Grouting Reinforcement Effect Research Articles

Numerical analysis of slurry flow in pile‐end grouting of the drilling with prestressed concrete pipes

AbstractUnderstanding the diffusion law of cement slurry is the key to analyzing and evaluating the reinforcement effect of grouting. This study aimed to reveal the flow grouting mechanism of slurry in the reserved space between piles and soil and the penetration diffusion rule of slurry in the soil around the piles. For this purpose, the grouting slurry was regarded as a Newtonian fluid. The Navier–Stokes equations of fluid mechanics and renormalization group k–ε model were used to study the flow diffusion of slurry in the reserved space around a pile for grouting the drilling with prestressed concrete pipes. The permeability of soil slurry was determined using Darcy's law, and the flow field of slurry during grouting was numerically simulated. The results showed that the flow velocity of slurry and the reinforcement effect of grouting decrease gradually as the flow path extends. The radial flow of slurry in the grouting pipe shows a clear trend of circumferential diffusion. The slurry thickness in the reserved space for grouting decreases with an increase in the distance from the grouting outlet. Its attenuation trend becomes more obvious with increasing grouting height. The grouting thickness directly reflects the filling effect of slurry and is an important index to evaluate the grouting effect of drilling with prestressed concrete pipes.

Effects of temperature and bleeding on rheology of cement paste

The bleeding and rheology of a cement paste affect the grouting reinforcement effect in a high-temperature stratum. However, the effect of the slurry bleeding on the rheology at high temperatures is not clear. This research examined the bleeding characteristics of slurries in a high-temperature environment and changes in the density and flow pattern during bleeding. The material was ordinary Portland cement with a strength grade of 42.5. The water-cement ratio (W/C) ranged from 0.6 to 2.0. An environment of 20 °C–90 °C was simulated in a laboratory. The bleeding process was divided into six stages according to the total bleeding rate and rheological tests were conducted at each stage. The results showed that the total bleeding rate of the slurry increased with the increase of the W/C and decreased approximately linearly with the increase of temperature. The density change rate before and after bleeding decreased with the increase of temperature and increased with the increase of the W/C. The final density change rate of the cement paste at different temperatures was determined by the W/C. Newtonian and power law models were used to describe the rheological characteristics of slurries with W/Cs ranging from 1.5 to 2.0 and 0.8 to 1.2, respectively, during the bleeding period. As the bleeding rate increased, the R2 of the Newtonian model decreased from 0.98 to 0.9. A constitutive equation considering the temperature and bleeding characteristics was proposed. The relationship between the flow characteristic and consistency indexes at different bleeding stages changed from non-linear to linear with increasing temperature.

Experimental and practical investigation of reinforcement mechanism on permeable polymer in loose area of drainage pipeline

Permeation grouting is one of the important methods of anti-seepage reinforcement when the drainage pipes crosses loose diseases caused by leakage. With the development of grouting materials, permeable polymer slurry is widely used in engineering practice. Due to its low viscosity, fast reaction and micro-expansion, the diffusion and reinforcement law of slurry in loose area of drainage pipeline is more complex. To better understand the effects of water head pressure, grouting pressure, sand particle size and clay content on the anti-seepage and reinforcement effect of permeable polymer grouting in loose area of drainage pipeline, several types of tests, including permeability and uniaxial compressive strength tests, were performed. Then, based on the model test results, a BP neural network prediction model for the anti-seepage reinforcement effect of permeable polymer grouting in loose area of drainage pipeline is constructed, and the research results are applied to the treatment project of loose area of drainage pipeline for verification. The results show that: 1) after grouting, the order of magnitude of permeability coefficient of the consolidated body is reduced to 10-7cm/s, the anti-seepage performance of the sand layer is greatly improved, and the grouting pressure is the main controlling factor affecting the anti-seepage performance of the consolidated body. 2) The compressive strength of the consolidated body is obvious different under different working conditions. The water head pressure is the main controlling factor affecting the strength of the consolidated body. 3) Due to the limitation of test conditions, the relative error between the predicted value of BP neural network model and the actual value is about 20%, which can meet the general prediction needs.

Pipe Piles and Key Stratum Modeling for Grouting Reinforcement of Mine Floors under Mining Disturbance and Microseismic Monitoring Evaluation

Owing to the increasing applications and popularity of grouting reinforcement technology for water control in mine floors, its control effect is becoming increasingly concerning. However, the lack of an effective evaluation method for the mine floor composite limestone aquifers under different treatment modes can lead to blindness and randomness in grouting engineering. Thus, based on engineering practices, we analyzed the prevention and control effect of water inrush from the working face floor under different grouting reinforcement and transformation modes. Moreover, we established a sub-model of “pipe pile” that was reinforced by cross-layer drilling grouting and a sub-model of “water-resistant key stratum” that was reinforced by regional treatment grouting, while we also simulated and analyzed the concrete function of the structural models formed by the two grouting modes. Different microseismic monitoring arrays were used to monitor and evaluate the grouting reinforcement effect of the working face floor. The monitoring results revealed noticeable differences in the microseismic characteristics of the floor limestone during the mining process under different treatment modes. This provides a basis for evaluating the grouting reinforcement effect.

Grouting reinforcement strategy for tunnel sand layer based on BP neural network

Abstract Tunnel sand layer grouting reinforcement is a major difficulty in the current development of underground space. Finding a suitable method strategy for grouting reinforcement of the road sand layer to ensure the smooth implementation of the construction is imminent. In this paper, by building a BP neural network model, using signal forward propagation algorithm and error back propagation algorithm, back propagation of the error signal through the implied layer to the input layer, increased accuracy of calculations. To prove that BP neural network based on can effectively enhance the effect of tunnel grouting reinforcement, propose strategies for tunnel sand layer grouting reinforcement. Proven by simulation experiments: the effect of grouting reinforcement is influenced by the grouting material, grouting pressure, and the condition of the injected medium. The grouting parameters, grouting compressive strength and grouting age are the three major factors affecting the grouting reinforcement effect as deduced from the BP neural network input layer and implicit layer, a BP neural network model can be built to derive the parameters of these three major influencing factors. The calculation shows that, BP neural networks can provide specific data that can be relied upon for grout reinforcement, its effect prediction accuracy can reach 98%. It can be seen that BP neural network has practical application in tunnel sand layer grouting reinforcement strategy.

Experimental Study on the Shear Properties of Soil around Piles with Permeation Grouting

While post-grouting is frequently reported to improve the engineering performance of piles, the shear strength of the soil around piles is not well understood. To investigate the strengthening mechanism of soil around piles with permeation grouting, laboratory tests were carried out on homemade cement soil from the aspects of shear strength and microstructure characteristics. The evolution rule of the shear stress–shear displacement curve of grouting soil with different cement contents was analyzed, and the influence of grouting parameters on shear strength was explained. A composite exponential model describing the shear stress and shear displacement of permeation grouting silty clay was established. Furthermore, the influence of different cement content on changes in the microstructural characteristic parameters of the soil around piles was studied. The results show that penetration grouting has a positive effect on improving the shear strength of the soil around piles, and the failure mode of silty clay changed from elastic–plastic failure to brittle failure after grouting. Permeation grouting makes the particle structure denser, which limits the changes in pore arrangement and distribution. The shear failure of the soil around piles under permeation grouting obeys the Mohr–Coulomb criterion of failure. It is recommended to increase the grout diffusion radius during construction, considering the reinforcement effect of permeation grouting on the soil around piles.

Experimental study on temperature characterization during cement grouting reinforcement

Grouting is a common reinforcement method for underground projects. However, with the hidden nature of grouting reinforcement projects, the grouting reinforcement effect is difficult to detect and evaluate, and the accuracy of existing testing technologies needs to be improved. Considering the heat generated during the hydration of the cement grout, this paper proposes to check the effect of grouting reinforcement based on the temperature change. The law of temperature changes in cement grouting reinforcement was studied by indoor tests and validated by the wave speed test. The results revealed a similar law in temperature changes when cement grouts with different water–cement ratios were used for reinforcement in various media. Specifically, grout hydration was completed within 48 h and tended to be stable, and the hydration temperature maximized 14–20 h after the start of grouting. The results of the wave speed test showed that the wave speed increased continuously during the first 24 h and stabilized after 48 h, indicating a relationship between the strength increase of geotechnical media and the temperature change after grouting. Therefore, the temperature change during cement grout hydration is a parameter that can characterize the grouting reinforcement effect. The results provide a basis for further exploration of efficient and accurate testing and evaluation methods for the grouting reinforcement effect.

Quantitative Design Method for Grouting in Sand Layers: Practice in Qingdao Metro Line 2

Grouting is an effective method to reduce permeability and improve the mechanical performance of sand layers, preventing a disastrous inrush of sand and water. A scientific grouting design scheme is the premise for satisfying grouting reinforcement requirements. Due to a lack of theoretical basis for current grouting designs, grouting projects are conducted empirically and blindly. This paper presents a quantitative design method for grouting in sand layers. Based on this method, a quantitative design is realized for judgment of the grouting mode, determination of grouting range and calculation of grouting reinforcement effect. Moreover, for the fracture–compaction grouting mode, a theoretical model is proposed to calculate the grouting process, considering the coupling effect of grout flow and sand layer deformation. Meanwhile, a calculation method for reinforcement is put forward, which can connect macroscopic performance of the grouted body and individual performance of grout veins, compacted sand and undisturbed sand. In order to verify the efficiency of the grouting design method, it has been used in a sand grouting project in Qingdao Metro Line 2. In this project, judgment of the grouting mode, selection of grouting type and determination of grouting parameters have been completed based on the design method. Several inspection approaches have been performed to evaluate the effectiveness of the grouting design, showing that engineering stability was guaranteed after the grouting operation.

Quantitative permeation grouting in sand layer with consideration of grout properties and medium characteristics

Proper implementation of grouting engineering projects in sand layers requires quantitative characterization of the influence of multiple parameters on the groutability and grouting reinforcement effect. A grout injection system was developed for a series of laboratory tests to determine the effects on groutability of particle size, relative compaction, water-cement ratio, clay content and grouting pressure. Based on the test results, a multivariate model was established to predict the potential groutability in sand layers. The uniaxial compressive strength, deformation modulus and permeability coefficient were selected as evaluation indices to investigate the grouting reinforcement effect. The significance of influencing factors was discussed with orthogonal tests. A series of single-factor evaluation formulas were obtained based on the relationships between the influencing factors and evaluation indices. Also developed are the quantitative characterization formulas for the grouting reinforcement effect in consideration of multiple factors and curing time.

Technical Analysis of Grouting Reinforcement Effect on Karst Roadbed of High-speed Railway

Technical Analysis of Grouting Reinforcement Effect on Karst Roadbed of High-speed Railway

Comprehensive Evaluation of the Reinforcement Effect of Grouting in Broken Surrounding Rock in Deep Roadways

Comprehensive Evaluation of the Reinforcement Effect of Grouting in Broken Surrounding Rock in Deep Roadways

Experiment and Numerical Simulation on Grouting Reinforcement Parameters of Ultra-Shallow Buried Double-Arch Tunnel

For an ultra-shallow buried double-arch tunnel with a large cross-section, the arching effect is difficult to form in surrounding rock, and grouting method is often adopted to reinforce the surrounding rock. Hence, examining the grouting reinforcement parameters is of great significance for potential failure and collapse prevention. The land part of Haicang undersea tunnel was selected as a case study; laboratory experiments, theoretical analysis, and numerical simulation were performed to determine the grouting solid strength and grouting reinforcement parameters. The effects of different water–cement ratios on slurry fluidity, setting time, bleeding rate, and sample strength were studied by laboratory experiments. A method was proposed to determine the shear strength parameters of grouted surrounding rock through the grout water–cement ratio and the unconfined compressive strength of the rock mass. Numerical simulations were performed for grouting reinforcement layer thickness and the water–cement ratios. The deformation and stability law of tunnel surrounding rock and its influence on surrounding underground pipelines were obtained considering the spatial effect of tunnel excavation and grouting reinforcement. The reasonable selection range of grouting reinforcement parameters was proposed. The initial setting time and bleeding rate of cement slurry increased with the increasing water–cement ratio, while the viscosity of cement slurry and sample strength decreased with the increasing water–cement ratio. The shear strength parameters of grouted surrounding rock were determined by the water–cement ratio of grout and unconfined compressive strength of rock mass before grouting. When the thickness of grouting reinforcement layer h = 1.5 m and the water–cement ratio of grout was suggested η = 0.85, the surface settlement, the deformation of the vault, and the deformation of the nearby pipeline all met the design. Moreover, the construction requirements were more economical. Research results can provide a reference for the selection of grouting reinforcement parameters for similar projects.

Effect of Grouting Reinforcement on Settlement of Existing Tunnels: Case Study of a New Crossing Underpass

In the construction of the new shield tunnels crossing existing tunnels, grouting rings are often installed in the existing tunnels for protection. To study the effect of grouting rings on the settlement of existing tunnels, the variations of soil properties and relevant parameters before and after the grouting are analyzed. By considering the effect of the grouting ring on the reduction of the stress and the reinforcement of the surrounding foundation soil, the stress reduction model of the heterogeneous soil layer and the model of the tunnel settlement calculation are proposed. The formula for the reduction of the stress after passing through the grouting ring is deduced. Moreover, by comprehensively taking the influences of the shield excavation and grouting ring into account, the formula for calculating the vertical displacement of the existing tunnel caused by the excavation of the new tunnel is derived. Further, the impacts of the length and the thickness of the grouting ring on the settlement of the existing tunnel are studied. The results of the theoretical calculation method proposed herein are well consistent with the data computed by the finite element model, and both follow a relatively similar change trend. According to the obtained results, installing the grouting ring on the existing tunnel can effectively reduce the tunnel settlement. Finally, the results demonstrate that increasing the length and the thickness of the grouting ring can strengthen the protection of the existing tunnel, but the effect gradually decreases.

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.

Study on Surface Grouting Reinforcement Effect of Small Clear Distance Tunnel in Soil-rock Composite Stratum

Based on the Yingxiongshan tunnel project in Jinan, a numerical calculation model of tunnel excavation considering the surface grouting reinforcement effect of soil-rock composite stratum is established, and the effects of elastic modulus and grouting width of grouting reinforcement zone on tunnel stability are studied. and the research results are applied to the supporting project to verify the rationality of the numerical calculation results. The results show that grouting reinforcement can effectively control the deformation of surrounding rock and supporting structure, and the absolute value of surface settlement is negatively correlated with grouting width and elastic modulus. The surface settlement value is not sensitive to the change of the width of grouting reinforcement zone, but is sensitive to the change of elastic modulus.

Model Test on Segmental Grouting Diffusion Process in Muddy Fault of Tunnel Engineering

In order to realize the diffusion law of segmental grouting in muddy fault of tunnel engineering, a three-dimensional grouting diffusion simulation test has been done. Three times of grouting operation have been done for three adjacent sections in grouting pipe. Grouting pressure, injection rate, soil pressure field, and seepage pressure field have been real-time monitored in three grouting stages. The effect of segmental grouting operation on soil pressure field and effective stress field has been analyzed. Results show that previous grouting operation can affect later grouting operation. Due to previous grouting operation, the grouted stratum can be compacted and grouting diffusion will conquer greater resistance in later grouting stages. Correspondingly, grouting pressure increases and injection rate decreases in the later grouting stage. There exists a limited influence range for a single grouting operation. For every grouting stage, soil pressure and effective stress in the section which the injection hole locates in are affected effectively by grouting operation. By contrast, soil pressure and effective stress in section away from injection hole are affected relatively weakly by grouting operation. With distance to injection hole increasing, compaction degree and reinforcement effect of grouted muddy fault decay in space. Multisegmental grouting method has significant advantages over single grouting method. Ineffectively compacted area by previous grouting operation can be effectively compacted by later grouting operation from adjacent injection hole. As a result, uniformity of grouting reinforcement effect can be improved, and weakly reinforcement area can be reduced.

Grouting Reinforcement Technology of Weak Fractured Rock Mass in Subway Open-cut Station

In the process of subway open-cut station construction, excavation deformation seriously threatens the safety of municipal pipelines and buildings. To ensure the effectiveness of grouting reinforcement, drilling exploration and pressure water test were conducted on the basis of the grouting reinforcement project of the excavation of an open-pit station in Qingdao metro, the permeability coefficient and crack characteristics were studied, and the equivalent crack width was calculated on the basis of cubic law. To determine the injectability index of grout and realize the optimal selection of grouting materials, the statistical distribution law of the equivalent crack width was analyzed on the basis of the Pareto distribution, and an effective method of grout selection was proposed. The PQT curve in the grouting process was analyzed by flow dimension theory to realize the dynamic adjustment of the grouting process. Finally, the grouting reinforcement effect was evaluated on the basis of the core sample and borehole TV. Results show that if the permeability coefficient is subject to Pareto distribution with parameters tmin and k, then the distribution curve of the permeability coefficient in the logarithmic coordinate is a straight line; the equivalent crack width obtained on the basis of the cubic law is also subject to the Pareto distribution with parameters bmin and 3k. Therefore, the equivalent crack width distribution curve can be obtained to provide a basis for the grout selection.

Experimental study on groutability and reconstructability of broken mudstone and their relationship

The reinforcement effect of grouting is different with different degrees of brokenness of rock mass, as this phenomenon is closely related to the groutability and reconstructability of the broken rock mass. In order to obtain the groutability and reconstructability of mudstones with different degrees of brokenness and their relationship, a permeability device was developed and used to test the permeability of broken mudstones with different particle sizes during the axial compaction process. A computed tomography (CT) scan, uniaxial compression, and non-contact full-field real-time measurement system VIC-3D tests were carried out on the grouted bodies of broken mudstone with different particle sizes. The results show that with the increase of the particle size (i.e., a decrease of the degree of brokenness), the porosity and crack opening formed by the accumulation of broken mudstone increase, so that its groutability will increase, while the volume defect ratio in the grouted body increases first and then decreases, so that its reconstructability decreases first and then increases. During uniaxial compression, the rock-rock contact and weak rock-cement interface in the grouted body are the initial locations of its re-failure, and the grouted body obtained by small particle size is mainly longitudinal splitting failure, while the grouted body obtained by large particles size is mainly shear failure. These above conclusions can provide an experimental data reference and valuable information for predicting and evaluating the groutability and reconstructability of the broken rock mass.

Analysis of ground collapse caused by shield tunnelling and the evaluation of the reinforcement effect on a sand stratum

Based on laboratory and field tests for a cross-river highway shield tunnel in China, the causes of ground collapse by shield tunnelling in a water-rich fine sand stratum were analyzed. To ensure the safety of subsequent shield tunnelling, reinforcement treatment was carried out, and then the reinforcement effect was comprehensively evaluated. The results showed that the fine sand properties, slurry circulation quality, support pressure set and excess pore water pressure fluctuation are the main reasons for the collapse of sandy ground. The comparative analysis of the permeability coefficient of the stratum and tunnelling parameters of the shield indicated that the grouting reinforcement effect on the fine sand stratum was obvious and that the disturbance to the stratum can be effectively controlled.

Experimental Study on Grouting Reinforcement Mechanism of Heterogeneous Fractured Rock and Soil Mass

To explore the grouting reinforcement mechanism of heterogeneous rock and soil in a fault fracture zone, based on the F2 fault grouting project of Yonglian Tunnel, the filling area composed of loose and soft media in the fault is defined as the advantageous grouting diffusion region, which is divided into loose and weak diffusion regions according to the slurry diffusion form. A self-developed grouting reinforcement test system is used to carry out grouting reinforcement tests on the heterogeneous rock and soil. The existence of the advantageous diffusion region can effectively improve the reinforced body strength. The slurry in the reinforced body containing the loose medium mainly expands outwards in the form of first infiltration and then compaction, and the slurry vein mainly remains in the advantageous diffusion region. The slurry in the reinforced body containing the soft medium mainly diffuses in the form of compaction splitting, which can form thicker splitting of the grouting veins. When the reinforced body is destroyed, the body containing the loose medium is mostly conically fractured, indicating complete lithology and homogeneous material. Moreover, the reinforced body containing the soft medium always forms a penetrating crack along the slurry vein or near the grouting vein. Focusing on the heterogeneous stratum consisting of fault breccia and soft plastic fault gouge, controllable slurry dynamic adjustment, same-hole multi-sequence sub-gradient grouting, and localized grouting control are proposed. The grouting control method is applied to the case of Yonglian Tunnel, and a superior grouting reinforcement effect is achieved.