Grouting Pressure Increases Research Articles

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.

Grout penetration process simulation and grouting parameters analysis in fractured rock mass using numerical manifold method

Grouting is a commonly used technique in rock engineering to enhance the joint strength and improve the stability of surrounding rock. Grout penetration characteristic is controlled by grouting parameters and has a significant role on practice. In the study, a numerical manifold method (NMM) for grout penetration process simulation in fractured rock mass is firstly proposed. The fluid flow behaviour of the grout is assumed to be a Bingham fluid and control equations are established using discrete fracture network model. The global discretization equation, element sub-matrixes and NMM simulation algorithm for grouting are presented. Then, numerical tests for grouting process in a single fracture and a regular fracture network are conducted firstly to verify the proposed NMM grouting model by comparing with analytical solutions and experimental results. Furthermore, the effects of mesh size, fracture and slurry parameters on the grouting performance are systematically investigated using a random fracture network example. The numerical results indicate that the grouted zone and propagation depth decrease as the mesh size of numerical model and yield strength increases, while it increases as initial fracture aperture and grouting pressure increases.

Experimental investigation of pressure grouting in sand

Pressure grouting technology has been widely adopted in ground improvement and soil stabilization. To better understand the grout evolution and diffusion process upon pressure grouting injection in sand, laboratory-scale tests were carried out on loose sand under confined boundary conditions, with different grout water/cement (w/c) ratios (0.5 and 1) and soil degrees of saturation (ranging from 5% to 60%) taken into account. By comparing the injected grout volume, the grout bulb volume and density, and the characteristics of the grouted bulbs (dimension and shape) obtained at increasing grouting pressure, the main features of the pressure grouting process were revealed. The injected grout volume increased almost linearly with the grouting pressure, and a lower volume of grout could be injected for a lower w/c ratio at the same grouting pressure, representing a lower injectability. An increase in the grouting pressure leads to an enlarged grout bulb dimension for both w/c ratios, and this increase shifts the grout diffusion process from being dominated by compaction to one involving a fracture-like pattern. Generally, a spherical grout bulb is obtained at a lower w/c ratio of 0.5; however, at the higher w/c ratio of 1, fracture starts to occur even at a low grouting pressure of 100kPa and continues to propagate as the grouting pressure increases. The influence of the degree of saturation of the soil was significant on both the injectability and the characteristics of the grout bulbs, since the cohesion of the unsaturated sand changed along with it. When Sr exceeds 5%, the volume of the injected grout decreases, but then increases after a threshold value of approximately 40%. Conversely, compaction grouting seems to be dominant at the threshold Sr value, while fractures tend to appear at both lower and higher degrees of saturation. A considerable amount of bleeding occurred with the two main diffusion processes during pressure grouting. The w/c ratio seems to be the most significant factor contributing to this behavior in sand samples.

Study on the Ultimate Pullout Force of Prestressed Cable Based on Triple Shear Unified Yield Criterion

Based on the triple shear unified yield criterion and the ultimate equilibrium principle, the ultimate pullout force of prestressed cable is studied. The ultimate pullout force of prestressed cable is related to the rock type, the shapes of rapture surface, grouting pressures and compressive strength of rock, etc. The results show that the intermediate principal stress effect parameter b have influences on the ultimate pullout force of prestressed cable. With the increase of the intermediate principal stress effect parameter b, the ultimate pullout force of prestressed cable increases too. When the grouting pressure increases, the ultimate pullout force of prestressed cable increases also.

Analysis on the Ultimate Pullout Force of Prestressed Cable Based on Nonlinear Mohr Strength Criterion

Based on parabolic Mohr strength criterion and the ultimate equilibrium principle, the ultimate pullout force of prestressed cable is studied. The ultimate pullout force of prestressed cable is related to the rock type, the shapes of rapture surface, grouting pressures and compressive strength of rock, etc. The results show that the grouting pressure increases, the ultimate pullout force of prestressed cable increases also. It can provide theoretical supports for some prestressed cable engineering practices.

Analysis of stratum grouting influence on shaft lining stress with the methods of simulation and in site measurements

According to the principle that stratum grouting can effectively release and restrain the vertical additional stress on the shaft lining, based on the actual measurement results of a project, we established a model for calculating the stress on the shaft lining during stratum grouting, studied the impact of grouting pressure change on shaft lining stress during shaft curing, obtained a quantitative result, compared the actual measurement data about the shaft lining stress increase and the shaft top settlement condition with the numerical simulation result, and finally proved the accuracy of the numerical simulation result. The results indicated that the parameters like shaft lining stress, shaft deformation, and grouting pressure must be under effective monitoring in the project of preventing and curing shaft-lining rupture through intermittent stratum-grouting under low pressure; the safety of shaft during grouting is tightly related with grouting pressure, especially the circumferential stress and radial stress with grouting pressure. The circumferential and radial stress increase by 0.96 MPa and 4.3 MPa respectively when the grouting pressure increases by 1 MPa. The results can be applied to similar shaft lining treatment projects.