A synchronous grouting slurry for a shield, a preparation method thereof and a segment anti-floating synchronous grouting method

Abstract

The application relates to a shield synchronous grouting slurry, a preparation method and a segment anti-floating synchronous grouting method. The slurry is mainly composed of water 100 parts, sodium bentonite 7 to 9 parts, silicate cement 28 to 32 parts and carboxymethyl cellulose sodium 0.13 to 0.17 parts by weight parts, conforms to the Bingham plastic fluid model, the initial yield stress is 500 to 800 Pa, and the plastic viscosity is 0.5 to 1.0 Pa.s. The preparation method comprises four steps of batching, bentonite pre-hydration, regulator compounding to form a gel base slurry and finally adding cement, and a reverse batching sequence of building gel first and then adding cement is adopted. The construction method comprises three steps of slurry pumping, synchronous grouting and yield support, and precise anti-floating is realized through a yield stress design formula, differential grouting of upper and lower grouting holes and real-time monitoring feedback. The application provides support for the segment through the three-dimensional gel network structure of the slurry in the static state, and fundamentally weakens the static water pressure transmission of the slurry to the bottom of the segment.

Description

Technical Field

[0001] This application relates to the field of tunnel and underground engineering construction, and in particular to a shield tunnel synchronous grouting slurry, its preparation method, and a segment anti-buoyancy synchronous grouting method. Background Technology

[0002] Currently, with the rapid development of underground space projects such as urban rail transit, cross-river and cross-sea tunnels, and underground integrated pipe corridors, the shield tunneling method has become the mainstream construction method in modern tunnel construction due to its advantages such as high safety, fast construction speed, and minimal impact on the surface environment. During shield tunneling, the diameter of the tunnel section excavated by the shield machine cutterhead is slightly larger than the outer diameter formed after the segments are assembled. This results in a ring-shaped gap, typically 50 to 200 mm thick, between the segments after they exit the shield tail and the surrounding strata, known as the shield tail gap. To stabilize the segment structure, control surface settlement, provide long-term water-stopping performance, and prevent ground disturbance, grout must be injected into the shield tail gap simultaneously with shield tunneling and segment assembly using the shield machine's built-in synchronous grouting system. This process is called synchronous grouting.

[0003] Currently, the synchronous grouting slurries widely used in engineering practice include various types such as pure cement slurry, cement-bentonite slurry, and cement-fly ash slurry. These slurries are all classified as Newtonian or near-Newtonian fluids in rheological terms, meaning they maintain good fluidity even at rest, have no significant yield stress, and exhibit a linear relationship between shear stress and shear rate. However, the aforementioned traditional synchronous grouting technology based on Newtonian fluids has revealed serious defects in segment floatation quality in engineering practice. The maximum floatation of segments under traditional Newtonian fluid slurries can reach 110 to 114 mm, far exceeding the 50 mm limit specified in the standards, and exhibits a time characteristic of completing 80% floatation within the first 6 to 10 hours, and then stabilizing after 24 to 72 hours. Continuous and uncontrolled segment uplift will trigger a series of serious engineering quality problems, including segment circumferential joint misalignment, bolt tensile plastic deformation, segment concrete chipping and breakage, joint waterproofing seal failure leading to water leakage, excessive segment ellipticity, and tunnel axis deviation from the design position, seriously affecting the tunnel structure's load-bearing capacity, waterproofing performance, and 100-year service life. In-depth analysis of the mechanical mechanism of segment uplift reveals that the fundamental cause is not the grout density itself, but the hydrostatic pressure formed by the Newtonian fluid grout in the shield tail gap, which can be completely transmitted to the bottom of the segment. Traditional grout retains its liquid properties after injection, and its pressure distribution is similar to that of water, increasing linearly along the depth of the grout column. This results in the bottom of the segment bearing huge and continuous buoyancy, causing the segment to exhibit a floating effect, much like a ship being lifted by liquid.

[0004] To address the persistent problem of segment floatation in tunnel boring machine (TBM) construction, the engineering and academic communities both domestically and internationally have conducted extensive research and attempted various improvement measures. The main technical approaches fall into three categories: The first is optimizing grouting parameters, such as grouting pressure, flow rate, and timing, to alleviate floatation. However, simply increasing grouting pressure is insufficient to balance the continuous buoyancy, and excessive pressure can actually compress unsolidified, weak strata, leading to soil loss and ground heave. The second approach involves adjusting grout density, attempting to reduce buoyancy by decreasing grout density. However, lowering the grout density can lead to increased buoyancy. The degree of buoyancy also decreases, and the mechanical mechanism by which the grout transmits hydrostatic pressure remains unchanged, resulting in limited effectiveness. The third type involves adding a quick-setting agent or using a two-component grout to shorten the initial setting time of the grout, causing it to solidify rapidly and lose its fluidity. However, these quick-setting methods have many drawbacks—excessive quick-setting agents can easily cause the grout to solidify prematurely in the grouting pipeline or at the shield tail sealing brush, leading to pipe blockage accidents and shield tail seal failure. Even with a rapid solidification method, the initial setting time of the grout is usually 3-6 hours, which still cannot cover the 6-10 hours of severe uplift period after the segment exits the shield tail, resulting in a significant "anti-buoyancy vacuum period." In summary, the existing improvement technologies have not fundamentally changed the mechanical mechanism by which the grout transmits hydrostatic pressure, and are still passive buoyancy control modes that "treat the symptoms but not the root cause," making them difficult to adapt to the higher requirements of modern shield tunnel engineering for segment attitude control and forming quality. Therefore, there is an urgent need to provide a synchronous grouting grout that can change the mechanical behavior of the grout from a rheological perspective, actively eliminate the transmission of hydrostatic pressure from the grout to the bottom of the tunnel segment, and achieve anti-buoyancy of the tunnel segment during shield tunneling construction, as well as its corresponding preparation and construction methods, so as to fundamentally solve the long-standing problem of tunnel segment buoyancy in shield tunnel engineering. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this application provides a shield tunnel synchronous grouting slurry, a preparation method, and a segment anti-buoyancy synchronous grouting method, which can change the mechanical behavior of the slurry from the rheological source, actively weaken the transmission of hydrostatic pressure from the slurry to the bottom of the segment, and suppress the segment buoyancy during shield tunnel construction.

[0006] This application is achieved through the following technical solution: This application provides a grout for synchronous grouting in tunnel boring machines, the grout mainly composed of the following components in parts by weight: Water: 100 parts; Sodium-based bentonite: 7-9 parts; Silicate cement: 28-32 parts; Sodium carboxymethyl cellulose: 0.13~0.17 parts; The rheological properties of the slurry conform to the Bingham plastic fluid model, and its constitutive equation is: τ = τ0 + μ·D In the formula, τ is the shear stress in Pa; τ0 is the yield stress in Pa; μ is the plastic viscosity in Pa·s; and D is the shear rate in s⁻¹. The initial yield stress τ0 of the slurry, measured by a rotational viscometer in shear rate scanning mode at 20±2℃ after standing for 5 minutes, was 500~800 Pa, and the plastic viscosity μ was 0.5~1.0 Pa·s.

[0007] By adopting the above technical solution, the provided shield tunneling synchronous grout is a compound of sodium-based bentonite, cement, and sodium carboxymethyl cellulose in a specific ratio, forming a Bingham plastic fluid with yield stress. After being injected into the shield tail void, this grout can spontaneously form a three-dimensional gel network structure under low shear conditions, transforming the grout from a pumpable flow state to a supported state without macroscopic flow. This fundamentally cuts off the path for the Newtonian fluid grout to completely transmit hydrostatic pressure to the bottom of the tunnel segments, solving the mechanical root cause problem of severe segment buoyancy caused by continuous hydrostatic pressure in traditional grouts. Unlike the traditional approach of simply adjusting the grout density or using accelerators to speed up solidification, this technical solution starts from the rheological constitutive relationship and utilizes the yield stress characteristics to provide vertical support force to the tunnel segments immediately after the grout is filled. It can suppress segment buoyancy without waiting for cement hydration and solidification, filling the anti-buoyancy gap in the traditional initial setting time range and realizing an active, instantaneous response anti-buoyancy mechanism for tunnel segments.

[0008] Optionally, the apparent viscosity of the slurry decreases by no less than 50% during the process of increasing the shear rate D from 0.1 s⁻¹ to 100 s⁻¹, exhibiting shear-thinning characteristics; when the slurry is tested in the linear viscoelastic region with an oscillation frequency of 1 Hz and a strain amplitude of 0.1%, the storage modulus G1 is greater than the loss modulus G2; and the compressive strength of the slurry after 28 days of curing is no less than 2.5 MPa.

[0009] By adopting the above technical solutions, the shear thinning characteristics, gel transition criteria, and long-term strength indicators of the grout were further defined. The apparent viscosity of the grout decreased by more than 50% as the shear rate increased from 0.1 s⁻¹ to 100 s⁻¹, indicating a significant reduction in viscosity during the high-shear pumping stage. This demonstrates good pumpability, enabling successful long-distance transport and full filling of the shield tail voids via the tunnel boring machine's built-in grouting pipeline. Under low-frequency, small-amplitude oscillation test conditions in a static state, the storage modulus was greater than the loss modulus. From a rheological dynamic mechanical analysis perspective, this confirms the formation of a stable three-dimensional gel network support structure within the grout. This criterion is objective and measurable, providing a quantitative basis for construction quality control and on-site effect verification. Furthermore, the compressive strength of the grout after 28 days of curing is not less than 2.5 MPa, ensuring stable support and water-stopping sealing performance for the tunnel structure in the long term.

[0010] This application provides a method for preparing synchronous grouting slurry for tunnel boring machines, carried out at an ambient temperature of 20±5℃, including the following steps: M1. Ingredients: Weigh out water, sodium bentonite, ordinary silicate cement and sodium carboxymethyl cellulose according to the above weight parts; M2, Bentonite prehydration: Add the sodium-based bentonite weighed in step M1 to the water weighed in step M1, and stir at a speed of 400 to 600 r / min for no less than 30 min to obtain a uniform bentonite suspension. M3, Conditioner compounding: Add sodium carboxymethyl cellulose weighed in step M1 to the bentonite suspension obtained in step M2, and shear and stir at a speed of not less than 800 r / min for not less than 10 min, so that the sodium carboxymethyl cellulose and the sodium-based bentonite form a three-dimensional gel network structure to obtain a gel-based slurry. M4. Cement compounding: Add the silicate cement weighed in step M1 to the gel-based slurry obtained in step M3 by continuous sprinkling. The addition time shall not be less than 2 minutes, and the mixture shall be continuously stirred at a speed of 600 to 800 r / min for not less than 5 minutes to obtain a shield synchronous grouting slurry with uniform composition.

[0011] By adopting the above technical solution, a method specifically designed for preparing grouting slurry with the desired yield stress is provided. This method involves progressively compounding the components in a specific order. First, sodium-based bentonite undergoes prolonged, low-speed pre-hydration, allowing the bentonite sheets to fully peel off and form a uniform suspension, establishing the initial gel framework. Then, sodium carboxymethyl cellulose is added under high-speed shear conditions. The high shear rate ensures the polymer chains fully extend and form a dense three-dimensional gel network structure with the bentonite sheets through hydrogen bonding and ion bridging, resulting in a gel-based slurry. Finally, cement is continuously added under moderate shear stirring, ensuring uniform dispersion without excessively damaging the established gel network. This reverse batching sequence—building the gel first and then adding cement—overcomes the destructive effect of calcium ions generated during cement hydration on the gel structure in conventional mixing methods. This is a key technological innovation for preparing slurries with the target yield stress and shear thinning characteristics.

[0012] Optionally, the shear rate D of the slurry during the high-speed shear mixing process in step M3 shall not be less than 500 s⁻¹; after the cement is added in step M4, the prepared shield synchronous grouting slurry shall be used up within 4 hours after the cement is added, so as to avoid the damage of the three-dimensional gel network structure caused by cement hydration.

[0013] By adopting the above technical solution, the key parameters in the preparation process were further optimized. In step M3, ensuring the shear rate the slurry withstands is not less than 500 s⁻¹ is crucial to fully stimulate the physical cross-linking reaction between sodium carboxymethyl cellulose and bentonite, guaranteeing the integrity and uniformity of the gel network structure, thereby stably obtaining the required yield stress level. The slurry prepared after cement addition is limited to use within 4 hours because beyond this time window, the early hydration reaction of cement will gradually weaken the gel network through ion exchange, leading to yield stress attenuation and affecting the anti-buoyancy effect. This time limit provides an operable process control boundary for the slurry delivery and usage plan at the construction site.

[0014] This application provides a method for anti-buoyancy synchronous grouting of tunnel segments, using the aforementioned synchronous grouting slurry for tunnel boring machines, and including the following steps: S1. Slurry pumping: The slurry is pumped by a screw pump or piston pump through the synchronous grouting system of the tunnel boring machine. During the pumping process, the shear rate D of the slurry satisfies D > τ0 / μ. Under the shearing action, the viscosity of the slurry decreases and it becomes fluid. It is then transported to the tail of the shield through the grouting pipeline. S2. Synchronous grouting: While the shield tunneling and segment assembly are underway, the grout pumped in step S1 is injected into the annular gap between the segment and the surrounding soil through the grouting hole at the shield tail, so that the grout fills the annular gap at the shield tail. S3, Yield Support: The shear rate D of the slurry injected into the annular gap of the shield tail is reduced to a state where the shear stress generated by the slurry itself is less than the yield stress τ0. The slurry maintains a three-dimensional gel network structure and does not undergo macroscopic flow, thus supporting the segments and ensuring that the floating amount Δh of the segments is not greater than 5 mm.

[0015] By adopting the above technical solution, the grout with yield stress is applied to the synchronous grouting construction process of shield tunneling. During the pumping stage, a shearing action is applied to the grout using a screw pump or piston pump, ensuring that the shear rate of the grout is always greater than the ratio of yield stress to plastic viscosity. The grout exhibits significant shear thinning behavior, with a substantial reduction in viscosity, enabling it to be pumped smoothly and completely fill the irregular annular void at the shield tail. After grouting is completed, the grout flow essentially stops, and the shear rate rapidly drops to near zero. At this point, the yield stress within the grout is activated and restored, maintaining a stable three-dimensional gel network structure inside the grout. No macroscopic flow occurs, forming a support structure for the tunnel segments and the surrounding soil. This support directly controls the uplift of the tunnel segments to within 5 mm, representing an order-of-magnitude improvement compared to the uplift of tens of millimeters often seen under traditional Newtonian fluid grout conditions.

[0016] Optionally, the design value of the yield stress τ0 of the slurry satisfies the following formula: τ0 ≥ k·ρ·g·e, where k is the safety factor, which is 1.5 to 2.0; ρ is the density of the slurry, in kg / m³; g is the gravitational acceleration, which is 9.8 m / s²; and e is the thickness of the annular gap at the tail of the shield, in m.

[0017] By adopting the above technical solution, an explicit calculation formula for the design value of the grout yield stress is given. This formula directly establishes the relationship between the yield stress and the minimum support force required to resist buoyancy, using the safety factor, grout density, gravitational acceleration, and shield tail void thickness as variables. The formula has clear dimensions and a well-defined physical meaning. Using this formula, engineers can quickly calculate the target value of the required grout yield stress based on parameters such as tunnel depth, geological conditions, segment outer diameter, and actual shield tail void thickness. This guides the grout mix design, avoiding the blindness of traditional experience-based mix proportions. It should be noted that the above formula is based on the principle of static equilibrium, requiring that the grout yield stress be able to at least balance the pressure generated by the grout's own weight at the bottom of the shield tail void, thus ensuring that the grout will not flow under gravity in a static state, providing effective support for the segments. The physical meaning of this formula is: the ultimate shear capacity provided by the grout, i.e., the yield stress, must be at least equal to the hydrostatic pressure generated by the grout column at the bottom of the shield tail void multiplied by the safety factor, to balance buoyancy.

[0018] Optionally, the screw pump or piston pump mentioned in step S1 is started using a smooth pressure increase method, and the starting outlet pressure P0 satisfies the following formula: P0 ≥ β·4L·τ0 / d, where β is the pipeline loss correction coefficient, which takes a value of 1.2 to 1.5; L is the total length of the grouting pipeline, in meters; d is the inner diameter of the grouting pipeline, in meters; and τ0 is the yield stress of the grout, in Pa.

[0019] By adopting the above technical solution, a calculation model for the pump outlet pressure is presented to address the starting characteristics of non-Newtonian grout with yield stress in pipelines. The correction factor considers local resistance losses from bends, diameter changes, and valves in the actual pipeline system. This formula ensures a smooth pressurization of the pumping system and successful breakthrough of the grout's yield stress barrier, avoiding construction risks such as pipe blockage due to insufficient starting pressure or segment disturbance caused by sudden pressure increases. This guarantees reliable pumping of high-yield-stress grout in existing shield tunneling grouting equipment, allowing this technical solution to be implemented on existing equipment without major modifications to the shield machine.

[0020] Optionally, the grouting holes at the shield tail in step S2 include upper grouting holes and lower grouting holes. The upper grouting holes are arranged in the circumferential region above the horizontal center line of the segment ring, and the lower grouting holes are arranged in the circumferential region below the horizontal center line of the segment ring. The number of upper grouting holes and lower grouting holes is 2 to 4 each. During grouting, the ratio of the grouting volume per unit time of the lower grouting hole to the grouting volume per unit time of the upper grouting hole is 1.5:1 to 3:1. Furthermore, the total amount of grouting in the synchronous grouting in step S2 is controlled according to 1.1 to 1.3 times the theoretical volume of the annular gap at the shield tail. The synchronous grouting completes single-ring grouting before the segment exits the shield tail.

[0021] By adopting the above technical solution, the layout of grouting holes and the grout volume distribution strategy during synchronous grouting were optimized. Grouting holes were set at the upper and lower parts of the segment ring, and the grout volume per unit time in the lower part was greater than that in the upper part. The increased grout volume in the lower part generated a reverse pressure difference, which actively counteracted the upward resultant force caused by the higher grout pressure in the lower part due to gravity, further reducing the net upward thrust acting on the segment. At the same time, the total grout volume was controlled at 1.1 to 1.3 times the theoretical volume of the shield tail void, and single-ring grouting was completed before the segment completely exited the shield tail. This ensured full filling to prevent voids and avoided excessive grouting that could cause formation fracturing or large-scale grout loss.

[0022] Optionally, the method further includes step S4, float monitoring and feedback adjustment: an attitude monitoring sensor is installed on the segment ring that has detached from the shield tail, the attitude monitoring sensor being one or more of a laser target, inclinometer, or displacement gauge, to monitor the segment float Δh in real time; when Δh exceeds 5 mm, at least one of the following adjustment measures is performed on the subsequent tunneling ring: (a) the weight of sodium carboxymethyl cellulose is adjusted upward within the range of 0.13 to 0.17 parts by weight, so that the yield stress τ0 is increased by 50 to 200 Pa; (b) the ratio of the grouting volume per unit time of the lower grouting hole to the upper grouting hole is adjusted upward within the range of 1.5:1 to 3:1; (c) secondary reinforcement grouting is performed on the segment ring that has detached from the shield tail and whose float Δh exceeds 5 mm.

[0023] By adopting the above technical solution, a closed-loop control system based on real-time monitoring data was constructed. This dynamic adjustment mechanism can quickly correct construction parameters according to real-time working condition feedback, ensuring continuous anti-buoyancy effect under different geological sections and tunneling conditions, and keeping the segment floatation within the allowable range. This technical solution upgrades the traditional passive remedial construction method to an intelligent construction method of active prediction-monitoring-feedback adjustment, significantly improving the forming quality and construction reliability of shield tunnels.

[0024] Optionally, based on the soil and water conditions of the strata traversed by the shield tunnel, the yield stress τ0 of the grout and the total grouting volume in step S2 are designed differently: when the traversed strata are water-rich sand layers or high-water-pressure soft soil layers, the yield stress τ0 of the grout is taken as 700 to 800 Pa, and the total grouting volume of the synchronous grouting is controlled at 1.2 to 1.3 times the theoretical volume of the annular void at the shield tail; when the traversed strata are general clay layers or weakly permeable strata, the yield stress τ0 of the grout is taken as 500 to 650 Pa, and the total grouting volume of the synchronous grouting is controlled at 1.1 to 1.2 times the theoretical volume of the annular void at the shield tail; when the traversed strata are karst development areas or fractured rock formations, the yield stress τ0 of the grout is taken as 650 to 750 Pa. Pa, the total amount of grouting in the synchronous grouting is controlled at 1.2 to 1.3 times the theoretical volume of the annular gap at the shield tail, and secondary grouting is carried out in the range of 3 to 5 ring segments behind the shield tail after step S2.

[0025] By adopting the above technical solution, a differentiated design strategy for grout parameters based on the characteristics of soil and water in shield tunnel engineering is provided, addressing the complex and variable geological conditions in such projects. This differentiated design scheme solves the dilemma of over-design or anti-buoyancy failure caused by traditional grouting processes using a single parameter to address all geological formations. This allows the invention to achieve stable anti-buoyancy effects under different geological conditions, significantly improving the engineering adaptability and economy of the technical solution.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. The shield synchronous grouting slurry provided in this application introduces non-Newtonian fluid characteristics with yield stress, which changes the mechanical mechanism of traditional slurry transmitting hydrostatic pressure in the shield tail gap from the rheological root. This allows the slurry to form a stable three-dimensional gel network structure in a static state and provide support. It reduces the floating amount of the tunnel segments during shield construction from tens to hundreds of millimeters under traditional Newtonian fluid slurry to less than 5 millimeters. This fundamentally solves the long-standing quality problems of shield tunnel engineering, such as segment misalignment, bolt deformation, concrete damage and joint leakage. 2. The slurry preparation method provided in this application adopts a reverse batching sequence of first establishing the gel skeleton and then adding cement, which overcomes the destructive effect of cement hydration on the gel network in conventional mixing methods. It can stably produce the target slurry with a yield stress of 500 to 800 Pa, providing a key process guarantee for the industrial implementation of the anti-buoyancy technology solution described in this invention. 3. The construction method provided in this application, through the coordinated use of multiple technical means such as yield stress design formula, pump start-up pressure formula, differentiated grouting of upper and lower grouting holes and real-time monitoring feedback adjustment, has constructed a complete closed-loop control system from grout design to construction execution and effect verification. This upgrades the shield tunnel synchronous grouting process from experience-based to quantitative science, and can be promoted and implemented without major modifications to existing shield tunneling machines. 4. This application adopts a differentiated design strategy for grout parameters based on strata and soil conditions, enabling the technical solution to adapt to various complex geological conditions such as water-rich sand layers, general clay layers, and karst development areas, significantly improving the engineering adaptability and economy, and possessing broad engineering promotion value. Attached Figure Description

[0027] Figure 1 This is a construction flowchart of the anti-buoyancy synchronous grouting method for shield tunnel segments in the embodiments of this application; Figure 2 This is a schematic diagram of the front arrangement of the grouting holes at the tail of the segment ring shield in an embodiment of this application; Figure 3 This is a schematic diagram of the arrangement of the annular gap and grouting holes at the shield tail of this application; Figure 4 This is a flowchart of the segment floating monitoring and feedback adjustment control in the embodiments of this application.

[0028] In the diagram: 1. Segment; 2. Annular gap at the tail of the shield; 3. Upper grouting hole; 4. Lower grouting hole; 5. Attitude monitoring sensor; 6. Horizontal centerline; 7. Grout. Detailed Implementation

[0029] The technical solutions of various embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Example 1

[0030] This application discloses a shield tunneling synchronous grouting slurry, which is mainly composed of four components: water, sodium bentonite, P.O42.5 ordinary Portland cement, and sodium carboxymethyl cellulose, blended in specific weight parts. The weight parts range of each component are: water 100 parts; sodium bentonite 7 to 9 parts; P.O42.5 ordinary Portland cement 28 to 32 parts; sodium carboxymethyl cellulose 0.13 to 0.17 parts.

[0031] In this embodiment, the sodium-based bentonite used is an industrial-grade sodium-based bentonite product with a montmorillonite content of not less than 75%, which can fully peel off in water to form a uniform and stable suspension. The PO 42.5 ordinary silicate cement used complies with the relevant provisions of GB 175-2007, providing the later strength and durability of the slurry. The sodium carboxymethyl cellulose used is an industrial-grade product with a viscosity grade of 800 to 1200 mPa·s, which acts as a rheology modifier. Through the hydrogen bonding and ion bridging between the carboxyl groups on its molecular chain and the bentonite sheets, it synergistically forms a three-dimensional gel network structure with bentonite.

[0032] The rheological properties of the prepared slurry conform to the Bingham plastic fluid model, meaning that when the applied shear stress is less than the yield stress τ0, the slurry does not undergo macroscopic flow and exhibits a supported state similar to a solid phase. When the applied shear stress exceeds the yield stress τ0, the slurry begins to exhibit linear flow with a plastic viscosity μ, and its constitutive equation is τ = τ0 + μ·D, where τ is the shear stress in Pa; τ0 is the yield stress in Pa; μ is the plastic viscosity in Pa·s; and D is the shear rate in s⁻¹. This constitutive relationship is fundamentally different from the constitutive relationship τ = μ·D of traditional Newtonian fluid slurries, as follows: Figure 3 As shown, a Newtonian fluid behaves as a straight line passing through the origin in the shear stress-shear rate coordinate system, while the Bingham plastic fluid described in this application has a yield stress intercept τ0 on the vertical axis.

[0033] The rheological parameters of the prepared slurry were tested under the following conditions: A slurry sample that had been left to stand for 5 minutes after preparation was placed in a constant temperature environment controlled at 20±2℃, and tested using a rheometer in shear rate scanning mode. The initial yield stress τ0 of the slurry obtained from the tests was 500 to 800 Pa, and the plastic viscosity μ was 0.5 to 1.0 Pa·s.

[0034] Furthermore, the shear thinning characteristics test results of the prepared slurry showed that when the shear rate D increased from 0.1 s⁻¹ to 100 s⁻¹, the apparent viscosity of the slurry decreased by no less than 50%. When the slurry underwent dynamic oscillation testing in the linear viscoelastic region with an oscillation frequency of 1 Hz and a strain amplitude of 0.1%, the storage modulus G1 was greater than the loss modulus G2, indicating that the slurry formed a stable elastic-dominated gel structure under static conditions; the compressive strength of the slurry after 28 days of curing was no less than 2.5 MPa.

[0035] This embodiment also provides three specific ratio examples: Example 1: 100 kg water, 8 kg sodium bentonite, 30 kg PO 42.5 cement, 0.15 kg sodium carboxymethyl cellulose. The measured τ0 of the prepared slurry was 650 Pa, the measured μ was 0.8 Pa·s, and the measured 28-day compressive strength was 2.8 MPa. Example 2: 100 kg water, 7 kg sodium bentonite, 28 kg PO 42.5 cement, 0.13 kg sodium carboxymethyl cellulose. The measured τ0 of the prepared slurry was 520 Pa, the measured μ was 0.55 Pa·s, and the measured 28-day compressive strength was 2.6 MPa. Example 3: 100 kg water, 9 kg sodium bentonite, 32 kg PO 42.5 cement, 0.17 kg sodium carboxymethyl cellulose. The measured τ0 of the prepared slurry was 780 Pa, the measured μ was 0.95 Pa·s, and the measured 28-day compressive strength was 3.1 MPa.

[0036] To compare and verify the beneficial effects of the slurry of this application, a comparative slurry was also prepared in this embodiment.

[0037] Comparative Example 1: Traditional cement-bentonite slurry, 100 kg water, 8 kg bentonite, 30 kg cement, without the addition of sodium carboxymethyl cellulose. The measured τ0 was only 80 Pa, far lower than that of the slurry described in this application; Comparative Example 2: 0.15 kg of sodium carboxymethyl cellulose was added to the mixture from Comparative Example 1, but the conventional preparation method of mixing all components simultaneously was used. The measured τ0 was 320 Pa, which is still significantly lower than the yield stress of the slurry obtained by the specific feeding sequence used in this application.

[0038] The implementation principle of this embodiment is as follows: By compounding sodium-based bentonite, cement, and sodium carboxymethyl cellulose in a specific ratio, the grout forms a stable three-dimensional gel network structure in a static state due to the physical cross-linking between the sodium carboxymethyl cellulose molecular chains and bentonite layers. This exhibits the rheological properties of a Bingham plastic fluid with a defined yield stress τ0. When the shear stress on the grout is less than τ0, the grout does not flow, providing support for the tunnel segment 3. When the shear stress exceeds τ0, the gel network is broken, and the grout exhibits shear-thinning characteristics, facilitating pumping. This grout overcomes the mechanical defects of traditional Newtonian fluid grouts, which cause severe floating of the tunnel segment due to the transmission of complete hydrostatic pressure, thus fundamentally suppressing the floating tendency of the tunnel segment 3. Example 2

[0039] This application discloses a method for preparing the shield tunneling synchronous grouting slurry described in Embodiment 1. The preparation method is carried out at an ambient temperature of 20±5℃ and includes the following steps: Step M1, Ingredient Preparation: Weigh water, sodium bentonite, PO 42.5 ordinary Portland cement, and sodium carboxymethyl cellulose according to the weight proportions described in Example 1. During project implementation, the ingredients are precisely measured using an electronic weighing device with a weighing accuracy of not less than 0.1%.

[0040] Step M2, Bentonite Pre-hydration: Gradually add the sodium-based bentonite weighed in Step M1 to the water weighed in Step M1. Start the slurry mixer and stir continuously at a speed of 400 to 600 r / min for no less than 30 minutes to fully peel off and evenly disperse the lamellar structure of the sodium-based bentonite in the water, forming a uniform and stable bentonite suspension. This step is the foundation of the entire preparation process, and the degree of pre-hydration of bentonite directly affects the yield stress level of the final slurry. In engineering implementation, the adequacy of pre-hydration can be judged by observing the uniformity of the suspension, the presence of unhydrated bentonite clumps, and whether rapid stratification occurs after standing.

[0041] Step M3, Conditioner Compounding: While the bentonite suspension obtained in step M2 is continuously stirred, the sodium carboxymethyl cellulose weighed in step M1 is slowly added to the suspension. The stirring speed is increased to no less than 800 r / min, and stirring is continued under this high-speed shear stirring condition for no less than 10 min. During this process, the shear rate D of the slurry is no less than 500 s⁻¹. High-speed shear stirring allows the polymer chains of sodium carboxymethyl cellulose to fully unfold in the slurry, and form a dense three-dimensional gel network structure with the pre-hydrated bentonite sheets through various physical interactions such as hydrogen bonding and ion bridging, resulting in a gel-based slurry with obvious gel-state characteristics.

[0042] Step M4, Cement Mixing: Adjust the mixer speed to 600 to 800 r / min. Slowly add the PO 42.5 ordinary Portland cement weighed in step M1 to the gel-based slurry obtained in step M3 by continuous sprinkling. The addition time should be controlled to be no less than 2 minutes to avoid cement clumping or accumulation on the slurry surface. After all the cement has been added, continue stirring at a speed of 600 to 800 r / min for no less than 5 minutes to obtain a uniformly composed shield tunneling synchronous grouting slurry.

[0043] The prepared grout should be used within 4 hours of adding cement. This is because the early hydration reaction of cement in the grout releases calcium ions. These calcium ions gradually weaken the gel network structure between sodium carboxymethyl cellulose and bentonite through ion exchange, causing the grout yield stress to decrease over time and affecting the anti-buoyancy effect. Experimental test data in this embodiment show that the τ0 of the grout decreases by only about 5% in the first hour after adding cement and by about 15% in the fourth hour, still meeting the anti-buoyancy requirements; however, after 8 hours, the τ0 decreases by more than 35%, making it unsuitable for synchronous grouting of shield tunnels.

[0044] To verify the advantages of this preparation method over conventional methods, a comparative experiment was conducted in this embodiment: Comparative Experiment 1: The slurry prepared using the sequence described in this embodiment achieved an initial τ0 of 650 Pa; Comparative Experiment 2: When all components were added to water and stirred at the same time, with other parameters remaining the same, the initial τ0 of the resulting slurry was only 320 Pa. Comparative Experiment 3: Cement was first added to prepare cement slurry, and then bentonite and sodium carboxymethyl cellulose were added. The initial τ0 of the slurry was only 180 Pa.

[0045] The results of the comparative experiments above demonstrate that the reverse batching sequence described in this embodiment—pre-hydrating bentonite, then compounding with sodium carboxymethyl cellulose to form a gel-based slurry, and finally adding cement—plays a decisive role in obtaining a slurry with high yield stress.

[0046] The implementation principle of this embodiment is as follows: By strictly controlling the order of adding each component and the stirring conditions, the lamellar structure of sodium-based bentonite is fully exfoliated under low-speed stirring to form a stable suspension. Then, sodium carboxymethyl cellulose is added under high shear to form a dense three-dimensional gel network structure. Finally, cement is added under moderate shear, avoiding premature cement hydration that could interfere with the gel structure. This preparation sequence ensures that the gel network is stably formed before cement hydration, and the cement particles are uniformly encapsulated in the gel network without damaging its structure, thereby stably obtaining a slurry product with a target yield stress τ0 of 500 to 800 Pa. Example 3

[0047] Reference Figures 1 to 4 This application discloses a method for anti-buoyancy synchronous grouting of tunnel segments. The method uses the synchronous grouting slurry for tunnel boring machines (TBMs) as described in Example 1, and is prepared by the method described in Example 2. The method includes the following steps: Step S1, Slurry Pumping: The slurry is pumped using the synchronous grouting system of the tunnel boring machine. The synchronous grouting system includes a grouting pump and grouting pipelines. The grouting pump is a screw pump or a piston pump. During the pumping process, under the high shear action of the grouting pump, the shear rate D of the slurry satisfies the condition D > τ0 / μ. At this time, the three-dimensional gel network structure inside the slurry is partially destroyed by the shear action, exhibiting significant shear thinning characteristics. The viscosity decreases significantly, and the slurry transforms into a flowable fluid state, which is then smoothly transported to the tail of the shield through the grouting pipelines.

[0048] The prepared grouting pump is started using a steady pressure increase method. The starting outlet pressure P0 satisfies the following formula: P0 ≥ β·4L·τ0 / d, where β is the pipeline loss correction coefficient, ranging from 1.2 to 1.5; L is the total length of the grouting pipeline in meters; d is the inner diameter of the grouting pipeline in meters; and τ0 is the yield stress of the grout in Pa. This formula ensures that the starting pressure is sufficient to overcome the initial yield stress barrier of the grout, avoiding pipe blockage accidents due to insufficient pressure.

[0049] Taking a specific engineering project as an example: the total length of the grouting pipeline is L = 60 m, the inner diameter of the pipeline is d = 0.08 m, the grout used is τ0 = 650 Pa, and the correction factor β is taken as 1.3. Then the starting outlet pressure P0 ≥ 1.3 × 4 × 60 × 650 / 0.08 = 2.53 MPa. The actual starting pressure of the project was set to 2.8 MPa, and the grout started smoothly and maintained stable pumping.

[0050] Step S2, Synchronous Grouting: During the simultaneous tunneling and segment 1 assembly of the tunnel boring machine, the grout pumped in step S1 is injected into the annular gap 2 at the tail of the shield between segment 1 and the surrounding soil through the grouting hole at the tail of the shield, so that the grout 7 fills the entire annular gap 2 at the tail of the shield.

[0051] The tail grouting holes include upper grouting holes 3 and lower grouting holes 4. The upper grouting holes 3 are located in the circumferential region above the horizontal centerline 6 of the segment 1, and the lower grouting holes 4 are located in the circumferential region below the horizontal centerline 6 of the segment 1. The number of upper grouting holes 3 and lower grouting holes 4 is 2 to 4, preferably 2 in this embodiment. During grouting, the ratio of the grouting volume per unit time of the lower grouting hole 4 to that of the upper grouting hole 3 is 1.5:1 to 3:1, preferably 2:1 in this embodiment, meaning the grouting volume of the lower grouting hole 4 is twice that of the upper grouting hole 3. This differentiated grouting generates a reverse pressure difference from bottom to top, actively counteracting the upward force caused by the weight of the grout, further reducing the net upward thrust on the segment 3.

[0052] The total grouting volume in step S2 is controlled to be 1.1 to 1.3 times the theoretical volume of the annular gap 2 at the shield tail. The theoretical volume is calculated using the formula V = π·(R0² - r²)·L1, where R0 is the outer radius of the segment, r is the inner radius of the segment, and L1 is the width of a single-ring segment. The total grouting volume is slightly larger than the theoretical volume to compensate for the slight seepage loss of grout in the stratum and to ensure that the annular gap 4 at the shield tail is fully filled. Synchronous grouting is carried out simultaneously with shield tunneling and must be completed before segment 1 completely exits the shield tail to ensure that segment 1 is immediately enveloped and supported by grout 6 the moment it leaves the rigid constraint of the shield tail 2.

[0053] Step S3, Yield Support: The grout 7 injected into the annular gap 2 at the shield tail loses the high shear force experienced during pumping, and its shear rate D rapidly decreases until the shear stress generated by the grout itself is less than the yield stress τ0. At this point, the three-dimensional gel network structure inside the grout quickly recovers, and the grout 7 does not undergo macroscopic flow, thus providing support for the segment 1 and the surrounding soil.

[0054] Traditional Newtonian fluid slurry exists as a complete liquid column in the annular gap 2 of the shield tail. The bottom of segment 1 bears the complete hydrostatic pressure generated by the slurry's own weight, resulting in a significant buoyancy force F. However, the non-Newtonian fluid slurry 7 described in this application, due to the supporting effect of the yield stress τ0, has its slurry pressure along the circumferential direction of the annular gap 4 of the shield tail dispersed and offset by the yield stress, greatly reducing the net buoyancy force acting on the bottom of segment 1. The pressure distribution of traditional slurry in the annular gap of the shield tail exhibits an unbalanced distribution with the bottom pressure being much greater than the top pressure, while the pressure distribution of the slurry in this application shows a more uniform distribution characteristic due to the attenuation effect of the yield stress.

[0055] According to actual engineering application monitoring, the floating amount Δh of segment 1 constructed using the method described in this embodiment is no more than 5mm, which is more than 80% higher than the floating amount of segment 1 under traditional Newtonian fluid slurry, which often reaches 15 to 20 mm or even higher.

[0056] The specific design value of the yield stress τ0 of grout 6 is determined according to the following formula: τ0 ≥ k·ρ·g·e, where k is the safety factor, ranging from 1.5 to 2.0; ρ is the grout density, approximately 1700 to 1900 kg / m³; g is the gravitational acceleration, taken as 9.8 m / s²; and e is the thickness of the annular gap 4 at the shield tail, in meters. Taking a certain shield tunneling project as an example: grout density ρ = 1800 kg / m³, shield tail annular gap thickness e = 0.1 m, safety factor k is taken as 1.8, then τ0 ≥ 1.8 × 1800 × 9.8 × 0.1 = 3175 Pa. However, in actual engineering, due to the viscous flow characteristics of the grout itself, the actual area of ​​shear stress is much smaller than the projected area of ​​the entire shield tail gap. Therefore, after conversion and engineering correction, a target value of 650 Pa for the grout is sufficient to meet the anti-buoyancy requirements.

[0057] Furthermore, the construction method also includes step S4, upward floating monitoring and feedback adjustment. An attitude monitoring sensor 9 is installed on the ring of the segment 3 that has exited the tail shield 2. The attitude monitoring sensor 9 is selected from one or more of a laser target, inclinometer, or displacement gauge. In this embodiment, a combination of a laser target and an inclinometer is preferred. The laser target is arranged on the top of the segment 3 to monitor the vertical upward floating amount Δh, and the inclinometer is arranged on the side of the segment 3 to monitor the rotational attitude of the segment 3. The attitude monitoring sensor 9 transmits the monitoring data to the control system of the tunnel boring machine 1 in real time.

[0058] When the detected segment uplift Δh exceeds the warning value of 5 mm, the control system shall implement at least one of the following adjustment measures for the subsequent tunneling ring: Adjustment measure (a): Adjust the weight of sodium carboxymethyl cellulose upward within the range of 0.13 to 0.17 parts by weight as described in Example 1. For example, if the original ratio of sodium carboxymethyl cellulose is 0.15 parts, it can be adjusted to 0.17 parts; after adjustment, the measured slurry τ0 increases from 650 Pa to 760 Pa, an increase of about 110 Pa, which falls within the range of 50 to 200 Pa increase.

[0059] Adjustment measure (b): Adjust the ratio of the grouting volume per unit time of the lower grouting hole 4 to the upper grouting hole 3 upward within the range of 1.5:1 to 3:1. For example, if the original ratio is 2:1, it can be adjusted to 2.5:1 or 3:1 to further enhance the anti-buoyancy effect of the reverse pressure difference on the segment 3.

[0060] Adjustment measure (c): Secondary reinforcement grouting shall be performed on the segment 1 ring that has detached from the shield tail 2 and whose upward float Δh exceeds 5 mm; the secondary reinforcement grouting shall be carried out through the grouting holes reserved in the segment, and the grout used shall still be the high yield stress grout described in Example 1, and the grouting pressure shall be controlled between 0.3 and 0.5 MPa.

[0061] The above adjustment measures can be implemented individually or in combination. In a feedback adjustment case of an actual project, the initial monitoring showed that the floating amount of the 50th ring segment reached 6.2 mm, exceeding the warning value. The engineer adopted a combination of adjustment measures (a) + (b), adjusting the sodium carboxymethyl cellulose content from 0.15 parts to 0.17 parts and the ratio of the upper and lower grouting holes from 2:1 to 2.5:1. After the adjustment, the floating amount of the 55th ring and subsequent segments was stably controlled within 3 mm.

[0062] Furthermore, this construction method differentiates the design of the yield stress τ0 of grout 7 and the total amount of grouting in step S2 based on the soil and water conditions of the strata being traversed: When the strata being traversed are water-rich sand layers or soft soil layers with high water pressure, due to the high groundwater pressure and the ease with which the strata are disturbed, the yield stress τ0 of the grout 6 is taken as 700 to 800 Pa, and the total amount of grout injected simultaneously is controlled at 1.2 to 1.3 times the theoretical volume of the annular void 4 at the shield tail.

[0063] When the strata being traversed are general clay layers or weakly permeable strata, the strata conditions are relatively stable. The yield stress τ0 of grout 7 is taken as 500 to 650 Pa. The total amount of grout injected simultaneously is controlled at 1.1 to 1.2 times the theoretical volume of the annular void 2 at the shield tail, which can reduce the amount of material used and the pumping pressure.

[0064] When the strata being traversed are karst development zones or fractured rock formations, there is a risk of grout escaping into caves or fissures. The yield stress τ0 of grout 7 is taken as 650 to 750 Pa. The total amount of grout injected simultaneously is controlled at 1.2 to 1.3 times the theoretical volume of the annular void 2 at the shield tail. After step S2, secondary grouting is carried out in the range of 3 to 5 ring segments 1 behind the shield tail to further seal any possible grout loss channels.

[0065] Taking a subway shield tunnel project as an example, the tunnel is 20 m deep, with a high groundwater level and a water-rich sandy stratum. Based on the aforementioned differentiated design principles, the target value for the grout τ0 was set at 750 Pa, and the total grouting volume was controlled at 1.25 times the theoretical volume of the annular void at the shield tail. During construction, the maximum segment uplift was monitored at 3.2 mm, far less than the control target of 5 mm and also far below the 50 mm limit specified in the standards. Furthermore, no quality problems such as segment misalignment, bolt deformation, concrete cracking, or water leakage occurred, indicating excellent tunnel forming quality.

[0066] The implementation principle of this embodiment is as follows: By combining the non-Newtonian grout with yield stress described in this application with differentiated construction technology, the pumpability and filling properties are ensured during the grout pumping stage using shear thinning characteristics, and the instantaneous support for the tunnel segments is formed during the grout static stage using yield stress characteristics. This eliminates the hydrostatic pressure transmission mechanism that causes tunnel segments to float from a mechanical perspective. Simultaneously, through the coordinated implementation of multiple measures such as parameter differentiation design based on geological conditions, asymmetrical grouting of upper and lower grouting holes, and real-time monitoring and feedback adjustment, precise and proactive control of tunnel segment floatation is achieved. This technical solution can adapt to various complex geological conditions such as water-rich sand layers, general clay layers, and karst development areas, and has wide engineering applicability.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of this application.

Claims

1. A shield tunneling synchronous grouting slurry, characterized in that, The slurry is mainly composed of the following components in parts by weight: Water: 100 parts; Sodium-based bentonite: 7-9 parts; Silicate cement: 28-32 parts; Sodium carboxymethyl cellulose: 0.13~0.17 parts; The rheological properties of the slurry conform to the Bingham plastic fluid model, and its constitutive equation is: τ = τ0 + μ·D In the formula, τ is the shear stress in Pa; τ0 is the yield stress in Pa; μ is the plastic viscosity in Pa·s; and D is the shear rate in s⁻¹. The initial yield stress τ0 of the slurry, measured by a rotational viscometer in shear rate scanning mode at 20±2℃ after standing for 5 minutes, was 500~800 Pa, and the plastic viscosity μ was 0.5~1.0 Pa·s.

2. The shield tunneling synchronous grouting slurry according to claim 1, characterized in that, The slurry exhibits shear-thinning characteristics, with its apparent viscosity decreasing by at least 50% as the shear rate D increases from 0.1 s⁻¹ to 100 s⁻¹. When tested in the linear viscoelastic region with an oscillation frequency of 1 Hz and a strain amplitude of 0.1%, the storage modulus G1 is greater than the loss modulus G2. The slurry's compressive strength after 28 days of curing is not less than 2.5 MPa.

3. The method for preparing the shield tunneling synchronous grouting slurry according to claim 1 or 2, characterized in that, The procedure is carried out at an ambient temperature of 20±5℃ and includes the following steps: M1, Ingredients: Weigh water, sodium bentonite, silicate cement and sodium carboxymethyl cellulose according to the weight parts of claim 1; M2, Bentonite prehydration: Add the sodium-based bentonite weighed in step M1 to the water weighed in step M1, and stir at a speed of 400~600 r / min for no less than 30 min to obtain a uniform bentonite suspension. M3, Conditioner compounding: Add sodium carboxymethyl cellulose weighed in step M1 to the bentonite suspension obtained in step M2, and shear and stir at a speed of not less than 800 r / min for not less than 10 min, so that the sodium carboxymethyl cellulose and the sodium-based bentonite form a three-dimensional gel network structure to obtain a gel-based slurry. M4. Cement compounding: Add the silicate cement weighed in step M1 to the gel-based slurry obtained in step M3 by continuous sprinkling. The addition time shall not be less than 2 minutes, and the mixture shall be continuously stirred at a speed of 600~800 r / min for not less than 5 minutes to obtain a shield synchronous grouting slurry with uniform composition.

4. The method for preparing the shield tunneling synchronous grouting slurry according to claim 3, characterized in that, In step M3, the shear rate D of the slurry during the high-speed shear mixing process shall not be less than 500 s⁻¹; after the cement is added in step M4, the prepared shield synchronous grouting slurry shall be used up within 4 hours after the cement is added, so as to avoid the damage of the three-dimensional gel network structure caused by cement hydration.

5. A method for synchronous grouting to prevent buoyancy of tunnel segments, characterized in that, The method uses the shield tunneling synchronous grouting slurry as described in claim 1 or 2, and includes the following steps: S1. Slurry pumping: The slurry is pumped by a screw pump or piston pump through the synchronous grouting system of the tunnel boring machine. During the pumping process, the shear rate D of the slurry satisfies D > τ0 / μ. Under the shearing action, the viscosity of the slurry decreases and it becomes fluid. It is then transported to the tail of the shield through the grouting pipeline. S2. Synchronous grouting: While the shield tunneling and segment assembly are underway, the grout pumped in step S1 is injected into the annular gap between the segment and the surrounding soil through the grouting hole at the shield tail, so that the grout fills the annular gap at the shield tail. S3, Yield Support: The shear rate D of the slurry injected into the annular gap of the shield tail is reduced to a state where the shear stress generated by the slurry itself is less than the yield stress τ0. The slurry maintains a three-dimensional gel network structure and does not undergo macroscopic flow, thus supporting the segments and ensuring that the floating amount Δh of the segments is not greater than 5 mm.

6. The method for synchronous grouting of shield tunnel segments for anti-buoyancy according to claim 5, characterized in that, The design value of the yield stress τ0 of the slurry satisfies the following formula: τ0 ≥ k·ρ·g·e, where k is the safety factor, which is 1.5~2.0; ρ is the density of the slurry, in kg / m³; g is the gravitational acceleration, which is 9.8 m / s²; and e is the thickness of the annular gap at the tail of the shield, in m.

7. The method for synchronous grouting of shield tunnel segments for anti-buoyancy according to claim 5, characterized in that, The screw pump or piston pump mentioned in step S1 is started in a stable pressure increase mode. The starting outlet pressure P0 satisfies the following formula: P0 ≥ β·4L·τ0 / d, where β is the pipeline loss correction coefficient, which takes a value of 1.2~1.5; L is the total length of the grouting pipeline, in meters. d is the inner diameter of the grouting pipe, in meters (m); τ0 is the yield stress of the grout, in Pa.

8. The method for synchronous grouting of shield tunnel segments for anti-buoyancy according to claim 5, characterized in that, The shield tail grouting holes in step S2 include upper grouting holes and lower grouting holes. The upper grouting holes are arranged in the circumferential area above the horizontal center line of the segment ring, and the lower grouting holes are arranged in the circumferential area below the horizontal center line of the segment ring. The number of upper grouting holes and lower grouting holes is 2 to 4 each. During grouting, the ratio of the grouting volume per unit time of the lower grouting holes to the grouting volume per unit time of the upper grouting holes is 1.5:1 to 3:

1. The total amount of grouting in the synchronous grouting in step S2 is controlled according to 1.1 to 1.3 times the theoretical volume of the shield tail annular gap. The synchronous grouting completes single-ring grouting before the segment exits the shield tail.

9. The method for synchronous grouting of shield tunnel segments for anti-buoyancy according to claim 8, characterized in that, The process also includes step S4, uplift monitoring and feedback adjustment: An attitude monitoring sensor is installed on the segment ring that has exited the shield tail. The attitude monitoring sensor is one or more of a laser target, inclinometer, or displacement gauge, to monitor the segment uplift amount Δh in real time. When Δh exceeds 5 mm, at least one of the following adjustment measures is implemented for the subsequent tunneling ring: (a) Adjusting the weight of sodium carboxymethyl cellulose according to claim 1 upward within the range of 0.13 to 0.17 parts by weight, thereby increasing the yield stress τ0 by 50 to 200 Pa; (b) Adjust the ratio of the grouting volume per unit time of the lower grouting hole to the upper grouting hole upward within the ratio range of 1.5:1 to 3:1 as described in claim 8; (c) Perform secondary reinforcement grouting on the segment rings that have detached from the shield tail and whose uplift Δh exceeds 5 mm.

10. The method for synchronous grouting of shield tunnel segments for anti-buoyancy according to claim 5, characterized in that, Based on the soil and water conditions of the strata traversed by the shield tunnel, the yield stress τ0 of the grout and the total grouting volume in step S2 are designed differently: When the strata being traversed are water-rich sand layers or high-water-pressure soft soil layers, the yield stress τ0 of the grout is taken as 700~800 Pa, and the total amount of grout injected during synchronous grouting is controlled according to 1.2~1.3 times the theoretical volume of the annular void at the shield tail. When the strata being traversed are general clay layers or weakly permeable strata, the yield stress τ0 of the grout is taken as 500~650 Pa, and the total amount of grout injected during synchronous grouting is controlled according to 1.1~1.2 times the theoretical volume of the annular void at the shield tail. When the strata being traversed are karst development zones or fractured rock formations, the yield stress τ0 of the grout is taken as 650~750 Pa. The total amount of grout injected during synchronous grouting is controlled at 1.2~1.3 times the theoretical volume of the annular void at the shield tail. After step S2, secondary grouting is carried out in the range of 3~5 ring segments behind the shield tail.

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