FIELD STUDY ON THE UPLIFT BEARING CHARACTERISTICS OF GROUTED MICROPILES IN SOFT SOIL

This paper presents a preliminary field study to investigate the bearing characteristics of grouted micropiles under uplift loading in soft soil. The results show that micropiles with single grouting did not improve the bearing capacity of the piles significantly, mainly because the grouting fluid was lost from the soil pores. However, micropiles with two-stage grouting showed better performance. The second grouting process improved the ultimate bearing capacity of the test micropiles by 31.4%-51.5%. During the loading process, the skin friction of the micropiles was gradually activated from the head to the tip. Compared with the first grouting process, the second grouting process improved the skin friction of the test micropiles by 14.2%-59.9% in the first test site and by 25.5%-122.0% in the second test site. Moreover, using an appropriate amount of grouting in the second grouting process greatly improved the micropile skin friction, especially in the muddy clay layer. In practical engineering, the bearing capacity of micropiles can be improved by enhancing the skin friction when the amount of grouting in the second grouting process is increased.