Geotechnical Characterization and Foundation Design for a Multi-Story Factory in the Bengal Delta: Insights from Sub-Surface Investigation.

ABSTRACT:

This study provides a geotechnical study of a six-story factory building in the proposed Liberty Knitwear Ltd. in Kaliakair, Gazipur, Bangladesh. The characteristics of the subsoils were identified using four boreholes that were 60 ft deep and found a typical Bengal delta stratigraphy: a thin surface of reddish, plastic clays (0–22 ft, SPT N=4-24) covered densely with silty sands (SPT N=14-50). The level of groundwater was observed 14-17 ft in to ground. Engineering design was based on laboratory tests, including grain-size distribution (top fines to 88 per cent and bottom sands to 92 per cent), Atterberg limits, and direct shear tests (φ = 26-40 degrees, c = 0.11 -0.049 tsf). The calculated bearing capacities of shallow foundations reached 1.68tsf at 10 ft depth (factor of safety = 3). Furthermore, 24-inch-diameter piles with pile capacities of more than 120 tons at a depth of 60 ft support the feasibility of deep foundations in terms of heavier loads. The location of the site in Seismic Zone- 2 (z = 0.20, BNBC 2020) requires a dynamic analysis and supports the suggestions for shallow foundations. These results provide a strong basis for cost-effective and secure foundation construction in the problematic deltaic soils of Bangladesh.

Keywords: SPT, bearing capacity, grain size distribution, Terzaghi equation, seismic Zone-2, pile design.