Experimental Investigation of Bamboo Micropiles to Increase the Bearing Capacity of Shallow Foundations with Variation of Undrained Cohesion

Undrained cohesion (c_u) is an important parameter to determine the bearing capacity of the sub-base, especially in soils with low permeability, such as soft clay. Low c_u values result in low shear strength and low bearing capacity, thus requiring soil strength to increase its bearing capacity. This experimental study examines the extent to which the ultimate bearing capacity of shallow foundations reinforced with bamboo micropiles increases compared with unreinforced conditions at different c_u values. Laboratory shear failure tests were conducted on soft clay c_u1 and medium clay c_u2, with and without bamboo micropiles reinforcement. A rectangular shallow foundation (B= 0.075 m) was modeled using variations in the length ratio L/B, diameter ratio d/B, and installation configuration (K= 0.67B). The test results are expressed as an increase in the ultimate bearing capacity ratio (Rq_ult-empirical = q_{ult-empirical}/q_{ult-Terzaghi,LSF}). The results show that Rq_{ult-empirical} increases with the increase in both L/B and d/B. The larger L/B value results in a significant increase in Rq_ult-emp, with a very strong coefficient of determination R² for c_u1 and c_u2. The increase in d/B also increases Rq_ult-emp to an optimum point at d/B = 0.04, then tends to stabilize with a very strong R²value for c_u1 and c_u2. Overall, the average increase in bearing capacity (Rq_u) ranges from 147–166% in c_u1 soil and 170–172% in c_u2 soil. The most effective increase in Rq_ult-emp in soil consistency levels c_u1 and c_u2, occurs at a diameter ratio d/B = 0.04 and L/B = 2.13.