A cylindrical permeation and diffusion model for Bingham grout in water-rich sand layers and its experimental research

The disaster prevention and control for water-rich sand layers pose a major challenge to the safe construction of tunnels and deep foundation pits. Typically, the impermeability and bearing capacity of highly water-rich and weakly cemented sand layers are enhanced through permeation grouting via sleeve valve tubes, with resulting grouting concretions being approximately cylindrical.

To explore the cylindrical diffusion mechanism of permeation grouting in sand layers, this study constructed a cylindrical diffusion model of radial tube flow for the permeation grouting of Bingham grout in sand layers while considering the tortuosity effects. Subsequently, this study developed a set of experimental devices for the cylindrical diffusion model. Using these experimental devices, the experiments of permeation grouting in sand layers were conducted under different grain-size distributions of sandy soils to be grouted, varying grouting pressures, and cement-based grout with different water-to-cement ratios to explore the grout diffusion patterns. Finally, the theoretical rationality was verified based on the experimental results.

The results indicate that in the case of small grain sizes and high clay content of sandy soils to be grouted, the grouting pressure exerted minor impacts on the diffusion radius, while the water-to-cement ratio of grout served as the dominant factor controlling grouting diffusion morphologies. In this case, a high water-to-cement ratio of the grout was associated with insignificant infiltration effects, a large grouting diffusion radius, and low susceptibility to grout leaking. However, the bond strength among sandy soil grains gradually decreased along the radial direction. In contrast, a low water-to-cement ratio of grout corresponded to significant infiltration effects. Consequently, pores in sandy soils were completely blocked after grout diffusion for a short distance, with the interfaces between sandy soil layers becoming dominant grout diffusion surfaces, leading to grout leaking. In the case of large grain sizes and low clay content of sandy soils to be grouted, both low-pressure thin grout and high-pressure thick grout can thoroughly diffuse in the sandy soils. However, the random distribution and spatial differences of pores in sandy soils, along with the tortuosity and infiltration effects of granular grout diffusion led to irregularly cylindrical grouting concretions. Grouting pressures were attenuated rapidly and then slowly in the diffusion direction. The theoretical calculation-derived grouting diffusion radii were 6.10% to 10.97% higher than the experimental values, and the relative errors between initial grouting pressures derived from theoretical calculations and experiments ranged from –0.48% to 18.62%. These findings provide valuable theoretical support and guidance for the parameter design of permeation grouting in sand layers.