Geotechnical Feasibility of Building Foundations in Low-Clay, Braided River Levee Deposits in Jamalpur Science and Technology University Site: An SPT Study

Abstract

Jamalpur Science and Technology University is located (24.9562° N, 89.8502° E) at Nayanagar Union in Melandaha upazila, Jamalpur district. According to geomorphological context, this university site is characterized as a natural levee within a braided river depositional setting of the Brahmaputra. The high-energy depositional conditions characteristic of braided fluvial systems is reflected in the subsurface strata, which are primarily composed of medium- to fine-grained sand with less than 10% clay content representing Holocene deposits. To evaluate the soil density and bearing capacity of the site for building foundations, Standard Penetration Test (SPT) N-values were acquired at 15 locations where the depth ranges from 1.5 ft, 3 ft, 4.5 ft, 6 ft, 7.5 ft, 9.0 ft, 10.5 ft, 12 ft, 13.5 ft, 15 ft, 16.5 ft, 18 ft, 19.5 ft, 21 ft, 22.5 ft, 24 ft, 25.5 ft, 27 ft, 28.5 ft, and 30 ft. Since disturbed soil was collected, the first 6’’ (15 cm), which is the seating drive, had not been counted. The Standard Penetration Test (SPT) blow counts (N-values) range from an average of 7.66 at a depth of 1.5 ft (corresponding to the first 12 in. or 30 cm penetration) to an average of 48 at a depth of 30 ft, based on measurements from 15 test locations. The soil at shallow depths, when SPT N-values are less than 10, reflects recently deposited, weakly compacted facies and is characterized by loose sand or soft clay. From a geotechnical perspective, these materials are more prone to settling, have a low bearing capacity, and are very compressible. On the other hand, highly dense sand, gravel, or stiff clay, which reflect older, well-compacted river deposits, dominate the soil profile at deeper depths when N-values surpass 40. These deeper layers are appropriate for supporting engineering foundations because of their increased stability, reduced compressibility, and great bearing capacity. However, the site's vulnerability to liquefaction during seismic stress may be increased; the low clay content decreases plasticity and compressibility. Across 15 drilling locations, groundwater was found at an average depth of about 20 feet, suggesting a rather shallow water table state that is characteristic of natural levee deposits. In the sandy stratum, the groundwater table's location has a significant impact on soil strength, settlement patterns, and possible liquefaction susceptibility. Because of their low bearing capacity and significant danger of settlement, the loose upper layers are not appropriate for direct shallow foundations without modification. While deep foundations, such as driven piles or bored piles, that terminate in the dense sand layer at about 25 to 30 feet are advised for medium to heavy structures or where differential settlement and liquefaction are concerns, shallow foundations may be used for light, low-rise structures only after ground improvement (such as compaction or stone columns) to achieve adequate density. This will ensure stability, adequate bearing capacity, and long-term performance.