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The complex mechanical characteristics of calcareous sand complicate comprehensive analysis of the bearing characteristics of pressure grouting piles. The bearing mechanism of pressure grouting piles is unclear. Field tests of the bearing characteristics of pressure grouting piles in calcareous sand foundations were carried out. On the basis of the field test data, the coupled finite difference method (FDM) and discrete element method (DEM) were applied to explore the settlement characteristics. The force transfer laws in calcareous sand foundations are analyzed using complex network theory. The results show that the ultimate bearing capacity of pressure grouting piles increases significantly with increasing pile diameter. An increase in the pile‒soil interface friction coefficient can increase the pile side friction resistance, which can then increase the ultimate bearing capacity of the pile foundation. The friction coefficient of calcareous sand foundations can also increase the ultimate bearing capacity of pile foundations. However, the settlement of the pile foundation also increases. The axial force of the grouting pile gradually increases as the burial depth increases. When the pile bottom is reached, the axial force of the pile body clearly increases. This study presents an effective tool for the comprehensive analysis of the bearing characteristics of pressure grouting in calcareous sand foundations. [ABSTRACT FROM AUTHOR]

This article uses the engineering background of the Zhengzhou Metro Line 5 with a cement-soil group pile composite foundation. It simplifies the composite foundation using the area-weighted composite modulus method and establishes a finite element model of a double-line EPBM passing beneath the cement-soil group pile composite foundation building. The calculation results were compared and validated against monitoring data. Based on this, the simplified model was used to analyze the effects of face pressure and grouting pressure on the settlement of the upper structure. The research results indicate that the numerical simulation curves of settlement at monitoring points F17, F16, F15, and F14, where the shield axis intersects the building plane, align well with the monitored values, thereby confirming the rationality of the simplified model. Additionally, appropriately increasing the face pressure and grouting pressure is beneficial in suppressing the settlement of the upper structure; however, when the face pressure increases to 0.20 MPa and the grouting pressure increases to 0.35 MPa, the suppressive effect significantly diminishes. [ABSTRACT FROM AUTHOR]

In trenchless pipe jacking engineering practice, the formation of high-quality slurry jacket on the outer wall of pipe section is the key to effectively reducing the pipe-soil frictional resistance, improving the construction efficiency, reducing the construction risk and ensuring the construction safety. Herein, the multifunctional experimental apparatus for the pipe-soil frictional resistance testing is improved to ensure the smooth implementation of the subsequent experimental research. The influences of the structural parameters of grouting holes in circular and rectangular pipe sections on the pipe-soil frictional resistance and the states of slurry jackets around the various pipe sections are investigated respectively based on orthogonal experiment. Key findings include the pipe-soil frictional resistances increase with the increase of the spacing between adjacent grouting holes and the deflection angle of grouting holes, the layout of grouting holes has the greatest influence on pipe-soil frictional resistance, reasonable and uniform layout of grouting holes around the pipe sections can form more complete high-quality slurry jackets, to show better pipe-soil frictional resistance reduction effect. Moreover, the optimal structural parameters of grouting holes in circular and rectangular pipe sections are the same, i.e. the layout is triple grouting holes, the spacing between adjacent grouting holes S is 417 mm, and the deflection angle of grouting holes α is 40°. These insights could provide some scientific and valuable guidance for pipe-soil frictional resistance reduction during trenchless pipe jacking. [ABSTRACT FROM AUTHOR]

An improved method tailored for anisotropic soft soils is presented, integrating theoretical models and field data to calculate the grouting quantity required for tunnel foundations. Given the complexities of soil interactions, particularly under variable geological conditions, this approach incorporates nonlinear behaviors and empirical field data to improve accuracy. Our findings reveal that integrating these theoretical frameworks significantly enhances the understanding of stress–strain behavior during grouting, enabling precise calculations of both axial and vertical expansion. Validation against numerical simulations demonstrates the model's reliability, highlighting the influence of soil types and grouting depths on expansion dynamics. This method not only helps mitigate risks in tunnel construction but also enhances foundation reinforcement strategies, driving progress in geotechnical engineering. It is particularly valuable for urban tunnel projects in complex geological conditions, where ensuring ground stability and safety is crucial. [ABSTRACT FROM AUTHOR]

Abstract Effective and safe support in soft rock roadways remains a critical challenge in underground coal mining due to the extreme weakness of the rocks and their susceptibility to weathering and water invasion. This paper examines the tailgate of longwall panel 2606, a typical soft rock roadway excavated along the edges of mined-out areas with thin pillars at the Lvtang Coal Mine in Guizhou, China. Despite employing a combination of rock bolts, cable bolts, and surface support systems, significant roadway deformation was observed. The mechanisms behind this deformation were analyzed through in-situ tests and clay mineral composition analysis. These analyses revealed that the primary causes of the roadway’s substantial deformation were the low strength and weathering susceptibility of the coal and surrounding rock. A novel synergistic control strategy combining anchoring, shotcreting, and grouting was proposed for supporting soft rock roadways. Detailed numerical simulations were conducted to evaluate the deformation and stability of the tailgate under various support scenarios, validating the effectiveness of the proposed support scheme. The synergistic support strategy was implemented to reinforce the 2606 tailgate, and field monitoring was conducted to assess its effectiveness. Monitoring data indicated that rib deformation with the new support design was reduced by 66% compared to the original design. The results demonstrate that the improved synergistic support system effectively mitigated large deformations and maintained the stability of the tailgate. These findings provide a valuable engineering reference for supporting and reinforcing soft rock roadways under similar geological conditions.

Abstract The stability of coal pillars in fault areas is crucial for ensuring the safe passage of working faces. Based on field observations, frequent coal pillar spalling and substantial tectonic coal crumbs leakage, as well as tilting of hydraulic supports, are observed when working faces transition from primary coal to tectonic coal. To analyze the instability mechanisms behind these phenomena, this paper establishes a mechanical model of coal pillars in fault areas and analyzes the distribution of tectonic stresses and factors affecting the stability of coal pillars. The results indicate that horizontal tectonic stress adheres to an exponential function dependent on the angle factor, where (k 0) is a parameter associated with the friction angle of the coal body, the dip angle of the fault, and the friction angle of the fault plane. The stability of coal pillars is influenced by factors such as roof and floor pressures, coal pillar integrity, mining height, and shield support force, with coal pillar integrity being the most critical. To ensure the smooth passage of working faces through faults, this study proposes a combined control technique of “inclined mining” and “grouting,” including reducing mining heights, adjusting the slope of working face advancement, and pre-grouting of coal pillars. Industrial experiments conducted on-site have shown improved integrity of tectonic coal, enabling the working face to pass through faults smoothly and significantly increasing production efficiency.

The existing mechanical and grouting anchors mostly use the expansion shell method to form a cavity on the borehole wall, and the cement slurry is poured to form multiple enlarged head plates, but the operation is more difficult and the diameter of the formed plate is smaller. In this paper, a new type of large-diameter multi-plate soil anchor and its reaming cavity forming tool are proposed, which can make the operation easier and form a large-diameter enlarged head plate. In order to study the influence of the diameter of anchor plate, the number of anchor plates and the spacing of anchor plates on the vertical uplift capacity of the large-diameter multi-plate soil anchor, 25 sets of comparative models were established for simulation analysis. The finite difference method of FLAC3D software is used to simulate the model. It is found that when the length of the anchor is 6 m and the diameter of the anchor rod body is 150 mm, the optimal diameter of the anchor plate of the large diameter multi-plate soil anchor is 590 mm, the optimal number of anchor plates is 6, and the optimal anchor plate spacing is 800 mm, which means the action range of the anchor plate on the lower soil is about 5 times the diameter of the bolt. When the number of anchor plates is too small or the spacing between anchor plates is too large, the structural advantages of large-diameter multi-plate soil anchor cannot be fully utilized, resulting in a decrease in the ultimate uplift capacity. When the number of anchor plates is too large or the spacing between anchor plates is too small, the stress superposition effect occurs in the soil, and the through shear failure occurs, which leads to the decline of the ultimate uplift capacity. Under the condition that the number of anchor plates and the spacing of anchor plates are fixed, the larger the diameter of the anchor plate is, the larger the ultimate pull-out capacity of the large-diameter multi-plate soil anchor is, the smaller the vertical failure displacement of the anchor head is, but the increase of the uplift capacity is gradually reduced. The creep rate of the new large-diameter multi-plate soil anchor bolt is 0.91 mm, and the creep rate of equal-diameter soil anchor bolt is 1.69 mm. It is verified that the new large-diameter multi-plate soil anchor can be effectively applied to various projects. [ABSTRACT FROM AUTHOR]

Effective and safe support in soft rock roadways remains a critical challenge in underground coal mining due to the extreme weakness of the rocks and their susceptibility to weathering and water invasion. This paper examines the tailgate of longwall panel 2606, a typical soft rock roadway excavated along the edges of mined-out areas with thin pillars at the Lvtang Coal Mine in Guizhou, China. Despite employing a combination of rock bolts, cable bolts, and surface support systems, significant roadway deformation was observed. The mechanisms behind this deformation were analyzed through in-situ tests and clay mineral composition analysis. These analyses revealed that the primary causes of the roadway's substantial deformation were the low strength and weathering susceptibility of the coal and surrounding rock. A novel synergistic control strategy combining anchoring, shotcreting, and grouting was proposed for supporting soft rock roadways. Detailed numerical simulations were conducted to evaluate the deformation and stability of the tailgate under various support scenarios, validating the effectiveness of the proposed support scheme. The synergistic support strategy was implemented to reinforce the 2606 tailgate, and field monitoring was conducted to assess its effectiveness. Monitoring data indicated that rib deformation with the new support design was reduced by 66% compared to the original design. The results demonstrate that the improved synergistic support system effectively mitigated large deformations and maintained the stability of the tailgate. These findings provide a valuable engineering reference for supporting and reinforcing soft rock roadways under similar geological conditions. [ABSTRACT FROM AUTHOR]

The stability of coal pillars in fault areas is crucial for ensuring the safe passage of working faces. Based on field observations, frequent coal pillar spalling and substantial tectonic coal crumbs leakage, as well as tilting of hydraulic supports, are observed when working faces transition from primary coal to tectonic coal. To analyze the instability mechanisms behind these phenomena, this paper establishes a mechanical model of coal pillars in fault areas and analyzes the distribution of tectonic stresses and factors affecting the stability of coal pillars. The results indicate that horizontal tectonic stress adheres to an exponential function dependent on the angle factor, where (k0) is a parameter associated with the friction angle of the coal body, the dip angle of the fault, and the friction angle of the fault plane. The stability of coal pillars is influenced by factors such as roof and floor pressures, coal pillar integrity, mining height, and shield support force, with coal pillar integrity being the most critical. To ensure the smooth passage of working faces through faults, this study proposes a combined control technique of "inclined mining" and "grouting," including reducing mining heights, adjusting the slope of working face advancement, and pre-grouting of coal pillars. Industrial experiments conducted on-site have shown improved integrity of tectonic coal, enabling the working face to pass through faults smoothly and significantly increasing production efficiency. [ABSTRACT FROM AUTHOR]

The study is based on a section of the Zhengzhou Metro Line 8 quasi-rectangular shield tunnel. Field excavation trials were conducted to analyze the surface settlement patterns caused by the construction of a large-section quasi-rectangular shield tunnel in the rich water sand layer in Zhengzhou. Based on the characteristics of the rich water sand layer, ground settlement control measures were proposed. The research findings show that the surface settlement caused by the construction of the large-section quasi-rectangular shield tunnel in the rich water sand layer exhibits a temporal curve pattern of slow settlement (Stage I: pre-arrival of the shield), rapid settlement (Stage II: shield passage, Stage III: shield tail exiting 14.4 ~ 18 m), and stable settlement (Stage IV: late settlement). In Stage I, controlling the excavation rate to maintain balance between the cutter face pressure and soil pressure is effective. In Stage II, injecting lubricating mud between the shell and the sand layer to reduce soil friction and shear slip is recommended. In Stage III, increasing the synchronous grouting volume at the shield tail and adjusting grouting pressure, as well as timely filling the shield tail construction gap, are effective methods to reduce surface settlement. The Peck formula was used to fit the transverse settlement trough on the surface, with a linear correlation coefficient R²=0.983, validating the use of the Peck formula to predict surface settlement troughs for quasi-rectangular shield tunneling in the rich water sand layer. These research findings can provide data support and reference for similar projects. [ABSTRACT FROM AUTHOR]

A significant number of steep cracks are frequently encountered in underground engineering, posing a threat to operation. The high-pressure grouting method is a commonly utilized repair technique. Nevertheless, conventional grout is prone to displacement due to its weight, making it challenging to ensure adequate filling of the cracks. Therefore, this study aims to develop a grouting material with targeted displacement and anchoring properties. Firstly, an optimal magnetic slurry composition was determined through an orthogonal test. Subsequently, XRD and SEM were used to analyze the impact of the magnetic field on the composition distribution, internal pore structure, and transient viscosity of the slurry. Afterwards, a model for localized grout diffusion under magnetic was established. The results show that the application of a magnetic field caused the slurry to compact due to magnetic forces, reducing its porosity. Moreover, the dynamic viscosity of the slurry increased exponentially with rising magnetic induction intensity. Notably, a 40.5% increase in the diffusion area was observed when the magnetic field intensity rose from 2500 to 4500 GS. The error between the measured and theoretical values of the magnetic slurry diffusion model was only 8.91%, indicating the model's accuracy in describing the slurry diffusion process under magnetic field influence. [ABSTRACT FROM AUTHOR]

The surrounding rock of tunnels in cold regions are susceptible to the freeze–thaw cycle resulting from the combination of low temperatures and moisture during tunnel service. The phenomenon will not only lead to the expansion of pores and fissures in the surrounding rock of the initial tunnel, but also destroy the integrity of the rock. This destruction will have a serious impact on tunnel structure and rail transit operation safety. At present, the commonly used thermal insulation measures have some problems such as maintenance difficulties, low economic efficiency, and safety hazards. Therefore, it is urgent to develop a kind of tunnel maintenance grouting material with insulation and anti-permeability, which has the characteristics of simple operation, easy preparation and application. We independently developed a composite grouting material composed of polyurethane (PU), epoxy resin (E-51) and acrylic powder (PMMA). Through the material combustion test, magnesium hydroxide was selected as the flame retardant additive. Moreover, we measured the thermal conductivity, water absorption, apparent density, porosity and strength characteristic parameters. The thermal insulation and anti-permeability characteristics of the composites were also analyzed. The results indicated that the thermal conductivity of the new composite grouting material is 6.3% lower than the PU before adding flame retardant. Compared with the PU with flame retardant, the water absorption decreased by 74.4% and the ultimate strength increased by 33.3%. For the area with an average temperature lower than − 10 °C, we recommend the ratio scheme of E-51: 3%; PMMA: 15%. For the area with high water content in the surrounding rock of the tunnel, we recommend the ratio scheme of E-51: 15%; PMMA: 3%. This study provides new ideas for material preparation and tunnel insulation methods for anti-freezing measures in tunnels during their operational period in cold regions. [ABSTRACT FROM AUTHOR]

The segment misalignment is a common defect in the segment installation of a shield tunnel construction, due to the complexity and uncertainty of its construction conditions. This raises a concerning about the safety of the segment lining for the shield tunnel. In this paper, the integrated numerical models with surrounding rock, peastone grouting and segment lining were built using three-dimensional finite element method, by introducing two kinds of misaligned defects of segments. One was the misalignment that elongated the horizontal axis of the transversal ring section of segment lining, another was the misalignment between adjacent rings of segments. To eliminate the impact of boundary on numerical results, seven rings of segments are built for the three-dimensional finite element models, and the middle ring is dealt with for the results analysis under V-class surrounding rock, including the circumferential stress of outer and inner layers of the segment, the contact stress on joint surface between segments, and the stress of locating pins between adjacent rings. Results indicate that the two kinds of misaligned defects create pronounced impact on tensile stress of segment at the bottom and the crown segments, respectively, which produces a greater tensile stress to increase cracking risk even abrupt fracture of segment. However, the misaligned defects have a slight impact on the contact stress and the locating pins stress. Therefore, attention should be paid to the cracking of bottom or crown segments in the segment lining of shield tunnel. [ABSTRACT FROM AUTHOR]

This paper is based on the proximity engineering project of the Baishiyi tunnel group passing under the Chongqing West Station track group. Considering the train load and the spatial relationship of the tunnel and track groups, the settlement patterns, horizontal displacement, and differential settlement of the tunnel–strata–tracks system during the excavation process are studied through theoretical calculations and numerical simulation methods. The results indicate that the tunnel vault, strata, and track settlement deformation patterns are similar. Throughout the tunnel construction process, the tracks underwent uplift, settlement, and eventually stabilized. The settlement trough formed by the excavation of the three tunnels below the track group has an impact range of 25–145 m. Between 35 and 75 m, the differential settlement of the double track gradually increases with excavation. As the tunnel face reaches 75 m, the track differential settlement gradually converges and tends to stabilize. To minimize the impact of underpass tunnel construction on track groups, it is recommended to use a combination of full-section hole grouting and surface reinforcement grouting for ground reinforcement. Additionally, optimizing the construction parameters, including the step length and primary support closure time, and strengthening the locking anchor can further reduce the impact. [ABSTRACT FROM AUTHOR]

In order to achieve the purpose of long-term stable mining of roadway, the strength and stability of rock mass are improved by means of grouting of fractured rock mass. In this paper, orthogonal test and numerical simulation methods were used to study the plugging performance of large amount of fly ash grouting slurry. The fluidity, water separation rate, compressive strength, setting time, stone rate and viscosity of the slurry were analyzed, and the optimal slurry ratio scheme was obtained. Under the optimal ratio scheme, the slurry transport process of the fractured rock mass was simulated, and the dynamic evolution law of the permeability of the slurry in the fractured rock mass was obtained. The study shows that the proportions of fly ash, ordinary Portland cement, loess, accelerant, expansion agent, bentonite water reducer and solidifying agent were 52.65%, 27.70%, 13.85%, 3%, 0.7%, 0.8%, 0.6% and 0.7% in the slurry ratio scheme, respectively. The slurry migration in the fractured rock mass experienced three stages, namely the filling and diffusion stage, the percolation and deposition stage and the sealing stage. The initial permeability was 971.9 mD and decreased to 45.79 mD after 1800 s, with a decrease of 95.3%. The slurry sealing performance was significantly improved, which has certain guiding significance for the application of underground grouting reinforcement engineering. [ABSTRACT FROM AUTHOR]

In order to solve the water and gas discharge hazard caused by gob water and harmful gases (such as CO), the method of grouting overburden fractures is adopted to achieve the purpose of safe and efficient mining production in coal mines. This paper carries out the experimental research on the permeability reduction effect of grouting in fractured rock mass, expounds the relationship between gas flow rate and pressure gradient, seepage pressure and permeability, confining pressure and permeability, and analyzes the permeability change law of fractured rock mass before and after grouting. Besides, the grouting migration and permeability reduction model of fractured fine-grained sandstone is constructed by combining grouting test and numerical simulation, which reveals the dynamic evolution law of rock mass permeability in the grouting process. The results show that the permeability of the grouting rock sample decreases from 700–13,000 to 15–300 mD than that of the ungrouting rock sample, and the decrease is more than 95%, which indicates that the sealing performance of grouting slurry is better. Besides, numerical simulations show that the initial permeability of rock samples is 971.9 mD, and the permeability decreases to 45.79 mD after 1800s, and the permeability decreases to 95.3%, which is basically consistent with the experimental results after grouting. The greater the grouting pressure is, the better the grouting effect is. With the increase of the grouting pressure, the increase of the grouting effect is no longer obvious. [ABSTRACT FROM AUTHOR]

The macroscopic characteristics of the fractured space and the microscopic pore features are critical factors determining the effectiveness of gangue slurry backfilling. To identify the key areas for slurry backfilling, a combination of theoretical analysis, simulation experiments, and on-site industrial trials was used to reveal the movement laws of backfilling space overlying the fractured zone. The distribution characteristics of voids available for slurry backfilling within the fractured space were explored, and the interaction between gangue slurry and goaf voids was clarified. A formula for calculating the void ratio in the caved zone was derived, and a model for the distribution of voids in the slurry backfilling space was established. This model identified the main areas where slurry backfilling should be focused, namely the overlapping space between the free accumulation zone and the load-influenced zone. Experimental results demonstrated that the porosity of the collapsed rock mass within the goaf follows a negative logarithmic function along both the dip and strike directions, which was consistent with the theoretical calculations. Through in-situ grouting backfilling experiments on the ground, the feasibility of gangue slurry backfilling in the goaf was verified, and the process of interaction between gangue slurry and goaf voids was elaborated. This process generally involves three stages: initial flow, vertical upwelling, and horizontal diffusion, all of which are closely interconnected. Practical engineering applications of gangue slurry backfilling were carried out in the free accumulation zone and the load-influenced zone at the Huangling No. 2 coal mine. The successful validation of underground gangue slurry backfilling technology demonstrated its feasibility and the correctness of the theoretical approach. This research provides new evidence for environmentally friendly disposal of gangue materials. [ABSTRACT FROM AUTHOR]

It is of great theoretical significance and engineering application value to research the diffusion law of slurry in mining fractures of rock strata to enrich grouting theory and improve grouting sealing effect. In this paper, the law of grout diffusion in fractures under different working conditions is systematically explored and analyzed, and a numerical simulation scheme of grout diffusion in a single slab crack is established. Then, the diffusion law of grouting slurry in crack under different rheological index and different consistency index is further investigated. The results show that the diffusion time of grouting slurry has no relation with the rheological index. The grout pressure at the same point increases with the increase of rheological index. When the rheological index increases by 0.1, the grout pressure increases by about 12.5%. The closer the grouting mouth is, the more the grouting pressure is affected by the rheological index. There is little relationship between the diffusion time of grouting slurry and consistency index. The grout pressure at each measurement point increases with the increase of the consistency index. When the consistency index increases by 1, the grout pressure increases by about 15% on the basis of the origin. The closer the grouting mouth is, the more the grouting pressure is affected by the consistency index. In engineering practice, when grouting slurry with large rheological index or consistency index exists, it is necessary to moderately increase the grouting pressure value. [ABSTRACT FROM AUTHOR]

Based on the greening and low interference disposal requirements of coal gangue in high-yield and high-efficiency mines in Inner Mongolia and Shaanxi, and by integrating the existing theories and technologies such as underground filling technology of coal gangue, mine yellow mud grouting technology, and the evolution law of mining overburden fractures, a technology of filling goaf with coal gangue slurry for green disposal of coal gangue is proposed. The principle and technical framework of the technology of filling goaf with coal gangue slurry are clarified. This paper expounds on the technological process of technology of filling goaf with coal gangue slurry, establishes three types of slurry filling systems, such as centralized ground layout, ground and underground coordinated layout, and centralized underground layout, and constructs three slurry filling methods, including low-level grouting, adjacent level grouting, and high-level grouting, forming seven kinds of technology models of filling goaf with coal gangue slurry, including ground centralized pulping + high-level grouting, ground centralized pulping + adjacent grouting, ground centralized pulping + low level grouting, ground and underground coordinated pulping + adjacent grouting, ground and underground coordinated pulping + low level grouting, underground centralized pulping + adjacent grouting, and underground centralized pulping + low level grouting, and gives the selection process of technology models of filling goaf with coal gangue slurry. Based on the different conditions and requirements of Haidaze Coal Mine and Huangling No. 2 Coal Mine, engineering tests were carried out on two different technology modes, namely, ground and underground coordinated pulping + low level grouting and ground and underground coordinated pulping + adjacent grouting, based on simulation tests of low level grouting and adjacent grouting. The tests prove the feasibility of filling goaf with coal gangue slurry and explore the way for the theoretical research of the technology of filling goaf with coal gangue slurry and greening and low interference disposal of coal gangue. [ABSTRACT FROM AUTHOR]

The disposal and utilization of solid waste of coal gangue is one of the main problems in coal mining in China. Injecting coal gangue into goaf in the form of slurry can effectively solve the problems of ground stacking and environmental pollution prevention. In order to obtain the flow law of gangue slurry in the void of the accumulated rock in the goaf, a visualization simulation test device for gangue slurry permeation grouting in the goaf was independently designed. The flow and diffusion characteristics, flow and diffusion velocity changes, void pressure changes, and viscosity changes of three mass concentrations (76%, 78%, 80%) of gangue slurry in the void between caved rock blocks in goaf were studied by visual grouting simulation test. The results show that: (1) The seepage process of gangue slurry in the goaf simulation test is divided into three diffusion forms, namely radial diffusion, axial diffusion, and bidirectional diffusion. The three diffusion forms are interrelated and inseparable. (2) The initial flow velocity of the slurry with different concentrations is different under the same permeation grouting pressure, and the higher the slurry concentration, the smaller the initial flow velocity of the slurry. The velocity of the slurry has a nonlinear relationship with the diffusion distance of the slurry. (3) With the permeation and diffusion of slurry, pressure sensors at different positions are subjected to pressure from bottom to top and enter the pressure boost stage, gradually forming stress peaks. When the slurry exceeds the position of the pressure sensor, the pressure on the pressure sensor is weakened and begins to enter the pressure relief stage, and the stress decline trend gradually becomes gentle with time. (4) The water loss effect occurs during slurry flow interaction with rock mass, resulting in slurry viscosity increasing. The viscosity of the slurry affects the difference in the amount of viscosity change. The research results can provide a certain theoretical basis for the goaf gangue slurry filling project. [ABSTRACT FROM AUTHOR]

Because of the deficiencies in safety and economy of the single hydraulic prop passive advanced support, the grouting anchor cable active advanced support technology is proposed with the Changping Coal Mine 53,081 roadway as the engineering background. By using a combination of theoretical analysis, laboratory tests, numerical simulation, and field tests, the influence of different grouting parameters on the diffusion law of grout is studied. Considering the effect of the stress field on grout migration, a grout seepage-stress coupling model is established. Grouting material ratio tests are carried out and grout parameters are tested. The grouting part of the advanced grouting anchor cable is modeled and solved using the COMSOL Multiphysics numerical software. The results show that the grouting material selected is Portland cement 42.5 and water glass double liquid grout, with a slurry ratio of 15% ACZ-1 type additive and 4% water glass content, and a water–cement ratio of 0.6. The grouting pressure for the 53,081 roadway grouting anchor cable advanced support is 5 MPa, the grouting time is 6 min, and the grouting anchor cable spacing is 2000 mm × 1000 mm. The engineering application shows that the maximum roof subsidence is 180 mm, the maximum separation value at a depth of 9 m is 24 mm, and the maximum separation value at a depth of 3 m is 90 mm. The research results have achieved effective advanced support for the 53,081 roadway, replacing the single hydraulic prop, and provided a theoretical basis for the subsequent design of advanced support parameters for mining roadways. [ABSTRACT FROM AUTHOR]

Colloidal silica grouting is a ground improvement technique capable of stabilizing weak problematic soils and achieving large reductions in soil hydraulic conductivities for applications including earthquake-induced liquefaction mitigation and groundwater flow control. In the conventional approach, chemical accelerants are added to colloidal silica suspensions that are introduced into soils targeted for improvement and the formation of a semi-solid silica gel occurs over time at a rate controlled by suspension chemistry and in situ geochemical conditions. Although the process has been extensively investigated, controlling the rate of gel formation in the presence of varying subsurface conditions and the limited ability of conventional methods to effectively monitor the gel formation process has posed practical challenges. In this study, a biomediated soil improvement process is proposed which utilizes enriched fermentative microorganisms to control the gelation of colloidal silica grouts through solution pH reductions and ionic strength increases. Four series of batch experiments were performed to investigate the ability of glucose fermenting microorganisms to be enriched in natural sands to induce geochemical changes capable of mediating silica gel formation and assess the effect of treatment solution composition on pH reduction behaviors. Complementary batch and soil column experiments were subsequently performed to upscale the process and explore the effectiveness of chemical, hydraulic, and geophysical methods to monitor microbial activity, gel formation, and engineering improvements. Results demonstrate that fermentative microorganisms can be successfully enriched and mediate gel formation in suspensions that would otherwise remain highly stable, thereby forgoing the need for chemical accelerants, increasing the reliability and control of colloidal silica grouting, enabling new monitoring approaches, and affording engineering enhancements comparable to conventional colloidal silica grouts. [ABSTRACT FROM AUTHOR]

In this study, a sump in the Xingdong coal mine (buried at a depth of over 1200 m) was used to analyze the surrounding rock's stability and control technology. Under the combined influences of various complex conditions, such as the burial depth of over 1200 m, ultra-high ground stress, and location under the goaf, the sump support became extremely difficult, severely restricting the efficient production of the mine. The overall pressure-relief mechanisms and degree of the sump surrounding the rock environment under the goaf were studied, and the rationality of the sump location was verified through numerical simulations and field tests. A more effective support scheme was proposed based on the deformation characteristics and failure mechanisms of the temporary sump-surrounding rock under the supporting conditions. The combined control technology employed the lengthened strong anchor bolts (cables), full-section concrete-filled steel tubular supports, and pouring full-section reinforced concrete and full-section long-hole grouting reinforcement. The field test results showed that after adopting the new support scheme, the sump-surrounding rock tended to be stable after three months. The sump roof subsidence amount, floor heave amount, and convergence of the two sidewalls of the sump were 17.2–19.2 mm, 13.9–16.5 mm, and 23.2–27.9 mm, respectively, thus satisfying the application requirements. This study provides an essential reference for deep-mine roadway support under a complex high-ground-stress environment. [ABSTRACT FROM AUTHOR]

Shield tunneling method is widely used in urban metro construction. The construction stability is closely related to the engineering geological conditions. Sandy pebble strata have a loose structure and low cohesion, resulting in great engineering-induced stratigraphic disturbance. Meanwhile, the high water-abundance and strong permeability are extremely detrimental to construction safety. It is of great significance to evaluate the dangerousness of shield tunneling in water-rich pebble strata with large particle size. In this paper, risk assessment of engineering practice is carried through with Chengdu metro project in China as a case study. Referring to the special engineering situations and assessment workload, seven evaluation indices, including compressive strength of pebble layer, boulder volume content, permeability coefficient, groundwater depth, grouting pressure, tunneling speed and tunnel buried depth are selected to establish an evaluation system. A complete risk assessment framework is established based on the cloud model, AHP and entropy weight method. Further, the measured surface settlement is taken as the risk degree characterization to verify the results. This study can provide reference for method selection and evaluation system establishment in the risk assessment of shield tunnel construction in water-rich sandy pebble strata, and contribute to proposing safety management in similar engineering projects. [ABSTRACT FROM AUTHOR]

For the interaction of crack on the soil–grout interface under fracture grouting, an approximate method to determine the stress intensity factor (SIF) of crack on the soil–grout interface was proposed based on the conservation J2-integral. With this method, the energy release rate of crack propagation under fracture grouting can be defined by the parameters of elastic–plastic soils and the grouting pressure. In order to study the change of strain energy near the crack of elastic–plastic soil under fracture grouting, a mechanical model of elastic–plastic soil with crack was established based on non-associated Mohr–Coulomb criterion model, and the SIF of crack with spring boundary was investigated. The influence of the crack depth ratio and crack aspect ratio on the SIF of cracks under the spring boundary were analyzed, and revealed the rule of crack growth under fracture grouting in elastic–plastic soils. The results showed that the variation of the crack depth ratio and crack aspect ratio had an effect on the change of the SIF of cracks. Increasing the crack depth ratio and crack aspect ratio caused an increase in the SIF of the crack. The results can provide the reference for foundation reinforcement in elastic–plastic soils. [ABSTRACT FROM AUTHOR]

Urban rail transit is widely used in major cities worldwide due to its high efficiency, safety, and environmental friendliness. Shield construction has a fast excavation speed and a negligible impact on ground transportation; thus, it is the preferred construction method for urban rail transit tunnels. Mudstone is a widely distributed soft rock characterized by large deformation, low strength, and significant rheological differences in different areas. Mudstone causes problems in the design and construction of subways. This paper uses finite element analysis to establish a three-dimensional numerical model of a double-line tunnel in a weathered mudstone area and analyze the influence of the stratum, design, and construction parameters on surface settlement and deformation during asynchronous and simultaneous shield construction. The research results show that the lateral surface settlement curve obtained from the simulation is consistent with the measured data, demonstrating the reliability and feasibility of the three-dimensional numerical model. The surface settlement is affected by the deformation modulus, cohesion, and the angle of internal friction, and the deformation modulus has the most significant impact. The surface settlement decreases as the buried depth of the tunnel or the distance between the two center lines of the two tunnels increases. As the buried depth of the double-lane tunnel decreases or the distance between the two center lines of the two tunnels increases to a certain value, the lateral surface settlement curve exhibits two peaks. The surface settlement shows a decreasing trend with an increase in the thrust of the shield machine and an improvement in the grouting quality. However, excess grouting pressure causes surface uplift and a subsequent increase in surface subsidence. [ABSTRACT FROM AUTHOR]

To quantify the diffusion range of slurry in grouting engineering, an active heating optical fiber (AHFO) monitoring method is proposed. The AHFO is arranged on the coal seam floor. The temperature is taken as the monitoring parameter to monitor the diffusion range and state of slurry in the injected medium. Considering the time-varying characteristics of slurry rheological parameters, the theoretical calculation formula of spherical diffusion radius based on the power-law fluid is deduced. The relationship between the void ratio and grouting diffusion radius is discussed. Considering the influence of the seepage effect, the "water cement ratio change matrix" in the process of mud seepage is derived, and the influence of the space–time change of the slurry water cement ratio on the temperature gradient of the injected medium is studied. According to the factors affecting grouting diffusion, four groups of small three-dimensional simulation tests and one large three-dimensional grouting test are designed to verify the feasibility of the proposed method. The results show that the relative error of the AHFO monitoring radius is between 3.00 and 14.67%, based on the actual diffusion radius. In the large-scale three-dimensional grouting test, the data from AHFO is used to generate the two-dimensional surface of the grouting diffusion form, and the grouting diffusion range is asymmetric oval. Compared with the theoretical calculation results, the maximum relative error of grouting diffusion radius is 9.6%, and AHFO shows prediction accuracy. With the decrease in the water-cement ratio of slurry, the temperature gradient of the injection medium monitored by AHFO increases, showing an obvious space–time effect. The application of AHFO in the grouting simulation test can effectively analyze slurry diffusion in the injected medium. [ABSTRACT FROM AUTHOR]

We have investigated the activation characteristics of mining faults and the effect of grouting reinforcement under thick loose layer and thin bedrock of the working face and evaluate their impact on the safety of mining at similar working faces. Implementing the geological conditions of the 331 working face of the Yangcun Coal Mine (China) of the Yankuang Energy Group Corporation, we have analyzed mechanically the process of fault activation at first. Subsequently, we have obtained the mechanical criterion of fault slip and the expression of relative strength of the nearby rock mass. Using numerical software we have simulated and analyzed the damage characteristics of different bedrock thicknesses on overlying rocks and faults in the fluid–solid coupling mode. In addition, we have studied the controlling effect of grouting reinforcement on fault activation, which has been verified in the field. The main results of our study show that: 1. The mechanical properties of the rock mass near the fault interface have changed and they are related to the cohesive force of the interface; 2. The water inrush mode of the working face changes under different bedrock thickness, and the thinner the bedrock, the less easily the fault is destroyed 3. The slip of the high-level fault is reduced after the grouting of the fault, the propagation of the fracture zone at the fault is suppressed, the seepage of the aquifer water is prevented, and the safe recovery is realized. The results of our study provide a scientific basis for the secure mining across the fault of the 331 working face of Yangcun Coal Mine. Based on the results of our study the working face can be mined safely from now on and in the future. [ABSTRACT FROM AUTHOR]

Groundwater level has to be lowered during deep excavation. A vertical curtain is usually adopted to control the drawdown inside and outside a foundation pit in a built-up area. However, the cost and working difficulty increases substantially with the rise in depth of vertical curtains. In the manuscript, a man-made horizontal seepage reducing body (HSRB) was introduced to shorten the vertical curtain depth and control drawdown. With the No. 4 shaft foundation pit of Guangyuan Project, Shanghai as background, HSRB was proposed in foundation pit dewatering. Microbially induced carbonate precipitation grouting technology was recommended to form an environment-friendly HSRB. Numerical method was used to simulate and understand the influence of position, thickness, and hydraulic conductivity of HSRB on groundwater level. The non-separated HSRB was better than the separate HSRB. Decreasing HSRB hydraulic conductivity was better than increasing HSRB depth. Four seepage modes were summarized considering vertical curtain penetration conditions into multi-aquifer, and the fifth seepage mode was formed for vertical curtain using man-made HSRB, which can be referred by similar engineering applications. [ABSTRACT FROM AUTHOR]

Deep coal seam mining often leads to water resource loss due to bedrock water entering the workings of the mine and is discharged adjacent to the mining area. Using the geological conditions of the Maiduoshan coal mine, this paper applied a physical simulation experiment. The specified rock above the coal seam was hydraulically fractured in advance to form a postmining grouted fracture network, followed by grouting to construct a flexible isolation layer that blocked the infiltration of groundwater from the aquifer into the water-conducting fracture zone. Stress sensors, flow sensors and strata displacement monitoring technology were deployed inside the experimental material to study the spatial distribution characteristics and evolution law of the water-conducting fracture zone in the overlying rocks. Analysis of the water-conducting fracture zone development law, stress variation, overburden evolution characteristics, fracturing and grouting sequence of the flexible isolation layer and the effect of postmining grouting on the water barrier was conducted. These experiments verified the feasibility of fracture and grouting of the flexible isolation layer. These research results will provide practical guidance for the transition from the current safe and efficient mining methods to safe and green mining methods of deep coal mining in the western mining areas of China. [ABSTRACT FROM AUTHOR]

The naturally formed aeolian sand dunes in northern Shaanxi exhibit unique engineering characteristics. Several challenges, such as the poor self-stabilization ability of the surrounding rock, difficultly in injecting grout, and insufficient construction experience, restrict the construction of road tunnels under this stratum. Therefore, in this study, a case study of the Shenmu No. 1 tunnel was conducted to investigate the engineering characteristics of aeolian sand tunnels, compare the grouting effects of commonly used grouting materials, and discuss the reinforcement effects of different construction schemes in aeolian sand tunnels. Based on a field grouting test, it was determined that it is difficult to inject ordinary cement grout into an aeolian sand layer. Furthermore, it was determined that superfine cement grout and modified sodium silicate grout can be injected, but the former exhibits a poor reinforcement effect. Additionally, results of numerical analysis indicated that an approach based on a concept of "horizontal jet grouting pile + benching partial excavation method with a temporary invert" is suitable for the construction of tunnels in aeolian sand in China. [ABSTRACT FROM AUTHOR]