Slurry Shield Research Articles

Infiltration behaviour and microstructure of filter cake from sand-modified bentonite slurry

This study uses a setup involving a scanning electron microscopy (SEM) to examine the infiltration behaviour and mechanism of the formation of filter cake from sand-modified bentonite slurry. We began by determining whether a filter cake can be formed by using water–bentonite slurry in samples of the fine, medium, and coarse sand (Series 1). Water–bentonite–sand slurries with different mass ratios of bentonite and fine sand (B:S) were subsequently tested using the medium and coarse sand (Series 2). The results show that for Series 1, a thin filter cake (<0.1 mm after drying) with extremely low permeability (∼10−8 m/s) was formed only when the fine sand was used. The filter cake consisted of layers of dense bentonite platelets arranged perpendicular to the infiltration direction. Similar results were obtained for Series 2 between the medium and coarse sand. Within the range of 1:1.5 ≤ B:S ≤ 1:0.5, the low permeable filter cake was formed on the deposited layer of fine sand and bentonite platelet. Contrary to expectations, adding more sand (B:S = 1:2) did not complete the formation of filter cake, and instead led to continuous deposition of fine sand and bentonite platelet, which may cause inadequate effective face support during slurry shield tunneling.

Effects of seawater on the infiltration behavior of bentonite slurry into sand

As a support fluid, bentonite slurry has been extensively used in slurry shield tunneling to stabilize the tunnel face by forming a low-permeable filter cake. However, the infiltration behavior of bentonite slurry in complex conditions such as when suffering from seawater intrusion has not been fully understood. In order to investigate the infiltration behavior and filter cake formation under seawater intrusion, seawater-based bentonite slurries with increased salt content were prepared to represent different seawater intrusion severities. The rheological properties and physical stability of these slurries were evaluated. A series of infiltration column tests were conducted on two saturated sand beds with different particle sizes. Scanning electron microscope (SEM) was performed to unravel the microstructure of the filter cake. The infiltration column test results show that the low-permeable filter cake can be formed on the fine sand bed regardless of the salt content of the slurry. The salt shortened the time span of the mud spurt and made the filter cake more permeable to water. For the medium sand, the filter cake cannot be formed when the salt content exceeds 1%, because the deterioration of rheological properties of the slurry weakened its rheological blocking effect when infiltrating the sand. Based on the SEM images, it was found that the filter cake under seawater intrusion contained many well-connected inter-agglomerate channels that reduced its sealing quality. The obtained results can provide guidance and reference for the application of bentonite slurry when tunneling in a sea environment.

Reusing Fine Silty Sand Excavated from Slurry Shield Tunnels as a Sustainable Raw Material for Synchronous Grouting

Using the Nanjing Dinghuaimen Yangtze River Tunnel project as a case study, we proposed a method to reuse the excavated silty-fine sand by adjusting the proportion of the waste sand to replace the commercial sand. This would address the issue of recycling the significant amount of waste sand generated when the slurry shield passes through the silty-fine sand stratum. Moreover, we have evaluated grout indicators such as density, fluidity, consistency, bleeding rate, volumetric shrinkage, setting time, and unconfined compressive strength and examined how the particle size and distribution of the sand affected the grout’s performance. The findings show that as the replacement ratio increases, the grout’s density, fluidity, consistency, and bleeding rate gradually increase; meanwhile, the volumetric shrinkage increases initially before decreasing; the setting time decreases gradually; the unconfined compressive strength initially decreases before increasing. The key factor altering the grout’s performance when the replacement ratio is less than 50% is the weakening of the adsorption effect of fine sand particles on water due to the increase in the sand’s fineness modulus. When it is greater than 50%, the particle size of the sand tends to be distributed nonuniformly and fine particles fill the voids between larger particles, thus contributing to the changes in grout properties.

A new pressure gradient model of slurry shield pipeline system coupling with rheological properties and wall slip behaviour under sandy stratum

Pipeline transport is of uttermost importance during slurry shield tunneling, and the precise calculation of the pressure gradient of the pipeline system is the premise for the optimal design of industrial slurry pipeline system. This paper proposed a new muck slurry pressure gradient model of slurry shield pipeline system coupling with the wall slip behaviour based on the Herschel-Bulkley rheological model (H-B model) to estimate the pressure gradient of the muck slurry under sandy stratum. Effects of the sands volume fraction and average particle size on the rheological properties of the muck slurry in pipeline system were investigated to construct the H-B rheological parameters prediction models, which were coupled into the proposed pressure gradient model. Besides, the accuracy and dependability of the proposed model were validated through the engineering field tests and model tests, and the prediction results of the proposed pressure gradient model has an average error of 10.6% and 8.2% with engineering field test data and model test data respectively. The results indicated that the muck slurry is a typical thixotropic fluid. The sand volume fraction and particle size both significantly affect the rheological properties of the muck slurry, the yield stress and plastic viscosity of H-B rheological parameters increase exponentially with the sand volume fraction increasing and increase linearly with the average particle size increasing, the power law index of H-B rheological parameters increases linearly as average particle size and sands volume fraction increase. Ultimately, the research results can provide reasonable suggestions and references for the designing of pipeline system and efficient tunneling of slurry shield.

Clogging Prevention of Slurry–Earth Pressure Balance Dual-Mode Shield in Composed Strata with Medium–Coarse Sand and Argillaceous Siltstone

The slurry–earth pressure balance dual-mode shield has an earth pressure balance (EPB) and slurry shield functions. Based on a shield tunnel project of Guangzhou Metro Line 12 in China, this study investigates the clogging prevention of a slurry–earth pressure balance dual-mode shield in a composed stratum with medium–coarse sand and argillaceous siltstone. The results show that the slurry mode was not applicable to the composed stratum with medium–coarse sand and argillaceous siltstone. The excavated soil accumulated easily in the slurry chamber, causing shield clogging. The total thrust force of the shield increased significantly, the tunneling speed gradually decreased to 0, and the torque of the cutterhead increased slightly after the slurry shield was clogged. The fluctuation in the total thrust force, the cutterhead torque, and the tunneling speed also increased significantly. The EPB mode is recommended for composed strata with medium–coarse sand and argillaceous siltstone. The dispersible foam agent and water needed to be used for soil conditioning. The injection amount of foam and water was determined according to the status of the mud discharged by the screw conveyor. Water absorption can be used to characterize the water absorption capacity of particles larger than 0.15 mm. The ideal soil state was that the consistency index of the particles smaller than 0.15 mm was less than 0.5 to prevent the EPB shield from clogging. The water absorption of soil with a particle larger than 0.15 mm should be removed when calculating the consistency index.

Investigation into the flow characteristics of slurry shield pipeline system under sandy pebble stratum: Model test and CFD-DEM simulation

Investigation into the flow characteristics of slurry shield pipeline system under sandy pebble stratum: Model test and CFD-DEM simulation

Analytical study and field investigation on the effects of clogging in slurry shield tunneling

The pressurized slurry is the essential part of the slurry pressure balanced shield (SPBS) for stabilizing the working face and transporting the excavated soil. If clogging occurs in case of adverse ground conditions or equipment failure, a series of consequences will happen, such as sudden changes in slurry pressure, massive ground loss, and deformation or even collapse at tunnel workface. The present study reviewed and summarized the clogging mechanism of the slurry shield under different ground conditions. Then, based on the law of conservation of mass and Bernoulli’s Equation, an analytical approach was developed to investigate the effects of clogging on the slurry velocity and pressure along with the deformation of tunnel workface. Furthermore, a case study and field measurements were conducted to validate the analytical method. The significant findings drawn from the study can be summarized as follows: (1) The clogging of a slurry shield imposes severe effects on the slurry pressure balancing mechanism of shield tunneling. It can occur in both cohesive and non-cohesive ground with different formation mechanisms. (2) During the initial clogging, the slurry pressure above the spring line increases, and that below the spring line decreases. With the clogging deteriorating, the slurry velocity drops considerably at the top of the deposit area and escalates near the discharging port. The presence and increase of deposit lead to a sharp rise of slurry pressure in the slurry chamber, especially in the clogging region. (3) The reverse circulation of the slurry system (RCSS) is useful to clear the clogging. Still, the slurry deposits at the bottom will obstruct the slurry reverse flow, resulting in inward deformation of the tunnel face and a drastic increase in overcutting volume. (4) The ultimate volume deviation ratio of the slurry was proposed as a useful index to alarm the potential risk of collapse induced by the RCSS. (5) The timely adoption of RCSS is strongly suggested when any abnormal changes in the slurry pressure or the ultimate volume deviation ratio are observed for the first time.

Retracted: Realization of Super-Large-Diameter Slurry Shield Passing through Settlement-Sensitive Area Based on Unreinforced Disturbance Control Technology.

[This retracts the article DOI: 10.1155/2022/6299645.].

Theoretical analysis on the deformation of existing tunnel caused by under-crossing of large-diameter slurry shield considering construction factors

With the expansion of underground space networks, new tunnels especially large-diameter shields under-crossing existing tunnels have been commonly practiced. To obtain a better understanding of the effect of large-diameter slurry shield under-crossing on the existing tunnel and provide a quick and effective tool for evaluating the deformation behaviors of the existing tunnel before construction, in this study a simplified analytical method is proposed. Based on the two-stage method, and considering the characteristics of construction factors such as additional thrust on the shield excavation face of the slurry shield machine, friction force of the shield shell, and grouting pressure of the shield tail, deformation of the existing tunnel caused by the crossing of the large-diameter slurry shield in saturated soil is calculated. The proposed method is verified with field measurement data from a case study. A parametric analysis is conducted to study the influence of typical factors on tunnel responses, including longitudinal bending stiffness, elastic modulus, clearance between two tunnels, and shield crossing angle. The parametric study indicates a significant influence of the crossing angle on maximum settlement and the influence range of settlement of the existing tunnel. Recommendations for safe values of shield crossing clearance are given. The proposed analytical solution can be used as a reference to predict the potential risk of new large-diameter slurry shield crossing on the existing tunnel in engineering practices.

A study on the excavation face failure of pressurized slurry shield

The Wuhan Metro Line 8 Crossing River Tunnel Project suffered manifest pressure fluctuations when opening the excavation chamber of the slurry shield. In this paper, numerical simulation and air pressure test are both carried out to analyze the causes of the pressure fluctuation. The analysis results show that the air pressure applied on the excavation face during the opening of chamber lies in the safe region, excluding the possibilities of active and/or passive excavation face failures. Then, calculated by empirical formula, the pressure on site is lower than the hydraulic fracture pressure, which means the pressure fluctuation is not related to the hydraulic fracture. At last, by air pressure tests, the break through pressure of the filter cake is found much smaller than the air pressure on site. Therefore, it is concluded in this paper that the quality of the filter cake does not meet the design standard, and the breakdown of the filter cake is the main cause of the observed pressure fluctuations on the excavation face. Furthermore, the mechanism of filter cake breakdown is investigated experimentally.

Recycling waste sand from slurry shield tunneling: A sustainable filter aid for waste slurry dehydration

The slurry shield tunneling construction process produces waste slurry (WSL), which is often dehydrated using lime as a filter aid. However, a high pH limits the reusability of the mud cake produced, leading to environmental problems. Slurry shield tunneling also produces waste sand (WSA), which the present study evaluates as a substitute for lime via belt filter press testing. The ability of WSA to reduce the mud cake water content and porosity is found to be the same as that of lime, although double the amount is required. Specifically, the optimal amounts of lime and WSA addition are 2% and 4%, respectively, which produce similar total drainage rates and mud cake moisture contents and porosities. Both lime and WSA reduce mud cake macropores, increase small pores and improve compactness. The addition of >2% lime increases the bound water and moisture contents of the mud cake, while WSA reduces the bound water without affecting dehydration. Finally, the use of WSA instead of lime as a filter aid reduces the pH of the mud cake from strongly alkaline (about 12) to near-neutral (about 8). The results show that WSL can replace lime as a filter aid, providing a novel approach to WSL dehydration treatment and WSA reuse that has both environmental and economic benefits.

Numerical Study on Fluid Flow Characterization of the Souring System in a Large-Sized Slurry Shield

Numerical Study on Fluid Flow Characterization of the Souring System in a Large-Sized Slurry Shield

Performance assessment and structural design of the atmospheric cutterhead of slurry shield machine

Performance assessment and structural design of the atmospheric cutterhead of slurry shield machine

Influences of polyanionic celluloses and temperature on the rheological property of seawater slurries

As an increasing number of submarine tunnels are being constructed by the slurry shield tunnelling method, seawater intrusion into slurries and variations in strata temperature are inevitably encountered during construction. They will lead to obvious deterioration in rheological properties of slurries, which can be adverse for the filter cake formation and even cause tunnel face instability. Considering the design of the slurry parameters and the actual slurry support effect, it is essential to select a suitable slurry ingredient and investigate the rheological properties of seawater slurries under different temperature environments. Using polyanionic celluloses (PAC) as the additive to seawater slurries was proposed in this paper. The influence of PAC contents on the rheology and physical stability of seawater slurries was investigated through laboratory experiments, with PAC contents varying from 0 to 0.4%. The rheology enhancement mechanism of PAC was also analyzed. Furthermore, the flow pattern and constitution relationship of seawater slurries with 0.4% PAC were studied at different temperatures from 2℃ to 30℃. The results show the presence of PAC can significantly enhance the viscosity and physical stability of seawater slurries. The seawater slurries incorporating 0.4% PAC and 12% Na-bentonite can maintain an excellent colloidal rate with 97.5% and a high viscosity, which was recommended to be a prospective mixing proportion used in slurry projects. Additionally, the flow characteristic of seawater slurries with different PAC contents can be described by the power law model very well. Moreover, with the increase in temperature, the rheological index showed an increasing trend, but the consistency coefficient gradually decreased. The constitutive equation of seawater slurries considering the effect of temperature was proposed. This research will provide significant guidance for the selection of slurry parameters and the establishment of seawater slurry infiltration theories during the construction of submarine tunnels.

Study on Comprehensive Technology of Preventing Mud Cake of Large Diameter Slurry Shield in Composite Stratum

When large-diameter slurry shields are tunneling in a composite stratum with a high clay content, the cutter head may form a mud cake. After the mud cake is formed, it will cover the cutter and reduce the opening rate of the cutter head, thus reducing the penetration of the cutter and the driving speed. Based on a road upgrading project, this paper studies the prevention and treatment of a mud cake and forms a set of comprehensive treatment methods. For a large mud cake, through theoretical analysis, two calculation methods of the cutter head sealing coefficient are obtained, and the cutter head sealing coefficient relationship model is established. Comparing the calculated cutter head’s actual opening coefficient with the required cutter head opening coefficient can provide a judgment basis for the time of manual warehousing. For medium and small mud cakes, the numerical simulation is carried out based on the cutter head and the scouring system, the distribution characteristics of the flow field near the cutter head are analyzed, and the angle of the central scouring hole is optimized. For a small mud cake, hydrogen peroxide is selected as an additive through microscopic mechanism analysis. The effect of the hydrogen peroxide solution concentration on dissolving a mud cake is obtained through laboratory tests, and its effectiveness is verified through field tests. The research results can provide a reference for the mud cake prevention of slurry shields in similar strata.

A novel evaluation model for carbon dioxide emission in the slurry shield tunnelling

Excessive carbon dioxide emission leads to climate change and severely threaten social sustainability. A novel model for evaluating carbon dioxide emission in slurry shield tunneling is presented. Firstly, the carbon dioxide emission from a slurry shield tunnel during construction was calculated using the emission coefficient method. Then, for predicting carbon dioxide emission in slurry shield tunneling, a support vector regression integrated sparrow search algorithm model was proposed. Random forest is used to select the input variables of the model. The predicted model accuracy is validated by comparing it to multiple machine learning models. The results show that the model can accurately predict carbon dioxide emission in the shield tunneling with acceptable errors. The influencing factors for carbon dioxide emission in the slurry shield tunneling are disscussed. The recommendations for low-carbon tunnel construction are given. This study provides reference for guiding the low-carbon tunnel construction.

Laws and Numerical Analysis of Surface Deformation Caused by Excavation of Large Diameter Slurry Shield in Upper-Soft and Lower-Hard Composite Stratum

Due to the large cross-section design of large-diameter shield tunnels, most of the rocks and soils it crosses are composite strata with upper soft and lower hard. In order to reduce the construction cost of shield working shafts, large-diameter shield launching is usually buried at a shallow depth. Based on the typical large-diameter slurry shield tunnel, the following research results were obtained according to field monitoring and PLAXIS 3D finite element simulation. (1) The electronic level is used to monitor the surface settlement, and the field monitoring data were obtained; the surface settlement duration curve at the axis of the shield tunnel during the construction period can be divided into four stages: pre-deformation, shield passing, shield tail exit and shield moving away, of which the surface settlement accounts for the largest proportion during the shield passing. (2) In order to ensure the accuracy of the numerical simulation results, the linear shrinkage of the shield needs to be considered in the modeling. (3) The maximum surface settlement value at the center of the tunnel increases with the increase of the support pressure; when the support pressure exceeds 300 kPa, the surface uplift and the settlement caused by the formation loss will offset, and the surface settlement will decrease instead. The maximum surface settlement value is inversely proportional to the grouting pressure, but with the increase of the grouting pressure, the maximum uplift of the surface continues to increase. (4) With the numerical simulation of excavation step construction, the surface uplift increases with the increase of grouting pressure and shield radius, and decreases with the increase of shield buried depth.

Dewatering characteristics of waste slurry from pipe jacking based on improved vacuum filtration method

A large amount of waste slurry with high water content generated in the construction of slurry shield and pipe jacking needs to be reduced urgently. Due to high clay content of the waste slurry, existing treatment technologies such as plate and frame pressure filtration and vacuum filtration encounter problems such as low dewatering efficiency and low soil strength. Aiming at these problems, an improved vacuum filtration method was proposed and verified, which can transform waste pipe jacking slurry with high water content into soil material with certain strength while rapidly dewatering. The new method combines traditional vacuum filtration with curing technology. The experiment results show that after using the new method, the slurry with a water content of 400 % can rapidly drop to 62 % within 150 s, and 7-day unconfined compressive strength of the dewatered soil (q7day) can reach 117.33 kPa. The key mechanism of the improved vacuum filtration method was discussed. The pretreatment of solidification-flocculation increases the dewatering efficiency of vacuum filtration. The solidifying agent added in pretreatment still enhance strength of dewatered soil. Meanwhile, the strength formation mechanism of dewatered soil was proposed. The strength is related to water content of the dewatered soil (ωfinal) and the solidifying agent content (COPC).

Effect of Viscosity on Slurry Infiltration in Granular Media

The infiltration of slurry in granular media plays an important role in face stability during slurry shield tunneling. This study investigates the effect of slurry viscosity in Fujian standard sand through a series of column tests combined with microstructural investigation, which remains unclear. The viscosity of slurry covers a wide range, from 1.8 to 2,248 mPa·s. Slurry particles in the low-viscosity test (1.8 mPa·s) fail to form an impermeable cake due to the loose stacking of slurry particles retained in sand voids, corresponding to a slight water pressure difference and relatively large permeability. For the high-viscosity test (2,248 mPa·s), an impermeable cake forms at a shallow depth; however, this internal cake is vulnerable to be disturbed and damaged due to its shallow thickness. Ultimately, one recommended viscosity, 56 mPa·s, is identified as a transition state with two-stage intact clogging, exhibiting an effective infiltration depth and intact internal cake that forms simultaneously. Experimental observations show a negative water pressure difference in the high-viscosity test, attributable to the siphonic principle. Furthermore, a measurement of slurry samples and solutes using the material observation apparatus could provide the microstructure evidence to interpret the effect of slurry viscosity in infiltration clogging. This study offers a reliable reference for interpreting the effect of viscosity on slurry clogging in infiltration performance.

Properties of Slurry Shield Tunnel Sand and Its Application in Large Flow Concrete.

The amount of Slurry shield tunnel slag (SSTS) from the Beijing East Sixth Ring Road renovation project is about 3 million m3, and it is mainly fine and silt sand. In order to realize its resource utilization, the properties of SSTS and the performance of concrete with strength grades from C30-C60, which used the mixed sand compound with SSTS and Coarse Manufactured Sand (CMS) as a fine aggregate, were investigated. The results showed that SSTS’ fineness modulus is 1.2, its clay content is 17.0% but its composition is mainly Inert Silt (IS), and SSTS replaced with 40% of the mass of CMS can obtain a mixed sand with a fineness modulus of 2.7 and a clay content of 7.0%. The morphological and filling effects of SSTS and IS will improve the workability and durability properties of concrete with no adverse effects on the compressive strength. On the other hand, clay lumps in SSTS adversely affect the workability, early cracking properties, and freeze resistance of concrete, which can be alleviated by dewatering and crushing the clay lumps in SSTS.