<p>This study investigates the mechanical and durability performance of silicate cement-modified sandy soil by evaluating the effects of varying cement content (5–15 wt%), temperature (25–125°C), salinity (0–12% NaCl), and external pressure (5–15 MPa) on compressive strength, shear strength, and permeability coefficient. Long-term immersion tests simulating oil and gas field environments were also conducted to assess the durability of the modified soil. The results demonstrate that, under ambient temperature conditions, increasing the cement content to 15 wt% significantly enhanced the compressive strength of sandy soil from 1.35 MPa to 5.75 MPa. When the temperature increased from 25°C to 125°C, the compressive strength of the modified soil improved by up to 37%. A salinity concentration of 6% NaCl further strengthened the cementitious matrix and reduced the permeability coefficient; however, excessive salinity weakened particle cohesion. Under high-temperature and high-pressure conditions (125°C, 10–15 MPa), the compressive strength reached a maximum of 6.10 MPa, accompanied by notable improvements in shear strength and durability. Field application results revealed that in pipeline installation areas with a salinity of approximately 5 wt% and a pH of 8.5, the use of 10 wt% silicate cement modification reduced ground settlement by approximately 51% compared to unmodified areas. Additionally, the compressive and shear strengths were increased by 58% and 50%, respectively, while the permeability coefficient was significantly reduced, demonstrating excellent load-bearing capacity and impermeability. In summary, silicate cement-modified sandy soil exhibits superior mechanical enhancement and durability under extreme conditions encountered in oil and gas pipeline foundations. These findings provide critical technical support and theoretical insights for future engineering applications.</p>