Experimental Study On Compaction Grouting And Fracture Grouting Of Soft Clay In The High-Speed Railway Foundation

In recent years, the leaping development of China’s high-speed railway requires us to pay more attention to the railway’s long term performance. The stability of the foundation and subgrade is the controlling factor to guarantee the operation safety of the high-speed railway, however the deteriorated performance of the foundation and subgrade will be a direct threat to the natural service of the high-speed railway. Therefore, on one hand, we need to develop the research about how to maintain the safe structural state and the long-term performance of the high-speed railway substructure. On the other hand, we should strengthen the research about the operation maintenance technology and especially the rapid repair techniques. At present, grouting reinforcement is one of the main methods to regulate the foundation disease, but the theory and research achievements which can be used to guide the grouting construction are deficient and behind the engineering practice. In this paper, the flowing and diffusion law of the grouting slurry and the strengthening effect of the soils are discussed by means of theoretical analysis and indoor model tests and the research results can be used to enrich the theory of grouting and provide reference for the practice of grouting reinforcement in the soft clay foundation.The research achievements are as follows:(1) The calculation model of reaming theory is established while the rheological characteristics of the grouting slurry and the soil characteristics are considered. It can be used to deduce the variation characteristics of stress and strain in the soft soil during grouting and the law of the reinforcing and lifting in the soil layer after grouting.Firstly, the soils around the grouting hole are divided into plastic and elastic areas, the stress field and displacement field of the area are calculated. Secondly, the rheology theory about the grouting slurry creeping in the soil is discussed according to the reaming theory, the rheological and time-varying properties of the single cement slurry and the characteristics of the soil. What’s more, the grouting range are effected by the grouting pressure, grouting capacity, grouting density and the soil parameters is analyzed by related theories.The methods to determine the splitting pressure are explored. Finally, the above mentioned grouting theories are extended to explore the uplifting amount through Principle of Mirror Image. The combination of the above theoretical research and the subsequent experimental study can help to form a series of regular recognition about grouting in the soft clay and predict the grouting effect correctly,which can also be used to provide the guidance to the project practice.(2) A set of device and system which can be used to carry out the grouting experiment under high-pressure environment were self-developed. What’s more, a complete range of experiment project that can be used to guide the laboratory test for grouting in the soft clay was designed.The developed experimental system can simulate different soil depths by applying different confining pressure to the soil, can simulate different consolidation degrees by imposing pre-consolidation load to the surface of the soil, can realize the separation between the soil affected by the grouting slurry and the undisturbed soil. The air pressure and the pneumatic-liquid transfer device can be used to realize the processes of pressure casting, the bilateral control of the grouting pressure can be realized by the pressure regulating valve and the pressure monitoring devices. In order to explore the grouting characteristics, a lot of earth pressure cells and pore pressure gauges were buried in the soil that can be used to monitor the changing law of the earth pressure and the pore water pressure.(3) According to the results of the laboratory model tests,many laws under different grouting parameters were put forward including the law about the diffusion of the grouting slurry in the clay and the law about the soil’s strengthening effects by the grouting slurry.The law about the diffusion of the grouting slurry in the clay and the law about the grouting characteristics affected by the different grouting parameters were analyzed by the pressure test information, the pore water pressure test information, the grout amount test information, the grouting pressure information during grouting and the characteristics of the grouting foams and the grouting choroids discovered in the processes of model excavation after grouting. The empirical value of the "splitting-opening pressure" was put forward under similar condition of the soil layer. The laws of the soil strengthening effect affected by the grouting parameters and the improvement degree of the soil’s physical and mechanical properties after grouting were educed by means of doing conventional shear tests and consolidation tests towards the samples extracted in the soil affected by the grouting slurry and the undisturbed soil after grouting in the laboratory.