| China’s construction industry has developed rapidly since the reform and opening up,but there are still a large number of weak foundation to be reinforced.Grouting technology stands out in many foundation reinforcement technology because of its advantages such as simple construction,low cost and high strength of pile body.However,a large number of engineering practices show that there are many deficiencies in the traditional grouting technology.The high-pressure rotary jet grouting technology without backflow is a new type of composite grouting technology combining new and old technology,aiming at the technical quality problems such as pile(wall)discontinuity,many defects,poor effect,waste of backflow grouting resources and so on,which commonly exist in the anti-seepage and reinforcement engineering of complex stratum of River retaining wall foundation.Different from the traditional grouting technology,the high-pressure rotary grouting composite grouting technology without backflow adopts cement stabilized slurry drilling and grouting in the whole hole.After reaching the target formation depth,the thixotropic cement-based slurry is used to conduct high-pressure jet grouting for the loose weak stratum from the bottom to the top.When the slurry shear force is less than the critical strength of the soil structure,the slurry will continue to be squeezed and split in the direction of high-pressure jet.The composite action is applied to the far formation.In this paper,based on the foundation grouting reinforcement project of a flood control dike reconstruction project,four aspects of research are carried out,the main research contents and results are as follows:(1)This paper maker a theoretical analysis of the working principle of the high-pressure rotary jet grouting technology without backflow;analyzes the filling,infiltration and wall protection function of the stable slurry to the soil in the integrated stage of drilling and grouting from top to bottom;the structure and nature of the high-pressure jet flow in the combined stage of high-pressure rotary jet grouting from bottom to top,and the impact of the high-pressure jet flow on the soil,including mixing,splitting and compaction.According to the physical and mechanical characteristics of thixotropic cement-based slurry,the sealing mechanism of "non-return slurry" is analyzed by theoretical deduction,and the pile forming mechanism and influencing factors of composite grouting and consolidation mechanism of cement soil are summarized and discussed.(2)Through laboratory experiments,the effects of plant glue on the density funnel viscosity,water evolution rate,setting time(initial setting,final setting)fluidity,flexural strength and compressive strength of cement-based slurry were studied.It was found that the addition of plant glue did not affect the density of slurry,greatly increased the viscosity of slurry and prolonged the setting time,improved the settlement stability of slurry,and reduced the water evolution rate.In the experimental stage,the optimal dosage of thixotropic cement-based slurry is 2%-3%.Based on SEM image and chemical theory,the thixotropic mechanism of plant gum was discussed from the perspective of molecular structure.It was considered that the polysaccharide and cellulose molecules in plant gum played a role of grid pulling in the slurry,combined with the film-forming role of fat molecules,blocked the hydration of some cement particles,and made the slurry present the above properties.(3)PFC2D5.0 software is used to simulate the process of fracture occurrence and development under the action of high-pressure jet flow The range of soil splitting under 3MPa、9MPa、20MPa grouting pressure and different grouting duration was compared.The change curve of soil particle porosity and pore pressure curve show that the soil particle is compressed by disturbance under low pressure and is still in equilibrium after fine adjustment,while the displacement of soil particle deviates from the grouting hole under high pressure.When the slurry energy is greater than the critical strength value of soil structure,the original structure is destabilized and destroyed,and the shear force and hydraulic split occur at the soil particle with larger contact tension of stratum.(4)Combining with the core test and pile head excavation test of foundation reinforcement and grouting project for a comprehensive flood control project,energy saving evaluation and economic evaluation are carried out.The advanced technology,technological feasibility,construction environmental protection and quality reliability of the high pressure jet grouting composite grouting technology without-back flow are summarized. |
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