Deriving Geotechnical Parameters for Foundation Design in Ea Trang, Vietnam, through Combined Seismic Methods

Effective geotechnical evaluation is crucial for the stability and safety of major infrastructure projects. This study presents a comprehensive geotechnical site characterization in Ea Trang, Dak Lak province, Vietnam, a region characterized by steep topography and complex geology. Utilizing integrated seismic refraction (SR) and multichannel analysis of surface waves (MASW) techniques, the primary objectives were to delineate the subsurface structure and derive essential dynamic soil parameters for foundation design for the proposed Buon Ma Thuot expressway. SR surveys provided P-wave velocity (Vp) distributions, while MASW surveys yielded S-wave velocity (Vs) profiles to an investigation depth of approximately 30 m. The combined results consistently defined a two-layer geological model. The upper layer, a clay mixture with a thickness of 10-15 m, exhibits Vp values from 350 to 1500 m/s and Vs values from 200 to 700 m/s. The lower layer, interpreted as completely to extremely weathered siltstone of the La Nga Formation extending to the investigation depth, shows significantly higher Vp values ranging from 1500 to ≥ 3500 m/s and Vs values from 700 to ≥ 2300 m/s. These geophysical interpretations align well with available geological borehole data, and a quantitative comparison shows less than a 2% deviation in layer depth, validating the integrated approach. This study emphasizes the practical application of combined seismic methods for providing reliable subsurface information essential for safe and resilient infrastructure development in challenging geological environments. Crucially, it demonstrates how this noninvasive characterization can identify significant geohazards, such as potential landslides, early in the design process.