| Summary: | 碩士 === 國立雲林科技大學 === 營建工程系碩士班 === 99 === The purposes of this study are to clarify the mechanism of tip grouting through model testing and to examine closely on the relationships among grout pressure, grout flow, pile tip pressure, and pile uplift, etc. Numerical simulations by PFC2D are also conducted to verify the observations in the physical models.
In this study, a two-dimensional scale model was first designed and tested for the accuracy of monitoring devices, as well as the setting time of cement grout and the relative density of test soils. The controlled factors of model testing included: soil type and density, overburden pressure, grout pressure and volume. In order to understand the mechanism of pile bearing capacity due to tip grouting, we observed the development of the slurry grout into the ground by using various sensing devices recorded during the injection. In addition, this study also conducted numerical analyses using a discrete element model (PFC2D) to simulate different stages of the testing, including: model formation, pile application, and grouting.
Results of the model testing showed the hydro-fracturing usually occurs at a certain peak pressure along with a rapidly increased injection rate, which is then followed by a decreasing pressure with the closure of hydro-fractures. As to grout injection mechanism, we found that fine Chuoswei sand was more difficult to be grouted than the Ottawa sand, due to a better graded particle distribution of the sand. When the grout pressure is low (e.g., 800kPa) or the soil density is high (e.g., Dr=68%), the grouted mass would generally be small. In the case of higher surcharge pressure (e.g., 400~600kPa), the grouted mass would be significantly smaller and rounded. Results of numerical simulations and physical model testing were similar and showed a compaction type of grouting. Based on numerical simulations, the pile was lifted relatively upwards than the surrounding soils in the depth range of about 2.25 times the pile diameter above the pile tip, showing a “pre-stressing” effect due to the grouting. On the other hand, the soil beneath the pile tip was compressed in the depth range of 3 times the pile diameter below the level of pile base, indicating a “pre-loading” effect of the grouting and thus enhancing the bearing capacity of the pile.
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