## 1 Introduction  
Saemangeum is one of the largest land reclamations in South Korea. Its development began in 1991, with the construction of the world's longest man-made seawall or dike [1, 2]. Saemangeum is a tidal flat located on the central western coast of Korea (see Figure 1). The Saemangeum project is underway for road, railway, and port constructions for internal development. With the geographical location of Saemangeum, acquiring good quality, granular fill materials for embankments becomes challenging. Suitable granular soil for embankment material is difficult to find in the Saemangeum area. However, silty clay is widely distributed. With the great demand for quantity, the procurement and transportation of good quality fill materials for embankments may be costly and uneconomical [3]. Therefore, this study will maximize the utilization of clayey soil, which will serve as an effective, alternative solution to the limited supply of good quality, granular fill materials in the Saemangeum projects.  
Why soft clay? Geologically, the Saemangeum area has vast wetlands and flat terrain wherein fine materials, like clay, are very abundant and readily available. Clay has high potential and may be suitable for road embankments if designed and conditioned properly. However, very limited studies can be found concerning the feasibility of soft clay as a road embankment material [4]. Soft clay is rarely used as a fill material and, because of its documented poor engineering properties, only few researchers have considered its high potential for road embankments. The Federal Highway Administration(FHWA) [5] states that granular soils, like sand and gravel, are highly desirable as embankment materials because they can facilitate drainage, prevent saturation, are well-graded, and are capable of being well-compacted. On the other hand, finer materials, like silts and clays, are considered as less desirable and unsuitable for use as embankment materials, again because of their poor engineering properties [4,5].  
High-strength, clayey soil can be attained when the soil has optimum water content, is properly compacted, and is clear of unsuitable materials. However, such conditions are very difficult to implement at the construction site. In such instances, clayey soil with high water content can probably be used on-site. Considering the poor engineering properties of clay, various soil improvements can be applied--such as adding reinforcements or stabilizing agents. It is expected that the soil should have a higher bearing capacity when reinforcements are added and proper soil conditioning is applied [6, 7, 8]. Geosynthetics are popular reinforcements that are widely used to improve the load-bearing capacity of soil [6, 9, 10, 11]. Granular materials, such as gravel and sand, are also used with clayey soils to hasten the consolidation process and increase the soil-bearing capacity. Several studies have also showed that adding reinforcements to soft clay reduces settlement and increases the soil strength [4, 12, 13, 14, 15, 16, 17, 18, 19, 20].  
In this present study, a series of model bearing capacity tests are carried out to investigate the capability of soft clay to support imposed loading and its viability for use as embankment material. Materials, like crushed gravel and composite geotextiles, are used as reinforcements for the soft clay. A desirable embankment material, such as sand, is also tested as a basis for comparison. Hence, this study undertakes eight mold model test cases and four box model test cases, which consist of clay, loose sand, dense sand, and combinations of clay with crushed gravel and composite geotextiles.