Method for monitoring steel box girder incremental launching construction of bridge crossing coal mine goaf

Abstract

This invention discloses a method for monitoring the jacking construction of steel box girders for bridges crossing coal mine goaf areas, comprising the following steps: 1) monitoring the deflection of the steel box girder and guide beam; 2) monitoring the axial deviation of the steel box girder; 3) monitoring the stress at the connection between the steel box girder and guide beam, and at the temporary pier support; 4) monitoring the displacement of the top of the temporary pier support; 5) monitoring the settlement of the temporary pier foundation; and 6) monitoring the girder lowering stage. This invention provides a method for monitoring the jacking construction of steel box girders for bridges crossing coal mine goaf areas, including monitoring parameters such as the axial deviation of the steel box girder, the horizontal displacement of the top of the temporary pier, the maximum cantilever deflection at the front end of the steel guide beam, the stress at the connection between the steel box girder and guide beam, and the stress at the bottom of the temporary pier. Corresponding measures are then taken to ensure that the uneven settlement on both sides of the temporary pier abutment is always controlled within 10mm, thereby significantly reducing the safety risks of jacking construction across existing coal mine goaf areas and meeting construction requirements.

Description

Technical Field

[0001] This invention relates to the technical field of tunnel construction monitoring methods, specifically a method for monitoring the jacking construction of steel box girders for bridges crossing coal mine goaf areas. Background Technology

[0002] The bridge jacking construction method differs from traditional methods such as the scaffolding method, hoisting method, rotation method, and cantilever method in terms of construction environment, technical requirements, and construction control. Due to the unique construction principle of the jacking method, the research on its construction process also differs from other construction methods. Temporary auxiliary pier structures can increase the cantilever length of bridge jacking construction and better control the stress-free alignment of the variable curvature vertical curve continuous beam. However, issues such as the temporary pier elevation due to uneven settlement of the pier columns, guide beam parameters, changes in the stress state of the beam during the jacking construction process, and local stability have always been key and challenging aspects of the jacking method. Jacking construction across existing coal mine goaf areas carries high safety risks. To ensure safe and normal construction, strict monitoring is required. Currently, no monitoring methods for jacking construction have been found. Summary of the Invention

[0003] The purpose of this invention is to provide a method for monitoring the jacking construction of steel box girders for bridges crossing coal mine goaf areas, which greatly reduces the safety risks of jacking construction across existing railway lines and effectively controls the construction process.

[0004] This invention is achieved through the following technical solution: a method for monitoring the jacking construction of steel box girders for bridges spanning coal mine goaf areas, comprising the following steps: (1) Monitor the deflection of the steel box girder and guide beam; (2) Monitor the axial deviation of the steel box girder; (3) Monitor the stress at the connection between the steel box girder and the guide beam, and at the temporary pier support; (4) Monitor the displacement of the top of the temporary pier support; (5) Monitor the settlement of the temporary pier foundation; (6) Monitor the beam dropping stage.

[0005] To better implement the method of the present invention, the specific process of monitoring the deflection of the steel box girder and guide beam in step (1) is as follows: one monitoring prism is arranged at the front end of the steel box girder and one at the front end of the guide beam. Deflection monitoring is carried out using a total station. Before each jacking operation and during the jacking process, the surveyors must observe the changes in the elevation of the measuring points and compare them with the calculated values. To better implement the method of the present invention, the specific process of monitoring the axial deviation of the steel box girder in step (2) is further as follows: According to the actual situation on site, monitoring prisms are fixed at the front and rear of the steel box girder. The surveyors use a total station to monitor the changes in the coordinates of the measuring points before, during and after the jacking. The lateral displacement deviation of the steel box girder is calculated based on the observed prism position. During the jacking process, the allowable value of the axial deviation of the steel box girder is 50mm. After each jacking stage (i.e. before assembling the subsequent steel box girder), the allowable value of the axial deviation of the steel box girder is 5mm, and the limit value is 10mm.

[0006] To better implement the method of the present invention, further, the specific process of monitoring the stress at the connection between the steel box girder and the guide beam and the temporary pier support in step (3) is as follows: stress monitoring points are arranged at the connection between the steel box girder and the guide beam to understand the stress changes during the construction process at the connection between the steel box girder and the guide beam, with a total of 2 measuring points arranged. The measuring points of the temporary pier are mainly arranged at the bottom of the temporary pier, and steel wire strain sensors are installed to test the stress changes of the temporary pier during the construction process. One steel pipe is selected for each temporary pier to arrange the monitoring point; when the maximum cantilever of the front end of the steel guide beam is 55m, the maximum vertical deflection is 314.6mm; the measured value of the maximum normal stress at the connection between the steel box girder and the guide beam is 164.4Mpa, which is less than the design limit of 250Mpa, and the measured value of the maximum shear stress is 32.1Mpa, which is less than the design limit of 140Mpa.

[0007] To better implement the method of the present invention, further, the specific process of monitoring the displacement of the top of the temporary pier support in step (4) is as follows: the displacement measuring points of the top of the temporary pier are arranged at the top of the outermost row of temporary piers, so as to understand the changes in the displacement of the temporary piers during the jacking construction process and ensure the safety of the temporary pier support during the jacking construction process. The displacement of the top of the pier is measured using a total station. Before each jacking construction, during the jacking process, and during the beam lowering stage after the jacking is completed, the surveyors must observe the changes in the displacement of the temporary piers. The measured value of the maximum horizontal displacement of the top of the temporary pier is 6.4 mm, which is less than the design limit of 15 mm, and the measured value of the maximum stress at the bottom of the pier is 113.8 MPa.

[0008] To better implement the method of the present invention, the specific process of monitoring the settlement of the temporary pier foundation in step (5) is as follows: the temporary pier foundation will settle under the action of vertical load. In order to monitor the settlement change of the temporary pier foundation, one settlement monitoring point is arranged on each temporary pier foundation. During the beam splicing and jacking process, an electronic level is used to monitor the settlement of the temporary pier foundation.

[0009] To better implement the method of the present invention, the specific process of monitoring the beam lowering stage in step (6) is as follows: the beam lowering is carried out by a hydraulic synchronous jacking system. Before the steel box girder is pushed into place and lowered, observation prisms are arranged at the corresponding positions of the temporary piers of the steel box girder. Four measuring points are arranged on the left side of the bridge and four measuring points are arranged on the right side of the bridge. During the beam lowering process, a total station is used to monitor the elevation of the prisms in real time to control the beam lowering speed and structural safety.

[0010] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention provides a method for monitoring the jacking construction of steel box girders for bridges crossing coal mine goaf areas. This includes monitoring parameters such as the axial deviation of the steel box girder, the horizontal displacement of the temporary pier top, the maximum cantilever deflection at the front end of the steel guide beam, the stress at the connection between the steel box girder and the guide beam, and the stress at the bottom of the temporary pier. Corresponding measures are then taken to ensure that the uneven settlement on both sides of the temporary pier abutment is always controlled within 10mm. This significantly reduces the safety risks of jacking construction across existing coal mine goaf areas, effectively controls the construction process, and helps simplify the guide beam structure to meet construction requirements. Attached Figure Description

[0011] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a diagram showing the left span of the bridge in a specific engineering example provided in Embodiment 8 of the present invention. Figure 2 This is a diagram showing the layout of the left span of the bridge in a specific engineering example provided in Embodiment 8 of the present invention. Detailed Implementation

[0012] To make the objectives, process conditions, and advantages of the present invention clearer, the present invention will be further described in detail with reference to the following embodiments. However, the embodiments of the present invention are not limited thereto. Various substitutions and modifications can be made based on common technical knowledge and conventional means in the art without departing from the above-described technical concept of the present invention, and all such substitutions and modifications should be included within the scope of the present invention. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0013] Example 1: This embodiment provides a method for monitoring the jacking construction of steel box girders for bridges spanning coal mine goaf areas, including the following steps: (1) Monitor the deflection of the steel box girder and guide beam; (2) Monitor the axial deviation of the steel box girder; (3) Monitor the stress at the connection between the steel box girder and the guide beam, and at the temporary pier support; (4) Monitor the displacement of the top of the temporary pier support; (5) Monitor the settlement of the temporary pier foundation; (6) Monitor the beam dropping stage.

[0014] Example 2: Based on the above embodiments, this embodiment further defines the specific process of monitoring the deflection of the steel box girder and guide beam in step (1) as follows: one monitoring prism is arranged at the front end of the steel box girder and the front end of the guide beam. The deflection is monitored using a total station. Before each jacking operation and during the jacking process, the surveyors must observe the changes in the elevation of the measuring points and compare them with the calculated values. The other parts of this embodiment are the same as those in the above embodiments and will not be repeated here.

[0015] Example 3: Based on the above embodiments, this embodiment further specifies the specific process of monitoring the axial deviation of the steel box girder in step (2): According to the actual situation on site, monitoring prisms are fixed at both the front and rear of the steel box girder. Surveyors use a total station to monitor the changes in the coordinates of the measuring points before, during, and after the jacking process. The lateral displacement deviation of the steel box girder is calculated based on the observed prism positions. During the jacking process, the allowable axial deviation of the steel box girder is 50mm. After each jacking stage (i.e., before assembling the subsequent steel box girder), the allowable axial deviation of the steel box girder is 5mm, and the limit value is 10mm. The other parts of this embodiment are the same as those in the above embodiments and will not be repeated.

[0016] Example 4: Based on the above embodiments, this embodiment further defines the specific process of monitoring the stress at the connection between the steel box girder and the guide beam and the temporary pier support in step (3) as follows: stress monitoring points are arranged at the connection between the steel box girder and the guide beam to understand the stress changes during the construction process at the connection between the steel box girder and the guide beam. A total of 2 measuring points are arranged. The measuring points of the temporary pier are mainly arranged at the bottom of the temporary pier, and steel wire strain sensors are installed to test the stress changes of the temporary pier during the construction process. One steel pipe is selected for each temporary pier to arrange the monitoring point; when the maximum cantilever of the front end of the steel guide beam is 55m, the maximum vertical deflection is 314.6mm; the measured value of the maximum normal stress at the connection between the steel box girder and the guide beam is 164.4Mpa, which is less than the design limit of 250Mpa, and the measured value of the maximum shear stress is 32.1Mpa, which is less than the design limit of 140Mpa. The other parts of this embodiment are the same as those in the above embodiments and will not be repeated.

[0017] Example 5: Based on the above embodiments, this embodiment further specifies the specific process of monitoring the displacement of the temporary pier top in step (4) as follows: the temporary pier top displacement measuring points are arranged at the top of the outermost row of temporary piers to monitor the changes in the temporary pier displacement during the jacking construction process and ensure the safety of the temporary pier support during the jacking construction process. The pier top displacement is measured using a total station. Before each jacking construction, during the jacking process, and during the beam lowering stage after the jacking is completed, the surveyors must observe the changes in the temporary pier displacement. The measured maximum horizontal displacement of the temporary pier top is 6.4 mm, which is less than the design limit of 15 mm, and the measured maximum stress at the pier bottom is 113.8 MPa. The other parts of this embodiment are the same as those in the above embodiments and will not be repeated.

[0018] Example 6: Based on the above embodiments, this embodiment further defines the specific process of monitoring the settlement of the temporary pier foundation in step (5) as follows: the temporary pier foundation will settle under vertical load. In order to monitor the settlement changes of the temporary pier foundation, one settlement monitoring point is arranged on each temporary pier foundation. During the beam splicing and jacking process, an electronic level is used to monitor the settlement of the temporary pier foundation. The other parts of this embodiment are the same as those in the above embodiments and will not be repeated.

[0019] Example 7: Based on the above embodiments, this embodiment further defines the specific process of monitoring the beam lowering stage in step (6) as follows: the beam is lowered gradually using a hydraulic synchronous jacking system. Before the steel box girder is pushed into place and lowered, observation prisms are arranged at the corresponding positions of the temporary piers of the steel box girder. Four measuring points are arranged on the left side of the bridge and four measuring points are arranged on the right side of the bridge. During the beam lowering process, a total station is used to monitor the prism elevation in real time to control the beam lowering speed and structural safety. The other parts of this embodiment are the same as those in the above embodiments and will not be repeated.

[0020] Example 8: This embodiment provides a specific engineering example to illustrate the technical content disclosed in the above embodiments.

[0021] A bridge spans the goaf of the Xiabulong Coal Mine and a mountain valley. It consists of two sections, left and right. The superstructure is as follows: the left section has three spans totaling 485 meters (2×55m + (60+70+60)m + (60+65+60)m), and the right section has three spans totaling 399 meters (63+70+63)m + (52+65+52)m continuous steel box girder + 2×17 cast-in-place box girders. The bridge is situated on a straight line with a longitudinal slope of +2.166%. A schematic diagram of the bridge span layout is shown below. Figure 1 , Figure 2 As shown.

[0022] The specific monitoring methods for this bridge are as follows: 1. Deflection monitoring of steel box girders and guide beams One monitoring prism is installed at the front end of the steel box girder and one at the front end of the guide beam. Deflection monitoring is carried out using a total station. Before each jacking operation and during the jacking process, the surveyors must observe the changes in elevation of the measuring points and compare them with the calculated values.

[0023] 2. Monitoring of steel box girder axis deviation Based on the actual site conditions, monitoring prisms were fixed at both the front and rear of the steel box girder. Surveyors used a total station to monitor the changes in the coordinates of the measuring points before, during, and after the jacking operation. The lateral displacement deviation of the steel box girder was calculated based on the observed prism positions.

[0024] 3. Stress monitoring at the connection between the steel box girder and the guide beam, and at the temporary pier support. Stress monitoring points were set up at the connection between the steel box girder and the guide beam to monitor stress changes during construction. A total of two monitoring points were set up. The monitoring points for the temporary piers were mainly set up at the bottom of the temporary piers, and steel wire strain sensors were installed to test the stress changes of the temporary piers during construction. One steel pipe was selected for each temporary pier to set up a monitoring point.

[0025] 4. Monitoring of displacement at the top of temporary pier supports The displacement measuring points for the temporary piers are arranged at the top of the outermost row of temporary piers to monitor the displacement changes of the temporary piers during the jacking construction process and ensure the safety of the temporary pier supports. The displacement measurement of the pier tops is carried out using a total station. Before each jacking operation, during the jacking process, and during the beam lowering stage after the jacking is completed, the surveyors must observe the displacement changes of the temporary piers.

[0026] 5. Temporary pier foundation settlement monitoring Temporary pier foundations will settle under vertical loads. To monitor the settlement changes of the temporary pier foundations, one settlement monitoring point is set up on each temporary pier foundation. Electronic levels are used to monitor the settlement of the temporary pier foundations during beam assembly and jacking.

[0027] 6. Monitoring during the beam lowering stage The girder was lowered gradually using a hydraulic synchronous jacking system. Before the steel box girder was pushed into place, observation prisms were placed at the corresponding positions of the temporary piers of the steel box girder. Four measuring points were set up on the left side of the bridge and four measuring points were set up on the right side of the bridge. During the girder lowering process, a total station was used to monitor the elevation of the prisms in real time to control the girder lowering speed and structural safety.

[0028] Based on the monitoring results, the following analysis of the jacking construction monitoring was conducted: 1. Axis misalignment Because the guide beam extends 36m forward, its axial deviation protrudes more than that of the steel box girder. The axial deviation of the guide beam is always controlled within 80mm, while that of the steel box girder is controlled within 50mm. During the jacking process, the axial deviation of the steel box girder is basically within 30mm.

[0029] 2. Guide beam deflection When the maximum cantilever of the steel guide beam reaches 55m, i.e., before the pier at the end of the guide beam, the vertical deflection is at its maximum, with a maximum value of 256mm, which is 81.4% of the calculated value of 314.6mm under the most unfavorable load combination. A second maximum value of 172mm appears before the temporary pier in the side span of the guide beam end, which is 79.5% of the calculated value of 216.3mm under the most unfavorable load combination. The deflection gradually increases between the temporary piers in the mid-span, reaching its maximum value before the pier; similarly, the deflection gradually increases between the temporary piers in the side spans, reaching its maximum value before the pier. This pattern of change is consistent with theoretical calculations.

[0030] 3. Stress at the connection between the steel box girder and the guide beam The stress at the connection between the steel box girder and the guide beam is at its maximum when the end of the steel guide beam passes the temporary pier of the main pier and the front cantilever is 18m. At this point, the top of the beam is under compression and the bottom is under tension, with a maximum stress of 131.2MPa, which is 79.8% of the calculated value of 164.4MPa under the most unfavorable load combination. The stress state at the top and bottom of the beam is always symmetrical. When the end of the guide beam is between the temporary piers at mid-span, the stress at the connection gradually increases. After the head of the guide beam passes the temporary pier of the main pier, the connection exhibits reverse bending. The stress reaches its maximum value when the end of the guide beam passes the temporary pier of the main pier 18m. After this, the reverse bending decreases, the deflection of the guide beam increases, and the stress at the connection becomes positive. The steel box girder and the guide beam are made of Q345 steel, with allowable compressive and bending stresses of 250MPa and allowable shear stress of 140MPa. The variation pattern is consistent with the theoretical calculation.

[0031] 4. Stress at the bottom of temporary piers The theoretically calculated maximum reaction force at the jacking support point is 357.7t, occurring at the left main pier temporary pier when the guide beam passes the main pier temporary pier by 12m. The actual measured maximum value on site is 321.4t, which is 89.8% of the calculated value of 357.7t under the most unfavorable load combination. In the initial stage of jacking, the stress at the bottom of the assembly platform temporary pier is relatively large, with the maximum stress of a single steel pipe column being around 28MPa. The stress at the bottom of the left side span temporary pier remains relatively stable, with the stress at the bottom of a single steel pipe column remaining below 20MPa. The stress at the bottom of the left main pier temporary pier gradually increases when the guide beam end is between the mid-span temporary piers, reaching its maximum value when the guide beam head passes the right main pier temporary pier by 12m, with the maximum stress of a single steel pipe column reaching 40.6MPa. The variation pattern of the right main pier temporary pier is similar to that of the left main pier, with the maximum stress of a single steel pipe column reaching 40MPa before the beam is lowered. The temporary pier steel pipe columns are made of Q235 steel, with allowable compressive and bending stresses of 170MPa and allowable shear stress of 100MPa. The stress variation law of the steel pipe columns is consistent with the theoretical calculation.

[0032] 5. Horizontal displacement of the top of the temporary pier During the jacking process, the magnitude of the horizontal displacement of the temporary pier top is related to factors such as the pier top load-bearing capacity, the height of the temporary pier, the synchronization status of the walking jacks, and the balanced force on the pier top platform. The displacement of the temporary pier top on the assembly platform is relatively large, mainly due to the low terrain and large pier height at the pier location. The horizontal displacement of the temporary pier top is always controlled within 15mm.

[0033] 6. Settlement of temporary pier cap During the jacking process, the settlement of the temporary pier cap is related to factors such as foundation treatment, pier top load-bearing capacity, the synchronous state of the walking jacks, and the balanced stress on the pier top platform. Considering the influence of the construction site environment, the temporary pier caps on one side of the assembly platform and the left side of the main pier showed significant settlement once, and then tended to stabilize, indicating that the inelastic deformation of the foundation was eliminated after bearing the load. The temporary pier on the right side of the main pier showed two significant settlements, the first being larger at 7.2 mm and the second smaller at 4.5 mm. This may be due to poor foundation soil layer and insufficient hardening thickness. In addition, the right side of the main pier had a large load, reaching a maximum of 316 tons. The assembly platform showed obvious elastic change characteristics, possibly due to poor foundation soil and elastic deformation, which later stabilized. If excessive settlement is found in the temporary pier cap during the jacking process, foundation treatment is crucial. This can be achieved by excavation and replacement, increasing the thickness of the hardened layer, and surface grouting to ensure the bearing capacity of the foundation. The uneven settlement on both sides of the temporary pier cap was always controlled within 10 mm.

[0034] The analysis results are as follows: (1) The deviation of the right steel box girder axis is basically within 30mm, and the deviation of the left steel box girder axis is basically within 12mm; the horizontal displacement of the top of the temporary pier is always controlled within 15mm; the control effect is good.

[0035] (2) The maximum measured vertical deflection at the front end of the steel guide beam is about 80% of the theoretical calculation value; the maximum measured stress at the connection between the steel box girder and the guide beam is about 80% of the theoretical calculation value; the maximum measured stress at the bottom of the temporary pier is about 90% of the theoretical calculation value; indicating that the theoretical calculation is conservative, the variation pattern is consistent with the theoretical calculation, and the results are safe and reliable.

[0036] (3) By taking measures, the uneven settlement on both sides of the temporary pier cap was always controlled within 10mm, which met the construction requirements.

[0037] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for monitoring the jacking construction of steel box girders for bridges spanning coal mine goaf areas, characterized in that, Includes the following steps: (1) Monitor the deflection of the steel box girder and the guide beam. The specific process is as follows: one monitoring prism is set up at the front end of the steel box girder and the front end of the guide beam. The deflection is monitored by a total station. Before each jacking operation and during the jacking process, the surveyors must observe the changes in the elevation of the measuring points and compare them with the calculated values. (2) Monitor the deviation of the steel box girder axis; the specific process is as follows: according to the actual situation on site, monitoring prisms are fixed at the front and rear of the steel box girder. The surveyors use a total station to monitor the changes in the coordinates of the measuring points before, during and after the jacking. The lateral displacement deviation of the steel box girder is calculated based on the observed prism position. During the jacking process, the allowable deviation of the steel box girder axis is 50mm. After each jacking stage, the allowable deviation of the steel box girder axis is 5mm, and the limit value is 10mm. (3) Monitor the stress at the connection between the steel box girder and the guide beam, and at the temporary pier support; (4) Monitor the displacement of the top of the temporary pier support; the specific process is as follows: the displacement measuring points of the top of the temporary pier are arranged at the top of the outermost row of temporary piers so as to understand the changes in the displacement of the temporary piers at any time during the jacking construction process and ensure the safety of the temporary pier support during the jacking construction process; the displacement of the top of the pier is measured by a total station. Before each jacking construction, during the jacking process, and during the beam lowering stage after the jacking is completed, the surveyors must observe the changes in the displacement of the temporary piers. (5) Monitor the settlement of temporary pier foundations; the specific process is as follows: the temporary pier foundations will settle under the action of vertical load. In order to monitor the settlement changes of the temporary pier foundations, one settlement monitoring point is set up on each temporary pier foundation. During the beam splicing and jacking process, electronic level is used to monitor the settlement of the temporary pier foundations. (6) Monitor the beam dropping stage.

2. The method for monitoring the jacking construction of steel box girders for bridges spanning coal mine goaf areas according to claim 1, characterized in that, The specific process of monitoring the stress at the connection between the steel box girder and the guide beam and the temporary pier support in step (3) is as follows: stress monitoring points are set up at the connection between the steel box girder and the guide beam to understand the stress changes at the connection between the steel box girder and the guide beam during construction. A total of 2 measuring points are set up. The measuring points of the temporary pier are mainly set up at the bottom of the temporary pier, and steel wire strain sensors are installed to test the stress changes of the temporary pier during construction. One steel pipe is selected for each temporary pier to set up a monitoring point.

3. The method for monitoring the jacking construction of steel box girders for bridges spanning coal mine goaf areas according to claim 1 or 2, characterized in that, The specific process of monitoring the beam lowering stage in step (6) is as follows: the beam is lowered step by step using a hydraulic synchronous jacking system. Before the steel box girder is pushed into place and lowered, observation prisms are arranged at the corresponding positions of the temporary piers of the steel box girder. Four measuring points are arranged on the left side of the bridge and four measuring points are arranged on the right side of the bridge. During the beam lowering process, a total station is used to monitor the elevation of the prisms in real time to control the beam lowering speed and structural safety.

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