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Shield tail grouting is an important measure to control tunnelling-induced ground deformation by injecting prepared grouting materials to fill the tail gap. The working performance of grout is usually invisible and hard to obtain in construction. This paper carries out an experimental study to investigate the tail grout behavior in ground. In the current research, a testing device is developed to explore the grout behavior in varying soils. The grout working performance is evaluated not only by the liquid grout properties such as fluidity, consistency, bleeding rate, stone rate and compressed deformation but also solid grout properties such as unconfined compressive strength and permeability. Three typical grouts are chosen and their behaviors in the various soils are observed. To take an insight on the behaviors, scanning electron microscopy and mercury intrusion porosimetry analysis are employed. The microstructure of solid grout is a sign of its working performance. The observation shows that the solid grout micro-structure is influenced by grout proportions, pressure, and ground permeabilities. The experimental results are applied in the case of Beijing Metro Line 12 for validation and as a result, the ground movement is inhibited due to high performance of tail grout.

Argillaceous surrounding rock is prone to weakening when exposed to water, which can cause significant long-term deformations and instability in roadways. This paper focuses on a high-injectability, high-strength nanosilica sol-based composite grout, characterizing its sealing patterns at both the macroscopic and microscopic levels within multilevel porous argillaceous rock bodies. It also explores the microscopic structural interactions at the grout-rock interface. Additionally, the paper compares the performance of this composite grout with traditional silica sol and cement grout, providing initial insights into the anti-seepage reinforcement mechanism of the composite grout when used in grouting argillaceous soft rock. The research results show that, for composite grouting (1) The porosity and sealing of the grout-rock cementitious body decrease with increasing particle size of the rock blocks, with a minimum permeability coefficient of 2.34 × 10−8 cm/s; (2) The presence and distribution pattern of multi-level pores of grout in rock fractures can be evaluated using the T2 spectrum of nuclear magnetic resonance (NMR). The pore volume of the cementitious body is mainly provided by large pores

Abstract The development and modification of grouting materials constitute crucial factors influencing the effectiveness of grouting. Given the pivotal role of water in the hydration of cement-based composite materials and construction processes, this study proposes an exploratory approach using green, economical magnetized water technology to enhance the performance of cement grouts. The research systematically investigates the effects of magnetized water on the fundamental grouting properties (stability, rheological behavior, and stone body strength) of cement grouts, prepared under varying magnetization conditions (including magnetic intensity, water flow speed, and cycle times). Through the conduct of specific physicochemical tests on water, the study elucidates the mechanism through which magnetized water influences these properties. The results indicate that magnetized water positively impacts the stability of cement grouts, significantly reducing their absolute viscosity, apparent viscosity, plastic viscosity, and yield stress, thus markedly affecting the rheological characteristics of the cement grouts. Additionally, magnetized water notably enhances the flexural and compressive strength of the cement grout stone body, with a particularly significant improvement in early strength. From a quantum mechanics perspective, a magnetization mechanism based on the competition between the strengthening of hydrogen bonds between water molecule clusters and the weakening or breaking of hydrogen bonds within clusters is introduced, providing a theoretical basis for explaining the variability observed in water magnetization experiments.

The low injectability and strong permeation of micro-fractures in argillaceous rock masses significantly impair the impermeabilization and reinforcement performance of conventional cement-based grouting materials. This study first develops a highly injectable and high-strength nano-silica sol-based composite grout. Then, the characteristics of silica sol, cement grout, and composite grout in argillaceous fractured rock masses are analyzed and compared. The permeation mechanism of the composite-grout grouting in these rock masses is preliminarily elucidated, and the grouting process is described in detail, showing its application prospects. The research results indicate the following: (1) The electrical conductivity and stone-formation rate of granular pulp can reflect the characteristics of pulp filtration. Silica sol is a grouting material with nanometer particles, and the stone rate and gel strength are weakly affected by rock mass infiltration. (2) A large amount of water cannot be combined into the gel network and separated during the cement slurry percolation process, resulting in a significant reduction in the stone rate and compressive strength of deep rock mass. The minimum stone rate decreased to 45.19%, and the minimum compressive strength decreased to 2.29 MPa. This reduces the sealing and reinforcement effect of cement grouting on deep rock masses. (3) Rock permeation primarily affects the compressive strength of the formed stones, with minimal impact on the stability and stone-formation rate of the composite grout. As permeability decreases, the position of rock permeation shifts closer to the rock surface, while the sealing of deeper rock masses is less affected, enabling the composite grout to achieve dual functions of superficial reinforcement and deep sealing. This study provides theoretical support for the practical application of composite-grout grouting in reinforcing argillaceous rock masses. [ABSTRACT FROM AUTHOR]

Cemented Sand, Gravel, and Rock (CSGR) dams have traditionally used either Conventional Vibrated Concrete (CVC) or Grout-Enriched Roller Compacted Concrete (GERCC) for protective and seepage control layers in low- to medium-height dams. However, these methods are complex, prone to interference, and uneconomical due to significant differences in the expansion coefficient, elastic modulus, and hydration heat parameters among CSGR, CVC, and GERCC. This complexity complicates quality control during construction, leading to the development of Grout-Enriched Vibrated Cemented Sand, Gravel, and Rock (GECSGR) as an alternative. Despite its potential, GECSGR has limited use due to concerns about freeze–thaw resistance. This project addresses these concerns by developing an air-entrained GECSGR grout formulation and construction technique. The study follows a five-phase approach: mix proportioning of C1806 CSGR; optimization of the grout formulation; determination of grout addition rate; evaluation of small-scale lab samples of GECSGR; and field application. The results indicate that combining 8–12% of 223 kg/m3 cement grout with 2–2.23 kg/m3 of admixtures, mud content of 15%, a marsh time of 26–31 s. and a water/cement ratio of 0.5–0.6 with the C1806 parent CSGR mixture achieved a post-vibration in situ air content of 4–6%, excellent freeze–thaw resistance (F300: mass loss <5% or initial dynamic modulus ≥60%), and permeability resistance (W12: permeability coefficient of 0.13 × 10−10 m/s). The development of a 2-in-1 slurry addition and vibration equipment eliminated performance risks and enhanced efficiency in field applications, such as the conversion of the C1804 CSGR mixture into air-entrained GECSGR grade C9015W6F50 for the 2.76 km Qianwei protection dam. Economic analysis revealed that the unit cost of GECSGR production is 18.3% and 6.33% less than CVC and GERCC, respectively, marking a significant advancement in sustainable cement-based composite materials in the dam industry. [ABSTRACT FROM AUTHOR]

Increasing population bring together the need for construction on weak soils. At this point, soil improvement methods gain importance in which the problematic properties of soils aimed to enhance. Among these, jet grout columns are widely applied method and have advantages such as increasing the bearing capacity, reducing settlements and the risk of liquefaction. In this paper, jet grout columns utilized to reduce settlements in weak soil layers and the effect of several parameters on settlement examined. The analyzes, performed with Plaxis 2D and Plaxis 3D. The jet grouts are modeled with both single columns and composite region by changing jet grout length, diameter and spacing. To assess the soft clay effect, columns were socketed into different clay layers. The results proved that improvement with jet grout reduces the settlements, but the change in diameter, length and spacing affects the results at different rates. Through 3D analysis, up to 22% reductions in settlements obtained in case where the longest columns were assigned at the lowest spacings. The most effective factor was found as spacing rather than diameter. The increase in diameter after a certain value led to lower the performance due to the group effect. In case of the composite region, 3D and 2D analyzes converge very much, so it would be practical to perform 2D analysis for the composites. However, the ones modelled with single columns predicted more settlement and remained on the safe side. Additionally, jet grout columns performed better than in weak soils.

Overburden separation grout filling (OSGF) technology compacts the fragmented rock mass in the goaf and changes the seepage characteristics and distribution of the “three zones” of spontaneous combustion in the goaf. In order to investigate the range of spontaneous combustion risks of residual coal in the goaf under the OSGF in the 22301 fully-mechanized caving face of the Tunlan Coal Mine, based on a combination of field measurement and numerical simulation, accurate demarcation of the spontaneous combustion “three zones” in the goaf was carried out. A three-dimensional mathematical model of borehole porosity was also proposed to evaluate the influence of different OSGF borehole locations on the goaf airflow field. The results show that the modified three-dimensional mathematical model of porosity can better reflect the gas flow field in the goaf after OSGF, and the residual accuracy of its simulation results is improved by 22% compared with the field measurement. Compared with the situation without OSGF, the danger of natural ignition in the goaf is effectively inhibited due to the compaction effect after OSGF. Meanwhile, the air leakage flow converges upward, resulting in an increase of oxygen concentration at higher positions in the caving zone of the goaf. The layout parameters of grouting holes will have an impact on the flow field of goaf, and the correlation degree is the spacing of holes, the number of holes and the influence radius of holes.