Field load tests on plastic tube cast-in-place concrete piles

An instrumented axial load test programme was conducted to study the load transfer behaviour of plastic tube cast-in-place concrete piles (TC piles), which are increasingly being used for support of embankments over soft ground in China. Additionally, in order to enhance the bearing properties of TC piles, the effects of shaft pre-grouting and increasing the diameter of the pile were investigated through load tests. Grouting was found to increase the capacity by 8–20%, while settlement decreased by 20–36%. Additionally, increasing the diameter from 16 to 20 cm resulted in a 10–17% decrease in capacity, due to the accompanying decrease in pile length to accommodate the capabilities of the available construction equipment. Also, increasing the diameter increased settlement by 14–33%. The effect of the pile set-up was investigated, and the capacity was increased by 20%, 8% and 11% for TC piles, gravity-grouted piles and enlarged-diameter piles for axial load tests conducted after 105 d relative to tests conducted after 24 d. In addition, three calculation models of single-pile settlement were evaluated with respect to predictions made of the bearing capacity and settlement.