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In an anchor support system, once the soil strength is improved by grouting with a geotextile, the pull-out force of anchors increases. To investigate the improvement of surrounding soils due to the grouting with a geotextile, a series of filtration and penetration tests under various parameters such as different initial degrees of compaction, water content and soil types were conducted via a self-developed device. In addition, microscopic tests were then carried out to obtain the soil's structure before and after grouting. The main conclusions are as follows: (1) The strength of surrounding soils is improved by grouting with a geotextile through the compaction effect and the slurry infiltration, while its strengthening effect gradually declines with the increase in the initial degree of compaction. (2) As the initial water content increases, the strengthening effect derived from the compaction effect and the cohesive substances infiltration decreases, while this improved efficiency of the soil strength declines due to the water infiltration during grouting. (3) Although the effect of grouting with a geotextile on different soils is obviously different due to the different efficiency of slurry (i.e., water and cohesive substances) infiltration, it can improve the soil strength regardless of soil type, especially for sandy soils. (4) Under the filtration of geotextile, a hardened layer is formed at the grout–soil interface due to the accumulation of cohesive substances, which is beneficial to the performance improvement in applications such as the capsule-type anchor. [ABSTRACT FROM AUTHOR]

Compared with conventional soil nails, the soil nail with grout bulbs (compaction-grouted soil nail) exhibits better performance in soil. In this study, a hyperbolic relationship was used to describe the relationship between pull-out stress (pull-out force divided by the cross-sectional area of a grout bulb) and displacement, in which the initial compressive modulus and ultimate compressive strength are the key factors that need to be determined in advance. In this case, the stress-strain behaviour of the soil around the grout bulb was investigated based on cavity expansion theory during compaction grouting and pull-out processes, and the initial compressive modulus with a compaction effect and the ultimate compressive strength were then quantified. Therefore, a cavity expansion theory-based hyperbolic model for the pull-out force of a compaction-grouted soil nail was proposed, in which the contribution of compaction grouting to the pull-out force was theoretically quantified. The proposed pull-out force model that combines the hyperbolic relationship and cavity expansion theory is simple and has high accuracy and will be useful for the design of the new soil nail with grout bulbs. [ABSTRACT FROM AUTHOR]

In this study, two series of physical modeling experiments, with and without a grouting process, were conducted under different grouting pressures to study the effect of compaction grouting on the performance of compaction-grouted soil nails. In addition, a hyperbola-based model was proposed to describe the variation of the pullout forces with and without grouting. Some of the main conclusions drawn are as follows. First, the compaction effect initially influences the mobilized pullout force, but not the final stage of pullout; the large difference between the two series of tests in regard to the pullout force at the initial stage led to the first part of this conclusion. However, the final pullout force results of the tests, both those with and those without grouting, were similar. Second, once the soil condition changes, the compaction effect on the performance of a soil nail depends on the grouting pressure rather than the diameter of the grout bulb. Third, the difference in the soil response (i.e., vertical dilatancy and the vertical and horizontal squeezing effects) derived from the compaction grouting effect will result in the initial difference in the increased rate of the pullout force between the tests with a grouting process and those without. Finally, a hyperbola-based model was proposed to describe the variation of the pullout force of the model tests with and without grouting, through which the pullout force is available of prediction for the given diameter of grout bulb and pullout displacement. [ABSTRACT FROM AUTHOR]

In this study, a latex membrane with a diameter of 50 mm and thickness of 0.5 mm is used to encase an injection hole. The gap between the membrane and the nail rod is fixed to achieve compaction grouting and to prevent fracturing and permeating; hence, a regular grout bulb is easily formed and locked into the soil matrix to provide a pullout force for a compaction-grouted soil nail. For this type of soil nail, two series of physical model tests for an embedded soil nail and a soil nail with a predrilled hole (the soil sample was moistened and could sustain the hole without collapsing during the placement of the nail rod) were conducted to study the influence of the installation methods on the performance of a compaction-grouted soil nail. The results of the two series of tests were compared, and some conclusions were drawn: First, the aforementioned installation methods for a soil nail had little impact on the mass of injected grout, whereas the shape of the cured grout bulb showed some differences based on the type of soil response. Second, compared with that of an embedded soil nail, the pullout force of a postplaced soil nail remarkably decreased because the hole drilled for installation led to a gap between the soil nail and the surrounding soil. In addition, the loss rate correlated with the grouting pressure (i.e., the diameter of the grout bulb). Third, because of the lower soil densification, dilation, and squeeze effect, a slower growth rate (with increasing grouting pressure) of the pullout force (i.e., resistance) was found for the postplaced soil nail relative to that of the embedded soil nail, during which the efficiency of the increasing pullout force decreased. [ABSTRACT FROM AUTHOR]

A series of large-scale model tests was conducted on compaction-grouted soil nails to study the influence of the degree of saturation on the soil response to compaction grouting and pull-out. The experimental results show that the initial degree of saturation of the soil strongly influences the grout injectability, thus the formed diameter of grout bulb. Subsequently, the diameter of the grout bulb alters the pull-out force, with larger grout bulbs generating higher pull-out forces and exhibiting greater hardening behaviour. Interestingly, the initial pull-out forces are the same for the same grouting pressure, regardless of the initial degree of saturation and the subsequently grout bulb. In addition, some of the main factors influencing the pressure grouting and pull-out of the soil nail, as the initial degree of saturation varies, are as follows. First, the variations in the soil pressure and density with the initial degree of saturation are similar to that of the volume of grout injected, and the compression of the soil induced by pressure grouting exhibits a similar evolution with the initial degree of saturation at different locations. Second, the initial degree of saturation of the soil sample plays a dominant role in the change in suction during pressure grouting and pull-out of soil nail. Third, the horizontal soil pressure derived from the pull-out of soil nail propagates closely in the soil sample of lower initial degree of saturation. The vertical soil pressure induced by the vertical soil dilation and squeezing effect varies in accidence with the initial degree of saturation and the grout bulb. [ABSTRACT FROM AUTHOR]

This study proposed a new soil nail known as the compaction-grouted soil nail, and a physical model was established to investigate its pull-out behaviour with different grouting pressures. The study on scale effect of the physical model was performed subsequently via numerical modelling. Additionally, interface shear tests were performed using the same boundary conditions as the physical model test. The strength parameters obtained were used to estimate the pull-out resistance of a conventional soil nail. The merits of these two soil nail types were compared based on their pull-out resistances. The physical model test results showed that the pull-out resistance of the compaction-grouted soil nail increases with increasing grouting pressure. In addition, the pull-out resistance exhibits hardening behaviour without a yield point, indicating that the compaction-grouted soil nail enables soils to remain stable against a relatively large deformation before ultimate failure. Furthermore, a higher grouting pressure results in a higher rate of increase for pull-out resistance versus pull-out displacement, which improves the performance of the compaction-grouted soil nail in the stabilization of large deformation problems. A comparison of the two types of soil nails suggests that the new compaction-grouted soil nail is more sensitive to grouting pressure than the conventional soil nail in terms of pull-out resistance improvement. In other words, the performance (pull-out resistance) of the compaction-grouted soil nail can be markedly improved by increasing the grouting pressure without inducing any accidental or undesired cracking or soil displacement. [ABSTRACT FROM AUTHOR]

A model test was conducted for a newly developed soil nail, the result of which was compared to that of a 3D finite element method (FEM) simulation. The shape angle ( β ) and friction coefficients ( μ ) contributed to the difference in pull-out force between the model test and the simulation. Further verifications were conducted, during which the pull-out mechanisms of the soil nail for different β and μ were analysed. It was found that both β and μ have a positive influence on the pull-out force; β only affects the increase rate, while μ influences the overall pull-out force level. Three components were found to govern the pull-out force, with the component applied to the expanded cement bulk surface accounting for approximately 80% of the total. This study proves that the optimal approach for increasing pull-out force is to enlarge the diameter of the cement bulk rather than extend the nail length. [ABSTRACT FROM AUTHOR]