Research method for preventing gushing and improving spoil in large-section rectangular pipe jacking in water-rich sand layer

Abstract

The application provides a kind of water-rich sand layer large-section rectangular pipe jacking prevention gushing spoil improvement research method, relating to the rectangular pipe construction technical field, comprising: S1: strong water-permeable stratum spoil physical property research, the strong water-permeable sand layer that pipe jacking crosses carries out field spoil soil sample nature test, and carries out index test to undisturbed soil;S2: carries out strong water-permeable stratum large-section pipe jacking spoil improvement indoor test;S3: completes spoil improvement field verification, spoil improvement field rework test is carried out to spoil improvement proportion that is prepared by indoor test, and the effectiveness of improvement scheme is verified;S4: by the cutterhead and breastboard of pipe jacking machine, injects modifier to the pipe jacking face;S5: collection sampling spoil that is cut in the pipe jacking process carries out the detection of parameters such as slump and permeability coefficient, and according to the dynamic adjustment of field spoil improvement scheme according to surrounding environment monitoring index.The application can effectively prevent spoil gushing phenomenon, and provides safety guarantee for pipe jacking construction.

Description

Technical Field

[0001] This invention relates to the field of rectangular pipe jacking construction technology, specifically a research method for improving the soil and preventing blowouts during large-section rectangular pipe jacking excavation in water-rich sandy layers. Background Technology

[0002] Large-section rectangular pipe jacking has a high probability of gushing under water-rich sandy geological conditions. It is necessary to improve the soil compaction and bearing capacity through spoil soil improvement, reduce soil activity during construction, thereby improving the stability of the excavation face, reducing the risk of collapse and gushing, controlling ground settlement, improving construction efficiency, and reducing environmental impact. This is of great significance to ensuring the safety of pipe jacking tunnel excavation.

[0003] Existing methods for improving construction waste mainly focus on the use of single chemical modifiers, such as foaming agents or bentonite slurries. These single modifiers have limited effectiveness under complex geological conditions. While foaming agents can reduce the viscosity of construction waste, they are easily washed away and diluted in high-water-pressure, highly permeable strata, affecting their improvement effect. Although bentonite slurries can increase the plasticity and fluidity of construction waste, large quantities are often required to achieve the desired improvement effect when used alone in water-rich sand layers, making it difficult to achieve the expected results in practice. Furthermore, the selection of modifiers in existing methods is often based on the results of engineering geological exploration before construction. As the tunnel jacking progresses, geological conditions may change, and the selected modifier may no longer be suitable for the changed geological conditions of the construction waste, resulting in poor improvement effects and potential waste flow, thus posing safety risks to the tunnel jacking construction. Summary of the Invention

[0004] In view of the above-mentioned prior art, this invention proposes a research method for improving the slag and debris generated during large-section rectangular pipe jacking in water-rich sand layers. The aim is to solve the technical problem that the improvement effect of a single modifier on the slag and debris generated during pipe jacking is not good in the prior art, as well as the problem of the lag in adjusting the slurry under different geological conditions during pipe jacking.

[0005] This invention provides a research method for improving the soil and preventing blowouts in large-section rectangular pipe jacking tunnels in water-rich sand layers, comprising the following steps:

[0006] S1: Study on the physical properties of slag soil in highly permeable strata, conduct on-site soil sample property testing on highly permeable sand layers traversed by pipe jacking, and conduct index tests on undisturbed soil.

[0007] S2: Conduct indoor tests on soil improvement for large-section pipe jacking in highly permeable strata;

[0008] S3: Complete the on-site verification of the improvement of the waste soil. Conduct on-site rework tests of the improved waste soil mix ratio determined by indoor tests to verify the effectiveness of the improvement plan.

[0009] S4: Inject modifier into the tunneling face of the pipe jacking machine through the cutterhead and breast plate;

[0010] S5: Collect and sample the excavated soil during the pipe jacking process to test parameters such as slump and permeability coefficient, and dynamically adjust the on-site excavated soil improvement plan based on the surrounding environmental monitoring indicators.

[0011] Preferably, in S1, the index tests on the undisturbed soil include particle size distribution test, normal permeability coefficient test, standard slump test, liquid limit and plastic limit analysis, and XRD component analysis.

[0012] Preferably, in S2, the indoor test for soil improvement includes the following steps:

[0013] A1: Through experimental research, the influence of parameters such as the concentration, foaming ratio, and doping ratio of different modified materials on the material properties is studied, and the optimal parameter range of the modified materials is determined.

[0014] A2: Conduct soil improvement tests under single-admixture conditions to analyze the effects of different admixture ratios on the workability and permeability of the improved soil; prepare soil improvement slurries of different mass concentrations in the laboratory, and select sodium bentonite, carboxymethyl cellulose (CMC), foaming agent, and polyacrylamide as soil improvement additives to conduct indoor geotechnical tests; the main contents of the geotechnical tests include slump test, permeability test, and mud viscosity test; the slump test is used to test the plastic flow state of the improved soil; the permeability test is used to compare the permeability coefficients of the soil before and after improvement, thereby judging the improvement effect of the improvement materials on the permeability of the soil; the mud viscosity test is used to ensure that the soil improvement mix ratio meets the performance of the pipe jacking machine injection pump;

[0015] A3: Based on the results of single-admixture tests and relevant engineering experience, conduct mixed improvement tests based on the performance of improved materials, and propose a slag improvement scheme that meets engineering application standards by comparing the improvement effects based on actual materials on site.

[0016] Preferably, in A2, to meet the requirements of large-section rectangular pipe jacking construction in water-rich sandy layers, the slump of the improved slag is controlled within the range of 10-15cm, and the permeability coefficient is less than 1×10⁻⁶. -5 cm / s.

[0017] Preferably, in A3, the improved mud mix ratio is water:bentonite:CMC=100:8:0.54, with a mixing ratio of 15% (the volume ratio of bentonite mud bath to improve slag).

[0018] Preferably, in S4, the pipe jacking machine has 12 2-inch soil improvement holes on its breast plate to enhance the workability and fluidity of the sandy soil in the soil chamber, facilitating the excavation of soil by the screw conveyor. The cutterhead of the pipe jacking machine has two injection holes for soil improvement. One hole enters the center cutter of the cutterhead, and the other hole enters the cutterhead panel from the cutterhead spokes. Each cutterhead spoke has three injection holes. At the same time, the mixing rod behind the cutterhead is used to fully mix the soil in the soil chamber, making the soil fluid and water-retaining, which is convenient for the screw conveyor to transport.

[0019] Preferably, in step S5, the step of dynamically adjusting the on-site waste soil improvement plan based on surrounding environmental monitoring indicators includes the following steps:

[0020] B1: Establish a performance coupling factor n=f(ξ,S) between the permeability coefficient ξ and the slump S, and determine the adjustment coefficient λ of the performance coupling factor; dynamically adjust the ratio of bentonite and polymer according to the adjustment coefficient λ; when λ>1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer, with the adjustment range being: Bentonite reduction = (λ-1)×base injection amount×bentonite ratio, polymer increase = (λ-1)×base injection amount×polymer ratio; when λ<1, increase the injection amount of bentonite slurry and decrease the injection amount of polymer, with the adjustment range being: Bentonite increase = (1-λ)×base injection amount×bentonite ratio, polymer reduction = (1-λ)×base injection amount×polymer ratio.

[0021] B2: When the pipe jacking tunnel crosses a river, the dynamic adjustment coefficient is adaptively modified, and the flow velocity influence factor γ is taken into account;

[0022] 河修 =

[0023] =1+0.1 ln(1+ )

[0024] In the formula, P w P0: Hydrostatic pressure of river water, kPa; K: Reference earth pressure, kPa; s : Current soil permeability coefficient, cm / s; K j : Reference permeability coefficient, cm / s; v: River flow velocity, m / s; v0: Reference flow velocity, m / s;

[0025] When λ 河修 When the value is greater than 1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer. The adjustment range is: Bentonite reduction = (λ) / (λ) 河修 -1) × Base injection volume × Bentonite blending ratio × Increase in polymer content = (λ) 河修 -1) × Base injection volume × Polymer doping ratio × ;

[0026] When λ 河修 When <1, increase the injection amount of bentonite slurry and decrease the injection amount of polymer. The adjustment range is: Bentonite increase = (1-λ) / ( ... 河修 × Baseline injection volume × Bentonite blending ratio × The reduction in polymer content = (1-λ) 河修 × baseline injection volume × polymer doping ratio × ;

[0027] B3: When the pipe jacking excavation passes through adjacent buildings, the dynamic adjustment coefficient is adaptively modified, and the influencing factors are taken into account. ;

[0028] 建修 =

[0029]

[0030] In the formula, η: building sensitivity coefficient, 0.3-0.5 for steel structure buildings, and 0.6-0.8 for brick-concrete / historical buildings; D 临 D: Design safety distance from the building foundation to the pipe jacking axis, in meters; S: Horizontal distance from the current pipe jacking machine to the building, in meters; max : Maximum allowable settlement, mm; S: Real-time monitored settlement, mm; μ: Formation loss compensation coefficient; Q: Current excavation rate (actual excavated volume / theoretical volume); Q0: Balanced excavation rate, set to 95%-98%;

[0031] When λ 建修 When the value is greater than 1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer. The adjustment range is: Bentonite reduction = (λ) / (λ) 建修 -1) × Base injection volume × Bentonite blending ratio × Increase in polymer content = (λ) 建修 -1) × Base injection volume × Polymer doping ratio × ;

[0032] When λ 建修 When <1, increase the injection amount of bentonite slurry and decrease the injection amount of polymer. The adjustment range is: Bentonite increase = (1-λ) / ( ... 建修 × Baseline injection volume × Bentonite blending ratio × The reduction in polymer content = (1-λ) 建修 × baseline injection volume × polymer doping ratio × .

[0033] Compared to existing technologies, the beneficial effects of this invention are as follows: This invention provides a method for improving the soil and slag mixture in large-section rectangular pipe jacking in water-rich sand layers to prevent blowouts. This method simultaneously prevents ground subsidence and collapse, as well as preventing soil blowouts. By conducting real-time analysis of the soil and slag mixture within the soil chamber, and considering the flow velocity influencing factors when crossing rivers and the ground loss compensation coefficient of adjacent structures, this invention dynamically adjusts the ratio of bentonite slurry and CMC. This ensures that the improved slurry maintains optimal performance under complex geological conditions, thereby significantly reducing the risk of ground disturbance, effectively preventing soil blowouts, and providing reliable safety assurance for pipe jacking construction. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the soil layer profile of the tunnel section according to an embodiment of the present invention.

[0035] Figure 2 This is a diagram showing the main characteristics of the soil layers at the tunneling section in an embodiment of the present invention.

[0036] Figure 3 This is a statistical chart of the physical and mechanical properties of the soil layer in an embodiment of the present invention.

[0037] Figure 4 This is a flowchart of the improved proportioning test study and dynamic control method of the present invention.

[0038] Figure 5 The image shows the XRD analysis results of the excavated soil in an embodiment of the present invention.

[0039] Figure 6 This is a graph showing the viscosity of the polyacrylamide solution over time in an embodiment of the present invention.

[0040] Figure 7 This is a graph showing the relationship between the expansion time and the slurry viscosity of sodium-based bentonite in an embodiment of the present invention.

[0041] Figure 8 This is a graph showing the change in slump of slag under different foam injection rates in an embodiment of the present invention.

[0042] Figure 9 This is a graph showing the change in the permeability coefficient of slag soil with the foam injection rate in an embodiment of the present invention.

[0043] Figure 10 This is a diagram showing the slump test verification of the improved mix proportion of bentonite-CMC mixed mud in an embodiment of the present invention.

[0044] Figure 11 This is a diagram illustrating the penetration test verification of the improved proportion of bentonite-CMC mixed mud in an embodiment of the present invention. Detailed Implementation

[0045] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0046] Example: Figure 1-11 The method for preventing blowout and improving the excavated soil in large-section rectangular pipe jacking tunnels in water-rich sandy layers, as shown, includes the following steps:

[0047] S1: Study on the physical properties of excavated soil in highly permeable strata. On-site soil sample property testing was conducted on highly permeable sand layers traversed by pipe jacking. Index tests were performed on the undisturbed soil, including:

[0048] 1) Particle size distribution test: Particle composition analysis of fine-grained sandy strata was performed by sieving.

[0049] 2) Normal water permeability coefficient test: Weigh a representative air-dried sample of 3000g-4000g, and use a 100-type constant water head permeameter device indoors. The inner diameter of the sealed metal cylinder is 100mm and the height is 400mm. The inner diameter of the glass pressure measuring tube is 6mm and the graduation value is 1mm.

[0050] 3) Standard slump test: The soil sample is poured into a slump cone with a bottom diameter of 30cm, a top diameter of 10cm, and a height of 30cm in three layers. The remaining height of the soil sample after the slump cone is lifted is measured, and the slump height of the soil sample is calculated to quantify the workability of the soil sample.

[0051] 4) Liquid and plastic limit analysis: The liquid and plastic limits of the test soil samples were measured using the LP-100D digital display liquid and plastic limit combined tester.

[0052] 5) XRD Composition Analysis: The slag was dried, and XRD analysis was performed on the fine-particle slag with a particle size of less than 0.0075 mm after grinding. The mineral composition of the strata where the slag was located was determined, and the results are as follows: Figure 5 The XRD analysis results of the slag soil are shown. Analysis of the XRD patterns of the slag soil from the site indicates that the main strata in this embodiment are composed of silt interbedded with silt. The main mineral in the silt is quartz, accounting for over 80%. In addition, this silt-silt interbedded strata contains attapulgite, chlorite, muscovite, and pale mica, etc. The mineral composition of the slag soil from the site is consistent with the results of the geological survey report from which the strata were taken. Quartz has the highest diffraction peak, while the diffraction peaks of other minerals such as attapulgite, chlorite, and muscovite are of similar height. The main compounds in the slag soil from this embodiment are oxides of silicon, magnesium, aluminum, calcium, and iron. Furthermore, the slag soil minerals are highly crystalline, with a minimum crystallinity of 89.62% and an average crystal diameter of 1177 Å. The quartz mineral, which has the highest content, has a unit cell volume of 112.6 Å. 3 .

[0053] S2: Conduct indoor tests on soil improvement for large-section pipe jacking in highly permeable strata, including the following steps:

[0054] A1: Through experimental research, the influence of parameters such as the concentration, foaming ratio, and doping ratio of different modified materials on material properties is studied to determine the optimal parameter range for the modified materials. Specifically:

[0055] 1) The relevant parameters of the foaming agent solution were tested to determine the concentration of the foam modifier. Foaming equipment was used, with the foaming agent solution placed in a pressure tank. The pressure tank had two pipelines: one outputting the foaming agent solution, and the other outputting compressed air. The two pipelines merged to generate foam. Flow meters were installed on both pipelines. After foaming, the half-life and expansion ratio of the foam were tested and compared. Under constant conditions, as the foaming agent concentration increased, the foam expansion rate and half-life also increased and eventually stabilized. When the foaming agent concentration was below 3%, the increase in foam expansion rate and half-life was very significant; when the foaming agent concentration was above 3%, the rate of increase in foam expansion rate and half-life gradually slowed down and stabilized, reaching its maximum at 5%. Therefore, a 3% concentration foaming agent solution was selected for subsequent experiments.

[0056] 2) Polyacrylamide solutions with concentrations of 1%, 2%, and 3% (mass ratio of polyacrylamide powder to solution) were selected as test concentrations. The change trend of the viscosity of the polyacrylamide solution with increasing concentration was measured. Figure 6 As shown.

[0057] 3) Swelling time-viscosity tests were conducted on sodium-based bentonite slurries prepared at concentrations of 10% (1:10), 12.5% ​​(1:8), and 15%. The relationship between slurry viscosity and swelling time was obtained through these tests. Figure 7 As shown in the figure, increasing the slurry expansion time to 24 hours effectively reduces the diameter and number of slurry lumps and increases the viscosity of the bentonite slurry to near its peak value. Therefore, in subsequent experiments, sodium-based bentonite slurry with a mass fraction of 10% and an expansion time of 24 hours was selected as the standard modifier.

[0058] A2: Conduct soil improvement experiments under single-admixture conditions to analyze the effects of different admixture ratios on the workability and permeability of the improved soil. Prepare soil improvement slurries of different mass concentrations in the laboratory, and select sodium bentonite, carboxymethyl cellulose (CMC), foaming agent, and polyacrylamide as soil improvement additives to conduct indoor geotechnical tests. The main contents of the geotechnical tests include slump tests, permeability tests, and slurry viscosity tests. To meet the needs of large-section rectangular pipe jacking construction in water-rich sand layers, the slump of the improved soil is controlled within the range of 10-15 cm, and the permeability coefficient is less than 1×10⁻⁶. -5 cm / s. Specifically:

[0059] 1) Foaming agent improvement test: The foaming rate was set to 10 (compressed air: foam solution = 9:1), and the foaming pressure was set to 0.3 MPa. Slump and permeability tests were conducted at six foam injection rates: 5%, 10%, 15%, 20%, 25%, and 30%. The test results are as follows: Figure 8 , Figure 9 As shown, under a 15% injection rate, the slump of the slag meets the workability requirements, and under a 30% foam injection rate, the minimum permeability coefficient of the slag is 2.53 × 10⁻⁶. -5 cm / s, which does not meet the improvement requirements.

[0060] 2) Polyacrylamide Improvement Test: The viscosity of polyacrylamide solutions of different concentrations was tested using 10 minutes as the standard. It was found that when the polyacrylamide concentration exceeded 2%, the solution viscosity increased significantly, with the 10-minute viscosity value exceeding 100s, which exceeded the upper limit of the earth pressure balance pipe jacking machine pump. Therefore, solutions with polyacrylamide concentrations of 1% and 2% were selected for soil improvement tests to obtain the relationship between the polyacrylamide flocculant injection rate and the soil permeability coefficient and slump. The slump of the soil under different polyacrylamide dosages of 1% and 2% failed to meet the construction requirement of 10-20cm.

[0061] 3) Bentonite slurry improvement test: Under the condition of sodium-based bentonite slurry with a mass fraction of 10%, the improvement effect was tested by selecting the addition ratio of 5%, 10%, 15%, 20%, 25%, and 30% (volume ratio of bentonite slurry to the slag to be improved). It was found that the improvement requirements of this embodiment could not be met by single-factor improvement through sodium-based bentonite slurry.

[0062] A3: Based on the analysis results of various materials in the geotechnical test, and considering the characteristics of high-permeability sandy strata in the pipe jacking section, sodium-based bentonite was determined as the main improvement material, while CMC and polyacrylamide were selected as alternative auxiliary materials for soil improvement.

[0063] 1) When sodium-based bentonite and polyacrylamide are mixed, the slurry separates into water and slurry. Flocculent matter floats on the surface, resulting in extremely poor fluidity. Bentonite settles at the bottom, and the mixed slurry loses its fluidity.

[0064] 2) Select sodium-based bentonite-CMC mixed slurries of different concentrations, stir thoroughly, and let stand for 24 hours to allow for full expansion before use. Based on the geotechnical test results, sodium-based bentonite slurries with water-to-soil ratios of 100:8, 100:9, and 100:10 (viscosity close to the upper limit of use) were selected to prepare mixed slurries with CMC admixture ratios (water:solvent) of 100:0.25, 100:0.5, and 100:0.75, and viscosity tests were conducted. Following the principle of mixing slurry concentration close to the upper limit of pumping capacity, two CMC-bentonite mixed slurry ratios of 100:8:0.5 and 100:9:0.25 (water:bentonite:CMC reagent ratios) were selected for slump and permeability tests. Two sets of mixed mud with different proportions were tested for slump and permeability coefficient of the excavated soil. The results showed that the two proportions met the requirements for preventing excavated soil gushing in this embodiment: a 100:8:0.5 CMC-bentonite mixed mud with 15% of the mud and a 100:9:0.25 CMC-bentonite mixed mud with 15% of the mud. The 100:8:0.5 CMC-bentonite mixed mud used less bentonite and had better permeability improvement and water retention effects.

[0065] S3: Complete the on-site verification of the improved soil and concrete mix. Based on the improved soil mix ratio determined through indoor tests (the improved slurry ratio is water:bentonite:CMC=100:8:0.54, with a mixing ratio of 15%), conduct on-site replication tests of the improved soil and concrete mix. Figure 10 , Figure 11 As shown, the effectiveness and feasibility of the improvement scheme are verified.

[0066] S4: Inject modifier into the tunneling face of the pipe jacking machine through the cutterhead and breast plate;

[0067] The pipe jacking machine has 12 2-inch soil improvement holes on its breast plate to enhance the workability and fluidity of the sandy soil in the soil chamber, facilitating soil removal by the screw conveyor. The cutterhead of the pipe jacking machine has two injection holes for soil improvement: one enters the center cutter of the cutterhead; the other enters from the cutterhead spokes onto the cutterhead panel, with three injection holes on each spoke. Simultaneously, the mixing rods behind the cutterhead thoroughly mix the soil in the soil chamber, giving it fluidity and water retention properties, facilitating screw conveyor transport.

[0068] S5: Collect and sample the excavated soil during the pipe jacking process to test parameters such as slump and permeability coefficient, and dynamically adjust the on-site excavated soil improvement plan based on the surrounding environmental monitoring indicators.

[0069] The dynamic adjustment of the on-site spoil remediation plan based on surrounding environmental monitoring indicators includes the following steps:

[0070] B1: Establish a real-time dynamic adjustment model:

[0071] 1) Determine target parameters: Set the target value for the permeability coefficient of the improved slag soil. slump target value The target slump range is 10-15 cm, and the target permeability coefficient is... < 1×10 -5 cm / s;

[0072] 2) Calculation of performance coupling factor: After each ring of tunneling is completed, samples of the excavated soil are taken to quickly determine its permeability coefficient ξ and slump S. The performance coupling factor n of the current ring is calculated using the following formula:

[0073]

[0074] 3) Determine the adjustment coefficient λ: Based on the performance coupling factor n, determine the adjustment coefficient λ through a predetermined control function, and dynamically adjust the ratio of bentonite and polymer based on the adjustment coefficient λ.

[0075] When n > N, λ = 1 + N

[0076] When |n|≤N, λ=1

[0077] When n < -N, λ = 1 - 0.5|n|

[0078] N is the response threshold, which is set to 0.1.

[0079] 4) Perform ratio adjustment: When λ>1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer. The adjustment range is: Bentonite reduction = (λ-1) × baseline injection amount × bentonite ratio, polymer increase = (λ-1) × baseline injection amount × polymer ratio.

[0080] When λ < 1, increase the amount of bentonite slurry injected and decrease the amount of polymer injected. The adjustment range is: Bentonite increase = (1-λ) × baseline injection amount × bentonite ratio, polymer decrease = (1-λ) × baseline injection amount × polymer ratio.

[0081] When λ=1, the injection amount of the baseline ratio remains unchanged.

[0082] B2: When the pipe jacking tunnel crosses a river, the dynamic adjustment coefficient is adaptively modified, and the flow velocity influence factor γ is taken into account;

[0083] 河修 =

[0084] =1+0.1 ln(1+ )

[0085] In the formula, P w P0: Hydrostatic pressure of river water, kPa; K: Reference earth pressure, kPa; s : Current soil permeability coefficient, cm / s; K j : Reference permeability coefficient, cm / s; v: River flow velocity, m / s; v0: Reference flow velocity, m / s;

[0086] When λ 河修 When the value is greater than 1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer. The adjustment range is: Bentonite reduction = (λ) / (λ) 河修 -1) × Base injection volume × Bentonite blending ratio × Increase in polymer content = (λ) 河修 -1) × Base injection volume × Polymer doping ratio × ;

[0087] When λ 河修 When <1, increase the injection amount of bentonite slurry and decrease the injection amount of polymer. The adjustment range is: Bentonite increase = (1-λ) / ( ... 河修 × Baseline injection volume × Bentonite blending ratio × The reduction in polymer content = (1-λ) 河修 × baseline injection volume × polymer doping ratio × .

[0088] B3: When the pipe jacking excavation passes through adjacent buildings, the dynamic adjustment coefficient is adaptively modified, and the influencing factors are taken into account. ;

[0089] 建修 =

[0090]

[0091] In the formula, η: building sensitivity coefficient, 0.3-0.5 for steel structure buildings, and 0.6-0.8 for brick-concrete / historical buildings; D 临 D: Design safety distance from the building foundation to the pipe jacking axis, in meters; S: Horizontal distance from the current pipe jacking machine to the building, in meters; max : Maximum allowable settlement, mm; S: Real-time monitored settlement, mm; μ: Formation loss compensation coefficient; Q: Current excavation rate (actual excavated volume / theoretical volume); Q0: Balanced excavation rate, set to 95%-98%;

[0092] When λ 建修 When the value is greater than 1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer. The adjustment range is: Bentonite reduction = (λ) / (λ) 建修-1) × Base injection volume × Bentonite blending ratio × Increase in polymer content = (λ) 建修 -1) × Base injection volume × Polymer doping ratio × ;

[0093] When λ 建修 When <1, increase the injection amount of bentonite slurry and decrease the injection amount of polymer. The adjustment range is: Bentonite increase = (1-λ) / ( ... 建修 × Baseline injection volume × Bentonite blending ratio × The reduction in polymer content = (1-λ) 建修 × baseline injection volume × polymer doping ratio × .

[0094] This embodiment analyzes the slag in the soil chamber in real time. Based on the slag state analysis results and considering the flow velocity influence factor when crossing the river and the stratum loss compensation coefficient of the adjacent structure, the ratio of bentonite slurry and CMC is dynamically adjusted to ensure that the improved slurry always maintains optimal working performance under complex geological conditions. This significantly reduces the risk of stratum disturbance, effectively prevents slag gushing, and provides reliable safety guarantee for pipe jacking construction.

[0095] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent solutions made using the contents of the present invention specification, whether directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of the present invention.

Claims

1. A research method for improving the soil and preventing blowouts in large-section rectangular pipe jacking tunnels in water-rich sand layers, characterized in that... Includes the following steps: S1: Study on the physical properties of slag soil in highly permeable strata, conduct on-site soil sample property testing on highly permeable sand layers traversed by pipe jacking, and conduct index tests on undisturbed soil. S2: Conduct indoor tests on soil improvement for large-section pipe jacking in highly permeable strata; S3: Complete the on-site verification of the improvement of the waste soil. Conduct on-site rework tests of the improved waste soil mix ratio determined by indoor tests to verify the effectiveness of the improvement plan. S4: Inject modifier into the tunneling face of the pipe jacking machine through the cutterhead and breast plate; S5: Collect and sample the excavated soil during the pipe jacking process to test its slump and permeability coefficient, and dynamically adjust the on-site excavated soil improvement plan based on the surrounding environmental monitoring indicators. In step S5, the dynamic adjustment of the on-site spoil remediation plan based on surrounding environmental monitoring indicators includes the following steps: B1: Establish a performance coupling factor n=f(ξ,S) between the permeability coefficient ξ and the slump S, and determine the adjustment coefficient λ of the performance coupling factor; dynamically adjust the ratio of bentonite and polymer according to the adjustment coefficient λ; when λ>1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer, with the adjustment range being: Bentonite reduction = (λ-1)×base injection amount×bentonite ratio, polymer increase = (λ-1)×base injection amount×polymer ratio; when λ<1, increase the injection amount of bentonite slurry and decrease the injection amount of polymer, with the adjustment range being: Bentonite increase = (1-λ)×base injection amount×bentonite ratio, polymer reduction = (1-λ)×base injection amount×polymer ratio. B2: When the pipe jacking tunnel crosses a river, the dynamic adjustment coefficient is adaptively modified, and the flow velocity influence factor γ is taken into account; 河修 = ； =1+0.1 ln（1+ ）； In the formula, P w P0: Hydrostatic pressure of river water, kPa; K: Reference earth pressure, kPa; s : Current soil permeability coefficient, cm / s; K j : Reference permeability coefficient, cm / s; v: River flow velocity, m / s; v0: Reference flow velocity, m / s; When λ 河修 When the value is greater than 1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer. The adjustment range is: Bentonite reduction = (λ) / (λ) 河修 -1) × Base injection volume × Bentonite blending ratio × Increase in polymer content = (λ) 河修 -1) × Base injection volume × Polymer doping ratio × ; When λ 河修 When <1, increase the injection amount of bentonite slurry and decrease the injection amount of polymer. The adjustment range is: Bentonite increase = (1-λ) / ( ... 河修 × Baseline injection volume × Bentonite blending ratio × The reduction in polymer content = (1-λ) 河修 × baseline injection volume × polymer doping ratio × ; B3: When the pipe jacking excavation passes through adjacent buildings, the dynamic adjustment coefficient is adaptively modified, and the influencing factors are taken into account. ; 建修 = ； ； In the formula, η: building sensitivity coefficient, 0.3-0.5 for steel structure buildings, and 0.6-0.8 for brick-concrete / historical buildings; D 临 D: Design safety distance from the building foundation to the pipe jacking axis, in meters; S: Horizontal distance from the current pipe jacking machine to the building, in meters; max : Maximum allowable settlement, mm; S: Real-time monitored settlement, mm; μ: Formation loss compensation coefficient; Q: Current excavation rate = actual excavated volume / theoretical volume; Q0: Balanced excavation rate, set to 95%-98%; When λ 建修 When the value is greater than 1, reduce the injection amount of bentonite slurry and increase the injection amount of polymer. The adjustment range is: Bentonite reduction = (λ) / (λ) 建修 -1) × Base injection volume × Bentonite blending ratio × Increase in polymer content = (λ) 建修 -1) × Base injection volume × Polymer doping ratio × ; When λ 建修 When <1, increase the injection amount of bentonite slurry and decrease the injection amount of polymer. The adjustment range is: Bentonite increase = (1-λ) / ( ... 建修 × Baseline injection volume × Bentonite blending ratio × The reduction in polymer content = (1-λ) 建修 × baseline injection volume × polymer doping ratio × .

2. The research method for preventing blowouts and improving slag in large-section rectangular pipe jacking excavation in water-rich sandy layers as described in claim 1, characterized in that, In S1, the index tests on the undisturbed soil include particle size distribution test, normal permeability coefficient test, standard slump test, liquid limit and plastic limit analysis, and XRD component analysis.

3. The research method for preventing blowouts and improving slag in large-section rectangular pipe jacking excavation in water-rich sandy layers as described in claim 1 or 2, characterized in that, In S2, the indoor test for soil improvement includes the following steps: A1: Through experimental research, the effects of different concentrations, foaming ratios, and blending ratios of modified materials on material properties are studied to determine the optimal parameter range for the modified materials; A2: Conduct soil improvement tests under single-admixture conditions to analyze the effects of different admixture ratios on the workability and permeability of the improved soil; prepare soil improvement slurries of different mass concentrations in the laboratory, and select sodium bentonite, carboxymethyl cellulose, foaming agent, and polyacrylamide as soil improvement additives to conduct indoor geotechnical tests; the main contents of the geotechnical tests include slump test, permeability test, and mud viscosity test; the slump test is used to test the plastic flow state of the improved soil; the permeability test is used to compare the permeability coefficients of the soil before and after improvement, thereby judging the improvement effect of the improvement materials on the permeability of the soil; the mud viscosity test is used to ensure that the soil improvement mix ratio meets the performance of the pipe jacking machine injection pump; A3: Based on the results of single-admixture tests and relevant engineering experience, conduct mixed improvement tests based on the performance of improved materials, and propose a slag improvement scheme that meets engineering application standards by comparing the improvement effects based on actual materials on site.

4. The research method for preventing blowout and improving slag in large-section rectangular pipe jacking excavation in water-rich sandy layers as described in claim 3, characterized in that, In section A2, to meet the requirements of large-section rectangular pipe jacking construction in water-rich sandy layers, the slump of the improved slag is controlled within the range of 10-15cm, and the permeability coefficient is less than 1×10⁻⁶. -5 cm / s.

5. The research method for preventing blowouts and improving slag in large-section rectangular pipe jacking excavation in water-rich sandy layers as described in claim 3, characterized in that, In A3, the modified mud mix ratio is water:bentonite:CMC=100:8:0.54, with a blending ratio of 15%. The CMC is carboxymethyl cellulose, and the blending ratio is the volume ratio of bentonite mud to modified slag.

6. The research method for preventing blowouts and improving slag in large-section rectangular pipe jacking excavation in water-rich sandy layers as described in claim 1 or 2, characterized in that, In the S4, the jacking machine has 12 2-inch soil improvement holes on its breast plate to enhance the workability and fluidity of the sandy soil in the soil chamber, making it easier for the screw conveyor to remove soil. The cutterhead of the jacking machine has two injection holes for soil improvement. One hole enters the center cutter of the cutterhead, and the other hole enters the cutterhead panel from the cutterhead spokes. Each cutterhead spoke has three injection holes. At the same time, the mixing rod behind the cutterhead is used to fully mix the soil in the soil chamber, making the soil fluid and water-retaining, which is convenient for the screw conveyor to transport.

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