A preloading device and construction method for thick-covering soil cantilever steel truss

Abstract

This application relates to the field of building construction technology, and provides a preloading device and construction method for thick-covered cantilevered steel trusses. The construction method includes: installing temporary prestressed cables between the cantilevered steel truss and the underlying anchor foundation; tensioning the cables to induce pre-deformation in the cantilevered steel truss; pouring the floor slab under pre-deformation; sealing the post-cast strip after re-tensioning the cables; and layering the soil, removing the cables after the first layer of soil is laid, and then constructing the subsequent layers of soil. The preloading device includes temporary prestressed cables and a tensioning device. This invention simulates the soil cover effect through external cable preloading, and combined with layered soil covering and cable removal timing, it controls the stress of the floor slab throughout the process, preventing cracking.

Description

Technical Field

[0001] This invention belongs to the field of building construction technology, specifically relating to a preloading device and construction method for thick-covered cantilevered steel trusses, which is particularly suitable for deformation and stress control during the construction of steel structures with large cantilever spans and heavy soil loads. Background Technology

[0002] With the increasing demand for large spaces and cantilevered designs in public buildings, the application of cantilevered steel truss structures is becoming more widespread. In these buildings, it is often necessary to cover the concrete floor slab above the cantilevered steel truss with a thick layer of planting soil for landscaping, with the soil layer reaching a thickness of 1.5 meters or even more. This massive, later-applied dead load is extremely detrimental to the structural stress, causing significant instantaneous downward deflection of the cantilevered steel truss. This results in the floor slab at the base experiencing tensile stress far exceeding the design expectations, leading to cracking of the concrete floor slab, the formation of leakage channels, and seriously affecting the building's functionality and durability.

[0003] To address these issues, the industry has attempted a preloading approach, which involves applying a load to the cantilever structure before backfilling, causing it to deform and stress in advance, before pouring or closing the floor slab. Traditional preloading methods, such as surcharge counterweights or water tank filling, require placing a huge load directly on the floor slab. The loading and unloading process is cumbersome and time-consuming. Furthermore, surcharges on an existing cantilever structure with significant safety risks, resulting in poor convenience and economy.

[0004] Regarding the deformation control problem during construction, there are existing technologies that utilize prestressed cables for active regulation, but these solutions are clearly insufficient when dealing with the specific problem of thick-covered cantilever trusses.

[0005] Patent document CN101200916B discloses a construction method for a suspended building structure. Its core principle is to control deformation and stress during construction by installing permanent prestressed cables inside the structure and employing a reverse construction method and staged tensioning. The drawback of this approach is that the prestressed cables are permanent load-bearing components, and the tensioning strategy is designed to serve the structural system's own construction process, failing to simulate the downward pre-deformation exerted on the cantilever structure by external uniformly distributed loads such as later-stage backfill. Furthermore, this method cannot guide the precise control of floor slab stress through the synergy of unloading and loading during layered backfill construction. Therefore, this approach cannot effectively solve the problem of stress concentration leading to cracking in the floor slab at the root of the cantilever truss under thick backfill conditions.

[0006] Patent document CN120291704A discloses a preloading method for suspended structure construction. This method applies an upward preload to the suspended structure by installing hydraulic jacks at the bottom of the structure, and releases the preload gradually during subsequent construction loading. The drawbacks of this approach are that the lifting device relies on the existing foundation structure for reaction force, resulting in a complex layout. Furthermore, the applied upward preload is opposite in direction to the downward load generated by the thick overburden, leading to fundamentally different simulated load types and structural responses. In addition, its step-by-step unloading control logic does not involve locking the pre-deformation state through supplementary tensioning before the floor slab is closed, nor does it provide a means for displacement compensation in conjunction with layered external loads during the release of preload, failing to meet the requirements for refined stress control under layered loading conditions with thick overburden.

[0007] In summary, the existing technology lacks a construction method and supporting device that can accurately simulate the downward load effect of thick soil cover, facilitate convenient and safe loading and unloading, and precisely control the stress of the floor slab at the root of the cantilevered steel truss to avoid cracking throughout the entire process of layered soil cover. Summary of the Invention

[0008] The purpose of this invention is to provide a preloading device and construction method for cantilevered steel trusses with thick soil cover, so as to solve the technical problems of inconvenient preloading methods, difficulty in controlling structural stress during construction, and easy cracking of floor slabs in the prior art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention proposes a construction method for cantilevered steel trusses with thick soil cover, comprising the following steps: Erect supporting frames and install cantilevered steel trusses; Remove the supporting frame and install at least one temporary prestressed cable between the cantilevered steel truss and the anchor foundation located below it. The temporary prestressed cable constitutes a preloading device. Install the tensioning device to perform the first tensioning on the temporary prestressed cables, apply a downward preload, and cause the cantilever steel truss to produce a pre-deformation equivalent to the effect of the soil load. While the cantilevered steel truss is in the pre-deformed state, the concrete floor slab above it, which will bear the soil load, is poured. The temporary prestressed cables are tensioned a second time to supplement or maintain the preload at a preset level; After the concrete floor slab reaches the design strength, the soil is covered in layers. After the first layer of soil is completed and before the subsequent layers are covered, the preload of the temporary prestressed cables is removed or the temporary prestressed cables are dismantled.

[0010] Furthermore, the steps for installing the cantilever steel truss include: installing the cantilever steel truss according to the pre-camber value required by the design, and the length of the temporary prestressed cable is determined based on the actual distance between the cantilever steel truss after pre-camber and the anchorage foundation. Because pre-camber changes the actual elevation of the pre-set ear plates on the cantilever steel truss, the length of the temporary prestressed cable should be customized or adjusted in conjunction with the actual distance between the first and second pre-set ear plates after pre-camber to ensure the effectiveness and accuracy of tensioning.

[0011] Furthermore, after the second tensioning step is completed, the reserved post-pouring strip in the concrete floor slab is sealed.

[0012] Furthermore, the layered construction of the backfill includes constructing a first layer of backfill and at least one subsequent layer of backfill; when the preload of the temporary prestressed cable is removed or the temporary prestressed cable is dismantled, the cantilever steel truss generates an upward elastic rebound displacement, which at least partially offsets the downward deflection displacement already generated under the action of the first layer of backfill; the construction of the subsequent backfill causes the cantilever steel truss to generate a final downward displacement, which matches the pre-deformation.

[0013] Furthermore, the thickness of the first layer of backfill and the subsequent backfill are determined through simulation analysis to ensure that the stress on the floor slab at the root of the cantilevered steel truss does not exceed the design allowable stress value when the construction of the first layer of backfill is completed.

[0014] The mechanical principle of the layered soil covering strategy is as follows: through tensioning, the cantilevered steel truss is subjected to a downward preload P1, reaching the stress state after soil covering is completed. After the floor slab is poured and the post-cast strip is closed, due to the structural system transformation and load sharing, the actual effect of the preload will decrease to P2. At this time, the remaining preload P3 in the temporary prestressed cables, i.e., the difference between P1 and P2, will independently cause the cantilevered steel truss to produce a deflection value L1. If all the remaining soil is applied at this time, the deflection value L1 will be superimposed with the deflection caused by the new load, leading to a sharp increase in floor slab stress and even cracking. This invention, by first constructing a first layer of soil with controlled thickness, ensures that the cantilevered steel truss only experiences a small deflection value L1, at which point the floor slab stress in the structure meets the design requirements. Subsequently, the temporary prestressed cables are removed, releasing the remaining preload P3, which is equivalent to an upward unloading process, causing the cantilevered steel truss to produce an upward elastic rebound displacement L2. Due to the deflection L1, the net displacement is the difference between L2 and L1. The final construction of the second layer of backfill soil causes the cantilevered steel truss to deflect again, ultimately reaching a value equivalent to the initial pre-deformation state achieved through pre-loading P1. This ensures that the final structural configuration and stress fully meet the standards. During this process, displacement compensation through cable unloading rebound and layered loading settlement ensures a smooth transition of floor slab stress throughout construction, preventing any excessive peak values.

[0015] Furthermore, the thickness of the first layer of topsoil is greater than the thickness of the subsequent topsoil.

[0016] Furthermore, the thickness of the first layer of soil cover is 70% to 80% of the total soil cover thickness.

[0017] Furthermore, the anchorage foundation is a concrete structure; one end of the temporary prestressed cable is connected to a first pre-set ear plate at the lower chord node of the cantilever steel truss, and the other end is connected to a second pre-set ear plate located at the top of the concrete structure; the directions of the first and second pre-set ear plates should be consistent with the direction of the cable head of the temporary prestressed cable to avoid deflection; the tensioning device is arranged at the second pre-set ear plate for easy operation on the ground or at a lower position. The second pre-set ear plate is connected to the embedded steel plate in the concrete structure using a first-class full penetration weld to ensure a reliable force transmission path. If the pull-out capacity of the concrete column or pile where the embedded part is located is insufficient to resist the tension force, counterweights need to be added around it to enlarge the anchorage foundation.

[0018] Furthermore, when the pull-out resistance of the concrete structure is lower than a preset threshold, counterweights are added around it to enhance the anchoring capacity.

[0019] Secondly, the present invention proposes a preloading device for cantilevered steel trusses with thick soil cover, applied to the above-mentioned construction method, comprising: At least one temporary prestressed cable is detachably connected at both ends to the cantilevered steel truss and the anchor foundation located below it; The tensioning device is used to apply, adjust, and remove the preload on the temporary prestressed cable, and the tensioning device is arranged at one end of the anchorage foundation.

[0020] The beneficial effects of this invention are: Regarding the preloading method, this invention uses removable external temporary prestressed cables as a tool. By tensioning between the cantilevered steel truss and the underlying anchored foundation, the load effect of thick soil cover is accurately simulated by dragging downwards. This method eliminates the need for dangerous surcharge operations on the floor slab and the need for a complex jacking reaction system. The device is recyclable, and construction is convenient, safe, and economical.

[0021] Regarding deformation control strategies, this invention eliminates additional stress on the floor slab caused by later deformation by casting the concrete slab in a pre-deformed state, ensuring that the initial stress-free state of the slab is coordinated with the final configuration of the structure after bearing the full soil load. The subsequent second tensioning effectively compensates for prestress loss during the slab hardening process and reliably locks this pre-deformed state within the closed, complete structural system. This strategy fundamentally solves the problem of floor slab cracking caused by thick soil cover and allows the floor slab to be designed with more favorable stress states, such as simply supported slabs, thus optimizing the economics of structural design.

[0022] In terms of stress control during construction, this invention proposes a refined control method that combines layered soil covering with mid-term cable removal. During the first layer of soil covering loading, the remaining preload and the first layer of soil cover ensure that the structure experiences only a controlled, small deflection, guaranteeing the safety of the floor slab stress. During the cable removal stage, the release of the remaining preload triggers elastic rebound of the structure, which precisely cancels out the existing deflection, avoiding the structural rebound impact that might occur with simple unloading. During the second layer of soil covering loading, the additional load compresses the structure back to its initial pre-deformed state. This method of stress control, utilizing the displacement compensation relationship between structural elastic rebound and layered loading, proactively and precisely ensures a smooth transition of floor slab stress throughout the construction process, effectively preventing stress exceeding limits. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the installation of a cantilevered steel truss provided in an embodiment of the present invention.

[0024] Figure 2 for Figure 1 A schematic diagram showing the removal of the support frame for the cantilevered steel truss and the installation of the preloading device.

[0025] Figure 3 This is a plan view of a cantilevered steel truss provided in an embodiment of the present invention.

[0026] Figure 4 This is a schematic diagram of a tensioning device provided in an embodiment of the present invention.

[0027] Figure 5 This is an enlarged structural schematic diagram of the fixing ear plate of the present invention.

[0028] Figure 6 for Figure 5 A schematic diagram of the structure viewed from below.

[0029] Figure 7 This is a schematic diagram of the structure of the double-section steel profile of the present invention.

[0030] Figure 8 This is a schematic diagram of the structure of the first preset ear plate of the present invention at a preset position on the cantilever steel truss.

[0031] Figure 9 This is a schematic diagram of the temporary prestressed cable of the present invention.

[0032] Figure 10 This is a three-dimensional model schematic diagram of the cantilevered steel truss of the present invention.

[0033] In the diagram: 1-Supporting frame; 2-Cantilevered steel truss; 21-Frame area; 22-Cantilevered area; 23-Connecting steel beam; 3-Concrete structure; 4-Second pre-set ear plate; 5-First pre-set ear plate; 6-Temperature prestressed cable; 7-Tensioning device; 8-Concrete floor slab; 9-Post-cast strip; 10-Soil cover; 71-Fixing ear plate; 72-Fixing nut; 73-Precision rolled threaded steel; 74-Double-section steel; 75-Through-type jack; 76-Cable head adjusting screw. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] To facilitate understanding of this invention, the structure of the cantilevered steel truss and its positional relationship with surrounding components are first described below. See [link to relevant documentation]. Figure 1 , Figure 10 The cantilevered steel truss 2 includes a central frame region 21 and cantilevered regions 22 located on either side of the frame region 21. The frame region 21 is directly supported by a concrete structure 3, while the cantilevered regions 22 maintain a gap with the concrete structure 3, thus creating a cantilevered state for the cantilevered steel truss 2 in this area. A support frame 1, as a temporary support structure, is installed between the cantilevered regions 22 and the concrete structure 3 to temporarily support the cantilevered regions 22 during the construction phase. The support frame 1 is removed after the cantilevered steel truss 2 is installed. Figure 8As shown, the first pre-set ear plate 5 is set at the lower end of the cantilevered steel truss in the cantilevered area 22, and the second pre-set ear plate 4 is set on the concrete structure 3 below the cantilevered area 22.

[0036] This example uses the cantilevered roof of the entrance hall of a public building. The cantilever structure adopts a steel truss system with a maximum cantilever span of approximately 40 meters and a truss height of approximately 3 meters. It is covered with soil for landscaping, with a total soil thickness of 1.5 meters, resulting in a huge load.

[0037] This embodiment provides a construction method for cantilevered steel trusses with thick soil cover. See [link to relevant documentation]. Figures 1 to 3 The specific steps are as follows: Step 1: Install the cantilevered steel truss.

[0038] According to the pre-arching requirements of the design, the arching value at the cantilever end is approximately 150 mm. The cantilever steel truss 2 is further designed and fabricated. The first pre-set ear plate 5 is fabricated at the main load-bearing nodes of the lower chord of the truss in the cantilever area 22. A support frame 1 is erected on-site, positioned between the cantilever area 22 and the concrete structure 3. Each segment of the cantilever steel truss 2 is precisely installed according to the three-dimensional coordinates after arching. Simultaneously, a second pre-set ear plate 4 with a pre-embedded steel plate is precisely embedded in the top of the concrete structure 3 at the corresponding position below the cantilever area 22 during pouring. To ensure the cantilever truss can deform freely during tensioning, the connecting steel beams 23 between the cantilever steel truss 2 and the adjacent frame columns are temporarily hinged and fixed. After all permanent welds of the cantilever steel truss 2 pass inspection, the support frame 1 is removed, allowing the cantilever area 22 to be fully cantilevered.

[0039] Step 2: Install temporary prestressed cables between the cantilevered steel truss and the anchor foundation located below it.

[0040] The actual spatial distance between the first preset ear plate 5 and the second preset ear plate 4 after pre-arching is measured, and the length of the temporary prestressed cable 6 is customized or adjusted accordingly. One end of the temporary prestressed cable 6 is connected to the first preset ear plate 5, and the other end is connected to the second preset ear plate 4. In this embodiment, the concrete structure 3 below the cantilever area 22 is the anchorage foundation.

[0041] Step 3: The temporary prestressed cables are tensioned for the first time, and a downward preload is applied to cause the cantilevered steel truss to undergo pre-deformation equivalent to the effect of the soil load.

[0042] See Figure 4The tensioning device 7 is installed on one side of the second preset ear plate 4. This tensioning device 7 mainly consists of a fixed ear plate 71, a fixed nut 72, a precision-rolled threaded steel bar 73, a double-section steel bar 74, a through-hole jack 75, and a cable head adjusting screw 76. The through-hole jack 75 is driven by an oil pump, simultaneously applying pressure and tightening the cable head adjusting screw 76, thereby applying force to the temporary prestressed cable 6. Based on the finite element analysis results of the full-process construction simulation, the oil pump pressure gauge reading is controlled to synchronously tension each cable in stages until the preset preload value P1 is reached. In this example, P1 is designed as an equivalent concentrated force that can simulate the total load effect of a 1.5-meter thick backfill. At this point, the cantilever area 22 undergoes downward elastic deformation and partial plastic development, and its configuration is essentially equivalent to the state after the final backfill is completed.

[0043] Step four: With the cantilevered steel truss in a pre-deformed state, pour the concrete floor slab above it to bear the soil load.

[0044] With the cantilevered steel truss 2 in the aforementioned pre-deformed state, a post-pouring strip 9 is reserved in the stress-sensitive area at its root. Then, the remaining concrete floor slab 8 above the cantilevered steel truss 2 is poured and cured to the design strength. During this stage, the formwork elevation and initial stress-free state of the concrete floor slab 8 are coordinated with the final deformation form.

[0045] Step 5: Perform a second tensioning on the temporary prestressed cables to supplement or maintain the preload at the preset level.

[0046] After the concrete slab 8 reaches its strength, the internal force of the temporary prestressed cables 6 will decrease due to the hardening shrinkage and stress relaxation of the concrete. Therefore, each temporary prestressed cable 6 is tensioned a second time to restore its tension to or slightly exceed the level of P1, in order to compensate for the loss. Afterward, the previously temporarily hinged connecting steel beams 23 are finally rigidly fixed, and all post-cast strips 9 are closed, so that the structure forms a complete load-bearing system.

[0047] Step 6: After the concrete floor slab reaches the design strength, the soil is covered in layers. After the first layer of soil is completed and before the subsequent layers are covered, the preload of the temporary prestressed cables is removed or the temporary prestressed cables are dismantled.

[0048] Specifically, finite element analysis determined that the construction thickness of the first layer of backfill 10 is 75% of the total thickness, i.e., 1.125 meters. This thickness is the maximum safe thickness to ensure that the tensile stress in the floor slab at the root of the cantilevered steel truss remains below the specification limit under the combined action of the remaining preload and the first layer of backfill. Backfilling of the first 1.125-meter-thick layer of backfill 10 began, and concentrated loading was prohibited.

[0049] After the first layer of backfill soil was completed, the structure stabilized. At this point, the temporary prestressed cable 6 still had a residual preload P3, the value of which was approximately P1 minus the load already borne. The tensioning device 7 was used to reverse the operation, gradually releasing the prestress and completely slack off the cable. The unloading of the temporary prestressed cable 6 was equivalent to relieving a downward tension P3 on the cantilever truss, causing the cantilever truss to produce an upward elastic rebound displacement L2. This rebound process was buffered by the weight of the first layer of backfill soil, effectively avoiding stress impact caused by excessively rapid or large upward movement of the structure. After the rebound stabilized, the temporary prestressed cable 6 was removed.

[0050] Finally, the remaining 0.375 meters, or 25% of the total thickness, is covered with a second layer of soil. The weight of this layer is precisely what causes the cantilevered steel truss 2 to deflect again from its rebound position to a final displacement value L3. Through precise simulation calculations, the final displacement value L3 coincides with the initial pre-deformation configuration height achieved in step three through the preload P1, thus realizing precise closed-loop control of stress and deformation of the structure throughout the entire construction process.

[0051] Through the above steps, this embodiment successfully ensured the stress safety of the cantilevered steel truss and its concrete floor slab throughout the construction process under the harsh conditions of thick soil cover, eliminated the risk of cracking, and achieved the design intent.

[0052] Based on the same inventive concept, the present invention also provides a preloading device for a thick-covered cantilevered steel truss. This device is applied in the above method embodiments to apply a downward preload simulating the soil cover load to the cantilevered steel truss.

[0053] See Figures 1 to 10 The preloading device in this embodiment mainly includes: at least one temporary prestressed cable 6 and a tensioning device 7.

[0054] The temporary prestressed cable 6 is a detachable external cable, which is installed between the cantilever area 22 of the cantilevered steel truss 2 and the anchoring foundation located below it. In this embodiment, the anchoring foundation is the concrete structure 3 below the cantilever area 22, specifically the top of the basement column.

[0055] One end of the temporary prestressed cable 6 is connected to the first pre-set ear plate 5, which is located at the lower chord node of the cantilevered steel truss 2 in the cantilever area 22. The other end of the temporary prestressed cable 6 is connected to the second pre-set ear plate 4, which is located on top of the concrete structure 3 below the cantilever area 22.

[0056] like Figure 8As shown, the first pre-set ear plate 5 is fabricated together with the lower chord steel member of the truss in the cantilever area 22 during the detailed processing of the cantilever steel truss 2, ensuring reliable stress distribution at the joint. The second pre-set ear plate 4 is cast integrally with the concrete structure 3 through an embedded steel plate. The ear plate and the embedded steel plate are connected by a first-level full penetration weld to provide a reliable force transmission path. The first pre-set ear plate 5 and the second pre-set ear plate 4 are oriented in the same direction and are both aligned with the direction of the cable head of the temporary prestressed cable 6 to avoid deflection of the cable under stress.

[0057] The tensioning device 7 is positioned at one end of the anchorage foundation, specifically on one side of the second pre-set ear plate 4, to facilitate operation by construction personnel at a low elevation. (See also...) Figures 4 to 7 The tensioning device 7 specifically includes a fixed ear plate 71, a fixed nut 72, a precision-rolled threaded steel bar 73, a double-section steel section 74, a through-hole jack 75, and a cable head adjusting screw 76. The double-section steel section 74 is bolted together to form a single unit, serving as a load-bearing frame. This frame is anchored to the fixed ear plate 71 via the precision-rolled threaded steel bar 73 and the fixed nut 72. The fixed ear plate 71 is connected to the second pre-set ear plate 4. The through-hole jack 75 is installed on the double-section steel section 74, with its piston passing through the cable head of the temporary prestressed cable 6. The cable head adjusting screw 76 is screwed into the end of the cable head. Driven by an oil pump, the through-hole jack 75 pushes the double-section steel section 74 while simultaneously pulling back the cable head adjusting screw 76, thus establishing prestress in the temporary prestressed cable 6. Reversing the operation releases the prestress.

[0058] When the pull-out resistance of concrete structure 3 is insufficient to resist tensile force, counterweights can be added around it, and the counterweights and concrete structure 3 can be used together as anchoring foundations to enhance anchoring capacity.

[0059] Combination Figure 2 , Figure 9 As shown, the core function of this preloading device is to apply a downward, precisely adjustable preload to the cantilever area 22 of the cantilever steel truss 2 by tensioning the temporary prestressed cables 6, causing it to deform in advance, equivalent to the effect of the soil cover load. After the concrete floor slab above the cantilever steel truss is poured and sealed in the pre-deformed state, and the first layer of soil cover is completed, the device can be unloaded and dismantled. It has the advantages of precise loading, convenient operation, and recyclability.

[0060] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A construction method for cantilevered steel trusses with thick soil cover, characterized in that, Includes the following steps: Install cantilevered steel trusses; At least one temporary prestressed cable is installed between the cantilevered steel truss and the anchor foundation located below it, the temporary prestressed cable constituting a preloading device; The temporary prestressed cables are tensioned for the first time, and a downward preload is applied to cause the cantilever steel truss to undergo pre-deformation equivalent to the effect of the soil cover load. While the cantilevered steel truss is in the pre-deformed state, the concrete floor slab above it, which will bear the soil load, is poured. The temporary prestressed cables are tensioned a second time to supplement or maintain the preload at a preset level; After the concrete floor slab reaches the design strength, the soil is covered in layers. After the first layer of soil is completed and before the subsequent layers are covered, the preload of the temporary prestressed cables is removed or the temporary prestressed cables are dismantled.

2. The construction method for a cantilevered steel truss with thick soil cover according to claim 1, characterized in that, The steps for installing the cantilever steel truss include: installing the cantilever steel truss according to the pre-camber value required by the design, and the length of the temporary prestressed cable is determined according to the actual distance between the cantilever steel truss after pre-camber and the anchorage foundation.

3. The construction method for a cantilevered steel truss with thick soil cover according to claim 1, characterized in that, After the second tensioning step is completed, the reserved post-pouring strip in the concrete floor slab is sealed.

4. The construction method for a cantilevered steel truss with thick soil cover according to claim 1, characterized in that, The layered construction of the backfill includes constructing a first layer of backfill and at least one subsequent layer of backfill; when the preload of the temporary prestressed cable is removed or the temporary prestressed cable is dismantled, the cantilever steel truss generates an upward elastic rebound displacement, which at least partially offsets the downward deflection displacement generated under the action of the first layer of backfill; the construction of the subsequent backfill causes the cantilever steel truss to generate a final downward displacement, which matches the pre-deformation.

5. A construction method for a cantilevered steel truss with thick soil cover according to claim 4, characterized in that, The thickness of the first layer of backfill and the subsequent backfill are determined through simulation analysis to ensure that the stress on the floor slab at the root of the cantilevered steel truss does not exceed the design allowable stress value when the first layer of backfill is completed.

6. A construction method for a cantilevered steel truss with thick soil cover according to claim 5, characterized in that, The thickness of the first layer of topsoil is greater than the thickness of the subsequent topsoil.

7. A construction method for a cantilevered steel truss with thick soil cover according to claim 6, characterized in that, The thickness of the first layer of soil cover is 70% to 80% of the total soil cover thickness.

8. A construction method for a cantilevered steel truss with thick soil cover according to claim 1, characterized in that, The anchoring foundation is a concrete structure; one end of the temporary prestressed cable is connected to the first pre-set ear plate at the lower chord node of the cantilever steel truss, and the other end is connected to the second pre-set ear plate set at the top of the concrete structure; the tensioning device is arranged at the second pre-set ear plate.

9. A construction method for a cantilevered steel truss with thick soil cover according to claim 8, characterized in that, When the pull-out resistance of the concrete structure is lower than a preset threshold, counterweights are added around it to enhance the anchoring capacity.

10. A preloading device for a thick-soil cantilevered steel truss, applied to the construction method according to any one of claims 1 to 9, characterized in that, include: At least one temporary prestressed cable is detachably connected at both ends to the cantilevered steel truss and the anchor foundation located below it; The tensioning device is used to apply, adjust, and remove the preload on the temporary prestressed cable, and the tensioning device is arranged at one end of the anchorage foundation.

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