Large-diameter shield tunnel portal end wall and construction method thereof

Abstract

The invention discloses a large-diameter shield tunnel portal end wall and a construction method thereof. The technical problems that a cast-in-place concrete tunnel portal wall of a traditional embedded sealing system is complex to construct, and the quality of the tunnel portal wall and the reliability of the sealing system are poor are mainly solved. A traditional cast-in-place concrete tunnel portal end wall is replaced by the profile steel wall body of the profile steel frame structure, the structural rigidity and integrity of the profile steel wall body are far better than those of traditional cast-in-place concrete, and therefore it is ensured that water and soil pressure and shield thrust can be effectively resisted, structural deformation is restrained, and then the tunnel portal sealing effect can be achieved; and reliable support is provided for the tunnel portal sealing based on the concrete base, and the problem that the tunnel portal sealing loses efficacy due to vertical displacement or deformation caused by the influence of external water and soil pressure, construction loads and the like is effectively solved through the rigidity and strength of the concrete base.

Description

Technical Field

[0001] This invention relates to the field of shield tunnel technology, specifically to a large-diameter shield tunnel portal end wall and its construction method. Background Technology

[0002] In shield tunnel engineering, especially large-diameter shield tunnel engineering, the portal wall, as a key transitional structure connecting the shield shaft and the tunnel, has the core function of providing accurate guidance for the safe launch and reception of the shield machine and ensuring the reliable sealing of the transition section.

[0003] Currently, the industry commonly uses cast-in-place reinforced concrete structures as the main form of portal walls (e.g., the reinforced concrete portal wall disclosed in publication number CN113944480A). However, the inventors have discovered through long-term engineering practice that: In terms of construction technology, the traditional cast-in-place concrete portal wall construction process is complex, time-consuming, and difficult to control in terms of quality. Concrete portal wall construction requires a series of wet operations on-site, including surveying and setting out, rebar tying, complex formwork erection, concrete pouring, and curing. This not only places high demands on the workspace and management coordination capabilities of the construction site, but the entire construction cycle is also constrained by factors such as ambient temperature and concrete setting and hardening time.

[0004] Regarding the installation accuracy of key components, traditional cast-in-place concrete portal walls incorporate portal sealing systems (such as steel rings and rubber sheets) as embedded parts, installed simultaneously with the concrete wall. During concrete pouring and vibration, the heavy embedded steel rings are highly susceptible to displacement, deflection, or settlement due to the impact of concrete flow and vibration. Even with temporary fixing measures, the final positioning accuracy cannot be absolutely guaranteed. This unavoidable installation deviation will directly lead to misalignment between the tunnel boring machine's outer shell and the portal sealing system during launch / reception, potentially causing accelerated wear of the seals or even seal failure and leakage risks.

[0005] Furthermore, regarding the structural stress system, in traditional pre-embedded sealing systems, the cast-in-place concrete portal wall bears all the water and soil pressure and shield tunneling load, which is directly transmitted and entirely absorbed by the cast-in-place concrete portal wall itself. This rigid connection makes the stress state of the sealing steel ring exceptionally complex. Any local deformation of the concrete wall (such as uneven settlement, temperature shrinkage, or external compression) will directly act on the sealing steel ring, causing it to undergo irreversible torsion or deformation. Once the steel ring deforms, the sealing rubber curtain on it cannot form a uniform and tight fit with the shield machine shell or tunnel segments, thus significantly reducing the reliability of the sealing system.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the background technology of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] In view of at least one of the above technical problems, this disclosure provides a large-diameter shield tunnel portal end wall and its construction method, which mainly solves the technical problems of cumbersome construction of cast-in-place concrete portal walls of traditional pre-embedded sealing systems and poor quality of portal walls and reliability of sealing systems.

[0008] According to one aspect of this disclosure, a large-diameter shield tunnel portal end wall is provided, comprising a steel wall body with a steel frame structure fixed relative to the foundation pit retaining structure, a portal seal fixed to the outside of the steel wall body with its corresponding central axis coinciding with the tunneling axis of the shield machine, a support member supported between the steel wall body and the foundation pit bottom plate and / or the foundation pit retaining structure, and a concrete base disposed on the foundation pit bottom plate at a position corresponding to the bottom of the portal seal for supporting the portal seal; the portal seal includes a sealing steel ring of a certain length with its corresponding end fixedly connected to the steel wall body, a sealing brush, a curtain, and a pressure plate disposed on the inner edge of the sealing steel ring; a waterstop plate perpendicular to the end face of the steel wall body is provided at the corresponding end face of the steel wall body near the foundation pit retaining structure; and a mortar layer is provided between the steel wall body and the foundation pit retaining structure.

[0009] In some embodiments of this disclosure, the steel wall includes an annular beam matching the diameter of the tunnel boring machine, frame beams disposed around the annular beam, and reinforcing beams connecting adjacent frame beams; the center of the annular beam coincides with the tunneling axis of the tunnel boring machine; and the exposed surface of the steel wall is correspondingly enclosed with steel plates.

[0010] In some embodiments of this disclosure, the support member is supported at the lower middle part of the steel wall; the top of the steel wall is connected to the anchor bolt of the foundation pit retaining structure.

[0011] In some embodiments of this disclosure, the thickness of the mortar layer is greater than the height of the waterstop plate perpendicular to the end face of the steel wall; the mortar layer is provided with a reinforcing mesh.

[0012] In some embodiments of this disclosure, the width of the concrete base matches the gauge width of the steel rails of the tunnel boring machine launching platform; the bottom of the steel wall is correspondingly embedded in the concrete base.

[0013] According to another aspect of this disclosure, a method for constructing a large-diameter shield tunnel portal end wall is provided, comprising the following steps: (1) Construct a foundation slab with a sinking section near the tunnel entrance in the foundation pit; and select the appropriate steel material for the steel wall after calculating the stress on the tunnel entrance end wall according to the shield machine diameter, starting position, tunnel depth and shield starting pressure. (2) The contact surface of the foundation pit retaining structure corresponding to the steel wall is roughened and smoothed, and then flushed with high pressure water; (3) After the steel wall is assembled, welded and verified at the ground, it is hoisted down into the well as a whole and placed at the sinking section of the foundation pit bottom plate; (4) Use support members to fix the steel wall to the foundation pit bottom plate; and use chemical anchors at the top of the steel wall to fix it to the foundation pit retaining structure; (5) After setting the reinforcing mesh between the steel wall and the foundation pit retaining structure, foaming agent is applied at the inner and outer positions where the steel wall and the foundation pit retaining structure are in contact, and a grouting port is left at the top position to form the grouting cavity of the mortar layer; micro-expansion self-compacting mortar is injected into the grouting cavity through the grouting port. (6) After the door seal is assembled and welded at the ground, the whole structure is hoisted down into the well and fixedly connected to the steel wall with bolts. (7) A template is set up at the bottom of the sealing steel ring and grouting and vibration holes are opened at the corresponding positions of the sealing steel ring to carry out grouting and vibration pouring of the concrete base; (8) Apply sealant to the edge of the steel wall that is in contact with the foundation pit retaining structure.

[0014] In some embodiments of this disclosure, in step (3), before the steel wall is lowered into the well, several positioning steel plates with coplanar end faces are set at the foundation pit retaining structure, and based on the anchor points set at the foundation pit retaining structure and / or the foundation pit bottom plate, the position of the steel wall is adjusted by hand-operated / electric hoist to fit with each of the positioning steel plates.

[0015] In some embodiments of this disclosure, in step (6), after the portal seal is assembled and welded and before it is lowered into the well, a temporary inner support is welded, and the temporary inner support is removed after the sealing steel ring is fixedly connected to the steel wall.

[0016] One or more technical solutions provided in the embodiments of this application have at least one of the following technical effects or advantages: 1. The steel frame structure of the steel wall replaces the traditional cast-in-place concrete portal end wall. Its structural rigidity and integrity are far superior to traditional cast-in-place concrete, thus ensuring effective resistance to water and soil pressure and shield thrust, and suppressing structural deformation. This, in turn, helps the portal seal to achieve its sealing effect and prevents the portal seal from failing due to deformation of the end wall body.

[0017] 2. By installing a waterstop plate on the end face of the steel wall and setting a mortar layer between the steel wall and the foundation pit retaining structure, an effective joint seal can be formed, thereby eliminating leakage channels; at the same time, the mortar layer is used to establish a load transfer path between the steel wall and the foundation pit retaining structure, ensuring the overall stability of the portal end wall.

[0018] 3. The concrete base provides reliable support for the tunnel portal seal, and its own rigidity and strength effectively prevent the tunnel portal seal from failing due to vertical displacement or deformation caused by external water and soil pressure and construction loads. Attached Figure Description

[0019] Figure 1 This is a longitudinal sectional side view of a portion of the shield wall structure of a large-diameter shield tunnel entrance in one embodiment of this application.

[0020] Figure 2 This is a cross-sectional front view of a portion of the shield wall structure of a large-diameter shield tunnel entrance in one embodiment of this application.

[0021] Figure 3 This is a schematic diagram of the mortar layer configuration in one embodiment of this application.

[0022] Figure 4 This is a physical diagram of the support components during actual construction in one embodiment of this application.

[0023] Figure 5 This is a schematic diagram of the positioning steel plate in one embodiment of this application.

[0024] Figure 6 This is a schematic diagram illustrating the application of the mortar layer in one embodiment of this application.

[0025] In the above figures, 10 is the diaphragm wall, 11 is the foundation pit bottom slab, 2 is the steel wall, 21 is the ring beam, 22 is the frame beam, 23 is the reinforcing beam, 3 is the mortar layer, 4 is the waterstop plate, 5 is the portal seal, 51 is the sealing steel ring, 52 is the sealing brush, 53 is the pressure plate, 54 is the curtain, 6 is the support component, 61 is the diagonal brace, 62 is the cross brace, 63 is the anchor bolt, 7 is the concrete base, and 8 is the expanding foam. Detailed Implementation

[0026] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inner", "outer", "vertical", "horizontal", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0027] To better understand the technical solution of this application, the above technical solution will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] The inventors of this application have discovered through long-term engineering practice that traditional cast-in-place concrete portal walls require a series of complex construction processes on-site, including surveying and setting out, rebar tying, and concrete pouring. This results in long construction periods and significant challenges in controlling the quality of the concrete. Furthermore, during the pouring of traditional concrete portal walls, portal seals are typically pre-embedded before pouring. However, during the pouring and vibration of concrete, the heavy pre-embedded portal seals are prone to displacement, deflection, or settlement due to the impact of concrete flow and vibration, potentially leading to seal failure during the launch or reception of the tunnel boring machine (TBM). Additionally, the steel ring extending from the concrete portal wall during TBM launch or reception is at risk of deformation, which can also cause seal failure. To address these issues, this application discloses a large-diameter TBM portal end wall, specifically comprising a steel wall body, a portal seal, supporting components, and a concrete base.

[0029] For details, see Figure 1 and Figure 2 To address the technical problems of complex construction and potential seal failure risks associated with traditional cast-in-place concrete portal walls, the inventors abandoned the traditional approach of modifying concrete portal wall structures and instead directly constructed steel-framed portal walls. This new approach avoids the reliability issues inherent in cast-in-place concrete portal walls. In this embodiment, the large-diameter shield tunnel portal end wall comprises a steel-framed wall 2, which is a load-bearing unit composed of steel profiles connected by high-strength bolts or welding. In some embodiments, the steel profiles used in the steel wall 2 are configured in double or triple layers, forming a composite steel structure with high bending and shear resistance. This ensures that the steel wall, after being stably installed close to the foundation pit retaining structure (specifically, the diaphragm wall 10 in this example), can effectively resist external soil and water pressure loads, fundamentally eliminating the risk of portal seal failure due to wall deflection or deformation, and ensuring the structural stability and reliability of the portal end wall.

[0030] In this embodiment, see Figure 2The steel wall 2 is specifically a spatial frame structure assembled from various modular beam units, including a ring beam 21, frame beams 22, and reinforcing beams 23. Specifically, the inner diameter of the ring beam 21 matches the outer diameter of the tunnel boring machine (TBM), and the center of the ring beam 21 coincides with the TBM's tunneling axis, serving as a positioning and load-bearing component for the TBM's tunneling, bearing the penetration or ejection loads. Each frame beam 22 is evenly distributed along the outer perimeter of the ring beam 21, forming a rigid outer frame that surrounds the ring beam 21. The contact nodes between each frame beam 22 and the ring beam 21 are reliably connected through full welding or other methods, forming the main load transfer path and evenly distributing the load borne by the ring beam 21 outwards. In this example, a reinforcing beam 23 is provided diagonally between adjacent frame beams 22. In order to improve the reliability of the load, the reinforcing beam 23 is also connected to the ring beam, thereby enhancing the shear and torsional stiffness of the entire steel wall 2, preventing the steel wall 2 from deforming under asymmetrical loads, and ensuring the geometric stability of the overall steel frame structure. Furthermore, after the steel wall 2 is installed and fixed, the side away from the foundation pit retaining structure, i.e., the diaphragm wall, is an open surface. In this embodiment, a steel plate is fixed to the frame formed by the combination of the ring beam 21, each frame beam 22, and the reinforcing beam 23 at the open surface of the steel wall 2 through continuous welding or high-strength bolt connection. This steel plate can work together with the steel frame behind it to form a composite steel frame structure with extremely high in-plane stiffness, thereby effectively ensuring the stability and reliability of the steel wall. This breaks the technical prejudice of most technicians that the stiffness and reliability of steel structures cannot replace the traditional reinforced concrete structure portal end wall. By using the high-strength and high-stiffness composite frame structure steel wall, a reliable structural foundation is provided for the safe and accurate launch and reception of the tunnel boring machine.

[0031] In practical engineering, the surface of the foundation pit retaining structure, such as the diaphragm wall 10 in this example, is uneven. In this example, when a steel wall is used instead of a traditional cast-in-place concrete portal wall, the uneven diaphragm wall prevents the steel wall 2 from making effective contact with the diaphragm wall 10. This results in the load at the steel wall 2 not being effectively transferred and diffused to the diaphragm wall, a problem that does not need to be considered with traditional cast-in-place concrete portal walls. Therefore, when the portal wall is poured in close contact with the diaphragm wall, the uneven diaphragm wall actually improves the reliability of the connection between the cast-in-place concrete portal wall and the diaphragm wall. Therefore, in this embodiment, see... Figure 1 and Figure 3A mortar layer 3 with a thickness of 5-10cm is set between the steel wall 2 and the foundation pit retaining structure, i.e., the diaphragm wall. This mortar layer is specifically made of high-strength micro-expansion self-compacting mortar with a strength of over 40MPa. Utilizing the good fluidity and plasticity of the mortar during injection, it fills the irregular gaps and pits between the back of the steel section and the uneven end face of the diaphragm wall, achieving close contact between the steel wall and the diaphragm wall. This transforms the originally discrete and uneven point or line contact into a uniform surface contact, avoiding stress concentration caused by the uneven surface of the diaphragm wall. Thus, the mortar layer buffers and evenly distributes the compressive and shear stresses transmitted from the steel wall to the diaphragm wall.

[0032] Furthermore, in this embodiment, considering that the portal structure is filled with pressurized slurry during the shield tunneling phase, although the mortar layer can effectively fill the gap between the steel wall and the diaphragm wall, the relatively smooth surface of the steel means that the bonding interface between the mortar layer and the steel is at risk of peeling and developing micro-cracks under long-term pressure fluctuations, thus forming a pressure leakage channel. To ensure the sealing of the connection between the steel wall and the diaphragm wall, see [reference needed]. Figure 3 In this example, several waterstop plates 4, perpendicular to the end face of the steel wall 2 and located near the foundation pit retaining structure, are installed circumferentially. Each waterstop plate 4 is welded to the steel wall 2 as a whole, using steel plates with a thickness of 3-10mm for full welding. Thus, after the mortar layer is poured and formed, each waterstop plate 4 is tightly embedded in the mortar layer, forming a physical water barrier, effectively switching the possible water seepage path along the contact surface. Therefore, even in extreme cases where the mortar layer peels off from the surface of the steel wall, the slurry pressure during shield tunneling (…) Figure 3 The leakage path (from the arrow position below the steel section) will also be effectively blocked by the waterstop plate 4, thus ensuring the sealing safety of the tunnel portal connection in the complex stress and muddy environment of shield tunneling.

[0033] To ensure the waterstop 4 effectively prevents water leakage, the mortar layer in this example is thicker than the waterstop's extension height perpendicular to the steel wall end face. This ensures the mortar layer 3 completely covers the waterstop 4, anchoring it within the mortar layer. This creates a more integrated composite waterstop system, preventing the waterstop 4's end face from directly contacting the diaphragm wall end face. Furthermore, a steel mesh is incorporated within the mortar layer 3, further enhancing its crack resistance and shear strength.

[0034] In this embodiment, see Figure 1On the outer side of the steel wall 2, a portal seal 5 is fixedly installed, with its central axis coinciding with the designed tunneling axis of the tunnel boring machine (TBM). This ensures that the TBM cutterhead and shield body can smoothly pass through the pit while reliably isolating the water and soil outside the pit during the TBM's launch or reception process. Specifically, in this example, the portal seal includes a sealing steel ring 51, which serves as the core support and load-bearing body. The sealing steel ring 51 has a certain length, and its side near the steel wall 2 is reliably fixed to the steel wall by high-strength bolts. In addition, on the inner edge of the sealing steel ring 51, multiple sealing elements, including a curtain 54, a pressure plate 53, and a sealing brush 52, are sequentially arranged along the tunneling direction of the TBM. The curtain 54, pressure plate 53, and sealing brush 52 are conventional sealing elements for portal seals in this field and will not be described in detail in this example.

[0035] To ensure the stable fixing of the steel wall, in this embodiment, several support members are installed for supporting and positioning the steel wall. Specifically, in this embodiment, see... Figure 2 A support member 6 is installed at the lower-middle position of the outer side of the steel wall to fix the steel wall in place. One end of the support member is fixedly connected to the end face of the steel wall, and the other end is supported by the completed foundation pit bottom slab or foundation pit retaining structure, thereby providing effective support, preventing the steel wall from tilting under stress, and sharing the load borne by the wall during the shield tunneling launch or receiving phase. See also... Figure 1 In this example, the supporting components include diagonal braces 61 and counter-braces 62. Diagonal braces 61 are positioned between the end face of the steel wall and the top of the foundation pit slab, while counter-braces 62 are positioned between the end face of the steel wall and the end face of the foundation pit slab, thus providing multi-directional fixed support for the steel wall. In some other embodiments, side braces are also provided between the side of the steel wall and the foundation pit retaining structure. See also... Figure 4 In this example, steel plates are welded to the ends of the diagonal braces or parallel braces, and the steel plates are fixed to the corresponding end faces of the pit bottom plate by expansion bolts, thereby achieving a reliable connection and fixation between the support components and the pit bottom plate.

[0036] In addition, considering that it is impossible to effectively install support components at the top of the steel wall, in order to achieve relative fixation between the steel wall and the diaphragm wall, see [reference needed]. Figure 3 In this example, anchor bolts 63 are installed at the top of the steel wall to achieve an anchored connection between the steel wall and the diaphragm wall. Specifically, chemical anchor bolts are used in this example, with a diameter of 20–40 mm and a spacing of 300–600 mm.

[0037] Traditional cast-in-place concrete portal seals embedded in tunnel portal walls are prone to structural deformation under vertical loads. To ensure the portal seals remain structurally stable and free from deformation during shield tunneling launch or reception, this embodiment refers to... Figure 1 and Figure 2A concrete base 7 is installed at the bottom of the sealing steel ring 51 of the tunnel portal seal. The concrete base 7 is poured at the bottom slab of the foundation pit. Through the tight contact between the concrete base 7 and the sealing steel ring 51, the sealing steel ring of the tunnel portal is directly supported. Utilizing its own rigidity and strength, it effectively prevents the tunnel portal seal from failing due to vertical displacement or deformation caused by external water and soil pressure and construction loads. It also distributes the load borne to a larger area of ​​the foundation pit bottom slab. At the same time, the concrete base 7 provides a stable bottom reference for the entire tunnel portal seal, ensuring the alignment of the tunnel portal seal axis with the shield tunneling axis. In addition, in this embodiment, the width of the concrete base 7 is matched with the gauge width of the steel rails of the shield machine launching platform, thereby enabling the concrete base 7 to support the launching platform rails. In this example, the concrete base 7 is constructed by pouring concrete, thereby encasing and embedding the bottom steel beam of the steel wall into the concrete base 7, improving the stress reliability of the concrete base 7 and forming a stable and reliable stress node.

[0038] This example also discloses a method for constructing a large-diameter shield tunnel portal end wall, which specifically includes the following steps: (1) Considering that the diameter of the portal seal is larger than that of the tunnel boring machine, a sinking section is set on the side of the foundation pit bottom plate near the portal to facilitate the subsequent installation of the portal seal. Based on parameters such as the diameter of the tunnel boring machine, the starting position, the tunnel depth, and the maximum water and soil pressure and construction load that the tunnel boring machine may bear during the starting or receiving, the design internal forces such as the maximum bending moment, shear force and axial force required by the portal end wall under the most unfavorable working conditions are calculated. Based on the mechanical analysis results, the steel material is selected for the steel wall, and the specifications and cross-sectional form of the steel material are specifically determined.

[0039] (2) In order to improve the bonding strength and integrity between the mortar and the foundation pit retaining structure in the subsequent mortar layer grouting process, a cavity is installed in the steel wall in this example. The contact area between the foundation pit retaining structure and the steel wall is roughened and smoothed, and high-pressure water is used to wash away the dust, debris, oil and other impurities attached to the surface to ensure that the interface is clean. This helps to bond the mortar layer and the foundation pit retaining structure, thereby ensuring the effective transfer of load through the bonding surface.

[0040] (3) On the ground area of ​​the construction site, the prefabricated steel wall is assembled and welded as a whole according to the design drawings and requirements. After the assembly is completed, the overall structural dimensions, flatness, verticality and the accuracy of the center position of the ring beam are checked. After confirming that the design requirements are met, the hoisting operation is carried out.

[0041] Because the surface of the foundation pit retaining structure is uneven, and a gap needs to be left between the steel wall and the foundation pit retaining structure to allow for the injection of expanding mortar to form a mortar layer, in order to ensure that the assembled and welded steel wall can be accurately and reliably positioned after being lowered into the well, in this example, before the steel wall is hoisted and lowered into the well as a whole, see [reference needed]. Figure 5 Several positioning steel plates are pre-installed on the predetermined contact surface of the foundation pit retaining structure, and the position of each positioning steel plate is verified by a total station to ensure that the end faces of each positioning steel plate are coplanar. Thus, after the steel wall is hoisted into the well as a whole, the corresponding end faces of the steel wall are adjusted to make close contact with each positioning steel plate and welded and fixed, so that the position of the steel wall can be accurately positioned and its central axis can be ensured to coincide with the tunneling axis of the shield machine.

[0042] Then, using large lifting equipment, the qualified steel wall is smoothly hoisted into the well and its bottom is placed in the sinking section of the foundation pit floor. Considering that the steel wall is relatively heavy, it is difficult to adjust its position manually when hoisting it into the well as a whole. Therefore, in this embodiment, before the steel wall is lowered into the well, anchor points are set at the foundation pit retaining structure or foundation pit floor. Hand-operated / electric hoists are then used to hang the anchor points to achieve fine adjustment of the position of the steel wall, so that its end face fits with the end face of each positioning steel plate.

[0043] (4) The steel wall is hoisted into the well and finely adjusted to fit the positioning steel plate. After verifying the accuracy of the steel wall's position by measurement, the steel wall is welded and fixed to each positioning steel plate. Then, each support component is installed to fix the steel wall relative to the pit bottom plate and / or the pit retaining structure. Then, anchor bolts are installed on the top of the steel wall. Specifically, in this embodiment, when installing the anchor bolts, anchor holes are first drilled with an electric drill, and these anchor holes penetrate deep into the pit retaining structure; then, after pressing anchoring agent into the anchor holes, chemical anchor bolts are installed. Thus, through the combined action of each support component and the anchor bolts, reliable fixing between the steel wall and the pit retaining structure is achieved.

[0044] (5) After the steel wall is positioned, apply the mortar layer.

[0045] Specifically, in this embodiment, after the steel wall is positioned, the wire mesh is cut and bent, and then stuffed into the gap between the steel wall and the foundation pit retaining structure as reinforcement in the mortar layer. The bent wire mesh is arranged so that both ends rub against the steel wall and the foundation pit retaining structure, thereby increasing the strength of the mortar layer. After the reinforcement mesh is installed, see... Figure 6Foaming agent is applied to the inner and outer edges of the gap between the steel wall and the foundation pit retaining structure to create a lateral seal. Simultaneously, a grouting port is pre-installed at the top of the gap, thus constructing a closed grouting cavity between the steel wall and the foundation pit retaining structure, with a pre-installed grouting port at the top and sealed sides. Micro-expansion self-compacting mortar is then injected into the grouting cavity through the pre-installed grouting port using a pressure grouting process. Under its own weight and injection pressure, the mortar flows evenly upwards from the bottom of the cavity, automatically and densely encapsulating the internal reinforcement mesh and filling the entire cavity space, forming a mortar layer.

[0046] (6) Assemble and weld the portal seal at ground level to form an integral unit. To ensure that the thin-walled annular structure does not deform during hoisting and installation, in this example, after welding is completed and before hoisting it into the well, a rigid temporary internal support is welded inside the sealing steel ring. This support can be a cross-shaped or grid-shaped structure to ensure that the sealing steel ring maintains its precise circularity and design dimensions. Then, the reinforced portal seal is hoisted into the well as a whole, and the portal seal is fixedly connected to the steel wall with bolts. Then, the temporary internal support is removed.

[0047] (7) To support the sealing steel ring, a concrete base is poured at the bottom of the sealing steel ring. Specifically, a formwork is first erected at the bottom of the foundation pit slab at the bottom of the sealing steel ring, and the sealing steel ring is used as the top formwork for pouring. Then, holes are cut at the inner arc surface of the sealing steel ring as grouting and vibration holes for subsequent grouting, vibration, and observation. After the concrete base is erected, concrete is pumped using a boom pump to pour the concrete base, and the compaction of the concrete is checked by vibration through the grouting and vibration holes.

[0048] (8) Apply sealant to the circumferential edge area where the steel wall and the foundation pit retaining structure finally meet, so as to seal the exposed interface of the joint and enhance the joint's ability to resist liquid water penetration.

[0049] The large-diameter shield tunnel portal end wall and its construction method proposed in this application can save more than 80 days of construction time compared with traditional concrete end walls. Moreover, the steel wall can be recycled after demolition, which greatly reduces the construction cost of the portal end wall.

[0050] Although some preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0051] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this application and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A large-diameter shield tunnel portal end wall, characterized in that, It includes a steel wall with a steel frame structure that is fixed relative to the foundation pit retaining structure, a portal seal fixed to the outside of the steel wall and whose corresponding central axis coincides with the tunneling axis of the tunnel boring machine, a support member that supports the steel wall between the foundation pit bottom plate and / or the foundation pit retaining structure, and a concrete base located on the foundation pit bottom plate at the position corresponding to the bottom of the portal seal and used to support the portal seal. The portal seal includes a sealing steel ring of a certain length with its corresponding ends fixedly connected to the steel wall, a sealing brush, a curtain, and a pressure plate located on the inner edge of the sealing steel ring. A waterstop plate perpendicular to the end face of the steel wall is provided at the corresponding end face of the foundation pit retaining structure; a mortar layer is provided between the steel wall and the foundation pit retaining structure.

2. The large-diameter shield tunnel portal end wall according to claim 1, characterized in that, The steel wall includes a ring beam that matches the diameter of the tunnel boring machine, frame beams around the ring beam, and reinforcing beams connecting adjacent frame beams; the center of the ring beam coincides with the tunneling axis of the tunnel boring machine; and the exposed surface of the steel wall is correspondingly enclosed with steel plates.

3. The large-diameter shield tunnel portal end wall according to claim 1, characterized in that, The support member is positioned at the lower middle part of the steel wall; the top of the steel wall is connected to the foundation pit retaining structure by anchor bolts.

4. The large-diameter shield tunnel portal end wall according to claim 1, characterized in that, The thickness of the mortar layer is greater than the height of the waterstop plate perpendicular to the end face of the steel wall; the mortar layer is provided with a reinforcing mesh.

5. The large-diameter shield tunnel portal end wall according to claim 1, characterized in that, The width of the concrete base matches the gauge width of the steel rails of the tunnel boring machine's launching platform; the bottom of the steel wall is correspondingly embedded in the concrete base.

6. A method for constructing the portal end wall of a large-diameter shield tunnel, characterized in that, The method for constructing the large-diameter shield tunnel portal end wall as described in claim 1 includes the following steps: (1) Construct a foundation slab with a sinking section near the tunnel entrance in the foundation pit; and select the appropriate steel material for the steel wall after calculating the stress on the tunnel entrance end wall according to the shield machine diameter, starting position, tunnel depth and shield starting pressure. (2) The contact surface of the foundation pit retaining structure corresponding to the steel wall is roughened and smoothed, and then flushed with high pressure water; (3) After the steel wall is assembled, welded and verified at the ground, it is hoisted down into the well as a whole and placed at the sinking section of the foundation pit bottom plate; (4) Use support members to fix the steel wall to the foundation pit bottom plate; and use chemical anchors at the top of the steel wall to fix it to the foundation pit retaining structure; (5) After setting the reinforcing mesh between the steel wall and the foundation pit retaining structure, foaming agent is applied at the inner and outer positions where the steel wall and the foundation pit retaining structure are in contact, and a grouting port is left at the top position to form the grouting cavity of the mortar layer; micro-expansion self-compacting mortar is injected into the grouting cavity through the grouting port. (6) After the door seal is assembled and welded at the ground, the whole structure is hoisted down into the well and fixedly connected to the steel wall with bolts. (7) A template is set up at the bottom of the sealing steel ring and grouting and vibration holes are opened at the corresponding positions of the sealing steel ring to carry out grouting and vibration pouring of the concrete base; (8) Apply sealant to the edge of the steel wall that is in contact with the foundation pit retaining structure.

7. The application method according to claim 6, characterized in that, In step (3), before the steel wall is lowered into the well, several positioning steel plates with coplanar end faces are set at the foundation pit retaining structure. Based on the anchor points set at the foundation pit retaining structure and / or the foundation pit bottom plate, the position of the steel wall is adjusted by hand-operated / electric hoist to fit with each of the positioning steel plates.

8. The application method according to claim 6, characterized in that, In step (6), after the portal seal is assembled and welded, a temporary inner support is welded in place before the shaft is lowered, and the temporary inner support is removed after the sealing steel ring is fixedly connected to the steel wall.

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