Grouting Pressure Research Articles

Performance evaluation of post-grouting for bored piles installed in inhomogeneous gravel pebble stratum overlaid by deep and soft soil layers

ABSTRACT To study the behaviours of post-grouted piles installed in an uneven pebble bearing layer overlaid deep and soft soil layer in Wenzhou, China, static loading field tests of three bored post-grouted piles were conducted, considering the key design parameters of post-grouting including the grout volume, grout pressure, and bearing capacity. According to the on-site geological conditions in the region, the theoretical values were calculated through applying different calculation equations for these three parameters, and the actual values obtained from the field tests were investigated to assess the improvement effect of load-bearing performance of grouted piles installed in these geological conditions as an extremely uneven pebble-bearing layer overlaid by the deep and soft soil layer. The calculation equations of key design parameters of post-grouting in this type of soil layers were then proposed. This study could provide a reference to evaluate the performance of post-grouted piles under various grouting parameters in analogical soil layers.

Simulation Study of Loess Split Grouting based on Discrete Element Method

Split grouting is a common method of stratum reinforcement. However, due to the concealment of grouting itself, it is difficult to observe the slurry diffusion of split grouting. Therefore, this paper uses PFC2D software to simulate the split grouting in loess to study the diffusion law of slurry and the change of formation porosity. The research results show that the number of fracturing cracks increases with the increase of time. The porosity of soil mass changes obviously after the first fracturing, and the change rate of porosity increases after the second fracturing. With the increase of the initial grouting pressure, the number of splitting cracks is increasing, and the change rate of soil porosity is also accelerating.

Study on Calcium Carbonate Deposition of Microorganism Bottom Grouting to Repair Concrete Cracks

Microbially induced calcium carbonate deposition (MICP) restoration technology has good restoration effects and low environmental pollution compared with traditional restoration methods, and this technology has been applied in actual projects. However, grouting components such as bacterial solutions are easily lost in vertical cracks due to their low viscosity as well as their self-weight. In this paper, cracks were repaired using microbial mineralization by sealing the bottom of vertical cracks and pressure grouting. Controlled tests were designed based on three variables: crack width, presence or absence of media in the crack, and grouting method. The results show that the smaller the crack width, the easier it is to achieve a seal. The addition of media in the cracks can improve the repair efficiency. As the amount of grouting increases, the amount of calcium carbonate production in the cracks gradually increases, and the height and thickness of calcium carbonate deposition also gradually increases. The bottom closure pressure grouting method can not only reduce the amount of grouting fluid, but also shorten the test period. This method overcomes the difficulty that grouting poses as it should not be left in vertical cracks and plays an important role in reducing costs and shortening repair time.

Hybrid Random Forest-Based Models for Earth Pressure Balance Tunneling-Induced Ground Settlement Prediction

Construction-induced ground settlement is a serious hazard in underground tunnel construction. Accurate ground settlement prediction has great significance in ensuring the surface building’s stability and human safety. To that end, 148 sets of data were collected from the Singapore Circle Line rail traffic project containing seven defining parameters to create a database for predicting ground settlement. These parameters are the tunnel depth (H), the tunnel advance rate (AR), the EPB earth pressure (EP), the mean SPTN value from the soil crown to the surface (Sm), the mean water content of the soil layer (MC), the mean modulus of elasticity of the soil layer (E), and the grout pressure used for injecting grout into the tail void (GP). Three hybrid models consisting of random forest (RF) and three types of meta-heuristics, Ant Lion Optimizier (ALO), Multi-Verse Optimizer (MVO), and Grasshopper Optimization Algorithm (GOA), were developed to predict ground settlement. Furthermore, the mean absolute error (MAE), the mean absolute percentage error (MAPE), the coefficient of determination (R2) and the root mean square error (RMSE) were used to assess predictive performance of the constructed models for predicting ground settlement. The evaluation results demonstrated that the GOA-RF with a population size of 10 has achieved the most outstanding predictive capability with the indices of MAE (Training set: 2.8224; Test set: 2.3507), MAPE (Training set: 40.5629; Test set: 38.5637), R2 (Training set: 0.9487; Test set: 0.9282), and RMSE (Training set: 4.93; Test set: 3.1576). Finally, the sensitivity analysis results indicated that MC, AR, Sm, and GP have a significant impact on ground settlement prediction based on the GOA-RF model.

A decision approach on risk-control scheme recognition for karst excavation engineering

Risk events can be frequently encountered in karst geological environments during excavation construction; thus, a suitable risk-control scheme is essential to reduce the negative impact of accidents. A decision-making approach based on the fuzzy VIKOR method is proposed to identify the optimal risk-control scheme, where a triangular fuzzy set is adopted to express the experts’ judgements. A decision hierarchy is constructed based on four criteria and 12 sub-criteria, which are determined based on engineering experience and the construction environment. The developed approach was utilized to determine the optimal risk-control scheme to address risk events for excavation construction in karst regions. A countermeasure scheme, that is, pressure grouting with a two-phase liquid system, was implemented. The basic principles and steps of the implementation of the proposed scheme are presented. The applicability of the identified scheme was verified by the core recovery and modified number of blows using a standard penetration test. A flowchart of optimal scheme identification for geotechnical engineering practice is provided.

Permeation grouting mechanism of viscous time-varying fluid considering diffusion path

Due to the hidden nature of the grouting project, it has not been possible to get a clear picture of the slurry transport law, and most of the existing permeation grouting theories have ignored the tortuous characteristics of the pore channels of porous media. Based on the fractal theory of porous media and the equation of seepage motion of viscous time-varying Bingham fluid, a theoretical model of permeation grouting with viscous time-varying Bingham fluid is established, and viscosity tests are carried out for C-S slurry to obtain the time-varying equation of viscosity of C-S slurry. A set of permeation grouting simulation experiment device was designed, and the permeation grouting simulation experiment of C-S slurry was carried out to obtain the variation curve of grouting pressure with time under different injection media and different grouting rates. The results show that the grouting pressure considering the diffusion path of the slurry is 0.9–1.1 times of the experimental results, the grouting pressure obtained from the experimental is 0.7–1.2 times of the theoretical value considering the diffusion path, and the calculated value considering the diffusion path agrees well with the experimental value. The theoretical model can provide scientific guidance for field grouting construction.

Study on the Parameters of Strengthening Soft Surrounding Rock by Electric Pulse Grouting in the Mining Face

As an effective measure for the rapid fracturing of coal and rock, electric pulse fracture technology has been successfully applied in oil extraction and natural gas discharge. Using the electric pulse fracture mechanism, this technology can be applied to grouting reinforcement to improve the infiltration efficiency of grouting. In this study, we used a numerical simulation method to establish numerical models with different electric pulse peak pressures, different grouting times and different drilling spacing conditions Through numerical simulation studies, we found that the influence range of grouting reinforcement grows with the increased maximum pressure generated by the electrical pulse. The most economical and reasonable electric pulse parameter setting is 5 MPa for static grouting pressure and 100 MPa for peak electric pulse pressure. The best grouting time to keep pressure in the borehole is determined as 9 h, and the best borehole interval is 10 m. In addition, through the treatment of the soft roof of the Caojiashan coal mine, we also found that the reinforcement sample within the grouting reinforcement range had a compressive strength of more than 1.1 MPa; after each grouting reinforcement was completed, the hydraulic bracket could advance 12 m each time, which shows that the electric pulse grouting reinforcement technology has an obvious effect on the treatment of soft roof slab.

Fracture analysis-based mode-I stress intensity factors of crack under fracture grouting in elastic–plastic soils

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.

Mechanics of the penetration and filtration of cement-based grout in porous media: New insights from CFD–DEM simulations

Cement permeation grouting is a standard ground improvement technique crucial for improving soil’s mechanical properties. This study applied the computational fluid dynamics and discrete element method (CFD–DEM) to investigate the penetration of cement-based grout in porous media and the filtration behaviours of the cement particles. A model of the interaction forces of cement particles from the literature is implemented and validated by comparing the simulation and experimental results. A series of simulations identified the different modes of penetration, the penetration-induced changes in pressure and the formation process of the filter cake. The size ratio of the available pore openings to the cement particle is critical among various factors that influence cement grouting because it determines the formation of a cement filter cake. The grouting pressures (from 100 kPa to 400 kPa) exert little effect on the penetration distance and cement distribution of the soil prone to filtration. The self-collapse of the retained particles was captured by visualising the filtration process to explain the filter cake’s destruction. Furthermore, four typical retention morphologies were discussed from a microscopic perspective. This study provides new insights into the mechanics of the penetration and filtration of cement-based grout in porous media.

Research on Mesoscopic Characteristics of Limestone Grouting Diffusion Based on Discrete Fracture Network

The limestone stratum has well-developed rock fissures and abundant groundwater. Under extreme rainstorm conditions, tunnel surrounding rock seepage is serious especially. In order to reveal the grouting diffusion mechanism of karst fractured rock mass and realize effective water plugging, in this paper, the basic mechanical parameters of limestone are obtained by laboratory triaxial test, and the porosity distribution of rock mass is obtained by nuclear magnetic resonance test. The PFC2D discrete element software is used to simulate the mechanical characteristics of compressive deformation and fracture propagation pattern of the limestone and compared with the triaxial test results. Discrete fracture network theory is used to establish PFC2D numerical simulation of grouting diffusion model of fractured rock mass. And the filling diffusion mechanism and stress variation rule of cement slurry in fractured limestone under different grouting pressure are studied. The results show that (1) During the grouting process, the micro-cracks expand along the tip of the existing cracks, and extend to the surrounding cracks to finally form through cracks, so as to achieve the effect of grouting reinforcement. (2) With the increase of grouting pressure, the maximum displacement of particles increases continuously, but with the prolongation of grouting time, the maximum displacement of particles reaches a stable state and no longer increases. (3) During the grouting process of the fractured rock mass, with the increase of grouting time, the stress of the fractured rock mass finally reaches a stable state. This study provides an important reference for the setting of grouting parameters of limestone rock mass.

РЕЗУЛЬТАТЫ ИЗЫСКАНИЙ И ЗАКРЕПЛЕНИЕ ГИДРОАКТИВИЗИРОВАННЫХ ПРОСАДОЧНЫХ ГРУНТОВ ПОД АВАРИЙНЫМ ЗДАНИЕМ ШКОЛЫ

Engineering-geological studies have established that subsidence loams form the basis of the foundations of the emergency building of the school. To stabilize the deformations of the building, pressure grouting of deconsolidated dispersed soils is used using a resource-saving cement-clay-carbonate formulation. On the basis of laboratory and field experiments, the parameters of fixing the base soils were substantiated and a high degree of technical and economic efficiency was proved in the reconstruction of the base represented by hydroactivated subsidence soils.

Evolution of pore structure and radon exhalation characterization of porous media grouting

Cracks and pores are considered as major sources of radon. Cement is widely used as a grouting material in mines, tunnels, and other projects for reinforcement, seepage prevention, and water plugging. This paper mainly experimentally studied the correlation between the radon exhalation rate of the porous medium after grouting and the sand grain diameter, grouting pressure, and slurry water-cement ratio. The pore characteristics of the samples before and after grouting were also studied based on the low field nuclear magnetic resonance (LF-NMR). The findings of the study show that the porosity of samples increases after the superfine cement solidification with an increase in the water-cement ratio, and the radon exhalation rate is proportional to porosity, the radon exhalation rate increases by 0.0005 Bq·m–2/s at W/C = 1.5, and by 0.0017 Bq·m−2/s at W/C = 2 increases, in comparison to the W/C = 1.The radon exhalation rate of porous media gradually increased after grouting in response to an increase in grouting pressure and the water-cement ratio. The radon exhalation rate of the porous media with larger pores was relatively higher and exhibited a positive correlation with the volume of micropores in porous media，the correlations of coarse, medium and fine media are 0.815, 0.826, and 0.859. The change in pore structure has an influence on radon exhalation. Although grouting changes the pore structure and reduces the connectivity between internal pores, the micropores generated after cement slurry solidification improves the radon exhalation rate by providing new channels, When the water-cement ratio is 1.5 and the grouting pressure is 1.5 MPa, the radon exhalation rate of porous media is 0.00273 Bq·m−2/s. The research results serve as a reference basis for the evaluation of the impact of rock masses on grouting reinforcement and pore sealing.

Analysis of factors influencing surface settlement during shield construction of a double-line tunnel in a mudstone area

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.

Numerical investigation on grout spread and grouting parameter analysis in fracture with flowing water

Grouting is crucial for oil and gas extraction as an economical and effective method for preventing subsurface water seepage in rock fractures. In this study, rough fracture surfaces were established based on the Synfrac program, and a modified Bingham model charactering the time-varying viscosity of grout was employed. The two-phase flows were numerically investigated using the level set method to capture the dynamic evolution of the interface by varying the parameters. Four types of grout spread and flow fields were analysed in the orthogonal simulation. The results indicate that the contact ratio α, grouting pressure P, diameter of the grouting hole b and water velocity vw have significantly influences the grout spread and sealing efficiency δ. The propagation pattern becomes irregular as the grout is continuously injected into the fractures owing to various parameters. Vortex zones emerge at the slurry-water interface, where dynamic water tends to be blocked in the fracture. The rapid increase in grout volume results in a longer spread distance and greater spread pressure. The diameter of the grouting hole and contact ratio have a greater influence on the grout volume. Compared with the grouting pressure, increasing the diameter of the grouting hole can appropriately improve the sealing efficiency of the slurry in the fracture. The volume reduction of water was calculated to provide a comprehensive understanding of the sealing efficiency of the grout under flow conditions. Finally, the relationship between the plugging efficiency and the four factors was obtained.

Analysis of Microtremor Exploration Application and Construction Monitoring in a Large-Diameter Shield Tunnel

In recent years, shield tunneling has shown many advantages with the development of underground rail traffic. Geological exploration plays a significant role in tunnel engineering, and detailed geological exploration results can guide the successful construction of a tunnel. This research relies on a super large-diameter shield tunnel construction, using microtremor exploration technology to collect data onsite. Combined with a comparative analysis of the borehole surveying, the reliability of microtremor exploration technology is verified. Moreover, the monitoring result of the impact of large-diameter slurry balanced shield construction on the surrounding environment is analyzed. The results show that microtremor exploration can obtain geological details that traditional detection methods cannot obtain, which can predict the possible local geology mutation in front of the tunnel in advance. The law of surface settlement curve conforms to the Peck formula. This can be divided into five stages: micro deformation, extrusion uplift, reciprocating uplift, detachment settlement, and consolidation settlement. The surface settlement on the eccentric loads side is more prominent. The maximum pressure outside the tunnel segment appears on the lower side of the monitoring section, approximately 0.41 MPa, which will increase with the grouting pressure and become stable in five days.

Experimental Study on Compaction Law of Rock Mass in the Caving Zone Under the Grouting Pressure of Overburden Isolation Grouting Filling

Experimental Study on Compaction Law of Rock Mass in the Caving Zone Under the Grouting Pressure of Overburden Isolation Grouting Filling

Prediction of maximum ground surface settlement induced by shield tunneling using XGBoost algorithm with golden-sine seagull optimization

In order to avoid damage during shield tunnel construction to adjacent buildings on the ground, it is of paramount importance to precisely predict the Maximum Surface Settlement (MSS) deformation induced by shield tunneling under the surface. In this paper, a hybrid algorithm model incorporating the Extreme Gradient Boosting (XGBoost) with the Golden-sine Seagull Optimization Algorithm (GSOA) is proposed, namely the GSOA-XGBoost model. A total of 323 datasets including torque, penetration rate, thrust, cutterhead rotation speed, slurry pressure, grouting pressure, cover depth, and distance between cutting face and monitored section are taken as input parameters, and the corresponding measured MSS deformation is adopted as the output parameter. This dataset is employed to train the MSS prediction algorithm model. The analysis results indicate that the proposed GSOA-XGBoost hybrid algorithm model is much superior to other models in terms of accuracy, stability and computation time, and strong correlations are discovered between the predicted and measured settlements. Our model can predict the MSS deformation caused by shield tunnel construction with higher reliability, strong robustness and fault-tolerant capacity, and greatly reduces the engineering risk. Simultaneously, the consistency of the slurry pressure and grouting pressure values is calculated by the SOA-XGBoost and the grid search method, which demonstrates the feasibility and rationality of proposed hybrid algorithm model.

Influence of double-line large-slope shield tunneling on settlement of ground surface and mechanical properties of surrounding rock and segment

The surface settlement formula of large slope tunnel is derived firstly. Then, the finite element model of shield tunnel is established by using ABAQUS software. Finally, the influences of tunnel slope, grouting pressure and shield tail clearance on ground surface settlement, and mechanical properties of surrounding rock and segments are studied by the field measurement and numerical simulation method. The results show that (1) For the slope is less than 4°, the slope increases by 1°, the settlement of ground surface increases by about 2.85 %, the shear stress of surrounding rock increases by about 4.5 kPa, and the tensile and circumferential stresses of segment increase by about 5 % and 3.1 %, respectively. (2) The proper grouting pressure is beneficial to the settlement of ground surface, and the mechanical properties of surrounding rock and segment. (3) For the shield tail clearance is less than 15 cm, the clearance increases by 1 cm, the settlement of ground surface increases by about 0.65 mm, the shear stress of surrounding rock increases by about 4.77 kPa, and the circumferential stress of segment reduces by about 0.02 MPa. Therefore, the grouting pressure with 200 kPa and the shield tail clearance with 10 cm are recommended.

Study of Construction Technology of Large Diameter and Ultradeep Cement Mixing Pile in Road Engineering

As the soft soil in the Pearl River Delta area is deep, 50 cm-diameter cement mixing pile composite foundation is often used for road engineering. A municipal road in the Hongwan District of Zhuhai adopted a mixing pile with a diameter of 80 cm and a length of 27 m, which brought great difficulty to the construction of the project. To ensure the engineering quality, the bit optimization scheme was adopted to improve the blades from the conventional two layer and four groups of blades to three layer and six groups of blades. The projection direction of each layer of blades was vertical, which could increase the mixing times and improve the mixing uniformity. At the same time, double-channel teeth were added to effectively increase the smoothness of slurry flow. The optimized nozzle is improved from a nozzle located at the bottom of the drill bit to the left and right sides of the bottom of the drill pipe to effectively relieve the blockage of the nozzle, silt backflow, and other problems. The grouting pressure is generally 0.4–0.6 MPa. After the optimization of the grout pressure, the upper limit of 0.6 MPa was used in the first stirring and spraying process, and 0.4 MPa was used in the second stirring and spraying process. The advantage is that in the first mixing, excess cement grout is ejected for mixing, and in the second mixing, the total grout dosage can be controlled by reducing the grouting pressure, which effectively improves the quality of pile body and controls the cost. To ensure uniform soil mixing, measures were taken to improve the drilling speed of the drill pipe, accelerate the speed when sinking, slow down the speed when lifting. Through the above measures, the strength of the mixing pile body was improved, and the integrity of the pile body was guaranteed. Pile integrity, effective pile diameter, pile length, and pile strength uniform accord with the design. The difficult problem of large diameter and deep cement mixing pile is solved, which provides a good reference value for similar engineering.

3D Evolution of soil arching during shield tunnelling in silty and sandy soils: A comparative study

AbstractDuring earth pressure balance (EPB) shield tunnelling, a three‐dimensional stress redistribution occurs, which leads to development of soil arching. In this paper, development of soil arching by stress redistribution in two types of soils, silty and sandy soil is studied. A three‐dimensional numerical model was first developed and validated using the case study of the extension of Dwaraka Najafgarh Metro Corridor of Phase‐III of Delhi MRTS. Using the validated model numerous simplified numerical analyses were carried out to determine the evolution of soil arching in both silty and sandy soil. The variation in stresses (σxx, σyy and σzz), deformation and shear strain were evaluated and, on this basis, the extent of the loosened region and soil arching region was determined for both soil types. Furthermore, impact of different parameters (i.e., face pressure, grout pressure, C/D ratio and diameter of tunnel) on the evolution of loosened region above tunnel crown was assessed. Based on the numerical analysis, the extent of loosened region in the vertical direction for silty soil was determined to be 1.21D from the tunnel crown and the extent for the sandy soil was determined to be only 0.73D. While in the horizontal direction, the loosened region extends up to 0.72D and 0.37D for silty and sandy soils respectively. An optimal range of different parameters which must be adopted at the time EPB shield tunnelling in silty and sandy soil is recommended.