# Effect of Heat-Treatment Remediation on the Mechanical Behavior of Oil-Contaminated Soil
## 1 Introduction  
Soil pollution is an important issue in relation to the environment and public health [1; 2]. Among pollutants, organic substances--including petroleum hydrocarbons, insecticides, and herbicides--are a major type of pollutants in soil [3; 4; 5]. In Taiwan, by the end of 2015, soil and groundwater pollution were controlled at 3090 sites, covering a total area of 15.2 million square meters [6], of which gasoline and diesel pollution were the most common forms of organic pollution. These pollutants are present as a result of leakage accidents, oil storage tanks, oil refineries, industrial parks, and other facilities [7; 8; 9].  
According to site research, the main pollution components of petroleum-contaminated soils include alkanes, olefins, naphthenes, aromatic hydrocarbons, ethers, and alcohols, such as benzene, toluene, ethylbenzene, and xylene (these four are collectively referred to as BTEX) and trimethylbenzene (TMB). Together, these pollution components constitute total petroleum hydrocarbon (TPH) [10; 11]. C10-C40 are hydrocarbons that are difficult to volatilize or attenuate in the environment. Once they leak, they accumulate in the soil for a long time and gradually leak into the groundwater, irreversibly polluting the environment. The remediation of affected soil is much more difficult than that of other media.  
When pollutants are distributed in soil pores, the conduction resistance increases the difficulty of soil remediation, and the physical and chemical properties of the pollutants influence the selected methods and effects of remediation.  
Several soil restoration techniques are available, each of which can be applied to soil of different properties with different forms of pollution. Before the use of such techniques, the treatment time, economic benefits, safety, and characteristics of the locale must be considered. Treatment methods can be divided into (1) physical and chemical treatment methods, (2) heat-treatment methods, (3) biological treatment methods, and (4) plant restoration methods. Among various methods for remediating soil with organic pollution, heat treatment is the most extensively used because of its high removal efficiency and short restoration time, and it has been actively developed in recent years. Heat-treatment methods include hot gas decontamination, thermal desorption, high-temperature incineration, and pyrolysis. All of these methods use heat to separate or accelerate the separation of pollutants. They take a short time and have a high treatment efficiency, and they have been successfully used to treat soil that is contaminated by gasoline, aircraft fuel, and even polychlorinated biphenyls, pesticides, and dense non-aqueous phase liquid (DNAPL).  
Most studies on the heat treatment of soil focus on the removal of organic pollutants, but few discuss the reuse of soil thereafter. In Taiwan, treated soil has been reused as a construction material in civil engineering, such as in backfill and road base materials. However, heat treatment changes the physical properties of the soil, which greatly affects the subsequent engineering application. The effect of heat treatment must be understood, but the related data are lacking. Therefore, this study investigates the percentage removal of total petroleum hydrocarbons (TPHs), as well as changes in soil physical properties upon the heat treatment of petroleum-contaminated soils. A high-temperature furnace in a laboratory was used to heat soil specimens and simulate heat treatment, including thermal desorption and high-temperature incineration. Test removal efficiency was obtained by varying the operating conditions. Heat-treated specimens were further subjected to soil mechanical experiments to compare their basic physical properties (including particle size distribution and Atterberg index), permeability, and mechanical properties, before and after heat treatment. The effects of various heat-treatment operating conditions on soil properties are investigated to provide a reference for future site remediation.