The accurate prediction of grouting upward diffusion height is crucial for estimating the bearing capacity of tipgrouted 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.

In the process of split grouting, soil will compress the surrounding soil under the action of expansion pressure, reduce the gap between soil particles. Based on this, the stress-strain relationship model describing the nonlinear compression characteristics of soil mass was established to simplify the dynamic development process of split grouting veins. Considering the loss of grouting pressure along the path, the corresponding relationship between the set value of the first sequence grouting circle cake pulse diffusion radius rmax1 and the set value of grouting pressure p0 was obtained, and the corresponding calculation method of grouting time was obtained. Under the condition that the previous sequence grouting changes the distribution direction of the major and minor ground stress, the corresponding relation between the secondary grouting diffusion radius rmax 2 and the set value of grouting pressure p ' 0 and the calculation method of grouting time are obtained. The model test of split grouting is carried out, and the test results show that the vertical split grouting can be achieved by setting the target pressure and grouting time after the horizontal split grouting and the direction of the ground stress change, which verifies the rationality of the theory.