Synchronous Grouting Research Articles

Deformation Control of Subway Tunnels Undercrossing Airport Facilities: A Case Study of the Xinzheng Airport Rail Transit Hub Project

The rapid expansion of urban areas due to China’s booming economy has led to a conflict between people and vehicular traffic. Consequently, rail transit, represented by subways, has become the primary mode of transportation for residents. However, the influence of soil damage on tunnel deformation is often overlooked in research on the safety of soft soil tunneling, leading to discrepancies between the results predicted by models and the actual settlement of tunnels. In this study, soil investigation and mechanical strength testing were carried out to analyze the impact of aircraft takeoff and landing activities on the Xinzheng Airport facilities. Damage variables are introduced into the Drucker‒Prager ideal elastic‒plastic criterion, and a soft soil tunneling model with soil deformation is established to investigate the spatial and temporal effects of the shield-cutting force, moving aircraft load, and tunnel deformation. Based on the synchronous grouting technique, a mechanical load-bearing system consisting of a concrete runway, solidified grout, and high-strength segments is formed to ensure the safety of flight activities.

Prediction of surface settlement caused by synchronous grouting during shield tunneling in coarse-grained soils: A combined FEM and machine learning approach

This paper presents a surrogate modeling approach for predicting ground surface settlement caused by synchronous grouting during shield tunneling process. The proposed method combines finite element simulations with machine learning algorithms and introduces an intelligent optimization algorithm to invert geological parameters and synchronous grouting variables, thereby predicting ground surface settlement without conducting numerous finite element analyses. Two surrogate models based on the random forest algorithm are established. The first is a parameter inversion surrogate model that combines an artificial fish swarm algorithm with random forest, taking into account the actual number and distribution of complex soil layers. The second model predicts surface settlement during synchronous grouting by employing actual cover-diameter ratio, inverted soil parameters, and grouting variables. To avoid changes to input parameters caused by the number of overlying soil layers, the dataset of this model is generated by the finite element model of the homogeneous soil layer. The surrogate modeling approach is validated by the case history of a large-diameter shield tunnel in Beijing, providing an alternative to numerical computation that can efficiently predict surface settlement with acceptable accuracy.

Optimization of the Grout Mix Ratio and Simulation Test of Shield Tail Grouting Similarities in a Water-Rich Fine Sand Layer

When shield tunneling is performed in water-rich silt and fine sand strata, the grout becomes runny when diluted by groundwater. After dilution, the filling effect of the grout is not significant, and the level of surface settlement is very high. In this study, based on bidding section 04 of Tianjin Metro Line 11, traditional grouting materials were selected to conduct response surface method (RSM) tests. The purposes of the RSM analysis were to analyze the interactions between materials and their influences on grout performance and to optimize the grout mix ratio. Various admixtures were compared to assess the effects of different admixtures and compositions on the dispersion resistance and flow performance of the grout. Finally, a shield synchronous grouting test system was developed, and a similar indoor grouting simulation test was performed to analyze the influences of the different admixtures on the filling effects and to determine a reasonable grout mix ratio. The following three results were obtained. (1) The RSM was suitable for grout performance prediction and grout mix ratio optimization, and hydroxyethyl cellulose could improve the grout performance and increase the bond performance between the cementing material and aggregate. (2) Admixture incorporation enhancement could improve the grout utilization rate and increase the diffusion distance at the top of the tunnel, which would be conducive to filling the gap at the tail end of the shield. (3) The optimal preparation scheme of grout in water-rich fine sand formations included a water–binder ratio of 0.72, cement–sand ratio of 0.80, fly ash content of 5%, bentonite content of 14.94%, and admixture content of 0.8%–0.9%

Developing of reinforced grouting mortar tenon and pseudo-static experimental test for seismic performance of precast shear wall

A high-performance grouting mortar is applied to the wall joint to improve the seismic performance of the precast shear wall. This study proposes a configuration and synchronous grouting construction method for preparing reinforced high grouting mortar tenons. Three precast shear wall specimens with the prepared tenon and one common precast comparison specimen were tested with pseudo-static experiments, and the experimental results, i.e., failure process and mode, hysteretic and skeleton curves, capacities, stiffness and ductility, were analyzed. The results showed that the failure mode of precast shear wall specimens with reinforced tenon belonged to bending-shear failure. The reinforced tenon increased the strength capacity, stiffness, and energy dissipation ability and the reinforced tenon joints achieved strength capacity equivalent to a common precast shear wall. The tenon height and axial ratio significantly influenced the mechanical properties of stiffness, ductility, and energy dissipation. Which is, the tenon height should be reasonably controlled for shear transfer considerations, and the specimens with higher axial ratio showed better performance.

The Effect of Asynchronous Grouting Pressure Distribution on Ultra-Large-Diameter Shield Tunnel Segmental Response

The complex distribution of synchronous grouting pressure results in excessive tunnel deformation and various structural diseases, especially for ultra-large-diameter shield tunnels. In this study, to reduce the risk of tunnel failure, a three-dimensional refined finite element model was established for the Wuhan Lianghu highway tunnel project, taking into account the non-uniform distribution of synchronous grouting pressure. This study focuses on investigating the development patterns of internal forces, deformations, and damages in segment structures under varying grouting pressure ratios. The results indicate that the primary failure mode of a segment is tensile failure occurring at the outer edge of the arch. Moreover, an increased ratio of grouting pressure between the arch bottom and top leads to a higher positive bending moment value and greater tensile damage at the arch waist. The tunnel ring gradually exhibits distinct “horizontal duck egg” shape deformation. When the grouting pressure ratio is 2.8, there is a risk of tensile cracking at the outer edge of the arch waist. At this time, the segment convergence deformation is 39.71 mm, and the overall floating amount reaches 43.12 mm. This research offers engineering reference for the prediction of internal forces and deformations in ultra-large-diameter shield tunnels during grouting construction, thereby facilitating their application in the development of resilient cities.

Study on the Applicability of Load Calculation Method for Large-Diameter Shield Tunnel in Argillaceous Sandstone Stratum under High Water Pressure

Surrounding rock pressure is an important factor to be considered during designing tunnel structures. In this research, the on-site surrounding rock pressure of a large diameter shield tunnel in argillaceous sandstone stratum was tested, and the evolution process of surrounding rock pressure was analyzed, based on which the variation law of surrounding rock pressure with buried depth and span of the tunnel was discussed. Combined with the numerical simulation method, the applicability of the load calculation method for the large-diameter shield tunnel in the argillaceous sandstone stratum was studied. The results showed that the variation of surrounding rock pressure generally changed from a rapid and substantial increase to a slight decrease and finally tended to be stable. Before reaching stability, the deformation pressure was dominant; then, the loosening pressure became the main pressure, and the surrounding rock pressure almost reached the maximum value in the synchronous grouting stage. Moreover, it was also found that the shield construction had a great influence on the surrounding rock pressure of the 15-ring segments behind the working face. While calculating the surrounding rock pressure, the tunnel section shape, buried depth and surrounding rock conditions should be fully considered. The Full Soil Column Theory, Terzaghi's Theory, Xie's Theory and Bierbauman's Theory were more suitable for tunnels with a buried depth of less than 2.5 hp. When the buried depth of the tunnel exceeded 2.5 hp, the calculation results needed to be enlarged by 2 ∼ 3 times if the Statistical Method or Protodyakonov's Theory was used for calculation. Xie's Theory can be used to calculate the surrounding rock pressure of shallowly buried argillaceous sandstone stratum large-diameter shield tunnel. For a deeply buried argillaceous sandstone stratum large-diameter shield tunnel, it is recommended to use Numerical Simulation Method.

Research on reuse of shield soil dregs on synchronous grouting materials and its application

Shield tunnel construction will produce a large amount of soil dregs. Transporting soil dregs directly to landfills raises costs and CO2 emissions. In this paper, the shield tunnel of Intercity from Shenzhen to Huizhou is taken as an example, based on the special treating agent of shield soil dregs, the soil dregs were prepared as synchronous grouting material. The working performance and mechanical properties of soil dregs grouting material were studied. The optimal dosage of the treating agent was proposed, and the curing mechanism of the soil dregs synchronous grouting material was analyzed. The soil dregs grouting material was applied to practical engineering, and the application effect was verified by surface subsidence monitoring. The results showed that the setting time, bleeding rate, stone rate and compressive strength of the soil dregs grouting material were better than cement mortar grouting material. The treating agent realized the cementation of soil particles through the synergistic effect of epoxy resin and nano-SiO2, and the optimum dosage is 0.02 % of the solid component. The maximum surface settlement of the soil dregs grouting construction section was 10 mm, which is smaller than the maximum surface settlement of the cement mortar grouting section. Through the life cycle assessment (LCA) method, the CO2 emission reduction capacity of the soil dregs synchronous grouting material was analyzed. The soil dregs grouting material reduced the production and transportation of fly ash and bentonite, and reduces the outward transportation of soil dregs. The use of 1 t soil dregs synchronous grouting material can reduce 59.05 kg CO2 emission.

Pressure Model Study on Synchronous Grouting in Shield Tunnels Considering the Temporal Variation in Grout Viscosity

The grout pressure in the shield tunnel tail void during synchronous grouting is the key to controlling ground settlement and restraining the segment. However, the circumferential, longitudinal, and radial distribution of grout pressure considering the temporal variation in grout viscosity has not been well explored yet. In this study, a theoretical model of grout pressure distribution and dissipation considering the temporal variation in Bingham grout viscosity was established. The simulation results of the pressure model were verified by field-measured data. The results showed that the radial and longitudinal distributions of grout pressure considering the temporal variation in grout viscosity were closer to the field-measured data. The impacts of the main parameters on the pressure distribution and dissipation were analyzed. Compared with the effect of the shield tail void thickness, tunnel radius and yield shear stress have greater effects on grout pressure during the circumferential filling phase. During the longitudinal and radial diffusion phases, the increase in soil porosity and permeability coefficient was conducive to grout diffusion. The increase in the grout viscosity reduces the pressure loss during the grout flow process. The results of this research can provide a theoretical basis for the grout design process in shield tunnels.

Research on the influence of clay shock on inert slurry in shield-tunneling construction

Shield-out synchronous grouting is a new technology used to fill temporarily shield-out spaces between the strata and the shield when creating subterraneous tunnels. The grouting materials are called ‘clay shock’, which is soft, plastic, sticky and easily dispersed by using a pressurized jet. This study analyzes the mixing process of clay shock and backfill grouting material (inert slurry) and investigates the influence of clay shock on the inert slurry through laboratory testing. The findings show that the fluidity and bleeding rate of the inert slurry continuously decrease with the clay shock volume. The unconfined compressive strength and flexural strength of the inert slurry increase initially before decreasing with the clay shock volume ratio. The X-ray diffraction and scanning electron microscopy results reveal that the alkalinity of the clay shock initiates an alkali excitation reaction, which generates more gelling products and increases the strength of the inert slurry. Excessive clay shock causes the inert slurry to retain a loose and porous structure, which then decreases its strength. To ensure the effect of the inert slurry on settlement control, the grouting volume of the clay shock should not exceed one-fourth of the inert slurry volume.

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.

The time-dependent grout buoyancy behavior based on cement hydration mechanism

The grout buoyancy has a great influence on the segment during synchronous grouting of shield tunnel. Traditionally, the large buoyancy leads to certain types of tunnel distresses, such as convergence deformation, differential settlement, cracks, and water leakage. This paper made a detailed study on the time-dependent grout buoyancy behavior. The hydration heat test and LF-NMR test were carried out. Then the four periods of hydration rate curve were revealed, and the evolution rules of gel water, capillary water and free water were also obtained. The time-dependent grout buoyancy was tested by self-designed equipment, and the theoretical formula of grout buoyancy considering w/c ratio and time was proposed. The indoor test results were compared with the theoretical solution. The theoretical formulas could effectively predict the size and variation rules of buoyancy. The indoor test results showed that variation trend of cement grout buoyancy is consistent with the hydration rules. The buoyancy mainly exists in the initial period and the induction period, and decreases sharply to zero before the acceleration period. The initial setting moment is the one in which hydration rate is the largest.

Study on the shear strength characteristics and source mechanism of early-age shield synchronous grouting materials

Study on the shear strength characteristics and source mechanism of early-age shield synchronous grouting materials

Feasibility Studies on the Utilization of Recycled Slag in Grouting Material for Tunneling Engineering

The construction of tunnels involves massive excavation work and generates an enormous amount of waste slag. The improper disposal of the waste slag may cause environmental pollution. The treatment of waste slag is usually costly. In this study, the feasibility of recycling waste slag as a component in the synchronous grouting material was investigated. A series of experimental measurements were conducted to evaluate the performance of grouting material with different proportions of recycled waste slag. The experimental results show that the grouting material with the selected proportion of recycled slag has a similar performance to the original grouting material mix. It was observed that waste slag can be recycled as one component of the grouting material for tunneling engineering.

Experimental Study and Simulation Analysis of Slurry Filling Process of Shield Tail Synchronous Grouting

Based on the inadequacy of groundwater pressure and other factors on interstitial pressure and slurry filling rate during synchronous grouting by groundwater action, a scaled-down simulation was carried out and the applicability of the simulation was verified by model tests based on the shield tunnel project of Metro Line 12 under Longzi Lake. The results show that during the synchronous grouting process, the pressure in the slurry filling area mainly depends on the grouting pressure, and the pressure in the gap increases with the increase of grouting pressure; the pressure distribution in the gap in the unfilled area is mainly controlled by the groundwater pressure, and the pressure in the gap is positively related to the groundwater pressure. After the slurry completely fills the gap, the overall pressure distribution in the shield tail gap is more uniform. The slurry filling rate decreases with increasing groundwater pressure and increases with increasing grouting pressure; the effects of changing slurry density and slurry viscosity on the pressure distribution in the interstitial space and the slurry filling rate in the shield tail are not significant. The degree of influence of each factor on the slurry filling rate was in the following order: grouting pressure > groundwater pressure > slurry density > slurry viscosity. The work carried out is a guide to the optimization of synchronous grouting process and parameter design in shield tunnels.

Research and evaluation on Water-dispersion resistance of synchronous grouting slurry in shield tunnel

When the shield tunnel passes through the watered stratum with high permeability, as the shield tail interspace prone to be filled with groundwater, resulting in the segregation and loss of ordinary grout slurry during synchronous grouting, then critically affect the physical and mechanical properties as well as the durability of the curing grouting ring. Hence, it is necessary to optimize the performance of the existing ordinary grouting slurry to improve its water-dispersion resistance on the premise of ensuring the original performance. By means of theoretical analysis and indoor tests, this paper systematically investigates the mechanism of water-dispersion resistance of synchronous grouting slurry in water-rich stratum with high permeability, establishing a set of testing process and detection method for water-dispersion resistance of synchronous grouting. Moreover, the influences of different flocculants with corresponding contents on the performance of synchronous grouting slurry have been revealed, and the evaluation criterion of water-dispersion resistance of synchronous grouting slurry in shield tunnel is also clarified. The results show that: 1) Turbidity has notable responses to the change of flocculant content, which could better reflect the clarity of water samples. So, the turbidity is considered as a main evaluation index of water-dispersion resistance of synchronous grouting; 2) On the other hand, pH and water-land strength ratio also demonstrates the acid-base changes of groundwater and the loss of cementitious materials respectively during grouting. Thus, the two indexes are applied as auxiliary evaluation indexes for water-dispersion resistance of synchronous grouting; 3) For the above evaluation indexes, corresponding critical values to satisfy the water-dispersion resistance of synchronous grouting slurry are ensured: turbidity < 100NTU, pH < 10, and water–air strength ratio at different curing ages greater than 80%.

Model Test Study on a Shield Tunnel Adjacent to Pile in the Sub-Clay of a Coastal Area

In this study, a model test system of shield driving adjacent to pile is realized to study the response of surrounding rock and pile induced by an advanced shield tunnel in silty clay layer in a coastal area. The function of automatic pushing and the synchronous grouting of the shield were partially simulated. Similar materials of lining, soft rock and pile, were developed. A total of 33 sets of orthogonal model tests were designed to study the progressive failure caused by excavation in silty clay and the change in stratum displacement and soil pressure; the displacement and internal force response of the pile were also analyzed. The following conclusions can be given: (1) the best grouting filling coefficient range of the shield test for the case study is 1.4 to 1.6; (2) the fitting of the experimental data to obtain the settlement through the width parameter suggests that the K value of the surrounding rock is decreased by 0.075 at least, and the K value increases with the increase in pile-tunnel distance and decreases with the increase in pile depth; and (3) the weak surrounding rock in the tunnel system can be divided into five zones according to the displacement and pressure change in soft surrounding rock and the pile response in the case study. The key condition control factor was also determined.

Study on the Floating of Large Diameter Underwater Shield Tunnel Caused by Synchronous Grouting

Synchronous grouting is the key factor causing segment floating during the construction of shield tunnel, especially the grout ratio and the control of the grouting pressure. In this paper, the ratio of grout material was optimized through multiple groups of physical and mechanical tests. The results showed that 0.3% content of water reducing agent in grout could improve the ability of water resistance significantly. 2.9% content of bentonite could reduce bleeding rate of grout and grout setting time and improve the fluidity in the meantime. Then, the distribution law of grout along the segment ring in the filling stage was studied based on a typical underwater tunnel in China. The results showed that the theoretical calculation of grouting pressure was between 0.15 MPa and 0.18 MPa, which were in good agreement with the measured data. The grouting pressure distribution is affected by four parts including the lateral earth pressure, foundation reaction, grout shear stress, and gravity.

Analysis of Shield Tunnel Ground Deformation Characteristics and Affecting Factors in Water-Rich Soft Stratum: A Case Study on the Section Tunnel of Tianjin Metro Line 6

With the increasing intensity of underground development, the planned metro lines will inevitably pass through water-rich soft stratum. The existing research results show that shield tunneling in water-rich stratum is prone to ground settlement and segment cracking due to the large moisture content and the low soil strength, which will pose risks to the safety of construction. The prediction of ground deformation characteristics and influencing ranges caused by shield tunneling in water-rich soft stratum has been a topical issue among the tunnel research community. Based on the shield tunnel project of Tianjin Metro Line 6, supported by the monitoring data, this paper analyses the ground deformation characteristics caused by shield tunneling in water-rich soft stratum. The results suggest that the surface settlement ranges from −14.20 mm to −28.00 mm in Tianjin’s water-rich soft stratum, which is at an acceptable level of engineering. A refined 3D model addressing fluid–structure interactions is developed to consider the construction process in water-rich soft stratum. Based on this technique, this article focuses on the effect of the support pressure at the excavation surface, the friction between the shield skin and the soil, and synchronous grouting quantity on the ground settlement and structural deformation. The results show that the friction between the shield skin and the soil is the most detrimental to deformation control, whereas the synchronous grouting quantity is the most advantageous to ground and segment deformation control. In practice, timely injection of bentonite slurry reduces friction between the shield skin and the soil, and effective synchronous grouting reduces shield tunneling disruption. This technique can provide calculation support in the optimization of shield tunneling schemes in water-rich soft stratum.

Numerical Study of the Effect of Grout Material Properties on Ground Deformation during Shallow TBM Tunneling

The full-face shield tunnel boring machine (TBM) has been widely used to build tunnels in urban area. Ground deformations usually occur during tunnelling processes, which is closely related to engineering geological property. A large ground deformation may lead to large-scale surface settlement or ground collapse, especially for shallow buried tunnels. In general, synchronous grouting is adopted to reduce the ground deformation. The temporal and spatial distribution of the grout pressure and consolidation processes of grouting have a significant influence on the deformation. For a better understanding the relationship between the grout material type and the ground deformation, the present study models a complex numerical model in FLAC3D based on the Guangzhou Metro line 18. A numerical method is proposed to reproduce the tunnelling process and the consolidation process of grout material. The effect of grouting material on ground deformation is discussed, i.e., immediately solidified type, quick hardening type, and good mobility type. The ground deformation of the numerical simulation are compared to those monitored in the field. The results indicate that the immediately solidified type grout can reduce the ground settlement effectively and is mainly applicable to secondary grouting. The quick hardening type can make the ground upheaval, which is smaller than that induced by immediately solidified type. The good mobility type can reduce the ground settlement and well control the ground deformation. The good mobility type recommends using in the numerical study for simulating the synchronous grouting.

Experimental Investigation of Synchronous Grouting Material Prepared with Different Mineral Admixtures.

Waste sediment generated during tunnel construction is applied to prepare synchronous grouting material, where the influences of fly ash, slag powder, and bentonite on the rheological properties (such as consistency, fluidity, setting time, drainage rate, and stone rate) are studied. The results show that adding fly ash content increases the initial consistency, setting time, and fluidity of grouting material, but also increases its drainage rate and decreases its stone rate. The addition of slag powder results in a slight increase in the setting time and fluidity of the grouting material, yet a decrease in the initial consistency value. In contrast, with the addition of bentonite, both the initial consistency and fluidity of the grouting material decrease. Finally, the optimal mix ratio of high-performance and low-cost grouting materials is fixed to be 30% fly ash, 50% slag powder, and 10% bentonite. Therefore, the fluidity of grouting material can be 170 mm, with an initial consistency of 122 mm, setting time of 1050 min, stone rate of 96.2%, drainage rate of 1.5%, and 28-day compressive strength of 8.3 MPa.