Test And Analysis Of The Long-Term Bearing Behavior Of Post-Grouting Bored Piles In Sand

Nowadays, the bored pile technology has been widely applied in the world. Engineering practice shows that post-grouting technology has significant effect in minishing bored piles defects and improving bearing behavior. However, research on the long-term bearing behavior of post-grouting bored piles is lacking at present. In the past practice of engineering, the effect has been tested by core drilling 30-50 days after post-grouting. And it is noticed that the soil consolidation around the pile is inadequate. The cement slurry has not been formed to high strength grout stone body, and is still in low degree of cementation. In some coring testing of post-grouting bored piles, the deep cement slurry is still unconsolidated after 2 years. The consolidation of the cement slurry is a long-term process, with complex chemical changes and physical changes of cement slurry loss and pressure dissipation which must effects the bearing behavior.To examine the long-term bearing behavior of post-grouting bored piles in sand, research works have been done as follows:1 Based on the project of Yellow River Bridge and Beijing Road extension in Yinchuan, the long-term bearing behavior was investigated up to two years to study the variations of skin friction and tip resistance with time in the local special geologic condition. It turns out that,compared with pre-grouting, the total skin friction averagely increasesd 8.38%?23.02%, the tip resistance averagely increasesd 21.03%?76.01%.Long term test turns out that, the skin friction had little increase,the tip resistance had some increase and tended to be stable after 10 months.2 The indoor model tests were conducted simulating the condition of groundwater flow to analyze the time-dependent change of the cement slurry distribution in soil, the skin friction and tip resistance of pile. It turns out that, the consolidation of the upward cement slurry is earlier.Under the groundwater flow effects, the consolidation of the bottom cement slurry needs needs longer,but make little effects to the bearing behavior.3 Numerical simulation of the field test was done with the FLAC 3D software, with considering the time effects.The long-term bearing behavior were analyzed under the effects of the strength of the grout stone body. It turns out that in the initial stage the bearing capacity increased rapidly, and gradually stabilized down.