To investigate the effect of interface temperature on the soil-reinforcement interaction mechanism, a series of pullout tests were conducted considering different types of reinforcement (geogrid and non-woven geotextile), backfill (dry sand, wet sand, and clay), and six interface temperatures. The test results indicate that at interface temperatures of 0 degrees C and above, reinforcement failure didn't occur during the pullout tests, whereas it predominantly occurred at subzero temperatures. Besides, the pullout resistance for the same soil-reinforcement interface gradually decreased as the interface temperature rose. At a given positive interface temperature, the pullout resistance between wet sand and reinforcement was significantly higher than that of the clayreinforcement interface but lower than that of the dry sand-reinforcement interface. Compared with geotextile reinforcements, geogrids were more difficult to pull out under the same interface temperature and backfill conditions. In addition, the lag effect in the transfer of tensile forces within the reinforcements was significantly influenced by the type of soil-reinforcement interface and the interface temperature. Finally, the progressive deformation mechanism along the reinforcement length at different interface temperatures was analyzed based on the strain distribution in the reinforcement.

The geogrid-soil interaction, which is crucial to the safety and stability of reinforced soil structures, is determined by the key variables of both geogrids and soils. To investigate the influence of backfill and geogrid on their interface behavior of the reinforced soil retaining walls in Yichang of Shanghai-Chongqing- Chengdu high-speed railway, a series of laboratory pullout tests were carried out considering the influence of water content and compaction degree of the backfill as well as tensile strength of the geogrid. The development and evolution law of pullout force- pullout displacement curves and interface characteristics between geogrid and soil under various testing conditions were analyzed. The results showed that with increasing water content, the geogrid pullout force decreased under the same pullout displacement. The interfacial friction angle of the geogrid-soil interface showed a slowly increasing trend with increasing water content. The variation of the interfacial friction angle ranged between 9.2 degrees and 10.7 degrees. The interfacial cohesion, however, decreased rapidly with increasing water content. With increasing degree of compaction, the interfacial friction angle and the interfacial cohesion of the geogrid-soil interface gradually increased. The change of the interfacial cohesion with the compaction degree was more significant. When the degree of compaction increased from 0.87 to 0.93, the interfacial cohesion increased around 7 times. The tensile strength of geogrid has certain influence on its pullout force-pullout displacement relationship. High-strength geogrid could significantly improve the mechanical properties of the geogrid-soil interface. The investigation results can provide some reference for the design and construction of geogrid reinforced soil structures.

The study investigates the interaction between geogrids and two distinct granular backfill materials, Yamuna sand and coal mine overburden through a combination of laboratory experiments and numerical simulations. It evaluates the physical and mechanical properties of coalmine overburden and Yamuna sand, and the pullout performance of geogrid embedded in both materials. A large-scale pullout box was utilised to conduct the experiments, and the results showed that coalmine overburden offers higher pullout resistance than Yamuna sand. The effect of physical parameters such as elasticity of geogrid, geogrid geometry and angle of inclination were analysed using the discrete element method. The pullout resistance of geogrids mainly depends on the elastic properties of the material. The study also shows the existence of an optimum spacing between longitudinal and transverse ribs.

The retaining wall with reinforced soil is exposed to various types of loads, including static active earth pressure caused by the self-weight of the backfill soil, seismic loads due to earthquakes, vehicle/railroad loads, and cyclic loads induced by seasonal temperature changes causing contraction/expansion. To ensure the internal stability of the retaining wall, the pullout resistance of the installed geogrid must be secured. This study presents the pullout load test results for a geogrid installed in sandy soil under cyclic loading, either in displacement-controlled or load-controlled conditions. In the pullout tests, factors such as the frequency, amplitude, and number of cycles of the pullout load were varied to consider various cyclic loading characteristics. The trends in the maximum pullout resistance and the initial pullout stiffness were analyzed. The analysis showed that under displacement-controlled cyclic loading, as the amplitude increased, both the pullout resistance and stiffness significantly decreased, with the degree of decrease intensifying as the displacement amplitude increased. This trend was also observed in the analysis of changes in pullout stiffness under cyclic loading. On the other hand, under load-controlled cyclic loading, the pullout resistance and cumulative pullout displacement both tended to decrease as the frequency increased over a fixed period, while the pullout resistance decreased and the cumulative displacement increased as the amplitude increased.

The majority of existing studies on the soil-geogrid interaction were based on the assumption that the surrounding geotechnical media was a homogeneous material. However, the different composition, structure and history of the geotechnical media resulted in significant differences in mechanical behavior. This discrepancy could lead to an overestimation of the pullout capacity of the soil-geogrid, which could in turn cause failures in the engineering practice. The influcence of the uncertainty of the geotechnical media on the pullout behavior of the soil-geogrid was investigated in this article. A number of groups of random distributions of the properties of soils, associated with the strain-softening constitutive model, were incorporated in the numerical simulation. The results demonstrated that the pullout behavior of the soil-geogrid, including the ultimate pullout capacity and the post-peak softening behavior, was highly impacted by the uncertainty of the mechanical properties of the surrounding inhomogenous media, in constrast to the case that with the homogeneous geotechnical media.

The tensile deformation of fibers is often overlooked in traditional analyses of fiber reinforcement mechanisms, with pullout failure being considered as the primary failure mode in fiber-reinforced soil. In recent years, flexible fibers have increasingly been used in fiber-reinforced soil. However, their failure modes have not yet been revealed. In this study, plastic fibers are used for pullout tests conducted by a modified horizontal tensile testing apparatus. The mechanical characteristics of the fiber-soil interface and the deformation characteristics of plastic fibers have been analyzed. It has been found that the failure modes of plastic fibers in reinforced soil can be categorized into three cases: pullout failure with elastic tensile deformation, pullout failure with plastic tensile deformation, and fracture failure with plastic tensile deformation. A theoretical calculation method is proposed to describe the progressive pullout behavior, and the pullout force-displacement relationship can be determined. The pullout force calculated using this method is less than that obtained from traditional methods due to the incorporation of the fiber's deformation characteristics. Through a comparison between the pullout test results and the predicted results, the effectiveness of the proposed method in capturing the pullout force-displacement relationship of flexible fibers in soil is verified.

The interface creep behavior of the grouted soil anchor subject to varying soil moisture was investigated using the combined incorporation of experimental and data-driven modeling methods to establish an efficient and robust forecasting framework. This study carried out the rapid and creep pullout tests of element anchor specimens at various saturations and then utilized machine learning methods to predict the development of interface creep displacement. The stepwise loading strategy and nonlinear superposition method were combined to generate the interface shear creep curves of the element anchor specimens. A total of 936 data groups of the interface shear displacement were collected with changing soil moisture contents, interface shear time, and interface shearing stress. Next, this study explored the Back Propagation Neural Network (BPNN) and four other machine learning algorithms in predicting the interface creep behavior of the grouted soil anchor under various moisture conditions. As for the hyperparameters, the beetle antennae search (BAS) approach was employed to optimize the BPNN and random forest (RF) models. Finally, the boxplot and Taylor diagrams proved the BASBPNN demonstrated a better performance than BAS-RF in predicting the interface creep behavior. The consequent correlation coefficients ranged from 0.9613 to 0.9805 for BPNN, indicating the accuracy and reliability of the interface creep prediction. A partial dependence plot (PDP) was also introduced to visualize the established machine learning model. The threshold of moisture content near 28.7 % is found to switch the interface shear stress-displacement response from strain-stabilizing to strain-softening behavior and to result in the main moisture-increase-induced interface strength degradation. The soil moisture fluctuation leads to the development of interface shear displacement mainly observed in the early phase of 20 h after the onset of moisture change. The uncovered coupled impact of soil moisture condition and interface shear stress state can provide insights into the evaluation of the time-dependent in-service performance of grouted soil anchors embedded in clayey soils.

Geosynthetics have increasingly been applied to geotechnical engineering works due to their numerous advantages, including cost-effectiveness and their significant role in sustainable development. When geosynthetics are used as reinforcement in earth structures, such as embankments, retaining walls and bridge abutments, soil-geosynthetic interface shear behavior is a critical parameter involved in the design. This paper presents a series of monotonic and cyclic/post-cyclic pullout tests carried out to examine the apparatus scale effect on the pullout response of a geogrid embedded in two different soils. To assess the small-scale equipment feasibility, comparisons were made between pullout test parameters derived from small- and large-scale equipment. The test results indicate that, under a low confining stress of 25 kPa, using a smaller-sized apparatus results in lower values of geogrid pullout resistance and maximum mobilized shear stress, but higher values of confined tensile stiffness at low strains. On the other hand, as the confining stress increases (i.e., 50 kPa and 100 kPa), the difference between the results becomes less significant and similar trends are observed regardless of the equipment type. Adopting small-scale equipment enables obtaining soil-reinforcement interaction parameters using test procedures that are less time-consuming than those associated with large-scale pullout tests. However, proper scale effect correction factors may be considered for more consistent estimates of the interface strength parameters under low normal stress values.

Grouted rock bolts subject to axial loading in the field exhibit various failure modes, among which the most predominant one is the bolt-grout interface failure. Thus, mechanical characterization of the grout is essential for understanding its performance in ground support. To date, few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout (FRG) in rock bolt reinforcement. Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression, indirect tension, and direct shear loading conditions. We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG. FRG was developed using 15% silica fume (SF) replacement of cement (by weight) and steel fiber to achieve highstrength and crack-resistance to overcome drawbacks of the conventional grout. Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality. The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined. Our experimental results showed that the addition of SF and steel fiber by 1.5% fiber volume proportion could lead to the highest compressive, tensile, and shear strengths of the grout. The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%. The scanning electron microscopy (SEM) analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout. Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar's load carrying capacity. Therefore, FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required. O 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

The benefits of geosynthetic-reinforced soil systems over conventional earth-retaining structures are now well established. These reinforced systems are often subjected not only to static loads, but also to seismic and/or traffic loads, in which case the effects of repeated loading on soil-geosynthetic interaction characteristics should be properly considered. This study investigates the behaviour of a geogrid typically used for soil reinforcement under cyclic pullout loading through load-controlled laboratory pullout tests. To examine the influence of cyclic loading amplitude, number of cycles and static pullout force acting on the geogrid at the onset of cyclic loading, distinct loading patterns are considered. A well-graded residual soil from granite is used as backfill material. A comparison between the cyclic and monotonic pullout response of the reinforcement is then established in order to identify any potential strength loss attributed to cyclic loading. The experimental results show that the ultimate pullout resistance of the geogrid embedded in medium dense residual soil from granite may be adversely affected by cyclic loading. The cumulative cyclic displacements of the reinforcement are more pronounced during the initial loading cycles, but tend to stabilize with the increasing number of cycles when the soil is densely compacted. In the presence of dense soil, the cyclic strains of the geogrid specimen are particularly significant at the front and almost negligible towards the back end.