Geotechnical response of Strip footing resting on oil-contaminated sand improved with stone columns: numerical study

Abstract

Abstract Ground improvement techniques are frequently employed in construction sites characterized by weak soil conditions that may result in suboptimal performance. The use of ordinary and encased stone columns aims to enhance endurance, shear strength, and soil hardness, thereby mitigating settlement issues and expediting the consolidation of contaminated sand soils. In this research, a comprehensive investigation involving 74 cases was conducted to assess the behavior of both ordinary stone columns and encased stone columns under strip footing in contaminated sand subgrade. The objective was to discern the impact and characteristics of encapsulation in comparison to encapsulated stone columns, employing a Finite Element Model (FEM) within the PLAXIS 3D software package. The study focused on stone columns with two different diameters (D = 0.5 m and 0.6 m), while the column length was 12 m across all cases. As the contamination level increases—at the variable contaminated sand levels of (2%, 5%, and 10%)—the viscosity of the soil rises, leading to a reduction in cohesion between soil granules. Consequently, the internal friction angle decreases, with values diminishing from 31° to 27° and then to 24°, respectively. The clean sand was placed to achieve relative density, a medium dense sand state (Dr = 50%). The two categories of stone columns examined were ordinary stone columns (OSC) without encapsulation and encased stone columns (ESC) encapsulated with varying degrees of hardening. Results obtained at variable internal friction angles (35, 40, and 45 degrees) revealed a notable increase in the endurance of ordinary stone columns on untreated soil conditions, reaching 100%, 125%, and 148% for column diameters (D = 0.5 m) and 130%, 145%, and 180% for column diameters (D = 0.6 m), respectively. The corresponding increase in the endurance of encased stone columns under untreated soil conditions was found to be 275%, 33%, and 345% for column diameters (D = 0.5 m) and reached 313%, 350%, and 375% for column diameters (D = 0.6 m), respectively. All preceding results were obtained under the condition of a contaminated sand content of 5%. The investigation aimed to provide valuable insights into the performance and efficacy of ordinary stone columns (OSC) and encased stone columns (ESC) as a geotechnical solution for improving soil conditions in construction projects.

Keywords

• Clean sand
• Contaminated sand
• Ordinary stone columns
• Encased stone columns
• PLAXIS 3D
• Applied load