Foundation reinforcing structure of salinized soil foundation influenced by underground fresh water and construction method

Abstract

The invention provides a foundation reinforcing structure of a salinized soil foundation influenced by underground fresh water and a construction method of the foundation reinforcing structure. The reinforcing structure comprises an anti-seepage curtain, a pile foundation reinforcing system and a newly-added floor slab structure, the pile foundation reinforcing system comprises an original pile foundation structure and an expansion pile foundation reinforcing structure, and the newly-added floor slab structure comprises a structural beam and a steel bar truss floor support plate; the construction is divided into three stages, in the first stage, an anti-seepage curtain is formed through sodium bentonite cement paste grouting, and an underground fresh water erosion path is blocked; in the second stage, bearing platform extension is combined with anchor rod static pressure pile reinforcement, and the foundation bearing capacity is improved; and in the third stage, structural integrity and non-deformability are enhanced by newly adding a steel bar truss floor support plate structure floor slab. The reinforcement problem is systematically solved from the source to the appearance, the effect is stable, construction is safe, the method is suitable for existing building foundation reinforcement projects in salinized soil areas affected by underground fresh water, and safety and stability of buildings within the service life period can be guaranteed.

Description

Technical Field

[0001] This invention relates to the field of building foundation reinforcement technology. Specifically, it is a foundation reinforcement structure and construction method for saline soil areas affected by groundwater. It is applicable to the foundation reinforcement of existing buildings and structures that suffer from problems such as foundation subsidence, pile bearing capacity reduction, uneven building settlement, and ground voiding and cracking caused by groundwater erosion of saline soil. It can ensure the long-term safe and stable use of buildings. Background Technology

[0002] Saline soil, a special type of soil, contains a large amount of easily soluble salt crystals. Under the infiltration of freshwater, these salt crystals dissolve, leading to reduced cohesion between soil particles and increased porosity, thus triggering a series of foundation problems. Saline soil foundations located near freshwater areas are frequently affected by groundwater, causing soil subsidence that significantly reduces the bearing capacity of the foundation's bearing layer and substantially increases the negative skin friction of pile foundations, resulting in actual bearing capacity lower than design requirements. Furthermore, over time, uneven foundation settlement can generate additional stress in the superstructure, causing wall cracking, ground subsidence, and floor slab tensile cracking, seriously threatening the safety of buildings.

[0003] Existing foundation reinforcement schemes for saline soils have significant limitations: most schemes focus solely on improving the bearing capacity of the foundation, such as using pile foundation reinforcement or ground grouting, failing to address the root cause of the continuous erosion of saline soil by groundwater, leading to recurring subsidence problems after reinforcement. Simultaneously, they neglect the issue of insufficient overall structural stiffness. Even with improved foundation bearing capacity, it remains difficult to prevent issues like voids and cracks caused by differential settlement between the ground and the main structure, failing to achieve comprehensive reinforcement from the root to the structure, and thus failing to meet the long-term stable use requirements of existing buildings. Therefore, a systematic reinforcement scheme with a synergistic effect of "source interception-reinforcement-stiffening" is urgently needed to completely solve the foundation reinforcement problem in saline soil areas affected by groundwater. Summary of the Invention

[0004] To address some problems existing in the prior art, the present invention aims to provide a foundation reinforcement structure and construction method for saline soil foundations affected by groundwater. This reinforcement structure, through the coordinated design of an anti-seepage curtain system, a foundation reinforcement system, and newly added structural floor slabs, fundamentally blocks groundwater erosion, improves the foundation bearing capacity, and enhances the overall structural rigidity, thereby achieving comprehensive and long-term reinforcement of the foundation in saline soil areas.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a foundation reinforcement structure for saline soil affected by groundwater, the reinforcement structure including a seepage-proof curtain, a pile foundation reinforcement system and a new floor slab structure;

[0006] The seepage-proof curtain is arranged in a ring around the foundation to be reinforced, including multiple grouting pipes and a solidified sodium-based bentonite cement grout body wrapped around the grouting pipes. The solidified sodium-based bentonite cement grout body is formed by vertically trenching the foundation soil layer, vertically arranging multiple grouting pipes in the trench, and injecting sodium-based bentonite cement grout through the multiple grouting pipes, followed by solidification to form a seepage-proof structure. The seepage-proof curtain penetrates the upper overlying soil layer of the foundation and enters the lower stable stratum by at least 1m. After solidification, the permeability coefficient is ≤1×10⁻⁶. -6 cm / s;

[0007] The pile foundation reinforcement system includes the original pile foundation structure and the extended pile foundation reinforcement structure. The original pile foundation structure includes the original pile foundation cap, the original pile cap cast-in-place piles, and columns. The extended pile foundation reinforcement structure includes the extended pile cap and anchored static pressure piles. The extended pile cap is a reinforcement structure formed by roughening and rebar installation on the original pile foundation cap, adding a reinforced cage to the top of the original pile foundation cap, and then pouring concrete. The width of the extended pile cap is at least three times the diameter of the original pile cap cast-in-place piles. Pre-reserved pile driving holes are provided on the extended pile cap. The anchored static pressure piles are driven into the lower stable stratum through the pre-reserved pile driving holes after the extended pile cap reaches the curing strength.

[0008] The newly added floor structure includes structural beams and steel truss floor slabs. The structural beams are arranged horizontally or vertically within the foundation beams of the foundation to be reinforced, and both ends of each structural beam are connected to the foundation beams. The steel truss floor slabs are fixedly laid on the structural frame formed by the structural beams and are connected to the structural beams and the foundation beams.

[0009] The preferred technical solution of the present invention is as follows: the sodium-based bentonite cement slurry is prepared by mixing sodium-based bentonite, slag cement and brine in a mass ratio of 2:8:4~5, and the slurry density is 1.45~1.55g / cm³; the grouting pipe is made of seamless steel pipe with a tapered tip at the lower end, and grouting holes are evenly distributed on the pipe wall. Angle steel is welded to the outside of the holes, and the grouting holes face the leakage direction.

[0010] The preferred technical solution of this invention is as follows: the trench of the seepage prevention curtain is opened to a stable stratum, and the upper ends of multiple grouting perforated pipes arranged in the trench are connected to the grouting conduit via flexible bends. The grouting conduit is made of steel pipe with an inner diameter of 100~127mm, assembled in sections, and each section is 4~6m long. After the grouting perforated pipes are inserted into the trench, the soil layer 0.8~1.2m below the ground surface at the borehole opening is sealed with cement and soil, and an exhaust pipe is inserted simultaneously during the sealing process. Water level observation wells are arranged on both sides of the seepage prevention curtain, and the water level observation wells are located near the underground erosion channels formed by the infiltration of groundwater into the foundation area to be reinforced.

[0011] The preferred technical solution of the present invention is as follows: the extended pile cap is a pile cap structure formed by expanding the top surface or the top surface and the upper surrounding area of ​​the original pile foundation pile cap after roughening. Pre-reserved pile driving holes are provided at the corners of the extended pile cap, and anchor static pressure piles are driven in. The extended pile cap is also pre-embedded with finely rolled threaded steel for fixing the anchor static pressure pile device. The centroid of the newly added anchor static pressure pile and the centroid of the original pile foundation structure both coincide with the point of application of the resultant force of the upper column load, i.e., the center of the column load.

[0012] The preferred technical solution of this invention is as follows: the rebar of the extended pile cap is made of HRB400 grade steel bar, which is implanted into the original pile cap to a depth of 15 times the diameter of the steel bar, with a pull-out force ≥70kN. The rebar is fixed with Grade A modified epoxy resin anchoring adhesive. The anchor static pressure pile is a seamless steel pipe pile with a cross-shaped steel sheet pile tip at the bottom of the pile body. The steel pipe pile contains a steel cage, which is filled with fine stone concrete and grouted to the opening of the reserved pile driving hole. The upper part of the anchor static pressure pile is connected to the extended pile cap with micro-expansion concrete. A hole sealing pile driving structure is set at the opening of the reserved pile driving hole.

[0013] The preferred technical solution of this invention is as follows: the structural beam is an H-beam, and the surface of the steel beam is coated with epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and aliphatic polyurethane topcoat, with a total paint film thickness ≥40um; after the steel truss floor deck is laid, the top surface elevation relative to the ±0.000m reference plane is 0.03~0.07m, and it is corrected before laying; the steel truss floor deck is connected to the structural beam by weld studs, and the weld studs are installed with dry ceramic rings and removed after welding.

[0014] This invention also provides a construction method for reinforcing the foundation of saline soil affected by groundwater, characterized by the following steps:

[0015] S1. Construction preparation: Before construction, the site is leveled, grouting process test is conducted, anchor static pressure pile test is carried out, site cleaning and surveying are completed, and the surveying deviation is ≤±20mm;

[0016] S2. Construction of the seepage barrier curtain: Excavate the construction trench for the seepage barrier curtain according to the survey line, extending the trench into the stable stratum. Vertically install grouting pipes in the construction trench, with the grouting holes of the grouting pipes facing the leakage direction. The space between the grouting pipes and the trench wall is filled with graded crushed stone. Multiple grouting pipes are connected to external grouting conduits. Sodium-based bentonite cement grout is injected into the trench in stages through the grouting conduits and grouting pipes. The initial grouting pressure is 0.2 MPa, which is increased to 0.4~0.5 MPa after stabilizing for 8~12 minutes. The flow rate is 5~10 L / min. Intermittent skip-hole construction is adopted, with an interval of ≥24 hours between adjacent holes. Grouting is stopped when the grouting volume stabilizes continuously for 30 minutes or the ground heave is ≥5 mm. After grouting, backfill the trench and compact it in layers. After curing for at least 28 days, test the permeability coefficient. Only after it meets the standard can the next stage be carried out.

[0017] S3. Pile Foundation Reinforcement System: Locate the pile positions, remove the affecting walls, and clean the backfill soil around the pile cap to the design elevation; roughen the original pile foundation pile cap and remove the slag, drill holes and install rebar and test the pull-out force, tie the rebar cage and pour concrete to form an extended pile cap, and cure for ≥14 days; install reaction frames and jacks, and insert anchor bolt static pressure piles in sections, with a weld height of ≥10mm for each pile section and a pile driving speed of ≤0.5m / min; after the pile foundation construction is completed, select no less than 1% of the total number of piles and ≥2 piles for static load testing, and restore the foundation beams and masonry walls after the test is qualified;

[0018] S4. Construction of the new floor slab structure: Verify the positioning axis and elevation, excavate the soil around the foundation to be reinforced to the design installation elevation of the structural beam, clean the loose soil layer at the bottom of the trench and compact it, install the new structural beam and fix it reliably to the foundation beam; after correcting the new steel truss floor deck, lay it according to the baseline, and complete the installation of the sealing plate and side formwork; use welding studs to connect the floor deck and the new structural beam, tie the floor deck surface reinforcement, and after removing debris from the floor deck surface, pour concrete into the closed floor area formed by the steel truss floor deck and the structural beam;

[0019] S5. Settlement monitoring: Continuous monitoring throughout the construction process and after completion. Observe once every 3 days during the construction period, once a month for the first 6 months after completion, and once a quarter thereafter; control the settlement difference between adjacent foundations to ≤2‰L, where L is the center distance between adjacent column foundations, and stop work if abnormality occurs.

[0020] The preferred technical solution of the present invention is as follows: After the anti-seepage curtain construction is completed in step S2, the location of the underground karst channel under the foundation to be reinforced is determined by surveying and determining. Water level observation wells are arranged on both sides of the anti-seepage curtain system near the underground karst channel. The bottom of the well is located at least 1m above the top of the stable stratum. The well pipe is a permeable pipe, and the outside is filled with graded sand and gravel filter material. The opening is sealed with cement and soil around the opening.

[0021] The preferred technical solution of the present invention is as follows: In step S2, the sodium-based bentonite cement slurry is prepared by mixing sodium-based bentonite, slag cement, and brine in a mass ratio of 2:8:4~5, with a slurry density of 1.45~1.55 g / cm³; each grouting pipe is connected to the grouting conduit via a flexible bend, and after grouting is completed, the grouting conduit and flexible bend are flushed with a clean water grouting pump; any overflow or leakage traces in the grouting area are investigated and repaired using slurry of the same mix ratio; the permeability coefficient is tested by a water pressure test or a pumping test.

[0022] The preferred technical solution of the present invention is as follows: In step S3, a pre-reserved pile hole is made on the extended bearing platform. After the anchor static pressure pile is implanted, the pre-reserved pile hole is sealed with fine stone concrete and reinforced with cross steel bars. After the pile body is welded, the weld needs to be visually inspected and non-destructively tested.

[0023] The seepage barrier in this invention consists of grouting pipes and a solidified sodium-based bentonite cement grout. Arranged around the building structure, it forms a closed seepage barrier, cutting off underground erosion channels and fundamentally preventing the infiltration and erosion of saline soil by groundwater. This avoids soil subsidence caused by the continuous dissolution of salt crystals, providing a prerequisite for subsequent foundation reinforcement and structural stability. The grouting pipes are made of seamless steel pipes with evenly distributed grouting holes on the pipe walls. Angle steel is welded to the outside of the holes to prevent soil particles from directly clogging them during grouting. The grouting holes face the direction of groundwater seepage, ensuring precise filling of erosion channels by the grout. The sodium-based bentonite cement grout possesses excellent expansibility and impermeability. After injection into the strata, it quickly fills cracks and solidifies, forming a dense and stable seepage barrier layer. The permeability coefficient of the solidified seepage barrier is ≤1×10⁻⁶. -6 With a speed of cm / s, it can effectively block the seepage of underground freshwater and ensure a long-lasting and stable seepage prevention effect.

[0024] The foundation reinforcement system in this invention addresses the problems of decreased pile bearing capacity and insufficient foundation stability caused by saline soil subsidence. Through the synergistic effect of pile cap expansion and the addition of anchor static pressure piles, it enhances the overall bearing capacity of the foundation, optimizes the load transfer path, solves the problem of uneven foundation settlement, and ensures stable load transfer from the foundation to the superstructure. The surface of the original pile cap is roughened to thoroughly remove surface laitance and loose layers, enhancing the bonding performance between the old and new concrete surfaces and preventing future cracking.

[0025] This invention introduces a new structural floor slab system. This system enhances the overall rigidity and deformation resistance of the building, coordinates the deformation differences between the ground and the main structure, and prevents ground voids and floor slab cracking due to foundation settlement. It also provides a stable load transfer path for the ground. H-beams are used as the new structural beams, arranged along the middle of the masonry walls and reliably connected to the main structural columns to form a stable horizontal load-bearing frame. The steel beam surfaces undergo rust removal treatment, followed by sequential application of epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint, and aliphatic polyurethane topcoat, with a total paint film thickness ≥40µm. This effectively resists the corrosive environment of saline soil areas and extends the service life of the steel beams. Products conforming to the "Steel Truss Floor Decking" (JG / T368) standard should be selected. Before laying, the floor decking should be visually inspected, and bent or deformed plates should be corrected to ensure a flat laying. The floor decking should be connected to the newly added structural beams with welded studs. Dry ceramic rings should be used during the welding process, and the ceramic ring residue should be removed after welding to ensure a firm connection. Before pouring concrete, the floor decking end caps and edge formwork should be installed to prevent concrete leakage. After the floor decking and the main structure form an integral whole, the ground load can be directly transferred to the foundation through the structural columns, avoiding ground damage caused by the load acting on the settled soil.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) This invention breaks through the limitations of the existing single reinforcement scheme and adopts a three-stage scheme of "seepage prevention curtain interception + foundation reinforcement + new floor slab stiffening". First, it blocks the erosion of underground fresh water, then improves the bearing capacity of the foundation, and finally enhances the structural stiffness, forming a full-dimensional reinforcement system from the root to the structure, which completely solves the multiple diseases of the foundation in the saline soil area and avoids the recurrence of problems after reinforcement.

[0028] (2) The anti-seepage curtain of the present invention forms a closed barrier around the building. After the sodium-based bentonite cement grout is cured, the permeability coefficient is low and the stability is strong, which can block the erosion of groundwater for a long time. Compared with traditional grouting anti-seepage, its expansion and anti-seepage properties are more suitable for the saline soil erosion environment, ensuring the anti-seepage effect is long-lasting and reliable.

[0029] (3) The foundation reinforcement system optimizes the load transfer path by expanding the pile cap and coordinating with the anchor static pressure piles, thereby improving the bearing capacity of the pile foundation while reducing the load on a single pile; the newly added structural floor system forms an integral whole with the main structure, greatly enhancing the structure's resistance to deformation, effectively avoiding damage caused by differential settlement between the ground and the main structure, and ensuring the long-term stability of the structure.

[0030] (4) Before construction, key parameters are determined through process tests and test piles. During construction, refined processes such as graded grouting and double-controlled pile pressing are adopted. The mechanical load is small and there is no vibration, which minimizes the disturbance to existing buildings. At the same time, the scheme strictly follows the current specifications and is suitable for the reinforcement of existing buildings in various saline soil areas affected by groundwater. It can be widely applied to office buildings, factories, civil buildings and other scenarios, and has broad applicability and economy.

[0031] This invention creatively integrates the technical logic of "source interception-reinforcement-stiffening" with the unique engineering characteristics of saline soil. Addressing core pain points in saline soil areas affected by groundwater, such as foundation subsidence, pile bearing capacity reduction, and uneven structural settlement, it proposes a technologically advanced, safe, reliable, and long-term stable systematic reinforcement solution. This not only fundamentally blocks the continuous erosion of saline soil by groundwater, overcoming the limitations of traditional reinforcement solutions that only address the symptoms but not the root cause, but also achieves coordinated deformation of the foundation, substructure, and superstructure through synergistic foundation reinforcement and structural stiffness enhancement, completely eliminating hidden dangers such as ground voids and floor slab cracking. The feasibility of this solution has been verified in existing building reinforcement projects in saline soil areas, demonstrating broad application prospects. It is particularly suitable for the foundation reinforcement and renovation of saline soil foundations eroded by groundwater in industrial parks, civil buildings, and public facilities, providing a replicable technical paradigm for similar projects. Attached Figure Description

[0032] Figure 1 This is a plan view of the reinforced foundation in this invention;

[0033] Figure 2This is the original foundation plan layout diagram of this invention;

[0034] Figure 3 This is an enlarged schematic diagram of the planar layout of the seepage-proof curtain in this invention;

[0035] Figure 4 This is a vertical cross-sectional view of the seepage-proof curtain in this invention;

[0036] Figure 5 This is a schematic diagram of the sealing structure and grouting pipe arrangement of the seepage prevention curtain in this invention;

[0037] Figure 6 This is a schematic diagram of the grouting pipe structure of the seepage-proof curtain in this invention;

[0038] Figure 7 This is a schematic diagram of the grouting pipe connection of the seepage-proof curtain in this invention;

[0039] Figures 8 to 13 This is a schematic diagram of the foundation reinforcement process in this invention;

[0040] Figure 14 This is a schematic diagram of the connection between the steel truss floor deck and the structural beam in this invention;

[0041] Figure 15 This is a schematic diagram of the connection between the steel truss floor deck and the column in this invention.

[0042] In the diagram: 1—Foundation of the building to be reinforced; 2—Original pile foundation structure; 2-1—Original pile cap; 2-2—Column; 2-3—Original pile cap; 3—Stable stratum; 4—Anti-seepage curtain; 4-1—Grouting pipe; 4-2—Sodium bentonite cement slurry solidified body; 4-3—Grouting influence radius; 4-4—Bent connecting hose; 4-5—Sealing structure; 4-6—Grouting outlet hole; 4-7—Grouting conduit; 4-8—Ventilation pipe; 5—Water level observation well; 6—Extended pile foundation reinforcement structure; 6-1—Reserved pile driving hole; 6-2 —Extended foundation, 6-3—Anchored static pressure pile, 6-4—Precision rolled threaded steel, 6-5—Roughened surface between old and new foundations, 6-6—Cross steel sheet pile tip, 6-7—Reinforcing cage, 6-8—Sealed hole pile structure, 7—Structural beam, 8—Reinforcing steel truss floor slab, 8-1—Reinforcing steel truss, 8-2—Floor slab reinforcement perpendicular to the reinforcing steel truss direction, 8-3—Welding stud, 8-4—Support reinforcement, 8-5—Support plate, 8-6—Edge sealing plate, 9—Covering soil layer, 10—Underground karst channel, 11—Anchored static pressure pile driving device. Detailed Implementation

[0043] To further understand the invention's content, features, and effects, the invention will be further described below with reference to the accompanying drawings and embodiments. (Appendix) Figures 1 to 15All accompanying drawings are simplified versions of embodiments and are intended only to clearly and concisely illustrate the embodiments of the present invention. The technical solutions shown in the drawings below are specific solutions of embodiments of the present invention and are not intended to limit the scope of the claimed invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0044] Example 1 provides a foundation reinforcement structure for saline soil affected by groundwater, such as... Figures 1 to 15 As shown, the reinforcement structure includes a seepage-proof curtain 4, a pile foundation reinforcement system, and a new floor slab structure; the seepage-proof curtain 4 is arranged in a ring around the foundation to be reinforced, and the foundation to be reinforced is as follows: Figure 2 As shown, the structure includes foundation beam 1 and the original pile foundation structure 2. The reinforcement structure performs triple reinforcement treatment on the foundation to be reinforced, forming a complete reinforcement system of "source interception-reinforcement-stiffening". Its specific structure is as follows: Figure 1 As shown.

[0045] Among them, the seepage-proof curtain 4, for example Figures 5 to 7 As shown, the structure includes multiple φ48mm grouting pipes 4-1 and a sodium-based bentonite cement slurry solidified body 4-2 wrapped around the grouting pipes. The sodium-based bentonite cement slurry solidified body 4-2 is a seepage-proof structure formed by vertically arranging multiple grouting pipes 4-1 within a trench after vertical trenching in the foundation soil layer, and injecting sodium-based bentonite cement slurry through the multiple grouting pipes 4-1, followed by solidification. The seepage-proof curtain 4 penetrates the upper covering soil layer 9 of the foundation and enters the lower stable stratum 3 by at least 1m. After solidification, the permeability coefficient is ≤1×10⁻⁶. -6 cm / s; the sodium-based bentonite cement slurry is prepared by mixing sodium-based bentonite, slag cement, and brine in a mass ratio of 2:8:4~5, with a slurry density of 1.45~1.55 g / cm³; the grouting pipe 4-1 is made of seamless steel pipe with a tapered tip at the lower end, and φ8mm grouting holes are evenly distributed on the pipe wall. L20 angle steel is welded to the outside of the holes to prevent soil particles from clogging them, and the grouting holes face the direction of leakage; the trench of the seepage prevention curtain is opened to the stable stratum and laid in The upper ends of the multiple grouting pipes 4-1 in the trench are connected to the grouting conduit 4-7 via a flexible bend 4-4. The grouting conduit is made of steel pipe with an inner diameter of 100~127mm, assembled in sections, each section being 4~6m long. After the grouting pipes are inserted into the trench, the soil layer 0.8~1.2m below the surface of the borehole is sealed with cement and soil. At the same time as sealing the borehole, the exhaust pipe 4-8 is inserted. The upper end of the exhaust pipe 4-8 extends out of the borehole, and the lower end passes through the sealing structure 4-5 and extends into the pile borehole to ensure that the gas is smoothly discharged during grouting.

[0046] In Example 1, the pile foundation reinforcement system is as follows: Figures 8 to 13As shown, the structure includes the original pile foundation structure 2 and the extended pile foundation reinforcement structure 6. The original pile foundation structure 2 includes the original pile foundation cap 2-3, the original pile cap cast-in-place piles 2-1, and the column 2-2. The extended pile foundation reinforcement structure 6 includes the extended pile cap 6-2 and the anchored static pressure piles 6-3. The extended pile cap 6-2 is a reinforcement structure formed by roughening and reinforcing the original pile foundation cap 2-3, adding a reinforcing cage to the top of the original pile foundation cap 2-3, and pouring concrete. The width of the extended pile cap 6-2 is at least three times the diameter of the original pile cap cast-in-place piles 2-1. The extended pile cap 6-2 has pre-reserved pile driving holes 6-1. The anchored static pressure piles 6-3 are added to the extended pile foundation cap 2-3 after roughening and reinforcing the original pile foundation cap 2-3. After the foundation 6-2 reaches the required curing strength, it is driven into the lower stable stratum 3 through the reserved pile driving hole 6-1. The extended foundation 6-2 is a foundation structure formed by expanding the top surface or the top surface and upper surrounding area of ​​the original pile foundation 2-3 after roughening. The roughening depth is ≥5mm. Reserved pile driving holes 6-1 are provided at the corners of the extended foundation 6-2, and anchor static pressure piles 6-3 are driven in. The extended foundation 6-2 is also pre-embedded with fine-rolled threaded steel 6-4 for fixing the anchor static pressure pile device 11. The centroid of the newly added anchor static pressure pile 6-3 and the centroid of the original pile foundation structure 2 coincide with the point of action of the resultant force of the load of the upper column 2-2, i.e., the center of the column load. The rebar for the extended pile cap 6-2 is made of HRB400 grade steel. It is implanted into the original pile cap 2-3 to a depth of 15 times the rebar diameter, with a pull-out force ≥70kN. Grade A modified epoxy resin is used for fixing the rebar to ensure the pull-out force meets design requirements. The extended pile cap 6-2 is constructed with C40 concrete, internally reinforced with extended pile cap reinforcement. After the extended section's steel reinforcement skeleton is tied and inspected, C40 concrete is poured to form the extended pile cap. The extended width is set to three times the diameter of the original pipe pile. By increasing the load-bearing area of ​​the pile cap, the load is evenly transferred between the piles, reducing the load on a single pile and improving the overall bearing stability of the foundation.

[0047] In Example 1, the anchor static pressure pile 6-3 is a φ273×11.5mm Q235B seamless steel pipe pile. The bottom of the pile body is equipped with a cross-shaped steel sheet pile tip 6-6. The entire length of the pile body is filled with C30 fine stone concrete and grout is poured back to the borehole opening. The centroid of the anchor static pressure pile 6-3 and the original pile foundation coincides with the load center of the column. After being inserted through the reserved pile driving hole 6-1, three 18mm steel reinforcement cages with stirrups are inserted within 2m of the borehole cap and the bottom of the cap. The stirrups are 6mm in diameter and spaced at 400mm. The borehole is sealed with C40 fine stone concrete and reinforced with two 16 cross steel bars to form a sealed pile driving structure 6-8. PSB830 precision rolled threaded steel 6-4 (32mm specification) is also pre-embedded on the extended cap 6-2 to fix the pile driving device to ensure construction stability. The piles are constructed using seamless Q235B steel pipes with a specification of φ273×11.5mm. The pile length is determined based on the site geological survey results, with the lower stable stratum serving as the bearing layer to ensure the pile foundation has long-term stable bearing capacity. During construction, a dual control standard is adopted for pile length and pile driving force to ensure that the pile foundation implantation depth and bearing performance meet the standards. After the pile is implanted, C30 fine stone concrete is filled into the steel pipe pile, and the concrete must be backfilled to the borehole opening to ensure that the pile body is dense and free of voids, avoiding the impact of pile defects on bearing capacity. The centroids of the newly added anchor static pressure piles and the original pile foundation are precisely aligned with the column load center. At the same time, the number of piles in the original pile cap is optimized and adjusted to form a synergistic force-bearing system between the old and new pile foundations, avoiding local settlement caused by load concentration and further improving the overall stability of the foundation.

[0048] In Example 1, as Figure 14 and Figure 15As shown, the newly added floor structure includes structural beams 7 and steel truss floor decks 8. The structural beams 7 are arranged horizontally or longitudinally within the foundation beams 1 of the foundation to be reinforced, and both ends of each structural beam 7 are connected to the foundation beams 1. The steel truss floor decks 8 are fixedly laid on the structural frame formed by the structural beams 7 and are connected to the structural beams 7 and the foundation beams 1. The structural beams 7 are H-beams, and the surface of the steel beams is coated with epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and aliphatic polyurethane topcoat, with a total paint film thickness ≥40um. The steel truss floor decks (8) are laid at an elevation of 0.03~0.07m relative to the ±0.000m reference plane (i.e., the top elevation of the floor deck) before laying and are corrected. The steel truss floor decks 8 and the structural beams 7 are connected by weld studs. Dry ceramic rings are used for welding stud construction and are removed after welding. The newly added steel truss floor decks 8 meet the requirements of "Steel Truss Floor Deck" (JG / T368). The newly added steel truss floor slab 8 is provided with an edge sealing plate 8-6, which is spot welded to the steel reinforcement. The newly added structural floor slab system also includes floor slab reinforcement, which is divided into floor slab reinforcement 8-2 (spacing 50mm and 70mm) in the direction perpendicular to the steel truss 8-1 and support reinforcement 8-4 (diameter 10mm, anchored into the column 25d). A 6mm thick support plate 8-5 is provided at the connection between the floor slab and the column 2-2 to enhance the connection stability.

[0049] In addition, the reinforcement structure also includes water level observation wells 5, arranged along both sides of the anti-seepage curtain system 4, for monitoring changes in groundwater level and timely understanding of the anti-seepage effect; the design location of the water level observation wells 5 is generally on both sides of the anti-seepage curtain 4 near the underground dissolution channel 10. The underground dissolution channel is a hidden water flow channel formed by the infiltration of groundwater in saline soil foundation. Under the action of osmotic pressure, the groundwater forms a continuous water flow path along the cracks, pores or dissolution voids of the saline soil stratum. When easily soluble salt crystals in saline soil infiltrate with groundwater, they dissolve, forming tiny dissolution voids. The continuous scouring of the dissolution voids by the water flow gradually expands the voids and interconnects them, forming an initial water flow channel; under long-term infiltration, the channel continuously widens and extends, eventually forming a continuous channel that runs through the upper overlying soil layer and the lower stable stratum, becoming the "path carrier" for the continuous erosion of saline soil by groundwater, and is the core hidden danger leading to saline soil subsidence and foundation instability.

[0050] Example 2 provides a construction method for the foundation reinforcement structure of saline soil affected by groundwater as described in Example 1, specifically including the following steps:

[0051] S1. Construction Preparation:

[0052] (1) Technical preparation: Organize technical personnel to familiarize themselves with the design drawings, geological survey reports and underground karst channel detection data, and clarify the construction scope and technical requirements of each system; hold technical briefing and safety training meetings to clarify the construction parameters, quality standards and safety precautions of each process to the construction personnel, and ensure that the construction process is standardized and orderly.

[0053] (2) Test preparation: Conduct grouting process tests, determine grouting parameters (such as pressure, flow rate, grout diffusion radius, etc.) suitable for site geological conditions through test injections with different grouting pressures and flow rates; conduct static pressure pile test tests of anchor bolts to verify the feasibility of pile construction process, test whether the vertical bearing capacity of a single pile meets the design requirements, and provide a basis for subsequent batch construction.

[0054] (3) Site preparation: Level the construction site, remove obstacles in the site, plan the walking route of construction machinery and the material stacking area; set up measurement control points and leveling points, and complete the measurement and layout of the anti-seepage curtain axis, pile position and new structural beam position. The layout deviation is ≤±20mm to ensure the accuracy of the construction position of each structure.

[0055] S2. First stage: Construction of the seepage-proof curtain 4, the specific process is as follows:

[0056] S201. Pre-construction preparation and surveying: Before the construction of the anti-seepage curtain, it is necessary to complete the confirmation of construction parameters and site preparation. Based on the results of previous process tests, the core construction parameters such as grouting pressure and grout diffusion radius suitable for the characteristics of the saline soil layer of this project should be determined. During the site preparation stage, the construction area should be leveled first, and obstacles such as large stones, tree roots, and underground domestic waste at the pile locations should be thoroughly removed to avoid affecting subsequent trench excavation and perforated pipe installation. Elevation control points and plane control points should be set up according to specifications. Professional surveying equipment such as total stations should be used to accurately lay out the anti-seepage curtain along the design axis, marking the trench excavation boundary and perforated pipe installation position, ensuring that the layout deviation is ≤±20mm, so as to provide accurate benchmarks for subsequent construction.

[0057] S202. Trench excavation and grouting pipe installation: Based on the planar design axis of the anti-seepage curtain, combined with the specifications of the grouting pipe, the radius of influence of grout diffusion determined by the previous grouting process test, and the on-site construction operation space requirements, determine the trench excavation dimensions. The trench depth must match the designed implantation depth of the grouting pipe 4-1, and it must penetrate the upper loose overburden layer so that the bottom of the grouting pipe 4-1 enters the stable stratum 3 where potential erosion channels are developed in the lower part, ensuring that the underground freshwater seepage path can be blocked in a targeted manner. After the trench excavation is completed, the trench walls and bottom are cleaned and trimmed to remove large impurities and loose soil layers, preventing the trench walls from collapsing or impurities from affecting the bonding effect between the grout and the stratum. Then, a drilling rig is used to drill holes according to the design positions, with the hole diameter 30-40mm larger than the outer diameter of the grouting pipe to ensure smooth insertion of the grouting pipe 4-1 and a uniform gap between the pipe wall and the hole wall. The prefabricated grouting pipe is slowly lowered into the drilled hole, and real-time monitoring and adjustment are performed using a level and total station to ensure that the vertical deviation of the grouting pipe 4-1 axis is ≤1%. After the grouting pipe 4-1 is in place, the hole opening is sealed with cement and soil 4-5, and an vent pipe is provided.

[0058] S203. Connection of Grouting Conduit 4-7 and Grout Preparation; Grouting conduit 4-7 is made of steel pipe with an inner diameter of 100~127mm, using a segmented assembly method, with each segment being 4~6m long, and the total length of a single conduit section controlled at 50m to facilitate on-site transportation and installation; Each grouting conduit 4-7 is connected to the corresponding area's grouting perforated pipe 4-1 via a flexible bend, and a single conduit can simultaneously connect to multiple perforated pipes to achieve batch grouting operations and improve construction efficiency. During the connection process, the sealing performance of the conduit and the flexible bend 4-4 must be checked, and the joints should be reinforced with sealing tape to prevent grout leakage during grouting; at the same time, ensure that the conduit axis is straight to avoid increased grout flow resistance due to conduit bending, which would affect the transmission of grouting pressure. The sodium-based bentonite cement grout used for grouting is a cement-based seepage-proof material formulated with sodium-based bentonite as the core raw material, in a mass ratio of sodium-based bentonite, slag cement, and brine of 2:8:4~5. Sodium-based bentonite possesses unique expansibility, adhesion, and seepage-proof properties. After being compounded with slag cement and brine, the grout density is controlled at 1.45~1.55 g / cm³. 3 Not only does it have the fluidity to meet grouting requirements, but it also spreads rapidly after being injected underground, filling tiny cracks and voids in the soil. As the water in the grout is absorbed by the strata, the sodium-based bentonite gradually expands and solidifies in conjunction with the cement, ultimately forming a dense and continuous seepage barrier that effectively blocks the flow and infiltration of underground freshwater. It also serves the dual purpose of reinforcing the foundation and preventing leaks. During grout preparation, a dedicated mixing device is used for uniform stirring at a speed of ≥5 minutes to ensure the grout components are homogeneous and free of lumps. After stirring, the grout density is tested, and only after passing the test can the grouting process begin.

[0059] S204. Staged batch grouting construction: A high-pressure grouting pump is used to inject sodium-based bentonite cement grout into the grouting perforated pipe 4-1 through the grouting conduit 4-7. Under pressure, the grout seeps out from the holes of the grouting perforated pipe 4-1, gradually filling the gap between the pipe wall and the trench wall, and spreading to the surrounding stratum fissures. Finally, it solidifies with the stratum soil to form a continuous and dense impermeable body, completely sealing the underground freshwater seepage channels and providing a waterless and stable stratum environment for subsequent foundation reinforcement construction. The specific batch grouting mode is as follows: The initial grouting pressure is controlled at 0.5MPa. After the grout injection stabilizes for 10 minutes and it is confirmed that there is no grout leakage in the conduit and perforated pipe, the pressure is gradually increased to 5.0~8.0MPa, and the grouting flow rate is simultaneously controlled at 40~80L / min to ensure that the grout fully penetrates into the depth of the stratum under pressure. To avoid grout crossflow between adjacent grouting holes, which could lead to localized grout accumulation or voids, an intermittent skip-hole construction method is adopted. The construction interval between adjacent holes is ≥24 hours. Grouting of subsequent holes is carried out only after the grout in the previously constructed hole has initially solidified. During the grouting process, a dedicated person is assigned to monitor the grouting volume and ground settlement in real time. When the grouting volume remains stable for 30 minutes (i.e., the grout no longer significantly seeps into the formation), or when a ≥5mm heave appears on the ground (to avoid excessive grouting that could disturb the formation), grouting of that hole is immediately stopped. This ensures that the grout fully fills the dissolution channels and fissures without wasting resources or damaging the formation.

[0060] S205. Post-treatment and quality inspection: After grouting at all boreholes is completed, immediately shut off the grouting pump and pipeline valves, pull out the grouting pipe, and thoroughly flush the grouting conduit 4-7, the connecting hose 4-4, and the grouting pump with clean water to ensure no residual grout inside the pipelines—to prevent grout from solidifying and clogging the pipelines, affecting subsequent equipment maintenance and secondary use. After the grout has cured for 28 days, ensuring the anti-seepage curtain is completely cured, restore the construction area: backfill the trenches in layers with plain soil or graded sand and gravel, with each layer ≤300mm thick. After backfilling, compact the layers with a small road roller or rammer, achieving a compaction degree ≥93%, restoring the original flatness of the site; at the same time, check for any overflow or leakage in the grouting area. For any gaps caused by local grout leakage, seal and repair them with sodium-based bentonite cement grout of the same mix ratio to ensure the overall integrity of the anti-seepage curtain.

[0061] S206. Quality inspection of the anti-seepage curtain shall be carried out by pressure water test or pumping test, with a focus on the curtain's permeability coefficient: During the test, observation holes shall be set on both sides of the curtain, and the permeability coefficient shall be calculated by measuring water level changes. The permeability coefficient of the cured anti-seepage curtain shall be ≤1×10⁻ 6 The grouting speed must be measured in cm / s to ensure effective blocking of underground freshwater leakage. Only after passing the test can the next stage of construction begin. If the test fails to meet the standards, the cause must be analyzed and the weak areas must be supplemented with grout until the design requirements are met.

[0062] S3. Second Stage: Reinforcement construction of foundation piles; such as Figures 8 to 13 As shown, where Figure 8 For the original pile cap structure, Figure 9 To expand the reinforcement plan of the pile foundation reinforcement structure, Figure 10 Extended cross-sectional view of reinforcement of pile foundation strengthening structure Figure 11 Schematic diagram of static pressure pile driving with anchor bolts Figure 12 Cross-sectional view of anchored static pressure pile cap. Figure 13 Extended structural drawing of the anchored static pressure pile foundation cap; the specific process is as follows:

[0063] S301. Preliminary Cleaning and Pile Position Verification: Remove masonry walls, foundation beams, and other components within the impact range of pile foundation construction; clean the backfill soil around the original foundation cap 2-3 to the design elevation to expose the original foundation cap structure; verify the positions of newly added anchor static pressure piles to ensure that the pile position deviation is ≤±20mm, and promptly adjust the pile positions with deviations exceeding the standard to ensure the accuracy of subsequent pile foundation construction.

[0064] S302. Foundation Pretreatment and Extension Construction: Roughen the surface of the original foundation foundation (2-3), and use a high-pressure water gun to remove surface slag and dust to ensure a tight bond between the old and new concrete; drill holes and install rebar according to design requirements, insert HRB400 grade rebar, and test the pull-out strength of the rebar. After passing the test, tie the extension foundation rebar skeleton and pre-embed threaded anchor rods; install the foundation formwork, and seal the joints of the formwork to prevent grout leakage. Then pour C40 concrete, compact it with a vibrator, and cure it for ≥14 days to ensure that the concrete strength meets the design requirements.

[0065] S303. Construction and Testing of Anchor Static Pressure Piles: Install reaction frames and jacks, and insert prefabricated steel pipe piles into the pile holes in sections. The pile sections are connected by welding, with a weld height ≥10mm. After welding, visual inspection and non-destructive testing are performed on the welds to ensure welding quality. During pile driving, control the pile driving speed ≤0.5m / min, and construct according to the dual control standard of pile length and pile driving force. Stop pile driving when the pile body is driven to the design depth and the pile driving force reaches the design value. Fill the steel pipe pile with C30 fine stone concrete, ensuring that the concrete slurry flows back to the hole opening to ensure the pile body is dense. After all pile foundation construction is completed, select no less than 1% of the total number of piles and ≥2 piles for static load testing to check whether the single pile bearing capacity meets the standard. After passing the test, restore the demolished foundation beams and masonry walls.

[0066] S4. Third Stage: Construction of New Structural Floor Slabs, the specific process is as follows:

[0067] S401. Installation and positioning of new structural beams: Verify the installation axis and elevation of the new structural beams, and use lifting equipment to hoist the H-beams to the design position; adjust the horizontality and verticality of the steel beams to ensure that the beams are flat (the pre-arched components are arched according to the design requirements), and then use bolts or welding to reliably connect the steel beams to the main structural columns.

[0068] S402. Floor decking installation and connection: Correct the newly added steel truss floor decking, remove deformed or excessively deformed plates, and lay the floor decking in an orderly manner from one end to the other according to the baseline; seal the joints of the floor decking, install sealing plates and edge formwork to ensure the overall sealing of the formwork; use welding studs to connect the floor decking to the newly added structural beams, use dry ceramic rings for welding stud construction, remove the ceramic rings after welding, and check the quality of the welding stud connection to avoid incomplete welding or missing welding.

[0069] S403 Reinforcement Binding and Concrete Pouring and Curing: Bind the surface reinforcement of the floor slab according to the design requirements, ensuring that the reinforcement spacing and protective layer thickness meet the specifications; before pouring concrete, remove debris and dust from the surface of the floor slab and clean it with a high-pressure water gun; when pouring concrete, use a plate vibrator to compact it, and cover and moisturize it in time after pouring. The curing time is ≥14 days to ensure that the concrete strength meets the standards.

[0070] S5. Settlement Monitoring: Settlement monitoring must be continuously carried out throughout the construction process and after completion, and a monitoring log must be established: Observations should be made every 3 days during construction, monthly for the first 6 months after completion, and quarterly thereafter, until settlement stabilizes; the monitoring content includes the settlement of the building foundation and the settlement difference between adjacent foundations, where the settlement difference between adjacent foundations must be controlled within ≤2‰L (L is the center distance between adjacent column bases). If abnormal settlement rate (such as daily settlement exceeding 0.1mm) or settlement difference exceeding the standard is found during the monitoring process, work should be stopped immediately and technical personnel should be organized to analyze the cause and take targeted treatment measures such as supplementary grouting and adding temporary supports. Construction can only continue after the settlement has stabilized to ensure the safety of the building.

[0071] The invention will be further described below with reference to a specific application example. The application example is an office building in an industrial park, a three-story frame structure with a pile foundation. The original design used two pile caps, with 800mm diameter cast-in-place concrete piles. After one year of use, problems such as wall cracking and ground settlement appeared. Testing revealed that the maximum cumulative ground settlement reached 23.2mm, with a settlement rate of 0.095mm / d. Due to the influence of the dissolution channels at the top of the upper halite layer, the soil was compressed, resulting in negative skin friction around the piles. The original pile foundation bearing capacity was significantly reduced, no longer meeting the building's safety requirements.

[0072] Detailed site investigation and supplementary investigation results show that within a drilling depth of 20m, the sediments are Late Pleistocene lacustrine deposits, consisting of 5 layers: ① artificial fill (Q4) ml ), layer thickness 0.30~2.40m; ② silty clay (Q3 l ), with a layer thickness of 4.00~10.00m, and a halite content of about 5%, belonging to medium compressibility soil; ③ Halite (Q3) ch), thickness 0.80~12.00m; ④ silty rock salt (Q3) ch ), thickness 1.20~7.40m; ⑤ rock salt (Q3) ch During the supplementary exploration, eight boreholes revealed that the groundwater level has risen from 7.0m during the detailed exploration to 1.5m during the current supplementary exploration. Some of the halite in the silty clay layer has been dissolved, causing ground subsidence and uneven settlement of buildings.

[0073] Ground-penetrating radar (GPR) data shows that the affected area is mainly the section from the new solvent pumping station to the industrial park office building, with a length of 258m and a width of 29-61m. The soil is loose and the depth is 0-8m (located in a silty clay layer). Adjacent to the industrial park office building on the east and west sides, there is a void in the strata, with a depth of 0.5-2m (located in a silty clay layer). Groundwater continuously erodes the saline soil through dissolution channels 10, causing soil subsidence and generating negative skin friction on the piles. The depth of this negative skin friction gradually increases, further exacerbating the risk of settlement.

[0074] According to Article 5.3.7 of the "Technical Specification for Building Pile Foundations" (JGJ94-2008), the standard value of the vertical ultimate bearing capacity of the original 800mm diameter cast-in-place concrete pile 2-1 is calculated as follows:

[0075] The original design pile length was L=12m, the bearing stratum was slightly dense silt, and the standard value of the ultimate end resistance of the pile was q. pk =2000 kPa;

[0076] Pile tip area A p =π×800² / 4=502654.8mm²=0.503m²;

[0077] The circumference of the pile is u = π × 800 = 2513.3 mm = 2.513 m;

[0078] Neutral point depth ratio l n / l0=1.0, ln=6.6m;

[0079] The average vertical effective stress measured from the ground is 78.4 kPa, the negative skin friction coefficient is taken as 0.4, and the standard value of negative skin friction is 31.36 kPa.

[0080] The negative friction of the second layer of silty clay: q s2k =31.36 kPa, L2 = 6.6 m;

[0081] Third layer of halite: q s3k =80kPa, L3=5.4m;

[0082] The standard value of the vertical ultimate bearing capacity of a single pile, Q, is calculated. uk =1470kN, characteristic value of vertical bearing capacity of a single pile R a =Quk / 2=735kN.

[0083] After being affected by negative skin friction, and following data correction and negative skin friction calculation, the characteristic value R of the vertical bearing capacity of a single pile was determined. a The load dropped to 450kN, lower than the original design requirement of 735kN, indicating a risk of slow pile settlement. Furthermore, differences in axial force among different columns led to uneven foundation settlement, posing a safety hazard to the superstructure. Therefore, foundation reinforcement is necessary. This project utilized the saline soil foundation reinforcement structure affected by groundwater, as described in this invention. The reinforcement structure was constructed according to the specific implementation steps in Example 2, as follows:

[0084] S1. Construction Preparation

[0085] (1) Technical preparation: Organize technical personnel to familiarize themselves with the design drawings, geological survey reports and underground karst channel 10 detection data, hold technical briefing and safety training meetings, and clarify the construction parameters and quality standards of each process.

[0086] (2) Test preparation: Conduct grouting process test to determine grouting pressure of 5.0~8.0MPa and flow rate of 40~80L / min; conduct static pressure pile test of anchor bolt to verify that the single pile bearing capacity meets the design requirement of 150kN.

[0087] (3) Site preparation: Level the construction site, remove obstacles, plan the walking route of construction machinery and the material stacking area; set up measurement control points and leveling points, and complete the measurement and layout of the axis of the anti-seepage curtain 4, the pile position, and the position of the newly added structural beam 7, with a layout deviation ≤ ±20mm.

[0088] S2. First Stage: The specific steps for constructing the seepage-proof curtain 4 include, in sequence, the following steps:

[0089] S201. Pre-construction preparation and surveying / setting out;

[0090] S202. Trench excavation and perforated pipe installation;

[0091] S203. Grouting Conduit Connection and Grout Preparation: Grouting conduits 4-7 are made of steel pipes with an inner diameter of 100-127mm, assembled in sections, each section being 4-6m long, with the total length of a single conduit section controlled at 50m. Each grouting conduit 4-7 is connected to the corresponding grouting pipe 4-1 via a flexible bend 4-4, and the joint is reinforced with sealing tape. Sodium-based bentonite cement slurry is stirred at a uniform speed using specialized mixing equipment for at least 5 minutes to ensure uniform slurry composition and no clumping. After stirring, the slurry density is tested; only after passing the test can the grouting process begin.

[0092] S204. Graded Batch Grouting Construction: A high-pressure grouting pump is used to inject sodium-based bentonite cement grout 4-2 into the perforated pipe through grouting conduit 4-7. The initial grouting pressure is controlled at 0.5 MPa, and after stabilizing for 10 minutes, it is gradually increased to 5.0~8.0 MPa. The grouting flow rate is controlled at 40~80 L / min. An intermittent skip-hole construction method is adopted, with an interval of ≥24 hours between adjacent holes. Grouting is stopped when the grouting volume stabilizes continuously for 30 minutes or the ground heave is ≥5 mm.

[0093] S205. Post-treatment and testing: After grouting, flush the grouting pipes 4-7, the flexible bends 4-4, and the grouting pump with clean water to prevent grout from solidifying and clogging. After 28 days of curing, a water pressure test is conducted to check the seepage prevention effect. The measured permeability coefficient of the seepage prevention curtain 4 is 0.8 × 10⁻⁶. -6 cm / s, which meets the design standards; the trench is backfilled with plain soil in layers (each layer is ≤300mm thick), and compacted in layers (compaction degree ≥93%) to restore the site to flatness.

[0094] S3. Second Phase: Foundation Reinforcement Construction

[0095] S301. Preliminary cleanup and pile location verification: Remove the walls on the ground floor of the office building that affect the pile foundation construction, clean the backfill soil around the pile cap to the design elevation, and expose the original pile cap structure; verify the pile location of 48 anchor static pressure piles to ensure that the pile location deviation is ≤±20mm.

[0096] S302. Foundation Pretreatment and Extension Construction: Roughen the surface of the original pile foundation foundation (2-3), and remove surface slag and dust using a high-pressure water gun; drill holes and install rebar according to design requirements, insert φ16mm HRB400 grade steel bars, and then conduct pull-out force testing (qualified standard ≥70kN), with an insertion depth of 15 times the rebar diameter; tie the extension foundation rebar skeleton, pre-embed PSB830 precision rolled threaded steel bars and threaded claw anchor rods, install foundation formwork (sealing joints to prevent grout leakage), pour C40 micro-expansion concrete, and cure for ≥14 days.

[0097] S303. Construction of Anchor Static Pressure Piles 6-3: Install reaction frames and jacks, and insert prefabricated φ273×11.5mm Q235B seamless steel pipe piles into the reserved pile driving holes 6-1 in sections. The pile sections are connected by welding (weld height ≥10mm). After welding, visual inspection and non-destructive testing are carried out. Control the pile driving speed ≤0.5m / min, and construct according to the dual control standard of pile length (18m) and pile driving force (720kN). Stop pile driving after the pile body is driven to the design depth and the pile driving force reaches the standard. Fill the steel pipe pile with C30 fine stone concrete. Insert 3 steel cages with a diameter of 18mm into the hole opening and within 2m of the bottom of the hole. The stirrups are 6mm in diameter and spaced 400mm apart. Seal with C40 fine stone concrete and reinforce with 2 cross steel bars of 16mm to ensure the pile body is dense.

[0098] S304. Inspection and Restoration: After all pile foundation construction is completed, select no less than 1% of the total number of piles and ≥2 piles (3 piles in this project) for static load test. After the single pile bearing capacity is tested and found to be up to standard, seal the reserved pile driving hole with C40 fine stone concrete and set cross reinforcement bars for reinforcement, and restore the demolished foundation beam and masonry wall.

[0099] S4. Third Stage: Construction of the new structural floor slab; verification of the installation axis and elevation of the new structural beam 7; hoisting of the H-beam to the design position using lifting equipment; adjustment of the horizontality and verticality of the steel beam; reliable connection to the main structural columns using bolts or welding; then correction of the new steel truss floor deck 8, removal of deformed plates exceeding the standard, and orderly laying from one end to the other according to the baseline; sealing treatment of the floor deck splice, installation of sealing plate 8-6 and edge formwork; connection of the floor deck to the new structural beam 7 using welding studs 8-3, removal of ceramic ring residue after welding, and inspection of connection quality to avoid false welding and missed welding; finally, binding of the floor slab surface reinforcement according to design requirements, ensuring that the reinforcement spacing and protective layer thickness meet the specifications; cleaning of debris and dust from the floor deck surface before pouring concrete, and washing it clean with a high-pressure water gun; setting temporary supports according to the span of the secondary beams, and compacting the concrete using a plate vibrator; covering and moisturizing in a timely manner after pouring, with a curing time of ≥14 days to ensure that the concrete strength meets the standards.

[0100] S5. Settlement monitoring; Settlement monitoring will be continuously carried out throughout the construction process and after completion. Simultaneously, 5 water level observation wells will be installed to monitor groundwater level changes, and a monitoring log will be established.

[0101] Observations will be conducted every 3 days during the construction period;

[0102] Observe once a month for the first 6 months after completion;

[0103] After 6 months, observations will be conducted once per quarter until the settlement stabilizes.

[0104] The monitoring includes the settlement of the building foundation and the differential settlement between adjacent foundations, with the differential settlement between adjacent foundations controlled to be ≤2‰L (L is the center-to-center distance between adjacent column foundations). If an abnormal settlement rate is found (single-day settlement exceeding 0.1mm) or the differential settlement exceeds the standard, work must be stopped immediately to analyze the cause and take measures such as supplementary grouting and adding temporary supports. Construction can only resume after the settlement has stabilized.

[0105] After reinforcement, continuous monitoring for 8 months showed that the maximum settlement difference between adjacent foundations was 1.8‰L, the settlement rate was stable at 0.01~0.03mm / d, and the settlement tended to converge. The original pile foundation 2-1 and the newly added 48 anchor static pressure piles 6-3 formed a synergistic force system, which significantly improved the overall bearing capacity of the foundation and met the design requirements. The newly added structural floor slab (including structural beam 7 and steel truss floor deck 8) enhanced the overall rigidity and deformation resistance of the building, effectively avoiding problems such as ground voids and floor slab cracking. The defects such as wall cracking and ground settlement were completely resolved, restoring normal use function and ensuring the safety and stability of the building during its service life.

Claims

1. A foundation reinforcement structure for saline soil affected by groundwater, characterized in that: The reinforcement structure includes a seepage-proof curtain (4), a pile foundation reinforcement system, and a new floor slab structure; The seepage-proof curtain (4) is arranged in a ring around the foundation to be reinforced, including multiple grouting pipes (4-1) and a sodium-based bentonite cement slurry solidified body (4-2) wrapped around the multiple grouting pipes. The sodium-based bentonite cement slurry solidified body (4-2) is a seepage-proof structure formed by vertically arranging multiple grouting pipes (4-1) in the trench after vertical trenching in the foundation soil layer, and injecting sodium-based bentonite cement slurry through the multiple grouting pipes (4-1) and then solidifying it. The seepage-proof curtain (4) penetrates the upper covering soil layer (9) of the foundation and enters the lower stable stratum (3) by at least 1m. After solidification, the permeability coefficient is ≤1×10. -6 cm / s; The pile foundation reinforcement system includes the original pile foundation structure (2) and the extended pile foundation reinforcement structure (6). The original pile foundation structure (2) includes the original pile foundation cap (2-3), the original pile cap cast-in-place pile (2-1), and the column (2-2). The extended pile foundation reinforcement structure (6) includes the extended pile cap (6-2) and the anchor static pressure pile (6-3). The extended pile cap (6-2) is a reinforcement structure formed by adding a pile cap steel cage on the top of the original pile foundation cap (2-3) after roughening and rebar installation and pouring concrete. The width of the extended pile cap (6-2) is at least three times the pile diameter of the original pile cap cast-in-place pile (2-1). A reserved pile hole (6-1) is provided on the extended pile cap (6-2). The anchor static pressure pile (6-3) is pressed into the lower stable stratum (3) through the reserved pile hole (6-1) after the extended pile cap (6-2) reaches the curing strength. The newly added floor structure includes structural beams (7) and steel truss floor decks (8). The structural beams (7) are arranged horizontally or vertically within the foundation beams (1) of the foundation to be reinforced, and both ends of each structural beam (7) are connected to the foundation beams (1). The steel truss floor decks (8) are fixedly laid on the structural frame formed by the structural beams (7) and are connected to the structural beams (7) and the foundation beams (1).

2. The foundation reinforcement structure for saline soil affected by groundwater as described in claim 1, characterized in that: The sodium-based bentonite cement grout is prepared by mixing sodium-based bentonite, slag cement, and brine in a mass ratio of 2:8:4~5, with a grout density of 1.45~1.55 g / cm³. The grouting pipe is made of seamless steel pipe with a tapered tip at the lower end. Grouting holes are evenly distributed on the pipe wall, and angle steel is welded to the outside of the holes. The grouting holes face the direction of leakage.

3. The foundation reinforcement structure for saline soil affected by groundwater as described in claim 1, characterized in that: The trench of the seepage prevention curtain is opened to the stable stratum. The upper ends of the multiple grouting pipes arranged in the trench are connected to the grouting conduit through the bend connecting hose. The grouting conduit is made of steel pipe with an inner diameter of 100~127mm, assembled in sections and each section is 4~6m long. After the grouting pipes are inserted into the trench, the soil layer 0.8~1.2m below the surface of the hole is sealed with cement soil. When sealing the hole, the exhaust pipe is inserted at the same time. Water level observation wells (5) are arranged on both sides of the seepage prevention curtain (4), and the water level observation wells (5) are located near the underground erosion channel (10) formed by the infiltration of groundwater in the foundation area to be reinforced.

4. The foundation reinforcement structure for saline soil affected by groundwater as described in claim 1, characterized in that: The extended pile cap (6-2) is a pile cap structure formed by expanding the top surface or the top surface and the upper surrounding area of ​​the original pile foundation pile cap (2-3). Pre-reserved pile holes (6-1) are provided at the corners of the extended pile cap (6-2), and anchor static pressure piles (6-3) are pressed in. The extended pile cap (6-2) is also pre-embedded with fine-rolled threaded steel (6-4) for fixing the anchor static pressure pile device (11). The centroid of the newly added anchor static pressure pile (6-3) and the centroid of the original pile foundation structure (2) coincide with the point of action of the load resultant force of the upper column (2-2), that is, the center of the column load.

5. The foundation reinforcement structure for saline soil affected by groundwater as described in claim 1, characterized in that: The rebar of the extended pile cap (6-2) is made of HRB400 grade steel bar, which is inserted into the original pile cap (2-3) to a depth of 15 times the diameter of the steel bar, with a pull-out force ≥70kN. The rebar is fixed with Grade A modified epoxy resin anchoring adhesive. The anchor static pressure pile (6-3) is a seamless steel pipe pile with a cross steel sheet pile tip (6-6) at the bottom of the pile body. The steel pipe pile is equipped with a steel cage (6-7) and filled with fine stone concrete, which is slurried to the opening of the reserved pile hole (6-1). The upper part of the anchor static pressure pile (6-3) is connected to the extended pile cap (6-2) with micro-expansion concrete. A hole sealing pile structure (6-8) is set at the opening of the reserved pile hole (6-1).

6. The foundation reinforcement structure for saline soil affected by groundwater as described in claim 1, characterized in that: The structural beam (7) is an H-beam. The surface of the steel beam is coated with epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and aliphatic polyurethane topcoat, with a total paint film thickness ≥40um. After the steel truss floor deck (8) is laid, the top surface elevation relative to the ±0.000m reference plane is 0.03~0.07m. It is corrected before laying. The steel truss floor deck (8) and the structural beam (7) are connected by weld studs. Dry ceramic rings are used for welding stud construction and removed after welding.

7. A construction method for a foundation reinforcement structure for saline soil affected by groundwater, as described in any one of claims 1 to 6, characterized in that, Specifically, the following steps are included: S1. Construction preparation: Before construction, the site is leveled, grouting process test is conducted, anchor static pressure pile test is carried out, site cleaning and surveying are completed, and the surveying deviation is ≤±20mm; S2. Construction of the seepage barrier curtain: Excavate the construction trench for the seepage barrier curtain according to the survey line, extending the trench into the stable stratum. Vertically install grouting pipes in the construction trench, with the grouting holes of the grouting pipes facing the leakage direction. The space between the grouting pipes and the trench wall is filled with graded crushed stone. Multiple grouting pipes are connected to external grouting conduits. Sodium-based bentonite cement grout is injected into the trench in stages through the grouting conduits and grouting pipes. The initial grouting pressure is 0.2 MPa, which is increased to 0.4~0.5 MPa after stabilizing for 8~12 minutes. The flow rate is 5~10 L / min. Intermittent skip-hole construction is adopted, with an interval of ≥24 hours between adjacent holes. Grouting is stopped when the grouting volume stabilizes continuously for 30 minutes or the ground heave is ≥5 mm. After grouting, backfill the trench and compact it in layers. After curing for at least 28 days, test the permeability coefficient. Only after it meets the standard can the next stage be carried out. S3. Pile Foundation Reinforcement System: Locate the pile positions, remove the affecting walls, and clean the backfill soil around the pile cap to the design elevation; roughen the original pile foundation pile cap and remove the slag, drill holes and install rebar and test the pull-out force, tie the rebar cage and pour concrete to form an extended pile cap, and cure for ≥14 days; install reaction frames and jacks, and insert anchor bolt static pressure piles in sections, with a weld height of ≥10mm for each pile section and a pile driving speed of ≤0.5m / min; after the pile foundation construction is completed, select no less than 1% of the total number of piles and ≥2 piles for static load testing, and restore the foundation beams and masonry walls after the test is qualified; S4. Construction of the new floor slab structure: Verify the positioning axis and elevation, excavate the soil around the foundation to be reinforced to the design installation elevation of the structural beam, clean the loose soil layer at the bottom of the trench and compact it, install the new structural beam and fix it reliably to the foundation beam; after correcting the new steel truss floor deck, lay it according to the baseline, and complete the installation of the sealing plate and side formwork; use welding studs to connect the floor deck and the new structural beam, tie the floor deck surface reinforcement, and after removing debris from the floor deck surface, pour concrete into the closed floor area formed by the steel truss floor deck and the structural beam; S5. Settlement monitoring: Continuous monitoring throughout the construction process and after completion. Observe once every 3 days during the construction period, once a month for the first 6 months after completion, and once a quarter thereafter; control the settlement difference between adjacent foundations to ≤2‰L, where L is the center distance between adjacent column foundations, and stop work if abnormality occurs.

8. The construction method for a foundation reinforcement structure of saline soil affected by groundwater according to claim 7, characterized in that: After the anti-seepage curtain construction is completed in step S2, the location of the underground karst channel under the foundation to be reinforced is determined by surveying. Water level observation wells are arranged on both sides of the anti-seepage curtain system near the underground karst channel. The bottom of the well is located at least 1m above the top of the stable stratum. The well pipe is a permeable pipe, and the outside is filled with graded sand and gravel filter material. The well opening is sealed with cement and soil.

9. A construction method for a foundation reinforcement structure for saline soil affected by groundwater according to claim 7, characterized in that: In step S2, the sodium-based bentonite cement slurry is prepared by mixing sodium-based bentonite, slag cement, and brine in a mass ratio of 2:8:4~5, with a slurry density of 1.45~1.55 g / cm³. Each grouting pipe is connected to the grouting conduit via a flexible bend. After grouting is completed, the grouting conduit and flexible bend are flushed with a clean water grouting pump. Any overflow or leakage marks in the grouting area are investigated and repaired using slurry of the same mix ratio. The permeability coefficient is tested using a water pressure test or a pumping test.

10. A construction method for a foundation reinforcement structure for saline soil affected by groundwater according to claim 7, characterized in that: In step S3, the pre-reserved pile holes on the extended bearing platform are sealed with fine stone concrete and reinforced with cross steel bars after the static pressure piles are implanted. After the pile body is welded, the welds need to be visually inspected and non-destructively tested.

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