# A Calculation Model of Grout Migration Height for Post-Grouting Technology
###### Abstract  
Post-grouting technology has been extensively used in geotechnical engineering to improve the bearing capacity of various piles, which overcomes the technical limitations of the bored piles and recovers the mechanical performance of strata. A considerable amount of earlier research has been conducted to investigate the bearing behavior and reinforcement mechanism of the grouted piles, while very few studies focus on the reinforcement area of post-grouting technique. The theoretical analysis on reinforcement area is of great significance, which is beneficial to correlate the grouting parameters with pile bearing capacity with a target of saving cost and acquiring an optimized design. This paper conducted a theoretical analysis on the grout migration height, and then proposed a new predictive model to estimate the ultimate migration height of cement slurry, where the grout rising process is considered as the flow of Bingham fluid in an axial annular space. A field test was conducted to verify the applicability of the proposed model, and the comparison results revealed that the calculated height is slightly overestimated as compared to the actual values, but it is acceptable in engineering design. The grouting pressure loss and induced permeation was warranted to be studied in future. bored piles; post-grouting; slurry migration height; theoretical model +
Footnote †: journal: Applied Sciences  
definition  
post-grouted piles in sand and clay layers. It is reported that the ultimate bearing capacity is found to be increased by 200-300%, which could greatly reduce the construction cost and create a huge economic benefit. [PERSON] and [PERSON] [22] had conducted the back analysis on the post-grouting piles, in which the deformation modulus and the average frictional resistance of soil along the shaft, respectively, increase by 33-67% and 30-40% after the posting-grouting treatment. [PERSON] et al. [8] measured the bearing capacities of bored piled at Suramadu Bridge before and after grouting. They reported that the side frictional resistance, the pile-base resistance, and the ultimate bearing capacity of the investigated pile, respectively, increase by 9-30%, 34-45%, and 17-62%. [PERSON] and [PERSON] [23] found that the post-grouting obviously reduced the downward displacement of bored piles as compared to the counterpart under the same loading conditions. These previous studies have demonstrated that the post-grouting technology possesses excellent performance of improving the bearing behavior of bored piles and the stability of superstructures. However, a clear understanding of the reinforcement mechanism of post-grouting technology has not been achieved presently. [PERSON] et al. [24] indicated that the plastic deformation of the soils around pile can be eliminated due to the pre-loading effect. In other words, an intact bulb is generated as a result of the compaction effect of post-grouting, which enlarges the bearing area compared with the shaft area at the tip. This pile bearing capacity improvement is mainly attributed to two facts: (i) the injected cement slurry solidifies the weak soil layers and losses sediments around and at the bottom of pile, respectively; (ii) the expansion of cement slurry at pile base increases the bearing area, resulting in an enhancement of pile-base resistance, and the slurry migration along the pile equals to make an increment in pile diameter. However, very little research has comprehensively addressed the intrinsic correlation of pile bearing capacity with post-grouting design parameters, especially for the migration height of slurry. This paper aimed to develop a theoretical model of grout migration height for the post-grouting technology. The rheological equation of Bingham fluid was employed to describe the upward migration of cement slurry along the pile shaft. Two filed loading tests were conducted on the posted-grouted piles of the Dukiapu bridge and Henan development plaza in China to verify the applicability of the obtained model.