Abstract: Helical piles have received extensive attention in recent years due to its advantages such as convenient construction, load-bearing capacity after installation, and recyclability. However, the previous research was mainly based on the premise of ignoring the installation effect. When the installation effect was considered, researches mainly focused on the degree of disturbance to the relative density of sand. The experimental study of the installation effect in clay is not enough. In response to this problem, a model test was carried out to obtain the load-displacement relationship curves of different types of helical piles. For the helical pile with a single plate, whether the installation effect is considered or not, the variation trends of the ultimate bearing capacity with the increasing of the embedment depth ratio are basically the same, but the ultimate bearing capacity decreases significantly when installation effect is considered. For double-plate pile, after the spacing is greater than 2D, the individual bearing model occurs, and each plate can play its bearing capacity independently. Increasing the number of plates can appropriately improve the bearing capacity, but when the failure model transitions from individual bearing model to cylindrical shear mechanism, the increase of bearing capacity is no longer obvious, and at this moment the critical spacing ratio (S/D)cr is between 1.5 and 2.0. Subsequently, a concept of “disturbance coefficient” is put forward to quantitatively evaluate the reduction of bearing capacity caused by helical pile installation. For the helical pile with a single plate, the disturbance coefficient varies from 0.5 to 0.6 when embedment depth ratio is greater than 4D, and increasing the spacing ratio will lead to an increase in disturbance coefficient ranging from 0.20 to 0.45. For multiple plates, the coefficient lies between 0.4 and 0.6.

Key words: helical piles, installation effect, uplift resistance, model test