A caisson construction method suitable for soft ground

Abstract

The present application relates to the sinking well construction technical field, specifically a sinking well construction method suitable for soft soil foundation, the steps include foundation pit excavation, foundation pre-reinforcement, cushion construction, sectional sinking well manufacturing, monitoring system layout, hierarchical pressure sinking, dynamic adjustment of hydraulic jacking force and final sinking bottom sealing; wherein, through the monitoring system layout, the dynamic adjustment of the hydraulic jacking force is realized, which is the main invention point of the present application, the inclination sensor, laser displacement meter and earth pressure sensor feedback data in the sinking process, the jacking force is corrected according to the formula, combined with dynamic correction and emergency control; the precision, intelligent control of sinking well construction is realized, and the safety, efficiency and quality of soft soil foundation sinking well construction are improved.

Description

Technical Field

[0001] This invention relates to the field of caisson construction technology, specifically a caisson construction method suitable for soft soil foundations. Background Technology

[0002] Caisson construction is an important technical method in underground engineering, widely used in bridge foundations, underground pump stations, subway shafts, and other engineering fields. However, traditional caisson construction methods still have significant technical bottlenecks under complex geological conditions and high-precision construction requirements, mainly in the following aspects:

[0003] 1. Insufficient precision of manual control: Traditional caisson construction mainly relies on manual experience for sinking control, with long measurement intervals (usually 2-4 hours / time), resulting in a lag in the deviation response; the correction operation lacks quantitative standards, which can easily lead to caisson displacement, tilting, or even cracking of the caisson wall due to uneven soil distribution; although existing improved technologies such as hydraulic jacking caisson method can control the sinking speed, they lack real-time monitoring and dynamic correction functions, and the jacking parameters are set in a fixed manner, which cannot be adaptively adjusted according to changes in sinking resistance, resulting in limited construction precision.

[0004] 2. Delayed Response of Correction Methods: Conventional correction methods (such as unilateral loading and water injection pressurization) exhibit significant lag, often requiring several hours to take effect. Furthermore, they are prone to secondary settlement or damage to surrounding soil due to localized stress concentration. In complex geological conditions such as quicksand layers and isolated boulders, sudden changes in settlement resistance make it difficult for traditional correction methods to adapt quickly, easily leading to sudden settlement or stuck settlement accidents. Although layered excavation methods (as described in the literature "Soft Soil Caisson Construction Technology") attempt to improve control accuracy through phased construction, this method requires frequent pauses for adjustments, resulting in low efficiency and difficulty in adapting to tight project schedules.

[0005] 3. Insufficient adaptability to complex geological conditions: In soft soil, quicksand layers, or strata containing boulders, the settlement resistance of traditional methods fluctuates greatly, and sudden settlement accidents occur frequently. For example, in quicksand strata, sand inrush is prone to occur at the cutting edge, causing disturbance to the surrounding soil. When encountering obstacles such as boulders, construction needs to be interrupted for manual removal, which seriously affects construction efficiency. Existing technologies are highly dependent on drag-reducing grout, which not only results in high construction costs, but also makes the grout performance unstable under high-pressure groundwater conditions and easy to dilute, further reducing the reliability of construction.

[0006] In summary, traditional caisson construction methods have significant shortcomings in terms of precision control, correction response, geological adaptability, and construction efficiency. Especially in modern densely populated urban areas and environmentally sensitive areas, there is an urgent need for a caisson construction technology that can achieve high-precision monitoring, intelligent control, and rapid emergency response to improve construction safety, economy, and environmental protection. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a caisson construction method suitable for soft soil foundations that enables high-precision monitoring, intelligent control, and rapid emergency response.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] A method for constructing caissons suitable for soft soil foundations, the specific steps of which are as follows:

[0010] S1. Foundation pre-reinforcement: Drill holes in the projection area of ​​the caisson cutting edge and inject composite grout to form a reinforcement layer with a thickness of 0.8-1.2m;

[0011] S2. Construction of the foundation layer and guide trench: A 10-15cm thick concrete foundation layer is poured on the reinforcement layer, and guide trenches are set at intervals around the outer side of the caisson projection area. The trenches are 0.5-0.8m deep and filled with graded sand and gravel with a compaction degree ≥95%.

[0012] S3. Caisson construction: Concrete shaft is poured in sections, each section being 5-7m high;

[0013] S4. Monitoring system deployment: Install tilt sensors and laser displacement gauges on the well casing, and deploy earth pressure sensors on the ground outside the well casing;

[0014] S5. Staged and pressure-divided sinking: The sinking process is divided into multiple stages. During the sinking project, the hydraulic jacking force is dynamically adjusted based on feedback data from tilt sensors, laser displacement gauges, and earth pressure sensors.

[0015] S6. Final Settlement and Bottom Sealing: After reaching the design elevation, concrete sealing construction is carried out.

[0016] As a preferred embodiment, a further technical solution of the present invention is:

[0017] Preferably, in step S2, the composite slurry includes nano-silicate and bentonite, the mass ratio of nano-silicate to bentonite is 1:(2-4), and the mass ratio of water to gel material is 0.45-0.55.

[0018] Preferably, in step S6, when the resistance fluctuation value ΔF exceeds 20% of the preset initial thrust F... static At that time, the jacking force correction mechanism is automatically triggered, and the hydraulic jacking force P out The dynamic adjustment formula is:

[0019] P out =k·(F static +ΔF·e -t / τ );

[0020] Where, k = 1.2-1.5, τ = 10-15s, Fstatic The initial thrust is preset, ΔF is the amount of resistance fluctuation; t represents the time from the moment of sudden change in resistance, that is, when ΔF exceeds the preset fluctuation threshold.

[0021] ΔF=|F real -F static |;

[0022] Among them, F real These are the measured values ​​from the earth pressure sensor.

[0023] Preferably, step S6 further includes:

[0024] Dynamic correction: When the caisson's tilt angle exceeds the target tilt angle threshold, increase the jacking force by 10-15% on the side that is lagging behind in sinking, and inject drag-reducing slurry on the side that is lagging behind in sinking.

[0025] Risk emergency control: When the subsidence rate exceeds the rate safety threshold, the grouting pump is triggered to inject quick-setting cement grout through the pre-embedded sleeve valve pipe to reinforce the surrounding soil.

[0026] Preferably, the drag-reducing grout consists of the following components: 0.3%-0.7% polyacrylamide, 1%-3% graphite powder, and the balance being water; the injection volume of the drag-reducing grout is 15-25m. 3 / Hour.

[0027] Preferably, the sinking rate safety threshold is 50 mm / h; the target deflection angle threshold is 0-0.3°.

[0028] Preferably, in step S2, the gap between the guide groove and the outer wall of the caisson is ≤30mm.

[0029] Preferably, in step S1, the composite grout is injected using a sleeve valve grouting process; the borehole diameter is 1m and the borehole spacing is 1m.

[0030] The present invention, which adopts the above technical solution, has the following prominent features compared with the prior art:

[0031] 1. In terms of precision control, by installing tilt sensors and laser displacement gauges in the wellbore and deploying earth pressure sensors on the outer ground, real-time monitoring of the construction process was achieved, solving the problems of long measurement intervals and insufficient accuracy in traditional manual control. During the graded and pressure-divided sinking, the hydraulic jacking force was dynamically adjusted based on sensor feedback data. When the resistance fluctuation value exceeded 20% of the static resistance, the jacking force was automatically corrected, avoiding control deviations caused by fixed parameters and significantly improving construction accuracy.

[0032] 2. In terms of correction response, a target deflection angle threshold is set. When the deflection angle exceeds the limit, drag-reducing slurry is injected on the lagging side, and at the same time, 10-15% jacking force is added on the oversinking side to form a correction torque. The response is rapid, overcoming the shortcomings of traditional correction methods such as lag and low efficiency.

[0033] 3. To address the issue of insufficient adaptability to complex geological conditions, the foundation pre-reinforcement employs high-pressure jet grouting to inject composite grout, forming a reinforcement layer. Combined with sand cushion and concrete cushion, this enhances foundation stability. In emergency risk control, when the settlement rate exceeds 50mm / h, quick-setting cement grout is injected through pre-embedded sleeve valve pipes to reinforce the surrounding soil, effectively preventing accidents such as sudden settlement. This method demonstrates stronger adaptability in complex strata such as soft soil and quicksand layers. It also reduces excessive reliance on drag-reducing grout, lowers costs, and improves reliability, significantly enhancing construction safety, economy, and efficiency. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the arrangement structure of the tilt sensor, laser displacement meter and earth pressure sensor in an embodiment of the present invention;

[0035] Figure 2 This is a side view of the caisson construction structure in an embodiment of the present invention;

[0036] Figure 3 This is a flowchart of the caisson construction process applicable to soft soil foundations in an embodiment of the present invention.

[0037] Explanation of reference numerals in the attached drawings: 1. Well shaft; 2. Inclination sensor; 3. Laser displacement gauge; 4. Earth pressure sensor; 5. Sleeve valve pipe; 6. Reinforcement layer; 7. Concrete cushion layer; 8. Jacking mechanism. Detailed Implementation

[0038] The present invention will be further illustrated below with reference to specific embodiments. The purpose of this illustration is solely to provide a better understanding of the invention. Therefore, the examples given do not limit the scope of protection of the present invention.

[0039] like Figures 1 to 3 As shown in the figure, this embodiment provides a caisson construction method suitable for soft soil foundations. The specific steps are as follows:

[0040] S1. Foundation pre-reinforcement: Drill holes in the projection area of ​​the caisson cutting edge, inject composite grout into the holes to form reinforcement layer 6, the thickness of reinforcement layer 6 is 0.8-1.2m; wherein, the composite grout includes nano silicate and bentonite, the mass ratio of nano silicate to bentonite is 1:(2-4), and the mass ratio of water to gel material is 0.45-0.55.

[0041] This application addresses the construction technology of caissons on soft soil foundations, employing foundation pre-reinforcement to replace traditional construction steps (excavation of foundation pit, replacement with crushed stone, and compaction). Besides improving construction efficiency, it also offers several advantages over replacing with crushed stone layers and injecting composite grout using a sleeve valve pipe grouting process after drilling to improve soil quality:

[0042] 1. More precise and durable reinforcement effect

[0043] The composite grout, injected through a sleeve valve pipe, allows for precise layered and segmented injection, ensuring uniform cementation of the foundation soil and avoiding the localized settlement risks caused by uneven compaction in traditional crushed stone replacement layers. After a chemical reaction between the grout and soft soil particles, a stable composite structure is formed, significantly improving impermeability and shear strength. It is less prone to strength degradation due to groundwater seepage or load changes during long-term use, making it more durable than reinforcement methods that rely solely on physical compaction of crushed stone layers.

[0044] 2. Less impact on the surrounding environment

[0045] Large-scale excavation of foundation pits is not required, reducing earthwork excavation and waste soil transportation, and minimizing damage to surrounding vegetation and roads during construction. The sleeve valve grouting process is a minimally invasive construction method with small borehole diameters (typically 50-100mm), minimizing disturbance to the existing foundation soil, effectively controlling ground settlement during construction, and protecting the safety of surrounding buildings and structures.

[0046] 3. Lower overall cost

[0047] This reduces the costs of purchasing, transporting, and disposing of building materials such as crushed stone, especially in soft soil areas far from material yards, where material costs are significantly lower. Simultaneously, the grouting process is highly mechanized, requiring less manual labor, which indirectly reduces construction costs. Because the foundation reinforcement quality is stable, problems such as tilting and cracking are less likely to occur during caisson sinking and use, reducing rework costs for caisson correction and foundation repair, and extending the project's service life.

[0048] S2. Construction of the foundation layer and guide groove: A 10-15cm thick concrete foundation layer 7 is poured on the reinforcement layer 6; and guide grooves are set circumferentially at intervals on the outer side of the caisson projection area, with a groove depth of 0.5-0.8m, filled with graded sand and gravel, with a compaction degree ≥95%, and the gap between the guide groove and the outer wall of the caisson ≤30mm.

[0049] S2. Caisson construction: Concrete caisson 1 is poured in sections, each section being 5-7m high.

[0050] S4. Monitoring system deployment: Install tilt sensor 2 and laser displacement meter 3 on well 1, and deploy earth pressure sensor 4 on the ground outside well 1.

[0051] S5. Staged and Pressure-Divided Sinking: The sinking process is divided into multiple stages. Before the first stage of sinking, the concrete cushion layer 7 needs to be broken. During the sinking project, the hydraulic jacking force is dynamically adjusted based on feedback data from the tilt sensor 2, laser displacement meter 3, and earth pressure sensor 4. The dynamic adjustment mechanism includes:

[0052] 1. When the resistance fluctuation value ΔF exceeds 20% of the static resistance F static At that time, the top thrust correction mechanism is automatically triggered.

[0053] Specifically, when the resistance fluctuation value ΔF exceeds 20% of the preset initial thrust F static At that time, the jacking force correction mechanism is automatically triggered, and the hydraulic jacking force P out The dynamic adjustment formula is:

[0054] P out =k·(F static +ΔF·e -t / τ );

[0055] Where, k = 1.2-1.5, τ = 10-15s, F static The initial thrust is preset, ΔF is the amount of resistance fluctuation; t represents the time from the moment of sudden change in resistance, that is, when ΔF exceeds the preset fluctuation threshold.

[0056] ΔF=|F real -F static |;

[0057] Among them, F real This is the measured value of earth pressure sensor 4.

[0058] 2. Dynamic Correction: When the caisson's deflection angle exceeds the target deflection angle threshold, a 10-15% jacking force is added to the side lagging in sinking, and simultaneously, drag-reducing grout is injected into the same side to create a correction torque. In this embodiment, the target deflection angle threshold is 0-0.3°. The drag-reducing grout consists of the following components: 0.3%-0.7% polyacrylamide, 1%-3% graphite powder, and the remainder is water; the injection volume of the drag-reducing grout is 15-25m³. 3 / Hour.

[0059] 3. Risk Emergency Control: When the settlement rate exceeds the safe threshold, the grouting pump is triggered to inject quick-setting cement grout through the pre-embedded sleeve valve pipe 5 to reinforce the surrounding soil. In this embodiment, the safe threshold for the settlement rate is 50 mm / h.

[0060] S6. Final Settlement and Bottom Sealing: After reaching the design elevation, concrete sealing construction is carried out.

[0061] This application achieves systematic control of caisson construction on soft soil foundations through steps such as foundation pit excavation, foundation pre-reinforcement, and cushion layer construction. Foundation pit excavation and foundation pre-reinforcement enhance foundation stability. The monitoring system, combined with graded and pressure-based sinking, dynamically adjusts the hydraulic jacking force using a formula when resistance fluctuations exceed a threshold. This allows for real-time responses to resistance changes during construction, preventing caisson tilting and sudden sinking caused by resistance fluctuations, thus improving the controllability of the sinking process. The dynamic correction mechanism can also promptly adjust caisson tilt, and the emergency risk control system can quickly reinforce the surrounding soil when the sinking rate exceeds the limit, effectively reducing construction accidents, ensuring construction safety, and guaranteeing that the caisson sinks as expected. Overall, this method improves the safety, accuracy, and efficiency of caisson construction on soft soil foundations.

[0062] Taking a city sewage treatment plant project as an example, the project requires the construction of a rectangular caisson as the foundation of the pump station. The caisson dimensions are 12m×10m×18m (length×width×height), the groundwater level is -1.5m, and the soil layer distribution is: 0-5m backfill soil, 5-15m silty clay, and below 15m silty clay.

[0063] S1. Foundation Pre-reinforcement: Composite grout preparation: Nano-silicate and bentonite are mixed at a mass ratio of 1:3, and the mass ratio of water to gel material is 0.5. After stirring, let it stand for 30 minutes. Then, drill holes in the cutting edge projection area and inject the composite grout into the holes using a sleeve valve grouting process. The hole diameter is 1m, the hole spacing is 1m, and the grouting pressure is 0.8MPa, forming a 1.0m thick reinforcement layer 6. The curing time is 48 hours.

[0064] S2. Construction of the foundation layer and guide groove: A 10cm thick concrete foundation layer 7 is poured on the reinforcement layer 6; and guide grooves are set circumferentially at intervals on the outer side of the caisson projection area, with a groove depth of 0.5-0.8m, filled with graded sand and gravel, with a compaction degree of ≥95%, and the distance between the guide groove and the outer wall of the caisson is 20mm.

[0065] S3. Caisson Construction: Caisson Design: 1.5m wall thickness, C40 concrete strength, constructed in 3 sections (6m each).

[0066] S4. Monitoring System Deployment: Install tilt sensors 2 (4 units, accuracy ±0.01°) and laser displacement gauges 3 (4 units, resolution 0.1mm). Tilt sensors 2 and laser displacement gauges 3 are located at the four corners of well shaft 1. Install earth pressure sensors 4 (4 units, range 0-500kPa), evenly distributed on the ground outside well shaft 1. The data sampling frequency of tilt sensors 2, laser displacement gauges 3, and earth pressure sensors 4 is 20Hz, and the data is wirelessly transmitted to the main controller of the central control platform.

[0067] S5. Staged and Pressure-Divided Sinking: A jacking mechanism 8 is installed at the top of the shaft 1 to be sunk. The jacking mechanism 8 includes a jacking device, a jacking angle beam, steel strands, force transmission connectors, anti-uplift piles, and a caisson jacking operation platform; for specific layout, please refer to the caisson jacking device and its construction method in authorization announcement number CN109972644B. Figure 2 As shown, the anti-pull piles in the jacking mechanism 8 can be set at the four corners of the outer side of the shaft 1 or at the four corners of the inner side of the shaft 1.

[0068] When the exposed part of the N-1 layer well shaft 1 is 1.7-2m high after sinking, the jacking mechanism 8 (jacking device, jacking angle beam, steel strand, caisson jacking operation platform), tilt sensor 2, and laser displacement meter 3 are removed, the N-1 layer well shaft 1 is poured, and the jacking mechanism 8 (jacking device, jacking angle beam, steel strand, caisson jacking operation platform), tilt sensor 2, and laser displacement meter 3 are installed on the N-1 layer well shaft 1. In this embodiment, N is 2-3.

[0069] In this embodiment, the three sections of the well shaft 1 are divided into three sinking stages:

[0070] Phase 1 (0-6m): Target sinking rate 30mm / h, F static =250kPa;

[0071] Phase 2 (6-12m): Target speed 40mm / h, F static =350kPa;

[0072] Phase 3 (12-18m): Target speed 25mm / h, F static =450kPa.

[0073] Dynamic correction operation: When the sinking reaches 3m in stage 1, the north side deviation angle reaches 0.35° (the south side is the lagging sinking side), triggering the correction mechanism: the hydraulic jacking force on the south side increases by 12% (from 250kPa to 280kPa); drag-reducing slurry (0.5% polyacrylamide, 2% graphite powder, and 97.5% water) is injected into the south well wall at a flow rate of 18m³ / h. 3 / h, lasting 1.5 hours.

[0074] Dynamic thrust adjustment: When the frictional resistance suddenly increases by 20% in stage 2, the system automatically adjusts according to formula P. out =1.3·(F static +ΔF·e -t / 12 ) = 1.3·1.2F static ≈546, increasing the top thrust to 546 kPa.

[0075] Correction result: The skew angle was restored to 0.18°, which meets the threshold requirement (≤0.3°).

[0076] Sudden Settlement Emergency Response: During Stage 3, when the depth reached 15m, due to the local collapse of the silty clay layer, the settling rate suddenly increased to 65mm / h. The system automatically executed the following: triggering the grouting pump (response time 1.8s); injecting quick-setting cement grout (water-cement ratio 0.4, grouting pressure 1.8MPa) through the pre-embedded sleeve valve pipe 5, with a grouting volume of 3m³. 3 After 10 minutes, the sinking rate returned to 28 mm / h.

[0077] S6. Final Settlement and Bottom Sealing: After reaching the design elevation, concrete sealing construction is carried out.

[0078] Construction results: Total sinking time: 82 hours, which is 25.5% shorter than the traditional method (110 hours); Final axis deviation: 0.25% in the north-south direction and 0.18% in the east-west direction, both ≤0.3%H; Well wall integrity: no cracks or leakage, and the surrounding surface settlement is ≤5mm.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. All equivalent changes made based on the description and drawings of the present invention are included within the scope of the present invention.

Claims

1. A method for constructing caissons on soft soil foundations, characterized in that, The specific steps are as follows: S1. Foundation pre-reinforcement: Drill holes in the projection area of ​​the caisson cutting edge and inject composite grout to form a reinforcement layer with a thickness of 0.8-1.2m; S2. Construction of the foundation layer and guide trench: A 10-15cm thick concrete foundation layer is poured on the reinforcement layer, and guide trenches are set circumferentially at intervals on the outer side of the caisson projection area. The trenches are 0.5-0.8m deep and filled with graded sand and gravel with a compaction degree ≥95%. S3. Caisson construction: Concrete shaft is poured in sections, each section being 5-7m high; S4. Monitoring system deployment: Install tilt sensors and laser displacement gauges on the well casing, and deploy earth pressure sensors on the ground outside the well casing; S5. Staged and pressure-divided sinking: The sinking process is divided into multiple stages. During the sinking project, the hydraulic jacking force is dynamically adjusted based on feedback data from tilt sensors, laser displacement gauges, and earth pressure sensors. S6. Final settlement and bottom sealing: After reaching the design elevation, concrete sealing construction is carried out; In step S5, when the resistance fluctuation value More than 20% of the preset initial thrust At that time, the jacking force correction mechanism is automatically triggered, and the hydraulic jacking force is adjusted. The dynamic adjustment formula is: ； in, , , To preset the initial thrust, This represents the resistance fluctuation. This indicates the moment of sudden change in resistance, i.e. The calculation begins when the fluctuation exceeds a preset threshold. ； in, These are measured values ​​from the earth pressure sensor. Step S5 also includes: Dynamic correction: When the caisson's tilt angle exceeds the target tilt angle threshold, increase the jacking force by 10-15% on the side that is lagging behind in sinking, and inject drag-reducing slurry on the side that is lagging behind in sinking. Risk emergency control: When the subsidence rate exceeds the rate safety threshold, the grouting pump is triggered to inject quick-setting cement grout through the pre-embedded sleeve valve pipe to reinforce the surrounding soil.

2. The caisson construction method for soft soil foundations according to claim 1, characterized in that: In step S1, the composite slurry includes nano-silicate and bentonite, with a mass ratio of nano-silicate to bentonite of 1:(2-4) and a mass ratio of water to gel material of 0.45-0.

55.

3. The caisson construction method for soft soil foundations according to claim 1, characterized in that: The safe threshold for sinking rate is 50 mm / h; the threshold for target deflection angle is 0-0.3°.

4. The caisson construction method for soft soil foundations according to claim 1, characterized in that: In step S2, the gap between the guide groove and the outer wall of the caisson is ≤30mm.

5. A caisson construction method suitable for soft soil foundations according to claim 1, characterized in that: In step S1, composite grout is injected using a sleeve valve grouting process; the borehole diameter is 1m and the borehole spacing is 1m.

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