Performance Analysis of Pipe-Jacking Waste Soils Solidified with Quick Lime and Fly Ash under Balanced Earth Pressure Conditions

Abstract

With its advantages of high cross-sectional utilization, shallow depth, and uninterrupted surface road traffic, the pipe-jacking method has been widely used in underground passages, metro stations, and other projects. However, this leads to a large volume of pipe-jacking waste soils that must be processed. Pipe-jacking waste soils are different from shield-tunneling waste soils. Therefore, it is not appropriate to simply use the same treatment method for shield-tunneling waste soils in the treatment of pipe-jacking waste soils. In this study, pipe-jacking waste soil samples were improved with 7% polyacrylamide (PAM) and 12% sodium-based bentonite solutions, with good performance being achieved. Based on this, quick lime and fly ash were used in the solidification of pipe-jacking waste soils, and experiments with different solution concentrations and solidification material additions were conducted, involving tests of compression, freeze−thaw cycling, wet−dry cycling, and microstructure. The results indicate that within the ranges of PAM and sodium-based bentonite addition ratios applied in this study, the solidification effects of quick lime and fly ash will not be significantly reduced during the improvement processes of pipe-jacking waste soils under balanced earth pressure conditions. Instead, it was found that there was an increase of up to 16% in the strength of pipe-jacking waste soils. Structural compactness can be primarily enhanced by gelatinous PAM, while sodium-based bentonite can promote the formation of hydrated colloids (such as C−S−H) and fill soil pores with hydrated gelatinous bentonite particles, thereby enhancing soil stability.