Geotextile tubes are used in dam construction because fine tailings are difficult to use. The shear characteristics of geotextile tubes during dam operation are closely related to those of the materials used to construct the tubes. Pull-out tests can accurately reflect the interfacial shear characteristics between geosynthetics in practice, so pull-out tests were carried out for different interfacial types of polypropylene woven fabrics under dry and wet states. The effects of the type of interface and dry-wet states on the interfacial shear characteristics were investigated, and the impact mechanisms were also discussed. The results indicated that P-type interfaces (the warp yarn on the interface is parallel to the pulling direction) tended to harden. However, PTP-type (the warp yarn on the interface is perpendicular to each other) and T-type (the weft yarn on the interface is parallel to the pulling direction) interfaces softened first and then tended to plateau after reaching peak shear stress, and softening became more obvious at higher normal stresses. The displacement corresponding to peak shear stress (referred to as “peak displacement” in this paper) of interfaces was positively correlated with the normal stress, and the wet state reduced the interfacial peak displacement. For different types of interfaces, the peak displacement of the T-type interface was the largest, followed by PTP-type and P-type. Interfacial shear characteristics conformed to Mohr–Coulomb strength theory and, compared with quasi-cohesion values ranging from 1.334 to 3.606 kPa, the quasi-friction angle significantly contributed to the interfacial shear strength. The quasi-friction angle of the interface was composed of a sliding friction angle and an occlusal friction angle. The shear strength of the interface was more sensitive to the interface types than whether they were in the dry or wet state. For different types of interfaces and dry-wet states, the change in the interfacial shear strength is respectively affected by the occlusal friction angle and the sliding friction angle on the interface.

Geotextile bag dams withstand the earth pressure of tailings in tailings reservoir by the shear stress on interface of geotextile bags. To improve the interfacial friction characteristics, pull-out tests were conducted on geotextile bags filled with fine tailings slurry containing various cement content, and the influences of cement content on the interfacial shear characteristics were explored. To describe the progressive failure of the interface, the theoretical analysis of interface pull-out behavior was performed. The results revealed that adding content cement into fine tailings slurry not only augmented the shear strength and residual strength ratio of the interface but also postponed interface softening. The optimal amount of cement was 3%, and the apparent friction angle which played a dominant role in interface strength was increased 17.4%, compared with no cement used. The elastic-plastic model and trilinear softening model were respectively improved to conform to the interfacial shear characteristics obtained in pull-out tests under low normal stress (< 60 kPa) and high normal stress (≥60 kPa). The interface shear stiffness of geotextile bag with the interfacial displacement within 20 mm and the dynamic compression modulus along the drawing direction were regarded as significant model parameters. The comparative analysis of shear stress-displacement curves, which were obtained from model calculating and test measuring, was carried out to verify the reliability and rationality of the model. The evolution patterns of the plastic zone, softening zone and residual zone of the interface were analyzed based on the model, and the warning values for interface failure were proposed. The development degree of interfacial plastic zone, softening zone and residual zone can be approximately calculated by quadratic polynomial of normalized pull-out force. The research results of this paper will provide reliable theoretical support for the design, construction and operation management of geotextile bag dams.

Constructing dams with geotextile bags filled with fine tailings can overcome the shortage of sand and gravel resources for dam construction. In addition, it can also prevent safety hazards caused by the deposition of fine tailings in tailings reservoirs. However, the geotextile bags were made of polypropylene woven fabrics, whose surface pore size can influence both the dehydration rate and the amount of tailings consolidated in geotextile bags. To optimize the construction efficiency of geotextile bag dams and improve the utilization rate of fine tailings, geotextile bags filling experiments, X-ray diffraction experiments and scanning electron microscopy experiments were performed by revealing the influence mechanism of low-cement content on the filling characteristics of geotextile bags from macro and micro perspective. The results showed that the addition of low-content cement as a curing agent effectively solved the contradiction between the permeability and the utilization rate of fine tailings. Compared with the fine tailings slurry without cement addition, when 1%, 3%, and 5% cement was added, the drainage efficiency increased by 12.90%, 23.39%, and 49.6% respectively; the sand retention ratio improved by 0.25%, 10.44%, and 13.62% respectively. Calcium silicate hydrate (C-S-H) calcium silicoaluminate hydrate (C-A-S-H), calcium carbonate, and calcium aluminate (CH) were found in the consolidated tailings. The hydration of cement within the geotextile bags formed a hydrated membrane layer that wrapped, adsorbed, and encapsulated fine tailings particles, accumulating on the surface of coarse tailings to create a composite particle structure. With the increase of cement content, the amount of hydration products mentioned above increased accordingly, and their diffraction peaks gradually enhanced, which not only contributed to effectively alleviate the surface blockage of geotextile bags but also improve the filling degree of geotextile bags, and thus increasing the effective normal stress transmitted to the contact surface of laminated geotextile bag in dam construction. Considering construction efficiency, the utilization rate of fine tailings, and construction cost, the optimal cement content was determined to be 3%. This research is expected to offer insightful and transferable experiences for dredging projects, coastline governance, soft foundation strengthening, among other applications.