Sapria Adi, Ferry Fatnanta, Syawal Satibi COMPRESSIVE CAPACITY OF HELICAL PILE FOUNDATION ON PEAT WITH VARIATION OF HELICAL PLATE DIAMETER 76 COMPRESSIVE CAPACITY OF HELICAL PILE FOUNDATION ON PEAT WITH VARIATION OF HELICAL PLATE DIAMETER Sapria Adi 1 , Ferry Fatnanta 2 , Syawal Satibi 2 1 Student of Civil Engineering Study Program, Riau University Pekanbaru, INDONESIA 2 Civil Engineering Study Program, Riau University Pekanbaru, INDONESIA e-mail: ferryfatnanta1993@gmail.com ABSTRACT The use of helical foundations to support structures on peat soil is still a new method. Research is needed to develop this foundation. There are 6 types of helical foundation tested on peat soil. To study the effect of helical plate diameter, plate diameters were varied with sizes 25 cm (M), 35 cm (L), and 45 cm (G). Plate positions (1, 2, 3 plates) are designed at 300 mm spacing. The axial compression bearing capacity test is carried out based on the constant rate of penetration procedure. At the beginning of loading, the load increases significantly. At a certain descent, the load begins to decrease slowly. The load-settlement curve shows that the larger the plate diameter, the greater the load it can withstand. The largest bearing capacity is produced by the GGG 30 foundation (3 plates dia.45 cm), which is 10.83 kN. LLL 30 helical foundation (3 plates dia.30 cm) provides a bearing capacity of 7.14 kN. These results clearly explain that the increase in plate diameter is directly proportional to the increase in the axial compression bearing capacity. Keywords: helical foundation; slab diameter; peat; bearing capacity. Received: 2021-10-25 Revised: 2021-12-11 Accepted: 2021-12-16 Available online: 2022-01-08 INTRODUCTION Helical foundations are foundations made of steel or concrete and equipped with helical plates in a certain number and spacing. This foundation has long been used to support structural stability against compressive, lifting, and lateral forces (D&B Engineering Contractors Inc, 2009). The use of helical foundations as structural supports on peat soils is still a new method. Designing a foundation on peat soil requires extra effort and precision. Helical foundations are a good choice for supporting structures. Research is urgently needed to apply this method to peat soils. In this study, a study was conducted on the behavior of the effect of helical plate diameter variations on the bearing capacity of helical foundations on peat soils. The background of the research is to determine the effect of plate diameter variations, so as to design the compressive bearing capacity of helical foundations on peat soils appropriately and efficiently. Helical foundation The helical foundation was discovered by an English inventor named Alexander Mitchell in 1833. At that time helical foundations were used to support light buildings in the area around the river (Sprince, 2010). Based on the mechanism, the bearing capacity of the helical foundation is determined by two methods, namely individual bearing and cylindrical shear (Perko, 2009). Individual bearing assumes the carrying capacity of the helical pile consists of two resistances, namely the bearing capacity of the soil under each plate and adhesion (skin friction). While the cylindrical shear method is a combination of the bearing capacity of the tip under the most basic plate, the shear strength formed by the soil cylinder with the soil, and adhesion. Research on helical foundations has been carried out by several experts. Rao et al. (1991) conducted tests on cohesive soils. The results of research by Rao (1991) show that the bearing capacity of the helical foundation increases as the slab diameter increases In addition, Sprince (2010) conducted helical foundation testing on 4 types of soil. The soils used are sandy, hard loam, floating loam, and find sand. The test results show that the bearing capacity of the helical foundation has increased due to the increase in the diameter of the slab.