Sediments from stable sand bars along a 40 km section of the Brahmaputra River in northern Bangladesh were analyzed for their major, trace and rare earth element contents to determine their provenance, compositional maturity, source area weathering and tectonic setting. Geochemically, the sediments were classified as litharenites and the Index of Compositional Variability (ICV) varied between 1.4 and 2.0, indicating low compositional and mineralogical maturity. A high mean SiO₂ concentration (72.9 wt.%) and low Al₂O₃ (11.1 wt.%) were consistent with a low abundance of shale and clay components. The depletion of the oxide components Na₂O, CaO and K₂O relative to average upper crustal compositions (UCC) reflected loss of feldspar during chemical weathering in the source region. Average TiO₂ values for most samples were higher than average crustal levels, consistent with the northern section of the Brahmaputra River being a potential resource for valuable Fe-Ti oxide heavy minerals. Major and trace element ratios indicated the sediments represented erosional products from typical felsic upper continental crustal materials with contamination (30%–40%) from more intermediate/mafic compositions. The rare earth element patterns showed negative Eu anomalies (0.57–0.71), indicating they were derived mainly from fractionated felsic rocks. Resemblance of the sediment compositions to mean compositions from Higher Himalaya crystalline rocks pointed to these being potential source rocks but with components from a mafic source also present. Major element chemistries and low to intermediate weathering indices for all sediments indicated a lack of substantial chemical weathering. Evidence from tectonic discrimination diagrams suggested the Brahmaputra River sediments were derived from rock types that formed in a transitional tectonic setting ranging from an ancient passive margin to an active continental margin. Deposition occurred under cool to semi-arid climatic conditions in an oxic environment.

Sand mining using dredging technology from channel bars is a common technique worldwide. To minimize adverse effects of dredging, geo-engineering nature of the soil should be evaluated before mining. Therefore, the present study deals with the potential risks associated with dredging for mineral sand extraction by analyzing the engineering geological properties of the soil from the Brahmaputra River bar and the surrounding areas, Bangladesh. A detailed engineering geological analysis was conducted using field and laboratory testing methods, including Standard Penetration Tests (SPT), mineralogy, grain size distribution (GSD), California Bearing Ratio (CBR), and direct shear tests. The findings divulge that the soil in the study area is light gray, unconsolidated, moderately sorted, poorly graded, and classified as fine-to-medium silty sand. SPT-based liquefaction potential assessments suggest that the soils are highly susceptible to liquefaction, particularly during dredging or seismic events. The study also identifies the risk of localized slumping and soil instability, which exacerbated by micaceous and quartz-rich sands. The CBR results further classify the subgrade as weak to medium-strong, indicating risks of slumping, erosion, and instability. The non-cohesive granular soil in the area may liquefy or be susceptible to erosion, wave attack, bank slope failures, and seepage development during and after dredging as indicated from GSD and direct shear test results. Thus, proper safety precautions, including soil stabilization techniques, controlled dredging, and slope reinforcement, should be taken before dredging on such river bar to minimize risk. This research offers practical guidance for dredging companies to minimize risks and improve soil stability, contributing to safer and more sustainable river bar dredging operations worldwide.