Grouting Parameters Research Articles

Investigations on Shear Properties of Soft Rock Joints under Grouting

Soft rocks are widely distributed in deep coal mines, and usually very difficult to keep stable. Grouting is widely used to strengthen the surrounding rocks, and to maintain roadway stability with other reinforcement methods. Because shear failure is one of the most common modes for deep surrounding rocks, research on shear behaviors of grouted soft rocks is very important for understanding the reinforcement mechanism. In this work, soft rocks from the Huainan coal mine were employed to achieve cubic specimens by a special method, and their shear properties under grouting were investigated using the direct mechanical tests. The results showed that grouting strongly affected both strength and deformation characteristics, and the shear mode was changed after grouting. In particular, the normal stiffness was obviously increased with grouting, and the residual shear strength was higher than that without grouting. Based on the grouting effects on the shear properties, the mechanism was revealed, and a strength model was proposed, which could be helpful for practical applications of soft rock grouting, such as optimal selection of grouting parameters, grouting scheme design.

Groundwater Inrush Control and Parameters Optimization of Curtain Grouting Reinforcement for the Jingzhai Tunnel

Based on the systematic study on the characteristics of water and mud inrush during the excavation of Jingzhai tunnel, the mechanism of water inrush seepage transformation caused by excavation disturbance is analyzed. By means of electromagnetic geophysical prospecting, the potential water bearing area of the tunnel was analyzed. The constitutive model of rock mass and grouting parameters are considered in the numerical simulation. The law of tunnel crack initiation and expansion under different curtain grouting parameters is proposed. The characteristics of seepage water inrush caused by excavation are described. It is considered that there are three stages in the seepage characteristics of tunnel: incubation, sudden, and stable. Numerical simulation was used to analyze the crack propagation track and water inflow characteristics under the grouting thickness of 3 m, 5 m, and 7 m. When the curtain grouting thickness was 3 m, the fracture field penetrated the curtain grouting area. The dominant seepage channel is formed, which greatly increases the probability of water inrush. When the curtain thickness is 5~7 m, the expansion of the crack zone can be controlled basically, so that the fracture and water bearing rock layer cannot form a seepage channel. At last, the grouting scheme of 6 m thick grouting and 20 m advanced grouting was selected, and the water seepage was reduced by 83%.

Study on Sensitivity Parameters Analysis of Grouting Reinforcement Underpassing Existing Subway Tunnel by Numerical Modeling

When carrying out construction that underpasses existing subway tunnels, the surrounding rock is frequently disturbed. Therefore, it can loosen easily and become unstable, which makes its stability difficult to control. Here, we considered an existing subway tunnel in a certain subway section and used orthogonal experiments to design a simulation program as well as the UDEC (Universal Distinct Element Code) simulation software to determine the influences of four factors (i.e., grout density, grouting pressure, dynamic shear force, and viscosity) on the grouting reinforcement effect. The following results were obtained: (1) the combination of the construction method and the grouting parameters strongly influences the reinforcement effect on the surrounding rock of the tunnel. The grouting pressure is not directly proportional to the stability of the surrounding rock. The dynamic adjustment of the relationship between the grouting pressure and the grout density can effectively improve the stress state of the surrounding rock of the tunnel, control surface settlement and deformation, and reduce the section reduction rate of the tunnel. (2) The distribution of joints is closely related to the failure area and form of the surrounding rock of the tunnel. For surrounding rock with well‐developed joint fissures, an excessively high grouting pressure should not be used as they are unstable. (3) The effective bearing range of grouting‐reinforced surrounding rock is dependent on the pore pressure and principal stress difference. The area where the pore pressure is 70–80% of the initial grouting pressure is the effective bearing range of the grouting‐reinforced surrounding rock. The stability of the surrounding rock increases with decreasing principal stress difference and increasing range. (4) The actual monitored data show that the surface settlement can be effectively reduced by handling of grouting reinforcement parameters flexibly, which can meet the control standards.

Grouting for water and mud inrush control in weathered granite tunnel: A case study

This paper presents a case study of curtain grouting to prevent water and mud inrush disasters for a weathered granite tunnel in Guangxi, China. First, the basic information of the Junchang tunnel is given, including ground conditions, water and mud inrush disasters, and the subsequent prevention countermeasures. Then, we present the original grouting design and procedure, and the field operation of 25 grouting cycles and excavations for the evaluation of the grouting effect and suggestion for future grouting work. Based on the field investigation, the values of the major grouting parameters are suggested, including grouting thickness of 5– 8 m, grouting length of 15– 18 m (3– 3.6 times of thickness), and per-meter grouting volume of 34.2 m3. Furthermore, the guidelines for composite materials selection are proposed for the various flowing water environments. Moreover, the space positions and water quality of the inspection boreholes and the original water richness of the ground should be taken into consideration in the grouting evaluation criteria. The optimized grouting parameters, materials selection and evaluation criteria provide important references for disasters prevention in similar projects.

Application of Artificial Freezing of Water-rich Sand Stratum in Metro Communication Passage

In view of difficult excavation of the water-rich sand stratum, the layout of freezing holes, the selection of freezing parameters, the thaw settlement control of the soil after natural thawing, and the grouting parameters optimization and other construction techniques in the freezing process of water-rich sand stratum in Fuzhou metro communication passage are introduced. For the active freezing construction process, analysis is made on the brine loop temperature, soil temperature, and pore pressure of pressure relief hole; the laws of soil temperature changes and freezing wall formation are summarized to accurately judge the timing of passage excavation. Relevant specific measures are proposed for existing problems in freezing construction of communication passage. Successful application of artificial freezing method in water-rich sand stratum is confirmed, thus providing reference for other similar projects.

Evolution of Interior and Exterior Bearing Structures of the Deep-Soft-Rock Roadway: From Theory to Field Test in the Pingdingshan Mining Area

Pingdingshan mining area is one of the typical deep mining areas in China, and most of the mines in this area are troubled by the difficulties of the deep-soft-rock roadway support. Based on the concept of synergistic interactions of the interior and exterior bearing structure of the surrounding rock and, considering the specific geological conditions of the research site, we establish the mechanical model of the interior and exterior bearing structure of the roadway. Based on numerical simulation, we reveal the influence of main factors, such as support strength and mechanical characteristics, of surrounding rock on the distribution and evolution of the interior and exterior bearing structure. We found that increasing the support strength and mechanical parameters of surrounding rock can make the exterior bearing structure close to the roadway enhance the bearing characteristics of the interior and exterior bearing structure and improve the roadway stability. The distribution characteristics of the interior and exterior bearing structure of the roadway under six different support strengths and six different grouting parameters were systematically investigated by field measurements. According to the field test results, an effective strategy for controlling the deep-soft-rock roadway is proposed, which provides a good reference for surrounding rock control of the deep-soft-rock roadway in the Pingdingshan mining area and mines with similar mining conditions.

Experimental-numerical investigation on grout diffusion and washout in rough rock fractures under flowing water

Interaction between grouts and groundwater is frequently encountered in geotechnical engineering. Based on the self-developed apparatus, it is indicated that grout washout under flowing water appears to be spatially heterogeneous and the residual grout pattern largely depends on fracture morphology. To provide an insight on the grout behaviour under water washing, standing on the image-processing technique, the two-phase rough rock fracture model is developed. Two-phase (i.e. grout and water) interface is tracked through an efficient volume-of-fluid (VOF) method. Grout behaviour is described via a non-Newtonian (Bingham) fluid regarding its time-varying viscosity. The proposed model is verified through comparing with the experiment. Sensitivity tests involving various grouting parameters are then carried out to determine critical parameters’ influences on the diffusion-washout process of grouts. Fracture morphology is accounted for from two aspects of fracture roughness and shear slip, where shear slip is regarded under an initial fracture aperture. The residual grout pattern demonstrates different characteristics with the variation of fracture morphology. After statistical analysis, it is found that, under the same roughness, grout effectiveness under flowing conditions can be correlated with the coefficient of variation (COV) of aperture width.

Method of Averaging the Effective Thermal Conductivity Based on Thermal Response Tests of Borehole Heat Exchangers

This work concerns borehole heat exchangers and their testing using apparatus for thermal response tests. In the theoretical part of the article, an equation was derived from the known equation of heat flow, on which the interpretation of the thermal response test was based. The practical part presents the results of several measurements taken in the AGH Laboratory of Geoenergetics. They were aimed at examining the potential heat exchange capacity between the heat carrier and rock mass. Measurement results in the form of graphs are shown in relation to the examined, briefly described wells. Result analysis made it possible to draw conclusions regarding the interpretation of the thermal response test. The method of averaging the measurement results was subjected to further study. The measuring apparatus recorded data at a frequency of one second, however such accuracy was too large to be analyzed efficiently. Therefore, an average of every 1 min, every 10 min, and every 60 min was proposed. The conclusions stemming from the differences in the values of effective thermal conductivity in the borehole heat exchanger, resulting from different data averaging, were described. In the case of three borehole heat exchangers, ground properties were identical. The effective thermal conductivity λeff was shown to depend on various borehole heat exchanger (BHE) designs, heat carrier flow geometry, and grout parameters. It is important to consider the position of the pipes relative to each other. As shown in the charts, the best (the highest) effective thermal conductivity λeff occurred in BHE-1 with a coaxial construction. At the same time, this value was closest to the theoretical value of thermal conductivity of rocks λ, determined on the basis of literature. The standard deviation and the coefficient of variation confirmed that the effective thermal conductivity λeff, calculated for different time intervals, showed little variation in value. The values of effective thermal conductivity λeff for each time interval for the same borehole exchanger were similar in value. The lowest values of effective thermal conductivity λeff most often appeared for analysis with averaging every 60 min, and the highest—for analysis with averaging every 1 min. For safety reasons, when designing (number of BHEs), safer values should be taken for analysis, i.e., lower, averaging every 60 min.

Research on the Reasonable Grouting Strength of Rock-Like Samples in Different Strengths.

One of the key points to make grouting reinforcement technology efficient and economical in engineering is to find out the optimal match relationship between different strengthsofrock mass and strength ofgrouting material. It can be called areasonable grouting strength. To explore that, 5 kinds of N (compressive strength of cement mortar) were used to make samples to simulate the different rock strengths. Five kinds of M (compressive strength of inorganic double-fluid material) were used to grout the structural plane of samples. Then the shearing experiment was carried out under the same normal stress conditions. Finally, based on the analyses of experimental results, the C (the reasonable range of grouting parameters) was proposed. The result shows that when M is the same, the smaller N is, the higher the τ(shearing strength of samples) growth rate is. When N is the same, with the increase of M, the growth rate of τ tends to zero. According to the shearing failure process and morphology of the samples, when N is the same, with the increase of M, the failure typeofsamples change from plastic flow failure to brittle sliding failure which is the same as the samples without the structural plane. C is equal to the ratio of M to N, and then the evaluation criteria of C is established by judging that if it is in the range from 1.19 to CMAX(CMAX = 0.0095N2 − 0.43N + 5.83). It will provide a certain basis to select the M in engineering in which N is known.

Diffusion-hydraulic properties of grouting geological rough fractures with power-law slurry

Different from the conventional planar fracture and simplified Newton model, for power-law slurries with a lower water-cement ratio commonly used in grouting engineering, flow model in geological rough fractures is built based on ten standard profiles from Barton (1977) in this study. The numerical algorithm is validated by experimental results. The flow mechanism, grout superiority, and water plugging of pseudo plastic slurry are revealed. The representations of hydraulic grouting properties for JRCs are obtained. The results show that effective plugging is based on the mechanical mechanisms of the fluctuant structural surface and higher viscosity at the middle of the fissure. The formulas of grouting parameters are always variable with the roughness and shear movement, which play a key role in grouting. The roughness can only be neglected after reaching a threshold. Grouting pressure increases with increasing roughness and has variable responses for different apertures within standard profiles. The whole process can be divided into three stationary zones and three transition zones, and there is a mutation region (10 10.8) on the permeability of surfaces cannot be underestimated. The determination of grouting parameters depends on the slurry groutability in terms of its weakest link with discontinuous streamlines. For grouting water plugging, the water-cement ratio, grouting pressure and grouting additives should be determined by combining the flow conditions and the apparent widths of the main fracture and rough surface. This study provides a calculation method of grouting parameters for variable cement-based slurries. And the findings can help for better understanding of fluid flow and diffusion in geological fractures.

Influence of fracture deformation on grout penetrability in fractured rock masses

Fracture deformation during grouting is a hydro-mechanical coupled dynamic process. Some studies indicated that an increase in grouting pressure can accelerate the grouting process, while some other investigations concluded that a high grouting pressure would weaken the grouting effect for fine fractures due to fracture deformation. Though the assumption that an increase of grouting pressure to shorten grouting time has been used in engineering practices for a long time, there is a lack of sufficient supporting theories to verify the assumption. Moreover, there are no existing criteria to quantify the magnitude and degree of impact of fracture deformation on grout flow through fractures. The present paper therefore aims to quantitatively evaluate the dynamic process of fracture deformation and its impact on grout penetrability. Fracture deformation is a dynamic process as both the range of grout penetration and injection pressure are time dependent, so a theoretical pseudo-coupling model is proposed, including an analytical model to determine time varying grouting parameters of two neighboring fractures and a numerical model to assess the associated fracture deformation. Design of Experiment (DOE) and sensitivity analysis are utilized to determine the characteristics of fracture deformation and critical factors affecting its magnitude and distribution. It is found that the apertures, the aperture difference, and the stiffness of the two neighboring fractures are the three most important factors, and a large deformation occurs when both fractures are of small apertures. The ratio of fracture aperture to D95 of cement particle has a significant impact on grout penetrability, whereas the associated impact could be much lower by considering dynamic fracture stiffness.

Air-leakage Model and Sealing Technique With Sealing–Isolation Integration for Gas-drainage Boreholes in Coal Mines

Sealing of boreholes for gas drainage is crucial for ensuring efficient gas drainage in coal seams. In this paper, the damage to coal masses where roadways were excavated and boreholes were drilled was separately simulated to determine the distribution ranges of pressure-relief plastic and elastic zones. Furthermore, the factors influencing air leakage of boreholes were analyzed to determine three patterns of air leakages-air leakage, air leakage, borehole fissure due to roadway fissure zones, borehole fissure zones and materials in borehole-sealing sections, respectively. In addition, a model for the air leakage of boreholes was established, and the principle underlying the sealing of boreholes with sealing–isolation integration was illustrated to separately determine the reasonable borehole-sealing depth, the position and depth of slots, and the grouting parameters. The borehole-sealing techniques for different parameters were compared to verify the applicability of the borehole-sealing technique with sealing–isolation integration. The gas-drainage concentrations after drilling for 30 days showed that, compared with the test borehole sealed using the traditional technique, the initial gas-drainage concentration in the boreholes sealed with sealing–isolation integration increased by 1.5–2 times, and the average gas-drainage concentration increased by approximately 2–3.5 times.

ДОСВІД ВИКОНАННЯ ҐРУНТОЦЕМЕНТНИХ ЕЛЕМЕНТІВ ПО ТЕХНОЛОГІЇ СТРУМЕНЕВОЇ ЦЕМЕНТАЦІЇ В ШЛАК ДОМЕННОГО ВИРОБНИЦТВА

The article describes the first experience in Ukraine in the implementation of ground-cement columns in the blast furnace slags. In accordance with the project to reinforce the soil base during the reconstruction of the place with a canopy in the station for the production of air separation products with the installation of VRU-1400 in the city of Enakievo, experimental work was performed on the territory of the plant to confirm the correctness of the selected technological parameters of Jet Grouting in the actual engineering-geological conditions of the construction site and control of the geometric and strength parameters of cement columns. Two test ground-cement columns were completed, visual and instrumental examination of the jet columns was performed (confirmation of the cylindrical shape, continuity of the shaft of the excavated part of the jet column, measurement of the actual diameter), the cores were drilled from the body of the jet column in the horizontal direction and the material was tested for compressive strength, as well as core sampling in the vertical direction for the entire length of the jet column, testing of soil-cement material. Based on the results of the visual examination, the cylindrical shape of the jet grouting elements was confirmed and the actual diameters were measured, which amounted to 610 ... 640 mm that is more than the required for the project - 600 mm. The selected vertical core confirms the design length of the jet column, the continuity of the body of the jet column and the absence of gaps in the treatment processing with a high-pressure jet of cement solution. According to the results of laboratory tests of cement-slag cylinders selected from horizontal cores, the strength of the material ranged from 4.76 to 7.68 MPa for 24 days of age and 7.96 MPa for 28 days. According to the results of testing cylinders made of vertical core, the minimum strength of cement-slag material was 7.3 MPa, the maximum - 11.2 MPa. The obtained results of the compressive strength of soil-cement material exceed the design strength equal to 2.5 MPa. As a result of the test work on the construction site of the VRU-1400, the correctness of the technical solution for the selection of Jet Grouting technology for reinforcement the foundation base in difficult engineering and geological conditions, namely blast furnace slags, was confirmed.

Field study of the effect of jet grouting parameters on strength based on tensile and unconfined compressive strength

The improvement of the mechanical soil characteristics of jet grouting technique is very attractive. The jet grouted soil cement columns in soft is a complicated issue because it depends on a number of factors such as, soil nature, mixture, influence among soil and grouting materials, jetting force of nozzle, jet grouting and water flow rate, rotation and lifting speed. This paper discusses the estimation of shear strength parameters of soil-cement column (soilcrete) in soft clayey soil based on the relationships between the unconfined compressive and split tensile strength for the soilcrete and the effect of the jet grouting and water pressure in the values of cohesion and internal friction. For this reason, theoretical and field work models have been developed. The relation between split tensile and unconfined compressive strength results were used to draw a Mohr’s circle and failure enveloped to define the shear strength parameters of soilcrete. According to that, the results indicate that the resistance of the jet grout columns increases by increasing the nominal resistance of the grouting material (cement), water and jet grouting pressure. The shear resistance variables are increased by increasing the unconfined compressive and tensile strength of the jetting column. The value of the unconfined compressive strength ranges from (2.78-5.52 MPa). While the internal friction angle varies from 38° to 44°. On the other hand, the tensile strength is increased by increasing the unconfined compressive strength and ranges from (0.66-1.02 MPa).

Numerical calculation and multi-factor analysis of slurry diffusion in an inclined geological fracture

Slurry grouting plays an important role in water plugging for hydrogeological engineering and there are multiple factors that restrict the slurry flow. This study investigates the restriction mechanisms, based on a single inclined rough fracture, employing a space stepwise method (SSM) using multi-direction sectors (MDS) for calculating the diffusion of variable-viscosity slurry under constant flow. The specifically developed numerical algorithm is validated by experimental results. The spatio-temporal effects of major factors on the flow, and the rock hydraulic properties, were analyzed for cement-based slurry. The results show that the slurry flow calculated by MDS-SSM exhibits strong fitting with experimental results. The diffusion pattern no longer exhibits a circular plane, but rather a double semi-elliptical distribution. The fracture direction angle, especially for the upward vertical flow, must be considered in the case of a larger dip angle. The main controlling factor of the pressure field is the higher slurry viscosity in regions far from the injection hole, and the influence of dip angle is significantly greater closer to the hole. Roughness has an influence on the fracture hydraulic properties, and the required grouting pressure increases with an increase in roughness. The fracture aperture, viscosity coefficient, and diffusion radius are three key factors with strong sensitivity affecting the forecasting accuracy of grouting parameters. The role of the fracture dip angle can be neglected only in narrow fractures and long-distance diffusion with higher-viscosity slurry or larger pressure. The key threshold value can be obtained with a fitting formula under given conditions.

Integrated Treatment Technology of Storage‐Mining Inclined Goaf under Expressway

An inclined goaf caused by storage mining is a serious risk to subgrades and pavements. In this paper, effective investigation and detection methods of goafs were discussed considering the project of the Urumqi East Ring Expressway crossing the existing goaf of Zhongxing no. 2 mine. Moreover, by theoretical analysis and a series of field comparative tests, reasonable grouting parameters and the treatment plan were obtained. By comparing the test results of the field and laboratory, the influence of groundwater on the effect of grouting was revealed to reduce the compressive strength of the consolidating objects of the slurry. The high‐density resistivity method presented strong anti‐interference ability and high accuracy in a depth range of less than 150 m in the investigation of the goaf. The results of the treatment showed that it is necessary to conduct research and analysis from multiple aspects to obtain the best treatment plan of a goaf and ensure the safety of a project.

Failure characteristics and control technology for large‐section chamber in compound coal seams—A case study in Tashan Coal Mine

AbstractThe coal production exploited from extra‐thick coal seams accounts for 45% of China's total coal production. With large coal output, the extra‐thick coal seams require that the chamber section be more than 100 m2. In case of parting (the noncoal rock, usually mudstone, sandwiched in the coal seam) in the extra‐thick coal seams, the integrity of the coal seams will be damaged and the large‐section chamber is extremely easy to occur rib spalling and roof leakage, which will increase the chamber's supporting difficulty. To solve such problems, this paper took the electromechanical chamber in Tashan Coal Mine as the engineering background and analyzed the deformation and failure characteristics of this chamber surrounding rocks by the numerical simulation method during the excavation process. The results indicated that the failure areas of surrounding rocks were mainly in partings, chamber ribs, and chamber dome with the failure depths of 15 m, 10 m, and 5 m, respectively. Based on the obtained deformation and failure characteristics, the supporting method of grouting integrated with high‐strength bolts and anchor cables was put forward. The grouting method was firstly used to improve the integrity of the chamber surrounding rocks, and the high‐strength bolts and anchor cables were used for supporting. Then, the supporting parameters of the bolts and anchor cables and the grouting parameters were optimized by the numerical simulation method. The optimized parameters were applied in the electromechanical chamber in Tashan Coal Mine, and the on‐site chamber ribs lateral displacement and roof separation amounts were only 0.018 m and 0.012 m, respectively, indicating that the surrounding rocks were controlled effectively.

Study on variation law of cement slurry density in porous media considering convection–diffusion–infiltration

Based on the law of conservation of mass and the law of linear infiltration, the theoretical model of slurry density in porous media under the combined influences of convection–diffusion–infiltration is established after applying the Laplace transform. Using a laboratory grouting test, the variation of cement slurry density for different grouting parameters and different times is studied. In addition, the differences between the experimental and theoretical values are analyzed. The results demonstrate that the experimental values of slurry density are positively correlated with time, while the average growth rates of each group are different. The experimental and theoretical values of slurry density are close in some test groups; the deviation rate between the experimental and theoretical values varies between − 12.9% and 30.1%. The average growth rate of the experimental value is smaller than that of the theoretical value. The results have some practical value and can provide a reference for construction design.

Grouting knowledge discovery based on data mining

The existence of highly complex and heterogeneous geological and hydrogeological conditions makes it cumbersome to determine grouting parameters for a cost-efficient grouting process. Although many empirical, numerical and analytical models have been proposed previously, there are still some gaps between the existing predictive models and practical grouting applications, leading to the fact that practical grouting design mainly depends on onsite engineers’ experience. In this study, we propose to use data mining to discover grouting knowledge from onsite data of a project in Singapore. After systematic analysis of data concerning the geological information, hydrogeological conditions and grouting records, an artificial neural network was structured to further extract grouting knowledge, based on which the grout take can be estimated under given geological and hydrogeological conditions. The grout take at individual station is found to be closely correlated with overall water inflow and Q value of rock mass, making it promising to estimate the potential grout take, once probe hole and face mapping information are given before pre-grouting. The degree of correlation between input parameters and the corresponding model accuracy are significantly affected by the classification methods used.

Firefighting of subsurface coal fires with comprehensive techniques for detection and control: a case study of the Fukang coal fire in the Xinjiang region of China.

Coal fires are global disasters, and China suffers the most serious coal fire disasters in the world. This paper introduces detailed detection and extinguishing methods for the wide range and complex coal fires at the No. 1 well in the Fukang mining area. First, the characteristics of the large and complex coal fire areas in the No. 1 well in the Fukang mining area are introduced, and 5 large fire areas are detected using the comprehensive detection range method, which detects fire areas before fire engineering practices are implemented. From the characteristics of this large-scale, complex coal fire, the zonal fire extinguishing scheme is formulated, designed, and applied, and the "shallow open fire stripping-construction of the boundary isolation zone-drilling and grouting in the deep fire area" series of events is utilized in the zonal fire extinguishing scheme. A new type of sodium silicate gel in compressive moisturizing plastic packing materials is used, an automatic grouting system is developed, and effective grouting processes are proposed, which can be adjusted according to the grouting effect analysis of the grouting parameters to determine the natural sedimentation and diffusion radius. After the construction was completed, the fire extinguishing effect was tested, revealing that the temperature in the fire zone cooled in a short time, and no subsequent heating phenomenon occurs. The method proposed in this paper provides guidance and a reference for other coal fires in the world.