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Geomechanics and Engineering
  Volume 37, Number 2, April25 2024 , pages 97-107

Pile tip grouting diffusion height prediction considering unloading effect based on cavity reverse expansion model
Jiaqi Zhang, Chunfeng Zhao, Cheng Zhao, Yue Wu and Xin Gong

    The accurate prediction of grouting upward diffusion height is crucial for estimating the bearing capacity of tip-grouted piles. Borehole construction during the installation of bored piles induces soil unloading, resulting in both radial stress loss in the surrounding soil and an impact on grouting fluid diffusion. In this study, a modified model is developed for predicting grout diffusion height. This model incorporates the classical rheological equation of power-law cement grout and the cavity reverse expansion model to account for different degrees of unloading. A series of single-pile tip grouting and static load tests are conducted with varying initial grouting pressures. The test results demonstrate a significant effect of vertical grout diffusion on improving pile lateral friction resistance and bearing capacity. Increasing the grouting pressure leads to an increase in the vertical height of the grout. A comparison between the predicted values using the proposed model and the actual measured results reveals a model error ranging from -12.3% to 8.0%. Parametric analysis shows that grout diffusion height increases with an increase in the degree of unloading, with a more pronounced effect observed at higher grouting pressures. Two case studies are presented to verify the applicability of the proposed model. Field measurements of grout diffusion height correspond to unloading ratios of 0.68 and 0.71, respectively, as predicted by the model. Neglecting the unloading effect would result in a conservative estimate.
Key Words
    bored piles; cavity reverse expansion; grouting diffusion; grouting pressure; post-grouting; soil unloading
Jiaqi Zhang: Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China
Chunfeng Zhao and Cheng Zhao: Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China;
Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China
Yue Wu: School of Civil Engineering, Chongqing Jiaotong University, 66 Xuefu Road, Chongqing 400074, China
Xin Gong: Institute of Civil Engineering, Jinggangshan University, Ji'an, Jiangxi 343009, China

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