## 1 Introduction  
Soil contamination has become a global environmental issue, as it has seriously affected both the environment and human health. Despite this, its effect on the geotechnical properties of soil has been investigated, including whether the contaminated soil maintains the geotechnical performances needed for earthwork foundation or fill materials. Some experts have researched several contaminated soil samples with various oil types and concentrations. [PERSON] et al. [1] studied the geotechnical properties (internal friction angle and permeability) of oil-contaminated Jumunjin standard sand of Korea with various relative densities of sand, oil types and concentrations. Some of these studies [2, 3] found that the viscosity of oils promotes slippage between the soil particles due to the lubrication of soil particles. [PERSON] et al. [2] carried out consolidation tests on clean and contaminated sand by heavy crude oil in the amounts of 0, 2 and 6% by weight. It was found that the compression index (C\({}_{c}\)) increased with the increase in oil contents.  
[PERSON] and [PERSON] [3] studied the change in the shear strength and bearing capacity of unsaturated oil-contaminated sand using three types of oil: Oman crude oil, engine oil and lamp oil. They found that an increase in oil contents significantly reduced the bearing capacity and shear strength, with a decrease in the internal friction angle (\(\varphi\)).  
Remediation technologies have been developed to treat hazardous contaminated sites because the chemical form of the contaminants can influence their solubility, mobility and toxicity on soil [4]. Remediation technologies are divided into physical, chemical, biological and thermal treatment methods. Each technology has been applied as an in situ or ex situ approach depending on the remediation cost, site conditions and contaminant characteristics.  
There are several limitations of physicochemical and biological methods for the remediation of heavy oils, as well as heavy metals. In other words, these methods are less cost-effective and require a long-term period when individually used [5]. However, thermal treatment methods, which heat the contaminated soil regardless of contaminant types, can be applied to multi-contaminated sites [5]. Even though the typical thermal treatment method is technically effective for remediating the contaminated soil, its production and operating costs are much more expensive, and its maintenance requires much attention and labor.  
Therefore, in order to overcome these limitations, electrical resistance heating technology, as one of the thermal treatment methods, was developed in this study for the remediation of heavy oils, as well as heavy metals, in multi-contaminated silty sand. An electrical resistance heating device simply consists of a power supply using the flow of AC electricity and a heating resistor. By allowing a high electric current to flow through a resistor installed in the soil, the soil volume is rapidly heated, resulting in an increase in temperature to remediate heavy oils, as well as heavy metals, in multi-contaminated soil.  
This paper presents the results of an environmental and geotechnical laboratory experimental program before and after thermal treatment, using electrical resistance heating technology. Finally, it is estimated whether treated silty sand is suitable as a construction fill material based on the effect of decontamination on the geotechnical properties of multi-contaminated silty sand and the recovered geotechnical properties of treated silty sand.