To solve the problems of waste accumulation and deep and narrow backfilling of foundation pit in the construction process, by adding polycarboxylate superplasticizer (PCE), cement, phosphogypsum (PG) and water glass (WG), the engineering residue is improved into fluid solidified soil for foundation pit backfill. The effects of various admixtures on the fluidity, strength and drying shrinkage of the improved fluid solidified soil were studied through laboratory mobility test, unconfined compressive strength test, drying shrinkage test and microscopic test, and the improvement mechanism was analyzed. The results show that: The flow property of the material can be greatly improved by adding PCE, but the flow rate decreases rapidly with the increase of cement content. PG can make the sample obtain higher strength in the later stage, while water glass can improve the early performance and drying shrinkage property of the sample. With the incorporation of cement, PG and water glass, various hydration products fill the pores in the soil, and the internal structure of the soil becomes more dense. In addition, the feasibility of using fluid solidified soil as backfill for foundation pit is verified by selecting test section for field backfill. This paper can provide reference for improving the performance of fluid solidified soil and the design of mix ratio.

In order to realize shield waste slurry recycling, waste slurry was applied to the preparation of tunneling slurry. The performance difference between waste slurry and bentonite was compared in an indoor test based on Nanjing Yangtze River Xinjizhou river crossing water supply corridor project, and the feasibility of preparing tunneling slurry from waste slurry was analyzed. The law of the influence of waste slurry viscous particle content and ratio on the performance of digging slurry was studied. A fitting formula for the performance indexes of the dredging slurry was established, and the ratio optimization analysis of the dredging slurry prepared from waste slurry was carried out based on the fitting formula. The research results effectively proved the feasibility of preparing tunneling slurry from waste slurry, and through ratio optimization, the reference ratio for the preparation of digging slurry from waste slurry in the relying project was determined: solid to water ratio 0.22, bentonite clay ratio 0.28, and CMC dosing 0.32%. The optimized ratio of the tunneling slurry can meet the performance requirements, which can provide a reference for determining the ratio of the tunneling slurry prepared by recycling the waste slurry in the project.

A closed-system unidirectional freezing experiment is conducted on the sandy silt found at the entrance and exit portal of the shield tunnel in Tianjin Metro. The test aims to investigate the temperature variation and frost heave deformation characteristics of frozen specimens under different freezing temperatures and moisture contents. Additionally, a numerical simulation of the unidirectional freezing process of sandy silt is performed using ANSYS finite element software. The test results indicate that: The higher initial moisture content in the soil, the longer duration of the stable freezing stage, and the initial freezing temperature of sandy silt increase with the increase of soil moisture content. Under the closed unidirectional freezing condition, the frost heave of the soil significantly grows with the increase of moisture content, while the influence of lower freezing temperatures on the final frost heave is relatively small. The simulated temperature variation trend corresponds well with the laboratory test results, except for an obvious mutation from the stable freezing stage to the slow cooling stage. As the freezing time progresses, the vertical frost heave increases at different depths within the soil. A more significant vertical displacement can be observed closer to the upper surface soil layer. After freezing for 500 minutes, the vertical frost heave displacement at different positions of the soil is linearly related to its depth.

This study is carried out to investigate the resource utilization of mud water shield residue. Industrial waste residues such as alkali slag and desulfurization gypsum are reasonably used to be combined with the traditional lime, in order to convert waste mud into qualified roadbed filling materials. Through the laboratory compaction tests, CBR tests, unconfined compressive strength tests, wetting-drying cycle tests and microscopic tests, the mechanical properties, immersion stability and durability of shield tunnel residue improved by lime-alkali slag and lime-desulfurization gypsum were studied, and the improvement mechanism was analyzed. The test results show that the mechanical properties of the soil were improved significantly after compound improvement. The water stability and durability were also greatly improved, with better mechanical properties for road use. Among them, the overall water stability performance and durability of the lime-desulfurization gypsum groups were better than the lime-alkali slag groups. During the wetting-drying cycles, the durability of the specimens mixed with 3% desulfurization gypsum was better, with only small cracks not penetrating the specimens during the cycles. The study shows that the shield tunnel residue has good mechanical properties after compound improvement of lime and desulfurization gypsum, and can be used as roadbed filling materials.