# Improvement of Subsurface Thermal Characteristics for Green Parks
###### Abstract  
The ground surface of green parks in arid and semi-arid areas may not be comfortable at specific times during the day and night due to the sun and the rate at which the subsoil gains or loses heat. Knowledge of the subsurface soil's thermal properties can provide designers with convenient and comfortable settings. Design focus is generally directed toward stability, density, and hydraulic conductivity. An assessment of the thermal properties of clay-sand mixtures of 10%, 20%, and 30% clay content is conducted. The proposed clay-sand layers are subjected to three different thermal gradients of 30, 20, and 10 degrees of magnitude. The profile of temperature changes was monitored using 5 TE sensors and data loggers. The mixtures were also subjected to cooling at room temperature. The results indicate that the clay type and the clay content govern the response of subsurface clay-sand liners to temperature gain and loss. Two field sections with clay-sand layers of 15% and 20% clay were examined for temperature changes over an extended period. In winter, green areas rich in clays were found to keep heat for several hours and provide relatively warm evenings. In summer, the mixture retains a cool temperature for some time during the day. temperature; heat; clay-sand liners; mixtures; thermal +
Footnote †: journal: _Sci._  
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Overall, the thermal properties of clay-sand mixtures used in green park post-applications constitute a developing field of study that still includes a number of knowledge gaps. Researchers can aid in the creation of more dependable and effective green park infrastructure through examining these gaps. Solid particles determine how heat moves and other thermal characteristics. Both air and water can be found inside these pores, and both have an impact on heat storage and transfer. The temperature profile of the soil below grade level is generally influenced by the type of material, moisture content, and degree of compaction of the soil, as stated by [PERSON] [1]. Temperature variations and the conditions of the strata's moisture content are closely related. The moisture content of clayey soil is significantly impacted by temperature variations. Considerable fluctuations in soil moisture levels can arise from temperature shifts between day and night, according to a study by [PERSON] et al. [2]. While colder nighttime temperatures encourage water intake, high daytime temperatures can enhance evaporation, leading to soil desiccation. These cycles of moisture fluctuation can have an impact on soil permeability and soil structure in general. [PERSON] and [PERSON] [3] investigated how various characteristics affect thermal conductivity. These included mineral composition, grain size distribution, particle shape, and porosity. Based on the aforementioned parameters, a model was created to forecast thermal conductivity. [PERSON] and [PERSON] [4] pointed out that thermal conductivity can increase with an increase in soil density and water content. Thermal conductivity decreases with the addition of salts. When the same salt type and same concentrations are considered, sand's thermal conductivity is higher than that of clay. Heat capacity is generally defined as the ability of a material to store heat energy. This is similar to specific heat. The higher the specific heat, the more heat a material gains or loses. Air and water phases show different thermal conductivities and can affect the overall flow of heat. Heat conduction is influenced by soil composition, structure, and density, and by the geometry of pores. [PERSON] [5] and [PERSON] et al. [6] considered three major parameters contributing to changes in the thermal conductivity of bentonite-sand mixtures. These are the proportion of bentonite/sand, the dry density (which can be a function of the void ratio), and the water content.