Grouting construction method for metro depot track prefabricated column

Abstract

The invention relates to the technical field of constructional engineering construction, and discloses a metro depot track prefabricated column grouting construction method which comprises the following steps that firstly, a prefabricated column is positioned above a structural bottom plate, and a grouting gap at the bottom is sealed through a plugging assembly comprising a rigid hoop and a flexible liner; then, a grouting device is connected to the lower grouting hole, and grouting materials are pumped from bottom to top to fill an inner cavity; when thick slurry overflows from the upper slurry outlet hole, pumping is stopped, a gravity slurry supplementing device is connected to the highest interface of the top surface, and other orifices are closed; injecting slurry into the funnel container to enable the liquid level to be higher than the top surface of the prefabricated column, supplementing the slurry into the funnel container by utilizing hydrostatic pressure until the liquid level is stable and does not descend any more, and sealing the hole. According to the method, the saturated surface dry treatment of the base surface and the rheological property control of the slurry are combined, through the two-stage operation of mechanical grouting and high-position gravity slurry supplementing, internal air bags and shrinkage disengaging are effectively eliminated, and the compactness and integrity of the prefabricated column connecting joint are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, specifically to a method for grouting precast track columns in a subway depot. Background Technology

[0002] As urban rail transit construction moves towards prefabricated and industrialized methods, the development of properties above subway depots is becoming increasingly common. Precast concrete columns, due to their advantages such as fast construction speed, low environmental pollution, and controllable quality, have become a major vertical load-bearing component. During the installation of precast columns, the quality of the connection between the column base and the structural base slab directly determines the overall structural safety and seismic performance, while the density and bonding strength of the grouting layer are key factors in ensuring effective stress transfer at this connection.

[0003] In existing technologies, grouting for large precast components typically employs a single mechanical pressure grouting process. The standard operating procedure involves connecting the grouting pipe to the bottom of the component, using pressure generated by a mechanical pump to force grout into pre-reserved gaps, and considering grouting complete once it flows out of the top outlet hole, followed by sealing. However, this traditional method has technical drawbacks in practical engineering applications. The main problem is that cement-based grout inevitably undergoes chemical shrinkage and plastic settlement during its initial setting stage as it transitions from fluid to solid. In traditional closed systems, once the mechanical pump stops operating and the hole is sealed, the internal high pressure dissipates rapidly, and the grout tends to settle under its own weight and shrinkage. Due to the lack of a subsequent pressure compensation mechanism, this volume loss often leads to tiny voids or cracks between the top surface of the precast column and the grout layer. For subway depot columns bearing enormous vertical loads and horizontal shear forces, this lack of compaction at the top severely obstructs the load transfer path, creating a potential stress concentration hazard.

[0004] Furthermore, due to the dense arrangement of reinforcing bars inside precast columns, the rapid flow field relying solely on mechanical pumping easily forms air pockets on the back surface of the reinforcing bars or in dead corners, resulting in a reduction in the effective bonding area. Simultaneously, in terms of interface treatment, existing technologies often neglect the impact of substrate moisture content on grout performance. If the structural base slab is too dry, it will absorb moisture from the grout, leading to a decrease in grout strength at the interface. In terms of sealing processes, commonly used rigid templates are difficult to fit tightly against the roughened substrate, making grout leakage and pressure drop highly likely during high-pressure grouting, further exacerbating the instability of grouting quality. Therefore, there is an urgent need for a grouting construction method that can maintain pressure throughout the entire process, automatically compensate for shrinkage, and ensure the quality of micro-interface bonding. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a grouting construction method for precast track columns in subway depots, which solves the problems in existing grouting construction of large-section precast columns, such as voids at the top of connection nodes, incomplete internal filling, and uncontrollable interface bonding quality caused by grout curing shrinkage and poor venting.

[0006] To achieve the above objectives, the present invention provides a method for grouting precast track columns in a subway depot, comprising the following steps: The construction process begins with hoisting and precisely positioning the precast column above the installation area of ​​the structural base slab, ensuring a grouting gap of a defined height is formed between the bottom of the precast column and the structural base slab. To enable this gap to withstand subsequent grouting pressure, sealing components are used to close the lateral openings of the grouting gap, thereby creating a closed pressure-bearing space at the bottom of the precast column.

[0007] The grouting operation is divided into two consecutive stages. The first stage is the mechanical pressure filling stage, in which the output end of the grouting device is sealed and connected to the grouting hole on the lower side of the precast column. The grouting device is then started, and under the drive of pump pressure, the grouting material is guided to gradually fill the internal cavity of the precast column from bottom to top. This process utilizes hydrodynamics to remove most of the air from the cavity.

[0008] When the fluid overflowing from the grout outlet on the upper side of the precast column undergoes a qualitative change—from a discontinuous fluid containing air bubbles to a thick grout without air bubbles—it signifies that the main space has been filled. At this point, mechanical grouting is stopped, and the second stage, gravity grouting, begins. The gravity grouting device is connected to the highest interface on the top surface of the precast column, and all orifices except this connection are sealed, forming a single-port connected system. Grout is then injected into the funnel container of the gravity grouting device until the liquid level is vertically higher than the top surface of the precast column.

[0009] The innovative principle of this stage lies in utilizing the hydrostatic pressure generated by the high-level liquid column to continuously pressurize the interior of the precast column. By establishing a communicating vessel physical model, the absolute pressure at the top surface inside the precast column exceeds atmospheric pressure. This continuous pressure difference overcomes the yield stress of the slurry in the micropores, compresses and expels the tiny air bubbles remaining in the blind zone, and automatically compensates for the volume shrinkage of the slurry caused by chemical reactions and sedimentation. When the liquid level in the funnel container remains stable and no longer drops, it indicates that the interior has reached a dense filling state, at which point the device is removed and the highest-level interface is sealed.

[0010] To ensure interfacial bonding strength, the structural base slab undergoes surface treatment before precast column installation. Mechanical impact is used to remove the laitance layer, exposing the aggregate and creating a roughened surface with a staggered pattern, increasing physical bonding points. Crucially, before installation, the roughened surface is sprayed with clean water to achieve a saturated, surface-dry state—meaning there is no visible water on the surface, but the pores are saturated with water—to prevent the base concrete from absorbing moisture from the grout and affecting the interfacial hydration reaction.

[0011] To address the difficulty of sealing rough surfaces, this invention employs a composite sealing component. This component consists of a rigid clamp, a flexible gasket, and sealing material. During construction, the rigid clamp, with the flexible gasket adhered to it, locks the perimeter of the grouting joint. The flexible gasket elastically deforms to fill the microscopic gaps between the rigid clamp and the rough substrate. Subsequently, quick-setting cement mortar is applied to the joint. This rigid-flexible sealing system can effectively withstand high-pressure grouting without bursting or leakage.

[0012] In terms of fluid control, to avoid air pockets, a sequential sealing strategy is adopted during the grouting process. This involves selecting one lower grouting hole for grouting while keeping the other holes open for venting; as grout is observed flowing from the remaining lower grouting holes, they are sealed sequentially, forcing the grout to rise only along the vertical channel. Simultaneously, strict criteria are defined for identifying thick grout; mechanical pumping is only considered ready to be stopped when the overflowing fluid transforms from a foamy flow into a uniformly dense grout without any gaps.

[0013] This invention also implements strict control over the rheological properties of the slurry. A simultaneous grouting and mixing method is adopted, controlling the temperature of the slurry mixture between 5°C and 25°C, and strictly limiting the mixing time to 120 to 150 seconds to balance the dispersion effect of the additives and bubble control. Before injection, the initial flowability is tested using a truncated cone mold to ensure the slurry has the ability to penetrate tiny voids under low pressure differentials.

[0014] Finally, to solve the problem of negative pressure backflow during the instant of dismantling the grouting device, a shut-off valve was used in conjunction with the dismantling operation. At the instant of disconnection, external force was used to press the orifice to limit backflow, and then a sealing plug with a self-locking structure was inserted to ensure that the system always maintains a positive pressure state until the grout finally sets.

[0015] This invention provides a method for grouting precast track columns in subway depots. It offers the following advantages: 1. This invention solves the technical problem of grout shrinkage that traditional single pumping processes cannot handle by using a two-stage operation mode of mechanical pressure grouting and gravity grouting via a high-level funnel. After the main body is filled by mechanical grouting, a gravity grouting device connected to the highest interface of the precast column is used to construct a communicating vessel model and maintain a high-level liquid column. The constant hydrostatic pressure generated by this liquid column can not only continuously compress and drive out residual air bubbles in the internal blind area, but also automatically compensate for the volume shrinkage of the grouting material caused by chemical reaction and sedimentation with fresh grout, thereby ensuring that there are no air pockets inside the connection between the precast column and the structural base plate and no voids at the top, thus improving the overall load-bearing capacity of the structure.

[0016] 2. This invention solves the problem of grout loss and pulverization at rough interfaces through a base surface treatment process. The mechanical impact creates a staggered, rough surface, increasing the physical interlocking area. More importantly, it ensures the structural base slab surface is saturated and surface-dry before grouting, guaranteeing that the capillary pores of the base concrete are saturated with water and preventing it from competing for mixing water in the grout during the grouting process. This ensures the full hydration reaction of the grout at the interface, resulting in a uniformly strong and durable bonding layer between the precast column and the foundation.

[0017] 3. This invention employs a composite sealing component comprising a rigid clamp, a flexible gasket, and sealing materials, solving the engineering challenge of sealing rough surfaces under high-pressure grouting. The rigid clamp bears the main lateral grouting pressure, while the inner flexible gasket utilizes its elastic deformation characteristics to fill the microscopic gaps between the clamp and the roughened base plate. Combined with the externally applied fast-setting cement mortar, multiple leak-proof barriers are formed. Furthermore, the temperature and time control during grout preparation and the sequential sealing strategy during grouting prevent grout leakage and air pockets, ensuring the controllability and safety of the construction process. Attached Figure Description

[0018] Figure 1 This is a block diagram of the overall system structure of the present invention; Figure 2 This is a flowchart of the two-stage grouting construction process of the present invention; Figure 3 This is a schematic diagram illustrating the structure and principle of the gravity grouting stage of the present invention.

[0019] Among them, 10, precast column; 11, grouting hole; 12, grout outlet hole; 13, keyway hole; 20, structural base plate; 21, embedded steel bar; 22, grouting gap; 30, grouting device; 31, grouting pipe; 32, storage hopper; 40, sealing plug; 50, sealing component; 51, sealing material; 60, gravity grouting device; 61, funnel container; 62, connecting pipe; 70, automatic mixer. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] See attached document Figure 1 The present invention provides a method for grouting construction of precast columns for subway depot tracks, which is carried out by a precast column grouting construction system, including a precast column 10, a structural base plate 20, a grouting device 30, and a gravity grouting device 60.

[0022] The precast column 10 is a reinforced concrete component with a rectangular cross-sectional shape. In this embodiment, the cross-sectional dimensions of the precast column 10 are set as follows: The specific value is 350mm. mm. A hollow grouting channel is provided inside the precast column 10, penetrating the internal space of the precast column 10. Several grouting holes 11 are provided on the lower part of the side wall of the precast column 10, several grouting outlet holes 12 are provided on the upper part of the side wall of the precast column 10, and a keyway hole 13 is provided on the top end face of the precast column 10. The grouting holes 11, grouting outlet holes 12, and keyway hole 13 are all in fluid communication with the internal grouting channel, forming a complete fluid circuit. In this embodiment, there are four grouting holes 11, evenly distributed on the lower side of the precast column 10; four grouting outlet holes 12, evenly distributed on the upper side of the precast column 10; and one keyway hole 13, located at the keyway position on the top surface of the precast column 10.

[0023] The structural base slab 20 is located below the precast columns 10, serving as a supporting foundation. Several vertically extending embedded steel bars 21 are installed on the structural base slab 20. The precast columns 10 are mechanically connected to the structural base slab 20 via the embedded steel bars 21. The bottom surface of the precast columns 10 and the top surface of the structural base slab 20 are not in direct contact, but rather form grouting gaps 22. The height of the grouting gaps 22 is set as follows: In this embodiment The thickness is 20mm. The surface of the structural base plate 20 within the projection area of ​​the precast column 10 is rough, and the rough surface has several pits distributed in a quincunx pattern.

[0024] A sealing assembly 50 is provided around the grouting joint 22. The sealing assembly 50 is used to close the lateral opening of the grouting joint 22, thereby forming a closed receiving space between the bottom of the precast column 10 and the structural base slab 20. The sealing assembly 50 includes a rigid clamp wrapped around the outer perimeter of the grouting joint 22 and a sealing material 51 filled between the inner side of the rigid clamp and the edge of the grouting joint 22. The sealing material 51 is made of quick-setting cement or mortar, used to prevent grout leakage and withstand grouting pressure.

[0025] The grouting device 30 includes a grouting pump and a grouting pipe 31. One end of the grouting pipe 31 is connected to the output port of the grouting pump, and the sealed connection interface adopts a quick coupling with external threads or an expansion rubber grout stopper structure. When a quick coupling is used, a matching internal threaded sleeve is pre-embedded in the inner wall of the grouting hole 11; when an expansion rubber grout stopper is used, the rubber component is compressed by tightening the nut to expand it radially, thereby generating frictional self-locking and sealing with the smooth inner wall of the grouting hole 11, and the other end is constructed to form an interface that can be sealed to any grouting hole 11. The grouting device 30 is configured to provide pressurized grout to the interior of the precast column 10. The system also includes several sealing plugs 40, the size of which is adapted to the diameter of the grouting hole 11, the grout outlet hole 12, and the keyway hole 13, for sealing the orifices during construction.

[0026] The gravity grouting device 60 includes a funnel container 61 and a connecting pipe 62. One end of the connecting pipe 62 is connected to the bottom of the funnel container 61, and the other end is configured to be sealed to the keyway hole 13 of the precast column 10 or any of the higher-positioned grout outlet holes 12. The funnel container 61 is used to contain the grouting material and is configured to keep the liquid level of the grouting material above the top surface of the precast column 10 during the grouting stage.

[0027] When the gravity grouting device 60 is connected to the precast column 10 and filled with grout, the hydrostatic state of the system satisfies the following relationship: ; in, This represents the absolute pressure of the fluid at the top surface inside the precast column 10, in Pascals (Pa). This represents the atmospheric pressure acting on the surface of the grout inside the funnel container 61, and is expressed in Pascals (Pa). This indicates the density of the grout, expressed in kilograms per cubic meter (kg / m³). 3 ); This represents the acceleration due to gravity, measured in meters per second squared (m / s²). 2 ); The vertical height difference between the grout level in the funnel container 61 and the top surface inside the precast column 10 is expressed in meters (m).

[0028] The aforementioned components together constitute a closed-loop system capable of bottom-up pressure grouting and top-down gravity grouting, provided by the gravity grouting device 60. Greater than The pressure environment maintains the density of the grout inside the precast column 10.

[0029] See attached document Figure 2 This section details a series of precision treatment steps implemented for the structural base plate 20 and the installation area before the installation and grouting of precast columns, in order to create a physical interface that meets the requirements of high-precision track construction.

[0030] First, surveying and benchmark positioning are carried out. Within the construction area of ​​the structural base slab 20, coordinate benchmarks are determined based on the densified benchmarks in the track engineering control network. Surveyors use a total station or other precision surveying equipment to transform the design coordinates to the physical surface of the structural base slab 20, and mark out the side positioning baselines for the precast columns 10. The side positioning baselines are marked as solid lines on the structural base slab 20, and the rectangular area they enclose corresponds geometrically to the cross-section of the precast column 10. Precise alignment. The side positioning baseline forms the planar position constraint boundary for the subsequent hoisting and positioning of the precast column 10.

[0031] After the baseline survey is completed, the position verification of the embedded reinforcing bars is performed. The embedded reinforcing bars 21 located within the side positioning baseline area are inspected. There are four embedded reinforcing bars 21, each with a diameter of 18mm. The verification includes measuring the vertical distance of each embedded reinforcing bar 21 relative to the side positioning baseline and the relative spacing between adjacent embedded reinforcing bars 21. This step is used to confirm whether the embedded reinforcing bars 21 are within the allowable tolerance range of the reserved ducts inside the precast column 10. If the position of the embedded reinforcing bars 21 deviates from the design position, causing spatial interference with the concrete structure of the precast column 10, the embedded reinforcing bars 21 are corrected or rectified before the base surface treatment.

[0032] Subsequently, the installation area defined by the side positioning baseline on the structural base plate 20 is roughened. This process removes the laitance layer and loose concrete layer from the surface of the structural base plate 20 through mechanical impact until the fresh concrete aggregate cross-section is exposed. The roughening operation follows a geometric distribution pattern, specifically a quincunx pattern. This pattern requires adjacent roughening points to be staggered to maximize the effective contact area of ​​the roughened surface.

[0033] The roughening process is controlled by two key geometric parameters: roughening depth. and chisel spacing In this embodiment, the chiseling depth is controlled. ≥5mm to ensure sufficient mechanical interlocking space is formed downwards from the surface of the structural base plate 20; at the same time, control the chiseling spacing. The roughening depth is ≤20mm, meaning the straight-line distance between the center points of any two adjacent roughened pits does not exceed 20mm. By limiting these parameters, a uniform and high-density rough texture is formed in the installation area of ​​the structural base plate 20. After mechanical roughening, high-pressure air or a pressure water gun is used to remove residual concrete debris and dust from the surface, ensuring that the installation surface of the structural base plate 20 is clean, hard, and has the specified roughness. After cleaning and before the installation of the precast column 10, the roughened surface of the structural base plate 20 is impregnated. Water is sprayed to bring the concrete base to a saturated surface-dry (SSD) state, meaning there is no visible water on the surface but the pores are saturated with water. This state prevents the dry structural base plate 20 from absorbing moisture from the subsequent grouting material, avoiding reduced strength or bonding failure of the grouting material due to interface water loss, and providing micro-mechanical interlocking conditions for the subsequent bonding of the grouting layer and the base plate.

[0034] This section details the spatial placement, positioning and locking of the precast column 10, as well as the construction process of the bottom pressure-bearing sealing system. This process transforms the precast column 10 from an independent precast component into part of an integral structure connected to the structural base plate 20.

[0035] The precast column 10 is hoisted to the installation area above the structural base slab 20 using lifting equipment. During the lowering process, the pre-drilled holes at the bottom of the precast column 10 are coaxially aligned with the pre-embedded reinforcing bars 21 on the structural base slab 20, allowing the pre-embedded reinforcing bars 21 to be smoothly inserted into the precast column 10. The lowering position of the precast column 10 is strictly constrained by the side positioning baseline measured in the aforementioned process, ensuring that the four bottom edges of the precast column 10 coincide with the side positioning baseline. In the vertical direction, the elevation of the precast column 10 is controlled by the support adjustment components, so that the bottom surface of the precast column 10 is suspended above the structural base slab 20, thereby forming a constant height between the two. The grouting gap 22 is mm in diameter. This grouting gap 22 serves as a horizontal channel for the subsequent flow of grouting material and as a forming space for the connecting layer.

[0036] After the precast column 10 is initially positioned, the rail panel is assembled and fine-tuned. The rail frame is installed on top of the precast column 10, and the track geometry is fine-tuned using high-precision rail panel adjustment equipment. Since the rail panel is rigidly connected to the precast column 10, the fine-tuning process of the rail panel is also the process of locking the final spatial position of the precast column 10. When the rail panel is fine-tuned to the design accuracy, the spatial position of the precast column 10 is fixed, and at this time the geometry of the grouting gap 22 is also solidified, ready for sealing treatment.

[0037] The installation of the sealing assembly 50 is carried out around the cured grouting gap 22, aiming to construct a sealed pressure-bearing cavity capable of withstanding subsequent high-pressure grouting and gravity-assisted grouting. The sealing assembly 50 includes a rigid clamp and sealing material 51. First, the rigid clamp is tightly wrapped around the outer opening of the grouting gap 22 along the perimeter of the precast column 10's cross-section. The rigid clamp is composed of four steel plates or high-strength templates spliced ​​together, each matching the width of the side of the precast column 10. Its inner surface spans the grouting gap 22, while also covering part of the side wall at the bottom of the precast column 10 and part of the top surface of the structural base plate 20. Adjacent steel plates are connected by bolts, and the inner diameter of the clamp is controlled by adjusting the tightness of the bolts. A closed-cell foam sponge strip or rubber gasket is attached to the inner side of the rigid clamp. The gasket undergoes elastic deformation under the action of bolt tightening force, filling the slight unevenness between the rigid clamp and the rough base plate surface after chiseling. It serves as the first leak-proof barrier, reducing the amount of subsequent sealing material 51 and preventing grout from leaking along the rigid contact surface.

[0038] After the rigid clamps are installed in place, sealant 51 is used to fill and smooth the contact gaps between the rigid clamps and the concrete surface. Sealant 51 is a fast-setting cement mortar, applied to the joint between the upper edge of the rigid clamp and the side wall of the precast column 10, and the joint between the lower edge of the rigid clamp and the surface of the structural base slab 20. After curing, sealant 51 forms a continuous water-stop curtain, sealing all lateral outlets of the grouting gap 22. This sealing system not only physically prevents grout leakage but, more importantly, provides mechanical support, enabling the grouting gap 22 area to withstand the hydrostatic pressure established within the system. This is to prevent mold bursting or pressure relief accidents under grouting pressure, and to ensure that the grout can fully fill the micro-voids at the bottom of the precast column 10 under pressure.

[0039] See attached document Figure 3 This section details the process for preparing the medium used to fill the internal cavity and grouting gap 22 of the precast column 10. This process aims to obtain a fluid with rheological properties and a steady-state bubble structure.

[0040] The grout preparation process takes place in an automatic mixer 70, which is configured to apply shear force to high-viscosity cement-based materials. The selected base material is an ultra-high strength, non-shrink grout, dry-mixed from cement, graded aggregates, and composite admixtures. Strict water-to-material ratio control is implemented during preparation; mixing water and dry materials are measured using precision weighing equipment to ensure a constant water-cement ratio. The temperature of the mixing water and the storage environment temperature of the dry materials are monitored, and the temperature of the final grout mixture is adjusted using physical methods. The temperature is maintained within the thermodynamic range of 5°C to 25°C. This temperature range is set to regulate the hydration reaction rate of the slurry, preventing excessive slump loss due to excessively high temperatures or delayed strength development due to excessively low temperatures.

[0041] The mixing kinetics process follows time-series control. With the automatic mixer running at speed 70, metered mixing water is injected into the mixing tank, followed by continuous and uniform addition of dry materials. The starting point for measuring the mixing time is set at the moment all dry materials have been added. The duration of a single mixing operation... Strictly limited to the range of 120 to 150 seconds (120s ≤ ≤150s). The determination of this time window is based on the rheological equilibrium mechanism: the stirring time is not less than 120 seconds, which aims to ensure that chemical components such as water-reducing agents are fully dissolved in the liquid phase and dispersed to the surface of cement particles, thereby destroying the flocculation structure and giving the slurry the initial fluidity required by the design; the stirring time does not exceed 150 seconds, which aims to limit the shear process of the mechanical blades on the slurry and prevent excessive ambient air from being entrained due to excessive turbulence, thereby forming tiny bubble nuclei that are difficult to be discharged inside the slurry.

[0042] The slurry delivery adopts a quasi-continuous simultaneous grouting and mixing operation mode. The automatic mixer 70 and the storage hopper 32 of the grouting device 30 are arranged adjacent to each other in space. Before the slurry is poured into the storage hopper 32, the fluidity of each batch of mixed slurry is randomly checked. The initial fluidity of the slurry is tested using a truncated cone mold. Only when the initial fluidity value is greater than or equal to 300 mm (or a specially designed value) can the batch of slurry be judged as qualified and allowed to be injected; if the fluidity does not meet the standard, the batch of slurry is discarded to prevent grouting blockage or incomplete filling due to insufficient fluidity. Once the automatic mixer 70 completes one cycle of mixing, the prepared slurry is immediately poured into the storage hopper 32 and sucked in by the pumping mechanism of the grouting device 30. While the slurry is being pumped, the automatic mixer 70 immediately starts the preparation cycle for the next batch. This dynamic connection mechanism ensures that the slurry entering the precast column 10 is always in a freshly mixed state, avoiding aggregate sedimentation and segregation or thixotropic thickening during the slurry settling process, thereby ensuring the homogeneity and rheological stability of the injected medium.

[0043] See attached document Figure 1 - Appendix Figure 3 This section details the two-stage process of injecting grout into the precast column 10 and finally achieving dense filling.

[0044] The first stage of the grouting operation is a mechanical pressure grouting process, which aims to quickly fill the main cavity of the precast column 10 and the grouting gap 22 at the bottom. First, an airtight connection is established between the output end of the grouting pipe 31 of the grouting device 30 and any one of the grouting holes 11 on the lower side of the precast column 10; this connected grouting hole 11 is defined as the initial grout inlet. The remaining grouting holes 11 on the precast column 10, the upper grout outlet hole 12, and the top keyway hole 13 are all kept open in the initial state, serving as venting channels. The pumping mechanism of the grouting device 30 is then activated, and the grout enters the interior of the precast column 10 under pumping pressure. During the pumping process, the fluid pressure inside the grouting pipe 31 is monitored in real time using a pressure gauge equipped with the grouting device 30. If a sudden change in pressure reading is detected and exceeds the preset safety threshold (e.g., 0.5 MPa), pumping should be stopped immediately and the grouting pipeline checked for aggregate accumulation and blockage. Grouting can only be resumed after the fault is cleared to prevent excessive pressure from damaging the column bottom sealing component 50 or the precast column 10 structure. The grout first settles under gravity and fills the bottom grouting gap 22. Subsequently, as the injection volume increases, the grout level gradually rises inside the precast column 10.

[0045] During pumping, operators continuously monitor the status of the remaining unconnected grouting holes 11 at the bottom of the precast column 10. When a continuous, uninterrupted flow of grout is observed from a particular grouting hole 11, the hole 11 is immediately sealed with a sealing plug 40. As all the lower grouting holes 11 are sealed in sequence, the grout is forced upward along the vertical channel of the precast column 10. When grout begins to overflow from the outlet hole 12 at the top of the precast column 10, operators must identify the physical form of the overflowing grout. Only when the overflowing fluid changes from a foamy flow containing a large number of air bubbles to a uniformly dense grout is it determined that the main space of the precast column 10 has been essentially occupied by fluid. At this point, the grouting device 30 is shut off, and the initial grout inlet is maintained in its connected state or temporarily sealed, in preparation for the next stage.

[0046] The second stage of the grouting operation is the gravity grouting process using a high-level funnel. This process aims to eliminate residual air pockets inside the grout and compensate for the volume shrinkage of the grout using hydrostatic pressure. After stopping the mechanical pumping, the port with the highest geometric position of the precast column 10 is selected as the grouting interface. In this embodiment, the keyway hole 13 located on the top surface is selected as the grouting interface (in a design without a keyway hole, the highest grout outlet hole 12 is selected). The connecting pipe 62 of the gravity grouting device 60 is sealed and connected to the grouting interface, and the funnel container 61 is vertically fixed above the precast column 10.

[0047] While installing the gravity grouting device 60, all remaining unsealed orifices on the precast column 10 (including all grout outlets 12 and the initial grout inlet of the first stage) are permanently sealed using sealing plugs 40, ensuring that the precast column 10 forms a completely sealed cavity except for the funnel interface. Subsequently, the prepared grout is injected into the funnel container 61 until the liquid level in the funnel container 61 is higher than the top surface of the precast column 10. At this point, the system establishes a static pressure state as shown in the aforementioned formula, i.e. .

[0048] During the gravity grouting stage, the liquid level in the funnel container 61 is continuously monitored. Initially, the liquid level in the funnel container 61 drops due to the upward displacement of residual air bubbles inside the precast column 10 under buoyancy and pressure differential, as well as the filling of microscopic blind zones by the grout. Once the liquid level drops, the operator immediately replenishes the funnel container 61 with grout, always maintaining the liquid level at least 200 mm above the top surface of the precast column 10 (this value is an exemplary technical parameter and depends on the design head) to maintain a constant driving pressure differential. This grouting and monitoring process continues until a steady-state characteristic is observed: the liquid level in the funnel container 61 remains constant for 5 consecutive minutes (or other observation periods specified in the design), and no air bubbles rise from the connecting pipe 62. This steady-state characteristic indicates that the free space inside the precast column 10 has been completely filled with incompressible fluid, and the initial chemical shrinkage of the grout has been compensated. At the moment of disconnecting the connecting pipe 62, the operator must use their fingers or a temporary pressure plate to press down on the orifice to minimize the amount of grout overflowing under positive pressure, and then quickly insert the sealing plug 40 with millisecond-level movements. After the sealing plug 40 is inserted, it is completely wedged into the hole using a hammer tool to ensure that its pull-out resistance is greater than the internal residual grout pressure. After confirming that a steady state has been reached, the gravity grouting device 60 is removed, and the keyway hole 13 is quickly sealed with the sealing plug 40 to complete the grouting construction.

[0049] This section, based on fluid mechanics and multiphase flow theory, provides an in-depth analysis of the physical mechanism by which the two-stage grouting process employed in this invention achieves dense filling of the precast column 10. The grouting system constructed in this invention is physically equivalent to a communicating vessel model with complex internal boundary conditions. The internal cavity of the precast column 10 is interconnected with the funnel container 61 of the gravity grouting device 60 through fluid channels, forming a quasi-static fluid equilibrium system. In this system, the grouting material inside the precast column 10 is considered a continuous phase fluid, while the air remaining in areas with dense reinforcement, keyway dead zones, or within the grout body is considered a dispersed phase air bubble.

[0050] Based on the aforementioned hydrostatic relationship, the height of the liquid column established within the funnel container 61 is... A constant additional hydrostatic pressure term is introduced at the top interface of the precast column 10. This additional pressure term alters the kinetic equilibrium of the gas-liquid two-phase system at the microscopic scale. For dispersed phase bubbles, their stable existence in the slurry requires an equilibrium between the internal force of the bubble and the external fluid force, as well as the surface tension term. This invention addresses this by introducing a pressure higher than atmospheric pressure. Internal fluid pressure This disrupts the original equilibrium. The increased environmental pressure forces the bubble volume to shrink according to Boyle's law. The reduction in bubble volume directly reduces the jamming effect it experiences in complex flow channels, making it easier for it to migrate with the micro-creep of the fluid.

[0051] Simultaneously, the additional hydrostatic pressure term constitutes the driving potential energy to eliminate microscopic air resistance. In the tiny gaps or inverted structures inside the precast column 10, the flow of slurry is often limited by capillary resistance and yield stress. The high potential energy provided by the funnel container 61 allows the slurry to obtain a continuous pressure differential driving force, which is sufficient to overcome the shear yield stress of the high-viscosity slurry, prompting the slurry to penetrate into the microscopic pores with greater resistance, displacing the air that originally occupied that space. The displaced air converges to the highest point of the system under buoyancy and is discharged from the system through the connecting pipe 62 of the gravity slurry replenishment device 60.

[0052] Furthermore, this invention discloses and utilizes a volume compensation mechanism for grout. During the initial setting stage of cement-based grout transitioning from a fluid to a solid state, chemical shrinkage and plastic shrinkage due to aggregate settling inevitably occur. In a closed, constant-volume system, this shrinkage directly leads to voids or negative pressure zones at the top of the solidified body. The gravity grouting device 60, as an open supply source, utilizes the principle of communicating vessels to convert the gravitational potential energy of the grout into automatic compensation for volume losses. As long as sufficient liquid phase is maintained within the funnel container 61, any small volume defects caused by shrinkage will be compensated. They will all be instantly absorbed by the fresh slurry above under the influence of gravity. The filling (i.e.) This ensures that the internal pressure of the precast column 10 remains positive, preventing the formation of structural voids or crack sources caused by shrinkage.

[0053] In summary, when the liquid level in the funnel container 61 reaches a steady state and stops declining, it physically signifies that the precast column 10 has reached two extreme states: first, all geometric spaces that can be occupied by fluid (including macroscopic cavities and microscopic pores) have been completely filled with slurry; second, the initial plastic shrinkage of the slurry has been fully compensated for. This state establishes that the connection formed between the precast column 10 and the structural base plate 20 has homogeneous and highly dense mechanical characteristics.

Claims

1. A subway depot track precast column grouting construction method, characterized in that, The method comprises the following steps: hoisting and positioning a prefabricated column (10) above a mounting area of a structural base plate (20), reserving a grouting gap (22) between the bottom surface of the prefabricated column (10) and the structural base plate (20), and forming a closed pressure-bearing space by closing the lateral opening of the grouting gap (22) with a blocking assembly (50); sealingly connecting the output end of a grouting device (23) to a grouting hole (11) in the lower lateral surface of the prefabricated column (10), starting the grouting device (23), and driving the grouting material to fill the internal cavity of the prefabricated column (10) from bottom to top; after observing that the grout outlet hole (12) in the upper lateral surface of the prefabricated column (10) overflows bubble-free thick grout, stopping the operation of the grouting device (23), and connecting a gravity grout supplementing device (60) to the highest interface on the top surface of the prefabricated column (10); closing all the orifices except the connection port of the gravity grout supplementing device (60), injecting grouting material into the hopper container (61) of the gravity grout supplementing device (60) until the liquid level in the hopper container (61) is higher than the top surface of the prefabricated column (10) in vertical height, and supplementing the internal cavity of the prefabricated column (10) with hydrostatic pressure; after continuously observing that the liquid level in the hopper container (61) remains stable and no longer decreases, removing the gravity grout supplementing device (60) and closing the highest interface.

2. The metro depot track precast column grouting construction method according to claim 1, characterized in that, Before hoisting and positioning the prefabricated column (10), performing base surface treatment on the mounting area of the structural base plate (20): removing the floating layer on the surface of the structural base plate (20) until the concrete aggregate is exposed by mechanical impact, and forming a rough surface in a quincunx distribution; and before mounting the prefabricated column (10), spraying clean water on the rough surface to make the surface of the structural base plate (20) reach a saturated surface dry state, i.e., the surface is free of obvious water but the pores are saturated with water.

3. The metro depot track precast column grouting construction method according to claim 1, characterized in that, The blocking assembly (50) comprises a rigid clamp, a flexible gasket, and a sealing material (51), and the step of closing the lateral opening of the grouting gap (22) specifically comprises: splicing and locking the rigid clamp with the flexible gasket along the periphery of the grouting gap (22), and filling the micro gap between the rigid clamp and the structural base plate (20) with the flexible gasket; then applying fast-hardening cement mortar as the sealing material (51) at the joint between the rigid clamp and the concrete surface.

4. The metro depot track precast column grouting construction method according to claim 1, characterized in that, The step of driving the grouting material to fill the internal cavity of the prefabricated column (10) from bottom to top specifically comprises: selecting one of the grouting holes (11) in the lower lateral surface of the prefabricated column (10) as the grout inlet to connect the grouting device (23), and keeping the remaining grouting holes (11) and the grout outlet hole (12) open; during the pumping process, when observing that grout flows out of the remaining grouting holes (11) in the lower part, sequentially closing the grouting holes (11) from which grout flows out with blocking plugs (40) to force the grout to rise along the vertical channel.

5. The metro depot track precast column grouting construction method according to claim 1, characterized in that, Before stopping the operation of the grouting device (23), the fluid form overflowing from the grouting hole (12) is identified, and only when the overflowing fluid changes from foam flow to slurry with uniform density and no accumulation, the thick slurry is determined, at which time the stop grouting operation is performed, and the connection state of the grouting device (23) and the grouting hole (11) is maintained or the grouting hole (11) is closed.

6. The metro depot track precast column grouting construction method according to claim 1, characterized in that, In the step of supplementing the grouting inside the prefabricated column (10) by using hydrostatic pressure, a communicating vessel physical model is constructed, so that the absolute pressure of the fluid at the top surface inside the prefabricated column (10) is equal to the sum of atmospheric pressure and additional liquid column static pressure; Wherein, by always maintaining the liquid level in the funnel container (61) to be at least 200 millimeters higher than the top surface of the prefabricated column (10), it is ensured that a driving pressure difference sufficient to overcome the yield stress of the grout and compress the residual bubbles is continuously generated.

7. The metro depot track precast column grouting construction method according to claim 1, characterized in that, The judgment criterion for observing that the liquid level in the funnel container (61) remains stable and no longer decreases is: Within a preset observation period, there is no visible change in the liquid level in the funnel container (61), and no bubbles float up from the connecting pipe (62) of the gravity grouting device (60), indicating that the macroscopic cavity inside the prefabricated column (10) has been filled and the initial and plastic shrinkage of the grout has been compensated in volume.

8. The metro depot track precast column grouting construction method according to claim 1, characterized in that, The grouting material adopts a preparation mode of grouting and mixing at the same time, and before being injected into the grouting device (23), the grouting material prepared in each batch is controlled in stirring parameters: The temperature of the slurry mixture is controlled between 5°C and 25°C, and the duration of a single stirring operation is controlled between 120 seconds and 150 seconds, so as to ensure that the admixture is fully dispersed and no excess environmental air is introduced.

9. The metro depot track precast column grouting construction method according to claim 8, characterized in that, Before injecting the grouting material into the grouting device (23), a flowability detection step is further included: The initial flowability of the grouting material is tested using a truncated cone circular mold, and only when the measured initial flowability value is greater than or equal to the preset threshold value, the grouting material is determined to be qualified and allowed to be injected, otherwise it is discarded.

10. The metro depot track precast column grouting construction method according to claim 1, characterized in that, The step of dismounting the gravity grouting device (60) and closing the highest interface specifically includes: Close the shut-off valve arranged on the connecting pipe (62) of the gravity grouting device (60); At the moment of disconnecting the connecting pipe (62), the orifice of the highest interface is pressed by external force to limit the backflow of the grouting material, and then a sealing plug (40) with a self-locking structure is immediately punched in, until the sealing plug (40) is completely wedged in the hole.

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