Geotechnical field studies and numerical modeling of pipeline-highway embankment interaction in Port Said, Egypt

Abstract Pipeline crossings beneath existing highways present significant geotechnical challenges, particularly in soft soils where differential settlements may compromise both pavement performance and buried utilities. This study investigates and compares different construction techniques to minimize deformation at pipeline–highway interactions in Port Said, Egypt. In-situ trial tests were conducted using reinforced concrete slab, biaxial geogrid, and several cement-stabilized sand mixtures. Static plate load tests with eight loading–unloading cycles were performed to evaluate stiffness and settlement behavior. Additionally, a three-dimensional numerical model was developed in PLAXIS 2024.1 to simulate the field trial using cement-stabilized sand surrounding empty pipes. Results indicated that the cement-stabilized sand mixture (150 kg cement and 180 l water per 1 m 3 of sand) provided the most favorable performance. Results of the static plate load test showed that the improved soil exhibited an elastic modulus comparable to that of the adjoining crushed stone base layer, confirming the effectiveness of the stabilization. Settlements were found to be very small, with 0.07 mm after the first cycle and 0.075 mm after eight cycles. According to the long-term logarithmic cycle predictions, the stabilized layer is expected to yield a settlement of 0.098 mm after one million cycles, in contrast to the significantly larger settlement of 0.682 mm predicted for the untreated soil. Numerical modeling confirmed these findings, showing maximum deformations of 0.851 mm at the highway surface and 0.785 mm in the pipeline under 300 kPa applied stress. This study demonstrates that cement-stabilized sand provides a practical and cost-effective soil improvement technique for pipeline crossings. Its ability to minimize differential settlement makes it suitable for public underground utilities beneath highways in soft soil environments.