Ahmed Al-Mahbashi

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 5TE 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.

The liner layers of natural sand-clay mixtures are extensively used in a range of geotechnical and geoenvironmental projects. In many of these projects, these layers are exposed to dynamic loads or waves due to natural seismic earthquakes or due to human activities, such as machine vibrations, traffic repeated loads, and other impact loads. The permeability of liners is a key property and should be adequately designed to sustain these loads during their lifetime of serviceability. This study sought to evaluate the possible effects of dynamic loads on the efficiency of two different sand-expansive clay (SCL) liners during their lifetime. This was achieved through experimental tests for two series; the first series was subjected to dynamic loads (up to 500 cycles) using the triaxial dynamic system and then tested for permeability for a long period of up to 100 days. The permeability results were compared with the second series tested without being subject to dynamic loads. The dynamic properties for both liners, such as the shear modulus (G), damping ratio (D), and degradation index (δ) were determined and discussed. The results indicated that both materials showed significant degradation with an increase in cycles of dynamic loads; most of the degradation took place during the first 100 cycles. In consequence, the dynamic loads induced a significant effect on the performance of the liners during their lifetime (reducing the permeability by more than six times). These effects were time-dependent and should be taken into account during the design phases.