Method for controlling ground heave in unloading stratum of overlying foundation pit excavation in multi-line parallel tunnel group

Abstract

The application discloses a method for controlling uplift of an overlying stratum of an existing multi-line parallel tunnel group during excavation, which comprises the following steps: stratum grouting reinforcement around the existing tunnel group, construction of a joint protection system for preventing uplift of the existing tunnel group and foundation pit support, layered, striped and segmented extraction of soil of the overlying foundation pit of the tunnel group, and prediction and prevention of uplift deformation of the existing tunnel group. The method fills the gap of an effective, feasible and scientific method for controlling uplift of an overlying stratum during excavation, which has a very high control requirement for uplift deformation of an existing multi-line parallel tunnel group. The method can improve operation safety of the existing tunnel group and stability of foundation pit excavation support, perfect the method for controlling uplift of an overlying stratum during excavation, achieve the safety goal of preventing uplift of the existing tunnel group and foundation pit support, has strong application value for overlying stratum excavation and unloading engineering in a densely populated urban underground space, and has important significance for ensuring safety of underground excavation and unloading engineering such as foundation pits.

Description

Technical Field

[0001] This invention belongs to the field of excavation and construction methods for foundation pits, specifically relating to a method for controlling ground uplift during excavation of foundation pits overlying existing multi-line parallel tunnel groups. Background Technology

[0002] With the accelerating pace of urbanization in my country, the scale of underground space development is also increasing, with a surge in underground engineering projects such as subways, tunnels, and foundation pits, all on a continuously expanding scale. Due to construction sequence issues, subsequent foundation pit excavation inevitably needs to be carried out above or near existing subways, tunnels, and other underground structures. Excavating foundation pits above existing tunnels will inevitably lead to stress release and soil rebound, and the deformation of the soil will inevitably affect the existing tunnel, causing changes in the tunnel's stress and displacement fields. In particular, the excavation of foundation pits for some building basements or urban underground roads will be carried out directly above the tunnel, altering the original tunnel's stress and deformation fields and disrupting its original stress equilibrium. As the load above the tunnel decreases, and under the buoyancy of groundwater, vertical deformation of the tunnel and rebound of the soil below the tunnel will occur, significantly impacting the safety of subway operations. When tunnel deformation exceeds a certain limit, it can lead to water leakage at tunnel joints, or in severe cases, significantly impact the safe operation of the tunnel, potentially rendering it unsafe to operate. Therefore, in the excavation of foundation pits near subways, tunnels and pipelines, it is necessary to strictly control the heave and deformation of the soil to ensure the safety of existing tunnels.

[0003] In the engineering field, numerous experts and scholars have conducted extensive research on soil deformation control measures. Common deformation control measures include segmented and layered excavation of the foundation pit, surcharge backfilling, installation of central partition walls, installation of anti-buoyancy anchors, installation of gantry-type restraint systems, and reinforcement of the tunnel structure itself. Among these, segmented and layered excavation of the foundation pit and anti-buoyancy anchors are effective in controlling soil deformation, but their planning and implementation are complex, making them difficult to meet the requirements of foundation pit projects with strict requirements for controlling tunnel uplift deformation. Reinforcement of the tunnel structure itself has limited effectiveness in controlling the overall displacement of the tunnel and cannot be used as a primary deformation control measure.

[0004] The above-mentioned methods for controlling ground heave during excavation and unloading of foundation pits are mostly designed for single foundation pit projects or cases with a single underlying tunnel. They are difficult to meet the requirements for controlling the uplift deformation of existing multi-line parallel tunnel groups and cannot provide scientific and effective early warning and prevention of uplift deformation of existing multi-line parallel tunnel groups. Therefore, given the current lack of an effective, feasible, and scientific method for controlling the heave of the overlying strata during excavation of existing multi-line parallel tunnel groups, which presents extremely high uplift deformation requirements, it is urgent to develop a scientific, efficient, and practical method for controlling the heave of the overlying strata during excavation of existing multi-line parallel tunnel groups. This method is of great significance and application prospects, especially for overlying strata excavation and unloading projects in densely populated urban underground spaces, and is crucial for ensuring the safety of underground excavation and unloading projects such as foundation pits. This approach aims to improve the operational safety of existing underground tunnel groups and the stability of foundation pit excavation and support, refine the method for controlling the heave of the overlying strata during excavation, and achieve the goal of preventing heave of existing tunnel groups and ensuring the safety of foundation pit support. The method employs methods such as grouting reinforcement of the surrounding strata of existing tunnel groups, construction of a combined protection system for preventing heave of existing tunnel groups and foundation pit support, layered, segmented, and sectioned excavation of the overlying foundation pit soil, and prediction and control of heave deformation of existing tunnel groups. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controlling ground heave during excavation and unloading of overlying strata in existing multi-track parallel tunnel groups. This method improves the operational safety of existing underground tunnel groups and the stability of excavation and support, perfects the method for controlling ground heave during excavation and unloading, and achieves the goal of preventing ground heave in existing tunnel groups and ensuring the safety of excavation and support. The method employs grouting reinforcement of the surrounding strata of existing tunnel groups, construction of a combined protection system for preventing ground heave in existing tunnel groups and excavation and support, layered, segmented, and sectioned excavation of the overlying soil, and prediction and control of ground heave deformation in existing tunnel groups. This method has strong application value for excavation and unloading projects in densely populated urban underground spaces and is of great significance for ensuring the safety of underground excavation and unloading projects such as excavation pits.

[0006] To achieve the aforementioned objectives, the present invention specifically includes the following steps:

[0007] The method for controlling ground heave during excavation and unloading of overlying strata in existing multi-track parallel tunnel groups includes the following steps:

[0008] S1, Determine the scope of the excavation pit to be excavated above the existing tunnel;

[0009] S2, grouting reinforcement of the strata surrounding the existing tunnel group;

[0010] S3, construction of the existing tunnel group anti-uplift-foundation pit support combined protection system;

[0011] S4, the soil overlying the tunnel group is unloaded and excavated in layers, sections, and segments.

[0012] S5, Prediction and control of uplift deformation of existing tunnel groups.

[0013] Further technology of the present invention:

[0014] Preferably, in step S1, the excavation plane range A and excavation depth H of the foundation pit are determined according to the foundation pit design requirements;

[0015] The width of the excavation area A is L1, and the length is L2;

[0016] The excavation width L1 is approximately perpendicular to the tunnel axis, and the excavation length L2 is approximately parallel to the tunnel axis.

[0017] Preferably, in step S2, the grouting reinforcement of the strata surrounding the tunnel group includes a first grouting reinforcement zone and a second grouting reinforcement zone;

[0018] Above the tunnel group is the first grouting reinforcement zone, which runs the entire length of the tunnels; outside the tunnel group is the second grouting reinforcement zone.

[0019] The first grouting reinforcement zone is located within a range of 0.5m to 1m from the top of the uppermost tunnel in the tunnel group and 0.5m to 1m from the bottom of the foundation pit. The first grouting reinforcement zone is grouted horizontally to 10m from the outermost tunnel in the tunnel group.

[0020] The grouting range of the first and second grouting reinforcement zones along the tunnel group axis is the same as the length L2 of the foundation pit.

[0021] Preferably, in step S2, the effective overburden depth h in the tunnel group s A third grouting reinforcement zone is formed above tunnels exceeding 8 meters in height. s The distance is from the top of the tunnel to the bottom of the first grouting reinforcement zone. In the third grouting reinforcement zone, there is one grouting point every 10m, and the grouting radius of each grouting point is 3m.

[0022] Preferably, in step S3, the anti-heave-foundation pit support combined protection system includes a horizontal pipe curtain, a first grouting anchor, a second grouting anchor, an anti-buoyancy anchor, a transverse connecting beam, a longitudinal connecting beam, an anti-heave cover plate, and a cement mixing pile wall;

[0023] The horizontal pipe curtain is set horizontally in the first grouting reinforcement zone above the tunnel, and grouting holes are opened on the pipe wall to perform horizontal grouting in the first grouting reinforcement zone;

[0024] The first grouting anchor is located on the axis of the second grouting reinforcement zone, and grouting is performed on the second grouting reinforcement zone;

[0025] The second grouting anchor is located on the central axis of the third grouting reinforcement zone, and grouting is carried out in the third grouting reinforcement zone;

[0026] The transverse and longitudinal connecting beams are connected to form a transverse and longitudinal intersecting connecting beam, which connects several first grouting anchors and anti-buoyancy anchors on the same transverse direction into one piece;

[0027] The second grouting anchor is located at the geometric center of the area enclosed by the transverse connecting beam and the longitudinal connecting beam;

[0028] A cast-in-place anti-bulging cover plate is constructed above the transverse and longitudinal connecting beams, with pre-reserved steel bar A embedded in the anti-bulging cover plate;

[0029] The cement mixing pile wall is located on the outside of the tunnel group, with two cement mixing pile walls on each side. The space between the two cement mixing pile walls forms a pipe curtain working shaft, and the two ends of the horizontal pipe curtain extend into the pipe curtain working shaft.

[0030] Preferably, the first grouting anchor, the second grouting anchor, and the anti-buoyancy anchor are equipped with steel strands.

[0031] Preferably, in step S4, the soil overlying the tunnel group is excavated in layers, sections, and segments using a strip-by-strip excavation method.

[0032] The layered, segmented, and sectioned excavation method vertically divides the soil overlying the tunnel group into N layers, where N is 2 to 6 layers, and each layer is 3 to 5 meters thick, with the thickness of each layer gradually decreasing from top to bottom.

[0033] It is divided into M horizontal sections, where M is 4 to 8 sections, and M is the same as the number of tunnels K.

[0034] The pit is longitudinally divided into O segments, with O consisting of 2 to 6 segments. The width of a single excavation along the direction perpendicular to the existing tunnel shall not exceed L2 / 8. When it exceeds L2 / 8, the width of a single excavation shall be twice the inner diameter of the tunnel.

[0035] Preferably, at the same plane location, the upper layer is excavated first, followed by the lower layer;

[0036] When dividing the tunnel into sections, first excavate the section above the tunnel with the greater burial depth, and then excavate the section above the tunnel with the lesser burial depth.

[0037] The section is divided longitudinally, and different sections on the same layer and the same strip are excavated in a longitudinal skip-slot manner.

[0038] Strictly control the excavation sequence in the transverse direction, and excavate symmetrically;

[0039] Different layers, strips, and sections are excavated in the order of first layering, then striping, and finally sectioning.

[0040] Compared with existing technologies, the beneficial technical effects of this invention are reflected in:

[0041] This invention discloses a method for controlling ground heave during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups. The method includes grouting reinforcement of the surrounding strata of the existing tunnel group, construction of a combined protection system for the existing tunnel group's anti-heave and foundation pit support, layered, segmented, and sectioned excavation of the overlying foundation pit soil, and prediction and control of heave deformation in the existing tunnel group. This method fills the gap in the current lack of an effective, feasible, and scientific method for controlling ground heave during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups, which currently have extremely high requirements for controlling uplift deformation. The method can improve the operational safety of existing underground tunnel groups and the stability of foundation pit excavation and support, improve the method for controlling ground heave during foundation pit excavation and unloading, and achieve the goal of preventing heave in existing tunnel groups and ensuring the safety of foundation pit support. It has strong application value for overlying strata excavation and unloading projects in densely populated urban underground spaces and is of great significance for ensuring the safety of underground excavation and unloading projects such as foundation pits. Attached Figure Description

[0042] Figure 1 A flowchart of a method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups;

[0043] Figure 2 This is a schematic diagram of the excavation area A of the foundation pit;

[0044] Figure 3 A schematic diagram of a method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups.

[0045] Figure 4 Schematic diagram of grouting reinforcement of the strata surrounding the tunnel group;

[0046] Figure 5 Schematic diagram of a combined protection system for preventing uplift and foundation pit support;

[0047] Figure 6 Top view of the combined protection system for preventing uplift and foundation pit support;

[0048] Figure 7 This is a schematic diagram of a layered, segmented, and sectioned excavation method.

[0049] Figure 8 A schematic diagram of the excavation and shaping of an overburden pit for an existing multi-line parallel tunnel group;

[0050] Figure 9 A schematic diagram of the excavation and shaping of an overburden pit for an existing multi-line parallel tunnel group;

[0051] Figure 10 A schematic diagram of the excavation and shaping of an overburden pit for an existing multi-line parallel tunnel group;

[0052] Figure 11 This is a schematic diagram of the horizontal tube curtain distribution.

[0053] In the diagram: 1. First Tunnel; 2. Second Tunnel; 3. Third Tunnel; 4. Fourth Tunnel; 5. First Grouting Reinforcement Zone; 6. Second Grouting Reinforcement Zone; 7. Third Grouting Reinforcement Zone; 8. Pipe Curtain Working Shaft; 9. Cement Mixing Pile Wall; 10. Horizontal Pipe Curtain; 11. First Grouting Anchor; 12. Second Grouting Anchor; 13. Anti-buoyancy Anchor; 14. Transverse Connecting Beam; 15. Longitudinal Connecting Beam; 16. Anti-heavy Cover Plate. Detailed Implementation

[0054] like Figure 1 A method for controlling ground heave during excavation and unloading of overlying strata in existing multi-parallel tunnel groups, characterized by the following steps:

[0055] S1, Determine the scope of the excavation pit to be excavated above the existing tunnel;

[0056] S2, grouting reinforcement of the strata surrounding the existing tunnel group;

[0057] S3, construction of the existing tunnel group anti-uplift-foundation pit support combined protection system;

[0058] S4, the soil overlying the tunnel group is unloaded and excavated in layers, sections, and segments.

[0059] S5, Prediction and control of uplift deformation of existing tunnel groups.

[0060] The tunnel complex is an existing project that was already in operation in the strata before the excavation of the foundation pit to be excavated;

[0061] Preferably, the tunnel group includes multiple parallel tunnels, with the number of tunnels being K, where K = 2 to 6; in this embodiment, 4 tunnels are selected, such as... Figure 2 The third tunnel 3 and the fourth tunnel 4 are located on the same plane and outside the tunnel group, respectively; the first tunnel 1 and the second tunnel 2 are located on the same plane and in the middle of the tunnel group; the first tunnel 1 and the second tunnel 2 are located at a higher position than the third tunnel 3 and the fourth tunnel 4.

[0062] like Figure 3-4 8. The top of the first tunnel 1 and the second tunnel 2, which are located at the top of the tunnel group, is h1 away from the ground surface.

[0063] In step S1, the excavation plane range A and excavation depth H of the foundation pit are determined according to the foundation pit design requirements;

[0064] Preferably, the width of the excavation plane area A is L1, and the length is L2;

[0065] Preferably, the excavation plane width L1 is approximately perpendicular to the tunnel axis, and the excavation plane length L2 is approximately parallel to the tunnel axis.

[0066] In step S2, the grouting reinforcement of the strata surrounding the tunnel group includes three grouting reinforcement zones, namely the first grouting reinforcement zone 5, the second grouting reinforcement zone 6, and the third grouting reinforcement zone 7.

[0067] Preferably, the first grouting reinforcement zone 5 is located within a range of 0.5m to 1m from the top of the first tunnel 1 and the second tunnel 2 and 0.5m to 1m from the bottom of the foundation pit, and the first grouting reinforcement zone 5 is grouted horizontally to 10m from the outside of the third tunnel 3 and the fourth tunnel 4, which are the outermost tunnels in the tunnel group.

[0068] Preferably, the second grouting reinforcement zone 6 is located within 2 to 10 meters outside the outermost third tunnel 3 and fourth tunnel 4 of the tunnel group. The second grouting reinforcement zone 6 is vertically grouted up to the lower edge of the first grouting reinforcement zone 5 and down to 5 meters below the bottom of the third tunnel 3 and fourth tunnel 4.

[0069] Preferably, the third grouting reinforcement zone 7 is used to grout and reinforce the tunnels in the tunnel group whose effective overburden depth hs is greater than 8m, where hs is the distance from the top of the tunnel to the bottom of the first grouting reinforcement zone 5;

[0070] Preferably, the third grouting reinforcement zone 7 is located 1-2m from the top of the third tunnel 3 and the fourth tunnel 4 and within the range of the bottom of the first grouting reinforcement zone 5. The central axis of the third grouting reinforcement zone 7, the central axis of the second grouting anchor 12 and the central axis of the third tunnel 3 (or the fourth tunnel 4) are on the same vertical plane. The horizontal width of the third grouting reinforcement zone 7 is the same as the diameter of the third tunnel 3 (or the fourth tunnel 4).

[0071] Preferably, the grouting range of the first grouting reinforcement zone 5 and the second grouting reinforcement zone 6 along the tunnel group axis is the same as the length L2 of the foundation pit, and the third grouting reinforcement zone 7 has one grouting point every 10m, with a grouting radius of 3m for each grouting point;

[0072] Preferably, the grouting reinforcement of the strata surrounding the tunnel group is carried out in the following order: second grouting reinforcement zone 6 → first grouting reinforcement zone 5 → third grouting reinforcement zone 7.

[0073] In step S3, the anti-uplift-foundation pit support combined protection system includes a horizontal pipe curtain 10, a first grouting anchor 11, a second grouting anchor 12, an anti-buoyancy anchor 13, a transverse connecting beam 14, a longitudinal connecting beam 15, an anti-uplift cover plate 16, and a cement mixing pile wall 9.

[0074] Preferably, the horizontal pipe curtain 10 performs horizontal grouting on the first grouting reinforcement zone 5; specifically:

[0075] The horizontal pipe jacking 10 is constructed inside the pipe jacking working shaft 8;

[0076] like Figure 9The horizontal pipe curtain 10 runs through the working wells 8 on both sides of the pipe curtain. The length of the horizontal pipe curtain 10 is L1, and grouting holes are opened on the pipe wall.

[0077] Grouting can be performed from one side, such as... Figure 10 On the left; or as Figure 11 ,on the right.

[0078] The grouting holes on the wall of the horizontal pipe curtain 10 are mainly distributed in the middle of the first grouting reinforcement zone 5, and preferably distributed between the centers of the second grouting reinforcement zones 6 on both sides.

[0079] During grouting, the horizontal pipe curtain 10 is simultaneously carried out from the middle of the foundation pit to both sides along the length L2 of the foundation pit, and skip grouting is used on the same side. Figure 11 In the middle stage, A0 is grouted first, then A11-A12...A1n and A21-A22...A2n are grouted simultaneously; finally, B11-B12...B1n and B21-B22...B2n are grouted simultaneously.

[0080] Preferably, the first grouting anchor 11 grouts the second grouting reinforcement zone 6;

[0081] Preferably, the first grouting anchor 11 is located on the axis of the second grouting reinforcement zone 6, that is, within 2 to 10 meters outside the outermost third tunnel 3 and fourth tunnel 4 of the tunnel group;

[0082] Preferably, the second grouting anchor 12 grouts the third grouting reinforcement zone 7;

[0083] Preferably, the second grouting anchor 12 is located on the central axis of the third grouting reinforcement zone 7;

[0084] like Figure 5-6 The transverse connecting beam 14 connects several first grouting anchors 11 and anti-buoyancy anchors 13 on the same transverse direction into one unit;

[0085] The longitudinal connecting beam 15 connects several first grouting anchors 11 or anti-buoyancy anchors 13 in the same longitudinal direction into one piece;

[0086] The transverse connecting beam 14 and the longitudinal connecting beam 15 are connected at the first grouting anchor 11 to form a transverse and longitudinal intersecting connecting beam.

[0087] The transverse connecting beam 14 and the longitudinal connecting beam 15 have the same thickness;

[0088] Low-permeability material is laid and compacted within the area enclosed by the transverse connecting beam 14 and the longitudinal connecting beam 15;

[0089] The second grouting anchor 12 is located at the geometric center of the area enclosed by the transverse connecting beam 14 and the longitudinal connecting beam 15.

[0090] The top of the first grouting anchor 11, the second grouting anchor 12 and the anti-buoyancy anchor 13 are reserved with steel bars A;

[0091] A cast-in-place anti-bulging cover plate 16 is constructed above the transverse connecting beam 14 and the longitudinal connecting beam 15, with a pre-reserved reinforcing bar A embedded in the anti-bulging cover plate 16.

[0092] The cement mixing pile wall 9 is located outside the tunnel group. There are two cement mixing pile walls 9 on each side. The space between the two cement mixing pile walls 9 forms the pipe curtain working well 8. The spacing between the two cement mixing pile walls 9 is determined according to the construction equipment of the horizontal pipe curtain 10.

[0093] Preferably, after the horizontal pipe curtain 10 is constructed, as the soil above the tunnel group is excavated, the excavated soil is filled into the pipe curtain working shaft 8, and the pipe curtain working shafts 8 on both sides of the tunnel group are symmetrically filled with soil.

[0094] In step S4, the overlying foundation pit soil of the tunnel group is excavated using a layered, segmented, and sectioned excavation method; such as... Figure 7 :

[0095] The layered, segmented, and sectioned excavation method vertically divides the overlying foundation pit soil of the tunnel group into N layers, where N is 2 to 6 layers, and each layer is 3 to 5 meters thick, with the layer thickness gradually decreasing from top to bottom; preferably, the upper layer A = 5m and the lower layer B = 3m.

[0096] It is divided into M horizontal sections, where M is 4 to 8 sections. M is the same as the number of tunnels K. Here, the preferred order is inner section A1, inner section A2, outer section B1, and outer section B2.

[0097] The pit is longitudinally divided into O segments, with O consisting of 2 to 6 segments. The width of a single excavation (segment width) along the direction perpendicular to the existing tunnel should not exceed L2 / 8. When it exceeds L2 / 8, the width of a single excavation should be twice the inner diameter of the tunnel. Here, the preferred segments are the front segment A, the middle segment B, and the rear segment C.

[0098] In step S4, the soil overlying the tunnel group is excavated in layers, sections, and segments using a strip-by-strip excavation method.

[0099] Preferably, the excavation sequence meets the following principles: (1) At the same plane position, the upper layer is excavated first, and then the lower layer is excavated; (2) When there are different sections, the section above the tunnel with a large burial depth is excavated first, and then the section above the tunnel with a small burial depth is excavated; (3) When longitudinally divided into sections, different sections on the same layer and the same strip are excavated in a longitudinal skip-slot manner (to control longitudinal uplift deformation); (4) The excavation sequence is strictly controlled in the transverse direction, and symmetrical excavation is carried out (to control lateral deformation); (5) Different layers, strips, and sections are excavated in the order of first layering, then striping, and then segmenting.

[0100] Preferably (or in the embodiments), the first layer (upper layer A) is excavated in the following order: front section A of outer strip B1 of upper layer A → rear section C of outer strip B1 of upper layer A → middle section B of outer strip B1 of upper layer A → front section A of outer strip B2 of upper layer A → rear section C of outer strip B2 of upper layer A → middle section B of outer strip B2 of upper layer A → front section A of inner strip A1 of upper layer A → rear section C of inner strip A1 of upper layer A → middle section B of inner strip A1 of upper layer A → front section A of inner strip A2 of upper layer A → rear section C of inner strip A2 of upper layer A → middle section B of inner strip A2 of upper layer A;

[0101] Preferably (or in the embodiments), the second layer (lower layer B) is excavated in the following order: front section A of outer strip B1 of lower layer B → rear section C of outer strip B1 of lower layer B → middle section B of outer strip B1 of lower layer B → front section A of outer strip B2 of lower layer B → rear section C of outer strip B2 of lower layer B → middle section B of outer strip B2 of lower layer B → front section A of inner strip A1 of lower layer B → rear section C of inner strip A1 of lower layer B → middle section B of inner strip A1 of lower layer B → front section A of inner strip A2 of lower layer B → rear section C of inner strip A2 of lower layer B → middle section B of inner strip A2 of lower layer B;

[0102] Preferably, the remaining layers are excavated using the method described above.

[0103] In step S4, steel strands are installed inside the first grouting anchor 11, the second grouting anchor 12, and the anti-buoyancy anchor 13. The steel strands apply stress to the anti-bulging cover plate 16 at the bottom of the pit, effectively controlling the bulging deformation of the pit bottom.

[0104] In step S5, after the construction of the cross-shaped beams and anti-heavy cover plate 16 at the bottom of the foundation pit is completed, dynamic monitoring of foundation pit heaving is carried out. When the bottom of the foundation pit shows a tendency to heave and deform, the heaving deformation of the tunnel group is controlled by the steel strands installed in the first grouting anchor 11, the second grouting anchor 12 and the anti-buoyancy anchor 13.

[0105] Preferably, the allowable heave deformation limit value at the bottom of the foundation pit is δ, and δ is determined according to the protection level of the foundation pit and tunnel, generally 20 to 40 mm;

[0106] Preferably, when the actual heave deformation value at the bottom of the foundation pit reaches 0.6δ, a yellow warning is issued, and the heave deformation is controlled by the steel strands inside the anti-buoyancy anchor 13; when the actual heave deformation value at the bottom of the foundation pit reaches 0.8δ, an orange warning is issued, and the heave deformation is controlled by the steel strands inside the first grouting anchor 11, the second grouting anchor 12, and the anti-buoyancy anchor 13; when the actual heave deformation value at the bottom of the foundation pit is greater than 0.95δ, a red warning is issued, and the heave deformation is controlled by the steel strands, and the heave deformation is also controlled by adding foundation pit dewatering or temporary surcharge methods.

[0107] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The descriptions in the foregoing invention and specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-parallel tunnel groups, wherein the tunnel group includes three or more parallel tunnels, and at least some of the tunnels are arranged in upper and lower layers, the method comprising the following steps: S1. Determine the excavation plane range A and excavation depth H of the foundation pit according to the design requirements. The excavation plane width L1 is approximately perpendicular to the tunnel axis, and the excavation plane length L2 is approximately parallel to the tunnel axis. S2 involves grouting reinforcement of the strata surrounding the existing tunnel group, including the first grouting reinforcement zone, the second grouting reinforcement zone, and the third grouting reinforcement zone. In step S2: A first grouting reinforcement zone with a continuous length is set above the tunnel group, and a second grouting reinforcement zone is set outside the tunnel group; The first grouting reinforcement zone is located within a range of 0.5m to 1m from the top of the uppermost tunnel in the tunnel group and 0.5m to 1m from the bottom of the foundation pit. The first grouting reinforcement zone is horizontally grouted to 10m from the outermost tunnel in the tunnel group. The grouting range of the first and second grouting reinforcement zones along the tunnel group axis is the same as the length L2 of the foundation pit; In step S2, grouting reinforcement is carried out above tunnels with an effective overburden depth hs greater than 8m to form a third grouting reinforcement zone. hs is the distance from the top of the tunnel to the bottom of the first grouting reinforcement zone. There is one grouting point every 10m in the third grouting reinforcement zone, and the grouting radius of each grouting point is 3m. S3 is a joint protection system for the existing tunnel group's anti-heave and foundation pit support, consisting of a horizontal pipe curtain, a first grouting anchor, a second grouting anchor, an anti-buoyancy anchor, a transverse connecting beam, a longitudinal connecting beam, an anti-heave cover plate, and a cement mixing pile wall. In step S3: The horizontal pipe curtain is set horizontally in the first grouting reinforcement zone above the tunnel, and grouting holes are opened on the pipe wall to perform horizontal grouting in the first grouting reinforcement zone; The first grouting anchor is located on the axis of the second grouting reinforcement zone, and grouting is performed on the second grouting reinforcement zone; The second grouting anchor is located on the central axis of the third grouting reinforcement zone, and grouting is carried out in the third grouting reinforcement zone; The transverse and longitudinal connecting beams are connected to form a transverse and longitudinal intersecting connecting beam, which connects several first grouting anchors and anti-buoyancy anchors on the same transverse direction into one piece; The second grouting anchor is located at the geometric center of the area enclosed by the transverse connecting beam and the longitudinal connecting beam; A heave-prevention cover plate is cast in place above the transverse and longitudinal connecting beams, and a pre-reserved steel bar A is embedded in the heave-prevention cover plate; the cement mixing pile wall is located outside the tunnel group, with two cement mixing pile walls on each side, and the space between the two cement mixing pile walls forms a pipe curtain working shaft, with both ends of the horizontal pipe curtain extending into the pipe curtain working shaft. S4, layered, segmented, and sectioned excavation method for unloading the soil overlying the foundation pit of the tunnel group; S5, Prediction and control of uplift deformation of existing tunnel groups.

2. The method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups as described in claim 1, characterized in that, In step S2, the grouting reinforcement of the strata surrounding the tunnel group is carried out in the following order: second grouting reinforcement zone, first grouting reinforcement zone, and third grouting reinforcement zone.

3. The method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups as described in claim 1, characterized in that, In step S3, during horizontal pipe curtain grouting, the grouting is carried out simultaneously from the middle of the pit to both sides along the length L2 of the pit, with skip grouting on the same side.

4. The method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups according to claim 1, characterized in that, The first grouting anchor, the second grouting anchor, and the anti-buoyancy anchor are equipped with steel strands.

5. The method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups as described in claim 1, characterized in that, In step S4: The layered, strip-segmented, and segmented excavation method vertically divides the soil overlying the tunnel group into N layers, where N is 2 to 6 layers, and each layer is 3 to 5 meters thick, with the layer thickness gradually decreasing from top to bottom; It is divided horizontally into M sections, where M is the same as the number of tunnels K. The pit is longitudinally divided into O segments, with O being segments 2 to 6. The width of a single excavation along the direction perpendicular to the existing tunnel shall not exceed L2 / 8. When it exceeds L2 / 8, the width of a single excavation shall be twice the inner diameter of the tunnel.

6. The method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups according to claim 5, characterized in that, The excavation sequence in step S4 must meet the following principles: At the same location on the same plane, the upper layer is excavated first, followed by the lower layer; When dividing the tunnel into sections, first excavate the section above the tunnel with the greater burial depth, and then excavate the section above the tunnel with the lesser burial depth. The section is divided longitudinally, and different sections on the same layer and the same strip are excavated in a longitudinal skip-slot manner. Strictly control the excavation sequence in the transverse direction, and excavate symmetrically; Different layers, strips, and sections are excavated in the order of first layering, then striping, and finally sectioning.

7. The method for controlling ground uplift during excavation and unloading of overlying strata in existing multi-line parallel tunnel groups according to claim 4, characterized in that, In step S5: The allowable heave deformation limit at the bottom of the foundation pit is δ, which is determined according to the protection level of the foundation pit and tunnel, and is 20~40mm. When the actual uplift deformation value at the bottom of the foundation pit reaches 0.6δ, a yellow warning is issued, and the uplift deformation is controlled by applying prestress through the steel strands in the anti-buoyancy anchor. When the actual heave deformation value at the bottom of the foundation pit reaches 0.8δ, an orange warning is issued. Prestress is applied to the steel strands in the first grouting anchor, the second grouting anchor, and the anti-buoyancy anchor to control the heave deformation. When the actual heave deformation value at the bottom of the foundation pit exceeds 0.95δ, a red alert is triggered. Heave deformation is controlled by applying prestress through steel strands, and dewatering or temporary surcharge methods are also used to control heave deformation.

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