Abstract:Composite geomembrane has been widely used in reservoir seepage prevention. Usually, composite geomembrane is composed of geomembrane and geotextile, which plays a protective and strengthening role and has an important influence on the swelling deformation of composite materials. The phenomenon of geotextile inflation was simplified as a hoop-constrained spherical bulging deformation model. With the help of the impermeable film laid under the geotextile, the bulging deformation test was carried out through bulging deformation test equipment, and the deformation characteristics and mechanical characteristics of geotextile bulging were studied. With the help of a microscope, the fiber structure change process and bursting mechanism during the deformation of geotextile are emphatically analyzed. The results showed that the bursting pressure of the geomembrane was about 50%～60% of the bursting pressure of the geomembrane. It could be seen that in addition to protecting the geomembrane, it would also restrain the deformation of the geomembrane and increase its resistance to deformation. In the bulging deformation of geotextile, the tensile stress–strain curve approximately showed the characteristics of plastic deformation, which could be divided into four stages: linear elasticity, yield, strengthening, and bursting and breaking. The swelling deformation shape of the geotextile was hemispherical, and the tear point generally appears at the crown top and further expanded to the spindle-shaped tear failure. The microstructure analysis showed that the twining point formed by the needled short fiber had a certain entanglement force, and the fiber between the twining points had a certain tensile strength. The gradual failure of the twining force of the twining point and the fiber fracture were the main reasons for the swelling deformation failure of the geotextile. The greater the mass of geotextile per unit area, the denser the fiber and the entanglement, the greater the swelling pressure that can withstand, and the stronger the ability to resist deformation. The research results had a practical significance for analyzing the contribution of geotextiles on the membrane to the strength of geomembrane bulging deformation.