Use of Soil Cement Bed to Improve Bearing Capacity of Micropiles, A Laboratory Study

Micropiles (MP) are gaining popularity due to their beneficial characteristics like increment in bearing capacity, reduction in settlement, and ease of application constructed in soft soil. However, MP can't replace the conventional pile foundation because of its insufficient load carrying capacity. But, sometimes, it is not possible to construct conventional pile foundations for its higher cost, particularly for medium to low raise structures. In that case, the bearing capacity of micropile can be increased by placing a soil cement bed (SCB) over the MP placed in soft soil. It is commonly acknowledged that a well-designed SCB constructed over MP can significantly enhance their bearing capacity. However, till today, there have been no experimental studies conducted on this topic. In this study, laboratory model tests were conducted to investigate the behavior of an SCB over MP embedded in soft soil. The SCB was constructed by mixing locally sourced c-phi soil with ordinary Portland cement (OPC) and an optimum amount of water. The plate load test was conducted to obtain the bearing capacity of the micropile underlying SCB. By varying different parameters like the diameter (d) of micropile, length (L) of micropile, the number (n) of MP, and the thickness (H) of the SCB. Plate load test results revealed a significant improvement in the bearing capacity of the soft soil. Compared to the untreated case, the bearing capacity increased by factors of 2.5, 9.2, and 21 for a single micropile (1MP), a group of three MP (3MP), and a group of three MP installed beneath an SCB (3MP + SCB), respectively. Moreover, the study revealed a 51-fold increase observed for 7 MP and an 82-fold increase for 9 MP beneath SCB. The findings of this study exhibit notable consistency when compared to previous numerical research. The parametric study was also carried out by using the experimental results to elucidate the influence of micropile diameter (d), micropile length (L), the number (n) of MP, and the thickness of the SCB (H).