A straight wall section tunnel connection plate-free integral arch construction method

Abstract

The application provides a straight wall section tunnel connection plate-free integral arch construction method, and belongs to the technical field of arch construction. The application implements bidirectional limiting and accurate positioning of the integral connection plate-free new arch by arranging a prefabricated positioning jig frame on the inner wall of the full-section floor inverted arch protection arch. The short stiffening rib is pre-welded according to the local stability prediction scheme of the I-beam web to eliminate the web buckling hidden danger. The segmented symmetrical jump welding process is adopted to complete the welding of the channel steel connecting rib, and the accumulated torsion angle of the integral connection plate-free new arch is controlled within 0.5°. The thin layer spraying process is adopted to complete the initial support sprayed concrete, and the residual cavity is filled with cement-water glass double-liquid slurry by supplementing injection through the reserved injection short pipe. The technical problem that the positioning accuracy and the structural overall stability of the straight wall section tunnel connection plate-free integral arch cannot be guaranteed due to the lack of lateral constraint in the installation process is solved.

Description

Technical Field

[0001] This invention belongs to the field of arch frame construction technology, and more specifically, relates to a method for constructing an integral arch frame without connecting plates in a straight-wall section tunnel. Background Technology

[0002] The initial support arch replacement construction in straight-wall tunnel sections is a crucial technical method for handling initial support encroachment in tunnel engineering. Traditionally, the support system is constructed using segmented arch frames with connecting plates, and the arch frames are installed gradually through segmental assembly and bolt connections. In current straight-wall tunnel arch replacement construction, the arch frames are typically fabricated in sections and assembled inside the tunnel. The connecting plates serve as the interface between adjacent segments, relying on the frictional contact between the arch waist and the rock wall to provide lateral restraint, thereby ensuring the positioning stability of the entire arch frame during installation.

[0003] However, when the arch replacement area is in a straight wall section, the wall surface is vertical and there is no arch waist. The lateral stability mechanism of the traditional segmented arch frame with connecting plates, which relies on the friction constraint of the curved surface, completely fails during the assembly process. This makes the integral arch frame without connecting plates prone to out-of-plane overturning and lateral displacement during the erection process. At the same time, the contact area at the bottom of the arch foot in the straight wall section is small, and the concentrated load far exceeds the design uniform distribution value. Under the condition of weak surrounding rock, the risk of punching shear failure of the arch foot increases significantly. In addition, the wedging force transmission state between the arch support and the surrounding rock cannot be quantified, the local buckling hazard of the I-beam web under concentrated load is difficult to identify in advance, and the filling density of the shotcrete in the narrow cavity is also difficult to guarantee.

[0004] In existing technologies, due to the lack of curved arch waist friction supports in straight wall sections, integral arch frames without connecting plates cannot achieve precise positioning during installation using traditional lateral constraint mechanisms. This leads to positioning deviations exceeding the design allowable range, resulting in a series of chain problems such as decreased welding quality and instability of the initial support structure. In other words, existing technologies present a technical problem where integral arch frames without connecting plates in straight wall tunnels cannot guarantee positioning accuracy and overall structural stability during installation due to the lack of lateral constraints. Summary of the Invention

[0005] In view of this, the present invention provides a construction method for an integral arch frame without connecting plates in a straight-wall section tunnel, which can solve the technical problem in the prior art that the integral arch frame without connecting plates in a straight-wall section tunnel cannot guarantee positioning accuracy and overall structural stability due to the lack of lateral constraints during installation.

[0006] This invention is implemented as follows: This invention provides a construction method for an integral arch frame without connecting plates in a straight-wall section tunnel, comprising the following steps:

[0007] Small pipe grouting reinforcement was carried out on the surrounding rock of the arch replacement area. A steel base plate was laid at the arch foot of the straight wall section. A C30 fine stone concrete leveling layer was poured under the steel base plate and the base was pre-grouted and cured to form a composite cushion layer of steel base plate and C30 fine stone concrete. The locking foot anchor plate was welded to the steel base plate to form a whole, which constitutes the arch foot support foundation of the straight wall section.

[0008] Along the two ends of the arch replacement pile number, the full-section ground-mounted inverted arch and protective arch are installed one by one towards the middle. The full-section ground-mounted inverted arch and protective arch are made of I18 I-beams. The straight wall section of the protective arch is a complete I-beam without connecting plates. A combination of wooden wedges and steel wedges is used to achieve multi-point wedging between the full-section ground-mounted inverted arch and the surrounding rock or initial support. Strain gauges are attached to the outside of the wooden wedges. The wedge compression strain value output by the strain gauges is collected in real time by a data acquisition instrument, and the wedge compression strain value is converted into the wedging contact stress. When the wedging contact stress is lower than the minimum effective force transmission wedging contact stress threshold of a single arch, steel wedges are added to increase the density, and the wedging status data of each arch is recorded in the database.

[0009] Weld a pre-positioning jig at the corresponding installation position on the inner wall of the full-section ground-supported arch. After inserting the integral new arch frame without connecting plates into the pre-positioning jig, use jacks to finely adjust the axis of the integral new arch frame without connecting plates. Combine the polar coordinate method of the total station to check the coordinates of the control points of the integral new arch frame without connecting plates in real time. After confirming that the positioning deviation of the integral new arch frame without connecting plates does not exceed the design allowable value, immediately spot weld the integral new arch frame without connecting plates to fix it temporarily, and install the foot anchor rods. The foot anchor rod support plate is welded to the steel base plate to form an integral whole.

[0010] Based on the local stability prediction scheme of the I-beam web, the stability safety factor of each section of the I-beam web of the new integral arch frame without connecting plates is calculated. For sections with a stability safety factor lower than the stability safety factor threshold, short stiffening ribs are symmetrically welded on both sides of the I-beam web. The old initial support concrete and old arch frame are removed one by one in the arch replacement area. After removing one old arch frame, the installation and temporary fixation of a new integral arch frame without connecting plates is completed immediately.

[0011] After the installation of the integral, unconnected arch frame is completed, the system anchor bolts and steel mesh are constructed. The channel steel connecting bars are welded to the rear side of the full-section ground-mounted invert arch support using a segmented symmetrical skip welding process. After welding, the reverse correction is performed using jacks. The coordinates of the control points of the integral, unconnected arch frame are monitored in real time using a total station to control the cumulative torsion angle of the integral, unconnected arch frame within the design allowable torsion angle range. After the channel steel connecting bars of two adjacent integral, unconnected arch frames are welded, the initial support shotcrete is completed using a multi-stage thin-layer spraying process. After the shotcrete is completed, cement-water glass double-liquid grout is injected into the residual cavity between the shotcrete layer and the surrounding rock through a reserved grouting short pipe. The density of the shotcrete layer is detected using ground-penetrating radar.

[0012] After the initial support shotcrete of each new monolithic arch frame without connecting plates has set and passed the cross-section test, the full-section ground-supported arch and protective arch are removed one by one from top to bottom. After removal, the arch and protective arch positions are promptly sprayed. After all the full-section ground-supported arch and protective arch are removed, the secondary lining construction is promptly carried out.

[0013] Specifically, the steel base plate and C30 fine stone concrete composite cushion layer are laid sequentially at the bottom of the arch foot of the straight wall section, with a C30 fine stone concrete leveling layer and a steel base plate with dimensions of 30×30×10mm. The base is pre-grouted and cured under the steel base plate, and the anchor rod support plate is welded to the steel base plate to form a whole.

[0014] Specifically, the pre-stress control wedge tightening scheme of the wooden wedge and steel wedge combination involves attaching strain gauges to the outside of the wooden wedges, collecting the wedge compression strain value in real time through a data acquisition instrument, and converting the wedge compression strain value into wedge tightening contact stress based on the elasticity contact theory. The minimum effective force transmission wedge tightening contact stress threshold for a single arch is not less than 0.05 MPa.

[0015] The data on the tightness of each truss is recorded in the database, which is used to guide the standardized management of subsequent construction. The data on the tightness of each truss includes the measured value of the contact stress of the tightness of each truss and the location and number of times the steel wedges are added.

[0016] The pre-positioning jig refers to a temporary steel guide groove structure pre-processed according to the cross-sectional dimensions of the integral new arch frame without connecting plates. It is welded and fixed to the corresponding installation position on the inner wall of the full-section landing arch support. After the integral new arch frame without connecting plates is inserted into the pre-positioning jig, it is subject to limiting constraints in both the out-of-plane direction and the left and right directions.

[0017] The design allowable value for the positioning deviation of the integral, unconnected new arch frame is 30mm. The coordinates of the control points of the integral, unconnected new arch frame are checked in real time using the polar coordinate method of a total station. After confirming that the positioning deviation does not exceed 30mm, temporary fixation is immediately spot welded.

[0018] The local stability prediction scheme for the web of the I-beam refers to calculating the critical compressive stress of the web of the I-beam under concentrated load using the buckling equation of elastic thin plate, and calculating the stability safety factor of each section of the web of the I-beam in combination with the measured axial force and bending moment. The threshold value of the stability safety factor is 1.5.

[0019] Among them, the short stiffening ribs are 100×8mm in size and 250mm apart. They are symmetrically welded on both sides of the web of the I-beam, which increases the stability safety factor of each section of the web of the I-beam to no less than the stability safety factor threshold of 1.5.

[0020] The segmented symmetrical skip welding process refers to the process of first completing symmetrical spot fixing on both sides and then alternately welding when welding the channel steel connecting bar to the flange of the integral new arch frame without connecting plate. The length of each weld segment does not exceed 80mm, and the welding sequence is from the middle to both ends. After welding, the integral new arch frame without connecting plate is corrected in the reverse direction using a jack.

[0021] Among them, the design allowable torsion angle range for the integral unconnected new arch frame is within 0.5°. The coordinates of the control points of the integral unconnected new arch frame are monitored in real time using a total station, and the cross-sections that exceed the design allowable torsion angle range are corrected in reverse using jacks.

[0022] The aforementioned multi-layer thin-layer spraying process refers to controlling the thickness of each sprayed layer to within 50mm during concrete spraying, and repeatedly spraying to the designed thickness. Each spraying direction is perpendicular to the sprayed rock surface, and high-pressure air is used to locally blow away air bubbles.

[0023] Among them, the reserved grouting short pipes are set on the outer side of the flange of the integral unconnected new arch frame, with a spacing of 1m. After the spraying is completed, cement-water glass double liquid grout is injected through the reserved grouting short pipes to fill the residual cavity between the sprayed layer and the surrounding rock.

[0024] The density of the sprayed layer is detected by ground-penetrating radar. The detection results are used to determine whether secondary grouting is required through the reserved grouting short pipe until the residual cavity between the sprayed layer and the surrounding rock is filled and compacted.

[0025] The demolition sequence for the full-section ground-supported arch and arch support is from top to bottom within the same truss, first the top arch and then the straight wall section. The next truss can only be demolished after the initial support shotcrete of each truss has fully set and passed the cross-section measurement.

[0026] The construction monitoring and measurement of the arch replacement area will begin 5m after the installation of the full-section ground-mounted inverted arch and protective arch. A monitoring section will be set every 5m, and 3 monitoring points will be set in each monitoring section, located at the top of the arch and the arch shoulders of the straight wall sections on both sides. The monitoring frequency will be no less than 2 times / day.

[0027] This invention implements out-of-plane and lateral bidirectional limiting of the integral, unconnected arch frame by setting a pre-positioning jig on the inner wall of the full-section landing arch support. Combined with jack fine-tuning and real-time verification of control point coordinates using a total station polar coordinate method, this mechanism replaces the traditional lateral stability mechanism relying on the friction constraint of the arch waist. This ensures the integral, unconnected arch frame remains constrained throughout the installation of the straight wall section, eliminating the physical causes of out-of-plane overturning and displacement. The invention quantifies the wedge-tightening force transmission state between the arch support and the surrounding rock into monitorable wedge-tightening contact stress through a combined wooden and steel wedge pre-pressure control wedge-tightening scheme. It also identifies and eliminates potential local buckling hazards in the web plate through a local stability prediction scheme for the I-beam steel web plate, and diffuses the concentrated load at the arch foot of the straight wall section to the deeper layers of the surrounding rock through a steel base plate and a C30 fine aggregate concrete composite cushion layer. The synergistic effect of these three elements maintains the overall stability of the support system during arch replacement from three dimensions: force transmission path, structural cross-section, and supporting foundation. In summary, the present invention solves the technical problem mentioned in the background art that the lack of lateral constraints during the installation of the integral arch frame without connecting plates in the straight wall section tunnel cannot guarantee the positioning accuracy and overall structural stability. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method of the present invention.

[0029] Figure 2 This is a schematic diagram of cross-sectional measurement and spray layer density detection in the arch replacement area.

[0030] Figure 3 This is a schematic diagram of the arch support installation.

[0031] Figure 4 A schematic diagram of the full cross-section of the arch support installation.

[0032] Figure 5 Side view of the arch installation and schematic diagram of the arch removal process. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0034] like Figure 1 The diagram shown is a flowchart of a construction method for an integral arch frame without connecting plates in a straight-wall tunnel, provided by the present invention. This method includes the following steps:

[0035] S10. Small-diameter pipe grouting reinforcement is carried out on the surrounding rock of the arch replacement area. A steel base plate with a size of 30×30×10mm is laid at the arch foot of the straight wall section. A C30 fine stone concrete leveling layer is poured under the steel base plate and the base is pre-grouted and cured to form a composite cushion layer of steel base plate and C30 fine stone concrete. The locking foot anchor plate is welded to the steel base plate to form a whole, which constitutes the support foundation of the arch foot of the straight wall section.

[0036] S20. Install full-section ground-supported inverted arches and protective arches one by one from both ends of the arch replacement pile number towards the middle. The full-section ground-supported inverted arches and protective arches are made of I18 I-beams with a spacing of 60-100cm. The arches in the straight wall section are complete I-beams without connecting plates. A pre-pressure control wedge tightening scheme using a combination of wooden wedges and steel wedges is used to achieve multi-point wedge tightening between the full-section ground-supported inverted arches and the surrounding rock or initial support. Strain gauges are attached to the outside of the wooden wedges. The wedge compression strain value output by the strain gauges is collected in real time by a data acquisition instrument, and the wedge compression strain value is converted into wedge tightening contact stress. When the wedge tightening contact stress is lower than the minimum effective force transmission wedge tightening contact stress threshold of a single arch, additional steel wedges are added to increase the density, and the wedge tightening status data of each arch is recorded in the database.

[0037] S30. Weld a pre-positioning jig at the corresponding installation position on the inner wall of the full-section landing arch support. After inserting the integral new arch frame without connecting plates into the pre-positioning jig, use jacks to finely adjust the axis of the integral new arch frame without connecting plates. Combine the polar coordinate method of the total station to check the control point coordinates of the integral new arch frame without connecting plates in real time. After confirming that the positioning deviation of the integral new arch frame without connecting plates does not exceed 30mm, immediately spot weld the integral new arch frame without connecting plates to fix it temporarily, and install the locking foot anchor. The locking foot anchor support plate is welded to the steel base plate mentioned in S10 to form an integral whole.

[0038] S40. Based on the local stability prediction scheme of the I-beam web, calculate the stability safety factor of each section of the I-beam web of the integral unconnected new arch frame. For sections with a stability safety factor lower than 1.5, weld short stiffening ribs symmetrically on both sides of the I-beam web. The size of the short stiffening ribs is 100×8mm and the spacing is 250mm. Remove the old initial support concrete and old arch frame one by one in the arch replacement area. After removing one old arch frame, immediately complete the installation and temporary fixation of one integral unconnected new arch frame according to S30. Complete the stability calculation of the I-beam web of the integral unconnected new arch frame and the welding of short stiffening ribs according to S40.

[0039] After the installation of the S50 integral unconnected arch frame is completed, the system anchor bolts and steel mesh are constructed. The channel steel connecting bars are welded to the rear side of the full-section ground-supported arch using a segmented symmetrical skip welding process. The length of each weld segment does not exceed 80mm. The welding sequence is from the middle to both ends. After welding, the reverse correction is performed using jacks. The coordinates of the control points of the integral unconnected arch frame are monitored in real time using a total station. The cumulative torsion angle of the integral unconnected arch frame is controlled within 0.5°. After the channel steel connecting bars of two adjacent integral unconnected arch frames are welded, the initial support shotcrete is completed using a multi-layer thin-layer spraying process. The thickness of each spray layer does not exceed 50mm. After the spraying is completed, cement-water glass double-liquid grout is injected into the residual cavity between the sprayed layer and the surrounding rock through the reserved grouting short pipe. The density of the sprayed layer is detected by ground-penetrating radar.

[0040] S60. After the initial support shotcrete of each integral unconnected new arch frame has set and passed the cross-section test, the full-section ground-supported invert arch and protective arch shall be removed one by one from top to bottom. After removal, the protective arch position shall be sprayed in a timely manner. After all the full-section ground-supported invert arch and protective arches have been removed, the secondary lining construction shall be carried out in a timely manner.

[0041] The aforementioned pre-stress control wedge tightening scheme, which involves attaching strain gauges to the outside of the wooden wedges and collecting the wedge compression strain values ​​output by the strain gauges in real time using a data acquisition instrument. Based on the elasticity contact theory, the wedge compression strain values ​​are converted into the wedge tightening contact stress between the full-section ground-supported invert arch and the surrounding rock or initial support. The minimum effective force transmission wedge tightening contact stress threshold for a single arch is not less than 0.05 MPa. When the measured wedge tightening contact stress is lower than the minimum effective force transmission wedge tightening contact stress threshold for a single arch, additional steel wedges are installed to increase the density. The wedge tightening status data of each arch is recorded in a database to guide subsequent standardized construction management.

[0042] The pre-positioning jig refers to a temporary steel guide groove structure pre-processed according to the cross-sectional dimensions of the integral, unconnected new arch frame. The pre-positioning jig is welded and fixed to the corresponding installation position on the inner wall of the full-section landing arch support. After the integral, unconnected new arch frame is inserted into the pre-positioning jig, it is constrained in both the out-of-plane and left-right directions. With the help of jacks, the axis is finely adjusted to eliminate the risk of out-of-plane overturning and displacement of the integral, unconnected new arch frame caused by the lack of arc-shaped arch waist friction support in the straight wall section.

[0043] The aforementioned local stability prediction scheme for the web of the I-beam refers to calculating the critical compressive stress of the web of the I-beam under concentrated load using the buckling equation of elastic thin plates, calculating the stability safety factor of each section of the web of the I-beam in combination with the measured axial force and bending moment, and pre-welding short stiffening ribs with dimensions of 100×8mm and a spacing of 250mm symmetrically on both sides of the web of the I-beam for sections with a stability safety factor lower than 1.5, thereby eliminating the potential for out-of-plane buckling failure of the web of the I-beam from the source.

[0044] The segmented symmetrical skip welding process refers to the process of welding the channel steel connecting ribs to the flange of the integral unconnected plate new arch frame. First, symmetrical spot welding is completed on both sides, and then welding is carried out alternately. The length of each weld segment does not exceed 80mm. The welding sequence follows the principle of first the middle and then the two ends. After welding, the integral unconnected plate new arch frame is corrected in the reverse direction with jacks. The coordinates of the control points of the integral unconnected plate new arch frame are monitored in real time using a total station. The cumulative torsion angle of the integral unconnected plate new arch frame is controlled within 0.5° to prevent the superposition of thermal stress from multiple welding points from causing the overall linear distortion of the integral unconnected plate new arch frame.

[0045] The aforementioned multi-layer thin-layer spraying process refers to controlling the thickness of each sprayed layer to within 50mm during spraying concrete, and repeatedly layering the sprays to the designed thickness. Each spraying direction is perpendicular to the rock surface being sprayed, and high-pressure air is used to locally blow out air bubbles. After the spraying is completed, cement-water glass grout is injected through short grouting pipes with a 1m spacing reserved on the outer side of the integral, unconnected arch frame flange to fill the residual cavity between the sprayed layer and the surrounding rock, and the density of the sprayed layer is detected by ground-penetrating radar.

[0046] The steel base plate and C30 fine stone concrete composite cushion layer refers to laying a C30 fine stone concrete leveling layer and a steel base plate with dimensions of 30×30×10mm sequentially at the bottom of the arch foot of the straight wall section. The base is pre-grouted and solidified under the steel base plate, and the anchor rod support plate is welded to the steel base plate to form an integral whole. The concentrated load at the bottom of the integral unconnected new arch frame is diffused and transferred to the deep stable area of ​​the surrounding rock through the steel base plate, preventing punching shear failure of the arch foot of the straight wall section under weak surrounding rock conditions.

[0047] The specific implementation of step S10 is as follows: First, small-diameter pipe grouting reinforcement is carried out on the surrounding rock in the arch replacement area, covering the area above the lower step. By injecting cement grout into the surrounding rock, the loose rock mass is consolidated, improving the overall bearing capacity of the surrounding rock and providing a stable foundation for subsequent arch replacement work. At the arch foot of the straight wall section, a C30 fine stone concrete leveling layer is first poured and the base is pre-grouted and cured. After the concrete hardens, a steel base plate with dimensions of 30×30×10mm is laid on it. The steel base plate and the C30 fine stone concrete leveling layer together constitute a composite cushion layer of steel base plate and C30 fine stone concrete. The mechanical effect of the composite cushion layer is that the force on the arch foot of the straight wall section is a concentrated load. The steel base plate, through its large planar stiffness, diffuses the concentrated load into a surface load and transfers it to the C30 fine stone concrete leveling layer. Then, after the base is grouted and cured, it is transferred to the deeper layers of the surrounding rock, effectively reducing the local stress concentration level at the arch foot. In this step, the anchor plate is fully welded to the steel base plate to form an integral load-bearing structure, ensuring the continuity of the force transmission path after the subsequent anchor installation and preventing punching damage to the arch foot under weak surrounding rock conditions.

[0048] The specific implementation method of step S20 is as follows: Install the full-section ground-supported inverted arch retaining arches frame by frame from both ends of the arch replacement pile number towards the middle. The installation sequence is: first the straight wall section and the inverted arch section, then the top arch section. The full-section ground-supported inverted arch retaining arches are made of I18 I-beams, with a spacing of 60-100cm. The retaining arches in the straight wall section are complete I-beams without connecting plates. Before installing the retaining arches, the loose soil and the surface of the initial support concrete at the installation location must be removed to ensure a flat contact surface. After the retaining arches are installed, a pre-pressure control wedging scheme using a combination of wooden wedges and steel wedges is used to achieve multi-point wedging between the full-section ground-supported inverted arch retaining arches and the surrounding rock or initial support. The specific operation is as follows: Strain gauges are pre-attached to the outside of the wooden wedges. The strain gauges are connected to a data acquisition instrument via wires. The data acquisition instrument collects the wedge compression strain value output by the strain gauges in real time. Based on the elasticity contact theory, the wedge compression strain value is converted into the wedge tight contact stress between the full-section ground-supported arch and the surrounding rock or initial support. The minimum effective force transmission wedge tight contact stress threshold for a single arch is set to be no less than 0.05 MPa. When the measured wedge tight contact stress is lower than the minimum effective force transmission wedge tight contact stress threshold for a single arch, steel wedges are immediately added to increase the density until the wedge tight contact stress is no less than the minimum effective force transmission wedge tight contact stress threshold for a single arch. The measured wedge tight contact stress values ​​of each arch and the location and number of times the steel wedges are added are recorded in the database to guide subsequent standardized construction management.

[0049] In step S20, the pre-stress control wedge tightening scheme involving the combination of wooden and steel wedges involves the calculation of converting the wedge block compressive strain value into the wedge tightening contact stress. The formula is expressed as follows:

[0050] ;

[0051] In the formula, The wedge contact stress is expressed in units of 1. ; This is a reference stress value, in units of... The value is usually 1. ; This refers to the elastic modulus of the wooden wedge, in units of... The experience value is 800-1200. ; This is a reference value for the elastic modulus, in units of... The value is usually 1000. ; The measured wedge compression strain value is dimensionless and was acquired in real time by a data acquisition instrument. The initial zero-point strain obtained from calibration before installation is dimensionless. The Poisson's ratio for the wooden wedge is typically taken as 0.3 to 0.4. This is a correction term for the contact theory of elasticity, in units of... This reflects the deviation caused by wedge surface roughness and contact non-ideality; the empirical value range is 0 to 0.01. This formula is based on the contact theory of elasticity, converting measured strain into contact stress. Below the minimum effective force transmission wedge contact stress threshold for a single arch support ( When this is done, additional steel wedges must be driven in to reinforce the seal.

[0052] The specific implementation of step S30 is as follows: A pre-designed positioning jig is welded to the corresponding installation position on the inner wall of the full-section landing arch support. The pre-designed positioning jig is a temporary steel guide groove structure pre-processed according to the cross-sectional dimensions of the integral, unconnected new arch frame. Its width matches the flange width of the integral, unconnected new arch frame, and a slight gap is left in the height direction for fine-tuning after insertion. After the integral, unconnected new arch frame is inserted into the pre-designed positioning jig, its out-of-plane and left-right degrees of freedom are geometrically constrained, thus eliminating the risk of out-of-plane overturning of the integral, unconnected new arch frame due to the lack of friction support from the arch waist in the straight wall section. Subsequently, jacks are used to fine-tune the axis of the integral, unconnected new arch frame. During the adjustment process, the coordinates of the pre-set control points on the integral, unconnected new arch frame are checked in real time using the polar coordinate method with a total station. When the deviation between the control point coordinates and the design coordinates does not exceed 30mm, the positioning is deemed qualified, and the integral, unconnected new arch frame is immediately spot-welded for temporary fixation. After the fixing is completed, lock foot anchor rods are installed at the connection plate position according to the design requirements. The lock foot anchor rod support plate is fully welded to the steel base plate already laid in S10 to ensure the integrity of the force transmission path of the arch foot.

[0053] The specific implementation of step S40 is as follows: Before the installation of the new integral, unconnected arch frame, the stability of each section is verified according to the local stability prediction scheme of the I-beam web. The principle of the prediction scheme is as follows: using the buckling equation of elastic thin plate, with the height-to-thickness ratio, elastic modulus and Poisson's ratio of the I-beam web as input parameters, the critical compressive stress of the web under concentrated load is calculated; combined with the measured axial force and bending moment, the stability safety factor of each section of the I-beam web is calculated, and the stability safety factor threshold is taken as 1.5; for sections with a stability safety factor lower than 1.5, short stiffening ribs with a size of 100×8mm and a spacing of 250mm are pre-welded symmetrically on both sides of the I-beam web. The short stiffening ribs increase the out-of-plane bending stiffness of the web, thereby raising the critical buckling load of the web to a safe level. During the arch replacement construction, the principle of immediately installing a new, integral arch frame without connecting plates after dismantling an old arch frame must be strictly followed. The removal of the old initial support concrete is carried out using a combination of pneumatic picks and small mechanical crushing operations. The height of each demolition is controlled within 1m, and blasting operations are strictly prohibited to minimize the disturbance to the surrounding rock.

[0054] In step S40, the local stability prediction scheme for the web of the I-beam involves calculating the critical compressive stress of the web and the section stability safety factor using the elastic thin plate buckling equation. The formulas are expressed as follows:

[0055] ;

[0056] In the formula, The critical compressive stress of the web of the I-beam is given in units of 1. ; The yield strength of the web steel is given by 100 g / cm². ; is the web buckling coefficient, which is dimensionless and its value is related to the load type and boundary conditions. Under concentrated loads, it is usually taken as 6.97. The elastic modulus of the web steel is given in units of 1. The value is usually 206000. ; Poisson's ratio for web steel is dimensionless and typically taken as 0.3. Web thickness, in units of ; This is a reference value for web thickness, in units of... The value is usually 1. ; Calculate the height of the web, in units of ; This is the reference value for web height, in units of... The value is usually 1. Safety factor for cross-sectional stability The calculation formula is expressed as follows:

[0057] ;

[0058] In the formula, The cross-sectional stability safety factor is dimensionless. This represents the actual compressive stress in the web section, in units of... Measured axial force (Unit is) ) and measured bending moment (Unit is) (This is obtained by synthesizing the cross-sectional geometric parameters.) At that time, symmetrical welding of dimensions 100×8 is required on both sides of the web. Spacing 250 Short stiffening ribs.

[0059] The specific implementation method of step S50 is as follows: After the integral, unconnected new arch frame is installed, system anchor bolts are installed in a quincunx pattern, and steel mesh is laid simultaneously. The welding of the channel steel connecting bars adopts a segmented symmetrical skip-welding process: first, tack welding is completed at symmetrical positions on both sides of the integral, unconnected new arch frame; then, welding is performed alternately in the order of first the middle and then the two ends, with each weld segment not exceeding 80mm in length. After welding, the integral, unconnected new arch frame is reverse-corrected using jacks, while the coordinates of the control points of the integral, unconnected new arch frame are monitored in real time using a total station to ensure that the cumulative torsion angle does not exceed 0.5°. The principle of the segmented symmetrical skip-welding process is to: by dispersing the welding heat input, avoid the superposition of thermal stress caused by multi-point synchronous welding, thereby suppressing the out-of-plane torsional deformation of the I-beam arch frame. After the channel steel connecting bars of two adjacent integral, unconnected arch frames are welded, the initial support shotcrete is applied using a multi-layer thin-layer spraying process: each layer is no more than 50mm thick, the spraying direction is perpendicular to the rock surface being sprayed, and high-pressure air is used to locally blow out air bubbles, and multiple layers are sprayed to the designed thickness; after the shotcrete is applied, cement-water glass grout is injected through the reserved grouting short pipes spaced 1m apart on the outer side of the integral, unconnected arch frame flange to fill the residual cavity between the shotcrete layer and the surrounding rock; finally, ground-penetrating radar is used to detect the density of the shotcrete layer, and secondary grouting is carried out in areas with insufficient density.

[0060] The specific implementation of step S60 is as follows: After the initial support shotcrete of each integral, unconnected new arch frame has fully set and the cross-sectional dimensions have been re-measured and confirmed by a cross-section measuring instrument to meet the design requirements, the full-section ground-supported invert arches at the corresponding locations can be dismantled. The dismantling sequence is from top to bottom within the same frame, first the top arch and then the straight wall section, advancing frame by frame to ensure that at any given time there is a sufficient number of full-section ground-supported invert arches to maintain the overall stability of the support system. After the arches are dismantled, the initial support shotcrete at the arch location is immediately completed to eliminate the exposed rock surface after the arches are dismantled and prevent the surrounding rock from loosening. After all the full-section ground-supported invert arches are dismantled and the monitoring and measurement data show that the surrounding rock is stable, the secondary lining construction is promptly carried out. The timing and length of the secondary lining are determined comprehensively based on the excavation of the lower bench and the monitoring and measurement results to ensure the long-term stability of the surrounding rock in the arch replacement area.

[0061] It should be noted that one of the key technical ideas of this invention is the pre-designed positioning jig with bidirectional limiting scheme. In traditional arch replacement construction, the positioning of the arch frame relies on manual support and repeated measurement and adjustment. In the absence of curved surface friction constraints in straight wall sections, the risk of out-of-plane overturning of the arch frame cannot be effectively eliminated through manual operation. The pre-designed positioning jig locks the out-of-plane and lateral degrees of freedom of the integral, unconnected new arch frame simultaneously through geometric constraints, changing the positioning process from passive adjustment to active limiting, thus altering the mechanical mechanism of arch frame positioning. The second key technical idea is the pre-pressure control wedging scheme using a combination of wooden and steel wedges. In traditional construction, the wedging state between the arch support and the surrounding rock relies on the experience judgment of construction personnel, which cannot be quantified, leading to uneven force transmission and persistent, difficult-to-detect, localized voiding problems. This scheme uses strain gauges and data acquisition instruments to convert the wedging state into quantifiable wedging contact stress, achieving closed-loop monitoring of the force transmission state and solving the problem of unmeasurability in traditional wedging methods. The third key technical idea is the combined application of a local stability prediction scheme for the web of the I-beam and a segmented symmetrical skip welding process. The web plate local stability prediction scheme moves the identification of structural failure to before load application, which is a form of pre-emptive intervention. The segmented symmetrical skip welding process controls welding deformation within the design allowable range by controlling the distribution of welding heat input, which is a form of process control. The two form a complementary relationship between pre-emptive prevention and process control in the time dimension, jointly ensuring the structural integrity of the integral, unconnected arch frame throughout the construction process. The synergistic effect of the above three key technical ideas is as follows: the pre-positioning jig bidirectional limiting scheme ensures the initial positioning accuracy of the integral, unconnected arch frame, laying the geometric foundation for subsequent welding and anchor bolt installation; the wooden wedge and steel wedge combination pre-pressure control wedging scheme ensures the continuous and effective support of the full-section landing arch and arch protection, providing stable boundary conditions for the overall support system during arch replacement; the I-beam web plate local stability prediction scheme and the segmented symmetrical skip welding process jointly ensure the stability of the arch frame cross-section and overall alignment. The three act on the three levels of positioning, force transmission, and cross-section stability, respectively, forming a complete arch replacement safety assurance system.

[0062] It should be noted that this invention also solves the following technical problems: First, it solves the technical problem of punching shear failure caused by concentrated loads at the arch foot of the straight wall section under weak surrounding rock conditions. The contact area at the bottom of the arch frame in the straight wall section is limited, and concentrated loads in weak surrounding rock can easily cause local stress exceeding the limit. The traditional solution of using only concrete pads cannot effectively diffuse the load. This invention combines a steel base plate with a C30 fine stone concrete composite pad layer and then grouts and cures the base. The high planar stiffness of the steel base plate diffuses the concentrated load into a surface load, which is then transferred to the deep layer of the surrounding rock through the cured base, thus eliminating the stress concentration conditions for punching shear failure from the mechanical force transmission path. Second, it solves the technical problem of insufficient compaction of shotcrete filling in the narrow gap cavity between the arch frame and the surrounding rock. The gap between the straight wall section arch support and the integral new arch frame without connecting plates is uneven. Conventional single-layer thick shotcrete process results in insufficient compaction due to aggregate ejection and air bubble sealing problems. This invention controls the thickness of each spray layer to within 50mm through a multi-layer thin-layer spraying process, combined with high-pressure air blowing to remove air bubbles, and then injects cement-water glass dual-liquid grout through a pre-reserved grouting short pipe to fill the residual cavity. The density is verified by ground-penetrating radar detection, thus ensuring the filling density of the sprayed layer from two dimensions: the spraying process and the subsequent supplementary grouting.

[0063] Specifically, the principle of this invention is as follows: The technical solution of this invention can solve the above-mentioned technical problems, and its principle lies in the following aspects. First, the pre-positioning jig serves as a temporary steel guide groove structure, which directly restricts the degrees of freedom of the integral, unconnected new arch frame in the out-of-plane and left-right directions through mechanical geometric constraints. This replaces the lateral stability provided by the friction constraint of the arc-shaped arch waist, transforming the positioning accuracy of the arch frame from passive stability dependent on contact friction to active stability dependent on geometric constraints, thus eliminating the conditions for out-of-plane overturning in principle. Second, the pre-pressure control wedge tightening scheme of the wooden wedge and steel wedge combination converts the wedge compression strain value output by the strain gauge into the wedge tightening contact stress through the elastic mechanical contact theory. This transforms the originally invisible arch support force transmission state into a quantifiable and comparable monitoring quantity, thereby achieving closed-loop control. Third, the local stability prediction scheme of the I-beam web plate is based on the elastic thin plate buckling equation. It predicts the buckling risk of the section before the load is applied and applies short stiffening ribs in advance, transforming the passive response to structural failure into active prevention of local buckling. Logically, this conforms to the pre-intervention principle of structural stability design. Finally, the steel base plate and C30 fine stone concrete composite cushion layer increase the contact area of ​​the bottom surface of the arch foot and solidify the base, thereby dispersing and transferring the concentrated load. This mechanically eliminates the stress concentration conditions for punching shear failure under weak surrounding rock conditions and ensures the continuous effectiveness of the overall support system.

[0064] The following provides a specific embodiment 1 of the present invention, and the specific implementation of each step in this embodiment 1 is described in detail below.

[0065] The section of the tunnel access road leading to the factory where the arch replacement is being carried out is from JT0+70.3 to JT0+85, involving a total of 26 arches to be replaced. A total of 29 arches are being built as full-section ground-supported inverts and retainers, with retainer pile numbers from JT0+70.6 to JT0+86.5. The surrounding rock is soft and fractured rock mass. The left straight wall section of the initial support severely encroached on the design clearance of the secondary lining, with the maximum encroachment measured by a cross-section instrument to be approximately 85mm. The original design thickness of the secondary lining was 50cm, and the original arch spacing was 50-60cm. The arch replacement is being carried out using the method described in this invention.

[0066] Before construction, technicians implemented small-diameter grouting reinforcement on the section above the lower step from JT0+73 to JT0+130. The small-diameter pipes were 42mm in diameter and 4m in length. The grouting pressure was controlled between 0.5 and 1.5MPa, and the grouting material was cement slurry with a water-cement ratio of 0.5:1. After grouting, steel base plates with dimensions of 30×30×10mm were laid at each arch foot of the straight wall section. A C30 fine aggregate concrete leveling layer with a thickness of 50mm was poured under the steel base plates, and the base was pre-grouted and cured to form a composite cushion layer of steel base plates and C30 fine aggregate concrete. The anchor bolt brackets were fully welded to the steel base plates, with a weld height of not less than 8mm.

[0067] The installation of the full-section ground-supported invert arch and protective arch was carried out simultaneously from both ends JT0+68 and JT0+85 towards the middle. The full-section ground-supported invert arch and protective arch were made of I18 I-beams with a spacing of 60cm. The spacing of the four arches under the pipe shed was reduced to 50cm. The protective arches in the straight wall section were complete I-beams without connecting plates. After the protective arches were installed, wedging was carried out according to the pre-pressure control wedging scheme of wooden wedges and steel wedges. Wedging monitoring points were set up for each protective arch, and strain gauges were attached to the outside of the wooden wedges. The data acquisition instrument sampled at a frequency of 1 time / min. The calculated wedging contact stress is shown in Table 1. For positions where the wedging contact stress was lower than 0.05MPa, steel wedges were immediately added to increase the density. After adding the steel wedges, the wedging contact stress was read again until the minimum effective force transmission wedging contact stress threshold requirement for a single protective arch was met.

[0068] Table 1 Summary of Monitoring Results of Weft-Tight Contact Stress for Each Support Arch

[0069]

[0070] Pre-installed positioning jigs were welded to the corresponding installation positions on the inner wall of the full-section landing arch support. One pre-installed positioning jig was installed on the inner wall of each support arch. The clear width of the guide groove matched the width of the I18 I-beam flange, leaving a 2mm adjustment gap. After the integral, plateless new arch frame was inserted into the pre-installed positioning jig, it was constrained in both the external and lateral directions. Then, the axis was finely adjusted using jacks, and the coordinates of the control points were checked using the polar coordinate method of a total station. The coordinate deviations of each control point are shown in Table 2. The coordinate deviations of all control points did not exceed 30mm, and the positioning was deemed qualified. Temporary fixation was immediately spot-welded. Figure 3The diagram shown illustrates the installation of the arch support, visually reflecting the installation status of the new, integral, unconnected arch frame after it has been inserted into the pre-positioned jig.

[0071] Table 2 Summary of Coordinate Deviations of Control Points for the Installation of the New Integral, Connecting Plate Arch Frame

[0072]

[0073] Based on the local stability prediction scheme for the web of the I-beam, stability calculations were performed on each section of the new integral, unconnected arch frame. The critical compressive stress of each section was calculated using the buckling equation of an elastic thin plate. The stability safety factor was calculated by combining the measured axial force and bending moment. For sections with a stability safety factor lower than 1.5, short stiffening ribs with dimensions of 100×8mm and a spacing of 250mm were symmetrically welded to both sides of the I-beam web. After the welding of the short stiffening ribs, the sections were recalculated, and the stability safety factor was improved to above 1.5. Figure 4 The diagram shown is a full-section schematic of the arch support installation, reflecting the relative positional relationship between the full-section ground-mounted inverted arch support and the integral, unconnected new arch frame, as well as the arrangement of the short stiffening ribs.

[0074] During the arch replacement, the channel steel connecting bars were welded using a segmented symmetrical skip welding process. Each weld segment was 60mm long, and the welding sequence was from the middle to both ends. After welding, the coordinates of the control points were monitored using a total station. The cumulative torsion angle monitoring results are shown in Table 3. The cumulative torsion angle of all arch frames was controlled within 0.5°.

[0075] Table 3 Summary of Cumulative Torsion Monitoring Results for New Integral, Connecting Plate-less Arch Frames

[0076]

[0077] The initial support shotcrete adopts a multi-layer thin-layer spraying process, with each layer controlled at a thickness of 40-50 mm, for a total of 5-6 layers to the designed thickness. After the shotcrete is applied, cement-water glass grout is injected through a pre-reserved grouting pipe at a pressure of 0.3-0.5 MPa and a volume ratio of 1:1. Ground-penetrating radar is used to check the compaction of the sprayed layer after grouting. Figure 2 The diagram shows the cross-sectional measurement and shotcrete compaction test results for the arch replacement area. The compaction test results all meet the design requirements. After the initial support shotcrete of each arch has fully set, a cross-sectional instrument is used for re-measurement. Once all cross-sectional dimensions meet the design requirements, the entire cross-section of the inverted arch support is removed one arch at a time from top to bottom. Figure 5The diagram shows a side view of the arch installation and a schematic diagram of the arch removal process, intuitively reflecting the step-by-step progress of the arch removal. After the arch was removed, the arch location was promptly sprayed with protective film. After the removal of all full-section inverted arches, the secondary lining construction was promptly carried out. Monitoring and measurement data throughout the arch replacement construction process showed that the deformation rate of the surrounding rock was always below 5 mm / d, and the cumulative deformation did not exceed 100 mm, indicating that the surrounding rock remained stable.

[0078] The technological advancements of this invention compared to traditional methods are reflected in the following aspects: In traditional arch replacement construction, the positioning of the arch frame in the straight wall section relies on manual experience, and the positioning accuracy cannot be quantified and guaranteed. This invention introduces geometric constraints into the arch frame installation process through a pre-designed positioning jig, transforming the positioning accuracy from subjective experience control to objective geometric control, thus eliminating the conditions for out-of-plane overturning in principle. In traditional construction, the wedging state of the protective arch is unmeasurable, leading to persistent and difficult-to-detect uneven force transmission problems. This invention, through the combined application of strain gauges and elasticity contact theory, transforms the wedging state into quantifiable wedging contact stress, achieving closed-loop monitoring of the force transmission state and changing the passive experience-dependent working mode of traditional construction. In traditional construction, the risk of local buckling of the I-beam web can only be detected after load application. This invention, through the elastic thin plate buckling equation, completes stability prediction before load application and pre-installs short stiffeners, shifting the timing of structural safety assurance forward, demonstrating the fundamental advantage of proactive intervention over reactive remediation in ensuring structural safety.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A construction method for an integral arch frame without connecting plates in a straight-wall section tunnel, characterized in that, Includes the following steps: Small pipe grouting reinforcement was carried out on the surrounding rock of the arch replacement area. A steel base plate was laid at the arch foot of the straight wall section. A C30 fine stone concrete leveling layer was poured under the steel base plate and the base was pre-grouted and cured to form a composite cushion layer of steel base plate and C30 fine stone concrete. The locking foot anchor plate was welded to the steel base plate to form a whole, which constitutes the arch foot support foundation of the straight wall section. Along the two ends of the arch replacement pile number, the full-section ground-mounted inverted arch and protective arch are installed one by one towards the middle. The full-section ground-mounted inverted arch and protective arch are made of I18 I-beams. The straight wall section of the protective arch is a complete I-beam without connecting plates. A combination of wooden wedges and steel wedges is used to achieve multi-point wedging between the full-section ground-mounted inverted arch and the surrounding rock or initial support. Strain gauges are attached to the outside of the wooden wedges. The wedge compression strain value output by the strain gauges is collected in real time by a data acquisition instrument, and the wedge compression strain value is converted into the wedging contact stress. When the wedging contact stress is lower than the minimum effective force transmission wedging contact stress threshold of a single arch, steel wedges are added to increase the density, and the wedging status data of each arch is recorded in the database. Weld a pre-positioning jig at the corresponding installation position on the inner wall of the full-section ground-supported arch. After inserting the integral new arch frame without connecting plates into the pre-positioning jig, use jacks to finely adjust the axis of the integral new arch frame without connecting plates. Combine the polar coordinate method of the total station to check the coordinates of the control points of the integral new arch frame without connecting plates in real time. After confirming that the positioning deviation of the integral new arch frame without connecting plates does not exceed the design allowable value, immediately spot weld the integral new arch frame without connecting plates to fix it temporarily, and install the foot anchor rods. The foot anchor rod support plate is welded to the steel base plate to form an integral whole. Based on the local stability prediction scheme of the I-beam web, the stability safety factor of each section of the I-beam web of the new integral arch frame without connecting plates is calculated. For sections with a stability safety factor lower than the stability safety factor threshold, short stiffening ribs are symmetrically welded on both sides of the I-beam web. The old initial support concrete and old arch frame are removed one by one in the arch replacement area. After removing one old arch frame, the installation and temporary fixation of a new integral arch frame without connecting plates is completed immediately. After the installation of the integral, unconnected arch frame is completed, the system anchor bolts and steel mesh are constructed. The channel steel connecting bars are welded to the rear side of the full-section ground-mounted invert arch support using a segmented symmetrical skip welding process. After welding, the reverse correction is performed using jacks. The coordinates of the control points of the integral, unconnected arch frame are monitored in real time using a total station to control the cumulative torsion angle of the integral, unconnected arch frame within the design allowable torsion angle range. After the channel steel connecting bars of two adjacent integral, unconnected arch frames are welded, the initial support shotcrete is completed using a multi-stage thin-layer spraying process. After the shotcrete is completed, cement-water glass double-liquid grout is injected into the residual cavity between the shotcrete layer and the surrounding rock through a reserved grouting short pipe. The density of the shotcrete layer is detected using ground-penetrating radar. After the initial support shotcrete of each new monolithic arch frame without connecting plates has set and passed the cross-section test, the full-section ground-supported arch and protective arch are removed one by one from top to bottom. After removal, the arch and protective arch positions are promptly sprayed. After all the full-section ground-supported arch and protective arch are removed, the secondary lining construction is promptly carried out.

2. The construction method of a straight-wall section tunnel with an integral arch frame without connecting plates according to claim 1, characterized in that, The steel base plate and C30 fine stone concrete composite cushion layer are specifically laid in sequence at the bottom of the arch foot of the straight wall section, with a C30 fine stone concrete leveling layer and a steel base plate with a size of 30×30×10mm. The base is pre-grouted and cured under the steel base plate, and the anchor rod support plate is welded to the steel base plate to form a whole.

3. The construction method of a straight-wall section tunnel with an integral arch frame without connecting plates according to claim 2, characterized in that, The aforementioned pre-stress control wedge tightening scheme for the combination of wooden and steel wedges involves attaching strain gauges to the outside of the wooden wedges, collecting the wedge compression strain values ​​in real time using a data acquisition instrument, and converting the wedge compression strain values ​​into wedge tightening contact stress based on the elasticity contact theory. The minimum effective force transmission wedge tightening contact stress threshold for a single arch support is not less than 0.05 MPa.

4. The construction method of a straight-wall section tunnel with an integral arch frame without connecting plates according to claim 3, characterized in that, After the wedge tightness data of each truss is recorded into the database, the database is used to guide the standardized management of subsequent construction. The wedge tightness data includes the measured value of the wedge tightness contact stress of each truss and the location and number of times additional steel wedges are driven in.

5. The construction method of a straight-wall section tunnel with an integral arch frame without connecting plates according to claim 4, characterized in that, The pre-positioning jig refers to a temporary steel guide groove structure pre-processed according to the cross-sectional dimensions of the integral new arch frame without connecting plates. It is welded and fixed to the corresponding installation position on the inner wall of the full-section landing arch support. After the integral new arch frame without connecting plates is inserted into the pre-positioning jig, it is subject to limiting constraints in both the out-of-plane direction and the left and right directions.

6. The construction method of a straight-wall section tunnel with an integral arch frame without connecting plates according to claim 5, characterized in that, The design allowable value for the positioning deviation of the integral, unconnected new arch frame is 30mm. The coordinates of the control points of the integral, unconnected new arch frame are checked in real time using the polar coordinate method of a total station. After confirming that the positioning deviation does not exceed 30mm, temporary fixation is immediately achieved by spot welding.

7. The construction method of a straight-wall section tunnel with an integral arch frame without connecting plates according to claim 6, characterized in that, The proposed local stability prediction scheme for the web of an I-beam refers to calculating the critical compressive stress of the web of an I-beam under concentrated load using the buckling equation of an elastic thin plate, and then calculating the stability safety factor of each section of the web of the I-beam by combining the measured axial force and bending moment. The threshold value of the stability safety factor is 1.

5.

8. The construction method of a straight-wall section tunnel with an integral arch frame without connecting plates according to claim 7, characterized in that, The short stiffeners are 100×8mm in size and 250mm apart. They are symmetrically welded on both sides of the web of the I-beam to increase the stability safety factor of each section of the web of the I-beam to no less than the stability safety factor threshold of 1.

5.

9. A construction method for an integral arch frame without connecting plates in a straight-wall section tunnel according to claim 8, characterized in that, The segmented symmetrical skip welding process refers to the process of first completing symmetrical spot fixing on both sides and then alternately welding when welding the channel steel connecting bar to the flange of the integral new arch frame without connecting plate. The length of each weld segment does not exceed 80mm, and the welding sequence is from the middle to both ends. After welding, the integral new arch frame without connecting plate is corrected in the reverse direction using a jack.

10. A construction method for an integral arch frame without connecting plates in a straight-wall section tunnel according to claim 9, characterized in that, The design allows for a cumulative torsion angle range of less than 0.5° for the integral, unconnected arch frame. A total station is used to monitor the coordinates of the control points of the integral, unconnected arch frame in real time, and jacks are used to correct sections that exceed the design allowable torsion angle range.

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