Calculation Method of Friction Coefficient of Old Frame Bridge and Construction Technology of Jacking out Old Frame Bridge

Abstract

The present invention relates to the field of road engineering and discloses a method for calculating the friction coefficient of an old frame bridge, which is calculated using the following formula: where μ is the friction coefficient between the old frame bridge and the original soil; N is the self-weight of the old frame bridge; A is the area of the bottom plate of the old frame bridge; c is the cohesion of the soil at the bottom plate of the old frame bridge and the internal friction angle φ. The construction process for jacking out the old frame bridge proposed by the present invention includes the following steps: D1. Reinforce the existing railway line for overhead, and slope-excavate the soil on both sides of the old frame bridge; D2. Chisel the soil inward along the perimeter of the bottom plate of the old frame bridge and remove the soil at the edge below the perimeter of the bottom plate. The construction process proposed by the present invention utilizes the characteristic that increasing the water content of the foundation soil can effectively reduce the cohesion and internal friction angle of the soil. By drilling holes to circulate and alternately inject water into the soil below the bottom plate multiple times, the purpose of reducing the comprehensive friction coefficient μ is achieved, and finally the required jacking force is very small, providing a prerequisite for the jacking-out construction.

Description

Technical Field

[0001] The present invention relates to the technical field of road engineering construction, and particularly to a method for calculating the friction coefficient of an old frame bridge and a construction technology for jacking out an old frame bridge. Background Art

[0002] With the development of social economy, the underpass bridges at the intersections of early-built urban roads and railways have gradually become traffic bottlenecks, unable to meet the growing traffic demand, and there is an urgent need to transform and upgrade urban roads. Therefore, there have emerged more and more engineering cases of demolishing old frame bridges and jacking in new frame bridges under existing railway operation lines.

[0003] Generally, methods such as mechanical crushing, diamond wire sawing and circular saw cutting, direct jacking out, and blasting can be used to demolish old frame bridges under railway operation lines. At present, the diamond wire saw cutting method is widely used in many projects to demolish old frame bridges, while the direct jacking out construction method is less used. The direct jacking out method is to jack out the old frame bridge outside the railway safety line and then carry out mechanical demolition. It has many advantages: the construction speed is relatively fast, there is no need to consider the protection of the old frame bridge during the jacking out process, and there is no need to specifically correct certain head drops or head raises during the jacking out process. After the old frame bridge is jacked out of the railway safety range, demolition is carried out. The operation space is large, and it can be carried out synchronously with the jacking in operation of the new frame bridge, without increasing the total construction period of the project.

[0004] However, the main limitation of the direct jacking out construction method for demolishing old frame bridges is that after years of use, the bottom plate of the old frame bridge is in close contact with the foundation soil and has formed a cementation, and the viscous force and frictional resistance between them are relatively large, resulting in a relatively large required jacking force. The jacking out operation requires more power equipment and a relatively large temporary backrest needs to be built, with a relatively high cost. At present, there is no method for determining the comprehensive friction coefficient between the old frame bridge and the original soil or empirical value, and the force mechanism of directly jacking out the old frame bridge is not clear, which restricts the engineering application of the direct jacking out construction method.

[0005] It can be seen that if the comprehensive friction coefficient between the old frame bridge and the original soil can be accurately calculated, and measures are taken to effectively reduce the frictional resistance between the bottom plate of the old frame bridge and the original soil, so that fewer power equipment are required, the backrest production is simpler, the construction period is shorter, and the cost is lower, then the cost performance of the jacking out construction can be improved, and its application in the demolition of old frame bridges can be promoted. Summary of the Invention

[0006] To make up for the deficiencies of the existing technology, the present invention provides a method for calculating the friction coefficient of an old frame bridge and a construction technology for jacking out an old frame bridge.

[0007] The present invention is realized by the following technical solutions: a method for calculating the friction coefficient between an old frame bridge and the original soil,

[0008] Calculate using the following formula:

[0009]

[0010] Among them, μ is the friction coefficient between the old frame bridge and the original soil; N is the self-weight of the old frame bridge; A is the bottom plate area of the old frame bridge; c and φ are the cohesion and internal friction angle of the soil at the bottom plate of the old frame bridge respectively.

[0011] The present invention also proposes a construction technology for jacking out the old frame bridge, which includes the following steps:

[0012] D1. Strengthen the existing railway line for overhead, and slope-excavate the soil on both sides of the old frame bridge; break and remove the original road surface structure inside and at both ends of the old frame bridge until the top surface of the concrete bottom plate of the old frame bridge is exposed; excavate and at least remove the foundation soil within the jacking range of the old frame bridge, so that the top surface of the surrounding foundation is lower than the bottom surface of the concrete bottom plate of the old frame bridge;

[0013] D2. Chisel the soil inward along the perimeter of the bottom plate of the old frame bridge, and remove the soil at the edge below the perimeter of the bottom plate to reduce the bonding and viscosity between the bottom plate and the original soil;

[0014] D3. Drill holes evenly on the bottom plate of the old frame bridge and insert corresponding plastic hollow spray pipes. Seal the spray pipes and the drill holes with engineering glue to prevent water and air leakage between the spray pipes and the concrete slab. The bottom of the spray pipe penetrates into the foundation;

[0015] D4. Inject high-pressure air and high-pressure water into the spray pipes in sequence;

[0016] D5. Take samples of the soil soaked by water injection at the bottom plate of the old frame bridge and conduct direct shear tests to determine the cohesion c and internal friction angle of the soil and substitute them into the formula to calculate the friction coefficient μ;

[0017] If the calculated friction coefficient μ is greater than 0.40, then repeat the operation described in D4; until the calculated friction coefficient μ is not greater than 0.40, then connect the top of each spray pipe to the high-pressure grouting machine through a hose one by one, and inject bentonite drag reduction slurry into the spray pipe through the high-pressure grouting machine. Inject the bentonite drag reduction slurry 2 - 3 times in a cycle and alternately, with an interval of 1 - 2 hours between each time;

[0018] D6. While performing the above-mentioned operations, make a simple backrest behind the old frame bridge, arrange the jacking equipment, and start the jacking operation after injecting the drag reduction slurry.

[0019] As a further improvement of the above solution, when chiseling the soil inward along the perimeter of the bottom plate of the old frame bridge, remove the soil within at least 10 cm extending inward from the perimeter below the bottom plate.

[0020] As a further improvement of the above solution, when uniformly drilling holes in the bottom plate of the old frame bridge, the diameter of the drilled holes is 2 - 4 cm.

[0021] As a further improvement of the above solution, the length of the bottom of the spray pipe penetrating into the foundation soil is not less than 1.0 cm.

[0022] As a further improvement of the above solution, the specific operation steps of sequentially injecting high-pressure air and high-pressure water into the spray pipe are as follows:

[0023] The top of each spray pipe is connected to an air compressor through a hose one by one. High-pressure air is injected into the spray pipe through the air compressor, and the air is pressed into the original soil of the bottom plate of the old frame bridge to form a series of fissure channels with irregular distribution, pre-opening channels for subsequent liquid injection. The air is injected cyclically and alternately 2 - 3 times.

[0024] The top of each spray pipe is connected to a water pressure pump through a hose one by one. High-pressure water is injected into the spray pipe through the water pressure pump, and the water is injected cyclically and alternately 2 - 3 times, with an interval of 4 - 6 h for each time. Finally, the water content of the soil layer with a thickness of 10 - 20 cm below the bottom plate is greater than the liquid limit.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. Based on the shear strength theory, the present invention derives a calculation formula for the comprehensive friction coefficient μ during the jacking construction process of the old frame bridge, which takes into account the strength characteristics of the original soil mass, i.e., the cohesion c and the internal friction angle The parameter characteristics of the frame bridge, i.e., the self-weight N and the bottom area A, while the traditional jacking construction friction coefficient cannot consider these factors.

[0027] 2. In the calculation method of the friction coefficient μ proposed by the present invention, the friction coefficient term induced by the cohesion c is cA / N, and the internal friction angle The induced friction coefficient term is Calculations show that cA / N is generally greater than The term, indicating that the contribution of the cohesion parameter of the foundation soil to the comprehensive friction coefficient μ is greater than that of the internal friction angle parameter. Therefore, if measures can be taken to reduce the cohesion of the foundation soil near the bottom plate, the comprehensive friction coefficient μ can be greatly reduced, setting the focus for the application of subsequent resistance reduction measures.

[0028] 3. Theoretical analysis shows that with the increase of the water content, the comprehensive friction coefficient μ between the bottom plate of the old frame bridge and the soil mass calculated according to the proposed method decreases sharply. Therefore, as long as the water content of the soil mass is increased, the comprehensive friction coefficient μ can be greatly reduced, providing an idea for solving the problem of excessive initial jacking force during the jacking construction process of the old frame bridge.

[0029] 4. The construction process proposed by the present invention utilizes the characteristic that increasing the water content of the foundation soil can effectively reduce the cohesion and internal friction angle of the soil mass. By drilling holes and circulating and alternately injecting water into the soil mass under the bottom plate multiple times, the purpose of reducing the comprehensive friction coefficient μ is achieved. Finally, the required jacking force is very small, providing a prerequisite for the jacking construction.

[0030] 5. In the construction process proposed by the present invention, drilling holes, high-pressure injecting air, high-pressure injecting water flow, and high-pressure injecting bentonite drag reduction slurry are carried out on the bottom plate of the frame bridge. The equipment is simple, the technology is mature, the cost is low, and it is feasible.

[0031] 6. Multiple processes in the construction process proposed by the present invention can be carried out synchronously. The overall construction period of the proposed old frame bridge jacking construction method, including the preliminary preparation, can be completed within 3 days, and the construction period is short. Moreover, the jacking operation of the old frame bridge can be carried out synchronously with the prefabrication and jacking operation of the new frame bridge. Therefore, the jacking operation of the old frame bridge will not increase the total construction period of the entire project. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the direct shear test of soil;

[0033] Figure 2 It is a schematic diagram of the force on the shear plane of the soil mass in the direct shear test;

[0034] Figure 3 It is a schematic diagram of the friction between the old frame bridge and the soil mass during jacking;

[0035] Figure 4 It is the influence of the soil cohesion c on the comprehensive friction coefficient μ;

[0036] Figure 5 It is the internal friction angle of the soil The influence on the comprehensive friction coefficient μ;

[0037] Figure 6 The friction coefficient characteristics calculated by back-calculation based on the measured parameters in Reference 1;

[0038] Figure 7 The friction coefficient characteristics calculated by back-calculation based on the measured parameters in Reference 2;

[0039] Figure 8 The friction coefficient characteristics calculated by back-calculation based on the measured parameters in Reference 3;

[0040] Figure 9 It is a schematic diagram of drilling holes and high-pressure injecting water on the bottom plate of the old frame bridge;

[0041] Figure 10 It is a process flow chart of the jacking construction technology of the old frame bridge under the existing railway operation line.

[0042] Main Symbol Explanation:

[0043] 1. Lower box; 2. Upper box; 3. Permeable stone; 4. Shearing surface; 5. Old frame bridge; 6. D-shaped temporary beam; 7. Railway track; 8. Bottom plate; 9. Drilling hole; 10. Spray pipe; 11. Connecting pipe; 12. Water pressure pump. Detailed implementation mode

[0044] Next, in combination with the accompanying drawings and specific implementation modes, the present invention will be further described. It should be noted that, on the premise of no conflict, any combination can be formed between the following-described embodiments or technical features to form a new embodiment.

[0045] Embodiment 1:

[0046] The calculation method of the friction coefficient of the old frame bridge proposed by the present invention is calculated using the following formula:

[0047]

[0048] Among them, μ is the friction coefficient between the old frame bridge and the undisturbed soil; N is the self-weight of the old frame bridge; A is the area of the bottom plate of the old frame bridge; c and φ are the cohesion and internal friction angle of the soil at the bottom plate of the old frame bridge, respectively.

[0049] The various parameters in the above formula are determined by the following methods:

[0050] Calculate the self-weight N of the old frame bridge 5 according to the design data; calculate the area A of the bottom plate 8 of the old frame bridge 5 according to the design data; take samples of the soil at the bottom plate of the old frame bridge for direct shear tests to determine the cohesion c and internal friction angle φ of the soil.

[0051] The above calculation method of the friction coefficient between the old frame bridge and the undisturbed soil is derived by the following method:

[0052] The calculation of the jacking force between the old frame bridge and the undisturbed soil can be simplified to

[0053] P = μ·N (1)

[0054] In the formula: P - maximum jacking force (unit: kN); μ - comprehensive friction coefficient; N - self-weight of the bridge and culvert (unit: kN). When the self-weight of the frame bridge is fixed, the magnitude of the jacking force actually depends on the value of the comprehensive friction coefficient.

[0055] Also according to the Mohr-Coulomb failure criterion, the shear strength of the soil is calculated according to Equation (2):

[0056] τ = c + σtanφ (2)

[0057] In the formula: τ is the shear strength (unit: kPa); σ is the total stress (unit: kPa); c is the cohesion of the soil mass (unit: kPa); φ is the internal friction angle of the soil (unit: °). The concept of equivalent internal friction angle is introduced:

[0058] τ = σtanφ d = c + σtanφ (3)

[0059]

[0060] In the formula: φ d is the equivalent internal friction (unit: °). Multiply both sides of formula (3) by the bottom area A of the frame bridge (unit: ㎡) to get:

[0061] τA = σAtanφ d (5)

[0062] For the jacking-out construction of the frame bridge, τA is actually the jacking force P (unit: kN); σA is the vertical downward load on the soil mass, which is actually the self-weight N of the frame bridge (unit: kN), as Figure 3 shown. Therefore, formula (5) is transformed into:

[0063] P = tanφ d ·N (6)

[0064] Combining formula (1) and formula (6), it can be known that:

[0065]

[0066] During the jacking-out construction of the old frame bridge 5, after years of use, the bottom plate 8 of the old frame bridge 5 has been in close contact with the foundation soil mass and has produced cementation. The viscous force and frictional resistance between them are relatively large, and the undisturbed and undamaged original soil at the bottom plate has a high strength. For the jacking-out construction of the old frame bridge 5, it is actually necessary to break the cementation between the bottom plate and the foundation soil mass and break the shear strength of the original soil. Therefore, the frictional resistance during the jacking-out construction is obviously much larger than that of the normal jacking-in construction of a new frame bridge, and the comprehensive friction coefficient μ is often greater than 1.0.

[0067] Based on the understanding that the jacking-out movement of the old frame bridge is actually that the shear stress borne by the original soil at the bottom plate reaches and exceeds the yield strength and fails and is damaged by the external force, the value of the comprehensive friction coefficient μ can be deduced by discussing the shear strength theory. The direct shear test in geotechnical tests is as Figure 1 and Figure 2 shown. Figure 1 In it, above the lower box 1 is the upper box 2. The soil sample 3 is stored between the upper box 2 and the lower box 1, and a permeable stone 3 is arranged at the top of the upper box 2. The splicing surface of the lower box 1 and the upper box 2 is the shear surface. The stress state of the soil mass at the bottom plate 8 during the jacking-out process of the old frame bridge 5 is as Figure 3As shown. By comparison Figure 2 and Figure 3 It can be seen that the relative movement between the bottom plate and the soil during the jacking-out process of the frame bridge is "exactly the same" as the failure state on the shear plane in the direct shear test, both of which are the slip and failure of the soil after reaching the shear strength and yield strength.

[0068] Taking a frame bridge in Hefei area as an example, the characteristics of the comprehensive friction coefficient μ are discussed. An old frame bridge under an existing railway operation line has a total width of 16.1m, a net width of 14.0m, a height of 6.20m, a length of 13.60m, a top plate thickness of 0.65m, and a bottom plate thickness of 0.75m. It needs to be demolished due to road reconstruction, and then a new frame bridge with larger dimensions and specifications will be jacked in. The self-weight of the old frame bridge N = 11090.8kN, and the bottom plate area of the old frame bridge A = 218.96㎡.

[0069] The bottom plate of the old frame bridge is located in the second layer of clay, which is grayish-yellow, hard plastic, has a shiny cut surface, no shaking reaction, high toughness, high dry strength, common iron and manganese nodules, and is locally interbedded with thin layers of silty clay. This layer is widespread. The parameters of the second layer of clay are: the foundation bearing capacity σ0 = 260kPa, the unit weight 19.9kN / m 3 , the cohesion c = 65.0kPa, and the internal friction angle φ = 14.8°. According to formula (7), the calculated comprehensive friction coefficient μ is:

[0070]

[0071] The jacking-out friction coefficient of the old frame bridge calculated according to formula (7) is relatively large, which conforms to the basic characteristics of the shear failure of undisturbed soil. The friction coefficient during the jacking-in process of the new frame bridge is relatively small, generally 0.5 - 0.80; the jacking-out friction coefficient of the old frame bridge is 1.5 - 2.0 times that of the jacking-in friction coefficient of the new frame bridge.

[0072] Figure 4 shows the influence of the change in the cohesion value of the foundation soil on the comprehensive friction coefficient μ when the internal friction angle takes a constant value; Figure 5 shows the influence of the change in the internal friction angle value of the foundation soil on the comprehensive friction coefficient μ when the cohesion takes a constant value. Figures 6 to 8 Furthermore, the characteristic curve of the friction coefficient obtained by inverting the measured data from multiple literatures is given. It can be seen that:

[0073] (1) The contribution of the cohesion parameter of the foundation soil to the comprehensive friction coefficient μ is greater than that of the internal friction angle parameter. When the cohesion c = 65.0kPa and the internal friction angle φ = 14.8°, the value of the friction coefficient term (cA / N) induced by cohesion in the comprehensive friction coefficient μ is 4.86 times the value of the friction coefficient term (tanφ) induced by the internal friction angle.

[0074] (2) When the cohesion of the foundation soil increases by 10% while the internal friction angle remains unchanged, the comprehensive friction coefficient μ increases by 6.3%. When the cohesion remains unchanged and the internal friction angle of the foundation soil increases by 10%, the comprehensive friction coefficient μ increases by 2.4%. This shows that the comprehensive friction coefficient μ is more dependent on the cohesion of the foundation soil.

[0075] (3) During the jacking-out process of the old frame bridge, the smaller the comprehensive friction coefficient μ, the better. Given that the comprehensive friction coefficient μ is more dependent on the cohesion of the foundation soil, if measures can be taken to reduce the cohesion of the foundation soil near the bottom plate, the comprehensive friction coefficient μ can be greatly reduced, indicating the direction for the application of subsequent drag reduction measures.

[0076] This scheme analyzes the influence of water content change on the friction coefficient:

[0077] Generally, as the water content increases, the shear strength of the soil gradually decreases, but the reduction amplitude is different at different stages. Therefore, based on the measured data in relevant literature, the influence of water content change on the comprehensive friction coefficient μ is explored. Taking the project of the underpass of Guzhen Road through Taohuadian Station and the Hefu High-Speed Railway overpass in Hefei as an example, the total length of the 1# frame bridge box body is 54.53m, the total height is 8.3m, the net height of the box culvert structure is 6.4m, the total width of the box culvert is 14.5m, the net width is 12.5m, the side wall width of the box culvert is 1m, the top plate is 0.9m, the bottom plate is 1m, the self-weight of the frame bridge is 57757.5kN, and the bottom area is 790.7m2.

[0078] References [1-3] give the influence of the change of soil sample water content on cohesion and internal friction angle in different regions and different projects. Based on this basic data and substituting it into formula (7), the numerical value of the comprehensive friction coefficient μ under different water content conditions can be obtained. As Figures 6 to 8 shown, it can be seen that as the water content of the soil increases, the comprehensive friction coefficient μ between the bottom plate of the old frame bridge and the soil decreases rapidly. Therefore, as long as the water content of the soil is increased, the comprehensive friction coefficient μ can be greatly reduced, providing an idea for solving the problem of excessive initial jacking force during the jacking-out construction of the old frame bridge.

[0079] There are more measured data in the literature to support the above conclusion, which will not be elaborated here.

[0080] The calculation method of the friction coefficient between the proposed old frame bridge and the undisturbed soil has the following advantages:

[0081] Based on the shear strength theory, the present invention derives the calculation formula for the comprehensive friction coefficient μ during the jacking-out construction of the old frame bridge, which takes into account the strength characteristics of the undisturbed soil mass (cohesion c and internal friction angle φ) and the parameter characteristics of the frame bridge (self-weight N and bottom area A), while the traditional jacking construction friction coefficient cannot consider these factors.

[0082] In the method for calculating the friction coefficient μ proposed by the present invention, the friction coefficient term induced by the cohesion c is (cA / N), and the friction coefficient term induced by the internal friction angle φ is (tan φ). Calculations show that (cA / N) is generally greater than the (tan φ) term, indicating that the contribution of the cohesion parameter of the foundation soil to the comprehensive friction coefficient μ is greater than that of the internal friction angle parameter. Therefore, if measures can be taken to reduce the cohesion of the foundation soil near the bottom plate, the comprehensive friction coefficient μ can be greatly reduced, setting the focus for the application of subsequent drag reduction measures.

[0083] Theoretical analysis shows that as the water content increases, the comprehensive friction coefficient μ between the bottom plate of the old frame bridge and the soil calculated according to the proposed method decreases sharply. Therefore, as long as the water content of the soil is increased, the comprehensive friction coefficient μ can be greatly reduced, providing an idea for solving the problem of excessive initial jacking force during the jacking construction of the old frame bridge.

[0084] The above-mentioned references 1 - 3 are respectively:

[0085] 1. Chen Haiming, Ban Fengqi, Liu Xiaowei. The relationship between the shear strength indexes c, Ф and water content ω of unsaturated soil [J]. Journal of Hefei University of Technology (Natural Science Edition), 2006, 29(6): 736 - 739.

[0086] 2. Cao Xiaoyi: Research on the influence of water content and stress state on the shear strength of loess in western Shanxi [D]. Chang'an University, 2011.

[0087] 3. Zhao Rui, Zuo Shuangying, Wang Song, etc. Experimental study on the triaxial shear strength of remolded red clay in Guiyang with different water contents [J]. Hydrogeology & Engineering Geology, 2015, 42(5): 90 - 95.

[0088] Example 2:

[0089] The present invention also proposes a jacking construction technology for an old frame bridge, including the following steps:

[0090] D1. Strengthen and jack up the existing railway line, and slope - excavate the soil on both sides of the old frame bridge; break and remove the original road surface structure inside and at both ends of the old frame bridge until the top surface of the concrete bottom plate of the old frame bridge is exposed; excavate and at least remove the foundation soil within the top - elevation range of the old frame bridge, so that the top surface of the surrounding foundation is lower than the bottom surface of the concrete bottom plate of the old frame bridge; usually, the railway track 7 is reinforced by a D - type movable beam 6, and both ends of the D - type movable beam 6 act on the reinforced concrete strip foundation, and the strip foundation is supported by manually dug piles. That is, before the jacking construction of the old frame bridge, the soil at both ends, both sides, and above the frame bridge has been excavated, and the old frame bridge no longer bears the railway load.

[0091] D2. Chisel the soil inward along the perimeter of the bottom plate of the old frame bridge, and remove the soil at the edge below the perimeter of the bottom plate to reduce the bonding and viscous force between the bottom plate and the undisturbed soil;

[0092] D3. Drill holes evenly on the bottom plate of the old frame bridge, and insert corresponding plastic hollow spray pipes. Seal the gaps between the spray pipes and the drilled holes with engineering glue to prevent water and air leakage between the spray pipes and the concrete slab. The bottom of the spray pipe extends deep into the foundation; as Figure 9 shown.

[0093] D4. Inject high-pressure air and high-pressure water flow into the spray pipes in sequence, as Figure 9 shown;

[0094] D5. Take samples of the soil soaked by water injection at the bottom plate of the old frame bridge and conduct direct shear tests to determine the cohesion c and internal friction angle φ of the soil, and substitute them into the formula to calculate the friction coefficient μ;

[0095] If the calculated friction coefficient μ is greater than 0.40, then repeat the operation described in D4; until the calculated friction coefficient μ is not greater than 0.40, then connect the top of each spray pipe to the high-pressure grouting machine through a hose one by one, and inject bentonite drag reduction slurry into the spray pipe through the high-pressure grouting machine. Inject the bentonite drag reduction slurry in cycles and alternately for 2 - 3 times, with an interval of 1 - 2 hours between each time;

[0096] D6. While performing the above-mentioned operations, make a simple backrest behind the old frame bridge, arrange the jacking equipment, and start the jacking operation after injecting the drag reduction slurry. The entire construction process flow chart is as Figure 10 shown.

[0097] As an optional implementation manner of the present invention, when chiseling the soil inward along the perimeter of the bottom plate of the old frame bridge, remove the soil extending at least 10 cm inward from the perimeter under the bottom plate.

[0098] As an optional implementation manner of the present invention, when drilling holes evenly on the bottom plate of the old frame bridge, the diameter of the drilled holes is 2 - 4 cm.

[0099] As an optional implementation manner of the present invention, the length of the bottom of the spray pipe extending deep into the foundation soil is not less than 1.0 cm.

[0100] As an optional implementation manner of the present invention, the specific operation steps for injecting high-pressure air and high-pressure water flow into the spray pipes in sequence are:

[0101] Connect the top of each spray pipe to the air compressor through a hose one by one, and inject high-pressure air into the spray pipe through the air compressor. The air is pressed into the undisturbed soil at the bottom plate of the old frame bridge to form a series of irregularly distributed fissure channels, which pre-open channels for subsequent liquid injection. Inject air in cycles and alternately for 2 - 3 times;

[0102] The top of each nozzle is successively connected to a water pressure pump 12 through a connecting pipe 11 (using a flexible hose). High-pressure water flow is injected into the nozzle through the water pressure pump 12, and the water is injected cyclically and alternately 2 to 3 times, with an interval of 4 to 6 hours between each injection. Finally, the water content of the soil layer with a thickness of 10 to 20 cm under the bottom plate is greater than the liquid limit.

[0103] The construction process flow proposed in the above embodiment is as Figure 10 shown, and the proposed construction process has the following advantages:

[0104] The proposed construction process utilizes the characteristics that increasing the water content of the foundation soil can effectively reduce the cohesion and internal friction angle of the soil. By drilling holes and injecting water into the soil under the bottom plate cyclically and alternately for multiple times, the purpose of reducing the comprehensive friction coefficient μ is achieved. Finally, the required jacking force is very small, providing a prerequisite for the jacking construction.

[0105] In the proposed construction process, drilling holes, injecting high-pressure air, injecting high-pressure water flow, and injecting bentonite drag reduction slurry are carried out on the bottom plate of the frame bridge. The equipment is simple, the technology is mature, and the cost is low, making it feasible.

[0106] The multiple processes proposed are carried out synchronously. The overall construction period of the proposed method for jacking out the old frame bridge, including the preliminary preparation, can be completed within 3 days, and the construction period is short. Moreover, the jacking operation of the old frame bridge can be carried out synchronously with the prefabrication and jacking operation of the new frame bridge. Therefore, the jacking out operation of the old frame bridge will not increase the total construction period of the entire project.

[0107] The innovative idea of the present invention is obtained through innovation and reflection based on the key points, difficulties, and limitations of the actual old frame bridge demolition project, making the demolition construction period of the old frame bridge short, the cost low, and the construction safety high.

[0108] The above implementation manners are only the preferred implementation manners of the present invention and cannot be used to limit the protection scope of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention belong to the protection scope required by the present invention.

Claims

1. The construction technology for jacking out an old frame bridge is characterized in that It includes the following steps: D1. Strengthen the overhead of the existing railway line, and slope-excavate the soil on both sides of the old frame bridge; break and remove the original pavement structure inside and at both ends of the old frame bridge until the top surface of the concrete floor slab of the old frame bridge is exposed; excavate and at least remove the foundation soil within the elevation range of the top of the old frame bridge, so that the top surfaces of the surrounding foundations are lower than the bottom surface of the concrete floor slab of the old frame bridge; D2. Chisel the soil inward along the periphery of the bottom slab of the old frame bridge, and remove the soil at the edge below the periphery of the bottom slab to reduce the bonding and viscosity between the bottom slab and the original soil; D3. Drill holes evenly on the bottom slab of the old frame bridge, and insert corresponding plastic hollow spray pipes. Seal the spray pipes and the drill holes with engineering glue to prevent water and air leakage between the spray pipes and the concrete slab, and the bottom of the spray pipes extends into the foundation; D4. Inject high-pressure air and high-pressure water into the spray pipes in sequence; D5. Take samples of the soil soaked by water injection at the bottom plate of the old frame bridge and conduct direct shear tests to determine the cohesive force of the soil c and the internal friction angle φ , and substitute them into the formula to calculate the friction coefficient μ ; If the calculated friction coefficient μ is greater than 0.40, the operation described in D4 is repeated; until the calculated friction coefficient μ is not greater than 0.40, then the top of each nozzle is connected to a high-pressure grouting machine one by one through a hose, and bentonite drag reduction slurry is injected into the nozzle through the high-pressure grouting machine. The bentonite drag reduction slurry is injected cyclically and alternately for 2 to 3 times, with an interval of 1 to 2 hours between each time; D6. While performing the above-mentioned processes, construct a simple backrest behind the old frame bridge, arrange the jacking equipment, and start the jacking operation after injecting the drag reduction slurry; The calculation method of the friction coefficient of the old frame bridge is calculated by using the following formula: ； Among them, μ is the friction coefficient between the old frame bridge and the original soil; N is the self-weight of the old frame bridge; A is the bottom plate area of the old frame bridge; c, φ are the cohesion and internal friction angle of the soil at the bottom plate of the old frame bridge, respectively.

2. The jacking construction process of the old frame bridge according to claim 1, characterized in that, When chiseling the soil inward along the periphery of the bottom slab of the old frame bridge, remove the soil within at least 10 cm extending inward from the periphery of the bottom slab.

3. The jacking construction process of the old frame bridge according to claim 2, characterized in that When drilling holes evenly on the bottom slab of the old frame bridge, the drilled hole diameter is 2 - 4 cm.

4. The jacking construction process of the old frame bridge according to claim 2, wherein The length that the bottom of the spray pipe extends into the foundation soil is not less than 1.0 cm.

5. The jacking construction process of the old frame bridge according to claim 2, characterized in that, The specific operation steps of injecting high-pressure air and high-pressure water into the spray pipes in sequence are as follows: Connect the top of each spray pipe to the air compressor through a hose one by one, and inject high-pressure air into the spray pipe through the air compressor. The air is pressed into the original soil of the bottom slab of the old frame bridge to form a series of irregularly distributed fissure channels, which pre-open channels for subsequent liquid injection, and inject air 2 - 3 times in a cycle and alternately; Connect the top of each spray pipe to the water pressure pump through a hose one by one, and inject high-pressure water into the spray pipe through the water pressure pump. Inject water 2 - 3 times in a cycle and alternately, with an interval of 4 - 6 h for each time, and finally make the water content of the soil layer with a thickness of 10 - 20 cm below the bottom slab greater than the liquid limit.

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