A double-row PLC work method pile cofferdam and steel trestle combined construction method for over-deep pit ponds

Abstract

The present application relates to the construction technology field of trestle, especially to a kind of double-row PLC method pile cofferdam and steel trestle combined construction method for deep pit pond, comprising: construction preparation;Positioning and pouring according to construction requirements;Pouring method pile;Inter-pile flat link;Anchor pulling;Water displacement method fills soil;Install load-bearing crossbeam and bailey beam;Pave bridge deck;Repeat the above steps until method pile cofferdam construction is completed;Remove steel trestle after construction is completed;Drainage well is also provided, and the interval between next dewatering well and current dewatering well is determined according to function f (T) and function f (h). Compared with the prior art, the beneficial effects of the present application are that by setting dewatering well in cofferdam and determining the layout of dewatering well according to the actual situation of construction, the soil moisture content is effectively reduced, the effective stress of soil is increased, the stability of soil body in cofferdam is ensured, and the safety of subsequent construction is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of trestle construction, in particular to a double-row PLC method pile cofferdam and steel trestle combined construction method for deep pit ponds. BACKGROUND

[0002] When a new urban road passes through a fish pond, a cofferdam, a temporary retaining structure, is needed to separate the road construction area to prevent water and soil from entering the construction site, so as to drain water and excavate the foundation pit in the cofferdam. At present, double-row steel sheet piles or PLC method pile cofferdams are commonly used for road construction through pit ponds in China. However, if the water depth of the pit pond is deep, the type of pile driver needed is higher, and the corresponding pile driver occupies a larger area. The double-row PLC method pile needs to be driven on the steel trestle.

[0003] Chinese patent publication No. CN 110847169 A discloses a construction method of a steel pipe pile steel trestle, comprising the following steps: step one, steel pipe pile manufacturing; step two, installation of assembly type cantilever guide frame positioning device; step three, steel pipe pile positioning; step four, vibration pile sinking; step five, inter-pile flat connection installation; step six, pillow beam construction; step seven, ring-shaped ear plate construction; step eight, Bailey main beam construction; step nine, I-beam distribution beam and bridge deck construction; and step ten, upper system preloading construction. It can be seen that the construction method of the steel pipe pile steel trestle has the following problems: during the construction process, equipment such as the assembly type cantilever guide frame positioning device needs to be installed, the period required for changing direction and other situations in the later stage is long, and the two rows of steel pipe piles in the middle of the trestle need to be held by a floating crane, which can easily cause unnecessary shaking of the steel sheet pile, affect the firmness of the pile, and affect the safety of subsequent construction. SUMMARY

[0004] The present application aims to provide a double-row PLC method pile cofferdam and steel trestle combined construction method for deep pit ponds to solve the problems of long construction period and inability to ensure construction safety in related technologies.

[0005] To this end, the present application provides a double-row PLC method pile cofferdam and steel trestle combined construction method for deep pit ponds, comprising:

[0006] Construction preparation is performed;

[0007] The steel pipe pile construction site is positioned and the first pair of steel pipe piles are driven according to the construction requirements;

[0008] The method pile is driven in the order of steel pipe pile-Larsen steel sheet pile-steel pipe pile;

[0009] After the method pile is sunk to the designed elevation, inter-pile flat connection is performed;

[0010] Steel bars are used to anchor the two sides of the flat connection;

[0011] The filling is carried out by using the water expelling method, and the filling sequence is pushed from the bank to the pond;

[0012] The load-bearing cross beam and the Bailey beam are installed;

[0013] The bridge deck is laid;

[0014] The next method pile is driven, and the steps of pulling the anchor, the water expelling method construction, the installation of the load-bearing cross beam and the Bailey beam and the laying of the bridge deck are continued until the method pile cofferdam construction is completed;

[0015] After the construction is completed, the steel trestle is removed;

[0016] The water expelling method construction is carried out, and a drainage well is arranged at the middle position of the two side flat links according to the depth function f(T) of the longitudinal coordinate as the distance A from the bank and the function f(H) of the horizontal coordinate as the underwater filling depth T and the distance d from the previous drainage well, the first drainage well is arranged at a distance of 3m from the bank.

[0017] Further, the interval of the drainage well is determined according to the underwater filling depth T and the permeability coefficient K, and the method further comprises:

[0018] The relationship between the distance from the bank and the water depth on the current construction route is detected;

[0019] The depth function A=f(T) of the longitudinal coordinate as the distance A from the bank and the horizontal coordinate as the underwater filling depth T is established;

[0020] The permeability coefficient K of the filled soil is detected;

[0021] The function f(H) containing unknowns of the current underwater filling depth T and the distance d from the previous drainage well is established according to the permeability coefficient K, the flat link spacing L and the diameter R of the drainage well;

[0022] The function f(T) and the function f(H) are solved to obtain the distance d between the next drainage well and the current drainage well.

[0023] Further, the calculation method of the distance d between the next drainage well and the current drainage well is:

[0024] The parameters in the construction process, including the permeability coefficient K, the flat link spacing L, the diameter R of the drainage well and the current underwater filling depth T, are obtained;

[0025] The obtained parameters in the construction process are substituted into the formula in the form of numerical values: Wherein, d is the distance between the next drainage well and the current drainage well, the permeability coefficient K, the flat link spacing L, the diameter R of the drainage well and the depth H of the drainage well.

[0026] Further, the installation of the load-bearing crossbeam further comprises the following steps:

[0027] Mark the position of the steel pipe pile on the load-bearing crossbeam;

[0028] Hoist the load-bearing crossbeam, and control the mark to coincide with the steel pipe pile during hoisting;

[0029] Weld arc-shaped limiting steel plates between the pile body and the load-bearing crossbeam to fix the load-bearing crossbeam.

[0030] Further, the installation of the Bailey beam further comprises the following steps:

[0031] Test the Bailey beam before the construction access, and access for assembly after the test is correct;

[0032] Measure and lay out on the load-bearing crossbeam before the installation of the Bailey beam to determine the accurate position of the Bailey beam;

[0033] Use the caterpillar crane to hoist the Bailey beam and place it at the water pond end of the installed Bailey beam in a straight line;

[0034] Align the lower chord pin hole of the Bailey beam with the pin and insert the pin, then lift the rear end of the Bailey beam, insert the upper chord pin body, and set the safety pin.

[0035] Further, the Bailey beam is firmly bound on the load-bearing crossbeam after being accurately positioned, then the limiter is welded, and then another group of Bailey beams is installed, and the two groups of Bailey beams are connected by the scissors support.

[0036] Further, the bridge deck panel used for laying the bridge deck includes two specifications, one is 16mm thick patterned steel plate, and the other is assembled bridge deck panel with specifications of 6m×2m and 3m×2m, wherein: the assembled bridge deck panel adopts 138mm thick customized steel panel, the horizontal rib spacing is 750mm, the vertical rib spacing is 250mm, the two ends are fixed on the secondary beam by screws, and 5*50 flat steel is additionally welded at the joint, the bridge deck steel plate adopts patterned anti-skid steel plate, and is coated with high-molecular anti-skid and anti-corrosion material, the anti-corrosion material adopts polyurethane oil-resistant, and the coating thickness is 1-2mm.

[0037] Further, the steel trestle further comprises a trestle abutment, and rubber pads are arranged at the trestle abutment and the trestle deck.

[0038] Further, the load-bearing crossbeam is composed of double-spliced I45a I-shaped steel, and the Bailey beam adopts 321 type Bailey beam.

[0039] Further, the construction preparation process specifically is the processing and storage of the steel cofferdam, wherein the steel cofferdam comprises: steel pipe piles, steel sheet piles, tensioned steel bars, and operation platforms.

[0040] Compared with the prior art, the application has the beneficial effects that, on one hand, the application can shorten the distance of the sheet pile driving, improve the safety during the construction and the success rate of the sheet pile locking connection by driving the sheet pile cofferdam in the water on the steel trestle erected on the double-row sheet pile cofferdam, and the system can play the role of temporary road when the road construction in the cofferdam, thereby shortening the construction period of the road construction in the cofferdam; on the other hand, the soil moisture content is effectively reduced, the effective stress of the soil is increased, the stability of the soil in the cofferdam is ensured, and the safety of the subsequent construction is ensured by setting the dewatering well in the cofferdam and determining the layout of the dewatering well according to the actual situation of the construction.

[0041] Further, the traditional empirical calculation method is replaced by the soil-related performance parameters and the constraint of the function, the previous empirical coefficient is replaced, the unstable drainage effect caused by the personal reason is excluded, the influence caused by the individual difference is avoided, and thus the stability of the soil can be ensured. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The step flow chart of the double-row PLC method pile cofferdam and steel trestle combined construction method for the over-deep pit pond according to the embodiment of the application;

[0043] Figure 2 The structure diagram of the double-row PLC method pile cofferdam and steel trestle combined for the over-deep pit pond according to the embodiment of the application;

[0044] Figure 3 The step flow chart of the interval of the dewatering well according to the underwater filling depth and the permeability coefficient according to the embodiment of the application;

[0045] Figure 4 The installation step flow chart of the bearing cross beam according to the embodiment of the application. DETAILED DESCRIPTION

[0046] The technical solutions of the application will be described clearly and completely below with reference to the drawings, obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all the other embodiments obtained by the person skilled in the art without creative labor belong to the protection scope of the application.

[0047] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", are only for the purpose of description, and cannot be understood as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions, and moreover, the "upper", "above" and "on" of the first feature to the second feature include the vertical direction of the first feature above and obliquely above the second feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The "below", "under" and "under" of the first feature to the second feature include the vertical direction of the first feature below and obliquely below the second feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0048] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0049] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation on the present application.

[0050] Please refer to Figure 1 As shown in the figure, the present application provides a double-row PLC method pile cofferdam and steel trestle combined construction method step flow chart for over-deep pit pond, comprising the following steps:

[0051] Step S1, construction preparation is carried out;

[0052] Step S2, according to the construction requirements, the steel pipe pile construction site is positioned and the first pair of steel pipe piles is driven;

[0053] Step S3, the method pile is driven in the order of steel pipe pile-larssen steel sheet pile-steel pipe pile;

[0054] Step S4, after the method pile is sunk to the design elevation, the inter-pile flat connection is carried out;

[0055] The flat connection is made of I16a channel steel, and the flat connection is constructed at the normal water level;

[0056] In step S5, the two flat connections are pulled and anchored by using steel bars.

[0057] In the pulling and anchoring, the two flat connections are pulled and anchored by using steel bars with a diameter of 25 mm, and the pulling and anchoring interval is 3000 mm.

[0058] In step S6, the soil is filled by using the water driving method, and the filling sequence is from the bank to the pond.

[0059] In step S7, the bearing cross beam and the Bailey beam are installed.

[0060] In step S8, the bridge deck is laid.

[0061] In step S9, the next method pile is driven, and the pulling and anchoring, the water driving method, the installation of the bearing cross beam and the Bailey beam, and the laying of the bridge deck are continuously performed until the method pile cofferdam construction is completed.

[0062] In step S10, after the construction is completed, the steel trestle is removed.

[0063] In the water driving method construction process, the interval d between the next dewatering well and the current dewatering well is determined according to the depth function f(T) of the longitudinal coordinate as the distance A from the bank and the transverse coordinate as the underwater filling depth T and the function f(H) of the interval d from the previous dewatering well.

[0064] The method pile is a steel pipe pile-Larsen steel sheet pile-steel pipe pile in turn and in sequence, and the positioning and the perpendicularity control of the first pile are particularly crucial because the size adjustment of the guide groove connected between the steel pipe pile and the Larsen steel sheet pile is limited in the transverse direction, and the guide groove is consistent with the center line of the pile row. Therefore, the pile top elevation should be strictly controlled during the construction process, and the perpendicularity of the steel pipe pile should meet the requirement of <1%. The position is checked in time, and the pile is pulled out and re-driven in time when a large inclination occurs in the initial sinking period (1m-2m). The overlapping between the piles is guaranteed by the small Larsen steel sheet pile, thereby achieving the water stopping effect.

[0065] Please refer to Figure 2 Fig. 1 is a structural diagram of the double-row PLC method pile cofferdam and the steel trestle combination of the over-deep pit pond according to the embodiment of the present application, which comprises a steel pipe pile 1, a reinforcing vertical rod 2, a 125A distribution beam 3, a support frame 4, a 3-meter Bailey beam 5, a bridge deck 6, a reinforcing support rod 7, a flat connection 8, a water level line 9, and a bearing cross beam (not shown in the figure, which is arranged below the 3-meter Bailey beam).

[0066] Please refer to Figure 3 Fig. 2 is a step flow chart for determining the interval of the dewatering well according to the underwater filling depth T and the permeability coefficient K, wherein:

[0067] Detect the relationship between the distance from the current construction route to the shore and the water depth;

[0068] Establish a depth function f(T) with the ordinate as the distance from the shore A and the abscissa as the underwater filling depth T, that is, A=f(T);

[0069] Detect the permeability coefficient K of the filled soil;

[0070] According to the permeability coefficient K, the flat spacing L, and the diameter R of the dewatering well, a function f(H) containing two unknowns, the current underwater filling depth T and the spacing d from the previous dewatering well, is established;

[0071] Wherein: the purpose of the present application is to reduce the water content in the soil after the construction of the water driving method, and to increase the stability of the trestle in the subsequent construction process, so the underwater filling depth is consistent with the depth of the dewatering well;

[0072] According to the above relationship, the distance from the next dewatering well to the shore is equal to the distance from the current dewatering well to the shore plus the spacing d between the next dewatering well and the current dewatering well, and by simultaneously solving the function f(T) and the function f(H), the spacing d between the next dewatering well and the current dewatering well is obtained.

[0073] Specifically, the calculation method of the spacing d between the next dewatering well and the current dewatering well is:

[0074] Obtain various parameters in the construction process: permeability coefficient K, flat spacing L, diameter R of the dewatering well, and current underwater filling depth T;

[0075] Substitute the obtained various parameters in the construction process into the formula in the form of numerical values: Wherein: d is the spacing between the next dewatering well and the current dewatering well, unit: m, permeability coefficient K, unit: m / s, flat spacing L, unit: mm, diameter R of the dewatering well, unit: mm, and depth H of the dewatering well, unit: m.

[0076] In the prior art, the calculation method for the spacing between dewatering wells is: d=K×H, wherein: d is the spacing between dewatering wells (m), K is an empirical coefficient, usually between 1 and 3, and H is the depth of the dewatering well (m). This method relies on the construction experience of construction personnel and is suitable for construction where the depth of the dewatering well is consistent, and is not suitable for the double-row PLC pile cofferdam and steel trestle combined construction method for deep pit provided by the present application;

[0077] Therefore, according to the current construction characteristics, the permeability coefficient K, the flat spacing L, the current underwater filling depth T, and the spacing between the dewatering wells are proportional, and the diameter R of the dewatering well is inversely proportional to the spacing between the dewatering wells. By substituting the values, it can be known that The order of magnitude of the value is 10 0 -10 9between, by means of the function f(x)=3-2 / x, so as to attribute the value of to the interval [1,3], which is in the range of selection of the empirical coefficient in the prior art, and eliminates the instability of the soil structure caused by precipitation, which is possibly caused by subjective judgment of the construction personnel, so as to ensure the safety in the construction process.

[0078] The specific implementation is that if the current known parameters are that the water permeation rate is 4*10 -7 m / s, the distance between the flat links is 3000mm, the diameter of the precipitation well is 300mm, the distance between the current precipitation well and the shore is 15m, T=H, and the calculation process of the distance between the next precipitation well and the current precipitation well is as follows:

[0079] Step 1: the above data is substituted into the function f(H), and d=(3-24 / 9*10 5 ) * H is obtained;

[0080] Step 2: the relationship A=15+d (that is, the distance between the next precipitation well and the shore is equal to the distance between the current precipitation well and the shore + the distance between the next precipitation well and the current precipitation well) is substituted into A=f(T), and 15+d=f(T) is obtained;

[0081] Step 3: d=(3-24 / 9*10 5 ) * H obtained in Step 1 and T=H are substituted into the formula in Step 2, and only one unknown number H exists in the formula, and H is solved, and then the values of other parameters are obtained.

[0082] It can be known that the method is a definite function relationship, the data in the early data monitoring stage can be coded by a computer, input parameters are directly converted into the distance between the next precipitation well and the current precipitation well, and therefore the construction speed is improved under the condition of ensuring the construction safety.

[0083] Referring to FIG. Figure 4 , which is a mounting step flow chart of the load-bearing cross beam, and wherein:

[0084] Marking the pile position of the steel pipe pile on the load-bearing cross beam;

[0085] Hoisting the load-bearing cross beam, and controlling the marking to coincide with the steel pipe pile in the hoisting process;

[0086] Welding an arc-shaped limiting steel plate between the pile body and the load-bearing cross beam to fix the load-bearing cross beam.

[0087] Specifically, the mounting of the Bailey beam further includes the following steps:

[0088] The Bailey beam is tested and spliced before entering the construction site, and the Bailey beam enters the construction site for splicing after the test and splicing are correct;

[0089] The measuring and lofting is carried out on the load-bearing cross beam before the installation of the Bailey beam, and the accurate position of the Bailey beam is determined;

[0090] The Bailey beam is hoisted by the crawler crane, and is placed at the water pond end of the installed Bailey beam and is in line with the same.

[0091] After the lower chord pin hole of the Bailey beam is aligned and the pin is inserted, the rear end of the Bailey beam is lifted, the upper chord pin body is inserted, and the safety pin is arranged.

[0092] Specifically, after the Bailey beam is accurately positioned, the Bailey beam is first firmly bound on the load-bearing cross beam, then the position limiter is welded, another group of Bailey beams is installed, and the two groups of Bailey beams are connected by the scissors support.

[0093] Specifically, the bridge deck panel used for laying the bridge deck further comprises two specifications, one is a 16mm thick patterned steel plate, which is suitable for all steel platforms and part of the main trestle; and one is an assembled bridge deck panel with a specification of 6m*2m and 3m*2m, which is suitable for all trestle bridges and part of the main trestle. The assembled bridge deck panel adopts a 138mm thick customized steel panel, the horizontal rib spacing is 750mm, the longitudinal rib spacing is 250mm, the two ends are fixed on the secondary beam by means of a screw rod, and at the same time, 5*50 flat steel is additionally welded at the joint to increase the strength, the bridge deck steel plate adopts patterned anti-skid steel plate, and is coated with high-molecular anti-skid and anti-corrosion material, the anti-corrosion material can adopt polyurethane oil-resistant, and the coating thickness is about 1-2mm. After the bridge deck panel is completely constructed, load testing can be carried out, and record materials are formed.

[0094] Specifically, the steel trestle further comprises a trestle bridge abutment, and rubber pads are arranged at the abutment and the trestle deck. The trestle bridge abutment adopts a reinforced concrete structure, the abutment size is 6.9m*3m*2.8m, 8 pieces of 400*400*10m steel plates are pre-buried on the abutment and are welded and connected with the Bailey beam; the foundation soil layer under the abutment needs to be compacted to ensure that the bearing capacity of the foundation is not less than 150Kpa, the abutment is close to the water side and the distance from the water side is not less than 1m, and the slope is protected at the abutment position to prevent the abutment from being unstable due to river scouring.

[0095] Specifically, the load-bearing cross beam is composed of double-spliced I45a H-shaped steel, and the Bailey beam adopts a 321 type Bailey beam.

[0096] Specifically, the construction preparation process is the processing and storage of the steel cofferdam, wherein the steel cofferdam comprises a steel pipe pile, a steel sheet pile, a tensioning steel bar and a working platform.

[0097] In the embodiment of the present application, the lengthening of the pile is carried out by factory splicing or splicing in the splicing site, and the specific lengthening method is not limited according to the actual situation, wherein the splicing in the splicing site splices two sections of steel pipe piles into one section of steel pipe pile, and the length meets the design requirements while being higher than the water surface by 2m.

[0098] Obviously, the above embodiments of the present application are merely exemplary but not intended to limit the embodiments of the present application. Based on the above description, any modification, equivalent replacement and improvement etc. within the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A construction method combining double-row PLC-based cofferdams and steel trestle bridges for deep pits, characterized in that... include: Prepare for construction; According to the construction requirements, the construction site for the steel pipe piles was located and the first pair of steel pipe piles were driven. Piles are constructed using the driven pile method in the sequence of steel pipe pile - Larssen sheet pile - steel pipe pile; After the piles are driven to the design elevation, horizontal bonding is carried out between the piles. Use steel bars to anchor the horizontal bracing on both sides; The method of driving away water is used to fill the soil, and the filling sequence is to advance from the bank to the inside of the pond. Install load-bearing crossbeams and Bailey beams; Pave the bridge deck; Drive the next pile using the construction method, and continue with the steps of anchoring, water-driving construction, installation of load-bearing crossbeams, and laying of the bridge deck using Bailey beams, until the construction of the cofferdam using the construction method piles is completed; After construction is completed, the steel trestle bridge will be dismantled. After the water-driving method is constructed, a drainage well is set in the middle of the two horizontal connections. The distance d between the next drainage well and the current drainage well is determined according to the depth function f(T) with the vertical coordinate being the distance A from the shore and the horizontal coordinate being the underwater filling depth T, and the distance d between the next drainage well and the current drainage well. The first drainage well is set at a distance of 3m from the shore. The spacing of the drainage wells is determined based on the underwater fill depth T and the permeability coefficient K, and also includes: Detect the relationship between the distance from the shore and the water depth along the current construction route; Establish a depth function with the vertical axis representing the distance A from the shore and the horizontal axis representing the depth T of the underwater fill: A = f(T); The permeability coefficient K of the filled soil was tested; Based on the permeability coefficient K, the horizontal spacing L, and the diameter R of the dewatering well, a function f(H) is established, which includes the unknowns: the current underwater fill depth T and the distance d between the current and previous dewatering wells. By combining the functions f(T) and f(H), the distance d between the next precipitation well and the current precipitation well can be obtained; The method for calculating the distance d between the next dewatering well and the current dewatering well is as follows: Obtain various parameters during the construction process: permeability coefficient K, horizontal spacing L, dewatering well diameter R, and current underwater backfill depth T; Substitute the obtained parameters from the construction process into the formula in numerical form: Where: d is the distance between the next dewatering well and the current dewatering well, the permeability coefficient K, the horizontal connection distance L, the diameter of the dewatering well R, the depth of the dewatering well H, and T = H.

2. The construction method for a combination of double-row PLC-based cofferdam and steel trestle bridge for deep pits according to claim 1, characterized in that, The installation of the load-bearing crossbeam also includes the following steps: Mark the positions of the steel pipe piles on the load-bearing beams; The load-bearing crossbeams are hoisted, and the control marks are aligned with the steel pipe piles during the hoisting process; An arc-shaped limiting steel plate is welded between the pile body and the load-bearing crossbeam to fix the load-bearing crossbeam.

3. The construction method for a combination of double-row PLC-based cofferdam and steel trestle bridge for deep pits according to claim 1, characterized in that, The installation of the Bailey beam also includes the following steps: The Bailey beams were trial-assembled before construction began, and were then brought to the site for final assembly after the trial assembly was confirmed to be error-free. Before the Bailey beam is installed, a measurement and layout are carried out on the load-bearing crossbeam to determine the accurate position of the Bailey beam. Use a crawler crane to lift the Bailey beam and place it in a straight line with one end of the already installed Bailey beam in the pond. After aligning the lower chord pin hole of the Bailey beam and inserting the pin, lift the rear end of the Bailey beam, insert the upper chord pin body, and set the safety pin.

4. The construction method for a combination of double-row PLC-based cofferdam and steel trestle bridge for deep pits according to claim 3, characterized in that, After the Bailey beams are accurately positioned, they are first securely tied to the load-bearing crossbeams, then the limiters are welded on, and then another set of Bailey beams is installed. The two sets of Bailey beams are connected by scissor bracing.

5. The construction method for a combination of double-row PLC-based cofferdam and steel trestle bridge for deep pits according to claim 1, characterized in that, The bridge deck panels used for the bridge surface include two specifications: one is a 16mm thick patterned steel plate, and the other is a prefabricated bridge deck panel with specifications of 6m×2m and 3m×2m. The prefabricated bridge deck panel uses a 138mm thick custom steel plate with a horizontal rib spacing of 750mm and a longitudinal rib spacing of 250mm. Both ends are fixed to the secondary beam with bolts, and 5*50 flat steel is welded at the joint. The bridge deck steel plate is a patterned anti-slip steel plate and is coated with a polymer anti-slip and anti-corrosion material. The anti-corrosion material is polyurethane oil-resistant, with a coating thickness of 1-2mm.

6. The construction method for a combination of double-row PLC-based cofferdam and steel trestle bridge for deep pits according to claim 1, characterized in that, The steel trestle also includes a trestle abutment, and rubber pads are installed at the abutment and the trestle approach plate.

7. The construction method for a combination of double-row PLC-based cofferdam and steel trestle bridge for deep pits according to claim 1, characterized in that, The load-bearing crossbeam is composed of double-span I45a I-beams, and the Bailey beam is a 321 type Bailey beam.

8. The construction method for a combination of double-row PLC-based cofferdam and steel trestle bridge for deep pits according to claim 1, characterized in that, The construction preparation process specifically involves the processing and storage of steel cofferdams, which include: steel pipe piles, steel sheet piles, tie bars, and working platforms.

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