Study On Control Parameters And The Effect Of Pile Forming Of High Pressure Rotary Jet-grouting In Deep Sand Layer

High pressure rotary jet-grouting as an high-efficiency means of pile forming,Compared with cement-soil mixing pile,it has stronger stratigraphic adaptability and is more and more widely used in foundation treatment and anti-seepage engineering.However,for deep soil layer,due to its high overburden pressure and complex stratigraphic environment,the effect of pile forming is often unsatisfactory.This paper takes the deep sand layer as the research object,obtains the key factors affecting of the pile forming and the optimal structure of water-air coaxial nozzle by means of mechanism study and numerical simulation,and provides the gist for parameter control of the indoor model experiment and equipment development.Then through model experiment to explore of the three parts about "relationship between the pressure of jet water and diameter of pile forming,unconfined compressive strength,integrity and uniformity of the pile forming." And then,finish the research on " the control parameters and the effect of pile forming of high pressure rotary jet-grouting in deep sand layer."The main achievements are as follows:(1)The water-nozzle of cone straight has the best overall performance and the processing technology is relatively simple.The air-nozzle with an outlet gap of 1.5mm can better reduce the disturbance to the high-pressure water and has better effect in terms of impact force and energy retention.Therefore,the water-nozzle of cone straight and air-nozzle of 1.5mm are relatively more practical.(2)Under the condition that other parameters remain unchanged,the diameter of high pressure rotary jet-grouting pile increases with the increase of jet water pressure.The jet water pressure is 4~24Mpa,and the corresponding pile diameter is 52.6~81.4cm.The increment of jet pressure keep constant,increase rate of diameter decreases with the increase of jet pressure.It is show that the energy decay rate increases with the increase of jet distance.(3)The unconfined compressive strength of the high pressure rotary jet pile in the deep powder-fine sand layer increases with the strength away from the pile center.From the center to the periphery of the pile,the approximate net slurry area,the mixing area of fine sand and slurry and the mixing area of relatively large sand and slurry are successively formed,which indicates that the rotary jet body is not a monomer structure of equal particles.The strength of the pile is too high in powder-fine sand layer.if it is used in anti-seepage engineering,it dose not work well.The pile parameters should be optimized.Under the condition of control parameters in this experiment,integrity of high pressure rotary jet-grouting pile is I class,at the same time,uniformity of the pile is well.There are 49 figures,16 tables and 85 references in this paper.