The application of solid waste cementitious materials to coal mining and mine filling is limited by high volume shrinkage and inadequate reactivity. In this study, a superabsorbent polymer was incorporated into a solid waste filling material to improve its workability. The effects of its dosage, particle size, and modulus of sodium silicate were investigated by means of slurry fluidity, initial and final setting time tests, compressive strength tests, and drying shrinkage tests. Microscopic characterization methods such as scanning electron microscopy, energy spectroscopy, and nuclear magnetic resonance tests were used to study the water absorption and release behavior of the superabsorbent polymer in solid waste filled slurries, and its effect on the properties of these slurries was analyzed. The results show that appropriate adjustment of the superabsorbent polymer admixture and particle size can optimize the working performance of the solid waste slurry and improve its stability, pumpability, and strength.
Soft and broken ground is a common geological condition for subway pit water damage. The complex hydrogeological environment is the main cause of frequent disasters. It relied on the inrush water project of the soft fluid‐plastic stratum in the pit of the Shang Yuanmen station in Nanjing. And based on the geological data and the actual site of the project, the station was evaluated for hazards and analysis of major and difficult points. Combined with a variety of geophysical exploration methods, the source of water in the foundation pit and the key areas for pulp reinforcement was obtained. Based on field tests and indoor tests of grouting reinforcement, the parameters before and after grouting reinforcement were analyzed. The effect of material proportioning and grouting pressure on the parameters of stratum reinforcement was studied. It revealed the effect of the behavioral mechanism of material properties and grouting pressure on different mechanical indexes. It creatively proposes a localized controlled grouting process and uses COMSOL modeling to explain its reinforcement mechanism. In addition, foundation pits applied a full set of monitoring system. Finally, a complete set of comprehensive control methods were formed for water inrush in soft fluid‐plastic stratum of complex urban strata. Then, the methods are implemented at the project site. Practice has proved that this method successfully seals the inrush water and reinforces foundation pits while ensuring the safety of foundation pits and surrounding construction pipelines. It is hoped that this method can be used as a reference for similar projects.
In order to obtain grouts with reduced leaching, desirable fluidity and sufficient penetrability for the filling of sand voids or microcracks, a microfine-cement-based grout (MCG) with microfine fly ash (MFA) was prepared and the maximum grain size (d max ) was controlled at 20 μm. The viscosity, hydration temperature, spreading ability, fluidity, flexural strength and unconfined compressive strength of MCGs with MFA and naphthalene-based superplasticiser (SP) were investigated. The relatively new concept of ‘static viscosity’ was considered. The ranges of water/MCG (w/MCG) ratios, MFA contents and SP contents were 0·8–3·0, 0–50% and 0·5–3·0%, respectively. The viscosity, hydration temperature and flow time were found to decrease with increasing w/MCG ratios, MFA and SP contents, but mini-slump diameter, bleed capacity and setting time increased. The effects of MFA were not as obvious as those of SP. The addition of 2·0% SP decreased the flexural strength and the compressive strength, while 40% MFA increased the flexural strength and decreased the compressive strength. The optimum w/MCG ratio, MFA and SP contents are recommended as 1·0–1·5, 30–40% and 1·5–2·0%, respectively. A low initial viscosity of the optimised MCG ensured desirable rheology properties and satisfactory mechanical properties of the hardened grout. To avoid instability, oversaturation or long setting times, SP dosages should not be excessive.
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