Pressure-cast-in-situ pile with spray-expanded frustum: Construction equipment and process

To make full use of skin friction of soils around pile, this paper presents a novel pile composed of ribbed plates, an expanded body with double frustum, and a pile body, named as the pressure-cast-in-situ pile with spray-expanded frustum. A multifunction auger drill is used to form the expanded body by spraying cement slurry rotationally at a given depth, pouring superfluid concrete, and vibrating and squeezing pile body. The ribbed plates are completed by spraying cement slurry fixedly with a hollow drill pipe. Due to the improvement of skin friction of the expanded pile body, the novel pile will get a large bearing capacity. Moreover, due to the squeezing effect of superfluid concrete during the pile construction, the soils around pile can be compacted, which also leads to an obvious increase in bearing capacity of the novel pile. The application of the proposed technique of the novel pile is verified by using static loading tests on three novel piles and one traditional cast-in-situ pile. Comparisons of the four test piles demonstrate that the ultimate bearing capacity of the novel pile increases by more than 45% under the condition of the same concrete consumption per unit volume. For practical purposes, the pressure-cast-in-situ pile with spray-expanded frustum is worthy of promotion due to the advantages of high bearing capacity and significant economic benefits.