# Dynamic Shear Degradation of Geosynthetic-Soil Interface in Waste Landfill Sites
## 1 Introduction  
Most of earth structures involve the combination of different materials such as soil, rock, concrete, geosynthetics, etc. due to the diversity of construction areas and materials. The area formed between adjacent materials is called the \"interface\". In engineering systems, discontinuities exist at the interface and the overall system shows discontinuous behavior due to the discontinuities. Therefore, the theoretical approaches that are based on continuum mechanics may exhibit limitations for the characterization of the interface response. Further, the difference of the intrinsic material properties at the interface entails complicated problems. With rapid industrialization, the quantity of waste has continuously increased. Waste comprises different forms and may degrade into harmless products, or it may be non-degradable or even hazardous. Worldwide, landfilling is the most popular means of hazardous- and municipal-waste disposal because it can be relatively safe and cost-effective when it is based on a precise design and managed with sufficient care [1]. However, landfills have also been identified as one of the major threats to groundwater resources [2], and hazardous- and municipal-waste landfill facilities therefore require lining and covering systems that are mainly organized by geosynthetics and soils. Various types of geosynthetics with diversefunctions such as reinforcement, filtration, drainage, protection, and separation are used in the facilities. These geosynthetic systems are currently an accepted and well-established component of the landfill industry [3], and the geosynthetic-soil interface inevitably appears at waste landfill sites. The interface is comprised in base and side slopes of the waste landfill as shown in Figure 1. Figure 1 displays the brief section of waste landfill and the concept of geosynthetic-soil interface. An important characteristic of the landfill-liner and -cover systems with respect to stability is the shear resistance along the interface between the various liner- or cover-system components [5]. The shear behaviors of geosynthetics are strongly related to the characteristics of the geosynthetic-soil interface because geosynthetics comprise a self-encompassing interface area that corresponds to conditions such as external forces, friction, and stiffness. Therefore, various studies on the shear behavior of the interface have been performed [6; 7; 8; 9; 10]. [PERSON] et al. [11; 12] proposed a mechanical model to simulate the relationship between the deflection of the soil and the contact pressure at the interface of the double-layer geosynthetic reinforced load transfer platform (LTP) and soft soil, based on analytical approach. The proposed model and parametric studies showed better prediction of LTP behavior. A study of the interface was also developed for soil-structure interaction. [PERSON] and [PERSON] [13] performed a 3-dimensional numerical analysis to investigate the characteristics of soil-structure interaction and its influence on the seismic response of building frames. The interface is modeled as spring-slider systems and it was revealed that the type of foundation is a major contributor to the seismic response of buildings with soil-structure interaction. [PERSON] et al. [6] also investigated the soil pile interface-induced effect on pile foundation, based on 3-dimensional numerical analysis. Results showed that the type and size of the pile elements influence the dynamic characteristics and seismic response of the building due to interaction between the soil, pile foundation, and the structure. Cyclic simple shear tests were performed for the present study in order to investigate the dynamic shear response of the interface, because the seismic stability must be considered in accordance with Article 35 of the Waste Management Enforcement Regulations in Korea.