Research On The Influence To The Bored Cast-In-Place Piles Bearing Capacity By The Post-Grouting Technique

Today, bored cast-in-place piles are more widely used in deep foundation engineering because of their many advantages, such as better adaptability to various ground condition, providing enormous bearing capacity by a single pile and smaller dosage of reinforcing steel bar.But,their own disadvantages, such as sediment under tip, clay slurry around pile, friction and tip resistance disagreement and initial ground stress freeing, limited their bearing capacity, lowered the utilization ratio of material and increased the settlement. Applied to bored cast-in-place piles, the post—grouting technique can increase pile bearing capacity largely and the utilization ratio of material, and decrease its settlement. Furthermore, this technique is better adaptable to various soil stratums and can make magnificent economic efficiency with simple facilities and construction method. But the present situation is the theory falls behind the practice application, therefore, it has the important theory value and practical significance to study the construction craft of post—grouting pile, the stress mechanism of post—grouting pile, and the bearing capacity calculation of post—grouting pile .Base on investigating and studying massive literature in the domestic and the foreign ,the article summarize the construction craft of post—grouting technique, at the same time take the grouting theory as the instruction, it discuss the serositypercolation rule and the seepage model in the underground; it also discuss the relationship between the parameters,such as the grating pressure, the grating time, the fluid viscosity,the extend radius of the serosity,and has produced the method of computating the grating radius.The paper propose the hyperbolic curve function as the load transfer function to analyze the load transmission of post- pressure grouting pile, and analyze how to make the parameter value, and optimized the parameter with the optimized method. With the practice project confirmation, its model result tally with the actual result. It showed that taking the hyperbolic curve function as the transfer function is reasonable to analyze the bored pile load transmission.The paper analyzed each factor which influence the load transmission rate in post—grouting pile, the pile bearing characteristic is analyzed by two kinds of different pile-body models, the constant section model is used before grouting, and the variable cross-section model is used after grouting. It proved the variable cross-section model is fitness by the post—grouting project practice confirmation.