Experimental Study On Pile-soil Stress Ratio Of Remolded Loess Non-compacted Lime-soil Pile Composite Foundation

Lime-soil pile is a kind of economical and effective method for the treatment of collapsible loess foundation above groundwater level.However,for the treatment of collapsible loess foundation in thick and arid areas of Weibei,Gansu and Ningxia,soil can not be crowded in this situation.At present,there are many researches on the treatment of collapsible loess fields by lime soil compaction pile,while the research on the utilization of non-compacted lime soil pile is rare.Based on this,the experimental study on the pile-soil stress ratio of the remolded loess non-compacted lime-soil pile composite foundation has engineering significance.The main work of this paper is as follows:(1)Based on the analysis by elastic theory and given the interaction between cushion and pile-soil,the method of determining pile-soil stress ratio of composite pile foundation is provided,the main influencing factors of which are further discussed.(2)In this paper,an indoor model test device under the rigid load plate(rigid foundation)is designed for the composite foundation of remolded loess non compaction lime soil pile to explore the load level,replacement ratio,age,displacement change and the influence of soaking etc.to pile-soil stress ratio at the dead load of 200 kPa.The results show that for the same age,the pile-soil stress ratio decreases with the increase of the replacement ratio rate before soaking;for the same replacement ratio,the pile-soil stress ratio increases as the age strength enhances.With the increase of loading grade and displacement,the pile-soil stress ratio and the load ratio of lime-soil pile will gradually reduce and the trend will slow down.The pile-soil stress ratio and displacement change of the composite foundation at the initial stage of soaking under the dead load of 200 kPa are distinct.With the soaking time going by,the pile-soil stress ratio reaches a certain degree of stabilization.After the soaking is completed,the replacement ratios are respectively 22.07%,27.11%,31.45% and 35.87%,the pile-soil stress ratio is about 17.67,12.04,9.37 and 8.11.The load sharing rate of the lime-soil pile almost reaches 85% at the 14 th day of age.When the replacement ratio is 31.22%,the load sharing rate of the lime-soil pile reaches 99% at the 33 th day of age,the pile-soil stress ratio is about 253,that the upper load is borne by the pile.(3)With the analysis of unconfined compressive strength test,it can be drawn that the deformation modulus of lime-soil decreases with the increase of lime-soil strain.The deformation modulus calculated by the stress-strain relation theory is 2.6times as many as the amount of secant modulus,and the modulus of gray soil during design of is smaller.(4)Based on the experimental analysis results,the non-self-compacting collapsible loess foundation with low water content treated by non-compacted lime-soil pile should have two layers of cushion on the top of the pile: gravel cushion as the lower layer while lime-soil cushion as the upper one.Lime-soil pile head is strengthened by reinforcing or expanding pile head to prevent the pile head damage.