Shear box tests to explore the soil-structure interface of model piles created using 3D printing techniques

Current research on piled foundations has focused on methods of reducing the size of piles whilst maintaining or increasing their capacity to conserve materials and reduce the amount of underground space needed. Generally, the ultimate capacity of a pile in clay is achieved through shaft friction between the pile and the soil. The proportion of undrained shear strength, Su, of a soil that is mobilised by a pile shaft depends on the adhesion factor, α. For bored piles in clay, α varies between 0.35-0.50, suggesting that a large proportion of Su along the pile shaft length is not mobilised. Recent advancement in research have investigated this complex soil-structure interaction by using 3D printing techniques to fabricate model piles, with a repeatable and known surface roughness, for subsequent use in centrifuge model testing. However, this technique has only provided the overall response of the foundation. At City St George’s, University of London, a series of 100 x100 mm direct shear box tests were undertaken on samples of 3D printed plastic and 3D printed metal to investigate the influence of this surface roughness. 3D printed samples were placed within one half of the shear box with the designed surface roughness exposed to the shear plane. The other half of the sample consisted of pre-consolidated Speswhite kaoli n clay. Tests were conducted at a vertical stress of 124 kPa to represent in-situ stress conditions at the mid-point depth along the length of a 9 m long prototype pile.