# Enhancing Clay Soil's Geotechnical Properties Utilizing Sintered Gypsum and Glass Powder
## 1 Introduction  
The continuous surge in solid-waste generation, driven by population expansion, urbanization, and economic growth, poses a mounting challenge regarding landfill management and recycling efforts. Indeed, waste management has become a paramount concern for researchers committed to sustainable environmental practices. In recent decades, geotechnical scientists have embarked on extensive investigations to restrain the production of diverse waste materials across the globe by integrating them into geotechnical applications, including pavement construction, retaining walls, and foundation structures. Among these increasing waste concerns is the disposal of PV panels at the end of their life cycle. PV panels, widely renowned for their role in electricity generation and sustainable energy production, paradoxically contribute to the growing solid-waste issue upon reachingtheir end-of-life stage, often due to malfunctions or inefficacy [1]. Projections indicate that, by 2050, there will be a significant amount of PV-panel waste, estimated to be about 60 to 70 million tons [2; 3]. These PV panels are primarily constructed from materials, such as silicon, glass, and metal, that possess recyclable attributes, albeit hindered by the limited global availability of a recycling infrastructure. Furthermore, PV panels consist of dangerous substances, posing significant threats to both human well-being and the natural surroundings [4; 5; 6; 7; 8]. These hazardous components, including selenide (Se), copper indium gallium selenide (CIGS) with cadmium (Cd), lead (Pb), crystalline silicon (c-Si) with Pb, and cadmium telluride (CdTe) featuring Cd and Pb [9; 10; 11], have prompted extensive research to mitigate the production of PV-panel waste materials. In response to more than two decades of large-scale PV panel deployment in various countries, particularly the United States and China, researchers have sought innovative solutions to decrease the environmental impact of PV-panel waste. This involves extending the longevity and resilience of PV panels through improved design and durability and enhancing the recycling processes to make them more accessible and cost-effective [12; 13]. Notably, one critical facet of EoL PV panels is their glass shields, which have motivated the present study's application of glass powder and sintered gypsum to improve the geotechnical properties of clay soil. Gypsum, or calcium sulfate dihydrate (CaSO\({}_{4}\cdot\)2H\({}_{2}\)O), enhances the unconfined compressive strength (UCS) of clay soils through chemical interactions that create cementitious bonds. However, its efficacy can vary in gypesous soils due to potential volumetric fluctuations from hydration and dehydration processes [14]. Additionally, sintered gypsum, produced by heating gypsum, exhibits pozzolanic properties that react with calcium hydroxide, Ca(OH)2, to form cement-like compounds, improving soil strength. Combining sintered gypsum with cement enhances the strength and stiffness features of stabilized clayey soil, and improvements in sulfate-rich soils are observed when cement and lime are used, benefiting from gypsum's pozzolanic reactions. Effective soil stabilization with gypsum requires understanding its interactions with each soil type [15]. Recent decades have witnessed a surge in research focusing on the integration of modern waste materials, including glass powder, plastics, and electronic waste, into soil-enhancement strategies. Glass powder, a significant global waste commodity, is exemplified by India's production of 2.48 million tons in 2019 alone [16]. This mechanical stabilization approach distinguishes itself from resource-intensive laboratory testing. Additionally, this method avoids environmental threats and inherently embodies sustainable waste management, offering an eco-friendly alternative to conventional landfill practices [17].