A municipal road subgrade soft foundation rapid reinforcement treatment method based on injection-discharge collaborative closed-loop control

Abstract

The application discloses a kind of municipal road subgrade soft foundation rapid reinforcement treatment method based on injection-discharge collaborative closed-loop control, belong to municipal road soft foundation treatment technical field.This method includes: soft foundation detection is carried out to the subgrade to be treated and different soft weak degree processing area is divided;According to each processing area, determine grouting parameter and drainage parameter;In the subgrade, staggered grouting hole and vertical water-permeable drainage part are arranged, and make vertical water-permeable drainage part and transverse drainage blind ditch communication;Solidified slurry is injected into grouting hole, and soft foundation soil body is cemented, filled and extruded, while pore water is discharged and pore water pressure generated by grouting is released;According to pore water pressure, surface uplift amount, settlement rate and slurry setting state, determine the opportunity of pressure compensation and carry out pressure compensation;After pressure compensation, maintenance detection is carried out, and after passing, subsequent road construction is entered.The application can improve the uniformity of soft foundation reinforcement, drainage pressure relief efficiency and subgrade forming stability.

Description

Technical Field

[0001] This invention discloses a rapid reinforcement method for soft soil foundation of municipal roads based on injection and drainage collaborative closed-loop control, belonging to the field of soft soil foundation treatment technology for municipal roads. Background Technology

[0002] During the construction, reconstruction, and repair of old urban roads, unfavorable geological conditions often exist beneath the roadbed, including soft soil, silty soil, loose mixed fill, plain fill, and high-water-content weak interlayers. These types of soft soils typically exhibit high water content, large void ratio, high compressibility, low shear strength, poor permeability, and long consolidation time. If the soft soil foundation is not effectively treated before road construction, uneven roadbed settlement, pavement cracking, potholes, collapses, bridge approach slab settlement, and localized frost heave are likely to occur after the road is opened to traffic, affecting road structural safety, driving comfort, and road service life.

[0003] Currently, commonly used technologies for soft soil foundation treatment in municipal roads mainly include replacement, surcharge preloading, vacuum preloading, cement mixing piles, CFG pile composite foundations, and grouting reinforcement. Among these, replacement is suitable for shallow soft soil, but its capacity is limited for treating medium-deep soft interlayers, deep high-water-content soil, and areas with local cavities, and it is prone to deep and continuous settlement during road operation. Surcharge preloading and vacuum preloading mainly rely on drainage consolidation to improve the strength of soft soil foundations, but they usually require a long static consolidation period, making them unsuitable for the rapid construction and traffic restoration needs of urban roads. While composite foundation treatment methods such as cement mixing piles and CFG piles can improve the bearing capacity of the foundation, the construction equipment is large, the construction procedures are complex, and the project cost is high. Furthermore, the soil between piles may still suffer from insufficient reinforcement, uneven overall stress, and local settlement.

[0004] Grouting reinforcement improves the overall strength of soft soil foundations by injecting cement grout, cement-water glass grout, or other solidified grouts into the soil. This grout fills soil pores, cements weak particles, and compacts the soil. However, current conventional grouting methods often employ uniform hole spacing, pressure, and grout mix ratios, lacking zonal identification and parameter matching based on the foundation thickness, moisture content, pore distribution, location of weak interlayers, and groundwater conditions. When the degree of weakness within the soft soil varies significantly, using fixed grouting parameters can easily lead to overtreatment in shallow areas, insufficient reinforcement in medium-deep areas, and unstable grout diffusion in areas with high water content. This can result in uneven distribution of the consolidated body, localized voids, edge leakage, or central bulging.

[0005] Patent CN102936892B discloses a rapid preloading drainage consolidation system and method for soft soil foundations. This method involves arranging a radial hydraulic pressurization device, a grouting system, a vertical drainage device, and a horizontal drainage device within the foundation to be reinforced. Grout is injected into the radial hydraulic pressurization device using the grouting system, causing the device to apply radial pressure to the surrounding soil, thereby promoting drainage consolidation of the soft soil foundation. This approach can shorten the drainage consolidation time of soft soil foundations to a certain extent and improve the efficiency of soft soil foundation treatment.

[0006] However, the aforementioned existing patents mainly focus on pre-loading drainage consolidation systems and radial hydraulic pressurization devices. Their technical focus is on applying radial pressure to the surrounding soil through the pressurization device to improve the long consolidation time of traditional pre-loading drainage systems. This solution does not address the characteristics of municipal road soft soil foundations, such as varying depths, uneven distribution of localized high-water-content weak interlayers, and short road construction windows. It fails to establish a matching relationship between soft soil foundation testing zoning results and grouting hole spacing, grouting pressure, grout gelation time, and drainage component spacing; nor does it disclose a coordinated grouting and drainage structure where grouting holes and vertical permeable drainage components are staggered and connected to transverse drainage blind ditches; furthermore, it does not disclose a feedback control method for determining the timing of pressurization construction based on pore water pressure drop, changes in roadbed surface heave, and grout setting state. Existing soft soil foundation treatment technologies for municipal roads still have the following shortcomings: First, there is a lack of linkage and matching between the soft soil foundation detection zoning results and the grouting, drainage, and pressure-reinforcing construction parameters, making it difficult to carry out differentiated treatment for soft soil foundations of different depths and degrees of weakness; Second, there is a lack of coordinated layout between grouting holes and drainage structures, making it difficult to release the excess pore water pressure generated by grouting in a timely manner, affecting the uniformity of grout diffusion and the stability of subsequent settlement; Third, when the same grouting pressure is used in the edge area and the central area, it is easy to cause grout leakage at the edge, bulging in the central area, or local voids; Fourth, the pressure-reinforcing construction lacks feedback triggering conditions based on pore water pressure and grout setting state, making it difficult to balance rapid forming and the integrity of the consolidated body.

[0007] Therefore, there is an urgent need to propose a reinforcement method suitable for the rapid treatment of soft soil foundations in municipal roads. This method should form a closed-loop control system that integrates soft soil foundation zoning detection, grouting parameter matching, staggered arrangement of grouting holes and drainage components, differentiated grouting, pore pressure feedback and pressure replenishment, and rapid maintenance and detection. This system can solve the problems of uneven grouting diffusion, untimely drainage and pressure relief, inconsistent treatment of shallow and deep soft soil foundations, and insufficient settlement control after rapid construction in existing technologies. Summary of the Invention

[0008] To overcome the problems of uneven soft soil foundation depth, uneven grout diffusion, slow dissipation of pore water pressure, and uneven settlement after rapid construction in existing technologies for municipal roads, this invention achieves rapid, uniform, and stable reinforcement of soft soil foundations by dividing the foundation into zones, matching grouting and drainage parameters, staggering the arrangement of grouting holes and drainage components, and employing low-pressure slow grouting at the edges and high-pressure segmented grouting in the middle, combined with pore pressure feedback and rapid curing.

[0009] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is: a method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage collaborative closed-loop control, which involves soft soil foundation detection of the municipal road subgrade to be treated, and dividing the soft soil foundation treatment areas with different degrees of weakness according to the detection results. The corresponding grouting and drainage parameters are determined based on the degree of weakness of the soft soil treatment area. Grouting holes and drainage structures are laid out in the roadbed to be treated so that the grouting area and the drainage area can work together. Injecting solidified grout into the grouting hole to cement, fill and compact the soft soil, while simultaneously draining pore water from the soft soil through the drainage structure and releasing the pore water pressure generated by grouting; The timing of additional compaction is determined based on the status feedback during the soft soil foundation reinforcement process, and the subgrade is compacted accordingly. After compaction is completed, maintenance and testing are carried out. Once the testing is passed, the subsequent road construction procedures will begin.

[0010] Furthermore, the soft soil foundation detection includes at least two of the following methods: ground-penetrating radar, borehole sampling, static cone penetration testing, water content detection, and pore water pressure detection, to obtain the soft soil foundation thickness, water content, pore distribution, location of weak interlayers, and groundwater status.

[0011] Furthermore, the soft soil treatment area includes a shallow soft soil area, a medium soft soil area, a deep soft soil area, and a localized key weak soil area; wherein, the shallow soft soil area is treated by excavation, replacement, and layered compaction, while the medium soft soil area, the deep soft soil area, and the localized key weak soil area are treated by grouting reinforcement and drainage pressure relief.

[0012] Furthermore, the shallow soft soil zone is a region with a soft soil thickness of no more than 1.5m, the medium soft soil zone is a region with a soft soil thickness of more than 1.5m and no more than 3.0m, the deep soft soil zone is a region with a soft soil thickness of more than 3.0m and no more than 6.0m, and the local key weak zone includes at least one of high water content silt interlayer, voids, loose miscellaneous fill soil zone and local low bearing capacity zone.

[0013] Furthermore, the grouting parameters include grouting hole spacing, grouting pressure, grout mix ratio, grout gelation time, and grouting segment height; the drainage parameters include the spacing of vertical drainage components, the location of horizontal drainage blind ditches, and the connection method of the drainage structure.

[0014] Furthermore, the grouting hole spacing in the middle soft soil layer is 900–1000 mm, and the grouting pressure is 0.30–0.45 MPa; the grouting hole spacing in the deep soft soil layer is 800–900 mm, and the grouting pressure is 0.45–0.60 MPa; and the grouting hole spacing in the local key weak areas is 600–800 mm.

[0015] Furthermore, the grouting holes and drainage structure are staggered. The drainage structure includes vertical permeable drainage components and horizontal drainage blind ditches. The vertical permeable drainage components are located between two adjacent grouting holes or within a grid area enclosed by multiple grouting holes, and are connected to the horizontal drainage blind ditches.

[0016] Furthermore, the vertical permeable drainage component is one of a permeable hose, a plastic drainage board, or a permeable drainage pipe. The outer side of the vertical permeable drainage component is provided with a geotextile filter layer, a gravel filter layer, or a permeable filter sleeve to reduce the blockage of drainage channels by soft soil particles or slurry.

[0017] Furthermore, the curing grout is a cement-water glass two-component grout, with a cement grout water-cement ratio of 0.8:1 to 1.2:1, a water glass content of 8% to 15% of the cement mass, and a grout gel time controlled at 30 to 60 seconds. During grouting, the edge holes of the roadbed are first grouted with low pressure and slow injection to form an edge-constrained closed zone, and then the holes in the middle of the roadbed are grouted in sections from bottom to top with relatively high pressure to form the main consolidation zone.

[0018] Furthermore, the status feedback includes pore water pressure, roadbed surface heave, settlement rate, and grout setting state; when the pore water pressure decreases from the grouting peak, the roadbed surface heave tends to stabilize, and the grout reaches initial setting but not final setting, the roadbed is compacted by additional pressure; the additional pressure compaction adopts static pressure or weak vibration compaction method, and after the additional pressure is completed, the roadbed bearing capacity, compaction degree, settlement, and consolidation uniformity are tested.

[0019] The beneficial effects of this invention are as follows: 1. This invention first conducts soft soil foundation detection on the subgrade of the municipal road to be treated, obtaining the thickness, water content, pore distribution, location of weak interlayers, and groundwater status of the soft soil. Based on this, it divides the soft soil into shallow, medium, deep, and locally key weak areas. Then, according to the degree of weakness of different soft soil treatment areas, it determines the corresponding grouting hole spacing, grouting pressure, grout gelation time, grouting segment height, and drainage component placement spacing. This avoids the problems caused by the use of uniform grouting parameters in existing soft soil treatment methods, such as overtreatment of shallow layers, insufficient reinforcement of medium and deep layers, and omission of local weak areas. It transforms soft soil reinforcement from experience-based construction to zoned and parameterized construction based on detection results, improving the overall consolidation uniformity and bearing stability of the subgrade. 2. This invention achieves a synergistic effect of grouting consolidation and drainage pressure relief by staggering the arrangement of grouting holes and drainage structures. While grouting holes are arranged in the subgrade to be treated, vertical permeable drainage components are set between adjacent grouting holes or in the grid area enclosed by multiple grouting holes. The vertical permeable drainage components are connected to the transverse drainage blind ditch to form a combined vertical and transverse drainage network. During grouting, the solidified grout diffuses from the grouting holes to the surrounding soft soil, filling, cementing and compacting the soil. The pore water squeezed out by the grout and the excess pore water pressure generated by grouting can be discharged in time through the staggered drainage structure. This structure makes the grout diffusion path and the drainage pressure relief path work together, which helps to reduce the risk of soil heave, local accumulation of grout and subsequent rebound settlement during the grouting process, and improves the rapid consolidation effect of soft foundation. 3. This invention improves the grout diffusion quality and reduces the risks of grout leakage, bulging, and voids by using low-pressure slow grouting at the edges and high-pressure segmented grouting in the middle. Cement-water glass dual-liquid grout is used as the solidification grout. During the grouting process, low-pressure slow grouting is first used at the edge holes of the roadbed to form an edge-constrained closed zone. Then, relatively high-pressure segmented grouting is used at the middle holes of the roadbed to form the main consolidation zone from bottom to top. The edge-constrained closed zone can reduce the possibility of ineffective grout loss to the outside of the roadbed. The high-pressure segmented grouting in the middle can enhance the filling and compaction effect of the grout on the medium and deep soft soil. This differentiated grouting method takes into account the needs of edge sealing, internal diffusion, and deep reinforcement, which is conducive to forming a continuous and uniform composite consolidated soil and reducing edge grout leakage, middle bulging, and local unreinforced voids. 4. By determining the timing of additional compaction through state feedback, the forming quality and later stability under rapid construction conditions can be improved. Pore water pressure, roadbed surface heave, settlement rate, and grout setting state are introduced as state feedback parameters during the grouting reinforcement process. When the pore water pressure decreases from the grouting peak, the roadbed surface heave stabilizes, and the grout reaches initial setting but not final setting, static or weak vibration compaction is then applied to the roadbed. This timing avoids premature compaction before the grout has initially set, which could damage the grout diffusion channels, and also avoids the problem of the solidified body hardening after the grout has fully set, making further compaction difficult. This allows the compaction to be completed within the time window when the consolidated soil has initial cementing capacity but still meets the conditions for secondary compaction. This improves the roadbed compaction degree, bearing capacity, and overall density. Furthermore, subsequent testing of bearing capacity, compaction degree, settlement, and consolidation uniformity forms a closed loop for construction quality, reducing the risk of uneven settlement and pavement defects after rapid traffic opening. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method for rapid reinforcement of soft soil foundation for municipal roadbeds according to the present invention; Figure 2 This is a schematic diagram of the soft soil detection partitioning of the present invention; Figure 3 This is a plan view showing the staggered arrangement of the grouting holes and the vertical permeable drainage components of the present invention. Figure 4 This is a cross-sectional schematic diagram showing the connection between the grouting hole, the vertical permeable drainage component, and the horizontal drainage blind ditch of the present invention. Figure 5 This is a schematic diagram illustrating the construction of the present invention, which involves low-pressure slow grouting at the edges and high-pressure segmented grouting in the middle. Figure 6 This is a control flowchart for determining the timing of pressure replenishment based on state feedback, as per the present invention. Figure 7 This is a schematic diagram of the composite consolidated roadbed structure after reinforcement according to the present invention. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The following detailed description, in conjunction with the accompanying drawings and specific embodiments, further illustrates this application. It should be understood that the following embodiments are merely illustrative of the technical solutions of this invention and should not be construed as limiting the scope of protection of this invention. Without departing from the core concept of this invention, those skilled in the art can routinely adjust some construction parameters based on actual soil conditions, road grade, groundwater level, construction equipment, and design bearing requirements.

[0022] like Figures 1 to 7As shown, this invention provides a rapid reinforcement method for soft soil foundations of municipal roads based on a closed-loop control system of grouting and drainage. This method is applicable to newly constructed urban roads, road reconstruction and expansion projects, renovation and repair of old roads, and local settlement treatment projects. It is particularly suitable for the rapid reinforcement of soft soil, silty soil, plain fill, miscellaneous fill, high-water-content weak interlayers, or locally low-bearing-capacity foundations. The core of this invention lies in: firstly, conducting soft soil foundation detection and zoning identification of the roadbed to be treated; then determining grouting and drainage parameters based on the degree of weakness of different soft soil treatment areas; subsequently, staggering the grouting holes with the drainage structure to create a synergistic effect between the grouting consolidation area and the drainage pressure relief area; during the grouting process, combining low-pressure slow grouting at the edges with segmented grouting at higher pressure in the middle, and determining the timing of pressure replenishment through feedback from pore water pressure, roadbed surface heave, settlement rate, and grout solidification state, thereby achieving rapid consolidation of the soft soil, rapid release of pore water pressure, and overall compaction of the roadbed.

[0023] Soft soil foundation detection is conducted on the subgrade of the municipal road to be treated, and soft soil foundation treatment areas with different degrees of weakness are divided according to the detection results; Specifically, soft soil foundation detection is carried out on the subgrade of the municipal road to be treated, and soft soil treatment areas with different degrees of weakness are divided according to the detection results. This can be achieved in the following way.

[0024] Before construction, the soft soil foundation detection range is determined based on the road design width, construction segment length, existing defects, or the boundary of the section to be treated. Surface water, loose soil, humus, and other debris affecting detection accuracy are removed from the subgrade. Then, longitudinal and transverse survey lines are established within the detection range. Ideally, gridded survey lines are laid out along the road's longitudinal and transverse directions. Longitudinal survey lines can be arranged along the road centerline, side lane lines, or the direction of the defect zone, while transverse survey lines can be arranged perpendicular to the road's direction at predetermined intervals to form a detection grid covering the area to be treated.

[0025] During the detection process, ground-penetrating radar (GPR) is first used to continuously scan the roadbed to be treated, identifying areas of abnormal reflection, abnormal water content, loose areas, cavities, and suspected locations of weak interlayers within the roadbed. After the GPR scan is completed, borehole sampling points are set up in areas with obvious abnormal reflection, representative normal areas, and areas with concentrated road subsidence, frost heave, cracks, and other defects. Soil samples at different depths are obtained through borehole sampling. The soil samples are then tested for water content, void ratio, soil type, liquid and plastic limits, compressibility, or natural density to determine the actual thickness, water content, and engineering properties of the weak soil layer. If necessary, static cone penetration testing, light dynamic cone penetration testing, or pore water pressure testing can be combined to verify changes in soil strength, groundwater conditions, and pore water pressure distribution.

[0026] After completing the above tests, the results of ground-penetrating radar detection, borehole sampling, moisture content testing, static cone penetration testing, and pore water pressure testing are comprehensively compared. When ground-penetrating radar shows continuous weak reflection, strong absorption, or anomalous interfaces, and borehole sampling shows the presence of high-water-content soft soil, silty soil, loose fill, or low-bearing-capacity soil layers at the corresponding depth, the area is identified as a soft soil foundation treatment area. For areas with only surface soft soil and a relatively stable bearing layer below, they are classified as shallow soft soil foundation areas; for areas where the soft layer extends downwards and is relatively thick, they are classified as medium-layer or deep soft soil foundation areas; for areas with localized high-water-content silty interlayers, cavities, loose fill, abrupt settlement zones, or abnormally high pore water pressure, they are separately classified as localized key soft soil areas.

[0027] Preferably, the shallow soft soil zone is an area with a soft soil thickness of no more than 1.5m; the medium soft soil zone is an area with a soft soil thickness greater than 1.5m but no more than 3.0m; the deep soft soil zone is an area with a soft soil thickness greater than 3.0m but no more than 6.0m; and the locally key weak zone is an area that, although small in area, has high water content, large porosity, low bearing capacity, and contains cavities or abrupt changes in weak interlayers. The above zoning standards can be adjusted according to road grade, design bearing requirements, and on-site geological conditions, but it should ensure that each type of soft soil treatment area corresponds to different grouting parameters, drainage parameters, and reinforcement treatment methods.

[0028] After zoning, the different soft soil treatment areas should be marked on-site. Specifically, surveying and setting out can be used to mark the boundaries of shallow soft soil areas, medium soft soil areas, deep soft soil areas, and locally key weak areas on the roadbed surface. The starting and ending station numbers, lateral range, soft soil thickness, representative moisture content, weak interlayer depth, and groundwater status of each zone should be recorded on the construction drawings or electronic coordinate diagrams. For locally key weak areas, their center location, boundary range, and anomaly type should also be marked separately to facilitate subsequent measures such as increasing borehole density, improving drainage density, or adjusting grouting pressure.

[0029] Through the aforementioned soft soil foundation detection and zoning, the subgrade to be treated can be divided from a single construction object into treatment units with different degrees of weakness. This allows shallow soft soil areas to be prioritized for excavation and replacement with layered compaction, while medium-layer, deep soft soil areas, and locally critical weak areas can proceed to subsequent grouting reinforcement and drainage / pressure relief treatment. Consequently, the subsequent grouting hole spacing, grouting pressure, grout gelation time, vertical drainage component spacing, and pressure replenishment timing can all be determined based on the zoning results, thus achieving a closed-loop matching between the soft soil foundation detection results and subsequent grouting and drainage coordinated reinforcement parameters.

[0030] The corresponding grouting and drainage parameters are determined based on the degree of weakness of the soft soil treatment area. Specifically, the grouting and drainage parameters are determined based on the degree of weakness of the soft soil treatment area, which can be implemented as follows: After completing the soft soil foundation detection and zoning, the construction personnel determined the grouting reinforcement strength and drainage pressure relief strength for different areas based on the soft soil thickness, moisture content, porosity, distribution of weak interlayers, groundwater status, and bearing capacity test results of each soft soil foundation treatment area. The grouting parameters included grouting hole spacing, grouting hole depth, grouting pressure, grout mix ratio, grout gelation time, single-hole grouting volume, grouting segment height, and grouting sequence. The drainage parameters included the spacing, depth, and location of vertical permeable drainage components, the location, size, and slope of the transverse drainage blind ditch, and the connection method between the vertical permeable drainage components and the transverse drainage blind ditch. Specifically, for shallow soft soil foundation areas, due to the relatively small thickness of the weak soil layer, excavation and replacement with layered compaction are preferred, and these areas are generally not considered the main grouting areas. If there are local water-bearing or loose interlayers below the shallow soft soil foundation area, a small number of reinforcing grouting holes can be installed after replacement, and drainage can be carried out in conjunction with shallow transverse drainage blind ditches. For medium-layer soft soil foundation areas, since the weak soil layer has a certain thickness but has not yet reached the level of deep soft soil foundation, the preferred grouting hole spacing is 900–1000 mm, the preferred grouting pressure is 0.30–0.45 MPa, the preferred grouting segment height is 400–600 mm, and vertical permeable drainage components can be arranged between adjacent grouting holes or at the center of the grid formed by four grouting holes. For deep soft soil areas, due to the large thickness of the weak soil layer and the long dissipation path of pore water pressure, the grouting hole spacing is preferably 800-900 mm, and the grouting pressure is preferably 0.45-0.60 MPa. The density of vertical permeable drainage components should be appropriately increased to ensure timely drainage of pore water generated during grouting compaction. For locally key weak areas, such as high-water-content silt interlayers, cavities, loose fill areas, or areas with low bearing capacity, the grouting hole spacing can be increased to 600-800 mm. The density of drainage structures or repeated grouting procedures can be added depending on the water content and pore water pressure. When determining the grout parameters, cement-water glass two-component grout is preferred as the curing grout. The water-cement ratio of the cement grout is controlled at 0.8:1 to 1.2:1, and the water glass content is controlled at 8% to 15% of the cement mass. The gel time of the grout is controlled at 30 to 60 seconds by adjusting the water glass content and the mixing ratio of the two components. For areas with low water content and small soil pores, a lower grouting pressure and a longer gel time can be used to facilitate grout penetration and diffusion. For areas with high water content, large porosity, or obvious weak interlayers, the water glass content can be increased, the gel time shortened, and the pore density increased and drainage enhanced to prevent the grout from being diluted or lost by pore water. When determining drainage parameters, the drainage capacity should be matched with the grouting intensity. For intermediate soft soil layers, vertical permeable drainage components can be staggered according to the grouting hole grid and connected to the transverse drainage blind ditches on both sides of the roadbed. For deep soft soil layers and locally key weak areas, vertical permeable drainage components should extend deep into the weak layer and are preferably located at the center of the grid between grouting holes. This allows the pore water squeezed out as the grout diffuses outward from the grouting holes to drain upward or laterally along the nearest vertical permeable drainage component to the transverse drainage blind ditch. The transverse drainage blind ditch is filled with crushed stone or graded permeable material and wrapped with geotextile to reduce the entry of fine soil particles into the drainage channel.

[0031] After the parameters are determined, a construction parameter table or construction layout drawing is generated for each soft soil foundation treatment area. The construction parameter table includes at least the soft soil foundation type, treatment depth, grouting hole spacing, grouting pressure, grout mix ratio, gelation time, grouting segment height, vertical permeable drainage component spacing, and horizontal drainage blind ditch location for each area. During construction, the hole layout, drainage structure installation, and grouting control are carried out according to the construction parameter table. If grout leakage, cross-contamination, excessive surface bulging, or persistent pore water pressure occurs during construction, the grouting pressure, grouting speed, single-hole grouting volume, or drainage component density for the corresponding area are adjusted. This ensures that the grouting and drainage parameters are matched to soft soil foundation treatment areas with different degrees of weakness, achieving zoned, parameterized, and closed-loop control of soft soil foundation reinforcement.

[0032] Grouting holes and drainage structures are laid out in the roadbed to be treated so that the grouting area and the drainage area can work together. Specifically, grouting holes and drainage structures are installed within the roadbed to be treated, so that the grouting area and the drainage area work synergistically. This can be achieved in the following way: After determining the soft soil foundation detection zones and construction parameters, the site layout is first carried out based on the boundaries of each soft soil foundation treatment area, the spacing of grouting holes, the spacing of drainage components, and the location of transverse drainage blind ditches. For the middle layer soft soil foundation area, the deep soft soil foundation area, and the local key weak areas, the grouting hole positions and drainage structure layout positions are marked on the roadbed surface. The grouting holes are preferably arranged in a matrix, floral, or quincunx pattern to allow the grout diffusion range of adjacent grouting holes to overlap and avoid the formation of unreinforced blank areas. The drilling depth of the grouting holes is determined based on the thickness of the soft soil layer. Ideally, the grouting holes should penetrate the weak soil layer and enter the lower, relatively stable bearing layer by 50–100 mm. The hole diameter can be controlled to be 50–70 mm. After drilling, the holes should be cleaned to ensure that there is no collapsed soil, mud clumps, or debris blocking the holes. For deep soft soil areas and key local weak areas, the number of grouting holes can be appropriately increased to ensure that the grout can fully cover high water-bearing interlayers, cavities, loose fill soil areas, or local low bearing capacity areas. The drainage structure includes vertical permeable drainage components and horizontal drainage blind ditches. The vertical permeable drainage components are not coaxially arranged with the grouting holes, but are staggered with them. Specifically, the vertical permeable drainage components can be set between two adjacent grouting holes, or at the center of a grid formed by four adjacent grouting holes, placing them between adjacent grouting diffusion areas. Through this staggered arrangement, the area where the grouting holes are located forms a grouting diffusion zone, and the area where the vertical permeable drainage components are located forms a drainage and pressure relief zone. The two are spatially adjacent but do not overlap, thus ensuring that the grout can diffuse to the surrounding soft soil while preventing the drainage components from directly becoming grout loss channels. Vertical permeable drainage components can be made of permeable hoses, plastic drainage boards, or permeable drainage pipes. The lower end of the vertical permeable drainage component extends into the interior of the weak soil layer, preferably extending to the lower part of the weak layer or the area where pore water accumulates. Its upper end or side connects to the transverse drainage blind ditch, which can be set on both sides of the roadbed, the low-lying side, or at the boundary of the construction section. The blind ditch is filled with crushed stone, pebbles, or graded permeable material, and wrapped with geotextile to prevent fine soil particles from entering the blind ditch. The outside of the vertical permeable drainage component is preferably covered with a geotextile filter layer, a gravel filter layer, or a permeable filter sleeve to reduce the entry of soft soil particles into the drainage component and reduce the risk of grout directly clogging the drainage channel. During construction, horizontal drainage blind ditches can be excavated first, and permeable materials can be laid in the blind ditches. Then, vertical permeable drainage components can be installed to connect the vertical permeable drainage components with the horizontal drainage blind ditches. Subsequently, grouting holes can be drilled and grouting pipes can be installed. Alternatively, the positions of the grouting holes and drainage components can be marked out first, and then the grouting holes and drainage structures can be constructed simultaneously. For soft soil areas with high water content, it is preferable to complete the layout of vertical permeable drainage components and horizontal drainage blind ditches first, so that the squeezed pore water can be discharged in time during the subsequent grouting process. During grouting, the solidified grout diffuses from the grouting holes into the surrounding soft soil, filling, cementing, and compacting the soft soil. Because the vertical permeable drainage components are located between adjacent grouting holes or at the center of the grouting hole grid, the pressure generated by the grout diffusion pushes the pore water in the soft soil towards the drainage components. This allows the pore water to enter the transverse drainage ditch through the vertical permeable drainage components and be discharged from the roadbed treatment area. Thus, a grout cementation and consolidation zone is formed around the grouting holes, and a pore water release zone is formed around the drainage components. Grouting consolidation and drainage pressure relief occur simultaneously, constituting a synergistic effect of grouting and drainage. To further improve the synergistic effect, the grouting construction sequence can be coordinated with the location of the drainage structure. It is preferable to first perform low-pressure, slow grouting at the edge holes of the roadbed, creating a confined and closed zone at the edge to reduce grout loss to the outside of the roadbed. Then, perform segmented grouting from bottom to top at the middle holes, gradually filling and compacting the weak soil in the middle. During the grouting process in the middle, pore water is discharged along the staggered vertical permeable drainage components, and the excess pore water pressure generated by grouting is released through the transverse drainage blind ditch, reducing the risk of roadbed surface heave and subsequent rebound settlement. During the grouting process, the outflow of water from the transverse drainage blind ditch, the turbidity of the outflow, the amount of roadbed surface heave, and the changes in pore water pressure can be observed. When the drainage blind ditch continues to drain water and the pore water pressure gradually decreases, it indicates that the grouting and compaction and drainage pressure relief are effectively coordinated. When a significant decrease in drainage volume, local grout leakage, or a continuous increase in pore water pressure is found, grouting in the corresponding area can be suspended, and the vertical permeable drainage components should be checked for blockage. If necessary, temporary drainage holes should be added, the grouting pressure reduced, or the grouting sequence adjusted. Through the above method, the grouting holes and drainage structures are spatially staggered and work synchronously during construction. Functionally, they respectively undertake the tasks of grout diffusion and consolidation and pore water discharge and pressure relief, thus forming a synergistic relationship between the grouting area and the drainage area. This synergistic layout can reduce the problems of uneven grout diffusion, pore water pressure accumulation, surface bulging, edge leakage, and subsequent settlement and rebound in traditional single grouting, thereby improving the integrity and stability of rapid reinforcement treatment of soft soil foundations. Injecting solidified grout into the grouting hole to cement, fill and compact the soft soil, while simultaneously draining pore water from the soft soil through the drainage structure and releasing the pore water pressure generated by grouting; Specifically, solidified grout is injected into the grouting holes to cement, fill, and compact the soft soil. Simultaneously, the drainage structure drains pore water from the soft soil and releases the pore water pressure generated during grouting. This can be achieved in the following manner: Before grouting, check the unobstructed state of the grouting holes, grouting pipes, vertical permeable drainage components, and horizontal drainage blind ditches. Confirm that there is no collapsed soil, mud clumps, or debris blocking the grouting holes, and that the vertical permeable drainage components and horizontal drainage blind ditches are in a connected state. Then, prepare the curing grout, preferably a cement-water glass two-component grout, wherein the water-cement ratio of the cement grout is controlled at 0.8:1 to 1.2:1, the water glass content is 8% to 15% of the cement mass, and the gel time of the grout is controlled at 30 to 60 seconds according to the soil moisture content and softness. During grouting, the grouting pipe is lowered to the bottom of the grouting hole, and grouting is carried out in sections from bottom to top. After each section is completed, the grouting pipe is raised to the next section to continue grouting, allowing the grout to spread gradually along the depth of the soft soil layer. Preferably, the lifting height of each section is 400-600 mm. For holes at the edge of the subgrade, a low-pressure, slow grouting method is first used to form an edge-constrained closed zone to reduce grout loss to the outside of the subgrade; for holes in the middle of the subgrade, a relatively high-pressure, section-by-section grouting method is used to allow the grout to fully penetrate into the medium-deep soft soil. After the grout enters the soft soil, it fills the soil pores and local voids, cements the soft soil particles, and under the action of grouting pressure, it compacts the surrounding soil, thereby forming a continuous grouting consolidation zone. During grouting, the diffusion and compaction of the grout promotes the migration of pore water in the soft soil to the surrounding area. Because the vertical permeable drainage components are staggered with the grouting holes and connected to the transverse drainage ditch, the squeezed-out pore water can enter the vertical permeable drainage components nearby and be discharged from the roadbed treatment area through the transverse drainage ditch. Simultaneously, the excess pore water pressure generated during grouting is gradually released as the pore water is discharged, preventing the continuous accumulation of pore water pressure within the soft soil. During construction, changes in grouting pressure, grouting volume, water outflow from transverse drainage blind ditches, roadbed surface heave, and pore water pressure can be observed simultaneously. When the drainage blind ditches continuously discharge water and the pore water pressure gradually decreases, it indicates that grouting consolidation and drainage pressure relief are effectively coordinated. When local grout leakage, excessive surface heave, or a continuous increase in pore water pressure occur, grouting at the corresponding holes should be suspended, and adjustments should be made by reducing grouting pressure, extending grouting intervals, clearing drainage structures, or adding temporary drainage holes. Through the above process, the solidified grout fills, bonds, and compacts the soft soil, while simultaneously allowing pore water and excess pore water pressure to be discharged and released in a timely manner, improving the uniformity of soft soil consolidation and its later-stage stability.

[0033] The timing of additional compaction is determined based on the status feedback during the soft soil foundation reinforcement process, and the subgrade is compacted accordingly. Specifically, the timing of additional compaction is determined based on the status feedback during the soft soil foundation reinforcement process, and the subgrade is compacted accordingly. This can be achieved in the following way: During and after grouting, continuous monitoring is conducted on the pore water pressure, roadbed surface heave, settlement rate, water discharge status of transverse drainage blind ditches, and grout setting status in the soft soil foundation reinforcement area. Pore water pressure can be detected using a pre-embedded pore water pressure gauge; roadbed surface heave and settlement rate can be measured using a level, total station, settlement plate, or displacement observation point; and grout setting status can be determined by on-site sampling or grout samples under the same conditions. When the pore water pressure reaches its peak and begins to decline during grouting, and the drainage ditch continues to drain or the drainage volume gradually decreases, it indicates that the excess pore water pressure generated by grouting compaction is being released. When the surface heave of the roadbed no longer increases significantly within the continuous observation period, and the settlement rate tends to stabilize, it indicates that the disturbance of the soft soil is gradually mitigating. When the grout sample under the same conditions reaches the initial setting state but has not yet reached the final setting state, it indicates that the solidified grout has acquired preliminary cementing ability while still retaining a certain amount of space for compaction. At this point, it can be determined that the compaction window has been entered. When compacting the soil, static compaction or weak vibration compaction methods are preferred to avoid applying high-energy, strong vibrations directly to the grouting-consolidated soil that has not yet fully hardened. During construction, a low-speed, low-energy static compaction test can be conducted first to confirm that there is no obvious grout seepage, frost heave, cracking, or abnormal heave on the roadbed surface before gradually increasing the number of compaction passes. The compaction sequence can proceed from the edge of the roadbed towards the center, or from low-lying, weak areas towards the surrounding stable areas, allowing for a gradual transition of soil stress and avoiding localized stress concentration. For the upper reinforcing fill layer, the thickness of a single compaction layer is preferably no more than 200 mm. If localized areas become soft, leak water, leak grout, or develop surface cracks during the compaction process, compaction in that area should be suspended. The problem should be addressed by extending drainage time, reducing compaction energy, installing temporary drainage holes, or performing localized secondary grouting. After compaction is completed, the roadbed compaction degree, bearing capacity, settlement, and consolidation uniformity should be tested to confirm that the soft soil reinforcement effect meets the requirements for subsequent road base or surface layer construction.

[0034] After compaction is completed, maintenance and testing are carried out. Once the testing is passed, the subsequent road construction procedures will begin.

[0035] Specifically, after compaction is completed, maintenance and testing are carried out. Once the testing is passed, subsequent road construction procedures can begin, which can be implemented as follows: After the roadbed compaction is completed, the surface of the treated area is first leveled, loose particles, laitance, and accumulated water are removed, and the transverse drainage blind ditches and vertical permeable drainage components are checked to ensure they are still functioning properly. Then, the compacted roadbed surface is sealed and cured. Preferably, geotextile, non-woven fabric, or plastic film is laid on the roadbed surface for covering, and water is sprayed to maintain moisture according to the ambient temperature and humidity, in order to reduce shrinkage cracks caused by rapid evaporation of surface moisture. Under normal temperature conditions, the sealing and curing time is preferably 24–36 hours; when the ambient temperature is low, the moisture content of the soft soil is high, or the design bearing capacity is high, the curing time can be appropriately extended. During the maintenance period, heavy vehicles, construction machinery, or concentrated loads should be avoided from directly acting on the reinforced roadbed that has not yet reached its design strength. At the same time, continue to observe the roadbed surface for any abnormal phenomena such as water seepage, grout seepage, cracks, local bulging, or subsidence. If any local abnormalities are found, subsequent procedures should be suspended, and the abnormal area should be re-measured. If necessary, additional drainage, local secondary grouting, or re-compaction treatment should be carried out. After maintenance, the treated roadbed is inspected and accepted. The inspection items include at least the roadbed bearing capacity, compaction degree, settlement, and consolidation uniformity. The roadbed bearing capacity can be confirmed using plate load tests, light dynamic penetration tests, or other testing methods suitable for municipal roadbeds; compaction degree can be tested using sand cone tests, ring cutter tests, nuclear density gauge tests, or other conventional testing methods; settlement can be re-measured using settlement plates, leveling points, or displacement observation points; consolidation uniformity can be judged using ground-penetrating radar re-measurement, core sampling, or penetration testing. Preferably, the qualified inspection conditions include an overall roadbed compaction degree of not less than 97%, a roadbed bearing capacity characteristic value of not less than 180 kPa, and no obvious localized softness, voids, continuous settlement, or abnormal water accumulation within the inspection area. Once the above test results meet the design and construction acceptance requirements, a roadbed reinforcement acceptance record is generated, allowing subsequent road base, subbase, or surface layer construction procedures to proceed. If some test indicators fail to meet the requirements, treatment measures are determined based on the test results of the non-compliant areas; for areas with insufficient compaction, local compaction is carried out; for areas with insufficient bearing capacity or uneven consolidation, supplementary grouting and re-curing are performed; for areas with poor drainage, drainage channels are dredged or added. Through maintenance, testing, and rework of non-compliant areas, a closed-loop control is formed for the soft soil foundation reinforcement results, ensuring that the roadbed is in a stable, uniform state and meets the bearing requirements before the construction of subsequent road structural layers.

[0036] Specifically, such as Figure 1 As shown, the method of this invention mainly includes steps such as soft soil foundation detection and zoning, determination of grouting and drainage parameters, layout of grouting holes and drainage structures, dual-liquid grouting consolidation, coordinated grouting and drainage pressure relief, state feedback pressure replenishment, and curing and monitoring. The steps are not simply sequentially superimposed, but rather the results of the previous stage's detection or monitoring serve as the basis for the construction parameters and timing of the next stage, forming a closed-loop construction control process. First, soft soil detection and partitioning are performed, such as... Figure 2 As shown, before reinforcing the subgrade of municipal roads, surface debris, accumulated water, and loose soil in the area to be treated should be cleared. The detection area should be delineated based on the road design width, the extent of the damage, or the length of the construction sections. Soft soil foundation detection can be performed using at least two of the following methods in combination: ground-penetrating radar, borehole sampling, static cone penetration testing, moisture content testing, and pore water pressure testing. Ground-penetrating radar is mainly used for preliminary identification of weak interlayers, cavities, loose areas, and areas with abnormal water content within the subgrade; borehole sampling is used to obtain soil samples and test moisture content, void ratio, liquid and plastic limits, compressibility, and soil type; static cone penetration testing is used to determine soil strength and the continuous distribution of weak layers; and pore water pressure testing is used to determine the internal water pressure state of the soft soil foundation and the difficulty of drainage and consolidation. After obtaining the soft soil thickness, water content, porosity distribution, location of weak interlayers, and groundwater status through the above-mentioned detection methods, the roadbed to be treated is divided into soft soil treatment areas with different degrees of weakness. Preferably, the soft soil treatment areas include shallow soft soil areas, medium soft soil areas, deep soft soil areas, and locally key weak areas. Specifically, the shallow soft soil area is defined as an area with a soft soil thickness of no more than 1.5m; the medium soft soil area is defined as an area with a soft soil thickness greater than 1.5m but no more than 3.0m; the deep soft soil area is defined as an area with a soft soil thickness greater than 3.0m but no more than 6.0m; and locally key weak areas include areas with high water content silt interlayers, cavities, loose fill soil areas, locally low bearing capacity areas, or areas showing abnormal reflections from ground-penetrating radar. The above thickness classification standards can be adjusted according to the soft soil properties, road grade, and design requirements of the project site, but it should be ensured that different areas can correspond to different reinforcement methods and construction parameters. For shallow soft soil foundation areas, the preferred treatment method is excavation, replacement, and layered compaction. During construction, the shallow soft soil, humus, silt, loose fill, and other soil unsuitable as the bearing layer of the roadbed are first excavated, reaching the bottom of the shallow soft soil or the designed treatment depth. Then, graded crushed stone, manufactured sand, lime-soil, cement-modified soil, or other replacement materials that meet the requirements of the roadbed are used for layered backfilling. The thickness of each layer is preferably controlled between 150mm and 200mm, and compaction is carried out using vibratory compaction, static compaction, or light compaction equipment to ensure that the shallow replacement area meets the designed compaction requirements. After the shallow soft soil foundation area is treated, its surface should be flat and dense, forming a continuous reinforced foundation with the subsequent medium-deep grouting area. For medium-layer soft soil areas, deep soft soil areas, and locally key weak areas, a combined approach of grouting reinforcement and drainage pressure relief is adopted. Unlike ordinary grouting methods, this invention does not apply a uniform hole spacing, pressure, and grout mix ratio to all areas. Instead, it determines the corresponding grouting and drainage parameters based on the degree of weakness of the soft soil treatment area. The grouting parameters include grout hole spacing, grouting pressure, grout mix ratio, grout gel time, and grouting segment height; the drainage parameters include the spacing of vertical drainage components, the location of horizontal drainage blind ditches, and the connection method of the drainage structure. Preferably, for intermediate soft soil layers, the grouting hole spacing is controlled at 900mm–1000mm, and the grouting pressure is controlled at 0.30MPa–0.45MPa; for deep soft soil layers, the grouting hole spacing is controlled at 800mm–900mm, and the grouting pressure is controlled at 0.45MPa–0.60MPa; for locally concentrated weak areas, the grouting hole spacing can be increased to 600mm–800mm. For areas with high local water content, large void ratio, or significantly low bearing capacity, the single grouting pressure can be appropriately reduced and the number of grouting operations can be increased to avoid excessive grout fracturing, soil heave, or concentrated grout loss. For areas with dense underground pipelines or adjacent structures, the grouting pressure and grouting volume should be controlled in conjunction with the surrounding environment to avoid adverse effects on existing facilities.

[0037] like Figure 3 As shown, grouting holes are laid out in the middle layer soft soil zone, the deep soft soil zone, and locally key weak areas. The grouting holes can be arranged in a matrix, floral, or quincunx pattern, with staggered arrangement between adjacent rows to improve the uniformity of grout coverage. The borehole diameter is preferably 50mm–70mm, and the drilling depth is preferably 50mm–100mm, penetrating the weak soil layer and entering the lower, relatively hard bearing layer. After drilling, the borehole should be cleaned to ensure that there is no large amount of collapsed soil, mud clumps, or other blockages inside the hole, to ensure smooth lowering of the grouting pipe and uniform grout output.

[0038] like Figure 3 and Figure 4 As shown, this invention employs a staggered drainage structure between grouting holes. This drainage structure includes vertical permeable drainage components and horizontal drainage blind ditches. The vertical permeable drainage components can be one of a permeable hose, a plastic drainage board, or a permeable drainage pipe, or other drainage components with permeability and anti-clogging capabilities can be used according to actual needs. The vertical permeable drainage components are not coaxially arranged with the grouting holes, but are positioned between two adjacent grouting holes, or within a grid area enclosed by multiple grouting holes. Preferably, the vertical permeable drainage components are positioned at the center of the grid enclosed by four adjacent grouting holes, allowing the squeezed-out pore water to drain along the nearest drainage path when the grout diffuses from the grouting hole to the periphery.

[0039] The upper end or side of the vertical permeable drainage component is connected to the transverse drainage ditch. The transverse drainage ditch can be set on both sides of the roadbed, or it can be set on the lower side of the roadbed cross slope or at the boundary of the construction section, depending on the terrain and drainage conditions. The transverse drainage ditch can be filled with crushed stone, pebbles, or graded permeable material and covered with geotextile to prevent fine soil particles from entering the ditch and causing blockage. It is preferable to set a geotextile filter layer, gravel filter layer, or permeable filter sleeve on the outside of the vertical permeable drainage component to reduce the entry of soft soil particles or grout into the drainage channel. Through the above staggered arrangement, the grouting holes form a grout diffusion path, and the vertical permeable drainage component and the transverse drainage ditch form a pore water discharge path. The two work together to form a synergistic effect of grouting consolidation and drainage pressure relief inside the soft foundation. In this embodiment, the cement-water glass dual-component grout is preferably used as the curing grout. The water-cement ratio of the cement grout is preferably 0.8:1 to 1.2:1, and the water glass content is preferably 8% to 15% of the cement mass. The grout gel time is controlled to be 30 to 60 seconds by adjusting the water glass content, grout temperature, and dual-component mixing ratio. The cement-water glass dual-component grout can quickly bond and solidify in the pores of soft soil, making it suitable for scenarios where the construction window for municipal roads is short and subsequent processes need to be completed quickly. It should be noted that a shorter grout gel time is not necessarily better; too short a time will affect the grout diffusion distance, while too long a time will hinder rapid molding. Therefore, this invention uses zoning parameter matching and segmented grouting to adapt the grout gel time to the grout hole spacing, grouting pressure, and drainage capacity.

[0040] like Figure 5 As shown, grouting employs a combination of low-pressure slow grouting at the edges and high-pressure segmented grouting in the middle. Specifically, low-pressure slow grouting is first applied to the boreholes at the roadbed edges to create an edge-constrained closed zone. This edge-constrained closed zone reduces grout loss to the outside of the roadbed and provides lateral constraint for subsequent grouting in the middle. Then, relatively high-pressure grouting is applied to the boreholes in the middle of the roadbed, preferably in segmented grouting from bottom to top. After the grouting pipe is lowered to the bottom of the borehole, grouting is first applied to the bottom weak layer. After completing one segment, the grouting pipe is raised, and then the next segment is grouted. The preferred lifting height for each segment is 400mm to 600mm, more preferably 500mm. Through segmented grouting, the grout can diffuse layer by layer at different depths, avoiding concentrated consolidation only near the borehole opening or in localized weak layers.

[0041] During grouting, the grouting pressure at the edge holes is lower than that at the center holes. Continuous slow grouting is preferred for edge holes to control grout overflow and slope disturbance; segmented lifting grouting is preferred for center holes to enhance the filling and compaction of medium-deep soft soil. For locally concentrated weak areas, targeted reinforcement can be achieved by increasing the density of holes, repeating grouting, or reducing the single-time pressure and extending the grouting time. During grouting, the surface bulging, grout leakage, grout cross-contamination, and drainage of the subgrade should be observed. If abnormal grout leakage or significant local bulging is detected, grouting at the corresponding hole should be suspended until the pore water pressure is released before resuming construction.

[0042] While the dual-liquid grout diffuses into the soft soil, generating cementation, filling, and compaction effects, pore water in the soft foundation is drained through vertical permeable drainage components and transverse drainage blind ditches, releasing the excess pore water pressure generated during grouting and compaction. This coordinated grouting and drainage pressure relief process is a key technical feature that distinguishes this invention from ordinary grouting methods. Ordinary grouting methods typically consider drainage or compaction only after grouting is completed, making it difficult to release the excess pore water pressure generated during grouting in a timely manner, easily causing soil disturbance, heave, uneven grout diffusion, and subsequent rebound settlement. This invention, by staggering the drainage structure with the grouting holes, allows pore water to drain along the nearest drainage path during the grouting process, thereby improving the uniformity of grout diffusion and the stability of the reinforced soil.

[0043] like Figure 6 As shown, this invention also determines the timing of additional pressure based on state feedback during the soft soil foundation reinforcement process. The state feedback includes one or more of the following: pore water pressure, subgrade surface heave, settlement rate, and grout setting state. Pore water pressure can be detected using pre-embedded pore water pressure gauges or construction monitoring points; subgrade surface heave and settlement rate can be monitored using levels, total stations, settlement plates, or other measuring equipment; and grout setting state can be determined through on-site sampling, grout gel time tests, or construction records.

[0044] When the pore water pressure decreases from the grouting peak, the surface heave of the subgrade stabilizes, the settlement rate is within the allowable range, and the grout has reached initial setting but not final setting, the subgrade is compacted by additional compaction. Preferably, a decrease in pore water pressure from the grouting peak by 30% to 60% can be used as one of the reference conditions for initiating additional compaction. The timing of additional compaction should comprehensively consider the soil condition and the grout setting state. If additional compaction is performed too early, the grout has not yet formed preliminary cementation, and the compaction action may damage the grout diffusion channels or cause grout outflow; if additional compaction is performed too late, the grout has already fully set and hardened, reducing the overall compactable space of the subgrade and making it difficult to further improve the density through additional compaction. This invention selects additional compaction after the grout has initially set but before it has fully set, so that the consolidated soil has preliminary cementation capacity while still maintaining a certain degree of plasticity and compactability, which is beneficial to improving the overall density and bearing capacity of the subgrade.

[0045] Compaction can be performed using static compaction or weak vibration compaction. For roadbeds that have just been grouted and are in the initial setting stage, low-energy static compaction is preferred initially. Weak vibration or gradual compaction can then be applied after the surface stabilizes to avoid damaging the consolidated structure. The compaction sequence can proceed from the roadbed edge towards the center, or from low-lying, weak areas towards the surrounding regions. For the upper fill layer, the thickness of a single compaction layer should preferably not exceed 200mm, with the compaction speed gradually increasing. The number of compaction passes should be adjusted as needed based on surface cracks, bulges, settlement, and drainage conditions. If localized softness, water seepage, or abnormal settlement is observed during compaction, compaction of that area should be stopped, and supplementary drainage or secondary grouting should be performed.

[0046] like Figure 7 As shown, after the above treatment, the subgrade to be treated forms a composite consolidation structure including a shallow replacement and compaction layer, a medium-deep grouting consolidation zone, a vertical and horizontal combined drainage network, and a pressure-reinforcing layer. The shallow replacement and compaction layer is used to eliminate weak surface soil and provide a uniform construction surface; the medium-deep grouting consolidation zone is used to improve the internal strength and overall bearing capacity of the soft soil; vertical permeable drainage components and horizontal drainage blind ditches are used to drain pore water and release excess pore water pressure; the pressure-reinforcing layer is used to further improve the overall density and the uniformity of subgrade stress. The above components work together to achieve zoned treatment and rapid, stable reinforcement of soft soil at both shallow and deep depths.

[0047] After compaction is completed, sealing and curing, and testing and acceptance are carried out. Sealing and curing can be achieved through geotextile covering, water spraying for moisture retention, temporary sealing, or other moisture-retaining curing methods. Under normal temperature conditions, the curing time can be determined according to the type of grout, ambient temperature, humidity, and road grade requirements, preferably 24 to 36 hours before preliminary testing. Testing items include one or more of the following: subgrade bearing capacity, compaction degree, settlement, deflection value, consolidation uniformity, and drainage patency. Preferably, the passing test conditions include at least an overall subgrade compaction degree of not less than 97% and a subgrade bearing capacity characteristic value of not less than 180 kPa. For important roads or main road projects, the grouting consolidation effect can also be verified through static load tests, core sampling, ground-penetrating radar re-testing, or light dynamic penetration testing. Only after passing the test can subsequent road base or surface layer construction procedures proceed.

[0048] The invention will be further explained below with reference to specific construction scenarios.

[0049] Example 1: Rapid reinforcement of deep soft soil foundation in newly built urban roads.

[0050] Before construction began on a newly built road section in a city, shallow soft soil and medium-deep, high-water-content soft interlayers were discovered within the roadbed area. The construction unit first conducted ground-penetrating radar surveys and borehole sampling on the roadbed to be treated, confirming the presence of a 0-1.4m shallow soft soil layer, a 1.4m-4.8m medium-deep soft soil layer, and locally high-water-content silt interlayers. Based on the survey results, the shallow soft soil area, the medium-deep soft soil area, and the locally concentrated weak areas were marked.

[0051] For shallow soft soil foundation areas, the surface silt, humus, and loose fill should be removed first, and all soft soil within 1.4m should be excavated. Then, a mixture of graded crushed stone and manufactured sand should be used for layered replacement. The thickness of each layer should be controlled at 180mm, and after each layer is compacted, a flat and dense shallow replacement layer is formed.

[0052] For medium-deep soft soil foundation areas, grouting holes are laid out in a matrix pattern with a hole spacing and row spacing of 900mm. In the roadbed edge area, the hole spacing is increased to 800mm. The drilling depth is 5.0m, penetrating the soft soil layer and reaching approximately 80mm into the underlying hard soil layer. The hole diameter is 60mm. After drilling, the holes are cleaned to ensure unobstructed flow.

[0053] Vertical permeable hoses are installed between adjacent grouting holes and connected to the transverse drainage blind ditches on both sides of the roadbed. The outside of the vertical permeable hoses is covered with a geotextile filter layer to reduce the blockage of drainage channels by soft soil particles. The transverse drainage blind ditches are filled with crushed stone and wrapped with geotextile to ensure unobstructed drainage.

[0054] A cement-water glass dual-liquid grout was prepared, with a cement grout water-cement ratio of 1.0:1 and a water glass content of 12% of the cement mass. The grout gel time was controlled to be approximately 45 seconds. During grouting, a low-pressure, stable grouting method was first used for the boreholes at the roadbed edge to create a confined and closed zone at the edge. Subsequently, a segmented grouting method was used for the boreholes in the middle, from bottom to top, with each segment having a lifting height of 500 mm and a grouting pressure controlled at approximately 0.45 MPa. During the grouting process, the water discharge from the drainage ditch, the roadbed surface bulging, and changes in pore water pressure were observed. When the pore water generated by grouting was discharged through the vertical permeable hose and the transverse drainage ditch, and the pore water pressure decreased significantly from its peak value and the surface bulging tended to stabilize, the pressure replenishment stage began.

[0055] The compaction stage was carried out using a progressive static compaction method, with a single layer thickness of 180mm. The compaction sequence proceeded from the edge of the roadbed towards the center. After compaction, geotextile was used for covering and moisture retention curing. Following curing, the roadbed bearing capacity, compaction degree, settlement, and smoothness were tested. The test results showed that the overall compaction degree of the roadbed met the design requirements, and the bearing capacity met the requirements for subsequent road base construction, allowing for the commencement of road base and surface layer construction.

[0056] Example 2: Repair and construction of local subsidence damage on roads in old urban areas.

[0057] A road in an old urban area experienced localized subsidence and pavement cracking. During construction, the existing damaged pavement and base course were first removed to expose the underlying subgrade. Ground-penetrating radar and borehole sampling were used to identify the distribution of weak soil beneath the subsidence area, revealing loose fill, high-water-content weak interlayers, and localized cavities in some areas. Based on the detection results, the affected area was divided into a shallow loose layer, a medium-layer weak layer, and a locally concentrated weak layer.

[0058] For shallow, loose areas, the loose fill is first excavated and replaced with graded crushed stone or cement-modified soil, then compacted in layers to form a stable construction surface. For medium-level weak areas and locally key weak areas, grouting holes are installed within the limited construction space of the road, with vertical permeable drainage components staggered between adjacent grouting holes. For areas with localized settlement centers, the spacing between grouting holes is increased to 600mm–800mm; for surrounding generally weak areas, the spacing is set to 800mm–1000mm. The vertical permeable drainage components are connected to temporary drainage blind ditches on both sides of the road to promptly drain pore water generated during grouting compaction.

[0059] During grouting, low-pressure, slow grouting is first applied to the outer edges of the affected area to create a confined zone, preventing grout from flowing ineffectively beyond the damaged area. Subsequently, grouting is performed in sections in the settlement center and the central weak area, allowing the grout to fill and cement the weak soil layer by layer from bottom to top. During grouting, the amount of grout injected per hole is controlled based on the amount of surface heave and drainage conditions. Once the pore water pressure decreases, the surface heave stabilizes, and the grout reaches its initial setting state, low-energy static pressure is applied using small compaction equipment. After compaction, sealing and curing are performed, and the bearing capacity, compaction degree, and settlement of the repaired area are retested. After passing the tests, the road base and surface layers are restored. This embodiment can complete the treatment of local soft soil defects in a relatively short time, making it suitable for scenarios with high requirements for urban road traffic organization.

[0060] Example 3: Construction of treatment for soft soil foundation with high water content and silt.

[0061] For silty soft soil areas with high water content, large porosity, and slow drainage consolidation, the density of drainage structures can be increased based on the above implementation methods. Before construction, the boundaries of high-water-content soft soil areas are determined by borehole sampling and water content testing, and these areas are designated as key local soft soil areas. Grouting holes are laid out with a smaller hole spacing, and vertical permeable drainage components are placed at the center of the grouting hole grid, with the spacing between the vertical permeable drainage components appropriately reduced. During grouting, the single grouting pressure is reduced, and multiple small-volume segmented grouting is adopted to avoid uncontrolled diffusion of grout in high-water-content soil or excessive surface heave. Transverse drainage blind ditches are strengthened within the grouting gaps, and the timing of subsequent grouting and pressure replenishment is determined based on changes in pore water pressure. Static pressure replenishment is then carried out after the pore water pressure has dropped, the grout has reached initial setting, and the surface has stabilized. By improving drainage capacity and controlling the grouting rhythm, the problem of excess pore pressure dissipation in high-water-content soft soil can be improved, and the uniformity of consolidation can be enhanced.

[0062] As can be seen from the above embodiments, this invention determines the treatment target by soft soil foundation detection and zoning, determines construction parameters by matching grouting parameters with drainage parameters, achieves synergistic grouting and drainage by staggered arrangement of grouting holes and drainage structures, improves grout diffusion quality through differentiated grouting, determines the timing of pressure replenishment through status feedback, and confirms the treatment effect through maintenance and testing. Compared with construction methods that only use replacement, single grouting, or ordinary drainage consolidation, this invention can better adapt to the characteristics of soft soil foundations in municipal roads, such as varying depths, uneven strength, and short construction windows, which is beneficial to improving the efficiency of soft soil foundation treatment, the uniformity of consolidation, and the later stability of the roadbed.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various equivalent changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control, characterized in that, Includes the following steps: Soft soil foundation detection is conducted on the subgrade of the municipal road to be treated, and soft soil foundation treatment areas with different degrees of weakness are divided according to the detection results; The corresponding grouting and drainage parameters are determined based on the degree of weakness of the soft soil treatment area. Grouting holes and drainage structures are laid out in the roadbed to be treated so that the grouting area and the drainage area can work together. Injecting solidified grout into the grouting hole to cement, fill and compact the soft soil, while simultaneously draining pore water from the soft soil through the drainage structure and releasing the pore water pressure generated by grouting; The timing of additional compaction is determined based on the status feedback during the soft soil foundation reinforcement process, and the subgrade is compacted accordingly. After compaction is completed, maintenance and testing are carried out. Once the testing is passed, the subsequent road construction procedures will begin.

2. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 1, characterized in that: The soft soil foundation detection includes at least two of the following methods: ground-penetrating radar, borehole sampling, static cone penetration testing, water content detection, and pore water pressure detection, to obtain the soft soil foundation thickness, water content, pore distribution, location of weak interlayers, and groundwater status.

3. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 1, characterized in that: The soft soil treatment area includes a shallow soft soil area, a medium soft soil area, a deep soft soil area, and a localized key weak soil area; wherein, the shallow soft soil area is treated by excavation, replacement, and layered compaction of weak soil, while the medium soft soil area, the deep soft soil area, and the localized key weak soil area are treated by grouting reinforcement and drainage pressure relief.

4. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 3, characterized in that: The shallow soft soil zone is a region with a soft soil thickness of no more than 1.5m, the medium soft soil zone is a region with a soft soil thickness of more than 1.5m and no more than 3.0m, the deep soft soil zone is a region with a soft soil thickness of more than 3.0m and no more than 6.0m, and the local key weak zone includes at least one of the following: high water content silt interlayer, voids, loose miscellaneous fill soil zone, and local low bearing capacity zone.

5. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 1, characterized in that: The grouting parameters include grouting hole spacing, grouting pressure, grout mix ratio, grout gelation time, and grouting segment height; the drainage parameters include the spacing of vertical drainage components, the location of horizontal drainage blind ditches, and the connection method of the drainage structure.

6. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 5, characterized in that: The grouting hole spacing in the middle soft soil layer is 900-1000 mm, and the grouting pressure is 0.30-0.45 MPa; the grouting hole spacing in the deep soft soil layer is 800-900 mm, and the grouting pressure is 0.45-0.60 MPa; the grouting hole spacing in the local key weak areas is 600-800 mm.

7. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 1, characterized in that: The grouting holes and drainage structure are staggered. The drainage structure includes vertical permeable drainage components and horizontal drainage blind ditches. The vertical permeable drainage components are set between two adjacent grouting holes or in a grid area surrounded by multiple grouting holes, and are connected to the horizontal drainage blind ditches.

8. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 7, characterized in that: The vertical permeable drainage component is one of a permeable hose, a plastic drainage board, or a permeable drainage pipe. The outside of the vertical permeable drainage component is provided with a geotextile filter layer, a gravel filter layer, or a permeable filter sleeve to reduce the blockage of drainage channels by soft soil particles or slurry.

9. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 1, characterized in that: The curing grout is a cement-water glass two-component grout, with a cement grout water-cement ratio of 0.8:1 to 1.2:1, a water glass content of 8% to 15% of the cement mass, and a grout gel time controlled at 30 to 60 seconds. During grouting, the edge holes of the roadbed are first grouted with low pressure and slow injection to form an edge-constrained closed zone, and then the holes in the middle of the roadbed are grouted in sections from bottom to top with relatively high pressure to form the main consolidation zone.

10. The method for rapid reinforcement of soft soil foundation of municipal road subgrade based on injection and drainage coordinated closed-loop control according to claim 1, characterized in that: The status feedback includes pore water pressure, roadbed surface heave, settlement rate, and grout setting state. When the pore water pressure decreases from the grouting peak, the roadbed surface heave tends to stabilize, and the grout reaches initial setting but not final setting, the roadbed is compacted by additional pressure. The additional pressure compaction adopts static pressure or weak vibration compaction. After the additional pressure is completed, the roadbed bearing capacity, compaction degree, settlement, and consolidation uniformity are tested.

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