Staple fiber needle punched geotextile, as an important engineering material, significantly affects the stability and durability of engineering structures through its frictional characteristics at interfaces with different soil masses. These frictional characteristics are not determined by a single factor, but rather are the result of the combined effects of material properties, soil properties, interfacial contact state, and environmental conditions.
The fiber type and surface morphology of staple fiber needle punched geotextile are core factors influencing its frictional characteristics. The fiber material (e.g., polyester, polypropylene) directly affects its chemical affinity and mechanical interlocking with soil particles. For example, polyester fibers have a higher surface roughness, allowing for a stronger mechanical interlocking effect with soil particles through the hairs at the fiber ends, thereby increasing the interfacial friction angle. Furthermore, the fiber crimp and arrangement are also crucial—crippled fibers increase the contact area with the soil, while oriented fibers may lead to anisotropy in frictional performance due to their orientation.
The physical properties of the soil itself play a decisive role in its frictional characteristics. The particle size distribution, particle shape, and gradation characteristics of the soil directly affect its contact pattern with the geotextile. Coarse-grained soils (such as gravel) have larger interparticle pores, making them prone to point or line contact with fibers. Friction in these soils primarily arises from the direct interlocking of particles and fibers. Fine-grained soils (such as clay), on the other hand, may fill the gaps between fibers, forming surface contact. In this case, friction relies more on intermolecular forces and adhesion. Furthermore, the soil's moisture content significantly affects interfacial friction strength by altering capillary forces between particles—moderate wetting enhances cohesion, but excessive moisture content can lead to a lubrication effect, reducing the coefficient of friction.
The interfacial contact state is the direct carrier of frictional properties. The three-dimensional mesh structure of staple fiber needle-punched geotextile, formed through a needle-punching process, directly influences the embedding depth of soil particles through its porosity and pore size distribution. When the soil particle size matches the geotextile pore size, particles can partially embed into the pores, creating an "anchoring" effect and significantly improving shear strength. If the pore size is too large, particles are prone to sliding, leading to a decrease in friction. In addition, the contact area and pressure distribution at the interface are also crucial—uniform pressure distribution avoids localized stress concentration, thus maintaining the stability of frictional performance. Environmental conditions indirectly affect frictional properties by altering the physicochemical state of the material and the soil. Temperature changes can cause fibers to expand and contract, altering the tightness of their contact with the soil; ultraviolet radiation can induce fiber aging, reducing surface roughness and thus weakening frictional performance. Chemically corrosive environments (such as acidic or alkaline soils) can damage the molecular structure of fibers, leading to strength degradation or changes in surface properties, ultimately affecting frictional stability.
Construction techniques have a crucial impact on the long-term performance of frictional properties. The tension, overlap method, and compaction degree of the geotextile during installation all alter the interfacial contact state. For example, excessive tension may cause fiber breakage or structural deformation, reducing frictional performance; while insufficient compaction may create voids between the soil and the geotextile, forming a weak interface. Furthermore, mechanical damage during construction (such as punctures or scrapes) can also damage the integrity of the fibers, affecting the durability of frictional properties.
Load history and time effects are important dimensions in the evolution of frictional properties. Under long-term cyclic loading, the interface between geotextile and soil may experience degradation in frictional properties due to particle rearrangement or fiber creep. For example, repeated traffic loads may cause soil particles to gradually compact, reducing the contact area with fibers; while fiber creep deformation may redistribute contact pressure, leading to a decrease in friction in localized areas. Furthermore, time effects may further alter the interfacial state through chemical processes (such as clay creep) or biological processes (such as microbial corrosion).
