A field study on the behavior of static drill rooted nodular piles with caps under compression

Abstract

The static drill rooted nodular (SDRN) pile is a new type of composite pile that consists of a precast pile and surrounding cemented soil. Its cost advantages and environmentally friendly construction have been proven in applications in Southeast China. Moreover, the composition of pipe pile and nodular pile is based on the load transfer mechanisms of a pile foundation, which is effective in optimal design. This paper presents a field study on the behavior of SDRN piles under compression. The load–displacement response, axial force, mobilized load of pile cap, skin friction, and tip resistance of the composite pile are discussed. Here, the bilinear base load–displacement model was adopted to analyze the test results. It is found that providing caps on the static drill rooted piles takes full advantage of the static drill rooted method, and drilling and grouting into the soil beneath the cap, which can be considered a type of ground improvement treatment, can increase the bearing capacity of the pile cap; thus, setting a pile cap for this type of piles is recommended. The existence of the caps in the field tests decreased the skin friction of the upper part of pile shaft because of the additional settlement of the surrounding soil, which developed owing to the pressure from the caps. The frictional capacity of the concrete–cemented soil interface was much higher than that of the cemented soil–soil interface. The skin friction of the lower part of the pile shaft was about 1.25 times in clayey soil and 2.0 times in sandy soil compared with the bored pile. It can be concluded that the cemented soil–soil interface of the SDRN pile was probably better than the concrete–soil interface of the bored pile. The test results fitted the first stage curve of the bilinear model well, and it can be supposed that the base soil was strengthened because of the permeation of the cement paste.