Experiment Investigation on Stress Characteristics of Grouting Microsteel Pipe Piles with Cement-Soil Wall

Microsteel pipe piles are widely used in excavation support owing to their excellent bearing capacity, flexural rigidity, construction speed, and adaptability. In this study based on a project in soil-rock layers in Qingdao, China, a new type of support combining microsteel pipe piles mounted in cement-soil piles and anchors was adopted and studied. The inner force change laws and bearing capacity of microsteel pipe piles were discussed through in situ stress measurement and laboratory antibending tests on three microsteel pipe piles. It was found that the bending moment of the piles gradually increased with the foundation excavation and maximized at the pile head. The bending moment was larger at the upper and smaller at the lower part along the depth direction, indicating it is reasonable to design and calculate microsteel pipe piles by the pile-anchor system. The variation law of the foundation pit displacement with the excavation depth was monitored. The horizontal displacement of the foundation pit is the maximum at the base top, which is 6.5 mm. The flexural strength of the miniature steel tube pile after grouting is 40% higher than that of the miniature steel tube pile without grouting. It was indicated that the grouting microsteel pipe piles could be implanted in cement-soil piles, which improved the flexural rigidity of cement-soil piles and limited the deformation of foundation pits. This study provides reference for the design and construction of soil-rock foundation pit supporting projects. At the same time, it provides reference for the application of miniature steel pipe piles in other fields.