Deep Soft Soil Pile Grouting Test And Research

The bored piles have been widely used in deep foundation engineering because of their advantages, such as well adaptability to various ground condition, enormous bearing capacity by a single pile and the smaller dosage of reinforcing steel bar. But their disadvantages such as sediment under tip, clay slurry around pile and etc. have limited their bearing capacity. Although the post-grouting technique applied to bored piles can increase pile bearing capacity largely and decrease its settlement, this technique is more adaptable to various soil stratums and can make magnificent economic efficiency with simple facilities and construction method. However, the present situation is the theory falls behind the practical significance to study the construction craft, the stress mechanism and the bearing capacity of post-grouting pile. Base on the engineering test results in the sixth part of the high-speed railway in Beijing-Shanghai and the related researching achievements in China and abroad, this thesis deals with the mechanism, construction technology, improvement effect and the stress of post-grouting piles by adopting synthesizing theory, field tests and numerical simulation. The research works and conclusions are mainly summarized as follows:(1) The law of two parameters varying with the load has been obtained by test components placed in pile body, and the parameters include: pile axial force, pile shaft resistance varying with the pile depth, and the load-displacement-time curve at the pile top.(2) The testing results of load-displacement-time of bored pile before and after pile grouting show that: grouting around pile may decline the pile top displacement by 22.2%-25.8%; while grouting at pile tip can decrease its top displacement by 30.1%-35.98%; moreover, the combined grouting at both pile side and tip gives a drop of 32.4%-35.5% to its top displacement.(3) After the grouting site test, a suit of construction parameters design method and construction technology for post-grouting pile in deep soft soil foundation have be gained, together with quality control and Acceptance Standard; besides, a simple pre-buried stalling of post-grouting construction has be explored.(4) The pile top displacement of bored pile has been numerically analyzed. The result shows that: when the load at pile top equals to 700 ton, the pile top displacement of un-grouting pile is 9.357mm, the pile top displacement of pile-side grouting is 6.99mm, the pile top displacement pile-tip grouting is 7.11mm (serum migrating up to 55 m), and that of combined grouting is 6.78mm. Additionally, the pile top displacement decline by 2.367mm, 2.247mm and 2.577mm respectively.(5) Numerical analysis has been performed on the ultimate bearing capacity of bored pile. The outcome shows that: the calculated ultimate bearing capacity of un-grouting pile is 1300 ton, that of pile-side grouting is 1800 ton, and that of pile-tip grouting hits 1700 ton (serum migrating up to 55 m), whereas, that of combined grouting of pile side and tip goes up to 1900 ton. The bearing capacities of pile foundation provided by these three grouting methods are 38.5%, 30.8% and 46.2% respectively.(6) The numerical results show that: post-grouting technology is an effective means to diminish the pile foundation settlement in deep soft soil foundation. As for over-length bored pile in deep soft soil foundation, pile-side grouting is a priority to reduce the pile foundation displacement. In this way, not only the grouting installation is simplified, but also the grouting construction can be more convenient; besides, combined grouting is suitable for the piles which need high bearing capacity or long-piles supporting by a fine supporting course.