Search Results (20)

The layered composite roof of a coal mine roadway exhibits heterogeneity, with pronounced variations in layer thickness and strength. Fully grouted rock bolts installed in such layered roofs usually penetrate two or more strata and bond with them to form an integrated anchorage system. Roof failure typically initiates in the shallow strata and progressively propagates to deeper layers; thus, the mechanical properties of the rock at the free surface critically influence the overall stability of the layered roof and the load-transfer behavior of the bolts. In this study, a layered rock mass model was developed using three-dimensional particle flow code (PFC3D), and a triaxial loading scheme with a single free surface was applied to investigate the effects of free-surface rock properties, support parameters, and confining pressure on the load-bearing performance of the layered rock mass. The main findings are as follows: (1) Without support, the ultimate bearing capacity of a hard-rock-free-surface specimen is about 1.2 times that of a soft-rock-free-surface specimen. Applying support strengths of 0.2 MPa and 0.4 MPa enhanced the bearing capacity by 29–38% and 46–75%, respectively. (2) The evolution of axial stress in the bolts reflects the migration of the load-bearing core of the anchored body. Enhancing support strength improves the stress state of bolts and effectively mitigates the effects of high-stress conditions. (3) Under loading, soft rock layers exhibit greater deformation than hard layers. A hard-rock free surface effectively resists extrusion deformation from deeper soft rocks and provides higher bearing capacity. Shallow free-surface failure is significantly suppressed in anchored bodies, and “compression arch” zones are formed within multiple layers due to bolt support. Full article

Cylindrical retaining structures are widely adopted in intercity railway tunnel engineering due to their exceptional load-bearing performance, no need for internal support, and efficient utilization of concrete compressive strength. Measured deformation data not only comprehensively reflect the influence of construction and hydrogeological conditions but also directly and clearly indicate the safety and stability status of structure. Therefore, based on two geometrically similar cylindrical shield tunnel shafts in Shenzhen, the surface deformation, structure deformation, and changes in groundwater outside the shafts during excavation were analyzed, and the deformation characteristics under the soil–rock composite stratum were summarized. Results indicate that the uneven distribution of surface surcharge and groundwater level are key factors causing differential deformations. The maximum horizontal deformation of the shafts wall is less than 0.05% of the current excavation depth (H), occurring primarily in two zones: from H − 20 m to H + 20 m and in the shallow 0–10 m range. Vertical deformations at the wall top are mostly within ±0.2% H. Localized groundwater leakage in joints may lead to groundwater redistribution and seepage-induced fine particle migration, exacerbating uneven deformations. Timely grouting when leakage occurs and selecting joints with superior waterproof sealing performance are essential measures to ensure effective sealing. Compared with general polygonal foundation pits, cylindrical retaining structures can achieve low environmental disturbances while possessing high structural stability. Full article

Climate change will have a significant impact on saltwater intrusion in coastal aquifers between now and 2150. Global sea levels are predicted to rise somewhere between 0.5 and 1.8 m. To mitigate sea level rise, coastal aquifers will require intensive management to avoid inland migration of seawater that could impact water supplies. In addition to reducing pumping of freshwater, the construction and operation of salinity barriers will be required in many locations. Eleven types of salinity barriers were investigated, including physical barriers (curtain wall and grout curtains), infiltration canals filled with freshwater paralleling the coastline, injection of freshwater (treated surface water or wastewater), pumping or abstraction barriers, mixed injection and abstraction barriers, combined abstraction, desalination, and recharge (ADR), ADR hybrid barriers using various water sources including desalinated water and treated wastewater, compressed air barriers, aquifer storage and recovery dual use systems, biofilm barriers, and clay swelling or dispersion barriers. Feasibility of the use of each salinity barrier type was evaluated within the context of the most recent projections of sea level changes. Key factors used in the evaluation included local hydrogeology, land surface slope, water use, the rate of sea level rise, technical feasibility (operational track record), and economics. Full article

To address the challenge of dynamic monitoring during grouting operations in coal mine fault zones under pressurized mining, this study proposes the Borehole–Tunnel Joint Resistivity Method (BTJRM). By integrating three-dimensional (3D) electrode arrays in both tunnels and boreholes with 3D resistivity inversion technology, this approach enables fully automated underground data acquisition and real-time processing, facilitating comprehensive dynamic monitoring of grout propagation. A case study was conducted on a coal mine fault grouting project, where tunnel and borehole survey lines were deployed to construct a 3D cross-monitoring network, overcoming the limitations of traditional 2D data acquisition. Finite volume method and quasi-Gauss–Newton inversion algorithms were employed to analyze dynamic resistivity variations, enhancing spatial resolution for detailed characterization of grout migration. Key findings include: (1) Grout diffusion reduced resistivity by 10%, aligning with electrical response patterns during fracture-filling stages; (2) 3D inversion reveals that grout propagates along the principal stress axis, forming a “Y”-shaped low-resistivity anomaly zone that penetrates the fault structural block and extends into roadway areas. The maximum planar and vertical displacements of grout reach 100 m and 40 m, respectively. Thirty days post-grouting, resistivity recovers by up to 22%, reflecting the electrical signature of grout consolidation; (3) This method enables 3D reconstruction of grout diffusion pathways, extends the time window for early warning of water-conducting channel development, and enhances pre-warning capabilities for grout migration. It provides a robust framework for real-time sealing control of fault strata, offering a novel dynamic monitoring technology for mine water inrush prevention. The technology can provide reliable grouting evaluation for mine disaster control engineering. Full article

The seepage diffusion of cement grouting materials into a sandy medium is influenced by the skeleton’s adsorption and the pore channels’ tortuosity, resulting in heterogeneous retention of cement particles during migration. This study established a theoretical model for the filtration coefficient based on the mass balance equation and linear filtration law. Grouting tests were conducted to determine the density of the cement slurry at various diffusion positions, and the filtration coefficient was calculated using the theoretical model. Results indicate that the filtration coefficient varies dynamically along the diffusion distance rather than remaining constant. The surface filtration range of Grade 42.5 Portland Cement slurry in sample S1 is approximately 30 cm, with a final diffusion distance of 190 cm. In contrast, the surface filtration ranges for the 800 mesh superfine cement in S2 and the 1250 mesh superfine cement in S3 are less than 10 cm, resulting in final diffusion distances of 69 cm and 87 cm, respectively. This demonstrates that a longer surface filtration range in the sand sample corresponds to a farther final diffusion distance of the slurry. Additionally, a larger ratio of sand pore diameter to cement particle size results in a smaller filtration coefficient and a greater slurry diffusion distance. Under a constant water–cement ratio, smaller cement particle sizes are associated with decreased slurry fluidity, which reduces the diffusion of cement slurry within the sandy medium. The research findings provide valuable insights for designing borehole spacing in grouting treatment for sandy media. Full article

To address the issue of uneven shear strength distribution in dredged sediment during electroosmosis treatment, a grouting system was employed to inject CaCl₂ into the anode region and Na₂SiO₃ solution into the central region. An experimental study was conducted to examine the effect of injection timing on the electrochemical treatment of dredged sediment. Five experimental groups, each with different Na₂SiO₃ injection timings, were established. The impact of injection timing on the macroscopic electrochemical reinforcement was assessed based on current, drainage volume, settlement, moisture content, and shear strength. Additionally, the ion concentration of effluent from the cathode was measured, and scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were employed to analyze ion migration and pore characteristics. The results indicated that when CaCl₂ was injected into the anode at the start of the experiment and Na₂SiO₃ was injected into the central region after the current had decayed by 70% from its peak, the drainage volume reached its maximum. Under these conditions, the average shear strength increased from nearly 0 kPa to 48.2 kPa, yielding the optimal reinforcement effect. The strength in both the central and cathode regions also improved, and the strength distribution between the anode and cathode became more uniform, with the strength ratio decreasing from 1.91 to 1.65, thereby enhancing the overall soil strength distribution. The Na⁺ concentration in the cathode effluent was highest, suggesting that Na⁺ migration played a predominant role in electroosmotic drainage. Furthermore, the electrochemical reactions generated cementitious materials that effectively filled the soil pores. SEM imaging and MIP pore size analysis revealed a reduction in porosity and an increase in soil compaction. Full article

The activation product chlorine-36 (³⁶Cl) is an important radionuclide within the context of the disposal of nuclear wastes, due to its long half-life and environmental mobility. Its behaviour in a range of potential cementitious encapsulants and backfill materials was studied by evaluating its uptake by pure cement hydration phases and hardened cement pastes (HCP). Limited uptake of chloride was observed on calcium silicate hydrates (C-S-H) by electrostatic sorption and by calcium monosulphoferroaluminate hydrate (AFm) phases, due to anion exchange/solid solution formation. Diffusion of ³⁶Cl through cured monolithic HCP samples, representative of cementitious materials considered for use in deep geological repositories across Europe, revealed a markedly diverse migration behaviour. Two of the matrices, a ground granulated blast furnace slag/ordinary Portland cement blend (GGBS–OPC) and an ordinary Portland cement (CEM I) effectively retarded ³⁶Cl migration, retaining the radionuclide in narrow, reactive zones. The migration behaviour of ³⁶Cl within the cementitious matrices is not strictly correlated to the measured sorption distribution ratios (R_d-values), suggesting that physical factors related to the microstructure can also have a distinct effect on diffusion behaviour. The findings have implications when selecting cementitious grouts and/or backfill materials for ³⁶Cl-bearing radioactive wastes. Full article

Regional grouting treatment is an effective technical means to prevent mine water disasters, and the grouting effect is affected by many factors. In actual grouting engineering, the single constant-rate grouting method is often transformed into a variable-parameter grouting process. However, research on grouting rates has been insufficient. This investigation focused on the issue of “the diffusion law of variable-rate grouting slurry in regional governance”. Methods such as theoretical analysis, numerical simulation, and field verification were used to evaluate the diffusion mechanism of variable-rate fracture grouting. The results indicated that the key parameters of variable-rate grouting, such as slurry diffusion distance and grouting pressure, were affected by the grouting rate. The decrease in the grouting rate reduced the migration speed of the slurry and the grouting pressure. The time for constant-velocity grouting and variable-velocity grouting to reach the same diffusion distance was 60 s and 108 s, respectively, which can be achieved with lower grouting pressure. When the grouting rate was 7.5 L/min and 30 L/min, the maximum grout diffusion distance was 2.81 m and 5.64 m, respectively, which required greater grouting pressure. The slurry diffusion rate decreased with the reduction in the grouting rate. Under the same diffusion distance conditions, variable-rate grouting took longer than constant high-rate grouting. In variable-rate grouting, the grouting pressure decreased stepwise with the grouting rate, with a final pressure drop of 77.4%. In grouting practice, the innovative use of the rate-reducing grouting method can greatly reduce the final grouting pressure under the premise of changing the slurry diffusion distance less, which can not only ensure the stability of surrounding rock but also reduce the cost of high-pressure grouting and the risk of grouting operation. The investigation results can provide scientific guidance for ground grouting renovation projects in deep coal mine water hazard areas. Full article

Cementitious materials are used to construct an engineered barrier in repositories for radioactive waste. The cement matrix may contain a variety of organic compounds, some of which are polymeric admixtures used as plasticizers. Superplasticizers (SPs) are highly effective organic cement additives for reducing water amount, increasing workability, homogeneity, plasticity and the non-segregation of mortars and grouts, improving mechanical properties and resistance to destructive environments. SPs in cement could have an impact on the long-term safety of the disposals of radioactive waste. These organic agents can leach from the cementitious matrix into groundwater and may affect the migration behaviour of radionuclides. The detailed chemical composition and other characteristics of the cement (CEM I 42.5 R, Sweden) used for the leaching experiments were evaluated. It contained mainly CaO (52.51 ± 1.37, %), and the surface area of the cement particles was 13.2 ± 1.3 m²/g. An insignificant increase in pH (from 12.6 ± 0.1 to 12.8 ± 0.1) was observed for the leachates over 10 days. A commercially available cement superplasticizer based on polymelamine sulphonate (PMS) Peramin SMF10 (Peramin AB, Sweden) was chosen for the research. The product’s chemical composition was analysed using wavelength-dispersive X-ray fluorescence (WD-XRF) spectroscopy, while other physico-chemical properties of the PMS superplasticizer were assessed by Raman spectroscopy and thermo-gravimetric analysis. In aqueous solutions and powders of PMS, the same most intensive features were observed at 774 cm⁻¹ (ring out-of-plane deformation), 977 cm⁻¹ (C-N-C bending, SO stretching) and 1055 cm⁻¹ (C-N=C bending) in the Raman spectra. At up to 270 °C, the polymer was thermally stable. Raman and UV/Vis spectroscopies were used to assess the rate of the alkaline degradation of PMS superplasticizer in different aqueous solutions. No changes were observed in the hydrolytic solutions with any of the above analytical methods over a period of 3 years. The results obtained revealed a good thermal and chemical stability (in highly alkaline media, pH = 9.9–12.9) of the PMS polymer. Full article

In this study, the mechanical behavior of fully grouted rock bolts in hydraulic tunnels subjected to elevated ground temperatures was investigated. A differential equation for axial displacement of the rock bolt was formulated, which considers the force equilibrium of infinitesimal bolt segments and the stress transfer mechanism at the anchor–rock interface. The distribution functions for axial stress within the bolt and the interfacial shear stress were obtained by solving the differential equation, which incorporated the displacement of the surrounding rock mass as a parameter. This study showed that the effectiveness of the bolt–shotcrete support system decreases over time, considering the displacement relaxation rate of the surrounding rock mass. The mechanical model’s variation laws at 20 °C, 50 °C, and 80 °C were summarized by integrating the thermal deformation equation for material parameters, and the numerical simulation results were compared and analyzed. The findings revealed that the bond strength between the rock bolt and the rock mass diminishes as the temperature of the surrounding rock increases, leading to a reduction of interfacial shear stress at both extremities of the bolt. Moreover, the maximum axial force within the bolt escalates as the neutral point migrates farther from the tunnel wall. Full article

The drawdown outside of a deep foundation pit has to be controlled during excavation. However, the vertical curtain cannot cutoff a deep and thick confined aquifer during deep excavation. In this study, a microbial-induced carbonate precipitation (MICP) horizontal seepage reducing body (HSRB) was proposed to control drawdown combined with a partially penetrating curtain. MICP HSRB is formed by using the seepage field generated by the recharge wells to drive the migration of a Sporosarcina pasteurii solution, stationary solution, and cementation solution into the deep confined aquifer. The migration of each solution was numerically simulated to study the HSRB formation process. The influence of different factors on solute migration was studied. The results show that the solutes in the fixed fluid and cementation fluid can reach the area under the driving of the seepage field, which proves that MICP HSRB can be formed. The calcium ions and urea in the cementation solution are more likely to migrate to the designated area than the bacterial solution. Increasing the injection rate of bacterial solution and adding recharge wells both made the bacterial solution migrate more quickly to the designated area. In the case of multiple grouting, the solute migration in the later stage will be hindered by the plugging of pores caused by calcium carbonate generated in the earlier stage. Therefore, different grouting methods need to be designed to drive the seepage field so that the solute injected in the later stage can continue to migrate. The MICP HSRB grouting technology can be used in foundation pit dewatering, providing reference for similar engineering. Full article

Using a soil improvement biotechnology based on microbial-induced carbonate precipitation (MICP) to form a horizontal water barrier in foundation pit dewatering can not only achieve a good dewatering control effect, but also control the cost and obtain good economic and environmental benefits. In this study, taking the Shanghai layer ⑨ sand as the research object, the solution injected into the layer ⑨ sand by MICP grouting technology includes bacterial solution (Sporosarcina pasteurii) and cementation solution (urea and CaCl₂ solution). The migration mechanism of the bacterial solution and cementation solution in groundwater was analyzed through batch experiment and column test, and the mathematical model of migration was established. The dynamic adsorption characteristics of the S. pasteurii, Ca²⁺, and urea were obtained by dynamic adsorption test. Through isothermal adsorption test, the Freundlich isotherm was used to describe the isothermal adsorption of S. pasteurii onto fine sand, and the partition coefficient of the S. pasteurii was found to be 1.5 × 10⁻⁷ L/mg. The Langmuir isotherm can be used truly reflect the isothermal adsorption of Ca²⁺ onto fine sand. The distribution coefficient of the Ca²⁺ was 7 × 10⁻⁸ L/mg. The maximum adsorption capacity of the solute was 2404.8 mg/kg. The adsorption capacity of the urea was very small. According to the sand column test, the vertical dispersion was 11.5 cm. Due to the obvious size effect of dispersion, the sensitivity of dispersion in actual working conditions should be analyzed in a subsequent numerical simulation. The determined solute transport parameters provide support for the further study of the numerical simulation of the solute transport process of the HSRB formed by MICP grouting technology and provide a basis for further field application. Full article

Post-grouting technology has been extensively used in geotechnical engineering to improve the bearing capacity of various piles, which overcomes the technical limitations of the bored piles and recovers the mechanical performance of strata. A considerable amount of earlier research has been conducted to investigate the bearing behavior and reinforcement mechanism of the grouted piles, while very few studies focus on the reinforcement area of post-grouting technique. The theoretical analysis on reinforcement area is of great significance, which is beneficial to correlate the grouting parameters with pile bearing capacity with a target of saving cost and acquiring an optimized design. This paper conducted a theoretical analysis on the grout migration height, and then proposed a new predictive model to estimate the ultimate migration height of cement slurry, where the grout rising process is considered as the flow of Bingham fluid in an axial annular space. A field test was conducted to verify the applicability of the proposed model, and the comparison results revealed that the calculated height is slightly overestimated as compared to the actual values, but it is acceptable in engineering design. The grouting pressure loss and induced permeation was warranted to be studied in future. Full article

The mining-induced overburden bed separation grouting technique can control surface subsidence through the high-pressure grouting and filling into the bed separation during mining. The physical simulation method can be used to objectively reproduce the dynamic migration process of filling slurry in the bed separation but the traditional similar-simulation materials are not suitable for the simulation of bed separation grouting. Considering the water disintegration, weak water storage capacity, and poor permeability of traditional simulation materials, the existing similar-simulation materials were modified in this study. The improved similar-simulation materials have adjustable physical and mechanical parameters, stable properties in a water-filled environment, and high water storage and permeability, and the reasonable ratio of similar-simulation materials was determined for hard rock, medium-hard rock, and soft rock. The similarity simulation function suitable for bed separation grouting was deduced and the time similarity coefficient and permeability similarity coefficient of the bed separation grouting simulation were obtained to judge the similarity and applicability of similar-simulation materials with specific proportions. This study provides a reliable experimental simulation scheme for the physical simulation of mining-induced bed separation grouting and provides a theoretical basis for the improvement of similar-simulation materials with fluid–solid characteristics. Full article

Grouting can effectively seal and reinforce broken rock masses in deep geotechnical engineering, which have an important impact on groundwater-related disaster prevention and control. Based on multi-field coupling mechanics and rotational viscosity experiments, an advance grouting migration model of cement slurry in tunnels with high-stress broken surrounding rock is built against the background of the Xianglushan Tunnel for water diversion in central Yunnan Province. The influence characteristics of water–cement ratio, grouting pressure, and initial permeability on the process of grouting material migration are analyzed by combining classical column theory and spherical theory. The results show the following: Overall, the growth rate of grouting radius is fast during the earlier 5 min and slows down later. At the fifth minute, the normal grouting ranges are 22 cm, 51 cm, and 58 cm, at water–cement ratios 0.6, 0.8, and 1.0, respectively, while the normal grouting ranges are 58 cm, 51 cm, and 36 cm at grouting pressures 2 MPa, 1 MPa, and 0.5 MPa, respectively; the normal grouting ranges are 58 cm, 24 cm, and 11 cm at initial permeabilities 5D, 0.5D, and 0.05D, respectively. At the 60th minute, the normal grouting ranges are 47 cm, 133 cm, and 155 cm at water–cement ratios 0.6, 0.8, and 1.0, respectively; the normal grouting ranges are 155 cm, 131 cm, and 96 cm at grouting pressures 2 MPa, 1 MPa, and 0.5 MPa, respectively; meanwhile, the normal grouting ranges are 155 cm, 63 cm, and 29 cm at initial permeabilities 5D, 0.5D, and 0.05D, respectively. This study can provide theoretical guidance for on-site grouting design in unfavorable geological treatment projects. Full article