The Identification of Hard Bottom Surface Structure using Correlation of Geoelectrical Resistivity Methods and SPT Data as Preliminary Studies for Laying the Foundation at Passing Cross Sumatera Toll Road, South Lampung Station

Abstract

The planting of the Upper pass foundation on the Sumatera toll road construction project in South Lampung requires proper planning in terms of both technical and safety aspect. Generally, in principle, the foundation should be able to reach soil layers, or in case the hard soil is not easily found, the compaction or soil recovery. To find out the geological condition below the soil surface, related to the planting and construction of the foundation, it is necessary to investigate and identify the geological structure of the area. The method used to identify the subsurface methods and the Standard Penetration Test (SPT). The resistivity geoelectrical method utilizes a variety of resistivity values for each rock, while the SPT method uses the amount of resistance (N) per depth of soil penetration in its process. The result of the investigation using these two parameters will then be correlated with the geological conditions of the research field to determine the hard surface structure. Hard layer on the research field had resistivity values above 250 Ω and N-SPT values are above 50, identified as a fine sand layer containing gravel breccia sandstone and granodiorite stones. The subsurface hard layer can be found from a depth of 0-25 meters at the research field.