second horizontal hole is drilled from C to D, and the second longitudinal anchor rod is installed and welded and fixed to the support of the left and right pilot tunnels so that the two longitudinal anchor rods are parallel in the plane and at the same elevation. The two intersecting oblique steel bar anchor rods are arranged as follows: the first oblique anchor rod starts from the vicinity of A or a certain distance inward, and an oblique hole is drilled in the direction of the upper right to the surrounding rock near D. A steel bar anchor rod is inserted, one end is welded to the first longitudinal anchor rod at A, and the other end is welded to D. The first longitudinal anchor is welded to the second longitudinal anchor, and grouting is performed inside the hole for reinforcement. The second diagonal anchor starts from near point B and drills a diagonal hole in the upper left direction to the surrounding rock near point C. A steel anchor is inserted, with one end welded to end B of the first longitudinal anchor and the other end welded to end C of the second longitudinal anchor. Grouting is also performed. The two diagonal anchors are arranged in an "X" shape in the plane, forming a planar truss unit together with the two longitudinal anchors.

[0007] Furthermore, it also includes step (9), which involves setting up the following monitoring items at the intersection of the upper and lower tunnels: including the settlement of the lower tunnel arch crown, the horizontal displacement of the arch waist, the invert heave, the width of the lining cracks, the settlement of the upper tunnel arch crown, and the perimeter convergence; the surface settlement and the deformation of existing buildings and pipelines; among them, some truss anchor units are selected to set up anchor stress or strain monitoring points; according to the monitoring data, early warning values ​​and control values ​​are set: when the monitoring is close to the early warning value, the single-cycle advance of the upper tunnel is reduced, the initial support thickness and reinforcement ratio are increased, the axial spacing of the truss anchor units is reduced, and the grouting reinforcement range of the surrounding rock in the middle is increased; when the monitoring results are stable and significantly lower than the control value, the construction efficiency of the upper tunnel is increased; if the settlement of the lower tunnel arch crown or the invert heave is found to be abnormally increased, auxiliary anti-buoyancy anchors are immediately added in the corresponding section or the inner lining is locally thickened, or the excavation of the upper tunnel is suspended for reinforcement.

[0008] Furthermore, before constructing the initial support reinforcement layer, a tunnel top pit is constructed longitudinally at the top of the lower tunnel, and steel arches and steel mesh are installed at the tunnel top pit to form a top support truss. Inner rods are installed on the top support truss, with the upper end of the inner rod slidingly sealed inside the outer rod. The outer rod is vertically installed inside the surrounding rock of the middle partition, and the upper end of the outer rod is detachably sealed with a cap. The inner side of the outer rod is filled with damping fluid, and a damping plate is installed in the middle of the outer rod. The outer rod is fixedly connected to the planar truss unit of the upper tunnel.

[0009] The beneficial effects of this invention are as follows: The construction method disclosed in this invention addresses engineering conditions where upper and lower tunnels intersect obliquely in the plane with a small vertical clearance and a construction sequence of "lower first, then upper." Through the coordinated design of a closed anti-floating ring for the lower tunnel, high-modulus grouting of the surrounding rock at the bottom of the upper tunnel, a truss-type anchor bearing system, and a stiffness transition at the top of the lower tunnel, the excavation disturbance of the upper tunnel is preferentially dispersed and reduced within the upper and middle surrounding rock areas, significantly reducing the additional impact on the lower tunnel and controlling the risk of overall floating and lining cracking of the lower tunnel. Attached Figure Description

[0010] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 This is a schematic cross-sectional view of the truss-type load-bearing system of the present invention. Figure 2 This is a top view schematic diagram of the truss-type anchor unit formed by the longitudinal anchor rods and the intersecting oblique steel bar anchor rods in the surrounding rock in this invention; Figure 3 This is a schematic diagram showing the positional relationship between the left and right lower pilot tunnels and the surrounding rock of the central partition in the upper tunnel intersection section of this invention; Figure 4 This is a schematic diagram of the tunnel excavation at the intersection of the upper and lower tunnels in this invention; Figure 5 This is a schematic diagram showing the location of the top support truss; Figure 6 for Figure 4 Enlarged view of point A in the middle; The following are the markings in the attached diagram: Upper Tunnel 1, Lower Tunnel 2, Truss-type Load-bearing System 3, Truss Anchorage Point 4, Initial Support Reinforcement Layer 5, Arch Secondary Lining Reinforcement Layer 6, Flexible Buffer Layer 7, Bottom Anchor 8, Bottom Pilot Tunnel of Upper Tunnel 9, Bottom Pilot Tunnel on the Left Side of Upper Tunnel 10, Bottom Pilot Tunnel on the Right Side of Upper Tunnel 11, Top Support Truss 12, Inner Rod 13, Outer Rod 14, Cover 15, Damping Plate 16. Detailed Implementation

[0011] like Figures 1-4As shown, the present invention discloses a method for disturbance isolation and anti-uplift construction under ultra-small clearance conditions for intersecting tunnels, characterized by comprising the following steps: Step (1), excavation and support of the lower tunnel 2, the lower tunnel 2 is excavated in sections along the designed line, and the single-cycle advance and blasting energy are controlled; after each cycle of excavation is completed, shotcrete is sprayed immediately, steel arch frame and steel mesh are installed, system anchor bolts are arranged, and the initial support reinforcement layer 5 is formed; Step (2): Local reinforcement of the arch crown and arch waist of the lower tunnel 2. Within the area affected by the tunnel intersection, supplementary arch frames are added between the existing steel arch frames. The supplementary arch frames are connected to the original arch frames by welding plates to form a continuous skeleton. Circumferential reinforcing bars or ring beams are set at the arch foot and welded to the arch frames on both sides to form the lower connection foundation of the arch reinforcement ring and the invert arch area to form an integral stress closed ring. On the outside of the densified arch frame, steel fiber sprayed concrete is used to thicken the arch crown and arch waist as a whole. The secondary spray layer is tightly combined with the initial support to form a continuous arch crown secondary lining reinforcement layer 6 in the longitudinal direction. Step (3): Construction of the anti-buoyancy anchoring components for the invert arch of the lower tunnel 2. The anchoring hole positions are laid out at a certain longitudinal interval on the bottom surface of the invert arch. Anchor holes are drilled vertically downward or inclined downward from inside the invert arch, with the hole depth penetrating the loose surrounding rock until the deep stable surrounding rock. The bottom anchor 8 is placed in the hole, and double anti-corrosion treatment (such as coating or galvanizing) is adopted. The hole is filled with cement-based grout to form an anchor body. When binding the invert arch and the bottom plate reinforcement, the exposed end of the anchor is connected to the invert arch reinforcement mesh and the arch foot circumferential reinforcement component. The anchor is connected to the invert arch structure by pouring concrete for the invert arch and the bottom plate, forming an anti-buoyancy system of invert arch-bottom plate-anchor-deep surrounding rock. It forms a closed rigid anti-buoyancy ring with the arch foot circumferential reinforcement component and the locally thickened reinforcement ring of the arch. Step (4): The flexible buffer layer 7 of the lower tunnel 2 sidewall and the secondary lining arch reinforcement layer are formed by setting a thin layer of flexible or compressible material, such as a fine aggregate lightweight concrete or mortar layer, on the inner side of the initial support. This layer is relatively thin and has a lower stiffness than the arch reinforcement layer. Under the excavation disturbance of the upper tunnel 1, it can preferentially produce small-amplitude compressive deformation, which plays a role in vibration reduction and mechanical buffering. During the secondary lining construction, high-performance concrete with a high elastic modulus and appropriate reinforcement are used along the tunnel axis at the arch of the lower tunnel 2 to form the arch reinforcement layer, such as... Figure 2 As shown in the reinforcement zone, the stiffness of the arch at the intersection is higher than that of the transition sections on both sides. Step (5): Excavation and support of the bottom pilot tunnel 9 of the upper tunnel. Before the upper tunnel 1 is excavated to the intersection, the outline of the pilot tunnel is laid out according to the lower left and right positions of the design section of the upper tunnel 1, ensuring that the middle partition surrounding rock is retained with sufficient width between the pilot tunnels; first excavate the bottom pilot tunnel 10 on the left side of the upper tunnel, using small-foot weak blasting or mechanical tunneling. After the excavation is completed, immediately spray concrete, install steel arch frame, arrange steel mesh and system anchor bolts to form stable support; after the support of the left pilot tunnel is stable, excavate the bottom pilot tunnel 11 on the right side of the upper tunnel in the same way, and keep the middle partition surrounding rock continuously open; the left and right pilot tunnels are continuously constructed along the entire length of the intersection and extended appropriately to both ends to form two stable lateral beams; Step (6): High-modulus grouting reinforcement of the central partition surrounding rock. In order to ensure that the truss anchor system has a reliable bearing body, after the initial support of the left and right pilot tunnels is completed, high-modulus cement-based grouting is applied to the central partition surrounding rock and its surrounding rock to significantly improve the rock stiffness in this area. The surrounding rock adjacent to the arch of the lower tunnel 2 is not grouted with high-modulus grouting, but is only treated with conventional stabilization to form a vertical stiffness transition, which is conducive to the priority diversion of disturbance load to the central partition surrounding rock and the support of the left and right pilot tunnels. Step (7): Construction of the truss-type steel reinforcement connection system for the central diaphragm surrounding rock. Several sets of truss-type anchor units are arranged in the reinforced central diaphragm surrounding rock. Each set includes two parallel longitudinal anchors and two cross-shaped oblique steel anchors. The two longitudinal anchors are arranged on the inner support of the left and right guide tunnels. Step (8): The main body and secondary lining of the upper tunnel 1 are excavated in sections. Under the protection of the truss-type load-bearing system 3 and the left and right pilot tunnels, the main body of the upper tunnel 1 is excavated in sections with a small advance starting from one end of the intersection section. The sequence of "arch first, then wall" can be adopted. After each cycle of excavation is completed, spray concrete and install steel arch frames immediately, and weld them to the left and right pilot tunnel supports and through the truss anchor points 4 to ensure that a closed support ring is formed as soon as possible. After the deformation of the initial support of the intersection section of the upper tunnel 1 tends to stabilize, the secondary lining is constructed by the trolley segmented pouring method, and the initial support of the left and right pilot tunnels and the truss-type anchor rods therein are completely wrapped in the lining concrete, so that the truss anchor rod system becomes part of the permanent structure of the upper tunnel 1 and plays a long-term role in load distribution and reinforcement.

[0012] In this embodiment, in step (1), before excavating the intersection of the upper and lower tunnels 2, advance drilling and advance small guide pipes are used to investigate the geological conditions ahead and pre-reinforce the weak sections, so as to provide a stable foundation for subsequent strengthening measures.

[0013] In this embodiment, in step (7), two longitudinal anchor rods are arranged on the inner support of the left and right guide tunnels. Four endpoints A, B, C, and D are laid out at the same horizontal elevation: A and B are the two ends of the first longitudinal anchor rod, and C and D are the two ends of the second longitudinal anchor rod. A horizontal hole is drilled from A to the vicinity of B in the direction of the right guide tunnel. A fully threaded high-strength steel bar anchor rod is inserted into the hole and grouting is performed. Both ends extend into the support of the left and right guide tunnels and are welded and fixed to the steel arch or steel mesh to form the first longitudinal anchor rod. On the same horizontal plane, a second horizontal hole is drilled from C to D, and the second longitudinal anchor rod is installed and welded and fixed to the support of the left and right guide tunnels so that the two longitudinal anchor rods are parallel in the plane and at the same elevation. The two intersecting oblique steel bar anchor rods are arranged as follows: the first oblique anchor rod starts from the vicinity of A or a certain distance inward, and an oblique hole is drilled in the direction of the upper right to the surrounding rock near D. A steel bar anchor rod is inserted, one end is welded to the first longitudinal anchor rod at A, and the other end is welded to D. The first longitudinal anchor is welded to the second longitudinal anchor, and grouting is performed inside the hole for reinforcement. The second diagonal anchor starts from near point B and drills a diagonal hole in the upper left direction to the surrounding rock near point C. A steel anchor is inserted, with one end welded to end B of the first longitudinal anchor and the other end welded to end C of the second longitudinal anchor. Grouting is also performed. The two diagonal anchors are arranged in an "X" shape in the plane, forming a planar truss unit together with the two longitudinal anchors.

[0014] In this embodiment, step (9) is also included, which involves setting up the following monitoring items at the intersection of the upper and lower tunnels 2: including the settlement of the lower tunnel 2 arch crown, horizontal displacement of the arch waist, invert heave, lining crack width, settlement of the upper tunnel 1 arch crown, and perimeter convergence; ground settlement and deformation of existing buildings and pipelines; wherein, some truss anchor units are selected to set up anchor stress or strain monitoring points; and setting early warning values ​​and control values ​​according to the monitoring data: when the monitoring is close to the early warning value, reduce the single-cycle advance of the upper tunnel 1, increase the initial support thickness and reinforcement ratio, reduce the axial spacing of the truss anchor units, and increase the grouting reinforcement range of the surrounding rock in the middle partition; when the monitoring results are stable and significantly lower than the control value, increase the construction efficiency of the upper tunnel 1; if the settlement of the lower tunnel 2 arch crown or the invert heave is found to be abnormally increased, immediately add auxiliary anti-buoyancy anchors or locally thicken the inner lining in the corresponding section, or suspend the excavation of the upper tunnel 1 for reinforcement.

[0015] like Figure 5-6As shown, as a further improvement of this embodiment of the invention, before constructing the initial support reinforcement layer 5, a top pit of the lower tunnel 2 is constructed longitudinally at the top of the lower tunnel 2, and a steel arch and steel mesh are installed at the top pit of the lower tunnel 2 to form a top support truss 12; an inner rod 13 is installed on the top support truss 12, the upper end of the inner rod 13 is slidably sealed inside the outer rod 14, the outer rod 14 is vertically installed in the surrounding rock of the middle partition, the upper end of the outer rod 14 is detachably sealed with a cap 15, the inner side of the outer rod 14 is filled with damping fluid, a damping plate 16 is installed in the middle of the outer rod 14, and the outer rod 14 is fixedly connected to the planar truss unit of the upper tunnel 1. By adopting the above method, local vibrations can be buffered during the construction of the upper tunnel 1 to prevent the lower tunnel 2 from floating.

[0016] This invention significantly improves the overall stiffness and anti-uplift capability of the lower tunnel 2 by forming a closed anti-uplift system at the intersection of the lower tunnel 2, consisting of a locally thickened reinforcing ring at the arch, circumferential members at the arch foot, and anti-uplift anchor bolts for the invert arch. A reinforcing layer is installed at the arch crown, and a flexible buffer layer 7 is installed on the sidewalls. At the bottom of the upper tunnel 1, high-modulus grouting is performed through left and right lower pilot tunnels, and high-modulus grouting of the surrounding rock in the middle, along with longitudinal anchor bolts. The combination of the truss-type load-bearing system 3 with intersecting oblique steel anchors allows the excavation disturbance of the upper tunnel 1 to be dispersed and dissipated primarily within the superstructure and the surrounding rock of the intermediate partition. At the same time, by performing only conventional stabilization treatment on the surrounding rock adjacent to the arch of the lower tunnel 2, a vertical stiffness transition is formed, avoiding the formation of a rigid bridge between the upper and lower tunnels 2 and reducing the risk of the disturbance load being directly transmitted to the lower tunnel 2. The use of steel fiber shotcrete in the arch enhances the collaborative working ability between the arch and the surrounding rock. With the monitoring and measurement within the intersection section and the information-based adjustment of construction parameters, the uplift and deformation of the lower tunnel 2 can be controlled within the preset safety range, thereby significantly improving the construction safety and reliability under the oblique intersection condition of the upper and lower tunnels.

Claims

1. A method for disturbance isolation and anti-uplift construction under ultra-small clearance conditions in intersecting tunnels, characterized in that, Includes the following steps: Step (1), lower tunnel excavation and support, the lower tunnel is excavated in sections along the designed line, and the single-cycle advance and blasting energy are controlled; after each cycle of excavation is completed, shotcrete is sprayed immediately, steel arch frame and steel mesh are installed, system anchor bolts are arranged, and the initial support reinforcement layer is formed; Step (2): Local reinforcement of the tunnel arch crown and arch waist. Within the area affected by the tunnel intersection, supplementary arch frames are added between the existing steel arch frames. The supplementary arch frames are connected to the original arch frames by welding plates to form a continuous skeleton. Circumferential reinforcing bars or ring beams are set at the arch foot and welded to the arch frames on both sides to form the lower connection foundation of the arch reinforcement ring and the invert arch area to form an integral stress closed ring. On the outside of the densified arch frame, steel fiber sprayed concrete is used to thicken the arch crown and arch waist as a whole. The secondary spray layer is tightly combined with the initial support to form a continuous arch crown secondary lining reinforcement layer in the longitudinal direction. Step (3): Construction of the anti-buoyancy anchoring components for the invert arch of the lower tunnel. The anchoring hole positions are laid out at a certain longitudinal interval on the bottom surface of the invert arch. Anchor holes are drilled vertically downward or inclined downward from inside the invert arch. Bottom anchors are placed in the holes and the holes are filled with cement-based grout to form an anchor body. When binding the invert arch and the bottom plate reinforcement, the exposed end of the anchor is connected to the invert arch reinforcement mesh and the circumferential reinforcement component at the arch foot. The anchor is connected to the invert arch structure by pouring concrete for the invert arch and the bottom plate, forming an anti-buoyancy system of invert arch-bottom plate-anchor-deep surrounding rock. It forms a closed rigid anti-buoyancy ring with the circumferential reinforcement component at the arch foot and the locally thickened reinforcement ring of the arch. Step (4): The flexible buffer layer of the lower tunnel sidewall and the secondary lining arch reinforcement layer are formed by setting a thin layer of flexible or compressible material on the inner side of the initial support. During the secondary lining construction, high-performance concrete and dense reinforcement are used along the tunnel axis at the arch top of the lower tunnel to form an arch reinforcement layer, so that the arch stiffness of the intersection section is higher than that of the transition sections on both sides. Step (5): Excavation and support of the pilot tunnel at the bottom of the upper tunnel. Before the upper tunnel is excavated to the intersection, the outline of the pilot tunnel is laid out according to the lower left and right positions of the upper tunnel design section. First, the pilot tunnel at the bottom of the left side of the upper tunnel is excavated using small-foot weak blasting or mechanical tunneling. After the excavation is completed, shotcrete is sprayed, steel arches are installed, steel mesh and system anchors are arranged to form stable support. After the support of the left pilot tunnel is stable, the pilot tunnel at the bottom of the right side of the upper tunnel is excavated in the same way, and the surrounding rock in the middle is also kept open. The left and right pilot tunnels are continuously constructed along the entire length of the intersection and extend to both ends to form two stable lateral beams. Step (6): High modulus grouting reinforcement of the central partition surrounding rock. After the initial support of the left and right pilot tunnels is completed, high modulus cement-based grouting is used to reinforce the central partition surrounding rock and its surrounding surrounding rock as a whole. The surrounding rock in close proximity to the lower tunnel arch is only treated with conventional stabilization to form a vertical stiffness transition. Step (7): Construction of the truss-type steel reinforcement connection system for the central diaphragm surrounding rock. Several sets of truss-type anchor units are arranged in the reinforced central diaphragm surrounding rock. Each set includes two parallel longitudinal anchors and two cross-shaped oblique steel anchors. The two longitudinal anchors are arranged on the inner support of the left and right guide tunnels. Step (8): The main body of the upper tunnel and the secondary lining are excavated in sections. Starting from one end of the intersection, the main body of the upper tunnel is excavated in sections using a small advance method. After each cycle of excavation is completed, concrete is sprayed immediately, steel arches are installed, and the support of the left and right pilot tunnels is welded to the truss anchor points. After the deformation of the initial support of the upper tunnel intersection tends to stabilize, the secondary lining is constructed using the trolley segmented pouring method. The initial support of the left and right pilot tunnels and the truss anchor rods therein are completely wrapped in the lining concrete, so that the truss anchor rod system becomes part of the permanent structure of the upper tunnel.

2. The method for disturbance isolation and anti-uplift construction under ultra-small clearance conditions of intersecting tunnels according to claim 1, characterized in that, In step (1), before excavating the section where the upper and lower tunnels intersect, advance drilling and advance small guide pipes are used to investigate the geological conditions ahead and pre-reinforce the weak sections, so as to provide a stable foundation for subsequent reinforcement measures.

3. The method for disturbance isolation and anti-uplift construction under ultra-small clearance conditions of intersecting tunnels according to claim 2, characterized in that, In step (7), two longitudinal anchors are arranged on the inner support of the left and right pilot tunnels. Four endpoints A, B, C, and D are laid out at the same horizontal elevation: A and B are the two ends of the first longitudinal anchor, and C and D are the two ends of the second longitudinal anchor. A horizontal hole is drilled from A to the vicinity of B in the direction of the right pilot tunnel. A fully threaded high-strength steel anchor is inserted into the hole and grouted. Both ends extend into the support of the left and right pilot tunnels and are welded and fixed to the steel arch or steel mesh to form the first longitudinal anchor. On the same horizontal plane, a second horizontal hole is drilled from C to D. The second longitudinal anchor is installed and welded and fixed to the support of the left and right pilot tunnels so that the two longitudinal anchors are parallel in the plane and at the same elevation. The two intersecting oblique steel anchors are arranged as follows: the first oblique anchor starts from the vicinity of A or a certain distance inward. An oblique hole is drilled in the direction of the upper right to the surrounding rock near D. A steel anchor is inserted. One end is welded to the first longitudinal anchor at A and the other end is welded to D. The first longitudinal anchor is welded to the second longitudinal anchor, and grouting is performed inside the hole for reinforcement. The second diagonal anchor starts from near point B and drills a diagonal hole in the upper left direction to the surrounding rock near point C. A steel anchor is inserted, with one end welded to end B of the first longitudinal anchor and the other end welded to end C of the second longitudinal anchor. Grouting is also performed. The two diagonal anchors are arranged in an "X" shape in the plane, forming a planar truss unit together with the two longitudinal anchors.

4. The method for disturbance isolation and anti-uplift construction under ultra-small clearance conditions of intersecting tunnels according to claim 3, characterized in that, The method also includes step (9), which involves setting up the following monitoring items at the intersection of the upper and lower tunnels: settlement of the lower tunnel arch, horizontal displacement of the arch waist, heave of the invert arch, width of lining cracks, settlement of the upper tunnel arch, and perimeter convergence; surface settlement and deformation of existing buildings and pipelines; among which, some truss anchor units are selected to set up anchor stress or strain monitoring points; and setting early warning values ​​and control values ​​according to the monitoring data: when the monitoring is close to the early warning value, reduce the single-cycle advance of the upper tunnel, increase the initial support thickness and reinforcement ratio, reduce the axial spacing of the truss anchor units, and increase the grouting reinforcement range of the surrounding rock in the middle partition; when the monitoring results are stable and significantly lower than the control value, improve the construction efficiency of the upper tunnel; if the settlement of the lower tunnel arch or the heave of the invert arch is found to be abnormally increased, immediately add auxiliary anti-buoyancy anchors or locally thicken the inner lining in the corresponding section, or suspend the excavation of the upper tunnel for reinforcement.

5. The method for disturbance isolation and anti-uplift construction under ultra-small clearance conditions of intersecting tunnels according to claim 4, characterized in that, Before constructing the initial support reinforcement layer, a tunnel top pit is constructed longitudinally at the top of the lower tunnel, and steel arches and steel mesh are installed at the tunnel top pit to form a top support truss. Inner rods are installed on the top support truss, with the upper end of the inner rod slidingly sealed inside the outer rod. The outer rod is vertically installed in the surrounding rock of the middle partition, and the upper end of the outer rod is detachably sealed with a cap. The inner side of the outer rod is filled with damping fluid, and a damping plate is installed in the middle of the outer rod. The outer rod is fixedly connected to the planar truss unit of the upper tunnel.

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