Study of Changes in the Ultimate Bearing Capacity Shallow Foundations in Soft to Medium-Consistency Clay Soils After Reinforcing Micro-Piles

Many contractors use micro-pile reinforcement to boost shallow foundations’ bearing capacity in soft soil. However, until now it is not known how big the increase will be. Therefore, this research aims to find out how much the ability of shallow foundations to support weight increases following the presence of micro-piles. The research was carried out using a laboratory scale with a square foundation width B = 7.5 cm; micro-pile length L = 16 cm (L/B = 2.13); micro-pile diameter d = 0.2 cm (d/B = 0.027); variations in the number of micro-piles (n = 4, 9, 16, and 25), and the distance between the outermost group of micro-pile K = 5 cm (K/B = 0.667). The undrained cohesion value used is c_u = 0.211 kg/cm² for soft-consistency clay and c_u = 0.375 kg/cm² for medium-consistency clay. The test results are expressed in the form of the ultimate bearing capacity ratio (=Rq) at a settlement of 0.1B which is a comparison of the empirical value of the ultimate bearing capacity with the Terzaghi formula for the bearing capacity of shallow foundations in local shear conditions (Rq = q_{ult − empirical}/q_{ult − local Terzaghi shear}). The results showed that the most significant increase in Rq occurred with the increasing number of micro-piles (n = 4, 9, 16, 25). There was a decrease in the Rq ratio along with the increase in land prices c_u, although the decrease was relatively small. Then a general formula for the increase in Rq as a function of the number of micro-piles (n) and undrained soil cohesion (c_u) is proposed.